mold filling characteristics and molecular …

MOLD FILLING CHARACTERISTICS AND MOLECULAR ORIENTATION IN INJECTION MOLDING OF LIQUID CRYSTALLINE COPOLYESTERS

OF POLY (ETHYLENE TEREPHTHALATE)

by

Chieu Dinh Nguyen

Thesis submitted to the Faculty of the

Virginia Polytechnic Institute and State University

in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

in

Chemical Engineering

APPROVED:

D. G. Baird, Chairman

J. E. McGrath G. L. Wilkes

December, 1982

Blacksburg, Virginia

ACKNOWLEDGEMENTS

The author wishes

Donald G. Baird

to express his appreciation to Dr.

for his advice, criticism and

recommendations during the course of this work. He would

also express thanks to Dr. Garth L. Wilkes and Dr. James E.

McGrath for their interests of being the members of the

graduate committee.

The author also wishes to thank Dr. G. Ifju for his

permission to use the Spencer 860 Sliding Microtome. He

would also like to express his deep appreciation to Billy

Williams for the excellent machine works in constructing the

capillaries and molds.

Last but not least, he would like to express his

sincere gratitude to his friends Eugene Joseph, Ramesh

Pisipati, Dr. Athanasios E. Labropoulos, Kao Chun Hawn and

Din-Shong Done for their help and guidance. All this would

not have been possible without the help, criticism and

encouragement of Thuy Tran.

ii

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ........................................ ii

TABLE OF CONTENTS ...................................... iii

LI ST OF FIGURES .......................................... v

LIST OF TABLE .......................................... xiv

Chapter Page I . INTRODUCTION ....................................... 1

II. LITERATURE REVIEW .................................. 5

Liquid Crystalline Order ........................ 6 General ...................................... 6 The Thermotropic Liquid Crystalline system

Poly (Ethylene Terephthalate) and p-Hydroxybenzoic Acid .................... 9

Rheological Properties of Thermotropic Liquid Crystalline Polymers .................. 14

The Mechanism of Skin-Core Formation in Injection Molding ........................ 22

The Flow of Polymer Melt in Injection Molding ............................... 22

The Skin-Core Morphology of Injection Molded Objects ........................ 26

Injection Molding Studies ...................... 33 Summary ........................................ 42

III. EXPERIMENTAL PROCEDURE AND MATERIAL ............... 44

Plan of Investigation .......................... 44 Instron Capillary Rheometer .................... 47 Mold Designed .................................. 51 Sample Preparation ............................. 57 Sample Preparation for Flow Visualization

Studies - Polymer Rod .................... 59 Injection Molding .............................. 62 Shrinkage Measurement .......................... 65

IV. RESULTS ........................................... 68

Capillary Rheometer ............................ 68 Mold Filling Characteristics ................... 90 Shrinkage Measurement of Microtomed Samples ... 100

V. DISCUSSION ....................................... 123

Viscosity Measurement ......................... 123

iii

Boundary Layer Effects on Viscosity ........... 136 Mold Filling Characteristics .................. 152 Molecular Orientation of Liquid Crystalline

Polymers in Injection Molding ........... 161

VI. CONCLUSION ....................................... 189

VI I. RECOMMENDATIONS .................................. 192

BIBLIOGRAPHY ........................................... 194

~ppendix Pag~

A COMPUTER PROGRAM FOR VISCOSITY CALCULATION ....... 205

B DATA TABLE ....................................... 210

C NOMENCLATURE ..................................... 227

VITA ................................................... 229

ABSTRACT ............................................... 230

iv

LIST OF FIGURES

2.1.1 Schematic representation of Mesophase Type ........ 18

2.1.2 Poly (Ethylene Terephthalate) and its Copolymers with p-Hydroxybenzoic Acid ............ 19

2.1.3 Effect of p-Hydroxybenzoic Acid Content on Melt Viscosity at 275 C (Jackson and Kuhfuss, 1976) ................................... 20

2.1.4 Effect of Shear on Melt Viscosity of PET Modified with p-Hydroxybenzoic Acid (Jackson and Kuhfuss, 1976) ...................... 21

2.2.1 Schematic Representation of the Flow Pattern in the Central Portion of the Advancing Front between two Parallel Plates (Tadmore, 1974) ........................... 28

2.2.2 Flow Pattern in the Advancing Front between Two Parallel Plates (Tadmore, 1974) .............. 29

2.2.3 Effect of Thickness on Along-The-Flow Flexural Modulus of PET Modified with 60 Mole % p-Hydroxy-benzoic Acid (Jackson and Kuhfuss, 1976) ......... 30

2.2.4 Schematic Diagram of the Velosity Profile of The Flow behind the Front and its Corresponding Shear Rate ....................................... 31

2.2.5 Tensile Bar (Schematic) Showing the Arrangement of the Morphologic Zones (Kantz et al., 1972) .... 32

2.3.1 Mold Filling Patterns in Different Geometry ...... 40

2.3.2 Mold Filling Characteristics in Rectangular Cavity ........................................... 41

3.2.1 Schematic Diagram of Instron Capillary Rheometer (Jerman, 1980) ................................... 49

3.3.1 Injection Molding Apparatus ...................... 53

3.3.2 Runner ........................................... 54

3.3.3 Photograph of Rectangular Mold .................... 55

v

3.3.4 Photograph of Circular Mold ...................... 56

3.7.1 Dimension of Sample Cut from Injection Molded Parts ............................................ 66

4.1.1 Typical Plot of Total Pressure versus Apparent Shear Rate for 60 Mole% PHB/PET ................. 71

4.1.2 Typical Plot of Total Pressure versus Apparent Shear Rate for 80 Mole% PHB/PET ................. 72

4.1. 3 Typical Plot of Total Pressure versus Apparent Shear Rate for PET Homopolymer ................... 7 3

4.1. 4 Typical Bagley Plot for 60 Mole % PHB/PET ........ 7 4

4.1. 5 Typical Bagley Plot for 80 Mole % PHB/PET ........ 7 5

4.1. 6 Typical Bagley Plot for PET Homopolymer .......... 7 6

4.1.7 Entrance Pressure Loss versus Apparent Shear Rate for 60 Mole% PHB/PET ....................... 77

4.1.8 Entrance Pressure Loss versus Apparent Shear Rate for 80 Mole% PHB/PET ....................... 78

4.1.9 Entrance Pressure Loss versus Apparent Shear Rate for PET Homopolymer ......................... 79

4. 1. 10 Wall Shear Stress versus Apparent Shear Rate for 60 Mole % PHB/PET at 275 c .............. 80

4.1.11 Wall Shear Stress versus Apparent Shear Rate for 80 Mole % PHB/PET at 305 c .............. 81

4 .1.12 Wall Shear Stress versus Apparent Shear Rate for PET Homopolymer at 285 c ................ 82

4.1.13 Melt Viscosity as a Function of Wall Shear Rate for 60 Mole % PHB/PET with Capillary Diameter of 0.027 inch ........................... 83

4.1.14 Melt Viscosity as a Function of Wall Shear Rate for 80 Mole %PHB/PET with Capillary Diameter of 0.05 inch ............................ 84

4.1.15 Melt Viscosity as a Function of Wall Shear Rate for 60 Mole % PHB/PET with Capillary Diameter of 0.07 inch ............................ 85

4.1.16 Melt Viscosity as a Function of Wall Shear Rate for 80 Mole % PHB/PET with Capillary

vi

Diameter of 0.027 inch ........................... 86

4.1.17 Melt Viscosity as a Function of Wall Shear Rate for 80 Mole % PHB/PET with Capillary Diameter of 0.05 inch ............................ 87

4.1.18 Melt Viscosity as a Function of Wall Shear Rate for 80 Mole % PHB/PET with Capillary Diameter of 0. 07 inch ............................ 88

4.1.19 Melt Viscosity as a Function of Wall Shear Rate for PET Homopolymer with Capillary Diameter of 0.027 inch ........................... 89

4. 2. 1 Di stance from Ga.te versus Time for Various Fluid Pigments in a Cold Mold (Mold Temp.= 100 C, Cavity thickness= 0.125 inch, Injection Speed = 40 cm/min) ..................................... 92

4.2.2 Distance from Gate versus Time for Various Fluid pigments in a Hot Mold (Mold Temp.= 200 C, Cavity thickness= 0.125 inch, Injection Speed = 40 cm/min) ..................................... 93

4.2.3 Velocity of Various Fluid Pigments versus Distance from Gate in a Cold Mold (Mold Temp.= 100 C, Cavity thickness= 0.125 inch, Injection Speed = 40 cm/min) ............................... 94

4.2.4 Velocity of Various Fluid Pigments versus Distance from Gate in a Hot Mold (Mold Temp.= 200 C, Cavity Thickness= 0.125 inch, Injection Speed = 40 cm/min) ............................... 95

4.2.5 Longitudinal Section of Short-Shot Type of Injection for 60 Mole% PHB/PET .................. 96

4.2.6 Longitudinal Section of Short-Shot Type of Injection for 80 Mole% PHB/PET .................. 97

4.2.7 Longitudinal Section of Short-Shot Type of Injection for PET Homopolymer .................... 98

4.2.8 Photograph of Section Cut Transverse to the Flow Direction ........................................ 99

4.3.1 Shrinkage of the Microtomed Samples of 60 Mole % PHB/PET (Mold Temp. = 100 C, Melt Temp.= 275 C, Injection Speed= 20 cm/min., Cavity thickness= 0.1250 inch) ................... 102

4.3.2 Shrinkage of the Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp. = 285 C, Injection Speed= 20 cm/min.,

vii

Cavity Thickness= 0.125 inch) .................. 103

4.3.3 Shrinkage of the Microtomed Samples of 80 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp. = 305 c, Injection Speed= 20 cm/min., Cavity Thickness= 0.1250 inch) ................. 104

4.3.4 Shrinkage of the Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp. = 275 C, Injection Speed= 40 cm/min., Cavity Thickness= 0.1250 inch) ................. 105








4.3.12 Shrinkage of the Microtomed Samples of 80 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp. =305 C, Injection Speed= 40 cm/min., Cavity Thickness= 0.0625 inch) ................. 113

4.3.13 Shrinkage of the Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 165 C, Melt

viii

Temp. = 275 C, Injection Speed= 20 cm/min., Cavity Thickness= 0.1250 inch) ................. 114





4.3.18 Shrinkage of the Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 165 C, Melt Temp. = 285 C, Injection Sp~ed = 20 cm/min., Cavity Thickness= 0.0625 inch) ................. 119


4.3.20 Shrinkage of the Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 165 C, Melt = Temp. = 285 C, Injection Speed= 40 cm/min., Cavity Thickness= 0.0625 inch) ................. 121

4.3.21 Comparison of the Across the Flow Shrinkage of The Microtomed Samples of 60 Mole % PHB/PET in two Seperate Runs (Injection Speed = 20 cm/min, Cavity Thickness= 0.125 inch) .................. 122

5.1.1 Viscosity versus Wall Shear Rate for PET/60%PHB at 260 c ........................................ 12 8



5.1.4 Viscosity versus Wall Shear Rate for PET/80%PHB at 305 c ........................................ 131

ix

5.1.5 Viscosity versus Wall Shear Rate for PET/80%PHB at 315 C ........................................ 132

5.1.6 Viscosity versus Wall Shear Rate for PET Homopolymer at 275 C ....... ~· ................... 133

5.1.7 Viscosity versus Wall Shear Rate for PET Homopolymer at 285 C ............................ 134

5.1.8 Schematic Diagram of Capillary Used in This Work (A) and That Used by Jerman (B), (Jerman, 1980) .................................. 135

5.2.1 Comparison of Viscosity for PET/60%PHB Measured at 260 C Using Capillaries with Different Diameters ........................ 141





5.2.6 Entrance Pressure Loss as Function of Apparent Shear Rate for 60 Mole % PHB/PET Measured at 260 C Using Capillary with Different Diameters .. 146





x

5.2.11 Viscosity versus Wall Shear Rate for 60 Mole% PHB/PET at 275 C (without Correcting for Pressure Entrance Loss) .................................. 151

5.3.1 Distribution of Colors in a Molded Plaque of PET Homopolymer (Mold Temp.= 100 C, Melt Temp.= 285 C, Injection Speed= 40 cm/min) .................... 156

5.3.2 Velocity of Various Fluid Pigments versus Time for PET Homopolymer (Mold Temp.= 285 C, Injection Speed = 40 cm/min, Cavity Thickness= 0.1250 inch) ................. 157

5.3.3 Longitudinal Section of Short-Shot type of Injection for 60 Mole% PHB/PET ................. 158

5.3.4 Longitudinal Section of Short-Shot type of Injection for 80 Mole% PHB/PET ................. 159

5.3.5 Proposed Mold Filling Mechanism for PET/PHB Copolymer Systems ............................... 160

5.4.1 Schematic Representation of the Bulk Structure of Liquid Crystalline Copolymers of PET modified with 60 and 80 Mole% PHB ....................... 168

5.4.2 Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to the Flow Direction for 60 Mole % PHB/PET (Mold Temp. = 100 C, Melt Temp. = 275 C Cavity Thickness= 0.125 inch) .................. 169

5.4.3 Effect of Injection Speed on Shrinkage of Microtomed samples Transverse to the Flow Direction for 60 MOle % PHB/PET (Mold Temp.= 100 C, Melt Temp.= 285 C, Cavity Thickness= 0.125 inch) .................. 170

5.4.4 Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to the Flow Direction for 80 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp.= 305 C, Cavity Thickness= 0.125 inch) .................. 171

5.4.5 Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to the Flow Direction for 60 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp.= 275 C, Cavity Thickness= 0.0625 inch) ................. 172

5.4.6 Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to the Flow Direction for 60 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp. = 285 C,

xi

Cavity Thickness= 0.0625 inch) ................. 173

5.4.7 Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to the Flow Direction for 80 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp.= 305 C, Cavity Thickness= 0.0625 inch) ................. 174

5.4.8 Effect of Cavity Thickness on Shrinkage Transverse to the Flow Direction for 60 Mole % PHB/PET (Mold Temp. = 100 C, Melt Temp.= 275 C, Injection Speed= 20 cm/min) ................... 175

5.4.9 Effect of Cavity Thickness on Shrinkage Transverse to the Flow Direction for 60 Mole % PHB/PET (Mold Temp. = 100 C, Melt Temp.= 285 C, Injection Speed= 20 cm/min) .................... 176





5.4.14 Effect of Injection Speed on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp. = 165 C, Melt Temp.= 275 C, Cavity Thickness= 0.125 inch) .................. 181

5.4.15 Effect of Injection Speed on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp. = 165 C, Melt Temp.= 285 C, Cavity Thickness= 0.125 inch) .................. 182

5.4.16 Effect of Injection Speed on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp. = 165 C, Melt Temp.= 275 C, Cavity Thickness= 0.0625 inch) ................. 183

5.4.17 Effect of Injection Speed on Shrinkage of

xii

Microtomed Samples for 60 Mole % PHB/PET (Mold Temp. = 165 C, Melt Temp.= 285 C, Cavity Thickness= 0.0625 inch) ................. 184

5.4.18 Effect of Cavity Thickness on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp. = 165 C, Melt Temp.= 275 C, Injection Speed= 20 cm/min) .................... 185




xiii

LIST OF TABLES

3.1.1 Temperature for Viscosity Measurement of Poly (Ethylene Terephthalate) and its Copolymer of PET & p-hydroxybenzoic Acid ...................... 46

3.2.1 Gear Ratio and Speeds for Instron Model 3211 Capillary Rheometer .............................. 50

3.5.1 Compression Molding Temperature for PET and its Copolymer with PHB ............................... 61

3.6.1 Injection Molding Conditions ..................... 64

3.7.1 Annealing Time and Temperature for Shrinkage Measurement ...................................... 67

xiv

Chapter I

INTRODUCTION

Liquid crystalline polymers are materials which possess

fluid-like mechanical properties but also are capable of

transmitting polarized light under static conditions, and in

some cases, they exhibit Bragg diffraction of X-rays (Wen-

droff, 1978). These optical properties are the result of a

high degree of molecular order in the fluid state of the po-

lymer. Thermodynamically, the liquid crystalline state is a

stable state existing between the solid and fluid phases and

is, therefore, referred to as a mesophase or ~ mesomorphic

state (Wendroff, 1978). For polymer to possess this meso-

morphic state, the structure of the molecule is invariably

highly ~anisotropic in shape, usually rod-like or lath-like

and composed of a rigid central section with some flexible

end group (Wissbrun, 1981).

Liquid crystalline polymeric systems have received con-

siderable interest in recent years for several reasons.

First, a study of liquid crystalline polymer literature re-

veals that liquid crystalline polymers in the solid state

possess exceptional physical and mechanical properties which

arise as a result of molecular structure and orientation

generated in the fluid state. Secondly, processing of these

1

2

materials can be carried out more rapidly with less expendi-

ture of energy due to lower viscosity than that of polymers

with the same molecular weight in the isotropic state.

Furthermore, liquid crystalline polymers may be spun to pro-

duce ultra-high strength fibers (Morgan, 1976).

Recent studies focussing on synthesis and rheology of

thermotropic liquid crystalline copolymers of polyethylene

terephthalate (PET) modified with p-hydroxybenzoic acid

(PHB) have appeared in the literature (Jackson &: Kuhfuss,

1976; Wissbrun, 1980; Jerman&: Baird, 1981). By increasing

the mole percent of PHB in the chain, the chain stiffness is

increased to the point that is sufficient to yield a polymer

system which exhibits liquid crystalline behavior (McFarlane

et al., 1977). The physical properties of injection molded

specimens of these materials were reported to be highly ani-

sotropic. Physical properties measured al·ong the flow direc-

tion were exceptionally higher than those measured across to

the flow direction. Furthermore, these properties were de-

pendent on melt temperature and the dimension of the mold.

In particular, they found that the physical properties were

highly dependent on the thickness of the mold and increasing

with decreasing mold thickness. According to these authors,

this is probably due to an increa·se in orientation as the

result of high shear rates and the increased cooling rate

3

which resulted in preserving more of the orientation pro-

duced during flow.

In general,the final properties of the injection molded

parts are directly related to its molecular orientation in

the melt state and its processed condition. This molecular

orientation may be influenced by a layer of molecules at the

boundary with different molecular orientation than those in

the core fluid. Fisher and Fredrickson (1969) have reported

this influence on viscosity of low molecular weight liquid

crystalline polymer. Leslie and Ericksen have developed

constitutive theories f0r nematic liquid crystalline fluids

which lead to the prediction that the viscosity depends on

some characteristic width, i.e. radius of the capillary, as

well as on shear rate. Because of this influence of the

boundary, the r,heological properties of liquid crystalline

polymer may change with the size of the flow channel, i.e.

radius of the capillary. In turn, the mechanical and physi-

cal properties of the molded parts may also be changed. It

is the purpose of this study to investigate this boundary

layer effect on the rheological property of the thermotropic

liquid crystalline polymer of PET modified with 60 and 80

mole % PHB. In particular, viscosities 9f these polymers

will be measured using different capillary diameters to det-

ermine whether viscosity depends on capillary diameter as

4

predicted from the liquid crystalline continuum theory de-

veloped by Ericksen (1969) and Leslie (1969).

The final physical properties of any injection molded

specimen depend on the molecular orientation generated in

the filling stage of injection molding. In this study, the

mold filling characteristics of PET/PHB copolymer in both

unidirectional flow and radial flow will be investigated by

means of a tracer technique. Pigmented fluid elements will

be used as tracers to illustrate flow patterns.

The fact that physical properties of injection molded

specimens of PET/60PHB are highest at 275°C as stated in the

publication of Jackson & Kuhfuss (1976) will be further stu-

died by injection molding this polymer at different melt

temperatures in an Instron rheometer. By microtoming the

injection molded parts, shrinkage measurement will be per-

formed to qualitatively determine the molecular orientation

of the molded test specimens. This, in turn, may help to

explain the dependence of the mechanical properties of these

materials on melt temperature and mold thickness.

Injection molding of these copolyesters in end-gate cavi-

ties leads to plaques which have anisotropic properties.

Studies will also be carried out using a center-gate disc

cavity in order to investigate the' possibility for obtaining

biaxial orientation.

Chapter II

LITERATURE REVIEW

The final mechanical properties of injection molded spe-

cimens of poly (ethylene terephthalate) modified with p-hy-

droxybenzoic acid are excellent and highly anisotropic. To

understand the reasons for these unusually high mechanical

properties, one must know its liquid crystalline behavior.

Therefore, the first section in this chapter will review the

nature of liquid crystalline polymers in general and specif-

ically the poly (ethylene terephthalate) modified with p-hy-

droxybenzoic acid. Since the mechanical properties are re-

lated with the skin-core formation generated during mold

filling process, the next section in this chapter will re-

view the mold filling mechanism in a rectangular cavity and

the skin-core morphology of the injection molded specimen.

Last, injection molding studies for different shape of molds

are also included in this chapter.

5

6

2.1 LIQUID CRYSTALLINE ORDER

2.1.1 General

A liquid crystalline polymer is one which exhibits physi-

cal and mechanical properties of regular fluids. However, it

also has a high degree of molecular order which is somewhat

characteristic of a crystalline solid. This high degree of

molecular order can be detected by light scattering, X-ray

techniques, or Bragg reflections of X-ray (Wendroff 1978).

This order occurs in many different forms and may exist in

local regions in either the melt state or solution. Because

of this ordering, liquid crystalline polymers have been

classified into thermotropic and lyotropic mesophases. Ther-

motropic liquid crystals are materials that are transformed

into a mesophase simply by heating these materials above

their melting points. Lyotropic liquid crystals mesophases

are formed by increasing the concentration of polymer in so-

lution. Soap and water is a typical example of liquid crys-

tals of this type. The distinction between thermotropic and

lyotropic liquid crystal is not exclusive, however. For lyo-

tropic case, the degree of liquid crystallinity is a func-

tion of both concentration and temperature. Any change in

temperature may affect the critical concentration, the con-

centration at which liquid crystalline domains are formed.

