Investigation of Aqueous Kaolin Suspensions:

a Rheological and Sedimentation Volume Study

Y ing Li

A Thesis

in the Department of

Mechanicd Engineering

FacuIty of Engineering and Cornputer Science

Presented in Partial Fuifiliment of the Requirements

for the Degree of Master of Applied Science at

Concordia University

Montreal, Quebec, Canada

Q Ying Li, 2001

Bibiidthèque nationale du Canada

uisiüons and "r Acquisitions et Bib iographic Setvices senrices bibiiographiques

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Investigation of Aqueous Kaolin Suspensions:

a Rheological and Sedimentation Volume Study

Coating colors are very complex colloid systems of which stabiiiq and rheological behaviors

are of impormnce in the coating process and in the mechanical, opticd properties of the

coated layer. Clay is one of the main ingredients of coaMg colors in the papa indusrry.

There can be very compiicated coiioid interactions that conml the smbility and ttieological

properrics of the coating coiors. The main purpose of this work is to get a bercer

understanding about the role of the colioid interactions in the rheologicai behavior of

suspensions which art composed of rnatuials having significant meanings in coating color

formulations (kaolin, sodium carboxyrnerhyl cellulose, and sodium cbloride). For practicai

applications in rnany cases, suspensions with a high solid concmt are requited which show

low viscosity, stgaiticant clasticiy, and thixouopy 3s well. The aim of this investigation is to

h d such a composiüon of above components which show the above mencioned rheological

propefles.

The colloid inttractioas were studicd by the rhmhgkai and sedimentation d u m e s

investigations. The d t s showed that hr (Iow viscosity) NaCMC was a bet ta stabiiiung and

thhning agent thaa mv (medium viscosiy) NaCMC; NaCl incnased die viscosity of CMC

added suspensions. 0.01% mv NaCMC increased the viscosity of 0.5% lv NaCMC addd

kaolin suspension supposedly due to b d p g tloccuiation. This is in a good agreement with

the tesuits of sedimenmion volume investigations. 0.1% lv NaCMC, 0.002% mv NaCMC

and 0.5% NaCI togethet caused the most signihcant chirottopy; without OC NaCi, the

suspension shows anti-thixowpy. Reai&Ecity was only found in the prcsace of mv

NaQMC. The samples, prepared kom the mixture of low and medium viscosiy NaCMCs,

were found to be the best composition for ge- Iow viscosiy, signifiant thixotropy and

elastiaty.

1 wish to express my sincere gratitude and appreciation to thesis

supervisors, Professor M N . Esmail and Dr. 2. Hbrvolgyi, for thek

guidance, encouragement and assistance throughout all stages of this

research program and the prepaoition of this thesis.

TABLE OF CONTENTS

w m OF FIGURES ix

LIST OF TABLES xi

LIST OF ABBREVIATIONS AND N O M E P i i C L A m xüi

CHAPTER 1 . INTRODUCTION 1

. 1.1) Introduction .................................... ............... ......................... ...................... 1

1.2) 2)Uoid &mi& badrground of the coating color Çotmulation ....................................... . 2

.................................................................. 121) Stn.~cture of concentra~d suspensions ........ 2

............................................... 12.2) Effect of polymer addition on behavior ~Çsuspensions 3

.................... 1.23) Methods to conuol the network structure in concentrated suspensions 6

1.2.3.1) ControUed flocdation (seif structured systerns) ............................................... 6

123.2) Addition of polperic thidreners .............................................................................. 7

1.2.3.3) Addition of pam&te-type thickeners .................................................................... 7

1.2.3.4) Use of mixture of polyrnets and particdate solids ........................................... 7

1.23.5) Hetero floccuiation ...................................... . ............................... 8

......... 123.6) Flocculation by addition of free polper (depletion flocculation) ............ .. 8

..................... 1.2.4) Methods for m d y of interactions and behaviors of flocs and network 8

124.1) Measurement of sedimentation rate and volume ............................................. 8

124.2) Rheologicai measurements ...--............... .. ........ ,.......,..., ................................... 9

124.3) Neutron scattering midies of floc structure ....................................................... 10

1.24.4) Cornputer simulation of floc structure ...............-.-.....Chi..-..Chi............................ 1 1

13) Rheobgical behavior of coating colors ...................................................................... 1 4

1.4) The role of NaCMC in the formdation of coating colors .................................... .. 16

Instruments for rheoIogical measurements ,, ............................................... ............. 18

23) Prepacation of samples ...................................................................................................... 20

23.1) fieparabon of samples for rheological study ............................................................... 20

23.2.1) Preparation of acpeous solutions oflow (IV) and medium (mv) viscosity NaCMCs ................................................................................. 20

23.1.2) Preparation of40°h kaolin suspensions (additions: mv NaCMC pourder and NaCi) .-.-.- .....-......-.+......-............................ - ................ 2 1

23.1.3) Preparation of 50% kaoiin suspensions (additions: Lv NaCMC. mv NaCMC and NaCI) ...................................... ................................................. 21

........................................... 2.34 Preparation of samples for sedimentation volume study 21

. . 3.1) Sedimentarion volume investigation ............................................................................ 27

3.2) Rheologicai propert~ Uivestigtion ........................................................................................ 29

3.3) Andysis O € rheological results ....................................................................................... î9

.. 3.3.1) halysis of flow cunes .................................... " ....................................................... 29

.......................................................................................... 33.2) Anaiysis of yield stress cumes 31

33.3) Analpsis of tfrixotmpy m e s ................................................................. - 3 4

3.3.4) Analysis of creep-recovery curves .................................................................................. 36

CHAPTER 4 . RESULTS AND DISCUSSION 38

4.1) Resuits of pqaration technique .......................... .., .................................................. . 38

4.2) ResuIts of sedimen~tion voIume investigations ..--.........O.-...O.O.........OOOO..O... .- 42

. . . . ......... 4.3) R d t s of heologd investigations O ............ ...... .. ..................... ,.- ............,... - ... 50 43.1) R e d & of viscosiy analysis -.. -- ..---.-.-.ïrsïrsO. .---. ... ..es....ïrs.ïrsïrs.ïrs.....-............. 50

43.1.1) Viscosity m e analysis of NaCMC queous solutions ............................. .. .... .. .50

43.1.2) Viçcosity m e analysis of sarnpks of400/0 kaolin suspensions ...-.......... ..-.- 51

43.1.3) Viscositg curve analysis OC samples of50% kaolin suspensio m.--.- ..--.-..-. 52

43.2) Results of yield stress anal+ -- .................................................. . ........................ , .. 64

4321) Yield stress analysis of smples of40% kaolin suspensions ................ ".-... ...... -64 4322) Yidd stress analysis of sarnples of MO/o kaolin suspensions ............... - ........ O ... 64

...................................................................................... 4.3.3) Results o f thkompy analysis 67

433.1) Thixompy cume analysis of samptes of 40% kaolin suspensions ................-.. 67

433.2) Th~otropy cumes of samples o f 50°/0 kaolin suspensions ................................. 68

43.4) h u l t s of creep-recovey anaiysis ................................................................................ 75

43.4.1) Creep-recoverg test for the 40% kaolin suspensions ..................................-....... 75

4.3.4.2) Creep-recovery test for the 50% kaolin suspensions ............................................ 76

43.5) Summary of rheological investigations of kaolin sarnples .......................................... 85

CHAPTERS . SUMMARY 87

LIST OF FIGURES

Positively charged particies with negatively charged counter ion doud in the eiectrostatidy stabilized suspension ...................................ilized.ilized - 12

Polymer molecules (macromolecules) in the sterically stabilized suspension - ..................................................... - .......................................... 12

Screening of charge in aggregated f o m in a non-stable (coagulateci) suspension d t i n g in increase of viscosity. .......................... 12

Low concentrated and adsorbed polymer chahs act as "bridges" or "Links" in aggregated fonn in a non-stable (flocculated) . . . ................................................... suspension cesuImg in m-e of viscosiq 1 3

