smiqs_mini_project

8/7/2019 SMIQS_Mini_Project

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Optimization of rheological & thermal properties of polypropylene – unsaturated polyester blend

Naveed Khan (1) , Izhar Ahmed Malik (2) , Moonis Ahmed (2),

Qasim Habib (2) , Sumair K halid (2) , Muhammad Shakeel (2)

(1 ) Lecturer Department of Polymer & Process E ngineering, UET, Lahore, Pakistan (2) Final Year Student Department of Polymer & Process Engineering, UET , Lahore, Pakistan

Abstract

Pure propylene and unsaturated polyester was used to prepare a PP -UP Blend, a compatibalizer with varying the compositions of PP & UP. Blending of the blends was done in Brabender Plasticorder at 180°C using a rotor speed of 90 rpm for 6 min , with dicumyl peroxide as aninitiator as well as a reacting agent. Cobalt was used as a catalyst/ accelerator. Rheological and thermal properties have been investigated with special effect to change in the PP/UP ratio. It isobserved that at an optimum ratio both the mechanical and rheological along with thermalproperties are improves of both components, also increase in melting point with increase of UPconc is observed.

1. Introduction

Unsaturated polyester is increasinglyused in the engineering type applicationsthese days. It is becoming moreimportant having the properties of highmodulus, good tensile strength, good

appea rance and god impact strength atambient to low temperatures. Polyesterswith good impact strength is very usefulin many applications, but it is notactually of the required impact strengthand other mechanical properties. So, themechanical properties of polyester are

increased by making its blend. Manymethods are available to increase theimpact strength of the UP, such likeblending UP with olefins [1], E P R(ethylene propylene rubber) [2] , EPDM [3] , maleic anhydride grafted rubber [4]and many others like this.

Although all these methods in some caseimprove the impact strength but at thecost of other physical properties [5]. Sowe get the modified polyester of higherimpact strength but with decreasedphysical properties. We need a method

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i n w h i c h UP’s impact strength isincreased as well as it maintains itsoriginal physical properties.

So according to some studies polyesterwhen reacted with polyolefin shows thisbehavior, that not only impact strength isincreased but also physical properties ar emaintained. Polypropylene is one of themost effective polyolefin used to modify the properties of polyester [6].PP(polypropylene), known asthermoplastic , is one of the most usefulpolymers all around the world. It has the

higher impact strength when u sed inblends and have good finishingproperties. But it has the lower meltproperties, so it is blended to increase itsmelt properties along with it increasesthe impact strength of the material it isblended with. So UP is blended with PPto modify the properties of both thesematerials [7] .

The process adopted for this purpose ismelt modification process [8] . In it boththe materials are melted and thenblended, and the reactive blending is themechanism of this reaction. Reactiveblending is the process which involvesblending along with some chemicalreaction.

The problem faced in blending of thesematerials is that these are totallyimmiscible. So an initiator is required tostart a reaction between them, peroxideserves for this purpose. Peroxide acts asan initiator and grafting is totally done

with peroxide, otherwise materials willjust mix but these are not miscible.

The purpose of this study is to make ablend of PP and UP using peroxide, withdifferent ratios, and study therheological, thermal and mechanicalproperties of the blend. Structural andphysical behavior is also examinedduring the study.

2 . Experimental

2.1. Materials

Polypropylene (PP) used in this studywas of injection molding grade, fromjameco (Kachahri bazaar), Faisalaba d,Pakistan with MFI value of 14 g/10 mina t 2 3 0 0C. UP was purchased fromDESCON engineering chemicals.

Peroxide used was (DCP) dicumyl

peroxide as an initiator and cobalt isused as a promoter or catalyst [9], whichjust makes the reaction faster.

2 . 2. Blend Preparation

UP - PP blends ha s generally beenprepared by melt mixing techniques.Melt -mixing is an easy and economical

way of blending to avoid problems of contamination, s olvent or water removaletc.Blends of PP, UP a n d DCP wereprepared by melt mixing PP, UP withDCP & cobalt in a Brabenderplasticorder (PLE-330) at a temperature





of 180 oC. The rotor speed was 9 0 rev / min and time of mixing was 6 min [6].The DCP was added after the addition of UP . The formulation is shown in the

Table 1 . this is the formulation for thetest run at the start. After this sampleswith different ration are prepared whichare named as P 100 , P 80 , P 60, P 40 , P20 and

P0 where the subscripts shows the weightpercentage of the polymer in the PP/UPratio . Brabender Plast icorder is shown inFig1. The blend products were grindedinto powder by using the grinder.