Therefore, for a lyotropic liquid crystal, transitions from

7

thermotropic to isotropic state can occur by changing both

the temperature and concentration of the solution.

Depending on the nature of the ordering, liquid crystal-

line polymers may be classified into three mesophases: ne-

matic, smectic, and cholesteric. The nematic mesophase is

one in which there is no long-range order of the position of

the molecule. In this mesophase, molecules tend to line up

in a preferred direction which is described by a "director".

The distribution of the director among the molecules is

characterized by the "order parameter" S (Du Pre, 1974):

S = 1 /2 < 3 Cos2 6 - 1 ) 2 .1.1

where e is the angle between the major axes of the molec-

ules and the direction of the pref erred alignment in the do-

main (nematic director). For complete isotropy, the value of

S equals zero. This value would equal to one for a perfectly

parallel arrangement of the molecules. For a typical meso-

phase, the range for the S values from 0.8 to 0.3 has been

reported (Saupe, 1969).

The preferred direction of the molecules discussed above

gives rise to the anisotropy to the fluid which, in turn, is

responsible for many optical properties such as birefrin-

8

gence (Tsvetkov et al., 1978), NMR splitting (Mcfarlane et

al., 1977) and light scattering (Wendroff, 1978). For the

systems displaying high strength or high modulus, it is gen-

erally the nematic morphology that is preferrably induced.

Because of the preferred direction of the molecules, the

nematic director can be easily influenced by interacting

with electric and magnetic fields (Filas, 1977) as well as

by shear (Porter and Johnson, 1967). In the proximity of the

surface, the molecules may be oriented at some angle to the

surface, forming a boundary layer of the molecules. This an-

gle is a strong function of the physical and chemical treat-

ment of that surface (Fisher and Fredrickson, 1969).

Similarly to the nematic mesophases,the cholesteric meso-

phases possess a preferred direction and do not exhibit

long-range positional order. However, unlike nematics, the

direction in space of the "director" varies helically along

an axis perpendicular to the plane in which the director

lies as shown schematically in figure 2.1.1 (Wissbrun,

1981). If the pitch of the helical structure is similar to

the wavelength of visible light, a selective reflection of

monochromatic light can be observed. This effect leads to

the irridescent colors often observed in cholesteric meso-

phases (Wendroff, 1978). Due to the lack of the overlap bet-

ween the long axis of the molecules, polymer systems of this

9

type do not possess high strength or high modulus in con-

trast to that of purely nematic mesophase.

Among the three types of ordering, smectic is the most

ordered mesophase. In smectics, the molecules are arranged

in well-defined layers so that they do have a long range po-

si tional order in one dimension which is perpendicular to

the layer plane (Wissbrun, 1981). Since smectic liquid crys-

tals possess a higher degree of order than that seen in the

nematic mesophase, it is natural to assume that the S values

will be higher. This is indeed the case. The S values for

this mesophase have been reported as high as 0. 9 (Du Pre,

1974). Al though possessing the highest degree of ordering,

materials having smectic morphology do not exhibit high

strength or high modulus. This is due to the lack of mole-

cular backbone overlap in the orientation direction.

2 .1.2 The Thermotropic Liquid Crytalline System of Poly (Ethylene Terephthalate) and p-Hydroxybenzoic Acid

Although poly (ethylene terephthalate), (PET), is widely

used in the fiber and film industry, it has only limited ac-

ceptance as a molding plastic. The reason for this is the

need of a hot mold (140-150°C) to allow the polymer to crys-

tallize (Jackson & Kuhfuss, 1976). In an attemp to solve

this problem and also to meet certain specific flammability

standards, the amount of aromatic character of PET was in-

10

creased by modifying it with p-hydroxybenzoic acid ( PHB)

(Jackson & Kuhfuss, 1976; Mcfarlane et al., 1977). This mo-

dification of PET can be accomplished by a, reaction illus-

trated in Jackson and Kuhfuss publication ( 1976). In this

copolymerization, p-acetoxybenzoic acid (I) reacts with it-

self at 275°C and consequently with PET (III) to give short

acetoxy-terminated and carboxyl-terminated segments.

0 II

C"l c- 0 u3 .I

0

-@-~-OH (I)

II II 11 ot o ot· c o--<Q>--c-o-@-c OH +

0 II

Cu c o·· •l 3 - ti

0 0 11~11

CP. 3 C - 0 --0--- C - OE + r ~ ~ ~-o- cn,cn,of-t (III)

+ g --@--L OII + CE 3 L 0 --@-- ~ - OCH2 CE, 0 ~

These products were then condensed by heating under high

vacuum conditions to give a high molecular weight polyester.

11

II II 11 0 0 0 -t C --@-- C - 0--@-- C - OC.:I 2CH 20 +

0 II

Cµ COTT ... ~ 3 ti

The molecular structures of the final product of this reac-

tion and of PET homopolymer are shown in figure 2.1.2.

The effect of having PHB segments in the copolyester is

to increase the chain stiffness of the polymer (McFarlane et

al., 1977). By increasing the mole percent of PHB in the

chain, the chain stiffneas is increased to the point that is

sufficient to yield a polymer system which exhibits liquid

crystalline behavior.

The physical and mechanical properties of PET modified

with 60 and 80 mole percent PHB are excellent when compared

to the other copolymers of different composition of PHB con-

tent. This is due to the presence of liquid crystallinity

in the melt state of PET modified with 60 mole percent of

PHB and to some lesser extent in PET modified with 80 mole

percent of PHB. The glass transition temperatures of both

of these copolyesters were not observed. The melting point

of PET/80PHB is 293°C and is shown to have a very weak en-

12

do therm while the melting point of PET/60PHB has not been

observed. The later phenomena is probably due to the forma-

tion of liquid crystallinity.

Probably, one of the most unusual properties of these co-

polyesters is the melt viscosity. The effect of PHB contents

on melt viscosity at 275°c is shown in figure 2.1.3. It is

noteworthy that the melt viscosities increased as the PHB

content was increased to about 30 mole percent and then de-

creased as the PHB content was increased further to 60 mole

percent. The effect of the shear on melt viscosities of

these copolyesters at 275°C is shown in figure 2.1.4. As the

PHB content increases, the polymer becomes shear-sensitive

at lower shear rates.

The mechanical properties of the injection molded speci-

mens of these copolymers are exceptionally high. When com-

pared to the same copolymers with different PHB content, PET

modified with 60 mole percent PHB is reported to have maxi-

mum flexural modulus, Izod impact strength, and minimum

Rockwell hardness. The absence of mold Shrinkage in composi-

tion containing 40.,-80 mole percent PHB is also reported.

This is probably due to the long relaxation time of these

polymers (Jackson & Kuhfuss, 1976).

The unusual high mechanical properties of liquid crystal-

line polymers probably arose from the orientation generated

13

in the melt state. Especially, in injection molding, the ef-

fect of molecular orientation on the mechanical properties

is more pronounced. For 60 mole percent PHB, as the tempera-

ture of the melt increases from 210°c to 260°C, the melt

viscosity decreased. If the speed of the polymer melt in-

jected into the mold increased, the orientation of the po-

lymer chains therefore would increase (Jackson &. Kuhfuss,

1976). The melt temperature at which this copolyester is

injection molded affects the orientation of the liquid crys-

tal polymer chains and therefore affects its mechanical

properties. The mechanical properties of PET/60PHB increase

as the melt temperature increases from 210 to 260°C. Above

280°C, the properties seem to decrease. According to Jackson

and Kuhfuss (1976), this decrease is probably due to some

loss of orientation of the polymer chains in the melt before

the solidification of the melt takes place.

The nature of the liquid crystalline polymer melt causes

it to be easily oriented by the shear force and extentional

flow during injection. Since the mechanical properties in-

crease as the degree of orientation of the copolyester in-

creases, it is expected that the properties of the "along

the flow direction" are higher than those of "across the

flow direction". In fact, this is observed in the work of

Jackson and Kuhfuss (1976). For 60 and 80 mole percent PHB,

14

the mechanical properties are reported to be highly aniso-

tropic. It is also reported that the mold shrinkage and

coefficient of linear thermal expansion are zero along the

flow direction but not across the flow direction.

In summary, the mechanical properties of injection molded

specimens of PET/PHB copolymer system are highly anisotrop-

ic. These properties are directly related with the molecu-

lar orientation generated in the melt state. Since the de-

gree of molecular orientation in a molded specimen depends

on the melt temperature, mold temperture, specimen's shape

and thickness etc, the mechanical properties are strongly

dependent of these same variables (McFarlane et al., 1977).

The phenomena of low melt viscosities and anisotropic prop-

erties can be explained on the basis of liquid crystalline

formation.

2 .1. 3 Rheological Properties Of Thermotropic Liquid Crystalline Polymers

In recent years there have been a number of papers con-

cerned with the rheology of lyotropic liquid crystalline po-

lymers and a variety of interesting effects; e.g concentra-

tion dependence of viscosity, long relaxation time, apparent

yield stress, and negative normal stress have been observed

(Baird, 1978). Not many comparable studies has been reported

on thermotropic liquid crystalline polymer besides some mea-

15

surements of viscosity as a function of temperature and of

shear rate for the copolyester of poly (ethylene terephth-

late) and p-hydroxybenzoic acid (Jackson and Kuhfuss, 1976;

Jerman and Baird, 1981). Wissbrun (1980) measured the rheo-

logical properties of PET modified with 60 mole percent PHB

using a Rheometrics Mechanical Spectrometer and a capillary

rheometer. In his work, Wissbrun reported a long relaxation

time for the melt, estimated from shear rate dependence of

viscosity and from melt elasticity. The long relaxation time

is presumably associated with the rotation of whole molec-

ules (or of units composed of many segments}, or perhaps of

the cooperative motion of many such molecules or units.

Wissbrun (1980) also observed many cases of unusual flow

behavior including rheopexy in some compositions, negative

normal stresses, and negligible die swell. The rheopexy phe-

nomena is explained to be due to the presence of "a struc-

ture of some sort in the melt." In systems that have an ap-

parent yield stress, but do not show appreciable thixotropy,

the time required for the formation of the structure res-

ponssible for the yield stress must be small compared to the

time between successive measurements. What that structure

might be is not stated clearly in his publication.

Using an Instron Capillary Rheometer, Jerman and Baird

(1981) measured viscosities and die swell of PET/60PHB and

16

PET/80PHB as well as PET homopolymer. The melt viscosity of

PET/60PHB was reported to be considerably lower than that of

PET homopolyrner. This is probably due to the orientation in-

duced from the shear flow and the present of the liquid

crystalline domain in the melt. During flow, these oriented

domains act as the flow unit rather than the individual mo-

lecules. The molecules slide smoothly over each other. Thus

less energy is dissipated than is the case for the randomly

oriented and/or entangled molecules (Jerman and Baird,

1981).

The viscosity of PET/80PHB is higher than that of

PET/60PHB when compared at the same temperature. As reported

by Jackson & Kuhfuss (1976), the PET/80PHB copolyester exhi-

bits a crystalline melting point at 293 ° C, whereas the

PET/60PHB copolyester exhibits neither a glass transition

temperature nor a melting point. Hence the higher viscosity

of PET/80PHB copolymer may be attributed to solidlike re-

gions. However, as the temperature increases, the viscosity

becomes extremely low.

Values of extrudate swell, Dj /D, were reported to in-

crease with increasing melt temperature for both of these

copolymers. This phenomena is probably due to the yield

stresses and negative normal stresses. According to Jerman

and Baird (1981), the lack of extrudate swell could be at-

17

tributed to the yield stresses which inhibit elastic recov-

ery of the extrudate. Furthermore, the shear field in the

capillary is limited to a narrow region near the wall with

the core of the melt passing through the capillary in plug

flow. Therefore, there exists some region in the melt in

which elastic recovery does not occur. At low temperature,

the formation of the yield stresses probably arose from the

crystalline regions. As the melt temperature increases, the

magnitude of the yield stress decreases, thus allowing some

extrudate swell to· occur.

Another possibility which explains this extrudate swell

phenomena is the presence of the negative primary normal

stress differences (N1 ) (Jerman and Baird, 1981). N1 is ne-

gative or negligible when ~/Dis less than or equal to 1.0.

Probably, as temperature increases, the formation of the

isotropic region increases which inturn leads to the posi-

tive values of N and therefore to the values of Dj/D greater

than 1.0. However, if the isotropic regions form, then the

viscosity of the melt is expected to increase but it does

not. These authors suggested that either one or the combina-

tion of these explanations may be respossible for the ob-

served behavior of extrudate swell.

18

NEMATIC

QQQQeG6QQ QQQGeGBUQ QQQQeGIJUQ QOGGeGGQ~ OOQBe~ooo

CHOLESTERIC

r \ r\J\ r\ 0 r, i\\\ (',I\ 0 nu· \j \J \j ·J\).J \J r. "(\ (\(\ .r·\({\ n ~ (\ UU \JU\J U.J\JUU\J 0000\JQ~OOOQ

SMECTIC A Figure 2.1.1: Schematic representation of Mesophase Types

(Wissbrun, 1981)

19

0 0 11~11 C~- C -0-CH2CH 2-0---4---

(A) PET HOMOPOLD,!ER

0 0 0 II -\Q)--11 . C 0 C-0-CH2CH2-0 ~--(Q}--o

m n (2) GENERAL STRUCTURE OF COPOLYESTER

60 Mole % Ph13/PET m = 0.4 n = o.6 80 Mole % PHB/PET m = 0.2 n = 0.8

Figure 2.1.2: Poly (ethylene terephthalate) and its copolymers with p-Hydroxybenzoic Acid

VISCOSITY (275°C), PJISE 105

10 0 20

20

40 60 p-HYDROXYBENZOIC ACID, M)LE %

•

80

SHE..\R RA.TE ,

• 15 0 100 ... 1600 0 54000

100

Figure 2.1.3 : Effect of p-Hydroxybenzoic Acid Content on Melt Viscosity at 275°C (Jackson and Kuhfuss, 1976)

S'""'cC-1

MELT VISCOSITY (275°C), POISE

104

10 1

• PET .A PET/20PHB 6 PET/40PHB 0 PET/SOPHB • PET/60PHB

10

• •

Figure 2.1.4 : Effect of Shear on Melt Visc©sity of PET Modified with p-Hydrox:ybenzoic Acid (Jackson and Kuhfuss, 1976)

22

2.2 THE MECHANISM OF SKIN-CORE FORMATION IN INJECTION MOLDING

The final properties of any injection molded article will

depend on the molecular orientation generated in the melt

state. These properties are also a result of the skin-core

formation in an injection molded article. However, the me-

chanism in which the melt fills in the mold would explain

the skin-core formation and the molecular orientation. It is

obvious, then, that the final properties of an injection

molded article would depend on the mold filling characteris-

tics and the skin-core morphology resulting from this flow.

In this section, the flow of polymer melt in injection mold-

ing is reviewed first. The skin-core morphology generated

from this flow is then discussed.

2.2.1 The Flow Of Polymer Melts In Injection Molding

In general, the mechanism of the flow can be visualized

by considering a velocity profile in the central portion of

the advancing front between the two parallel plates (figure

2 . 2 . 1 ) ( Tadmo re, 19 7 4) .

flow is:

The velocity for two dimensional

VX 0

V"t = Ky

Vz = -Kz

23

where K is the rate of elongation. These equations imply

that a rectangular fluid element while moving toward the

front will decelerate in the axial direction, will acceler-

ate in the perpendicular direction, and during this process

will be stretched in the y direction at a constant rate.

In such a steady elongational flow, macromolecules are

stretched and oriented in the y direction. The degree of or-

ientation of these molecules is then dependent on the rate

of elongation. Tadmore (1974) assumed for an order of mag-

nitude calculation that at a distance of 2B upstream of the

front, a fully developed shear flow exists. Therefore, the

rate of elongation is given by the following expression:

- K = Vmax - <v)

2B (2.2.1)

where:

flow

= maximum velocity of the fully developed

<V> = the mean velocity If the power law fluid

model is used in this flow:

2n + 1 n + 1 <v)

Equation (2.2.1) and (2.2.2) can be combined to give:

(2.2.2)

24

- K = n <v) 2(n + 1 )B

(2.2.3)

The flow pattern in figure 2. 5 implies an elongational

orientation perpendicular to the melt flow ( y-direction),

whereas the experimental observation reveals an orientation

in the direction of the flow. This apparent discrepancy can

be better understood by considering the actual shape of the

advancing front, which is almost semicircular in shape.

Therefore, the macromolecule will actually follow the free

surface in a curved path until it.reaches the wall as shown

in figure 2.2.2. At this point, macromolecules will have an

orientation which is parallel to the wall. If the rectangu-

lar channel is a wide slit, the flow can be considered to be

two dimensional flow and the orientation will be exclusively

in the flow direction. But if the rectangular channel is not

a wide slit, the flow cannot be considered as a two dimen-

sional flow, and the orientation in both the direction of

flow and transverse to it would be expected. If the cross

section is a square or circular shape, longitudinal and

transverse direction should be similar to each other.

The fluid particles which hit the wall will immediately

solidify, thus freezing the orientation induced by the elon-

25

gational flow. The amount of orientation will depend on the

rate of elongation. Equation (2.2.3) shows that an increase

in injection speed and a decrease in cavity thickness will

result in an increase in orientation. For liquid crystalline

polymers, the latter effect has been observed in the work of

Jackson and Kuhfuss ( 1976). The mechanical properties of

these polymers when measured along the flow are reported to

be higher for the thin cavity than that for the thick cavity

(figure 2.2.3). This measurement indicates that decreasing

cavity thickness will result in an increase in molecular or-

ientation (along the flow only).

The foregoing discussion only addresses the flow mechan-

ism at the flow front. Behind this flow front, an entire

different flow mechanism (shear flow) exists as discussed by

Menges and Wubken (1973). From the section along the flow

direction ( figu.re 2. 2. 4), there exist frozen surface layers

with no motion. The highest velocity gradients, greatest

shear rate, are below the frozen surface layers. Here, the

melt is intensively sheared. This gives rise to a relative

maximum molecular orientation below the frozen surface lay-

ers. Behind the front, as shown in figure 2.2.5, the veloc-

ity vectors of the flow are parallel to the x-axis (flow di-

rection). The average velocity of the melt in this section

is much greater than the velocity of the flow front. There-

26

fore, the melt particles behind the front would rapidly

catch up with it and flow transversally to the front as dis-

cussed earlier in this section.

2.2.2 The Skin-Core Morphology Of Injection Molded Objects

It is generally recognized that the final properties of

injection molded parts are strongly dependent on morphology,

orientation and stress applied during processing (Baer,

1964; Bayer, 1960; Maxwell, 1965; Stein, 1964). Many studies

of various polymers have shown that injection molded objects

have a skin made up of molecules that are highly oriented in

the flow direction and an essentially unoriented central

bulk region which is called a core region. This morphology

has been observed in both glassy and semicrystalline polym-

ers and has been reported throughout the literature (Jackson

and Ballman, 1960; Kantz et al., 1972; Wales, 1972; Ballman

and Toor, 1960). The high degree of molecular orientation in

the skin has been observed in certain instances to cause

warpage, shrinkage and premature fracture during impact and

flexural testing (Keskkula et al., 1965; Morris, 1968).

Optical microscopy shows that the injection molded parts

under any processing condition displayed the skin-core mor-

phology as previously discussed. Kantz et al. (1972) studied

the skin-core formation of a polypropylene tensile bar. They

27

observed that there exist intermediate layers parallel to

the flow direction and between the skin and core. This in-

termediate layer, the shear zone, is spheruli tic and its

morphology differs from that in the core region. The spheru-

li tes are randomly nucleated in the core region while those

in the shear zone are row nucleated. The latter indicates a

higher degree of molecular orientation than that in the core

region. In figure 2. 2. 5, the morphological structure of a

typical tensile bar is shown. This bar is made up of a core,

two layers of shear zones on either side of the core and two

skin zones on each of the two large surfaces.

28

2

Advancing Fr~

-y

Center Ll.ne

LIQUID

GAS

Direction of Flow

+Y

Fi~e 2.2.1 : Schematic Representation of the Flow pattern in the Central Portion of the Advancing Front between Two Parallel Plates (Tadmore,1974)

Advancing Front

29

Cold Wall ---B-----

Figure 2.2.2 Flow Pattern in The Advancing Front Between Two Parallel Plate (Tadmore, 1974)

FLEXURAL MODULUS, 105 PSI

26

24

22

20

18

16

14

12

10

8

6

30

PEI'/60PHB

~\ ~ \

I

\

4

2

ACROSS~

-0

0.0 0.1 0.2 0.3 0.4

TIUCKNESS, IN.

0.5

Figure 2.2.3 : Effect of thickness on Along-The-Flow Flexural Modulus of PET Modified with 60 Mole % p-Hydroxybenzoic Acid (Jackson & Kuhfuss, 1976)

Velocity Profile

,,.--- Solidifying Layer

Shear Rate

Flow Direction

Figure 2.2.4: Schematic Diagram of the Velocity Profile of the Flow Behind the Front and its Correspondin~ Shear Rate

32

Fi~ure 2.2.5 : Tensile Par (Schematic) Showing the Arrangement of the Morphologic Zones

33

2.3 INJECTION MOLDING STUDIES

Injection molding flows are highly complex as a result of

the unsteady and non-isothermal conditions. This process in-

volves the injection of molten plastics into cold, complex

cavities in which they solidify to form fabricated parts.

The mechanical properties of a molded part are strongly de-

pendent on the molding morphological features which in turn

are related to cavity flow as well as packing pressure and

cooling rate (Schmidt, 1977). One qualitative method for in-

vestigating the kinematics of melt flow is to observe flow

patterns in different channels. The first scientific study

of the injection molding process was carried out by Spencer

and Gilmore (1950,1951). In their.publications, the authors

studied the orientation, residual stresses,_ pressure losses

and the fluid mechanics of mold filling. Using a glass win-

dow, these authors observed that polymer melt flows only in

a central region of the mold and there exist stationary lay-

ers next to the mold walls. They proposed that when polymer

melt reaches the advancing front (polymer-air interface), it

contacts the mold wall, cools and stops flowing.