High concentrated and adsorbed polyrners in the steric stabilization suspension resulting in no increase ofviscosity ......................... 13

Diagrarn of flow m e of suspensions in the sheir stress versus shear rate coordinate systern ............................................................................ 31

Diagrarn of yieid stress andysis of suspensions in the shear stress versus shear rate cwcdinate system. ................................................................ 3 3

Diagrarn of aeep-cecovery andysis of viscoelastic materials ........................ 37

Diagram of aeep-recoveq analysis of Newtonian liquid materialS.. ........................................ "27

Sedimentation volumes (VJ of 25% kaolin suspensions as a function oFNaCMC concentration (C,& ................................... .. ...... 46 Sedirnentation vo[urnes (VJ of 25% kaolin suspensions as a hct ion of NaCMC concentration (GiW,J in the presence of 1% NaCl.. ..........,..-.-....-..,.............-.-..w..-......-.....-...-....-............................. 47

Sedimentation volumes (VJ of 25% kaolin suspensions as a h c ü o n of NaCl concennation (CN& ......................................................... ..48

Viscosity curves of aqueous NaCMC solutions... ........................... ..-.....-.. ...... 56

Vicosity a m e s 0140% kaolin suspensions - ...-..--.-......... .. .... L

Vicosity w e s of 50% kaolin suspensions .. ......................................... . 5 8

Flow c w e s of aqueous NaCMC solutions .- .................................................. 59

Flow curves of40°h kaolin suspensions ................................................... ... 60

Flow cuves of 50% kaolin suspensions .. ...-..............-. ......................... 6 1

Thiiotropy curpes of 40% kaolin suspension with additions of NaCMC and NaCI ................ - .. ....................................... .............. 69

Thixotropy w e s of 50% kaolin suspension with additions of NaCMC and NaCL [l] ......................................... .......................................... 70

Thixotropy cumes of 50% kaoiin suspension with additions of NaCMC. [2] , ................................................................................................. 71

Anti-thixotropy curves of 50% kaolin suspension with additions ofNaCMC . [3] ........................... ".- .................................................. 72

Creep-recovery curve of40°/o kaolin suspension (t = 50Pa) ....................... 78

Creep-recovery curve of 40% kaolin suspension with addition of mv NaCMC (t = 50Pa) ....................................................... .. ............ .- ...... ........ 79 Creep-recove ry cume of 40% kaolin suspension with addition of NaCl (t = 50Pa) .................................................................................................. 8 0

Creep-recovery curve of 40% kaoiin suspension with additions of mv NaCMC and NaCl (z = 50Pa) ............................................................... 81

Creep-recovery cume of 50% kaoiin suspension with additions of NaCMC . (r = Spa) ......................................................................................... 82

Creep-recovery m e of 50% kaolin suspension with addition of r n ~ NaCMC (r = Wa) ...... .. ................ ... ............................................................ 83

Creep-recove ry cume of 50% kaolin suspension with addition of IV NaCMC . (T = O.Pa) ...-- ................................................. . . 8 4

TABLE DESCRIPTION PaQe No.

2.3.1.1 The compositions of samples prepared fEom low (lv) and medium (mv) viscosity NaCMC solutions

2.3.1.2 The compositions of samples prepared h m 40% kaolin suspensions (addition: mv NaCMC or NaCi)

23.13 The compositions of samples prepared fiom 50°h kaoliu suspensions (addition: NaCMC or NaCI) group 1

2.3.1.4 The compositions of samples prepared h m 50% kaoiin suspensions (adciitioa NaCMC or NaCl) group 11

23.2.1 The compositions of samples prepared fiam 2.5% kaolin suspension (addition: NaCMc)

23.22 The compositions of sarnpks prepared from 2.S0/o kaolin suspension (additions: IV and mv NaCMC and NaCI)

2.3.2.3 The compositions of samples prepared h m 25% kaolin suspension (addition: NaCi)

4.1.1 Viscosity [Pa%] of sanipies prepared h m NaCMC powder

4 . 1 Viscosity Faes] of 50% kaoh suspensions prepared h m NaCMC solution

4.13 Vs (Sedimentation volumes) of 2.5% kaolin suspensions in mi, [equilibrated data, after dispersing again]

4.21 Vs (Sedimentation volumes) of 25% kaolin suspension with the addition of IV aad mv NaCMC. For a cotai volume of l O d after shakiag thoroughiy

4.2.2 Vs (Sedimentation volumes) of 2.5% kaolin suspension with the addition of NaCMC. For a total vohme of 1OmL after shaking thoroughiy [1% NaQ in each rubel

4.2.3 Vs (Sedimentation volumes) of 25% kaolin suspension with the addition of NaCt For a toml volume of 1 0 d after shaking thoroughiy

43.1.1 Effea of samples of NaCMC aqwous solutions on A and n accordhg to the Oddde-Waeie equation

Effea of samples of 40% kaolin suspensions on k and n according to the Herschel-Bulkiey equation in a steady- state condition

Effect of samples of 40% kaolin suspensions on t, and qp according to the Bingham equation

Effea of samplcs of 50% kaoh suspensions on A and n accordtng to the H e n c h e 1 - B ~ ep t ion in a steady- state condition

Effect of samples of 50% kaolin suspensions on 7, and q, accordmg to the Biogham equation

The Herschd-Buikiey and B i yield stresses of samples of 40% kaoh suspensions in a non steady-state condition

The Herschd-Buikiq and B- yidd stresses of samples of 50% kaolin suspensions in a non steady-state condition

Hysteresis ''area" (Pa/s) of samples of 40% kaolin suspensions

Hysreresis "area" (Fa/s) of samples of 50% kaolin suspensions

Elastiay ratios of two different smpies: 50% K + 0.5% mv NaCMC and 50% K + 0.25% IV NaCMC and 0.25% mv NaCMC

Elastiaty ratios of two differrnt samples: 50Yo K + 0.5% IV NaOK and 50% K + 0.5% Iv NaCMC + 0.01% mv NaGMC

Elastiaty ratios of mo different sampks: 50% K + 0.5% IV NaOK and 50°/o K + 0.5% mv Na-

The calculated heologid propeities for the 40% kaolin samples

The dcuiated rheological p @ e s for the 50% kaolin samples

LIST OF ABBREVIATIONS AND NOMEMCLATURES

CS

OSC

medium weights

low weights

stomge moduIus

Ioss moduluç

complev s h m moduius

residud viscosity

insmtmeous shear modulus

s r n i c d factor

sodium catbo.xpethy1 ceiiuiose

sodium chloride

kaoiin

controiied shear m e

controiied shear stress

oscihion

shear stress

de formation

viscosity

corque

atea

r o u a o d speed

lom viscositg

xiii

VP

vs

Na'

CMC

medium viscosiy

viscosiy panmeter

shear rate

Bingham yidd stress

piasac viscosiey

sedimenmuon vohmes

sodium iron

cybo'tgmetfipl cellulose iron

xiv

CHAPTERI

INTRODUCTION

1.1) Introduction

The aqueous day suspensions are of p t importance in many fieids of indusmat

applications (eg. cetamics production, dnllirip fluids, paper coating [l-3D. Neuuai polymers

or polydectrolytts arc frequmtiy uscd as dispusant or fioccuIant ageats. The combination of

different polymers can cause qmergctic e E i . Due to the pmcticd and theoreticai

importance, the cornpetitive adsorption of neutrai (Csempesz and Rohrsetzer, 1984;

Csempz et ai., 1987; Csempesz and Cs&, 2000)[* and ionic (Tanaka et al., 1997; Swuin

et aL, 1996; Sweria et ai., 1997)p-91 maaomoldes was intcnsively studied in the p a s

decades MammoIeculcs can cause bridging flocculation if the molecular wught is great

enou& and the adsorption iaya is not saruratcd The cfficacy of floccuiation can be

improved, adding simultaaeously a lowcr and a highu moIecrJar wught polpcr (Tanaka et

ai., 1997; Sw& et aL, t996; Swcrin et ai., 1997)r-9 in the suspension. ln most cases

cationic (Tanaka et aL, 1997; Swcrin et ai., 1996; SweEn et al, 1997)P-91 or oppositely

chged (Aksberg and Odberg, 1990)[10] polyeiectrolp are used for initiaring flocculation

resdting in smng floc StNCtuIe. In the fim case, the lower molecular weight poIymer

enhances the possiiiiiy of bridgmg formation of its higher molecular w@t cornterpan,

blocking the active adsorption sites. Smng floc maure is r e q d eg. in papemahg

(Main and Sirnonson, 1999) pl] reiatiug to the high speed p a p e r b d procesçing. The usage

of the mixtures of cationic polymers has ken suggested for this parpose (ïanaka a ai.,

1997; Swerin et ai, 1996; S d et al, 1997) p-q.