Table 1 Ingr edients

composition (phr)PP 41.50 UP 41.50 DCP 3.500 COBALT 14.50

2.3. Rheological Testing

The Test apparatus used in the study wasMelt Flow Basic (Karg industritechnik), with die diameter 2.095 mm and length8 mm shown in figure below .Experiments was performed at 190 C inaccordance with ASTM D1238. Testloads were varied from 2.16 kg to 5 kg

for the characterization of rheograms.





2.4. Reaction Mechanism

We have already stated that UP and PPare not miscible and these will not reactunless peroxide is introduced in thereaction. In fact UP and PP behaves inthe totally opposite way in reacting withDCP, but after that these are able to reactwith each other also.When PP reactswith DCP the backbone chain broke up,known as β scission of PP, while UP

undergoes the macro radical

recombination pr ocess. Both UP and PPhave very high reactivity with DCP butin the opposite way. In UP DCP takesthe hydrogen from the chain and producea macro radical, where in PP it breaksthe chain and produce a double bond andan active site for the further reactionbetween UP and PP, which is the basisfor whole process. General reaction isshown in the next figure showing themechanism in figure below

.

Macro radical recombination:

Here we can see that peroxide attacksthe hydrogen atom in UP chain and forman alcohol and produce an active site forreaction with PP.

Β

– Scission:

And in PP, it degrades as the chain isbroken into two and producing a doublebond as well as an active site for thereaction with UP. This is reactionmechanism for the PP/UP blending andafter this PP and UP will be cross linked.Although some UP and PP will remainsunreacted but in a brabender thispossibility is very less as the efficiencyof the mixer is very high, so we ignoredthe amount of UP and PP unreacted, if itis greater in amount it can be separatedwith some methods [ 10]. In some caseshot xylene is used and lowering the

temperature is also one of the techniquesto separate them.





3. Characterization:

3.1. Rheological Characterization:

To study the rheological properties of the blend, we used the capillaryrheometer. Ca pillary rheometer availableto us is the Melt Flow Basic. Using thisrheometer, one can find the Melt FlowIndex or Melt Flow Rate. With the helpof it viscosity can be find out as well asshear rate and shear stress relation canbe developed after applyin g s o m ecorrections for the polymer blends.Although stress/ strain relations arealready available but these are applicablefor Newtonian fluids, but as this blend ismade from a pseudoplastic material, sosome corrections have to be applied to

make them useful in our study.

Melt flow index (MFI) is a goodindicator of most suitable end use forwhich the particular grade of polymercan be used. From the definition of MFI [11 ].

MFI =10×60× w

Where, w is weight rate of flow (in

g/sec). In capillary vi scometers, theshear stress is determined from the

pressure applied by a piston. The shearrate is determined from the flow rate.

After finding the shear rate andpressure, we applies Bagley’s correctionas we are using the polymers which arethe non -New tonians fluids [12 ], so wehave to apply the corrections and correctour results. After applying the correctionwe plot a graph between the pressure orstress applied and the strain rate obtainedand interpret our results.

3.2. Thermal Characterization: Thermal analysis comprises a group of techniques in which a physical propertyof a substance is measured as a functionof temperature, while the substance issubjected to a controlled temperatureprogram.

Polymers typically display broad meltingendother ms and glass transitions as

major analytic features associated withtheir properties. Both the glass andmelting transitions are stronglydependent on processing conditions and

dispersion in structural and chemicalproperties of plastics. Characterization





of polymers requires a detailed analysisof these characteristic thermal transitionsusing either differential scanningcalorimeter (DSC) or differential thermalanalysis (DTA) [13]. Additionally,

polymers are viscoelastic materials withstrong time and te mperaturedependencies to their mechanicalproperties. Temperature scans across thedynamic spectrum of mechanicalabsorptions are commonly required forcharacterization of polymers, especiallyfor elastomers. Thesethermal/mechanical properties arecharac terized in dynamicmechanical/thermal analysis (DMTA).

Additionally, weight loss with heating isa common phenomena for polymers dueto degradation and loss of residualsolvents and monomers. Weight loss onheating is studied using thermalgravimetric anal ysis (TGA).

A complete thermal analysis of a plasticsample yields inferential informationconcerning the chemical compositionand structure of the material. Examples:

1. The Hoffman -Lauritzen description of the crystalline melting point associ atesshits in the melting transitiontemperature with the thickness of lamellar crystallites in polymers. Suchstructural based shifts would suggestfurther study using the Scherrerapproach for diffraction peak broadeningand small -angle x- ray and TEM ana lysis.