To investigate the flow front as polymer fills up the

mold, many reseachers adapted the flow visualization techni-

que used by Spencer and Gilmore to study mold filling in

many different complicated geometries. The flow patterns of

34

polystyrene in a disc-shaped cavity were photographed by

Beyer and Spencer (1960). They observed a circular spread-

ing front as shown in figure 2.3.1.a.

More recently, mold filling in a rectangular channel was

investigated visually (figure 2.3.1.b) (White et al., 1974;

Schmidt, 1977). White and Dee (1974) studied mold filling

characteristics of polymer melts in a rectangular mold as

shown in figure 2. 3. 1. b for isothermal and non-isothermal

flows. The apparatus used in their work was a modified In-

stron Rheometer where in stead of a capillary die, a com-

bined nozzle and mold assembly were attatched to the lower

end of the barrel. The mold is primary designed for flow vi-

sualization and the outer clamping blocks are fitted with

Pyrex plate glass windows. For isothermal flow, they ob-

served that there are two basic flow regimes,mold filling

and jetting phenomena, depending upon the injection rate of

the molten polymer into the mold. Figure 2. 3. 2 shows the

slow isothermal flow of polymer melts into a rectangular

mold. The mold filling may be divided into three stages.

First, on passage from the narrow constriction at the gate

into the mold, the melt spreads in an approximately radial

manner. Secondly, after the corner are filled, there is a

transition region in which the front changes from a circular

shape to an almost flat profile. Finally, the nearly flat

35

front continues to move forward un:til the mold is filled.

The front shape seems flat except for some convex curvature

near the mold wall. In this final region, the velocity of

the center of the mold appears more rapid than near the

walls. This observation, in general, is in good agreement

with the observation made by Spencer and Gilmore (1951). At

high injection rate, White and Dee observed jetting flow in

the mold. This phenomena is also reported in the work by

Spencer and Gilmore (1951).

For non-isothermal flow of melts into a rectangular mold,

the flow is also divided into three stages as described in

the isothermal case. However, the non-isothermal flow dif-

fers from the isothermal one in two aspects. First, the

greater channeling of flow from the gate through the center

of the cavity to the front. Second, the greater degree of

curvature of the front has been observed as it moves through

the mold. These phenemena probably are the result of the

variation in rheological properties of the melts with temp-

erature across the cavity cross-section. The lower tempera-

ture of the melt in the vici~ity of the mold walls means a

higher viscosity. As a result, the velocity of the melt in

the core is higher due to a lower viscosity than that in the

vicinity of the walls. This type of flow is interpreted as

channelling. The channelling of the melt in the center com-

36

bined with the solidification of the polymer near the wall

must lead to the curvature of the moving front (White and

Dee, 1974).

To study the skin-core formation of injection molded

parts, Schmidt (1974,1977) used the same equipment as de-

scribed in the work of White and Dee (1974). Flow patterns

in the mold cavity were illustrated using a visual tracer

technique. Basically, five different inorganic pigments were

introduced in the polymer rod, in an identified color order,

which had been made from compression molding of the polymer

and load into the Instron barrel. Schmidt found that the

first tracer to enter the cavity is located near the gate

while the last tracer to enter is found near the bottom of

the mold. Thus the order of the tracers is inverted during

mold filling. In the vicinity of the gate region, the melt

decelerates as it exits the gate and flows into a diverging

channel. The first part of the tracer entering the cavity

is decelerated by a slowly moving melt pool ahead of it. The

diverging channel in the gate region decelerates the tracer

even further as it moves radially from the gate. Because of

this radial flow, the tracer becomes extended as a circular

arc. Schmidt found that the shape of the core is elliptic

instead of a rectangular shape as defined by the steel mold.

He also found that the tracer splits at the midplane and

37

this tracer is found on the front. This occurs probably be-

cause the flow front is continuously splitting. The split-

ting action adds an additional velocity component to the

velocity vector. Therefore, the trajectory of the midplane

tracer material is an arc from the midplane to the cavity

wall. This flow mechanism produces the molecular orientation

as reviewed in the previous section.

As discussed previously, the flow of the polymer melt in

the entrance region is classified as radial flow. Kamal and

Kenig (1972) proposed a model for this type of flow. In this

work, these authors used a semicircular mold as shown in

figure 2.3.1.c. This mold was chosen in order to study ra-

dial flow without the interference from the wall of the

mold. The model is based on setting up the equation of con-

tinuity, motion and energy for the system during each of the

stages of the injection molding cycle i.e. filling, packing

and cooling. Using numerical techniques, they were able to

solve for the flow rate, velocity profiles at different

times and front positions in the cavity, and the progression

of the melt front.

The radial flow in which the melt is fed at the center of

the mold (figure 2.3.1.d) has also been studied by many au-

thors (Berger and Gogos, 1973; Wu, Hwang, and Gogos, 1974;

Laurencena and Williams, 1974; Winter, 1975; Schmidt, 1976).

38

Berger and Gogos (1973) and Wu et al. (1974) used the gener-

al transport equations, i.e. continuity, momentum and energy

equations to solve the transient and non-isothermal problem

of filling a disc-shape cavity with poly (vinyl chloride).

From this result, these authors predict pressure gradients,

fi 11 time and short shots. Furthermore, the velocity and

temperature fields were obtained throughout the formation of

a frozen surface layer during filling.

Following the work of Berger and Gogos and Wu et al. ,

Winter (1975) conducted a similar investigation but included

poly (ethylene) and polystyrene. He chose to modify the pow-

er-law model to include the normal stress components and

used in this model to predict pressure gradients and normal

stress distribution. The computed result differ by about 20

percent with the experimental pressure profiles.

In all of the work involving_ radial flow discussed so far

the flow at the entry region has been ignored. All of these

investigators obtained numerical solutions to the equations

of continuity, motion and energy based on a power-law const-

itutive relationship. From the numerical solution, they com-

puted temperature and pressure gradients, velocity profiles,

and the position of the advancing front as a function of

time. The inlet effects due to the stagnation flow were also

assumed negligible, and the solution started at a point bey-

ond this stagnation region.

39

Schmidt (1976) studied both the stagnation flow and

diverging radial flow between the parallel plates. He used

pigmented fluid elements as tracers to illustrate the flow

patterns which were recorded on a movie film. The data taken

from this movie film served as a basis to measure the veloc-

ity of the fluid elements as a function of both time and

distance. He found that the complex entrance region associ-

ated with stagnation flow leading to diverging radial flow

between parallel plates is large and of the order of 5 to 10

times the plates seperation. The flow in this region is a

combination of extensional flow and shear flow resulting

from the rearrangement of the velocity profile. Beyond the

entrance region, the flow is less complicated and can be de-

scribed as a combination of plannar extension and simple

shear flow.

40

!

---

(a) (b)

0 (c) (d)

Figure 2.3.1 Mold Filling Patterns in Different Geometry

Rffi!ON 3

GATE ENTRANCE ' \

\ I

I I

/ ,,.

.F'LOW DIRECTION FLOW FRONT

Figure 2.3.2 Mold Filling Characteristics in Rectangular Cavity

42

2.4 SUMMARY

In summary, the work of Jackson and Kuhfuss (1976) on the

liquid crystalline copolyester of PET has raised many ques-

tions with regard to the physical and mechanical properties

of these copolymers. Probably, as a result of molecular or-

ientation induced in the melt state, low viscosity and the

excellent properties of these materials had been observed.

As found by Fisher and Fredrickson (1969), viscosity of li-

quid crystalline polymers of nematic type is influenced by a

layer of molecules, at the boundary, with different molecu-

lar orientation than that of the core fluid. It is the pur-

pose of this study to investigate this boundary layer effect

on viscosity of thermotropic liquid crystalline copolyester

of~ PET modified with 60 and 80 mole percent PHB. Further-

more, the molecular orientation induced during the flow may

be attributed by the flow front and the shear flow behind

the front as discussed by Tadmore (1974) and Menges & Wubken

(1973). The mechanism of mold filling both by the advancing

front and shear flow is further investigated in this work

for liquid crystalline PET/PHB copolymer systems. Last, the

state of molecular orientation generated in the melt flow

depends on injection speed, cavity thickness, melt tempera-

ture, mold temperature etc.. It is also the purpose of this

study to investigate the molecular orientation of the injec-

43

tion molded parts under different molding condition by mea-

suring at the shrinkage of their microtomed samples.

Chapter III

EXPERIMENTAL PROCEDURE AND MATERIAL

3.1 PLAN OF INVESTIGATION

The experimental work in this study of thermotropic li-

quid crystalline polymers was carried out on an Instron

rheometer. The possibility of a boundary layer effect on

rheological properties of PET/PHB polymer system was inves-

tigated by measuring viscosity of PET,PET/60PHB, PET/80PHB

as a function of shear rate using capillaries with different

diameters. The dependence of melt viscosity on capillary

diameter might be indicative of a possible layer of molec-

ules with different orientation at the boundary from those

in the core. Temperature dependence of the boundary layer

effect was also investigated by repeating these experiments

at different melt temperatures (see Table 3.1.1).

A mold filling study was carried out using the Instron

rheometer as an injection molding unit. The polymer melts

were injected into a mold attached to the bottom of the In-

stron barrel. Two types of molds were designed in order to

generate two types of polymer melt flow. The end-gated mold,

where the melt is fed at one end of the mold, was designed

for unidirectional flow. The center-gated mold, where the

melt is fed at the center of the mold, was designed for ra-

44

45

dial flow. The purpose of having the center-gated mold is to

make an attemp to generate biaxial orientation. Flow visual-

ization was accomplished by introducing different color pig-

ments into the melt and using a TV camera to record the

movements of these colored pigments through glass windows in

the mold. The mechanism of the melt filling the cavity was

investigated by making short-shots in which the fluid par-

tially fills the cavity. Finally, the molecular orientation

in these flows, i.e. radial and unidirectional flows, was

qualitatively studied by measuring the shrinkage of the mi-

crotomed samples.

Table 3.1.1: Temperature for Viscosity Measurement of Poly (ethylene terephthalate) and Copolymers of PET and p-Hydroxybenzoic Acid

Temperature, PEI' 0 c Homopolymer

260

275 x

285 x

305

315

60 Mole % PHB/P'.ET

x

x

x

80 Mole % PHB/PET

x

x

47

3.2 INSTRON CAPILLARY RHEOMETER

The viscosity measurements were carried out using Instron

cappillary rheometer (Instron model 3211). A schematic dia-

gram of the various parts of the rheometer is shown in fig-

ure 3. 2. 1. The rheometer consists of a resevoir barrel,

heated by four band heaters which are controlled through a

PID (Proportional Integral Derivative) controller located on

the rheometer front pannel. The polymer under investigation

is placed in the preheated barrel. a stainless steel plun-

ger, sealed near the front tip by a double 0-ring, is placed

in the barrel and used to drive the sample out through the

capillary installed at the bottom of the barrel. The plunger

is driven by a constant speed drive system resulting a cons-

tant flow rate. The available speeds are listed in table

3.2.2. The retarding force on the plunger is measured by a

load cell which is capable of measuring forces up to 2000

KG.

There are certain problems associated with measuring the

correct value of the force in capillary rheometer. In gener-

al, two types of forces contributed to the force r~corded on

the chart recorder. The first type is due to the pressure

drop across the capillary. The second type is due to the

friction between the plunger and the barrel. The latter

type (with magnitude of 0.08 to 0.16 Kg) varies depending on

48

the position of the plunger in the barrel (the amount of

contact between the plunger and the barrel). In measuring

low forces as in the case of the polymer involved in this

study, this friction force becomes a serious problem. To ob-

tain a repeatable value, the Instron barrel was half-filled

with polymer and care was taken to record the values of the

force at the same position of the plunger for every run.

49

INSULATION

~--;-,._HEATERS

r----+-1- CAPILLARY

---RETAINING RING

Figure 3.2.1: Schematic Diagram of Instron Capillary Rheometer (Jerman, 1980)

50

TABLE 3.2.i

Gear Ratio and Speeds For Instron Model 3211 Capillary Rheometer

(Cm/Min)

Gear Ratio

1 :1 1:2 2:1

o.06 0.03 0.12 0.20 0.10 0.40 0.60 0.30 1.20 2.00 1.00 4.00 6.oo 3.00 12.0 20.0 10.0 40.0

51

3.3 MOLD DESIGNED

The injection molding apparatus used in this study was a

modified Instron rheometer where a combined-runner mold as-

sembly is attached to the lower end of the barrel as shown

in figure 3.3.1. Two runners are made of stainless steel 302

and have lengths of 4. 445 centimeters ( 1. 75 inches). The

inside diameter of one runner is 0.3175 centimeter (1/8

inch) and of the other is 0.1588 centimeter (1/16 inch) cor-

responding to the two cavity thicknesses of 0.3175 and

0. 1588 centimeter used in this work. The runners were de-

signed to be analogous to the Instron capillary (figure

3. 3. 2) so that it can be easily inserted into the Instron

barrel just as inserting the capillary. The Instron barrel

and the runner apparatus results in the as semblance of an

extruder with a 90 degree angle nozzle entrance.

Two molds were designed corresponding to two types of

melt flow, unidirectional and radial flows. The first mold

is constructed in four parts and clamped together by six

symmetrically placed screws (see figure 3.3.3). It is

threaded at one end to accept the mating thread of the run-

ner. For flow visualization purposes, the two large plates

associated with the cavity were replaced with two Pyrex

plate glass windows 1.27 x 2.54 x 8.89 centimeters (or 1/2 x

1 x 3. 5 inches), obtained from Lab Glass Inc. Kingsport,

52

Tennessee. The cavity thickness can be changed by changing

the spacing between the two large surfaces of the mold. The

cavity is rectangular in shape and has a dimension of 2.54 x

8.89 x 0.3715 (or 0.1588) centimeters. The mold temperature

was controlled by four 150 watts catridge heaters connected

in parallel to an Omega model 4001 controller. The heaters

were inserted in holes drilled on the wall of the mold and

perpendicular to the large surface. An Iron-Constantan ther-

mocouple was placed near the top of the mold. In this way,

the mold temperature is always kept within ±1°C from the set

point. The temperature variation over the mold surface was

checked by means of a thermocouple attached at the bottom of

the mold. It had been observed that no temperature gradient

existed over this large surface of the mold.

The second mold was designed for radial flow. Basically,

it is same as the first mold except its size and the posi-

tion of the ·gate entrance. This mold has a dimension of

10.16 x 10.16 x 4.445 centimeters (or 4 x 4 x 1 .. 75 inches.

Instead of being end-gated, it has a threaded hole at the

center of the large surface to accept the mating thread of

the runner (see figure 3.3.4). Because of this position of

the runner, this mold is called center-gated mold.

53

~ ..... ..... ..... ..... . ..... I-..... ..... .... -.... -.... .... ..... -..... ..... .... ..... -..... ....

. .... . ~ ... -.... -r--._

~-... -,

I - I I I I I I I I

--~ · - - r--._ "---~-

FIGURE 3.3.1: INJECTION MOLDING APPARATUS

Plunger

Insulation

Polymer Melt

Rheometer Barrel

Capillary Screw Nut

Rtmner

Mold Assembly

Glass Window

Cavity

54

+ 0. ?>

//

_.____-t 0. 185"

t.5o"

0.38 Fine Thread

FIGURE 3.3.2: RUNNER

55

Figure 3. 3. 3: Photograph of Recta.."1.gular Mold

56

77

Fi.gure 3.3.4: PhotofSraph of Circular :fold

57

3.4 SAMPLE PREPARATION

The polymers used in this study are poly (ethylene ter-

ephthalate) and two copolyesters of PET, 60 and 80 mole %

p-hydroxybenzoic acid. The PET homopolymer is milky white

with glossy surface. The 60 mole percent pellets are an off

white with a soft sheen. The 80 mole percent pellet is beige

color wi;th rough appearance. All three polymers were pre-

pared and supplied by Tennesse Eastman Laboratories at

Kingsport, Tennesse.

According to Jackson and Kuhfuss (1976), the flow behav-

ior of these polymers is a function of temperature, shear

rate, and moisture content. Due to the chemical structure of

this polymer system, care had to be taken to avoid the pres-

ence of water or moisture during the experiments. This ne-

cessitated a carefull drying and special loading techniques.

Polyester such as PET is extremely hygroscopic (Van Der

Wielen, 1976) and the polymer will undergo a degradation in

the presence of moisture, resulting in a decrease in molecu-

lar weight and consequently, a decrease in viscosity (Wiss-

brun, 1979).

In this work, polymer pellets were stored in small glass

containers (28.3 ml) with sealable lids. The specimens were

placed in a vacuum oven and dried at a temperature of 110°c

and under a vacuum of 63. 5 centimeters of mercury for 72

58

hours. At the end of the drying time, the pressure of the

oven was returned to atmospheric pressure by bleeding in

prepurified nitrogen. On reaching atmosheric pressure, the

glass containers were covered, sealed using electrical tape

and allowed to cool to room temperature. All of these con-

tainers were then kept in a dessicator.

During each loading of polymer into the Instron barrel,

care was taken to retain as much of inert atmosphere as pos-

sible. A prepurified nitrogen line was connected to flow

downward into the rheometer barrel. This would displace the

moist air in the barrel. A small amount of polymer pellets

was rapidly fed into the barrel with the nitrogen still

flowing. The polymer was then tamped down to remove any

trapped gas bubles as the polymer melted. This process of

loading was repeated until the barrel had been half-filled

with polymer. The plunger was

slight pressure was applied,

then put in position and a

sealing the polymer from the

surrounding atmoshere as it was allowed to reach the running

temperature.

59

3.5 SAMPLE PREPARATION FOR FLOW VISUALIZATION STUDIES --- ---POLYMER ROD

For the visual tracer technique, five different colors of

pigmented polymers were placed into the polymer melt column

in the rheometer barrel. This was accomplished by inserting

these pigments into a precompression-molded polymer rod. The

rod is then fed into the rheometer from the bottom. In this

experiment, the polymer rod was prepared using the Instron

plunger-barrel as a compression unit. First, the barrel was

preheated to a compression molding temperature. This temp-

erature was chosen to be different depending on the type of

polymer (see Table 3. 5. 1). The bottom of the barrel was

blocked with a small disk which was held in place by the ca-

pillary screw nut. A small amount of polymer pellets was fed

into the barrel. The polymer was then compressed by the

plunger to a pressure of 1. 4 x 10 7 N/M 2 . Th f e process o

loading small amounts of pellets and compression was repeat-

ed until the barrel had been completely filled. At this

time, the barrel was allowed to cool down to a "cooling

temperature" to solidify the polymer inside the barrel. To

get the polymer rod out of the Instron barrel without using

a great amount of force, the temperature of the barrel was

slightly raised to a higher temperature. The rod was then

pushed out by means of the plunger.

60

To insert the pigmented polymer into the polymer rod,

five small holes were drilled partially through the rod,

perpendicular to the axis of symmetry. Pigmented polymer

pellets were inserted into these holes and plugged with the

original unpigmented polymer. The polymer rod was then fed

into the hot rheometer barrel.

Type of Polymer

PET Homopolymer

60 Mole % PHB/PET

80 Mole % PHB/PET

61

TABLE 3.5.1

Compression Holding Temperature for PET and its Copolymer with PHB

Compression Temperature,°C

230

220

270

Extrusion Temperature,°C

200

180

220

62

3.6 INJECTION MOLDING

In this experiment, the runner was held in place at the

bottom of the Instron barrel by the capillary screw nut. The

polymer pellets were then loaded using the same technique

discussed in section 3.4. At this time, the polymer was al-

lowed to reach the injection temperature before the mold as-

sembly was attached. During this heat-up period, a small

steel plug was placed in the runner to prevent the melt from

flowing down under the influence of the gravity. The plug

was quickly removed just before the mold assembly was at-

tached at ~he end of the runner. The mold was preheated by

four catridge heaters to an appropriate temperature. Final-

ly, the material was injected into the mold cavity at a

constant flow rate of 0.2375(10-4 ) and 0.475(10-4 ) cubic me-

ters per second. Similar experiments were run for a variety

of conditions. A summary of these conditions is shown in Ta-

ble 3.6.1

For short-shot type of injection, the same procedure de-

scribed above was used except that the polymer rod was fed

into the rheometer barrel from the bottom before the runner

was placed at the end of the barrel. The injection step was

stopped when the second fluid pigment showed up on the wall

of the cavity. This color can be seen through the glass win-

dow of the mold. The short-shot injected plaque was then cut

63

along to the flow direction and the photographs of these

sections were taken.

Type of Polymer

PET Homopolymer

60 Mole % PHB/PET

80 Mole % PHB/PET

TABLE 3.6.1: INJECTION MOLDit\lG CONDITIONS

Melt Temperature,°C

275

275, 285

305

Mold Temperature,°C

Rectangular Mold Circular Mold

100 165

100 165

100 165

O" .p-..

65

3.7 SHRINKAGE MEASUREMENT

Melt flow during the molding of injection molded parts

always causes an orientation of macromolecules along the

flow direction. This orientation significantly influences

the properties of the molded parts. To qualitatively study

the macromolecular orientation development of the molded

parts, a small sample of the molded plaque was cut and mi-

crotomed. The geometry and dimension of this cut are shown

in figure 3. 7 .1 for both rectangular and circular plaque.

This sample was microtomed using the Spencer 860 sliding mi-

crotome machine. The thickness of the microtomed specimen is -5 approximately 2.54(10 ) meter. The dimension of each of

these specimens was measured using a caliper. The thickness

was measured using a micrometer. From these thicknesses,

the distance from surface of each microtomed sample was det-

ermined. These samples were then heated in the oven above

their softening temperatures. These temperatures and the

heating times for different polymers are shown in Table

3.7.1. Finally, the dimension of the annealed samples was

remeasured and the percent shrinkage was calculated.