In paper coating Iiqyids, induding kaoh, NaCMC is a commody used addition (Iamstrom

et ai., 1987; El-Saied et ai., 1996; Makinm and Eklmd, 1996; Persson et ai., 1997; Wang et

ai., 1996)[12-161. Them are many coafücting requiremeats for the coating color. High soiid

c o n t a for example, but low shear viscosi y and a certain d e p e of thixotropy and elastiuy

are requled. It means that mng flocculation of the pigments shouid be avoided in the

coating colors. That is why the site-bloçIang based floccuiation, conceming the coathg

colors, has not bem studied, yet But a weak flocculaaon of pigments c m result in au

advtintageous optical propertlk of the coating laye (Persson et ai., 1997).

The main purpose of this work is to show dut these advantageous theologicai propaties are

fcaslile in the aqueous kaolin suspensions using the mixture of a Iowa and a higher

molecular weight NaCMC and in certain cases in inorganic electrolyte, NaCL Due KI the

positiveiy charged edgcs of kaolinite particies, the anionic polyclcctrolytes c m cause a weak

flocculation based on the siteblocking mechanism. The rheologicai propaties ~ K C aramificd

by cone-plate viscornetry. In order to gct a bctter undastanding of the rheologicai resdts,

the resuits of sedimentation volume investigations are comparcd.

1.2) Coîioid chernid background of the coating colot formukition

121) Structure of concentrated suswnsio~

In the concentrated suspension, forces berneen the @des play an important roie in

determinkg the overali properties of dispcrsioa, Types of @de-pariide interaction arer

the hard-sphere interaction, the eIeCmcai double layer repuision, the Van der Waais

attraction and the stxxic interaction. The maintenance of parcides in suspension as individuai

primer unie or their combination intb aggregates depends on the baiance of interaction

hrcu that operares bemcrn them. By controllhg the interaction forces, one is able to d e

at the d&d units, ie. primer partide or various types of aggqates.

Various fomis of aggregates map lomi dependmg on the range and magnitude of attractive

forces. For example, a aght dusm of partides, saongly held togctbet by Van der Waals

forces may fom [usually r c f d to as coaguiation) and these aggregates cannot be

separated under the normai shear 6eid applied to the suspension. On the otha hmd, loose

merastable strucams (usualiy rcfmed to as flocs or flocdes) may fom. Such ffocs may bc

desmyed to a grata or lesser exteri5 by application of stresses, and teforni, under certain

conditions. When the stresses arc removed, it may be possible to disnnguish between weak,

open structures or fioccuks and tight but weak smactures or aggiomates.

122) Effcct of ~olvrner addmon on be havior of sumea60~ . *

Many polymers have a tendency CO adsorb on the surface of dispersed @des. Polymer

adsorption may lead to coiIoid stability or to p d e flocculation. W'hich occurs depends on

haors such as the concenttation, the charge densiy and chernid structure of piper, the

nature of the partide surface and so on. At Iow poiymei concentration the predominant

effect is bridging flocdation. Bridgîng Boccuiation is h r e d when the adsodxd polymer

has long c h a h (rails) da&@ into the dispmed phase and the amount adsorbed is beiow

saturation average. Under these conditions &e flocs are heid mgcthu by individual

moldes . At higtier polymer concentration for which partides are fi@ coated wirh a

polymtr iayer, the s e c stabhuon may occur. Whm &e s t a i d y stabilizing iayer k thin,

the effea of the short-range Van der Waak intezpartidt attraction may lead to weak

coaguiaaon. When the particles are large, or the s o h t @y is reduced to pou= than

theta condition, s m i d y stabilized patticlcs may &'bit secondaq muUmum-@

floccuiation. The flocculaaon may also be induced by non-adsorbing [fke) polymas tw. It

is usually refmd m as depIetion ûoccufation. A large concentration of non-adsochng

poiyrners may Iead CO dcpIetion (re)stabilizatïon,

In systems w h e polymer &cules have oppositc net charges to chat of the partide

sudice, the flocculation or stabilization is adequady descnkd by a charge neutralization or

charged masal mechanism. In such a case, Mabire et ai. 1171 were able to explain in a

semiquantitative way the effccts of mok& wUgbt of polymer and polymer charge density

on se* rate and M c a t i o a of siIica suspensions by using a "elecaostacic patch" mode!.

The flocdation or stabiIization processes can be very complicated in suspensions with two

or more polymcrs. Two-component floccuiant systems are comrnody used nowadays [la].

The polymer and particies will interam with tht added second polymer in either a more or

less complex way. Mi* of oppositely charged polyeiectmlptes may r d t in complex

coacervation or polydectrolyte complex formation. me latter rnay be in the fonn of

dissohed complexes, coiioidal dispersion or macroscopic precipicates. The polymer-p"de

or polymer-polymtr interaction may came pmblems, for example; restxictions in floceulant

ef5aency and floc proptrcies. Howmer, it cm be used as an advantage as in the case of the

duai polymer retention spstem used in papefmaking. in this uchni~e, one combines the

smng adsorption of highly carhic poE@kctroiytcs of Iow molecdar weight with the

bridging effcct of hi&-mol&-weight anionic polydcxtrolytes [19].

In the case of more than one polyrner in swpen"on, one m m take k m account the e f k t

of cornpetitive adsorption of polymers. Theoretid investigations of non-ionic polymtrs

have predicted the prefaential adsorption of tht &ha mokcuiar wcigbt compnent

and displacmimt of Iowcr polymers by polymers of tygher MW. Experimenrai iavcsdptions

are consistent with tttis theory.

For plyeiectmlp, the situation is more complicated because of strong inteuelauons

bctween cIecwsmtic and mnhrmationai effccts. Tanaka et al. [19] have studied the

individuai and cornpetitive adsorption of mm cationic polyacrylamides with diffcrent

molecular wwts but with very similar charge densicies onto oppositely cirarged surfaces

(polysyrcne latex, cciidose btads and cddose fias).

Swerin et ai. [20] studitd tht adsorption of two cationic p l p e r s wirh Waent rnokedar

weigtits flow and medium MW) and of cationic polyacryiamide with hi& MW onto

m i w t s i U i n e cduiose and the flOCClJation of the suspension. The two polymcis wcrc

added id sequence or simulmmdy. The combination of two poipers gave a site-blocking

effect by the low MW poI- which pve a charge reversai at a Iowa total amount of addcd

polymer. The bdging &ciency by the bgh MW polpex was sriü maintained The r d t s

indicated that the simuim~ous addition mode could be btn&ciai.

1-24 Mdods c o w d fmsvo=k smmtue in concentrad =wsshE

In industtial applications, it is o h necessary CO conaol the propedes of a nispensions for

adequate sheif Mc, on the one band, and for ease of appiication, on the other. For these

reasons, it is neces- to control the physicai stability and the ffow charatteristics of the

suspension. For the most concentratcd suspensions encouattred in pmctice, it is necessaq

to have a three dimensional network structure (gtl sanime) in the suspension CO avoid

sedunmtation and such a structure could be broktn down by shear in a rnanner that is

dictatcd by application. Moreover, it is necessary for the "gel structure" CO form fier

application CO avoid rapid fiow.