2. Dramatic weight loss in a TGAanalysis of nylon at temperatures above100deg.C indicate some association of water with the nylon chemical structure.Such an observation would suggestfurther study using spectroscopictechniques.

3. In a polymer alloy (blend), theobservation of two glass transitiontemperatures indicates a biphasicsystem, a single glass transition, amiscible system following the Flory -Fox

equation. Further support for miscibilitywould come from microscopy andscattering (neutron, x -ray and light canall be used to characterize miscibility).

Generally, thermal analysis is the easiestand most available of techniques toapply to a sample and for this reasonthermal analysis is often the firsttechnique used to analytically describe aplastic material.

Usually we prefer to repeat themeasurement for the sake of minimizingthe error risks.

3.3. Structural Characterization(FTIR Analysis):

Scope:

FTIR is used for material identificationof polymer. It can also be used to





examine contaminants and some fillerwithin the polymers. Us ing AS TMstandard E 1252

Procedure:

The sample is inserted into a detectorand the amount of Infrared Lightabsorbed at each frequency isdetermined. A spectrum is produced andmatched to known spectra in acomputer -based library. A spectrum isproduced with varying peaks at differentfrequencies which is further interpreted [14] .

FTIR ANALYSIS ADVANTAGES:

Fourier Transform InfraredSpectrosco py (FTIR) identifies chemicalbonds in a molecule by producing aninfrared absorption spectrum. Theresulting spectra results produce aprofile of the sample, a distinctivemolecular fingerprint that can be used toeasily screen and scan samples for manydifferent components.

FTIR is an effective analyticalinstrument for detecting functionalgroups and characterizing covalentbonding information. FTIR is a superbtool for screening and profiling samples.

FTIR is often used in conjunction withother molecular spectroscopy techniquesavailable, including NMR, GC/MS, NIRand Raman scattering.

These different techniques providecomplementary data regarding amolecule's molecular structure. Whenused together they prove very effectiveinthe identification of unknowns.

4. Results/ Conclusions:

4.1. Rheological Results:

After preparing the blend in theBrabender Plasticorder, it has to berheological characterized. For thatreason MFI is used. Sample prepared

through Brabender Mixer is grind forfurther use.





PP-UP blend is used as acompatibalizer, because of its improvesimpact strength and also rheologicalproperties, its rheological propertiesvaries as proportions is varied of PP inUP. After performing certainexperiments on the capillary rheomete r,which in our case is MFI, we haveinterpreted some result, as you can see

the graphs in the figures below, in Fig 1,all results are shown of different

proportions but through a die of 4mm,we have three things to discuss here, oneis the change in the die and the other isthe proportion and the third one is thechange in the pressure.

When the proportion is changed, whenproportion of PP is high, strain rate ishigher, as there is less grafting produced

between PP and UP, but as theproportion is increased, the grafting

effect is increased, PP degrades more,and more cross linking is produced inthe UP, so lesser will be the strain rate,as it can be seen through the graphs inFig 1. And in the same figure you cansee that as the pressure is higher t hegreater will be the strain rate, which isobvious, because as the pressure ishigher, means the applied load is higherthe greater will be the stress applied, andas the blend is polymer and pseudoplastic , so affect against stress is in the

Fig 1. ( PP -UP Blend, 4 mmdie, PP varies from 80,50,40 &





form of more strain, so higher will be thestrain.

The third effect is in the change of die,as the die of greater length is used, lesserwill be the strain rate, it can seen in the

Fig 2, (PP-UP Blend, 10 mm die)

F i g 3 , ( P P -

UP Bl e nd , 3 0 mm d i e )





Fig 2 and Fig 3, that as the die of greaterlength is used, the lesser will be thepressure drop, so lesser will be the strain

rate, and the fluid is somewhat attain thelaminar behavior, so its easy to flow inline for the fluid, and so producing less

strain rate. Fig 2 shows the graphs forpressure vs strain rate when 10 mm di e

is used and Fig3 shows the graphs whena die of 30 mm is used in the capillaryrheometer.

The next step was the use of different

temperature, in this step we have usedthe blend of fixed compositions but atthe various temperatures, we havenoticed that as the temperature is variedwe get the different strain rate, for thesame die and the same pressure, in Fig 4,die of 4mm is used, a blond of 50 -50composition is used and the pressure isvaried with varying the temperature. It isinterpreted that as the temperature isincreased, viscosity will decrease, and

the fluid approaches to be the laminarfluid, and so greater strain rate isproduced, when the temperature ishigher, the strain rate for the blends of same composition and at the samepressure, th e strain rate is higher. And itis the same behavior observed in all thethree dies, as shown in the Fig 4.