66

(a) Rectangular Plaque

~ o. 2"

(b) Circular Plaque

Figure 3.7.1: Dimension of Sample Cut From Injection Molded Parts

'fype of Polymer

60 Mole % PHB/PRI'

80 Mole % PHB/PET

67

TABLE 3.7.1

Annealing Time and Temperature for Shrinkage Measurement

Annealing Time, Min.

10

10

Annealing Temp., °C

200

260

4.1 CAPILLARY RHEOMETRY

Chapter IV

RESULTS

From the force and plunger speed data of the Instron ca-

pillary rheometer, viscosity of poly (ethylene terephtha-

late) and its copolyesters with 60 and 80 mole % p-hydroxy-

benzoic acid were determined. First, the graphs of total

pressure drop, !:::.. P, versus the apparent shear rate, 'kAP? ,

were contructed. Examples for this type of graphs are shown

in figure 4. 1. 1 to 4. 1. 3. Pressures at constant apparent

shear rates were taken from these graphs and plotted against

the capillary length to diameter ratio, L/D. This type of

plot is commonly called a Bagley plot. The lines of the Bag-

ley plot appear to be nearly linear and were fit into a line

least squares program. From this program, the intercepts of

these lines with the ordinate give the end pressures (in-

cluding entrance pressure loss and exit residual pressure)

for various shear rates. In general, the exit residual

pressure is small and the end pressure can be assumed as

entrance pressure loss (Han, 1976). Typical examples of

Bagley plots corresponding to figure 4. 1. 1 to 4. 1. 3 are

shown in figure 4.1.4 to 4.1.6. Figures 4.1.7 to 4.1.9 show

the results of entrance pressure loss, /:J. Pen , as a function

68

69

of shear rate. The shear stress at capillary wall, t:w , was

corrected using the following equation:

fl? - 6 PeY\ 4(1/D)

4.1.1

Figure 4.1.10 to 4.1.12 show the graphs of corrected wall

shear stress versus apparent shear rate. The slopes of these

lines were determined by a linear least square fit and used

to calculate the corrected wall shear rates, Ow :

. (;'w =

Jn + 1

4n i App

4.1.2

Figures 4.1.13 to 4.1.15 show the graphs of corrected wall

shear rate. From the values of corrected wall shear stress

and shear rate, the viscosity can be found from:

= 4 .1. 3

Figures 4 .1. 13 to 4. 1. 19 show the plots of viscosity as a

function of wall shear rate.

70

Throughout the viscosity measurement a fortran program

was used based on the above outline. A copy of this program

is shown in appendix A.

The results of these calculations are presented in tabu-

lar form in appendices B-1 through B-3 Values of raw

data, apparent and wall shear rates, corected wall shear

stresses, melt viscosities and entrance pressure losses are

given.

-c-J • () Q)

Cl) • :::

...........

~ ........ Q)

~ f/l f/l Q)

J::

~ E-t

106

105

60 MOLE % PHB/PET at 275°C (Capillary Diameter= 0.027 inch)

0 L/D= 55.63

0 L/D= 37.11

6 L/D= 15.26

2(1of '---L-__.___._.___.__.__._._~_.___._-L---l-L-L.JL.L.L.~--'~_._..J__l__J___j~.L_~_J___L__._-'--'--LL~ 2.5(10)1 102. . 10 3

'(w (Sec.-• ) 1oir

Figtn'e 4.1.1: Typical Plot of Total Presstn'e versus Apparent Shear Rate for 60 Mole% PHB/PET

-.J __.

107

-"' . 0

r93 • ~ .......... ~ .......... Q)

~ (Q (Q Q)

106 ~ r-1

~ E-t

105

10'

80MOLE % PHB/PET at 305°C (Capillary Diameter= 0.027 inch)

102 i. (Sec.- 1 ) w 103

0 L/D= 55.63

8 L/D= 37.11

b L/D= 15.26

10""

Figure 4.1.2: Typical Plot of Total Pressure Versus Apparent Shear Rate for go Mole % PHB/PET

-J l\J

.......... ...a.

()

~ • ~

.......... ~ .......... Q) a (/) (/) Q)

~

~ ~

107

10b

PET HOMOPOLYMER at 285°C (Capillary Diameter= 0.027 inch)

c::J L/D= 55.63

0 L/D= 37.11

0 L/D= 15.26

2(1of ..._._~_._~_._.......~~_.__.__._-'--'L._L_Jl-Li.~~-'---L--L--L-JL--L-l--'--L~~J.._--'--'---L.....l---'-'....L.I 2.5(10)1 10 2. 3 . 10 I 15-w (Sec.- )

104-

Figure 4.1.3: Typical Plot of Total Pressure Versus Apparent Shear Rate for PET Homopolymer

-..J VJ

74

60 MOLE % PHB/PET at 275°C (Capillary Diameter = 0.027 inch)

15 0 2000 ~ 1000 ~ 900 0 800

\/) ~ 700 0 (;:::, ,..- 600 >< 0 ........ 500

N, Q GJ 400 Q>

C') • 10 0 300 ~ ............

~ ..........

~ ~ ~ p..,

~ 0 E-t

5

o.oo 15.26 37.11 55.63 L/D

Figure 4.1.4: Typical Bagley Plot for 60 Mole % PHB/PET

30

\0 0 ..-><

........ c-a •

0 ID

(/) • :<::

...........

~ 20 -~ ~ p...

~

o.oo

0 tJ ~ 0 ~

0:,

0 8 0

2000 1000

900 800 700 600 500 400 300

15.26

75


37.11 55.63 L/D

Figure 4.1.5: Typical Pagley Plot for 80 Mole % PHB/PET

15

..$) 0 ,.... ::< -"'· () (1)

U,l • 10 ::::;:: ...........

~ -~ §3 ~ p...

~ 0 E-1

5

o.oo

0 ~ 0 ~

8 0 [!]

0

1000 900 800 700 600 500 400 300

15.26

76

L/D

PET HOMOPOLYMER at 285°C (Capillary Diameter = 0.027 inch)

37.11 55.63

Figure 4.1.6: Typical Bagley Plot for PEI' Homopolymer

Figure 4.1.7:


102 103 10"' 105" "i(APP (Sec .-1 )

Entrance Pressure Loss versus Apparent Shear Rate for 60 Mole % PHB/PET

.......... "' . ~ 107 • ::?.:: .........

M ~ ......... Cl) Cl)

8

~ ~ fl...

~ 10'1

~ ~


6(10*)~L-J..--'--.j~-'-;;-~~----L~L__L-L-L-L.L.l~~--L~-L--1-L...L..LLLL~___!_l_--1.....1....J 30 10 1 o3 10 lf-

y _, o APP (Sec. )

Figure 4.1.8: Entrance Pressure Loss versus Apparent Shear Rate for 80 Mole % PHB/PET

"""' cl • ()

~ • ::?.: ...........

~ ..._., Cl) Cl) .s Q) s Cl) Cl) Q)

~ Q) ()

§ _fj iS

" 10

105

PET HOHOPOLYMER at 285°C (Capillary Diameter = 0.027 inch)

0

0

0 0

0

0

0

103

0

1APP (Sec.-1) Figure 4.1.9: Entrance Pressure Loss versus Apparent Shear Rate for PET Homopolymer


/ /

103

'j{ APP (Sec.-1) 10't

Figure 4.1.10: Wall Shear Stress versus Apparent Shear Rate for 60 Mole% PHB/PET at 275t>C

00 0

-cJ • (.)

~101+ ~

.......... ~ ........ (/) (/) Q)

b Cl)

fd Q)

61 ~ 10 !>

200 25

80 ;,10LE % PHB/PET at 305°C (Capillary Diameter = 0.02? inch)

2.. 10 10 3

".:./ I 0 APP (Sec.- )

101.t

Figure 4.1.11: Wall Shear Stress versus Apparent Shear Rate for 80 Mole% PHB/PET at 305°C

co ~

PET HOMOPOLYMER at 285°C

- (Capillary Diameter =0.027 inch) <"I •

0 Q)

ti) • ::E: .........

105 ~ .._.. (I) (I) Q)

_f3 ti)

m 83 r-l

~ 101+

2(1of ,_.___.__..__,'--'---'~~~____.~__.___.___,.___._-'--'-'L-L--~-'---JL-JL...-L-L-l_i_J__J-_~_.____.___.__J__J_j_~ 25 10 103 101t 105

l5APP (Sec.-') Figure 4.1.12: Wall Shear Stress versus Apparent Shear Rate for PET Homopolymer at 285°C

CXl lV

~ t) Q)

U) • ~ t) I'll

~ .........

c'

10 1 -... ...

...

10° f-- 0 260°C c:J 275°C 0 285°C

60 MOLE % PHB/PET (Capillary Diameter = 0.027 In.)

-I I I I 10 ._.__,_1___,__.___.--'-'-_.__~_,_~_.__~1_._~,~·'-'-'--'-~---'-'~_.____.___.__. • ._._.._._.~~-·.___.__.__.__,_11_._.1_._.1

25 10 2. 10 ~ 10 It 1 o5

¥w (Sec:') Figure 4.1.13: Melt Viscosity as a Function of Wall Shear Rate for 60 Mole % PHB/PET with

Capillary Diameter of 0.027 inch

-0 Q)

Cl) •

'd 0 (J)

~ ....._...

I 10 -

0 260°C ['.] 275°C (> 285°C

60 MOLE % PHB/PET (Capillary Diameter= 0.05 In.)

0 G

0

2 ( 10-I ).__...___._-.1--~__._._..__ , _ __.__..___,__~-1-1.--L...L1 ----'-----L------'L.....-J..-'-.LJ_Ul------'--J.....__..J...• __L_-'--1.--L-1..J

25 1 oz. 10 "3 10 Lt v O, (SeG:1) ~

Figure 4.1.14: Melt Viscosity as a F\mction of Wall Shear Rate for 60 Mole % PHB/PET with Capillary Diameter of 0.05 inch

......,. 0 (1) I (/) 10 • -

M aj 0 (/) aj

p..,

s::.'

10° -

25

0 260°C c:J 275°C 0 285°C

• I I I

60 MOLE % PIIB/PET (Capillary Diameter = 0.070 In.)

I I I

103

~w (Sec:1)

l

10Lt

Figure 4.1.15: Melt Viscosity as a Function of Wall Shear Rate for 60 Mole% PHB/PET with Capillary Diameter of 0.07 inch

co '-"

----·

0 305°C

El 31s 0c


I I

10~

(Sec.-•)

Figure 4.1.16: Melt Viscosity as a Function of Wall Shear Rate for 80 Mole % PHB/PET with Capillary Diameter of 0.027 inch

80 MOLE % PIIB/PET I (Capillary Diameter = 0.05 In.)

10 -() Q)

CJ) • ~ () Ul cd p_., .........

~ 0 305°C

10 0

-I 10

101

8 315°C

1oir

'if w Figure 4.1.17: Melt Viscosity as a Function of Wall Shear Rate for 80 Mole % PIIB/PET with

Capillary Diameter of 0.05 inch

00 .....J


,,......, 10 I (.) Q)

(/) •

'cl (.) Ul cd

ri. .........

s:-'

t)

10 O 305°C

EJ 315°C

2(10\.__,~-L...~L-.l-1-L...-'--'-~~~---'~_L__L__J__j'-'-L'-1.~~_.____._--'--L-'-l_L.l_J_~-l.~..L-1

10 10 103 104-'i{ W (Sec: 1 )

Figlll'e 4.1.18: Melt Viscosity as a function of Wall Shear Rate for 80 Mole% PHB/PET with Capillary Diameter of 0.07 inch

co co

PET HOMOPOLYMER (Capillary Diameter = 0.027 In.)

2 ........ 10 (.)

~ • «1 (.) I'll

~ .......

s;-' ~ 275°C

I 0 285°C 10

2 101 103

'if w (Sec:1 )

Figure 4.1.19: Melt Viscosity as a Function of Wall Shear Rate for PET Homopolymer with Capillary Diameter of 0.027 inch

CXl

'°

90

4.2 MOLD FILLING CHARACTERISTICS

The investigation of mold filling characteristic of these

liquid crystalline polymer systems composes of two parts:

Flow visualization of color pigmented polymers and short-

shot type of injection. First, from the video tape recorded

during experiment, the distance of fluid pigments from gate

was plotted against the time of injection. Examples of this

plot for the flow visualization of PET are shown in figure

4.2.1 and 4.2.2. Figure 4.2.1 shows the data of these plots

of PET injected into a cold mold whereas figure 4.2.2 shows

a similar plot for injection into the hot mold. The slopes

of these data points on these curves

of the fluid pigments at that time.

represent the velocity

Figure 4.2.3 and 4.2.4

show the velocity of these pigments as a function of their

positions in the mold (distance from gate).

The flow visualization experiments described above only

show the movement of the pigmented polymers in two dimen-

sions: along the flow and across the flow direction. To see

the complete picture of the filling patterns of the melt

flow, one must see the filling pattern of these pigments in

the section perpendicular to the large surface of the melt

flow and parallel to the direction of flow. Figures 4.2.5

to 4.2.7 show the photographs of a short-shot type of injec-

tion for PET, PET/60PHB and PET/80PHB respectively. Lastly,

91

a photograph of a section transverve to the flow direction

and perpendicular to the large surface of the melt flow is

shown in figure 4.2.8.

......... ~

'--"

$ ~ s 0 H

CH Q) t)

~ £Jl a

300

PET HOMOPOLYHER at 285°C 0

0 ~

0 Flow front b,

~ Violet 0 200 0 Orange b,

6 Green () b,

0Red 0 0

[J Blue ~ 0 ~ &

0 & 0 &

() & 100 ~

0 &

~ 0 <) 0 0 0 <)

8 Q [] [] Q [] [] G ~

8 f! 0 0

'------'--- ·-----0 10 20 30 40 50 60 70 80 90 1UU

Play I3ack Slow Time (Sec.)

Figure 4.2.1: Distance from Gate versus Time for Various Fluid Pigments in a Cold Mold (Mold Temp.= 100°C, Cavity Thiclmess = 0.125 inch, Injection Speed= 40 cm/min.)

,_Q I\)

300 PET HOMOPOLYIIER at 285°C

8 Flow front

[;:::, Violet

0 Orange

8 Green

0Red (J Blue

jg ~ El

0 6 ~ 0 0

G

0 ~ 6 0

0

(J

0

0 ~ b.

0 b.

0 0 0 ~ 0

0 6 6 6 6

0 0 0 0

0 EJ (J G

0 ..___. __ , _____ __. _______ .___ _ ___._ __ ___. ___ ___._ __ ___._ __ ___._ __ -'----J. __ _

0 10 20 30 40 50 60 70 80 90 100 Slow Time (Sec.)

Figure 4.2.2: Distance from Gate versus Time for Various Fluid Pigments in a Hot Mold (Mold Temp.= 200°C, Cavity Thiclmess = 0.125 inch, Injection Speed = 40 cm/min.)

,0 'vJ

PET IIOMOPOLYHER at 285°C 0 Fl.ow frmt

~ Violet ~ 0 Orange

8 Green

0 Red

~ El filue

20 0

......... 6 ~ t) Q) Cll 00 8 .......... 0 0 0 0 0 0 0 ~ 0 !:::.

v 8 ~ ~ ~ ~ ·rl 10 t) 0 rl & 0 Q) :> 0

8 0 El El 8 0

El & 0 El 0 & 0 0 ____ ______.__, ________ ________.

0 50 100 150 200 Distance from Gate (mm)

Figure 4.2.3: Velocity of Various Fluid Pigments versus Distance from Gate in a Cold Mold (.Mold Temp.= 100°C, Cavity Thickness= 0.125 inch, Injection Speed= 40 cm/min.)

,_Q l'-

-() Q) rJl ......... ~ ~

$ •r-1 () 0 rl ~

PET HOHOPOLYMER at 285°C 0 now frcmt ~ Violet

0 Orange 8 Green

0 Red

~ EJ Blue

20 8 ~

~

0 00 ~ 0 0 0 0

~ ~

8 0 8

10 ~ 0 8 0 EJ 0

8 ~

EJ 0 0

0

EJ 0 8 EJ 0~ ~ EJ

0 .~ 0 50 100 150 200

Distance from Gate (mm)

Figure 4.2.4: Velocity of Various Fluid Pigments versus Distance from Gat~ in a Hot Mold (Mold Temp.= 200°C, ~,avity Thickness= 0.125 inch, Injection Speed= 40 cm/min.)

'° \J1

96

Figure 4.2.5: Longitudinal Section of Short-Shot type of Injection for 60 Mole % PHB/PET

97

Fisure 4.2.6: Longitudinal Section of Short-Shot Type of Injection for 80 Mole ~ PHB/PET

98

Figure 4.2.7: Longitudinal Section of Short-Shot type of Injection for PET homopolymer

99

Figure 4.2.s: Photograph of Section Cut Transverse to the Flow Direction

100

4.3 SHRINKAGE MEASUREMENT OF MICROTOMED SAMPLES

Molecular orientation generated during the injection

molding of polymer melt influences significantly the proper-

ties of the molding.

face to the core of

This orientation varies from the sur-

the ~njection molded part. Since

shrinkage depends on this state of orientation, one method

to qualitatively rate the degree of orientation is to mea-

sure the shrinkage of the microtomed samples of the injec-

tion molded parts. The state of orientation depends on many

injection molded variables, i.e. speeds of injection, cavity

thicknesses, mold temperatures, type of melt flow. Conse-

quently, the degree of shrinkage will vary with these varia-

bles as well. In this section, the plots of the percent

shrinkage of microtomed samples versus the distance from the

surface of the molded parts are shown for various injection

molded conditions. Figures 4.3.1 to 4.3.12 show the shrink-

age measurement data for the injection molding of liquid

crystalline polymer into a rectangular channel (unidirec-

tional flow). Figures 4.3.1 to 4.3.3 show these data with

injection speed of 20 centimeter per minute and cavity

thickness of 0. 125 inch. Figures 4. 3. 4 to 4. 3. 6 show data

with the same cavity thickness but with a higher injection

speed, 40 centimeter per minute. For a smaller cavity

thickness, 0.0625 inch, figures 4.3.7 to 4.3.9 show shrink-

101

age data with injection speed of 20 centimeter per minute

whereas figures 4. 3. 10 to 4. 3. 12 show shrinkage data with

higher speed of injection, 40 centimeter per minute. With

the same injection molding conditions as in the case of uni-

directional flow above, figures 4. 3. 13 to 4. 3. 18 show the

shrinkage data for radial polymer melt flow.

8

2

0 0

0

o.oo

UNIDIRECTIONAL FLOW 60 MOLE % PHB/PET at 275°C

0 0

0 0 0

[] across-the-flow direction

G) along-the-flow direction

0 0 0 Center

\ G.vi 0.02 O.OJ 0.04 0.06

Distance from Surface (inch)

Figure 4.3.1: Shrinkage of The Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 275°C, Injection Speed= 20 Cm/Min., Cavity Thickness= 0.1250 inch)


8

c:J across-the-flow direction

() along-the-flow direction 6

4

8

2 Center

G 0 0

0 0 0

0 0 0

0 0

0~00 0.01 0.02 0.03 0.04 0.05 0.06 Distance from Surf ace (inch)



8 (] across-the-flow direction

c::> along-the-flow direction

2

0 0 0 0 G 0 0 0

0 o.oo 0.01 0.02 0.03 0.05 0.06



8

0

2

0 0

o.oo o.ot


0 0.02 0.03

GJ across-the-flow direction

0 along-the-flow direction

Center \i

0.04 0.05 0.06 Distance from Surf ace (inch)


_. 0 Vl

8

6

4

2

0 0 00 0

0 o.oo 0.01 0.02


8

0 0 0 ___a__ ___

0.03

(:J across-the-flow direction


0 0

0 Cent\

0.04 0.05 o.06 Distance from Surface (inch)


8

6

4

2

0 o.oo

UNIDIRECTIONAL FLOW 80 MOLE % PHB/PET at 305QC

0 0 00 0 0 0

0.01 0.02

Q

[]

0 0.03

r::J across-the-flow direction

~ along-the-flow direction

Center 0 0 ~

0.04 0.05 o.06 Distance from Surface (inch)

Figure 4.J.6: Shrinkage of The Microtomed Samples of 80 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 305°C, Injection Speed= 40 Cm/Min., Cavity Thickness= 0.1250 inch)

..... 0 -.J


8

G] across-the-flow direction

6 0 along-the-flow direction

4

2 Center--

0 0 0 0 0 0 0 0

0 Q 0 0 o.oo 0.01 0.02 0.03


Figure 4.3.7: Shrinkage of The Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 275°C, Injection Speed= 20 Cm/Min., Cavity Thiclaless= 0.0625 inch)

~

0 (X)


16

4

oOElO 0

o.oo

0 0

0.01



0 0

0.02 Distance from Surface (inch)

Center

0 \ 0.03

Figure 4.3.8: Shrinkage of The Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 285°C, Injection Speed= 20 Cm/Min., Cavity Thiclmess= 0.0625 inch)

__. 0 ,0


8 8 across-the-flow direction

() along-the-flow direction

2

Center

0 0 0 0 0 \p 0

o.oo 0.01 0.02 0.03 Distance from Surface (inch)


16

Q) J 12

Jj

1 8

4

0 0 o.oo


0 0 0.01


() along-the-flow direction

Center---.