Below some methods arc shown for forming a network sauchire in suspensions.

in an deem>staticaiiy stabilizcd suspension, the stnicture rnay be conmiicd by the partide

size and shapc, and the charge on partides and clectrolyte concentration. In this manna,

weak floccuiation of the suspension in the sccondary minimum is possiile and a three

dimensional network of suspension may be produced. In a stericaiiy-stabiiized dispersion,

the secondaq minimum-type flocculation is ako possiile by controlling the adsorbed Iayer

chickness.

MacromoIecuies of nonionic or ionic type with high mole& weight at moderate

concentration produe thixotropic systems. Such materias are, thdore, ideai for

controiiiag the rheology of suspensions.

Sodium montmodonite and oxidcs (silica or alurnina) can f o q under specSed conditions

(pH, demolyte concentration, phase volume concmaation) a ''thme dimensional gel

nenvork ". With sodium monnnorillonitc, the mechanism by which such a gel-smcture is

formed is u s d y ataibutcd to a combiuation of double l aye repulsion and edge-dace

ffoccuiation [21]. W h silica, the "gelation" may take place as a tesult of double layer

cepuision or formation of chain aggqation (depending on the pH) [22].

1.2.3.4) Use ofmkt~n f p o ~ andparhhbte sokdr

Bp using a combination of sodium monmoriiünate and an oxïde with polymers, it is possible

to fomi a three dimensional structure. The solid parcicies act as centers co~ccting the

polyrner chains. In other words, the polyma chaius act as '%bridges" or ''iinks" betwem the

particies @ridging floccuiation) [BI.

By addition of smaü oppositely charged pimides to a coarse suspension, it is possible to

fomi a network structure by bridghg \ni& small partides. The degree of flocculation and its

"strength" a n be controlled by conmlling the poIymez iayer and elemlyte concentration

~ 4 1 -

The addition of a free 0.e. non-adsorbing) polymer CO a sterically stabilized dispersion may,

under specific conditions of polyrner mole& weight and concentraaon, ptoduce a weakIy

stmctured suspension. Such a suspension showed marked viscoelastiuy indica~g the build-

up of a ''stnicture" in the suspension [25].

124) Methods for studv of interactions and behaviocs of flocs and network

In a strucnired suspension, the flocs settie at a rate depending on the size and porosity of the

aggregated mass. Micbaei and Bolger [26] suggested a relationship to caiculate the average

size of the aggregates and the mm-solid ratio within the aggregates fiom the sedimentation

curves. The e@brïum sedimenration volume may provide qualitative idonmaon on is

structure (dose-packed or open strucnire). From &e tedispersion exp&ena, iafonriation

on strengrh of the interaction berneen the partides can be obtaiued

This is by far the best qyntitative method available to obtain infornaon on the prophes

of conceritmted suspension. In p e r d one may distinguish berneen two types of

masurement. Measurment during which ttie network structure is not disturbed i.e. at s d

defocrnations, and measurement during which the neework smcture is broken down, Le. at

large deformation. BeIow, a brief accomt is @en of the possible methods of measurunent

avdable at present:

The steady-state Bow curve (shear stress vs. shear rate) of concentrated suspensions can be

characterked by three distinct parameters: the shear race, the plastic viscosity, and the

Bingharn yieid value. Various theories have been put f o r w d to ucplain the flow behavior of

floccolateti and strucrured suspensions [27]. Howevery the relationship berneen interpartide

interactions and rheolopicai characteristics of concentrated suspensions is fat h m being

adequately determined. There are s e v d rheobgical models which can be used to Eit the

measured viscosity vs. sheac rate data.

La dynamic measuremenc, an oscilIating deEomaaon / stress with an angular frequency is

applied to the system. It is possible to measure the storage modulus G' 0.e. a measure of the

elastic compnent] aad the loss rnodulus G" (ie, a mcasure of the viscous component). The

complev shear modulus G * = G' + iG". The Iimiting value of G* depends on the second

differenaal with respect to distance of the equdi'biuxn interacâon potenad

Thae are two mctbods for perfonning static (transi4 defomtion measumnents on

concentratcd suspensions: by meamring the change of the stress with t h e at constant snain

(uansient smss response) or rneasuring the change of saaLi with time at constant stress

(creep m e ) . n i e zero shear viscosity Ccresidual viscositg") Y, and the instantaneous sheac

modulus GD = r / y obrained h m creep curves can be used to obtain information on the

interacrion forces between the partides in a concentrated suspension. The thixotropy and

a e e p recovery investigations can provide useful information about the t h e dependence of

stnrcntre management in concentratad systems.

Application of the small-angle neutron scattering technique is based on the fact that the

inttrference pattem of scatteted radiation is dctemined by the dismbution of sepatation

bttwcen partides centered in the floc. Inforniauon on floc sttucture is contuncd in the

smcturt factor S(Q). Cabane and coworkers 1281 have investigated the structure of

monodisperscd silica partides floccuiated bp polymers of variable charge densiy. The

neutron scattering experiments indiate two tgpes (l and II) of aggregatcs. Type 1 Aggregates

@roduced by uncharged or low-chaqed polymers of high moIecular weight) were fomed by

bEdging mechanism wïthout fidi neuPalization or saeenulp of the c h q e s on the silica

sudice. The residuai elecmistaac tepuision dowed spheres to reorganize thtmselves into

lower potencial enexgy states and d t e d in a short-range liquid-liquid order in the floc

Type II Aggregates (produced bp intemiediate or high-diarged polymers near the isoeiecmc

point of silica, or high ionic strengtr) fonned by eiectrostaac patch neutràlizaaon have a

rigid, bmched tenuous structure.

At a very simple levei, a system of plymer and parndes can be modeied as a binarly mixture

of small and large spheres interacting with a square-weii potentiai. The equiiiirium

proper& can be detemiined by Monte Cado simukaon [29]. Calculation fiom simple

algebraic expressions shows [29] ttiat relativeIy weak attractive interactions (1 or 2 kT) may

cause txtensive, weak, reversible bedging flocculation (and geiation) in a concenmted

dispersion. Further work on this sort of simulation modei is required to examine more

cornplex types of partidepartide, phde-polymer and polymer-polymer intermion.

Figure 1.2.1. Positively charged particles with negatively charged counter ion cloud in the electrostaticalIy stabilized suspension (this is the result of electrical double layer repulsion).

Figure 1.2.2. Polyrner molecules (macromolecules) in the stencally stabilized suspension ( t h is the tesult of the sterical barrier).

Figure 1.2.3. Screening of charges in aggregated fom in a non-stable (coaguiated) suspension resulting in increase of viscosity.

Figure 1.2.4. i o w concentrated and adsorbed polymer chahs act as ''bridges" or "links" in aggregated form in a non-stable (fiocdated) suspension resulting in increase of viscosity.

Figure 1.2.5. High concentrated and adsorbed polyrners in the steric stabilization suspension resulting in no increase of viscosity.

1.3) Rheologicll behaviot of coating colora

Rheology is the saence of understanding the flow and deformation of materials. Rhtology

phys a very important rote during the coating process. In high sohd content kaolin

suspensions, viscosity varies with shear rate. Such non-Newtonian fluids exhibit several types

of cornplex rheological flow behaviots - shear thurning, yieid stress, thiuotropy, diiatancy,

viscoelastiaty, etc By connolhg the rheological properties, a satisfactory performance

durhg high speed coaàng can be obtained [30]. In addition, the rheology of coating colors

has been found to affect the quality of coated and printed papas [31].

Zn application of the coating, ease of spreaduig and leveling to a thin laper on the papa

requises a high degree of fluidity of the color, despite the rather high sohds concentration. In

the modern coatiag technique there is an exact requirement for thkxotropy of coating colors.