Fig 4 (PP -UP Blend, at temp 210,220 &230)

After the interpretation of therheological results, it is concluded thatthis blend is better than the single UP orPP, and it can be best used as it iscompatible and it can be used in thevarious engineering applications.

4.2. Thermal Results: The term melting point when applied topolymers, suggests not a solid - liquid

phase transition but a transition from acrystalline or semi -crystalline phase to asolid amorphous phase. Thoughabbreviated as simply T m , the property inquestion is more properly called thecrystalline melting temperature. Amongsynthetic polymers, crystalline melting isonly discussed with regards tothermoplastics, as thermosetting





polymers will decompose at hightemperatures rather than melt.

The objective of melting point apparatusis to find the melting point of given

sample .

Procedure :

1.

First of all , cut a very small piece of sample from the prepared sample of PP/UP blend.

2.

With the help of some solvent cleanthe metallic plate carefully so thatr i s k o f impurity addition can beeliminated .

3. Turn on the apparatus, set some

temperature limit on theLCD screen on equipmen t.

4.

Place the sample on plate , and notethe tempera tur e at which samplestarts melting.

5.

This is called initial meltingtemperature point

6.

Then note the temperature at whichsample is completely melted

Results :

From the obtained measurements , wedraw a graph between composition andthe melting point. In our performance,we use three samples of knowncompositions. From the graph, we find

out that as the amount of UP increases ,the melting point of blend also increasesrespectively.

Reason:

Appar ently the melting point of UP isquite low , so as the amount of UPincreases , the melting point should beincreases.. but due to grafting of UP andPP , the behavior turns to be opposite. Somelting is quite difficult for the blendcontaining large amount of UP.

4.3. Structural Results (FTIRAnalysis):

Various samples of PP- UP blends weretested with varying compositions i.e. PPranging from 20 Wt % to 70 Wt %. Let’sanalyze the peaks at 3 different wavenumbers e.g. 700, 1750 & 3000 cm -1 .





Up to the composition of PP 40 % thereis very small change in the peak depthwhile reaching at PP 50 % the effect of cross linking becomes pronounced andthe value of %T increases by about 10points and this trend continues up to thecomposition of PP 70 % with littlevariation, thus indicating the pronounced

effect of cross linking due to reactiveblending of PP with UP. But as a wholethe variation is very small at specifiedpoints which indicate the stability of theblend.





Acknowledgement

The Authors would like to thank Dr GMMamoor, The Chairman of Polymer &Process Engineering Department, U.E.T,Lahore for providing financial andlaboratory support. The Authors are gratefulto Mr. Naveed Khan for providing guidanceand study support. The Authors are tha nkfulto all the faculty members and students of 2005 Session of Polymer and Process

Engineering Department for theircooperation.

Referrences:

1.

US Patent 4771108.

2. US Patent 4558096.

3.

US Patent 4956501.

4.

US Patent 4175859.

5.

US Patent 5 342892.

6.

US Patent 5432230.

7.

Reactive Melt Modification of Po lyp ropylene / Unsa tu ra t edPolyester Blends By

M. Xanthos and C. Wan(Polymer Processing Ins tituteand New Jersey Institute o f Technology,Newark, NJ 07102-1982 USA)

8.

Study on PP grafted with ULPcontaining rare earth By PanYuanfenga, Zheng Anna, XiaoHuining , Hu Fuzeng

9.

Unsaturated polyester resins:influence of the styreneconcentration on the

miscibility and mechanicalproperties By E.M.S. Sanchez,C.A.C. Zavaglia, M.I.Felisberti.





10.

Reactive Modification Of Polyesters And Their Blen ds ByChen Wan.

11.

Vlachopoulos . J.David strutt,

“The Role Of Rheology InPolymer Extrusion”.

12.

Aroon V Shenoy, D.R. Saini,‘Thermoplastics Melt RheologyAnd Processing’.

13. Http://www.eng.uc.edu/~gbeaucag

/Classes/Analysis/Chapter3.html

14.

Jasco FTIR Seminar.



http://www.eng.uc.edu/~gbeaucag/Classes/Analysis/Chapter3.html

http://www.eng.uc.edu/~gbeaucag/Classes/Analysis/Chapter3.html

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