0 0 0.02 0.03


Figure 4.3.10: Shrinkage of The Microtomed Samples of 60 Mole% PHB/PET (Mold Temp.= 100°C, Melt Temp.= 275.°C, Injection Speed= 40 Cm/Min., Cavity Thickness= 0.0625 inch)


16 c:l across-the-flow direction


Center-~

4

0 () 0 0 0 0

o.oo 0.02 0.03 Distance from Surface (inch)

Figure 4.3.11: Shrinkage of The Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 285°C, Injection Speed= 40 Cm/Min., Cavity Thiclaless= 0.0625 inch)


8

Q. across-the-flow direction CD

i 0 along-the-flow direction 6

~ Cl)

fil e CD p... 4

Center

2

0 0 0 0 0 0 0 0 0 0 0 0 o.oo o.o-i 0.02 0.03


Figure 4.3.12: Shrinkage of The Microtomed Samples of 80 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 305°C, Injection Speed= 40 Cm/Min., Cavity Thicknes~= 0.0625 inch)

_. _. \.JJ

RADIAL FLOW f:IJ MOLE % PHB/PET at 275°C

20

0 8-direction

Q) ~ r-direction

I 15 ~ +> fa (.) J.t 0 if 10

Center 5

0 o.oo 0.01 0.02 0.03 0.04 O.C5 o.06

Distance from Surf ace {inch)

Figure 4.3.13: Shrinkage of The Microtomed Samples of 60 Mole % PUB/PET (Mold Temp.= 165°C, Melt Temp.= 275°C, Injection Speed= 20 Cm/Min., Cavity Thickness= 0.1250 inch)

__.. __.. ~

RADIAL FLOW 60 MOLE % PHB/PET at 285°C

20 0 e -direction

~ r-direction Q) jo

15

M +> ai C)

~ 10

5

Center

0 \ o.oo 0.01 0.02 O.OJ 0.04 o.os 0.06



__. __. \J'l


20

0 9-direction

r-direction

5

0 o.oo 0.01 0.02 O.OJ 0.04 0.05 o.06




16

8

4 () e-direction

r-direction

Center

0 \ o.oo 0.01 0.02 0.03 0.05 o.06


Figure 4.3.16: Shrinkage of The Microtomed Samples of 60 Mole% PHB/PET (Mold Temp.= 165°C, Melt Temp.= 285°C, Injection Speed= 40 Cm/Min., Cavity Thickness= 0.1250 inch)


20 0 9-direction

~ r-direction

15

10

5

6

0 Cente~


Figure 4.3.17: Shrinkage of The Microtomed Samples of 60 Mole% PHB/PET (Mold Temp.= 165°C, Melt Temp.= 275°C, Injection Speed= 20 Cm/Min., Cavity Thickness= O.o625 inch)

-' -' 00


20 0 6-direction

6 r-direction

(1)

I 15

~ 0 +> 53 (.) J..I 10 Cl)

p.,

5

Center

0 ~ o.oo 0.01 0.02 0.03

Distance from Surf ace (inch)


_. ...... -..o

20

Q)

J 15

~ ~ Q) 0 J... 10 ~

5

0 o.oo

RADIAL FLOW 60 MOLE % PHB/PET at 2?5°C

0 6-direction

~ r-direction

0.01 0.02 Distance from Surface (inch)

G 0 0

Center

~ 0.03

Figure 4.3.19: Shrinkage of The Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 165°C, Melt Temp.= 2?5°C, Injection Speed= 40 Cm/Min., Cavity Thiclmess= 0.0625 inch)

__. /\.) 0

20

Q)

J 15

~ +:> ~ Q) () ~ Q)

p.. 10

0 o.oo


0.01 0.02

0 8-direction

6 r-direction

0

Center ~

0.03 Distance from Sl.ll"f ace (inch)

Figure 4.3.20: Shrinkage of The Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 165°C, Melt Temp.= 285°C, Injection Speed= 40 Cm/Min., Cavity Thiclmess= 0.0625 inch)

..... /\) .....

UNIDIRECTIONAL FLOW 60 MOLE % PHB/PET at 275 C

8

0

6 0 -Q) [] hf) m 0 ~

•rl l:! D U)

0 -+> ~ 4 (.) 0 H Q)

P-.

8 0 B

2 ..

0 o.oo o.01 0.02

0 oD

0 0

0

0.03 0.04

0

0

r

0 00 0

Cienter . I

0.05 o.06 Figure 4.3.21: Comparison of the Across the Flow Shrinkage of the Microtomed samples of 60 Mole %

PHB/PET in two separate runs (Injection Speed= 20 Cm/Min, Cav. Thick.= 0.125 inch)

Chapter V

DISCUSSION

5.1 VISCOSITY MEASUREMENT

The first objective of this work was to determine whether

a boundary layer effect existed for liquid crystalline po-

lymers. The approach used to determine this effect was to

measure viscosity of these polymers as a function of shear

rate at different temperatures using capillaries with diffe-

rent diameters. As observed in chapter 4, the shear rate

range was limited to fairly high shear rates (from 40 to

5000 sec1 ) in the capillary rheometer. As a result, the vis-

cosity shear rate curves show the high-shear behavior of

these liquid crystalline fluids. The procedure to obtain

the viscosity-shear rate curves was outlined in chapter 4.

Basically, the corrected wall shear stresses were obtained

from the pressure data and corrected for the entrance pres-

sure loss by constructing the Bagley plot. The power law

melt flow indices were calculated from the slope of log of

wall shear stress versus log of apparent shear rate. This

value was then used to calculate the corrected wall shear

rate, and from this the viscosity-shear rate curves were ob-

tained.

123

124

The viscosity-shear rate curves of these polymers are

shown in figures 4.1.13 to 4.1.19. When compared at the same

melt temperature, PET/60 mole % PHB shows a much lower vis-

cosi ty than that of PET homopolymer. Typically, at 275° C -·1 and shear rate of 1000 sec ,viscosity of PET homopolymer is

61. 73 Pascal. Sec. whereas that of PET/60%PHB is 2. 8 Pas-

cal.Sec .. This can be explained in terms of an ordering ef-

feet. In general, the 60%PHB/PET molecules are more rigid

than PET molecules. During flow they are readily oriented

along the lines of the flow by the shear field. This re-

sults in lower viscosity than in the isotropic state.

In figures 4.1.13 to 4.1.15, viscosity of PET/60%PHB at

275cC shows an overlap with those at 260 and 285°C. This is

due to a change in viscosity when measured using capillaries

with different diameters. This phenomena will be discussed

in more detail in the next section (boundary layer effect).

Many difficulties were encountered in obtaining repeata-

ble values of viscosity, i.e. the position of plunger in the

Instron barrel, the thermal history of the melt before ex-

periment. A special experimental technique was developed

and reported in chapter 3 in order to obtain repeatable re-

sults. For the purpose of confirming this experimental tech-

nique, figures 5.1.1 to 5.1.7 show the viscosity-shear rate

curves between the data of this work, the data obtained from

125

the cone & plate rheometer (RMS) and from Jerman' s work

(1980). In these figures, the cone and plate data show vis-

cosity of the liquid crystalline polymer for a low shear

rate range (from 1 to 200 sec-~). Even though the cone and

plate data show a higher degree of scatter at shear rates

above 100 sec-i , the viscosity-shear rate curves obtained

from C&P matches fairly well with the capillary data. For

80% PHB/PET, the difference between the viscosity data in

this work and in Jerman's is due to the different capillary

design used in Jerman' s work. According to Jerman' s work

( 1980), a long portion of the designed capillary was pro-

truded to the outside of the Instron barrel (figure 5.1.8).

This portion was heated and controlled by a seperate heating

unit from that of the Instron barrel. Probably because of

this difference, the temperature of the portion outside the

barrel is lower than the temperature inside of the barrel.

As a result, a higher force was measured and a higher vis-

cosity was reported. Typically I at shear rate of 100 sec1

from Jerman's data, the viscosity measured using the capil-

lary design of Jerman is 18.2 percent higher than that mea-

sured using the standard capillary. For 60 mole % PHB/PET,

the same designed capillaries were used. However, the vis-

cosity data in this work is slightly higher than that of

Jerman's. This is due to different loading technique used in

126

Jerman's work. In this work, the polymer pellets are loaded

into the Instron barrel in a standard experimental procedure

as described in chapter 3. However, according Jerman, he

found that the 60 mole % PHB/PET pellets melted too rapidly

and adhered to the side of the resevoir, causing a bridging

effect across the month of the barrel. As a result, he used

a different loading procedure to perform his experiment. In

his work, the 60 mole % PHB/PET polymer pellets were com-

pression molded into a polymer rod and subsequently, the rod

was loaded into the Instron barrel. This procedure would

cause the polymer to decrease in molecular weight. The ef-

fect of the higher viscosity results from the use of the

protruding capillary of Jerman is probably less than the ef-

fect of the lower viscosity results from the loss in molecu-

lar weight. As a result, for PET/60%PHB, a lower viscosity

was measured in Jerman' s work than that reported in this

work.

As shown in figures 5.1.6 and 5.1.7, values for melt vis-

cosities of PET homopolymer are less than those measured by

RMS and Jerman. This could possibly due to degradation or

hydrolysis of the sample. Extrudate was collected for PET

homopolymer and run again to check for changes in pressure,

as a check for possible polymer degradation. For PET homo-

polymer at 275 and 285°c, with the resident time of the melt

127

in the Instron barrel of one minute, the pressure reading

was the same as that of the original run. This indicates

that PET samples used in this experiment had been degraded.

The process of degradation is probably due to hydrolysis of

the polymer (Van Der Wielen, 1975). Since degradation is the

result of a chemical reaction, it is evident that the extent

to which the material degrades will not only depend upon the

amount of moisture present but will also depend on the time

over which the reaction is allowed to proceed, i.e. the re-

sident ,time of the melt. To show this effect, a sample of

PET was run at 275 and 285°C, with the resident time of five

minutes, the pressure reading was lower on this run by 48.7

% at 275°C and 59.5 % at 285°C when compared with the ori-

ginal run. From these experiments, it is obvious that the

rheological property of PET is a strong function of both

moisture content and the resident time of the melt. Care

must be taken to eliminate these interference in future ex-

periments with this material.

t I s:-10 ~

10°

60 MOLE % PHB/PET at 260°C

101

6 Cone & Plate data (0.1 rad.)

D Jerman's data

() Capillary data

t _, (Sec. ) w

0 8

+ 8 0

~

[3)~ (8)Cl

Figure 5.1.1: Viscosity Versus Wall Shear Rate for PET/60%PHB at 260°c

_. I\) 00

0

........... • (.)

J3 • ~ (/)

~ ......... 1o'

~ f-


e 8one & Plate data (0.1 rad.)

0 Jerman's data

0 Capillary data

a 10°.__~---L-~-'-----'----'---'-~'-L-L·~~-'-~"'--~'-'--'-'---1-1..~·~~_i___J~L__j_J_l_L_L_J_i_l~~i·~-L---l

10° i"w (Sec.- I)

Figure 5.1.2: Viscosity Versus Wall Shear Rate for PET/60%PHB at 275°C


102 i-.. 6 Cone & Plate data (0.04 rad.)

0 Jerman's data - 4 ~ 0 Capillary data • 4 () <I> t Cl)

t • ~ t t/l t __. ~ w

0 .._,. I 4 ~

10 ... 4o 0 £x:J

[] Ooo [] 0

0 [] 0 Dc:::i 0

10° I I I I I I

10° 10 1 t (Sec.- 1 ) 102 103

w Figure 5.1.3: Viscosity Versus Wall Shear Rate for PET/60%PHB at 285°C


~ Cone & Plate data (0.1 rad.) 102 - 0 Jerman's data

~ ~ 0 Capillary data - Cl •

~ () Q)

Cl) ~ • 8 c::i (/) ...

~ 0 8! ...... "" ........ 0 ......

I c::i c:J 0 s:--' 10 f- (:J (:J

@00 8 r::J

['.] [:J 0 ·o

0 Oo

10°1--~_._·~~·_._-'-~'-'-'--Jl'-----~~·'------'-~·L_J._·~·L-L.JL.LL.l~~~'~~·__,__..___._11~•~·__._.__'~~-'--'-4-'-i..'-'----'-'..L-J

10° 101 Yw (Sec. -I)



6 Cone & Plate data (0.1 rad.)

10'f 0 Jerman's data

1 0 Capillary data ........

• & () Q) ...

Cf.)

~ • ~ & rJl

~ ... &

_. 'v.J ......... I\)

~101 ¢ [] -

b 0 ... 4 4 0 ... f 00

0 8 Oo 0 Oo

0 10° I I I I I I I I I I I I I I I I I I I I I I I I I I I I

10° 10 1 ow (Sec.- 1 ) 10 2 10 3


,....... •

()

~ • 'cl () t/l

&! .._..

s;:..J

~ 10

2.. 10

10 I

EJ

0 .IO

PEI'/HOMOPOLYMER at 275°C

6 6 ~ 6 6 6 66 EJ [J EJ [J 8 EJ ....... w r:J w

0 0 0 00 00 0 0 0 Cone & Plate data (0.1 Rad.)

& Jerman's data

0 Capillary data

LI

10 1 10a 103

0-\J _, (Sec. )

Figure 5.1.6~ Viscosity Versus Wall Shear Rate for PET/Hornopolymer at 275°C

10'

10° 10' -/ {Sec.- I ) Ow

0 0 . 8 0 00 8 8

Figure 5.1.7: Viscosity Versus Wall Shear Rate for PET/Homopolymer at 2g5cic

135

RETAINING RING

CAPILLARY

/ / .__..._

(A) SIANOARO DESiGN (3) REVISED DESIGN

Figure 5.1.8: Schematic Diagram of Capillary used in this Work (A) and That used by Jerman (B), (Jerman,1980)

136

5.2 BOUNDARY LAYER EFFECTS ON VISCOSITY

In. connection with the first section of this chapter,

this section will discuss the possibility of a boundary lay-

er effect in more detail. The viscosity of PET/60%PHB and

PET/80%PHB was measured using three capillary sets with

different diameters _ 6. 858 ( 10-4- ) , 1. 27 ( 10-3 ), and 1. 778 ( 163

) meter (corresponding to 0.027, 0.050, and 0.070 inches).

For each capillary diameter, three capillaries with diffe-

rent L/D ratio were used to obtain the entrance pressure

loss by constructing the Bagley plot. Viscosity data using

capillaries with diameters indicated above are plotted

against wall shear rate. For 60 mole % PHB/ PET, the viscos-

ity-shear rate curves are shown in figures 5.2.1 to 5.2.3 at

temperatures of 260, 275 and 285°c. Similarly, for 80 mole %

PHB/PET, in figures 5.2.4 and 5.2.5, these curves are shown

at two temperatures of 305 and 315 ° C. From these curves,

only the viscosity data of PET/60%PHB measured at 275 ° C

shows an increase with increasing capillary diameter. As a

result, this causes an overlap in viscosity data when plot-

ting viscosity-shear rate curves for different temperatures

on the same graph (see figures 4. 1. 13 to 4. 1. 15) . This re-

sult leads to two immediate questions: (1) How does this

possible phenomena occur ? (2) Why does it only occur at

275°c and not at 260°c nor at 285°c ? These questions will

be discussed seperately in the subsequent paragraphs.

137

Before trying to answer these questions, one needs to

investigate the role of entrance pressure loss in this pos-

sible phenomena. Entrance pressure loss can be thought of

as the pressure associated with the energy needed to over-

come a polymer's elastic resistance to converging extension-

al flow. According to the theory of capillary rheometry,

this entrance pressure is independent of the capillary geo-

metry, i.e. the L/D ratio. Figures 5.2.6 to 5.2.10 show

plots of 0 ~n vs apparent shear rate for the three capil-

lary sizes used. In general, the entrance pressure data

show good agreement with the hypothesis of capillary flow -f stated above in the range of shear rates up to 200 sec

Above this range, deviation from the theory occur. To minim-

ize the effect of entrance pressure loss, a long capillary

was used so that the pressure drop over the entrance region

was negligible compared with the pressure drop over the en-

tire length of the capillary. Figure 5.2.11 shows the vis-

cosity of 60 mole % PHB/PET at 275°c using the longest ca-

pillaries for each capillary diameter. Again, the dependence

of viscosity on capillary diameter is observed.

The answer to the first question may be related to the

molecular orientation at the boundary which can be caused by

physical defects or textures on the surf ace or any chemical

treatment of that surface (Berreman, 1973). Throughout the

138

experimental procedure, no chemical treatment was applied

and it is assumed that none was applied to the inside of the

capillaries during their manufacture. Using a scanning elec-

tron microscope, Jerman ( 1980) showed that there exists a

strong pattern of grooves running longitudinally in the flow

channel. This pattern is probably the result of the drawing

process commonly used in manufacture of tubing. The texture

in the tubing is clearly one of long parallel grooves in the

flow direction which would cause an orientation parallel to

the grooves and consequently parallel to the flow (Berreman,

1973; Fisher and Fredrickson, 1969; Jerman, 1980). Probably,

the increase in viscosity with increasing in capillary diam-

eter is due to this texture of the tube wall (capillary

wall). This result is in agreement with the work by Fisher

and Fredrickson (1969) who found similar results for the ca-

pillary flow of low molecular weight liquid crystalline po-

lymer (p-azoxyanisole) with the capillary specially treated

with sulfuric acid-dichromate.

This boundary layer effect can be summarized as follows.

At the boundary, there exists a layer of molecules with

different orientation from those in the core. Because of the

special molecular orientation, this layer has its own vis-

cosity which is less than that of the core fluid. The thick-

ness of this layer is presumably a function of both tempera-

139

ture and shear rate. As the cross section of the capillary

decreases (capillary diameter decreases), the cross section

area taken up by this boundary layer increases. Consequent-

ly the bulk viscosity of the fluid inside the capillary is

affected by this boundary layer and thus decreases (with de-

creasing capillary diameter).

The fact that the boundary layer effect only occurs at

275°c may be explained from the molecular kinetic energy as-

sociated with the solid-nematic and nematic-isotropic tran-

sition. From Boltzman distribution, ifA E is the difference

in free energy per molecule between solid state and nematic

mesophase, then the number of molecules having this energy

is proportional to exp (-~ E/kT) (Pincus and de Gennes,

1977). At low temperature, not many molecules possess this

energy to undergo solid-nematic transition; a semicrystal-

line results in the melt. As the temperature increases, more

molecules obtain this energy, thus the solid-nematic transi-

tion occurs. Consequently, at this temperature, the boundary

layer effect on viscosity is observed. Further increase in

temperature would make these molecules to gain more energy,

sufficient to undergo Brownian motion. As a result, nematic-

isotropic transition occurs and therefore the boundary layer

effect on viscosity is not observed.

140

Molecules in isotropic state are freely rotating. In con-

trast, molecules in nematic mesophase are packed such that

they have freedom of rotion about one axis only (R. Wil-

liams, 1963). The heat for solid-nematic-isotropic transi-

tions thus involved energy for both molecular seperation and

internal rotation (Barrall et al., 1964). To further inves-

tigate this explanation, future works should study the heat

required for these transitions using differential scanning

calorimetry. Also, since the molecular rotation of molecules

in isotropic state is different from that of nematic meso-

ph~se, NMR spectra for melt in nematic mesophase is expected

to be different from that in isotropic state. Further work

should include NMR studies for these states.

1 () 0

10 1


t"°' (Sec.- I )

Capillary Diameter, i!!£!1

0 0 6

0.02?

0.05

o.o?

104-

Figure 5.2.1: Comparison of Viscosity for PET/60%PHB Measured at 260°C Using Capillaries with Different Diameters

10 2

......... •

()

t93 • r-1 m () Cl)

&! ......... 10 1

c-


Capillary Diameter, ~

CJ 0.070 Q o.oso 0 0.027

\Pq) (}) cp cp cP

i{l iii qi q:i ~ qi <P c:D $

<P ell ~ <P <!> <1)

© (f)¢cp

10 1 10 2 • 10 3 10* ~ (Sec.-')

w Figure 5.2.2: Comparison of Viscosity for PET/60 mole % PHB Measured at

2?5°C Using Capillary with Different Diameters

_. .p-... I\}


Oapillary Diameter, i!!£h.

Q 0.07

a 0.05

0 0.027

~w (Sec.- 1 )


102.

-• ()

J3 • ~ [I}

~ ....... ~ 101

80 MOLE % PHB /PET at 305°C


0 0.01

8 0.05

0 0.027

0 ~62@

4)~ ~o~lR 8 00

~~ (Sec.- I )

Figure 5.2.4: Comparison of Viscosity for PET/80%PHB Measured at 305°c Using Capillaries with Different Diameters

_. ~ ~

-• t}

~ • .-I ~ {/)

~ .._..

£'""' 101

0 ·10

80 MOLE % PHB/PET at 315 °C

'( (Sec.-' ) w


CJ 0.07

a 0.05

0 0.02'/

8 0 ·0 0

101+


-... • ()

c?3 • ::E: ......... ~ -~ ~

P-t <J

10 5

104


Capillary Diameter, !!!5ll:! 0 0.027

D 0.05

6 0.07 0

0

0 0

"--;-~-J-~~--'---'--4-'-l-L.L-;;-~_L_~L--.L__l-L--'----L--L-L---.--~_J___Jl__L__J"---.L..LL-1-L.-,-~..L_--1--1

10 1 10~ 103 10~ t. (Sec: I ) w Figure 5.2.6: Entrance Pressure Loss as Function of Apparent Shear Rate for 60 Mole % PHB/PET

Measured at 260°C Using Capillaries with Different Diameters ·

-('I • (.)

JJ • ~ ......... ~ ........ ~

~I/I

<J 105



0 0.027

0 0.05

u 0.01

0

0

0 (i)

0

1 -.'+-i,) ,___ _ __,__.....___.__.__.___.__,__._._ __ _.___,.__..__.'---L--'---L....L..L. __ _.____J_L_J-.L..LJ._.L.l----L---1---1

101 iw (Sec_- I)

Figure 5.2.7: Entrance Pressure Loss as F\Jnction of Apparent Shear Rate for 60 Mole % PHB/PET Measured at 275°C Using Capillaries with Different Diameters

-°' • (.)

c?J • :::E: ......... ~ ..._..

t: fl.. QI

<l 105


Capillary Diameter, i!!£h

0 0.027

0 0.05

6 0.07

0 0

0 0 0

0

10* .__~--i.~~~~~~~~~~~~.._..~.__._._~~~~~-'-'--'-_.__.._._._~~__.___.~

10 1 . I '6 w (Sec.- )

Figure 5.2.8: Entrance Pressure Loss as Function of Apparent Shear Rate for 60 Mole % PHB/PET Measured at 285°C Using Capillaries with Different Diameters

-"' • t) Q)

Cl) • ~ ........ ~ ......... ~ 1\1 p..