Thixonopy is a very time dependent propery. Thixotropic substances are colloiciai gels

when solid and sols when liquefied. Clay suspensions which are more or less flocculated

show the phenomenon of thixotropy. in the coating process, higbiy ttllxompic coatings

d y have better ninnabiliq on blade coaters [32]. Yidd stress is the characteristic stress

above which some materiais will flow. Above the yieid stress, the stress and saain rate are

neariy lineariy reiated. Suspensions of floccuiated particies ohen show plastic behavior.

These suspensions do not flow und the yieid mess has been exceeded. W d stress has a

greac relevance in the coatjng process [33]. in the pper coaàng process, the yield saess is an

important parameter for hydrodynamic instabiliy phenornena in the £low under the bhde

[Ml. In the determination of yieid stress of a kaolin suspension with ChCC, Davis [353 related

the vaiue of yieid stress to the adsotpaon of CMC, due to hydrogen bonding on kaolin

@cies ushg the Casson equaaon Lepoutre et al, [36J have also shown chat the addition of

eiectrolytes incceases the suspension viscositv, the yieid stress value and the shwr-thinninp

character. Obviously, this codrms the importarit roIe of the ionic strengtti in the

aggregation of kaolin suspensions.

Viscoeiastic properties of coating colors bave been found to have a bearing on the

performance or runnability of the colors in blade coaMg [37,38]. The relationship between

visco~tici ty and high shear viscosity of coarings was studied in conneaion with the short

dweii runnability. In the hm-based papa coating processes, the 6J.m-forming behavior of

the latex and the coating's compressive response to calendatiag depend on the viscodastic

properties of the latex binder and the coahg. In the printing process - coating suength,

rotogram printability, stiffiess, aadring resisrance, foicimg endurance, blista resistance -

are al1 proptrges that are affected by the viscoelastic properties of the latex and coachg [38].

The rheological properties mostly depend on the cotioidai chemid interactions between the

coating coIour components [3]. As is wd known, the coating colour is a veq complex

colioid systern ( d y composed of a verg dense suspension of pigment micropartides, cg.

kaoiin, tieanium-dioxide, calciumi-arbonate, latex bindas and ciiffixent additions like

extender nanoparticles and smbiliWlg polyclectrolytes). By conmlling the colioidd chernid

interactions, the rheological propezties of coacing coIours can be controiied.

1.4) The mle of NaCMC in the fomiuiation of coatiag colors

The fonnuiation of coating colors using &y, latex and sodium carboxymethyl celIuiose

(NaCMC) has received more and more attention in recent years [39]. Some researchers [40f

compared the coiioidai stabilizing effea of NaCMC and stardi: they showed chat

ffocculaaon of latex by NaCMC occurred after cenmfuging the coating colors but not by the

starch. The other researchers [41] compared the rheological behavior of a NaCEUfC

containing color with those of a starch containhg color. They have demonstrated that 1

d h of NaCMC conferred about the same elastic charaaer on the colors as oxidized starch

added at a level of 6 eP/o. They showed chat there was a change in suspension saucniee when

either polymer was added, which they interpreted as an aggiegation process. Zaman, et ai.

[42] emphasized that the flow properties of siiica suspensions are highly affected by the pH

of the suspendmg media and concentraâon of the added sait

Kaolin powder (K-7375, hydrated duminum silicate), was purchased from Sigma Chernical

Company, S t Louis, Missouri U.SA The partide size of tbis kaolin is in the range of 0.1-4.0

p., containiag 90% by weight of kaolinite partides < 2 p . The parrides are platelet-shaped

but Form larger stacks. Below pH = 8, the edgcs of partides are positively charged and the

faces aee negatively charged. In this study, kaolin powders were dispened with disded watu

to get NO/o & 50% concenmtiom at room temperame by an overhead stixra for the

rheological investigations; while 10°/o concentration kaolin suspension was made using s d e d

glas tubes for the sedimenration volume study. The pH of the prepared samples was fomd

to be between 5 and 6. The approximate measurements were carried out by indicator paper.

Sodium Carboxymethyl Cellulose, NaCMC powder of two viscosities: low (N0.C-8758) and

medium (N0.C-4888) viscosity were ordezed h m Sigma, Thek solutions were prepared

with distiiied water for examhhg flow propetties and for the composition with kaoh

suspensions at room temperame, depending on the concentration, sdlïaent cime was given

to achieve the homogeneity of the solutions without rnixïng or any e x t d source of heat or

power to atroid any decomposition of the polymer moledes. GMC n o d y a m as

thickening agent [437, and most CMC soluaons show pseudopiastic behavior, that is,

viscosiy is deaeased by sheazing [Ml. in this mdy, low Co) and medium (mv) viscosity

NaCZMC powders and solutions were added at different c~ncent~tions into kaolin

suspensions as thküag agent. NaCi (sodium chloride, BDH, analyricd reagent), is water-

soluble and ionhes d y . The NaCl in solution accommodates both positiveiy (Na*) and

negativdy charged (Ci] ions. Distüied watcr, pH-value around 5-6, was used for preparation

of samples.

2.2) Instnunents for rheologicai measurements

Rheological measurements of our sampIes were carried out using a rotational controIied

Rheometer (Rheostress RSlOO), equipped with a cone and plate sensor. The RSlOO is an air-

b* rheometa aiiowing characterization of sensitive stnicnues which cm be appiied to

low and medium viscosity materials using low stresses and low shear rates. It is designed

with a Erame which is especiaiiy stiff to aiiow precise strain and n o d force measurernents;

the motot is the most p o w d drag cup with an excdmt dynamic respoase and low

cutrent to minimize heat generation; the fictionless au-bearing design d o u a a hi& axial

and radiai force togcther with a srnail mechanical sm-up torque. At a pressure of 25 bar

and a flow rate of 6 l/rnin [451, it s~arts rotating with a torque of less than 1pNm; the sensor

design, cone and plate is preferred when deaning is a problern or ody a limited sample

volume is available; it is conmiied by a sophisticared application software package which

contains aii the rouMes desired and required in ody one rheometer; The resdting shear rate

registered into the sensor systern is detected with a stabIe and precke digitaI encoder with up

to 10 million impuIses for one revotution which is abk to rneasure a smaii yieId d u e and

low strain or shear rates. The air bearing with the highest specificaüons availabie with

respect to sran up torque, &ction and stability for precisely applying stress. The resulting

stcain is detected digitaiiy with 10 million impulses for 360'. Theze are more specid feanues

in Ml00 for arampIe toque calibration; autogap/thermogap controls; microstress control;

compüance correction; and inertia correction, etc..

WhiIe the Rheometer is nianing, there is a gap between the cone and the plate to ensure no

damage to either surface, and the gap is designed smaii enough to keep the angle '8' between

the cone and plate as srnail as 4 degrees for keeping the ratio of angular speed and disrance

to the plate consmnt. That is, Cor any point within the gap, a constant shear rate ' y ' can be

assumed. Some operathg modes such as conmlied rate (CR) mode, controlled stress (CS)

mode, and oscillation (OSC) mode which are conducted altematively and interchangeably in

the RS 100 are performed easily using the compute. control. In CR mode, the toque is

rneasured at a certain preset speed, and both steady flow C I K V ~ ~ and thixotropy behavior can

be perfectiy determineci; in CS mode, the speed is measured at a cenain preset torque, and

both yicld point of samples, which is measured within a loop composed by an up and d o m

m e s with the innease of suess fiom zero to a h e d d u e , and the creep-recovecy

behavior, where a constant stress is applied on sarnpIes and the correspondmg s& is

obtained, can be measured. In OSC mode, the torque is applied as a sine wave at varying

frequencieç; when it is operacing, there is no destruction of samples and no desmying the

structure of samples. In this mode, both the suess and fiequenq sweeps cm be measuted.