<l


105

10 1

'{ (Sec.-' ) w

8 0 0

Capillary Diameter, 1!!£h 0 0.027

0 0.05

6 o.o?

10 u.

Figure 5.2.9: Entrance Pressure Loss as Function of Apparent Shear Rate for 80 Mole % PHB/PET Measured at 305°C Using Capillaries with Different Diameters

-('I •

()

~ • ~

.......... ~ ........ ~ (:I

P-4 <l

80 MOLE% PHB/PET at 315°C

105

0 0 8 0

Capillary Diameter, .!!!£h 0 0.027

0 0.05

6 0.07

10*'--~--'---~---'---'-_L_Jc_L_LLJ.~~_l_~L__J_.L_L~--LJ_~~_j___JL__l_L_j__J_J__j_J_~~J___J~ 102 10 1

't (Sec.- 1) w Figure 5.2.10: Entrance Pressure Loss as Function of Apparent Shear Rate for 80 Mole% PHB/PET

Measured at 315°C Using Capillaries with Different Diameters

~

V1 0

~

() Q)

Cl) •

'cl () (J)

~ .........

s:- 10 1

60 MOLE% PHB/PET at 275°C

0 0 Oo D OR

103

iw (Sec- 1)

Capillary Diameter,

0 0.070, 42.86

0 0.050, 60.0

6 0.027, 55.63

10~

L/D

Figure 5.2.11: Viscosity versus Wall Shear Rate for 60 Mole% Prill/PET at 275°C (without Correcting for Pressure .Entrance Loss)

~

VI ~

152

5.3 MOLD FILLING CHARACTERISTICS

The second objective of this work was to investigate the

mold filling behavior of liquid crystalline polymers. The

procedure used to observe the flow front behavior was dis-

cussed in chapter 3 and 4. The behavior of the flow front of

PET, PET/ 60 mole % PHB, and PET / 80 mole % PHB melts for

flow into a rectangular mold is observed as reviewed in sec-

tion 2.3. The mold filling may be divided into three stages

(figure 2.3.2). First, at the region near the gate, the melt

enters the mold in a radial manner. Secondly, as the melt

reaches the corners, the flow front starts changing its

shape from circular to a nearly flat flow front. Third, the

melt continues to move forward, until the mold is completely

filled by an advancing front mechanism.

Pigmented polymer was introduced into the barrel in an

order so that the blue would enter the mold first, then the

red, green, orange and finally violet. From the video tape

recorded during the flow, it is observed that the order of

the colors which enter the mold is reversed. The blue color

enters the mold first but ceases to flow near the entrance

of the mold. The red color enters next and also ceases to

flow just next to the blue color and away from the gate. Si-

milarly, the green and orange colors move in the same fash-

ion as the red color. The violet color is located at the

153

other end of the mold. Figure 5. 3 .1 shows the shapes of

these colors in a molded plaque. Near the entrance of the

mold, the blue color forms a circular shape corresponding to

the radial flow in the first stage discussed above. The cir-

cular shape of these colors changes to a flat profile as the

polymer melt flows down the cavity away from the gate re-

gion. This would correspond to the second and third stages

of the filling.

The reversion of the order of GOlors entering the mold

can be further investigated by observing their velocities as

a function of time. For the injection of PET homopolymer

into a regtangular mold (figure 5.3.2), the blue and red co-

lors enter first and cease to flow after a certain amount of

tme flowing in the mold. The green and orange colors enter

the mold successively with a velocity higher than those of

the blue and red colors. The violet color enters the mold

last with a higher velocity than the rest of the colors.

From the foregoing discussion, it is evident that at one

time a fluid particle had been flowing in the core and must

reach the flow front. At this point, the fluid particle is

split and flows up to the cold wall of the mold. It is then

frozen and ceases to flow due to this cold wall. Similar ob-

servations have been reported in the work of Schmidt (1976).

154

The mechanism of the splitting pattern at the flow front

is discussed by Tadmore (1974) and reviewed in chapter 2. To

actually investigate this mechanism for the liquid crystal-

line polymer, one must be able to see the movement of these

colors in the core. Figure 5.3.3 and 5.3.4 show photographs

of "short shots" sectioned along the flow for PET/ 60 mole %

PHB and PET/ 80 mole % PHB, respectively. For PET/ 60 mole

% PHB (figure 5. 3. 3), the blue and red colors lay on the

wall. The green color is splitting at the front. What is un-

usual is that the orange and violet colors are splitting

even when they are in the core. On the other hand, according

to Tadmore (1974), the splitting pattern only occured at the

flow front. The same phenomena is observed for the case of

PET/ 80 mole % PHB. The blue, red, and green colors lay on

the wall. The violet and orange colors are splitting in the

core.

From figure 5.3.3 and 5.3.4, it is noteworthy that the

"V" shape of the color pigments lay at wall is formed in a

fashion which the arrow of this shape is in the direction

opposite to that of the flow. Whereas, in the case of Poly

(Butylene terephthalate) (Schmidt, 1974), this arrow is in

the same direction as that of the flow. This phenomena is

believed to be unique to the mold filling characteristics of

liquid crystalline polymers.

155

From these observations, the mechanism for mold filling

of liquid crystalline polymer is proposed and summarized

schematically in figure 5.3.5. The splitting pattern of the

fluid elements occurs right in the core. This pattern be-

comes bigger as the fluid pigment moves to the flow front.

As a result, the pigments lay on the wall with the direction

of the "V" shape in the direction opposite to that of the

flow.

156

Figure 5.3.1: Distribution of Colors in a Molded Plaque of PET Homopolymer (Mold Temp. = 100 C, Melt Temp. * 285 C, Inj. Speed= 40 Cm/Min)

158

Figure 5.3.3: Longitudinal Section of Short-Shot type of Injection for 60 Hole % PHB/PET

Figure 5.3.4: Lon~itudinal Section of Short-Shot type of Injection for 80 Mole ~~ PHB/PET

FLOW FRONT

SOLIDIFYING RF...GION

=·.:·,~ ... -.. ~: .......... ··.· ~: .··;'. · .. , ... ;·.· • • ; .t. • •• ,. ' •• ·- • - • .. - • ••• •••• : ••• •• • ';• • ...... _ ,,.":' ...... , ...

. . .. . . . . .. ·. ·~:···· ·.'· .. :: ,: ): ::. · .. i- .. ··:·: • ....... .

FLOW DIRECTION

FLUID PIGMENT SPLITTING

Figure 5.3.5: Proposed Mold Filling Mechanism for PET/PHB Copolymer Systems

161

5.4 MOLECULAR ORIENTATION OF LIQUID CRYSTALLINE POLYMERS IN INJECTION MOLDING

Melt flow during the molding of ·plastics parts always

causes an orientation of macromolecules. This molecular or-

ientation influences significantly the properties of the

molding. The crack behavior, tendency to distort, corrosion

and shrinkage depend on this state of orientation (Menges

and Wubken, 1973). For liquid crystalline polymers, oriented

parts show highly anisotropic physical properties (Jackson

and Kuhfuss, 1976). This molecular orientation is due to

both the shear deformation of the melt and the flow front.

The last objective in this work is to qualitatively study

the molecular orientation generated during unidirectional

and radial types of flow. The first type of flow is thought

to result in anisotropic molecular orientation whereas the

second type of flow is thought to result in biaxial orienta-

ti on.

For unidirectional flow, the percent shrinkage of the mi-

crotomed samples as a function of distance from the surface

of the molded parts is shown in chapter 4 for 60 mole %

PHB/PET and 80 mole % PHB/PET. .All shrinkage data show a

negligible amount of shrinkage along the flow direction

whereas across to the flow direction, it is significantly

higher. To qualitatively confirm that no density change oc-

cured, the thfckness of the molded part was measured before

162

and after annealing. It was noticed that a 5 percent in-

crease in thickness results from the annealing process. The

shrinkage across to the flow direction shows a maximum peak

away from the surface of the parts. This maximum peak cor-

responds to high molecular orientation in the shear zone

layer which was discussed in chapter 2. This is not to say

that maximum orientation is found away from the surface of

molded part. According to Menges and Wubken (1973), the ab-

solute maximum orientation is always found at the surface,

since the oriented state is frozen immediately and no possi-

bility for relaxation exists. Away from the shear zone lay-

er, the percent of shrinkage decreases corresponding to less

orientation in the core.

For liquid crystalline polymer, the data in chapter 4

shows a higher shrinkage across the flow direction than that

along the flow direction. This is contrast to amorphous po-

lymer. For the latter type, higher shrinkage would be ob-

served along the flow than that of across to the flow. The

explanation for this phenomena may be found base on the work

by Joseph, Wilkes and Baird (1982). Basically, the polymer

melt of PET/PHB copolymers has been reported to be nonho-

mogenous (Zachariades et al., 1982; Meesiri et al., 1982;

Joseph et al., 1982). Using chemical etching technique on

the pressed film, Joseph et al. have shown that these copo-

163

lymers contain two phases: PET rich and PHB rich phase. For

copolymer of 60 and 80 mole % of PHB, the PHB rich phase ap-

pears to be more continuous than the PET rich phase (figure

5.4.1). They suggested that when the melt undergoes deforma-

tion, the PHB rich region would have a lower viscosity and

thus would orient along the flow and migrate towards the

surface of the injection molded parts while the more viscous

PET phase preferentially remains in the core (Joseph er al.,

1982). Since PHB segments are rigid, they do not relax much

upon annealing. Therefore, along the flow direction, the

maximum shrinkage peak close to the surface is absent.

Furthermore, since not much of shear deformation occurs in

the core and the PHB rich phase is found in the skin region,

negligible shrinkage of the microtomed sample (along the

flow direction) is observed. Consequently, the rest of the

discussion for unidirectional flow will only concern the

shrinkage across to the flow direction.

The effect of injection speed on molecular orientation

can be easily understood. With increasing injection speed,

higher force is applied and thus more oriented molecules

will immediately be frozen at the mold surface as a result

of the increases in rate of elongation and cooling rate.

Therefore, the relative maximum molecular orientation would

move to the surface. This is actually seen in figures 5.4.2

164

to 5.4.7. From these figures, the relative maximum shrinkage

corresponding to the molecular orientation of the shear zone

moves closer to the surface as the injection speed increas-

es. The fact that the magnitude of the relative maximum is

nearly the same at lower and higher injection speed is pro-

bably due to the combination of the relaxation process dis-

cussed above and the slow speed of injection (which is lim-

ited by the capability of the instrument). A lower injection

speed will result in a longer injection time and therefore a

thicker frozen layer. A higher injection speed will result

parts with higher molecular orientation along the flow. This

would give rise to anisotropic mechanical properties of the

molded parts.

The effect of gap thickness on molecular orientation can

be seen in figures 5.4.8 to 5.4.13. In these figures, the

across the flow shrinkage at the same injection speed and

different gap thickness is shown. Similar to the case of

higher injection speed, with constant injection speed, the

smaller the cavity thickness, the larger the rate of shear

deformation and the larger amount of heat removal will oc-

cur( for a smaller cavity). As a result, the thinner the fro-

zen layer will be and therefore, the relative maximum orien-

tation will move toward the surface as the cavity thickness

decreases. This is indeed observed in figures 5.4.8 to

5.4.13 for across the flow direction.

165

The discussion so far about the relative maximum

orientation beneath the surface of the molded parts may also

hold for the case of radial flow. Evidence can be seen in

figures 5.4.14 to 5.4.21. The effect of injection speed on

shrinkage of microtomed samples is shown in figures 5.4.14

to 5. 4. 17. With decreasing injection speed, the relative

maximum orientation (peak) moves toward the center of the

plaque due to a thicker frozen layer developed. The effect

of cavity thickness on the amount of shrinkage is shown in

figures 5.4.18 to 5.4.21. Similar to unidirectional case,

holding the injection speed constant and decreasing the cav-

ity thickness which lead to a larger amount of heat being

removed,. Therefore, the thinner frozen layer will be and the

relative maximum orientation will move toward the surface of

the molded parts.

The major difference between the shrinkage of parts re-

sulting from unidirectional and radial flow is that a signi-

ficant amount of shrinkage along the flow direction exists

in the radial flow case whereas it is negligible in the uni-

directional flow case. For radial flow, the radial velocity

for any type of incompressible fluid is:

Vr = V(r,z) (5.4.1)

166

The equation of continuity is:

\] • v = 0

Therefore:

= 0 and f (z)

r

The rate of deformation tensor becomes:

2 oVr ar

i = 0 -

0

2 Vr r

0

0

0

(5.4.2)

(5.4.3)

The diagonal components are related by the continuity equa-

tion (5.4.2):

d- Vr = - Vr O r r

(5.4.4)

The term on the left side of equation 5. 4. 4, )V,. , reflects or the amount of elongational strain generated along the flow

direction (r-direction). The term on the right side of the

167

equation (5.4.4), V..-. r reflects the amount of elongational

strain generated normal to the flow direction ( e -direc-

tion). These two terms would qualitatively be respossible

for the molecular orientation generated in redial flow. Ac-

cording to this equation 5.4.4, the degree of the molecular

orientation, hence the percent of shrinkage, should be in

the same order of magnitude for the flow direction and its

transverse direction (r and 6-directions respectively). In

the publication by Schmidt (1976), it was found that the ra-

dial flow beyond the entrance region can be described as a

combination of planar extension and simple shear whereas the

equation 5.4.4 only describes the planar extensioal flow be-

havior. Therefore, the magnitude of shrinkage is not the

same in the r and e-directions. Of course, more work must be

done to confirm this explanation.

In summary,from the shrinkage data shown in this section,

biaxial orientation has been generated in radial flow. The

amount of shrinkage in both the e and r-directions becomes

significant. This is the result of planar extension and

shear flow. Increasing injection speed or decreasing cavity

thickness would make the relative maximum shrinkage peak

move toward the surface as a result of higher deformation,

168

PET RICH PHASE

PHB RICH PHASE

Figure 5 .4. 1 Schematic Representation of the Bulk Structure of Liquid erYstalline Copolymers of PET Modified with 60 and 80 Hole % PHB (from Joseph et al., 1982)

Q)

:f ~ ~ C>

~

8

6 6

4

2


0

Injection Speed, Cm /Min.

40

20

Center

O.__~~_._~~-'-~~~J__~~--'--~~---'-~~~~~----1 0·00 0.01 0.02 0.03 0.04

Distance from Sl.U"face(inch) 0.05 0.06

Figure 5.4.2: Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to 'lhe Fl.ow Direction for 60 Mole % PHB/PET (Mold Temp..=100°C, Melt Temp •. :;:275° C, Cavity 'lhiclmess==0.125 inch)

8

6

4

2

0 o.oo 0.01



8

0

0.02 0.03 0.04 Distance from Surface {inch)

40

20

0

6

~~nter 0.05 o.06

Figure 5.4.3: Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to The Flow Direction for 60 Mole% PHB/PET {Mold Temp.=100°C, Melt Temp.=285°C, Cavity Thickness=0.125 inch)


8 Injection Speed, Cm /Min.

8 40

G 20 6

Q)

J 61 4 ~ w (.) J-f Q)

p.. 6 2

Center 0 \

o.oo 0.01 0.02 0.03 0.04 0.05 0.06 Distance from Surface (inch)

Figure 5.4.4: Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to The Flow Direction for 80 Mole % PHB/PET (Mold '.i.'emp.=100°C, Melt Temp.=305°C, Cavity 'l'hiclmess=0.125 inch)

..... -...J .....


16 Injection Speed, Cm /Min.

~ 40

12 0 20 Q)

J ~ ~ 08 Q) 0 0 ~

04 c.ente7r 6

~ 00


Figure 5.4.5: Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to The Flow Direction for 60 Mole % PHB/PET (Mold Temp.=100°C, Melt Temp.=275°C, Cavity Thickness=0.0625 inch)

_.. -..J I\)

16

12

08

00 o.oo


0.01


0.02 Distance from Surface (inch)

Center

""' Figure 5.4.6: Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to The Flow D::;rection

for 60 Mole % PHB/PET (Mold Temp.=1004C, Melt Temp.=285°C, Cavity Thickness=0.0625 inch)

8

6

4

2

0 o.oo

UNIDIRECTIONAL FLOW 0 80 MOLE % PHB/PET at 305°C

Injection Speed, Qn/Min.

6 0

0.01

40 20

0.02 Distance from Surface(inch)

Cen~

0.03

Figure 5.4.?: Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to The Flow D:trection for 80 Mole % PHB/PET (Mold Temp.=100°C, Melt Temp.=305°C, Cavity Thickness=0.0625 inch)


8 Ca.vi ty Thickness, !!!9b.:

~ 0.1250 6 0 0.0625

4

2

Center 0 \

0.02 0.03 0.04 Distance from Surface (inch)

o.o 0.01 0.05 0.06

Figure 5.J,..8: Effect of Cavity Thickness on Shrinkage Transverse to The Fl.ow Direction for 60 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 275°C, Injection Speed= 20 Cm/Min.)

..... -J

"'

UNIDIRECTIONAL FLOW 60 MOLE % PHB/PET at 2a5°c

16

Cavity Thickness, ~:

~ 0.1250 0 0.0625

4

Center

0 ·\ 0 o.o 0.01 0.02 0.03 0.04

Distance from Stn"face (inch) 0.06

Figure 5.4.9: Effect of Cavity Thickness on Shrinkage Transverse to The Flow Direction for 60 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 285°C, Inject;Lon Speed= 20 Cm/Min.)


8


~ 0.1250

0 0.0625

2

0 Cente~

o.o 0.01 0.02 0.03 0.04 0.05 o.o6 Distance from Surface (inch)

Figure 5.4.10: Effect of Cavity Thickness on Shrinkage Transverse to The Flow Direction for 80 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 305°C, Injection Speed= 20 Cm/Min.)

UNIDIRECTIONAL FLOW 60 MOLE % PHB/PET at 2?5°C

16

Ca.vi ty Thidmess, E.!£h:

~ 0.1250 12 0 0.0625

8

4

G Center 0 0 ~

o.o 0.01 0.02 0.03 0.04 0.06 Distance from Surface (inch)

Figure 5.4.11: Effect of Cavity Thickness on Shrinkage Transverse to The Flow Direction for 60 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 2?5°C, Injection Speed= 40 Cm/Min.)


16


~ 0.1250

0 0.0625

4 0

Center 0 ~

o.o 0.01 0.02 0.03 0.04 0.05 o.06 Distance 1from Surface (inch)

Figure 5.4.12: Effect of Cavity Thickness on Shrinkage Transverse to The Flow Direction for 60 Mole % PHB/PET (Mold Temp.=100°C, Melt Temp.=285°C, Injection Speed.=40 Cm/Min.)

UNIDIRECTIONAL FLOW

8 80 MOLE % PHB/PET at 305°C

Q) 6 Cavity Thiclmess, ~:

J ~ 0.1250 ~ 0 0.0625 ~ C) 4 ~

2

Center 0 ~

o.o 0.01 0.02 0.03 0.04 Distance from Surface (inch)

0.05 o.06

Figure 5.4.13: Effect of Cavity Thickness on Shrinkage Transverse to The Flow Direction for 80 Mole % PHB/PET (Mold Temp.=100°C, Melt Temp.=305°C, Injection Speed=40 Cm/Min.)

-' ()'.) 0

20

15

10

5

0 o.o 0.01

RADIAL FLOW 60 MOLE % PHB/PET at 275°c

Direction/Injection Speed

~ 9-direction, 40 Cm/Min.

0 r-direction, 40 Cm/Min.


• r-direction, 20 Cm/Min.

0

Center \

0.02 0.03 0.04 0.05 0.06 Distance from Stn"face (inch)

Figure 5.4.14: Effect of Injection Speed on Shrinkage of Microtomed Samples for 60 Mole% PHB/PET (Mold Temp.= 165°C, Melt Temp.= 275°C, Cavity Thickness= 0.125 inch)


DirectionLinjection S~ed

~ 6-direction, 40 Cm/Min. 20


l 6-direction, 20 Cm/Min.

• r-direction, 20 Cm/Min.

~

Q) 15 ~ J 1:! CJ)

fil 10 ()

~ p...

5

Center 0 ~

o.o 0.01 0.02 0.03 0.04 0.05 0.06 Distance from Surface (inch)

tigure 5.4.15: Effect of Injection Speed on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp.= 165°C, Melt Temp.= 285°C, Cavity Thiclmess= 0.125 inch)

__. (X) [\)


Di.rectionlinjection S.el!ed

20 ~ 8-direction, 40 Cm/Min.


~ 8-direction, 20 Cm/Min •

j 15 • r-direction, 20 Cm/Min.

~ ~ ~ +> ti} 10 C> '-4 ~

• 5

• Center 0

o.o 0.01 0.02 0.03 Distance from Surface (inch)

Fig1..&re 5.4.16: Effect of Injection Speed an Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp.= 165°C, Melt Temp.= 275°C, Cavity Thickness= 0.0625 inch)

_. 00 \..V


20 Directionlinjection S~ed


0 r-ctirection, 40 Cm/Min.

~ e-direction, 20 Cm/Min.

• r-ctirection, 20 Cm/Min. 15

10

~

5

0 Center

0 ~

o.o 0.03 0.01 0.02 Distance from Surface (inch)

Figure 5.4.17: Effect of Injection Speed on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp.= 165°C, Melt Temp.= 285°C, Cavity Thickness= 0.0625 inch)

__. 00 ~

20

15

10

5

0 o.oo 0.01


Direction/Cavity Thickness

0 e -direction, 0.1250 c;J r -direction, 0.1250

• e-ctirection, 0.0625 A r-ctirection, 0.0625

0 0 0

0.02 0.03 0.04 Distance from Surface (inch)

0.05 o.06

Figure 5.4.18: Effect of Cavity Thickness on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp.=165°C, Melt Temp.= 275°C, Injection Speed= 20 Cm/Min.)