Geomemd factors convert physicai quantiy into theological quantity as below:

2.3) Pteparation of samples

23.1) prebaration ofsam~les for rheoloeicai studv

Using an analytical balance with a four *tai resoiution, kaoiin powder, NaCMC low and

medium viscosiy powders, and sodium chioride NaCJ powder were exady rneasured to

make samples with the content of 40% & 50% kaolin suspensions. Stock solutions of

NaCMC and NaU were prepared as d. During the preparation, the components for everg

sample wexe inaoduced simuitaneously. In this work, W/O and 50% kaolin suspensions were

prepared by ad* one and half weight of distiiied water, and haif weight of distiiied warer

to kaolin powders. Dispersed at room temperature was performed h t l y using a glass rod by

hand, then by an overhead stixer at I500rpm for Gve minutes for rheological investigations.

A 10% concentration kaoiin stock suspension was dispased wich a glass rod and stored in

the scaled glass tubes for the tîmher study of sedimenmion volumes. The CiMC sohtions

were prepated by ad- distilled watcr at the specific concentrations for low and medium

viscosities respectivdy at mom temperature.

For a total 50g weight of soIution for each sample, the caiculated amount of IV N a C K and

mv NaCMC powders were put in each glass beaker, discilied water was added to get ciiffirent

concentrations h m 1% - 5%. The solution of 1% mv NaCMC and 1% NaU was made the

same way. The compositions of samples are shown in Table 23.1.1.

For a t o d 50g weight for each sample, 4 kinds of samples of 40% kaoiin suspensions were

prepaxed. The compositions of samples are shown in Table 23.12

2.3.13) Prepmation $JO% h o h qûmJl'on.r (aaiaW0n.s: /v NaCMC, m NaGMC and NaCJ

For a total Gog for each sample, 10 kinds of different composites were prepared in two

groups (Tables 2.3.1.3 & 23.1.4). in Table, 23.1.3,0.Z0/o and 0.5% solutions were prepared

Erom 5% IV NaCMC stock solution, while 0.25% and 0.5% solutions were prepared Erom 3%

mv NaCMC stock solution. in Table, 2.3.1.4,0.1% and 0.5% soIutions wtre prepmd from

5% IV NaCnlC stock solution, whiie 0.01% and 0.002O/o solutions were prepared h m 1°/o

mv NaCMC stock solution

2.3.2) Prepmtion of -les for sedirnentation volume s n i d p

For a t o d voIume of lOrni, the samples were prepared lrom suitable amouncs of the stock

solutions (kaoiin, NaCMC and NaCI). in this study, 2.5% kaolin suspension was prepared

from 20% kaolin stock suspensions, different concmnations of IV NaCMC solutions were

p r e p a d from 0.25% IV NaCMC stock solution and différent concentrations of mv NaCMC

solutions were prepared fiom 1% mv NaCMC stock solution. Different concentrations of

NaCI solutions were preparcd h m 10% NaCI stock solutions. Ail the samples were made

by adding the necessary amount of d i d e d water in scaled cubes, and homogenized by

shaking the tubes thoroughiy- For practical rasons, we prepared more dituted (2.5%) kaolin

suspensions for the sedimentation volume investigations. During the same obsemation

periods (fier 3, 21,27 and 72 hours), three groups of experiments were carried out The

compositions of prepared samples are givm in Tables 23.2.1 to 2.3.2.3.

Table 2.3.1.1 The compositions of prepared low (IV) and medium (mv) viscasity NaCMC solutions

Table 2.3.1.2

Iv: low viscosity; mv: medium viscosity

The compositions of samples prepared from 40% kaolin suspensions (addition: mv NaCMC or NaCI)

Samples

NaCMCII

mv: medium viscosity I I I

Content of NaCMC solution

hr NaCMC

5%

Samples

K4011

K4012

K40/3

KM14

mv NaCMC -

Content of âiierent components

NaCl -

Kaolin

40%

40%

4aQ/o

40%

Distilled water

95%

mv NaCMC

- 1%

- 1%

NaCl

1%

1%

Distilled water

60%

59%

59%

58%

TaMe 2.3.1.3 The anpsikm of sarnples prepared from 50% kaolin suspensians (adcnüons: NaCMC or NaCl) Group I

IK medium viscosity

Content of diierent components

Table 2.3.1.4 The compositions of sarnples prepared from 50% kaolin suspensions (additions: NaCMC or NaCI) Group II Iv: low viscosity; mv: medium viscosity

I

Samples

Content of diierent components

Kaolin NaCi Oistilled iv NaCMC mv NaCMC

Table 2.3.2.1 The compositians of sampies prepared from 2.5% M i n suspension (add'r'r: Na=) Iv: low viscosity; mv: medium viscosity I 1 1

Sarnples(l)

Tube II11

I Tube (1)s 1 2.5% 0.01 % 0.01% 1 97.5% 1

Tube (1)2

Tube (1)3

Tube (114

Content of diierent wmponents

Kaolin (10%)

2.5%

2.5%

2.5%

2.5%

Tube (1)6

Tube (117

1 Tube (1) 10 2.5% 1 0.005% 97.5% 1

Tube (1)8

Tube (119

Table 2.3.2.2

IV NaCMC

(0.25%)

0.04% - ---

- 0.02%

-

2.5%

2.5%

The compositions of samples prepared from 2.5% kaolin suspension (additions: h, and w NaCMC) and NaCl

2.5%

25%

IV: low vismsity; mv: medium viscosity , 1

mv NaCMC

(1 %) -

- - -- -

0.04% -

0.02%

O.O20/a

0.01 %

Distnled water

97.5% -- - ---

97.5%

97.5%

97.5%

0.01 %

0.02%

97.5%

97.5%

Samples(ll)

97.5%

97.5%

Tube (II)1

Tube (1112

Content of different components

Tube (11)3

Tube (11)4

Tube (1115

kolh

(1 0%)

2.5% 1 2.5%

Tube (11)6

2.5%

2.5%

2.5%

IV NaCMC

(0.25%)

-

2.5%

- 0.01 %

0.02%

mv NaCMC

(1 %)

0.01 %

0.02%

0.04%

0.04%

- -

NaCl

(1 0%)

1%

1%

-

Distilied

Water

96.5%

96.5%

1%

1%

1%

96.5%

96.5%

96.Wo

1% 96.596

The mpositions of sarnples prepared from 2.5% kaolin suspension (addition:

Samples(1II)

Tube (III)1

Tube (111)2

Tube (111)3

Tube (111)4

l Tube (111)5

1 Tube (111)6 2.5%

Content of diierent components

1 .O%

2.5%

96.5%

Distilled water

97.5%

97.3%

97.1%

96.9%

Kaolin (10%)

2.5%

2.5%

25%

2.5%

NaCl (lm)

- 02%

0.4%

0.6%

0.8% 96.7%

CHAPTER 3

METHODS

3.1) Sedimenmion volume investigation

To get qualitative information about the effect of different additions on the cofloidal

interactions of kaolin partides and structure formation, sedimenmtion volume investigations

were performed. This method provides information about the partide-particle intuactions

(p-p adhesion). As is well known, the bigger the sedimentation volume, the strongcr the

panide-particle adhesion. The explanauon can be given as Çoiiows (the figures are shown

below):

iF the system is stable, thue are only individual partides and aggregation does not

happen. They settle down in the bottom of the tube individually, and the fomiing

sediment is very dense. There is no attraction between the partides.

if the system is unstable, the @de-partide adhesion is strong and the panides

aggregate. The stmcture of the aggregate is usually loose. Due to the strong partide-

p d e attraction, they can not shrink in the sediment, so the structure of sediment

is ako loose, that is, the sedimentation voiume is large.

if the systern is unstable, but the pade-pamde adhesion is weak, the partides

aggregate but they can shrink in the sediment due to the gravity. Hence, the

sedimentation volume in this case is srnall

(2)

loose-compact, Vs is large

î l e sedimentarion volumes were measured at ambient temperame (23 + 1 O C ) . The encire

homogenization was obmined by a standard shaking method afier preparation. The

equtltbrated values were recorded after shakmg (homogenization), at 3 hours, 21 hom, 27

hours and 72 hom. n i e apparent sedimenotion volumes were examined by reading the

value in each tube. In order to check the equilibration, reading the near constant values of

volumes, the samptes were homogenized again and measured the seàimentation volumes.