20

15

10

5

0 o.oo 0.01


0.02 0.03 0.04

Direction/Cavity Thickness

0 e -direction, o. 1250

~ r-direction, 0.1250

B-direction, 0.0625

r-direction, 0.0625

0.05 o.06 Distance from Surf ace (inch)

Figure 5.4.19: Effect of Cavity Thickness on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp.= 165°C, Melt Temp.= 285°C, Injection Speed= 20 Cm/Min.)


20 Direction/Cavity Thickness

0 B-direction, 0.1250 c:'.:) r-direction, 0.1250

• 8-direction, 0.0625

A r-direction, 0.0625

5

0

o.oo 0.01 0.02 0.03 0.04 0.05 0.06 Distance from Surface (inch)

Figure 5~4.20: Effect of Cavity Thickness on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp.= 165°C, i"1elt Temp.= 275°C, Injection Speed= 40 Cm/Min.)


DirectionLCavit~ Thickness 20 0 e -direction, 0.1250

~ r -direction, 0.1250

• e-direction, 0.0625

• r-direction, 0.0625

10

5

0 o.oo 0.01 0.02 0.03 0.04 0.05 o.06


Figure 5.4.21: Effect of Cavity Thickness on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp.= 165°C, Melt Temp.= 285°C, Injection Speed= 40 Cm/Min.)

Chapter VI

CONCLUSIONS

The dependence of viscosity on capillary diameters for

PET/PHB copolymer has been investigated. The mold filling

characteristics and molecular orientation in injection mold-

ing have been qualitatively studied. The following conclu-

sions may be drawn from the results of this work.

1. Unlike PET homopolymer, this liquid crystalline po-

lymer system is highly non-Newtonian and pseudoplas-

tic fluid. Increasing the degree of stiffness of the

polymer chain by increase the percentage of PHB con-

tent does not show a decrease in viscosity of the

melt as the 60 mole % PHB/PET copolymer shows lower

viscosity than the 80 mole % PHB/PET copolymer.

2. Melt viscosity of 60 mole% PHB/PET measured at 27S0 c shows a slight dependence on capillary diameter. This

is probably caused by a boundary layer of molecules

oriented parallel to the flow direction. At the

boundary, the viscosity of the melt is less than that

of the core fluid. For smaller capillary diameters,

the boundary occupies a greater percentage of the

flow channel. This explains the decrease in viscosity

with decrease in capillary diameter.

189

190

3. The reverse of the order of colors suggests that the

first material entering the mold would lay on the

wall and remained near the gate. The succeeding ma-

terial accelerates in the core, to the front, splits

and lays on the walls away from the gate.

4. Unlike amorphous polymers where the splitting pat-

terns only occur at the flow front, for liquid crys-

talline polymers, the splitting occurs even when the

fluid pigment is in the core. This splitting magni-

fies gradually and accelerate to the flow front. Upon

contacting with the cold wall, the splitting of the

fluid pigments stops and forms a "V" shape which has

the direction opposite to that of the flow.

5. The negligible amount of shrinkage along the flow di-

rection arises from the orientation of the PHB rich

region at the surf ace of the molded part and the much

less orientation of the PET region in the core. Upon

heating up to annealing temperature, the induced or-

ientation of PHB region relaxes more slowly than that

of flexible chain polymer. Also, the PET region in

the core is not oriented. Therefore, insignificant

amount of shrinkage along the flow direction is ob-

served.

191

6. For unidirectional flow, neglegible shrinkage along

the flow direction and low viscosity observed for li-

quid crystalline polymer suggest a high degree of mo-

lecular orientation developed along the flow direc-

tion during extrusion. Because of this orientation,

the molded parts possess anisotropic mechanical prop-

erties as reported by Jackson & Kuhfus (1976).

7. For radial flow, biaxial orientation was observed.

Flow beyond the gate region is a conmposi tion of

shear and planar extensional flow.

8. In general, maximum orientation due to shear zone

moves to the surface for higher injection speed and

smaller cavity thickness due to a larger rate of

shear deformation and the larger amount of heat remo-

val.

Chapter VI I

RECOMMENDATIONS

Based on the results of this work, the following is the

list of recommendations for future study in the area of pro-

cessing and rheology of copolyester of PET with p-hydroxy-

benzoic acid.

1. The behavior of viscosity for liquid crystalline po-

lymer at high shear rate should be investigated. This

can be done by measuring viscosity of these melt us-

ing capillaries with smaller diameters (i.e. !) =

0. 009 inch).

2. Since the molecular rotation of molecules in isotrop-

ic state is different from that of nematic mesophase,

further work should include NMR studies for the melts

at these states.

3. Future study should investigate the phase transition

of 60 mole % PHB/PET copolymer using differential

scanning calorimetry, X-ray diffraction, and electron

microscopy.

4. Since boundary layer effect occurs at 2 75° C for 60

mole % PHB/PET, injection molding in unidirectional

flow with the wall specially treated is a direct ap-

plication of the boundary layer.

192

193

5. Mold filling studies should be carried out at higher

injection speed for both radial and unidirectional

flow.

6. Center-gated type of injection should be further stu-

died with the lower plate rotating to further inves-

tigate the biaxial orientation of these copolymers.

7. Physical properties of each layer of injection molded

parts (from surface to core) should be measured both

along and across the flow directions to correlate

with the shrinkage data shown in this work.

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Appendix A

COMPUTER PROGRAM FOR VISCOSITY CALCULATION

Comment: c

This program is to calculate the viscosity of polymer melt from the raw data of Instron capillary rheometer model 3211. Entrance pressure loss is also calculated from the linear regression of total pressure drop vs L/D ratio (Bagley plot). Corrected wall shear stress and wall shear rates are thus obtained.

c c c c c c c c c c c c c c

c c c c c c c

c

1 100

101

2

5 6

3

Input: Speed of Plunger and Pressure readings for capillaries with different L/D ratio.

Output: Entrance pressure loss, corrected Wall Shear Stress, Apparent Shear Rate, Wall Shear Rate and Viscosity.

REAL D,TEMP,L(10),SPEED(l8),FORCE(18),LNGAMA(l8) REAL LNPRES(18),C(ll),LNTW(6,30),LNTWS(30) REAL APGAMA(30),PRESS(6,30),RATI0(6),PEN(30),TW(6,30) REAL LNAPGA(30), GAMAW(6,30),ETA(6,30),APRESS(6) REAL FORCES(l8,4),AGAMA(18),PRESUR(l8,4),PRESSE(30,6) INTEGER N,NDATA(18),DATA,M,K,I,S,Y INTEGER DOTS(4,130),DOT,POLYMA,POLYMB,POLYMC DATA DOT/lH*/

The data is input here: N = number of capillary, i.e. 03 D = Capillary Diameter TEMP = Melt Temperature POLYMA, POLYMB, POLYMC = name of polymer

READ (5,100) N,D,TEMP,POLYMA,POLYMB,POLYMC FORMAT (I2,lX,F7.5,lX,F5.l,lX,3A4) IF (N .EQ. 0) GOTO 600 WRITE (6,101) FORMAT (lHl) DO 6 I=l,4 DO 2 J=l,130 DOTS(I,J)=DOT CONTINUE WRITE(6,5) (DOTS(I,J),J=l,130) FORMAT(lX,130Al) CONTINUE WRITE (6,7) WRITE (6,3) POLYMA, POLYMB, POLYMC, TEMP, D FORMAT (lX, 'RHEOLOGICAL PROPERTY OF I ,3A4, 'AT I ,FS.l,lX,

+' DEGREE CENTIGRADE' ,SX, 'CAPILLARY DIAMETER= ',F7.5)

205

206

C Input of Raw Data: C L(I) = Length of capillary (inch) C NDATA(I) = number of data points C SPEED(J) = speed of plunger (cm/min) C FORCE(J) = Pressure reading (kg) c

DO 40 I=l,N READ (5,200) L(I),NDATA(I) DATA= NDATA(I) DO 10 J=l,DATA READ (5,300) SPEED(J), FORCE(J) FORCES(J,I)=FORCE(J)

10 CONTINUE c C Calculation of apparent shear rate and total pressure C drop from raw data c

DO 20 K=l,DATA AGAMA(K)=2.0*SPEED(K)*((0.9525)**2)/(15.0*(((D*2.54)**3))) LNGAMA(K)=ALOG(AGAMA(K)) PRESUR(K,I)=(l.375E05)*FORCE(K) LNPRES(K)=ALOG(PRESUR(K,I))

20 CONTINUE c C Using linear least square to compute entrance pressure C loss from Bagley Plot c

CALL LEAST (LNGAMA,LNPRES,l,C,DATA) APGAMA(l)=lO.O DO 30 M=l,28 LNAPGA(M)=ALOG(APGAMA(M)) PRESS(I,M)=EXP((C(2))*LNAPGA(M)+C(l)) PRESSE(M,I)=PRESS(I,M) IF (APGAMA(M).LT.100.0) GOTO 22 IF (APGAMA(M).LT.1000.0) GOTO 24 IF (APGAMA(M).LT.10000.0) GOTO 26 GO TO 31

22 S=M+l APGAMA(S)=APGAMA(M)+lO.O GO TO 30

24 S=M+l APGAMA(S)=APGAMA(M)+lOO.O GO TO 30

26 S=M+l APGAMA(S)=APGAMA(M)+lOOO.O

30 CONTINUE 31 DO 40 Y=l,11

C(Y)=0.0 40 CONTINUE

WRITE (6,7) DO 60 M=l,28 DO 50 I=l,N RATIO(I) = L(I)/D

50 APRESS(I) = PRESS(I,M)

c

207

CALL LEAST (RATIO,APRESS,l,C,N) PEN(M) = C(l) DO 60 J=l,11 C(J) = 0.0

60 CONTINUE WRITE (6,45) (RATIO(I),I=l,3)

45 FORMAT (lX, 'SPEED*******FORCE, L/D = I ,6(2X,F6.2)/) WRITE (6,46)

46 FORMAT (lX, I (CM/MIN)' ,4X, I (KG)'//) DO 41 J=l,DATA WRITE(6,42) SPEED(J),(FORCES(J,I),I=l,N)

42 FORMAT (1X,F4.l,4(5X,F7.2)/) 41 CONTINUE

WRITE (6,7) WRITE (6,47) (RATIO(I),I=l,3)

47 FORMAT (lX, 'APGAMA*******PRESSURE, L/D = I ,6(2X,F6.2)/) WRITE (6,48)

48 FORMAT (lX, I (SEC-1)' ,6X, I (KG/M.SEC2)'//) DO 44 J=l,DATA WRITE(6,43) AGAMA(J),(PRESUR(J,I),I=l,N)

43 FORMAT (1X,F7.l,4(5X,Ell.4)/) 44 CONTINUE

C Write apparent shear rate, total pressure drop for C each capillary and entrance pressure loss. c

c

WRITE (6,7) WRITE (6,66) (RATIO(I),I=l,3)

66 FORMAT (lX, 'APGAMA******PRESSURE, L/D = I ,3(2X,F6.2),3X, +'PRESS. ENTRANCE '/)

WRITE (6,67) 67 FORMAT (lX, I (SEC-1)' ,6X, I (KG/M.SEC2)' ,33X, '(KG/M.SEC2)'//)

DO 64 J=l,28 WRITE (6,63) APGAMA(J),(PRESSE(J,I),I=l,N),PEN(J)

63 FORMAT (1X,F7.l,5(5X,Ell.4)/) 64 CONTINUE

WRITE (6,7) 7 FORMAT(lX,' '//////)

C Calculation of corected wall shear stress from total C pressure drop and entrance pressure loss c

DO 80 I=l,N WR I TE ( 6 I 3 5 0 ) I WRITE (6,400) WRITE (6,450) DO 61 M=l, 28 TW(I,M)=(PRESS(I,M)-PEN(M))*D/(4.0*L(I)) LNTW(I,M)=ALOG(TW(I,M)) LNAPGA(M}=ALOG(APGAMA(M))

61 CONTINUE DO 65 S=l,28 LNTWS(S)=LNTW(I,S)

65 CONTINUE

208

DATA = 28 c C Using Linear least square to compute the power law C index of the polymer c

CALL LEAST (LNAPGA,LNTWS,l,C,DATA) c C Calculation of corrected wall shear rate and its C corresponding viscosity c

c c c c c

c c c c c

70

80 200 300 350

400

450

500

600

DO 70 M=l,28 GAMAW(I,M)=((3.0*C(2)+1.0)/(4.0*C(2)))*APGAMA(M) ETA(I,M)=TW(I,M)/GAMAW(I,M)

Print output: Pressure entrance, Wall shear stress, Apparent shear rate, corrected wall shear rate and Viscosity

WRITE (6,500) PEN(M),TW(I,M),APGAMA(M),GAMAW(I,M),ETA(I,M) CONTINUE DO 80 J=l,11 C(J)=O.O CONTINUE FORMAT (F5.3,1X,I2) FORMAT (F5.2,F7.2) FORMAT(lHl,lX, 'THE CALCULATED RHEOLOGICAL PROPERTIES ',

+I USING CAPILLARY' I I2, lX, I ARE: I//) . FORMAT(lX, 'ENTRANCE PRESSURE' ,13X, 'WALL SHEAR STRESS' ,13X,

+'APPARENT SHEAR' ,13X, 'WALL SHEAR RATE' ,13X,' VISCOSITY') FORMAT(lX, 'LOSS (KG/M.SEC2)' ,16X, I (KG/M.SEC2)' ,16X,

+'RATE (SEC-1)' ,19X, I (SEC-1)' ,17X, I (PASCAL.SEC)'//) FORMAT(4X,Ell.4,19X,Ell.4,21X,F7.l,22X,F8.2,18X,F8.2) GOTO 1 STOP END

This subroutine is to calculate the slope and y-intercept of a straight line from a set of data using the linear least square method

SUBROUTINE LEAST (X,Y,M,C,DATA) DIMENSION X(200),Y(200),A(ll,ll),B(ll),C(ll),P(20) INTEGER DATA NUMBER = DATA MX2 = M*2 DO 13 I=l,MX2 P(I) = 0.0 DO 13 J=l,NUMBER

13 P(I) = P(I)+X(J)**I N = M+l DO 30 I=l,N DO 30 J=l,N K =I+J-2 IF(K) 29,29,28

28 A(I,J) = P(K) GO TO 30

29 A(l,l) =NUMBER 30 CONTINUE

B(l) = 0.0 DO 21 J=l,NUMBER

21 B(l) = B(l)+Y(J) DO 22 I=2,N B(I)=O.O DO 22 J=l,NUMBER

209

22 B(I)=B(I)+Y(J)*X(J)**(I-1) NMl=N-1 DO 300 K=l,NMl KPl = K+ 1 L=K DO 400 I=KPl,N IF(ABS(A(I,K))-ABS(A(L,K))) 400,400,401

401 L=I 400 CONTINUE

IF(L-K) 500,500,405 405 DO 410 J=K,N

TEMP = A(K,J) A(K,J) = A(L,J)

410 A(L,J) = TEMP TEMP = B(K) B(K) = B(L) B(L) = TEMP

500 DO 300 I=KPl,N FACTOR= A(I,K)/A(K,K) A(I,K) = 0.0 DO 301 J=KPl,N

301 A(I,J) = A(I,J)- FACTOR * A(K,J) 300 B(I) = B(I)-FACTOR*B(K)

C(N) = B(N)/A(N,N) I = NMl

710 IPl = I+l SUM = 0.0 DO 700 J=IPl,N

700 SUM= SUM + A(I,J)*C(J) C(I) = (B(I)-SUM)/A(I,I) I = I-1 IF (I) 800,800,710

800 RETURN END

Appendix :3

DATA TABLES

Table B.1.1 Raw Data for PET, De= 0.0270

Speed Force (cm/min) (kg)

L/D=15.26 L/D=37.11 L/D=55,63

i.o 20.48 34.80 54.00 2.0 35,20 65 ,45 92.00 4.0 63.27 120.00 1?7.60 6.o 88.80 163.20 232.00

10.0 134.50 258.~0 369,34 temp. = o.6 13.29 24.00 34.88 275 °c 1.2 23,38 42.20 62.08

12.0 152,76 298.20 421.56 3.0 49,37 93.10 132.00 0.2 5.16 9,45 14.18

i.o 10.91 26.60 35,72 2.0 20.36 46.40 68.47 4.0 37,09 8L~.80 125.24 6.o 55 .27 122.18 178,89 temp. =

10.0 84.J6 1$9,09 277,86 285 °c o.6 6.91 17.09 25.72 1.2 12.73 J0.40 45,38 3.0 29.09 70.00 104.67

210

Table B.1.2 Viscosity Calculation Data for PET, De= 0.0270

Entrance Pressure Wall Shear Stress Apparent She~ Wall Shear Rate Viscosity Loss (kg/m.sec2) (kg/m.sec2) Rate (sec- ) (sec-1) (Pascal.sec)

0.2284E+06 o.7189E+04 70.0 73,64 97,62 o.2556E+06 0,8029E+04 80.0 84.16 95,40 0.282JE+06 0.8852E+04 90.0 94.69 93,49 o.3086E+06 0,9658E+04 100.0 105.21 91.80 0,5536E+06 0 .1714E+05 200.0 210.41 81.47 0.7793E+06 0.2J98E+05 300.0 315.82 75,97 0.9934E+06 O.J042E+05 400.0 420.82 72.30 0.1199E+07 Q.J660E+05 500.0 526.03 69.57 temp. = 0 .1J99E+07 0.4256E+05 600.0 631.24 67.42 275 OC 0 .1593E+07 0,48J5E+05 700.0 736.44 65.65 0 .178JE+07 0.5400E+05 800.0 841.65 64.15 0 .1969E+07 0.5952E+05 900.0 946.85 62.87 [\.) __. __. 0 .2152E+07 0.6495E+05 1000.0 1052.06 61.73 0 ,386JE+07 0.1153E+05 2000.0 2104.12 54.78 0 ,5440E+07 0.:t.612E+05 3000.0 3156 .18 51.08 0.6935E+07 0.2045E+05 4000.0 4208.24 48.60 0,8J72E+07 0.2460E+05 5000.0 5260 .JO 46.77

O.J422E+05 0.1J64E+05 200.0 208.75 65,33 0.66J4E+05 0.1926E+05 300.0 313 .13 61.51 0.1014E+OC 0.2460E+05 400.0 417.50 58,93 0 .1384E+06 0.2975E+05 500.0 521.88 57.00 0 .1769E+06 O.J474E+05 600.0 626.25 55,47 temp. = 0.2167E+06 O.J961E+05 700.0 730.63 54.21 0,.2573E+06 o.44J8E+05 800.0 ·835.01 53.14 285 °c 0.2987E+06 0.4905E+05 900.0 939,38 52.22 0 .J407E+06 o.5365E+05 1000.0 1043.76 51.40 0.785JE+06 0.9674E+05 2000.0 2087,52 46,34 0 .1254E+07 0 .1366E+06 3000.0 3131.28 43.61

212

Table B.2.1.a Raw Data for 60 Mole% PHB/P£T, De= 0.0270


L/D=15.26 L/D=37 .11 L/D=55.63

1.0 2.33 3,93 5,96 2.0 3.24 6.04 8.30 4.0 5.08 8.51 13.09 6.o 5 .<;6 10.91 15.78 temp. = 10.0 8.29 14.91 21.09 260 oc o.6 1. 71 3.20 4.58 1.2 2.40 4.51 6.55

12.0 8,73 16.00 23.64 3.0 4.07 7,49 10 .91

1.0 1.60 2.47 3.42 2.0 2.50 3,85 5,45 4.0 4.07 6.18 8,73 6.o 5.24 8.22 11.64

10.0 7,64 11.27 16.73 temp. = 0.6 1.16 1.?8 2.47 275 OC 1.2 1. 78 2.76 3,93

12.0 8.36 13.09 18.18 3.0 3,35 5,09 7.30

20.0 11.64 17.45 25.45

1.0 1.60 2.74 3,71 2.0 2.33 4.14 5,67 4.0 3.60 6.22 8.44 6.0 4.65 7,92 10.69

10.0 6.04 10.64 14.54 temp. = 0.6 1.16 2.08 2.87 285 oc 1.2 1.74 3.08 4.22

12.0 6.98 11.67 15.64 J.O J.05 5.41 7.42

20.0 9.31 15.88 21.45

213

Table B.2.1.b Raw Data for 60 Mole% PHB/PET, De= 0.0500


L/D=20.00 L/D=40.00 L/D=80.00

2.0 1.36 2.48 4.44 4.0 2.07 3.36 6.54 6.0 2.40 4.46 8.44

10.0 3.20 5,90 10.76 temp. = 1.2 1.02 1.84 3,34 260 °c

12.0 3.64 6.64 12.36 3.0 1.67 3.12 5.67

20.0 4.80 8.63 16.36

2.0 0.84 1.53 2.73 3.0 1.82 2.00 3.56 4.0 1.38 2.47 4.29 temp. = 6.0 1.82 3.13 5.60

10.0 2.47 4.29 7.64 275 °c 12.0 2.76 4.87 8.73 20.0 3.85 6.84 12.22

2.0 1.06 1.76 3.05 3.0 1.30 2.21 3,78 4.0 1.52 2.64 4.51 temp. = 6.o 1.84 3.20 5.45

10.0 2.24 4.08 6.84 285 oc 12.0 2.72 4.40 7,76 20.0 3,36 5.81 10.04

214

Table B.2.1.c Raw Data for 60 Mole % PHB/PET, De= 0 .0700


L/D=14.29 L/D=21.43 L/D=42.86

2.0 0.57 0.75 1.34 4.0 0.88 1.20 2.00 temp. = 6.0 1.13 1.56 2.73

10.0 1.53 2.14 . 3,85 260 oc 12.0 1.78 2.47 4.22 20.0 2.40 3.34 5:82

4.0 0.74 1.02 1. 74 6.0 1.02 1.34 2.33 temp. = 10.0 1.45 1.93 3.42 275 °c 12.0 1.74 2 .18 3,85

20.0 2.33 3.27 5.6o

4.0 0.76 0.97 1.56 6.o 0.94 1.20 2.00 temp. = 10.0 1.17 1.56 2.58

12.0 1.34 1.69 2.87 285 °c 20.0 1.78 2.18 J.64

Table B.2.2.a Viscosity Calculation Data for 6o Mole% PHB/PET, De= 0.0270

Entrance Pressure Wall Shear Stress Apparent Shear Wall Shear Rate Viscosity Loss (kg/m.sec2) (kg/m.sec2) Rate (sec-1) (sec-1) (Pascal.sec)

0. 7847E+05 0.2245E+04 200.0 240.99 9.32 0,9844E+05 0.2805E+04 300.0 361.48 7,76 0 .1156E+06 0.3286E+04 400.0 481.97 6.82 0.1310E+06 0.3714E+04 500.0 602.47 6.11 0 .1451E+06 0.4106E+04 600.0 722.96 5.68 0 .1581E+06 0.4469E+04 700.0 843.45 5,30 temp. = 0 .1704E+06 0.4809E+04 800.0 963,95 4.99 0.1820E+06 0 .5131E+04 900.0 1084.44 4.73 260 °c 0 .1930E+06 0.5436E+04 1000.0 1204.93 4.51 0 . 28Ll4E+06 0.7957E+04 2000.0 2409.87 3.30 0.3567E+06 · 0 . 9942E+04 3000.0 3614.80 2.75 0.4190E+06 0 .1165E+05 4000.0 4819.80 2.42 0 .4747E+06 0.1J16E+05 5000.0 6024.67 2 .19 [\) _.