3.2) Rheological properry investigation

Using the Rheosuess RSlOO, the properties of kaolin suspensions for different compositions

were obtained quantitaàvely by measuring four kinds of nwes in CS & CR modes. These

m e s are: 1) stmdy-state flow m e ; 2) tkxotropy loop; 3) yield stress loop; 4) a e e p

recovexy m e .

The rheologicai properties were measured at ambient temperature (23 f 1 OC) using a cone-

plate (Rheometer RSIOO). Both the viscous and elastic properties were studied The apparent

and piastic viscosities, the Bingham yield stresses, the Herschel-Bulkley yidd stresses, and

rhixompy were examined by measuring the steady-stace flow cuves and chixoaopy Ioops

"ares". The elastic behaviour was investigated by measurinp and analyshg the creep-recovq

functions.

3.3) Anaiysis of rheologicai tesuits

33.1) hnalvsis of flow cuves

Obswhg fiow behaviors of the investigated sarnples and measuring viscosity values at

differeac shear rates were performed with the steady-state flow cwes. There is a

reiationship berneen the assigned shear saress and the resulting sheat rate in CS mode, or

berneen the assigned shear rate and the resulting sheat stress in CR modc La this study, the

CR mode aras chosen in order to get a high shear rate. A constant shear rate was applied

through the flow field in each rneasuzement to smdy the deformation of the sample as a

function of shear rate. By choosing a minimum value for the start point of shear rate to a

maximum value for the end point of shear rate, a series of data £iom which one shear rate

corresponded CO one shear mess were obtained.

The flow and viscosity m e s were fimd to the O d d d e - W a e l e equation for the CMC

solutions, and the flow and viscosity curves were fitced to the Herschel-Buikiey and Bingtiam

equacions for the k a o h suspensions. The fiow cuves of the kaolin samples c m be separated

into two main parts manually suitable for the andysis. The Herschel-Bulkley equation firs

weU for the first part sincc the flow cume is non-iinear at low shear rate, and the Bingtiam

e w a o n is reiated ro the second part since the flow curve in this part shows n d y hear

behaviors at high &ear rate. Regression caicuiaaons for the power iaw and hear modd were

canied out Cor the suspensions and sohtions. Aii ttic dopes of the d g h t liaes in the flow

cuves indicate the degree OC deviation fkom Newtoniau behavior. AU the kaolin samptes

showed plasac (shcar-- behavior with n c 1 (a reflem the degret of dcviation kom

the Newtonian behavior. The greatcr the deviauon fiom 1, the greatcr the deviarion from

the Newtonian bchavior.). Ail the NaCMC soIutions showed pseudoplastic b h v i o r with n

< t as well. The power law model can be presented by:

Osddde-Waele equation for solutions

f = k f "

wherein k is viscosi ty parameter.

Heachd-BulkIey equatïon for suspensions

7=rfHBf ky'

wherein r,is the Herschel-BulkIey yield stress.

The linear model c;ui be presented by the Bingham quarion for suspensions

7=rB + 5y (6)

wherein r, is the Bingham yield mess, 5 is the piasac visc~sity~

F i 3.3.1. Diagram of tlow m e of suspensions in the shear stress versus shear rate cmrdiaate system. Herschel-Buikiey yieid stress; 7,: Bingham yield stress.

The yidd stresses (rm and 7 , of the invcstigated sarnples can be detexmined fiom the above

flow curve. Suspensions of flocculated particies ofka show plastic behavior. These

suspensions do not flow und an iniaal stress Ievei has bem urceeded. This suess is caiied

the yieid stress. Above the yield stress, the mess and shear rate are lineady reiattd for the

ideally plastic behavior. The Binghm equation describes the shear stress/shear rate behavior

of many shear-chmmg materiais at high shear rates. The intercept of the linear portion of

the flow N v e @es the Bingham yieid stress and the dope gives the plastic viscosicy of the

suspensions. Hence, by choosing the nearly iiaear range of the second part of the flow

m e s , the Bingham yieid mess (?$ and plastic viscosity (ïQ of different sampies cm be

compared with each other. The Herschel-Bulkley ( rd yield saess, can be determincd h m

the Hetschd-Buikiey equation. These two yidd stresses shouId be in a good agreement with

each other, although the Bingham yicid value should alwap be higher than the other one.

The Herschel-Bulkley (rd yield s u a s of the investigatcd samples was pesforrned by

formirig a hysteresis loop in stress ramp measurements of CS mode. in this test, the

conaoiied s e s was applied and controlled, the s t m shear stress was set to zero. However

it wili not masure any rneanligful shear rate as long as the end stresses were not high

uiough to cause the fluid to flow. For the 50% kaolin suspension, the end shear stress is

much higher than IV NaCMC added kaolin suspension since its low viscosity. If you inaease

the shear Suess, you might inaease the eime, in order to keep the veioaty of devaaon of the

stress ramp constant. Thercfore, the rneanhghi tests should be camied out under the same

rate of velouty elevation during the yield stress measurements. The correspondmg results of

samples be cornpared with each other.

Apparent viscosiy of fluid gives much uscful bchavioral and predictive informaaon for

various products, as w d as knowledge of the effects of processing, formulation changes,

aging phenornena, etc. FIow behavior is used as an indirect rneasure of product consistency

and +y, and flow behavior studies are also deuned as a direct assessrnent of

processabili y. For example, a high viscosiy liquid rcquires more power to pump than a low

viscosity one. Knowing its flow behavior, is u s h i when designing purnping and piping

systems 14q-

ModelIing &y, driüing muds and cextain pigment dispersions are examples of piastic

dispersions. Suspensions of carbon black in hydrocarbon oil o h acquire a yield value on

standing and become conducting, owing to the contact berneen the carbon partides which is

devdoped thtoughout the sysnm. Above the yieid stress ttic i n ~ c l t contacts break in

the floc. Once these contacts are broken, the suspension behaves as though the particies

were dispused. The concept of the yield stress is very usehi for pradcai purposes, for

example, in diara- the ability of a grease to resist slumpiag in a rolier bcaring, ia

determiniag the stability of suspensions and the appearance of coated materiai, etc. [41.

F i e 3.3.2. Diagram of yield sucss anaiysis of suspensions in the shear stress versus shear rate coordinate sysœm. T,,: Herschel-Bulldey pield stress; t,: Kinghani yield stress. ilp piastic viscosity.

Clay suspensions which are more or les floccuiated show the phenornenon of thixotropy.

Thixotropic propery of materials is deçied as a graduai decrease of the viscosiy under

sheat stress foiiowed by a graduai recovq of structure when the suas is removecl. The

opposite type of behavior, invoIving a graduai inczea~e in viscosity, uuder suas, foliowed by

recovq, is calIed 'negatme thixompy' or 'anti-rhixotropy'. The ana-cbixotropy materials

fiequently show diiatancy. A dilapant substance is one bt deveiops inaeasing rrsistance to

flow as the rate, of shear inmases. A household example of a dilatant material is a chi&

dispersion of cornstarch in water. This appears to be a fice-flowing liquid wbm poured, but

whm it is s k e d , it becomes very hm. The thùroaopic behavior is reversible whcn thc

shearing is stopped, the viscosity is recovered over a remonable pMod of time. Vatious

mecfianisrns cm cause thixotropic behavior. For a gel system, agitation disrups the ttuee-

dimensional structure thar binds the system into a gel. Agitation might also i n d u c e arder

into the system. In a system contairing long polp&c molecules, these molecules can be

disordered in the gel. When the gel is agitated, the molecules can align in the direction of

flow, reducing the tesistance to flow [Ml.