Vl

0.1024E+06 0.1J81E+04 300.0 335,49 4.12 0.1234E+06 0 .1679E+04 400.0 447.33 3.75 0 .1427E+06 0.1954E+04 500.0 559 .16 3,49 0 .1606E+06 0.2211E+04 6oo.o 670.99 3.30 0.1775E+06 0.2455E+04 700.0 782.82 3.14 0.1936E+06 0.2688E+04 800.0 894.65 3.00 0.2090E+06 0.2911E+04 900.0 1006.48 2.89 temp. = 0.2238E+06 0.3127E+04 1000.0 1118.31 2.80 275 °c 0.3509E+06 0.5006E+04 2000.0 2236.63 2.24 0 .L~566E+06 0.6591E+04 3000.0 3354,94 1.96 0.5503E+06 0.8012E+04 4000.0 4473.26 1.79 0.6360E+06 0.9321E+04 5000.0 5591°57 t.67 0.7159E+06 0 .1055E+05 6000.0 6709.89 1.57 0.7911E+06 0 .1171E+05 7000.0 7828.20 1.50

Table B.2.2.a (Continued)

Entrance Pressure Wall Shear Stress Apparent Shear Wall Shear Rate Viscosity Loss (kg/m.sec2) (kg/m.::;ec2) Rate (sec-1) (sec-1) (Pascal.sec)

0.6751E+05 0.1335E+04 200.0 238,65 5,59 0 .8?16E+05 0 .1678E+o4 300.0 357,97 4.69 0 .1045E+o6 0 .1974E+04 400.0 477,30 4.14 0 .1202E+o6 0.2239E+04 500.0 596.62 3,75 0 .1348E+06 0.2481E+o4 600.0 715.95 3.47 0 .1485E+o6 0.2706E+04 700.0 835.27 3.24 0 .1615E+o6 o· .2918E+04 800.0 954,59 3.06 0 .1739E+06 0.3118E+04 900.0 1073,92 2.90 1.cinp0 = 0.1858E+o6 0.3309E+04 1000.0 1193 .24 2.77 265 c 0 .2868E+o6 0.4891E+04 2000.0 2386.49 2.05 0.3697E+o6 0.6146E+04 3000.0 3579,73 1.72 /\.)

-'

0.4426E+06 0. 7227E+04 4000.0 4772.97 1.51 °' 0.5088E+o6 0.8195E+o4 5000.0 5966.22 1.37 0 .5702E+o6 0 .9081E+04 6000.0 7159.46 1.27 0.6Z78E+06 0.9904E+o4 7000.0 8352.71 1.19 0.6824E+06 0 .t068E+o5 8000.0 95lJ.5 ,95 1.12

Table B.2.2.b Viscosity Calculation Data for 60 Mole % PHB/PET, De= 0.0500

Entrance Pressure Wall Shear Stress Apparent Sherr Wall Shear Re.te Viscosity Loss (kg/m.sec2) (kg/m.sec2) Rate (sec- ) (sec-1) (Pascal.sec)

0 .4370E+05 0.1609E+04 ioo.o 118.66 13.56 0.5945Et05 0.2394E+04 200.0 237,31 10.09 0.?097E+05 0.3020Et04 300.0 355,97 8.48 0.8036E+05 0.3560E+04 400.0 474.63 7,50 0.8841E+05 0.4046E+04 500.0 593.29 6.82 temp. = 0.955JE+05 0.4491E+04 600.0 711.94 6.31 260 °c 0 .1019E+06 0.4905E+04 700.0 830.6o 5.91 0 .1078E+06 0.5295Et04 800.0 949.26 5,58 0 .1132E+06 0.5664E+04 900.0 1067. 91 5.30 0 .1183E+06 0.60t6E+04 1000.0 1186.57 5.07 0 .1567E+06 0,8946E+04 2000.0 2373.14 3,77

o.5389E+05 0,8861E+03 100.0 111°79 7,93 /\)

0.7338E+05 O.i423E+04 200.0 223.58 6.36 ....... --..]

o:~8736E+05 o.1875E+04 300.0 335,36 5,59 0.9855E+05 0.2280Et04 400.0 447.15 5.10 0.1080E+06 0.2653Et04 500.0 558,94 4.75 temp. = 0 .1162E+06 0.3002Et04 600.0 670.73 4.48 0.1234E+06 0.3333E+04 700.0 782.51 4.26 275 °c 0 .1300Et06 o • .:;.648E+04 800.0 894,30 4.08 0.1359E+06 0.3951Et04 900.0 1006.09 3,93 0 .1414E+06 0.4243E+04 1000.0 1117.88 3.80 0 .1804E+06 o.6776m+o4 2000.0 2235,76 3.03

0,5328E+05 0.1051E+04 100.0 123,37 8.52 0.7413E+05 0 .1504E+04 200.0 246.74 6.10 0.8991E+05 o.1855m+o4 300.0 370.11 5.01 0.1031E+06 0.2152E+04 400.0 493.48 4.36 0.1146E+06 0.2415E+04 500.0 616.85 3.91 temp. = 0 .1250E+06 0.2654E+04 6oo.o 740.22 3,58 285 °c O • C·l~5E+06 0.2874E+04 700.0 863.59 3,33

Tahle B.2.2. b (Continued)

Entrance Pressure Loss (K~/m.sec2)

0.1433E+06 0.1516E+06 0.1593E+06 0.22131~+06

\•!all Shear Stress (h;/m.sec2.)

O. 3079F~+04 0.3272E+04 0.3455E+04 0.4944E+04

Apparent Shear Rate (sec1)

800.0 900.0

1000.0 2000.0

1,<fall Shear Hate (sec-1 )

986.97 1110.34 1233.71 2467.41

Viscosity (Pascal. se~)

3.12 2.95 2.80 2.00

Ta~;le B.2 .2 .c Viscosity Calculation Data for 60 Mole % PHB/PET, De= 0.0700

Entrance Pressu2e Wall Shear Stress Apparent Shear Wall Shear Rate Viscosity Loss (kg/m.sec ) (kg/m.sec2) Rate {sec-1) {sec-1) {Pascal.sec)

0.2534E+05 0.8648E+03 40.0 45.20 19.13 0.2887E+05 0.1002E+04 50.0 56.50 17.73 0.3210E+05 0.UJOE+04 60.0 67.80 16.66 0.3512E+05 0.1250E+04 70.0 79.10 15.81 0.3796E+05 0.1J65E+04 80.0 90.40 15.10 temp. = 0 .Ll-065E+05 0.1475E+04 90.0 101. 70 14.51 0.4322E+05 0 .1581E+04 100.0 113.00 13.99

26o OC 0.6464E+05 0.2495E+04 200.0 226.00 11.04 0.8174E+05 0.3258E+04 300.0 339.01 9.61 0.9652E+05 0.3937E+04 400.0 452.01 8.71 0 .1098E+06 0.456oE+04 500.0 565.01 8.07

/\.) -"

0.3459E+05 0.1122E+04 80.0 87.27 12.85 -..o 0.3751E+05 0 .1223E+04 90.0 98.17 12.46 o.4034E+05 0.1J21E+04 100.0 109.08 . 12 .11 temp. = o.6504E+05 0.2197E+04 200.0 218 .16 10.07 275 OC 0.8597E+05 0.2958E+04 300.0 327.24 9.04 o.1048E+06 0.3653E+04 400.0 436.33 8,37 0.1222E+06 0.4J03E+04 500.0 545.41 7.89

0.4555E+05 0.9610E+03 80.0 97.30 9,88 0.4821E+05 0.1024E+04 90.0 109.46 9,35 0.5071E+05 O .1083E+04 100.0 121.62 8.91 temp. = 0. 7078E+05 0 .1571E+04 200.0 243.24 6.46 285 OQ 0.8599E+05 0 .1953E+04 300.0 364.86 5,35 0.9872E+05 0.2279E+04 400.0 486.48 4.68 0.1099E+06 0.2569E+04 500.0 608.10 4.22

220

Table B.3.1.a Raw Data for 80 Mole% PHB/PET, De= 0.0270


L/D=15.26 L/D=37.11 L/D=55.63.

1.0 3.40 5,27 6.86 2.0 5,58 8.71 11.36 4.0 9 .14 14.36 18.78 6.0 12.20 19.25 25.22 temp. = 10.0 17.58 27.84 36.55 0.6 2.36 3~65 4.74 305 °c 1.2 3,87 6.02 7,83

12.0 20.01 31.76 41.73 3.0 7,45 11.67 15.24

1.0 1.93 2.76 4.00 2.0 3,13 4.36 6.11 4.0 4.95 6.90 9.80 6.o 6.40 9.20 12.56

10.0 9,45 12.32 18.40 temp. = 0.6 1.38 2.04 2.73 315 °c 1.2 2.25 3.05 4.44

12.0 9.82 14.55 20.48 3.0 3,93 5.80 8.29

20.0 14.54 20.73 29.09

221

Table B.3.1.b Raw Data for 80 Mole% PHB/PET, De= 0.0500


L/D=20. L/D=40. L/D=80.

1.0 1.10 1.53 2.51 2.0 1.75 2.55 3.93 4.0 2.69 3.78 6.11 6.0 3.64 5.16 8.65 temp. = 10.0 4.94 7.13 11.64 1.2 1.27 1.78 2.87 305 °c

12.0 5.82 8.36 1J.82 3.0 2.40 3.27 5.09

20.0 8.00 11.64 18.18

1.0 0.75 1.02 1.71 2.0 1.14 1.60 2.58 4.0 1.80 2.54 3,93 6.o 2.33 3.34 5.45 temp. = 10.0 3.20 4.58 6.91 315 °c 1.2 0.88 1.24 1.93

12.0 3.56 4.94 8.00 3.0 1.60 2.11 3.42

20.0 4.87 7,05 10.84

222

Table B.3.1.c Raw Data for 80 Mole% PHB/PET, De= 0.0700


L/D=14.29 L/D=21.43 L/D=42.86

2.0 0.97 1.16 1.74 4.0 1.41 1.68 2.49 6.0 1.76 2.09 3.08 temp. = 10.0 2.33 2.75 4.03 305 °c 12.0 2.57 3.03 4.43 3.0 1.21 1.44 2 .15

20.0 3.40 4.00 5,79

4.0 0.81 1.04 1.44 6.0 1.09 1.27 1.89

10.0 1.53 1.82 2.58 temp. = 12.0 1.71 2.07 2.91 315 °c 3.0 0.71 o.84 1.24

20.0 2.36 2.84 4.00

Table B.3.2.a Viscosity Calculation Data for 80 Mole% PHB/PET, De= 0.0270

Entrance Pressure Wall Shear Stress Apparent Shear Wall Shear Rate Viscosity Loss (kg/m.sec2) (kg/m.sec2) Rate {sec-1) {sec-1) (Pascal.sec)

0.2460E+06 0.2501E+04 300.0 326.50 7.66 0.3007E+06 0.3093E+04 400.0 435.33 7 .10 0.3513E+06 0.3647E+04 500.0 544.16 6.70 0.3990E+06 0.41)7E+04 600.0 653.00 6.39 0.4442E+06 0.4677E+04 700.0 '761.83 6.14 temp. = 0.8476E+06 0.5161E+04 800.0 870.66 5.93 305 °c 0. 52c1lE+06 0.5631E+04 900.0 1088.31 5,59 o. 5r;96~~+06 0 .6o86E+04 1000.0 10RR,33 5.59 0.9233E+06 0 .1016E+05 2000.0 2176.66 4.67 0.1255E+07 0 .1370E+05 3000.0 3264.98 4.20 0 .1496E+07 0 .1694E+05 4000.0 4353.31 3.89 0 .1748E+07 0 .1998E+05 5000.0 5441.64 3.67 N

/\) 'vJ

0.1355E+06 0 .1469E+04 300.0 336.91 4.36 0 .1640E+06 0 .178tE+04 400.0 449.21 3,97 0 .1902E+06 0.2068E+04 500.0 561.51 3.68 0.2146E+06 0.2337E+04 600.0 673.81 3.47 0.2377E+06 0.2592E+04 700.0 786 .12 3.30 temp. = 0.2598E+06 0.2834E+04 800.0 898.42 3.15 315 OC 0.2809E+06 0.3067E+04 900.0 1010.72 3.03 0.3012E+06 0.3292E+04 1000.0 1123.02 2.93 0.4772E+06 0,5238E+04 2000.0 2246.05 2.33 0.6245E+06 0.6873E+04 3000.0 3369.07 2.04 0.7558E+06 0,8JJ5E+04 4000.0 4492.09 1.86 0.8765E+06 0.9679E+04 5000.0 5615.11 1.72 0.9892E+06 0 .1094E+05 6000.0 6738 .14 1.62 0 .1096E+07 0 .1213E+05 7000.0 7861.16 1.54

Table B.J.2.b Viscosity Calculation Data for 80 Mole% PHB/PET, Dc=0.0500


0.7982E+05 0.7094E+03 50.0 55,85 12.70 0.8976E+05 0.80J2E+03 60.0 67.02 11.98 0.9913E+05 0.8922E+03 70.0 78.20 11.41 0 .1080E+06 0.9772E+03 80.0 89,37 10.93 0.1165E+06 0.1059E+04 90.0 100.54 10.53 0 .1247E+06 0 .1138E+04 100.0 111. 71 10.18 0 .1948E+06 0.1824E+04 200.0 223.42 8 .17 0.2528E+06 0.2405E+04 300.0 335 .12 7 .18 temp. = 0 .3042E+06 0.2925E+04 400.0 446.83 6.55 305 °c 0 .3511E+06 0.3405E+04 500.0 558,54 6.10 O.J948E+06 O.J855E+04 600.0 670.25 5,75 0.4359E+06 0.4282E+04 700.0 781.96 5.48 j\)

0.4750E+06 0.4690E+04 800.0 893.67 5.25 N ~

0.512JE+06 0 .5081E+o4 900.0 1005.37 5,05 0.5482E+o6 0 .5459E+o4 1000.0 1117.08 4.89 0.8557E+06 0.8751E+04 2000.0 2234.16 3,92

0.5429E+05 0.4946E+OJ 50.0 58.00 8,53 0.6099E+05 0.5528E+03 60.0 69.60 7,94 0.6730E+05 0.607JE+03 70.0 81.20 7,48 0 .7J29E+05 0.6589E+03 80.0 92.80 7.10 0.7901E+o5 0.7080E+OJ 90.0 104.40 6.78 0.8451E+05 0.7550E+oJ 100.0 116.00 6.51 0.1J15E+ot 0 .1152E+04 200.0 231.99 4.97 0 .1704E+06 0 .1475E+04 JOO.O 347.99 4.24 temp. = 0.2047E+ot 0 .1758E+04 400.0 463,99 3,79 315 °c 0 .2J60E+06 0.2015E+04 500.0 579,99 3,47 0.2651E+o6 0.2252E+04 600.0 695.98 J.24 0.2926E+o6 0.2474E+o4 700.0 811.98 3.05

Table R.3.2.b (Continued)

Entrance Pressure Loss (I\c;/rn.sec2 )

0.3186E+06 0.3434E+06 0.3673F.+06 0.5715E+06

\fall Shear Stress (Kg/rn.sec2 )

0.2683E+04 0.2883E+04 0.3074E+04 0.4691E+04

Apparent Shear Rate (sec-')

800.0 900.0

1000.0 2000.0

\·rall Shear Rate (sec- 1 )

927.98 1043. 98 1159.97 2319.95

Viscosity (Pascal.sec)

2.89 2.76 2.65 2.02

/\) /\) \J'l

Table B.3.2.c Viscosity Calculation Data for 80 M8le % PHB/PET, De= 0.0700


0.8739E+05 0.9975E+03 50.0 63.03 15.83 0.9713E+05 0 .1091E+04 6o .o 75.64 14.43 0 .1062E+06 0 .1177E+04 70.0 88.24 13.34 0 .1147E+06 0 .1257E+04 80.0 100.85 12.47 0 .1228E+06 0 .1333E+04 90.0 113 .46 11.75 temp. = 0 .1J05E+06 0 .1404E+04 100.0 126 .06 11.13 305 °c 0 .1947E+06 0 .1973E+OLJ. 200.0 252 .12 7,83 0.2459E+06 0.2408E+04 300.0 378 .19 6,37 0.2902E+06 0.2772E+04 400.0 504.25 5.50 0.3300E+06 0.3093E+04 500.0 630.31 4.91 /\)

/\)

°" 0.7002E+ 0.7002E+05 0.71J3E+03 80.0 94.15 7.58 0.7588E+05 o.7645Frt03 90.0 105.92 7.22 0.8153E+05 0 ,81J5E+03 100.0 117.69 6.91 temp. = 0 .1307E+06 0.1223E+04 200.0 235,37 5.20 315 °c 0 .1722E+06 0 .1552E+04 300.0 353.06 4.40 0.2093E+06 0.1837E+04 400.0 470.75 3.90 0.2436E+06 0.2093E+04 500.0 588.43 3.56

Appendix C

NOMENCLATURE

A Cross Sectional Area of Plunger (m 2 )

B Cavity Thickness

Db Diameter of Barrell (m)

Dj Diameter of Extrudate (m)

de Diameter of Capillary (m)

dp Diameter of Plunger (m)

K Rate of Elongation

L Length of Capillary (m)

M Entrance Length Correction (Dimensionless)

N~ First Normal Stress Difference (Kg/m.secz)

n Power-Law Index

P Pressure (Kg/m.sec2)

Q Flow Rate (cm /sec)

R Radius (m)

S Molecular Order Parameter (Dimensionless)

S Plunger Speed (m/sec)

Sr Recoverable Shear Strain

T Temperature (°K)

T~ Glass Transition Temperature (°K)

Tm Melt Temperature (°K)

Vi Velocity in i direction (m/sec)

(V) Average Velocity (m/sec)

227

228

iAPP Apparent Shear Rate (l/sec)

~W Wall Shear Rate (1/sec)

APeri Entrance Pressure Loss (Kg/rn.sec 2 )

~ Melt Viscosity (Pascal.Sec)

n• ., Complex Viscosity (Pascal.Sec)

Yl~ Viscosity at Core (Pascal.Sec)

V'l.w Viscosity at Wall (Pascal.Sec)

~ Apparent Viscosity (Pascal.Sec) ' \Af P p Density (Kg/rn3)

The vita has been removed from the scanned document

MOLD FILLING CHARACTERISTICS AND MOLECULAR ORIENTATION IN

INJECTION MOLDING OF LIQUID CRYSTALLINE COPOLYESTERS OF POLY

(ETHYLENE TEREPHTHALATE)

By

Chieu D. Nguyen

(ABSTRACT)

The boundary layer effect on viscosity and injection

molding studies in radial and unidirectional flows were

investigated for liquid crystalline

(ethylene terephthalate) using an

copolyesters of poly

Instron model 3211

capillary rheometer. Two copolyesters of PET modified with

60 and 80 mole percent parahydroxy benzoate were examined.

Melt viscosities were measured as a function of temperature

and wall shear rates. Mold filling characteristics were

investigated by introducing different fluid pigments into

the melt before injection. Molecular orientation of the

molded parts was studied by measuring the shrinkage of the

microtomed samples

speeds, and cavity

at various temperatures, injection

thicknesses for these two molds. For

PET/60 mole % PHB, the viscosity was found to be some

funct~on of the capillary diameter, showing a marked

decrease with decreasing capillary diameter at 275 C; this

possible phenomenon is not found in most polymer melts.

During mold filling stage, fluid pigments indicated that

these liquid crystalline melts flow and split in the core

before they approach the flow front. Molecular orientation

studies showed that high shrinkage across the flow direction

than that measured along the flow direction. Studies also

indicated that there existed a relative maximum molecular

orientation away from the surf ace of the parts,

corresponding to the shear zone. As the cavity thickness

decreases or injection speed increases, this relative

maximum peak moves to the surface of the molded parts.

mold filling characteristics and molecular …

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