The thutotropy tests were conducted in CR mode of RSZOO, the hysteresis loop was fomcd

with the up c w e which was staned at shear rate 0.15 s" continuously inaeased to the ended

d u e at shear rate 749.79 s*', and the down currre which was irnmediatety stmed at the

maximum ended shcar rate deaeased continuously to the minimum shear rate value as

quickly as possible (Green-method). During this study of thixotropy, aii the up cwes were

obtained in the period of 450s (steady-state condition), while aii the d o m curves were

obmined in the period of 60s (not steady-state condition). Sincc the thixotropy is very the -

dependent, the up cuve is set in a suffiCient tirne for -ch test to let the network stnicture of

samples break down to -ch an equÏiibrated situation causing reductioa in viscosity. When

plotring shear sues venus shear rate, the area bemeen the up and down m e s deçies the

degree of the thixompy. It has the dimension of energy reiated to voIume of the sheared

sample indicacing the energy required CO break down the thixompic structure [49]. If the

tluid is a.-thkotropic, the dom m e wili be above the up m e . In case of t h e

independent fluids, the upper and Iower m e s will be idenacai.

ïhixotropy is hvorabk in cemin applications such as paiat, ink and coating. Paht chat thins

fast by mkes of brush can be eady painted. Whm the applied paint tayet rethickens fast, it

preveats sagging. Ia coaüng mills, bighly thixotropic coatings usualIy have bctter d i i i y

on blade coaters [32]. la phamiaceuticais, additions are added to dmgs to get a thixotropic

spnip that prevents dissolving or sepamion of dnigs h m the syrup base. in the application

of process conuol design, when a thixompic fluid enters a long pipe fiom a large vessd

where it has bem dowed to ~ s t , the devdopmcnt of the velocity and pressure 6dd in the

pipe is very complicated [SOI.

The creeprecovery test is the static merhoci which is used to determine linear viscoelastic

bchavior of m a t d s . When a typicai elastic solid is stresseci, it k d i a t d y defomis by an

amount proportional to the applied stress and maintains a constant deformation as long as

the stress runains constant On removai of the stress, the elastic energy stored in the solid is

reIeased and the soiid immediately recovers its origiaaI shape. Newtonian liquids, on the

other hand, deform at a rate propotrioml to the apptied stress and show no recovcry when

the stress is removed, the atcigg involmd ha* been dissipated as heat in overcoming the

intemal &crional resismnce. When oiscoeIastic mat* are stressecl, some of the e r t q

invofved is stored ~ücally; variou parts of the syçtem being defonned into new non-

equiiiirium positions d a v e to one another. n e remahder is dissipated as heaç various

parts of the system flowing into new eqdbrium positions dative to one another. If the

reIah motion of the segments into non-equilibrium positions is hampered, the elastic

deformacion and r~covery of the materjais is ümedepmdent (retarded elasaciy) [521.

Static test involves the imposition of a stcp change in stress (or main) and the obsmtion

of the subsequent d d o p m e n t in cime of the strain (or stress). VPhile the dynamic test

method kvoives the applicaaon of a hamonically varying strain. Whatever methoci is

applied, the very i m p o m t point is that, the measuremmts are made in the lia-

viscoelasac range. Otherwise, the results will be dependent on expeximental details and wili

not be unique to the materiai. The test for lineatiy is to check that the computed viscoelastic

functions are independent of the magnitude of the stresses and strains applied.

The determination of the iinear viscoelastic response is very meaningful for the properties of

materials. There is the possibiliy of eluadating the molecular structure of materials from the

linear viscoelastic response; The material parameters and functions measured in the devant

experiments sometimes prove to be usefui in the quality-conml of indusmai products; A

background in iinear-viscoeiastiay is helpful before proceeding to the much more difiïcuit

subjea of non-iinear viscoeiastiaty; Fmally, a further motivation for some past snidies of

viscoeiasticity came tiom mbology, where knowledge of the steady shear viscosity fiuiction

was needed at high shear rates. Measurements of this function on Iow-viscosity

'Wewtonian" lubricants at high shear rates were made diEcuit by such hctors as viscous

heating, and this led to a search for an analogy between shear viscosiy and the

correspondmg dynamic viscosiy [52].

recoverd )le elastic portion

loss port on due to floaüng

t

Figure 3.3.4. Diagram of aeeprecovery analysis of viscoelastic materials. y-: maximum deformation; Y, &tic defomiation.

Figure 3.3.5. Diagram of creep-recovery anaiysis Figure 33.6. Diagram of aeeprecovery of of elastic solid materials analysis of Newtonian Iiquids

marerials

CHAIpTER4

RESULTS AND DISCUSSION

4.1) ResuIts of preparation technique

Zn order to check the effect of the technique of NaCMC addition to the kaolin samples, the

rheological and sedimenmion volume investigations were carried out. Concerning the

rheologid investigations of samples for 4û0h kaolin suspensions, the timedependence of

viscosity was found in samples prepared fiom mv NaCMC powder. The timedependence

was also fond in viscosiy of samples for 50% kaolin suspensions, in the case of the

samples prepared h m 0-m)v NaCMC powders. Moreovez, from the observation and

viscosity measurements, it was also shown that the IV NaCMC-added 5û% kaolin

suspensions were significandy thinnu than thae of mv NaCMC-added suspensions.

However, the timedependence was not found in the viscosity of some 50°/o kaolin

suspensions, of which thc samples were prepared h m 0-m)vNaCMC solutions. To reach a

near-equilibtated siniaàon for macromolecules ac a solid-lied incetface takes more time if

one prepares the sampIes h m NaCMC powders than NaCMC solutions. It also takm more

time to reach an eqdi'brated situation in adsorption and in the conformation. In Table 4.1.1,

the viscosity of some 50% kaolin suspensions samples prepared directly fiom 0-m)v

NaCMC powder was rneasured and recorded after one day of pceparation and after two

weeks of preparation at m m temperame. The viscosiy of these samples dewased aEtm

two weeks. However, in Table 4-12 there was no change at di duxjng the kinetic study of

viscosity for 50% kaolin suspensions prepared hom NaCMC solution. The viscosity were

constant during the investigation period.

Conce-ininp the sedimmtation volumes investigaaons of samples for 2.5% kaoiin

suspensions, the tirnedependent properry was even found for sarnpIes prepafed h m

NaCMC solutions. In Table 4.1.3, 10 kinds of samples were prepared and r n d at

eqyiiirated state afier 3 sets of shakirip: for each shakitiP_ the sedimentation volumes (Vs)

were recorded. Cocresponding CO each sample, the Vs deaeased with time, which showed

@tant time-dependence. This is not in a good agreement with the rheological results that

can be interpreted as foiiows. In the rheological investigations, by applying a stronger force

than the pvitational force, one c m destroy me.y structure independently of the structurai

strength provided that the structurai saengths are not too high. Hence, the cone-plate

viscomety does not make any ciifference between the samples.

Table 4.1.1 Viswsity [Pas] of samples prepaied fmn NaCMC powder Iv: low viscosity; mv: medium viçcosity

1

50% K with 0.5% iv NaCMC and 0.5% mv NaCMC

Table 4.1.2 Viscasily [Paq of 50% kaolin suspensbns prepared from NaCMC soiution Iv: low viscosity; mv: medium vismaty

50% K with with 0.5% iv NaCMC and 0.5%

mv NaCMC and 1 % NaCl 50% K with 1% iv NaCMC and 1 % NaCl

TRne

X

"

After 1 &y

After 2 weeks

0.4 - 3.6

0.09 - 3

After 1 &y Mer 2 wwks After 1 day )Ifter 2 weeks

0.5 - 13 0.1 - 1.3 025 - 21 0.16 - 1.7

Table 4.1.3 Sedimentath vdumes of 2.5% W i n suspensions in mL [equilibrated data, after dispershg agah] r without adartions) Iv: low viscosity; mv: medium viscosity.

1

1.0.04% IV NaCMC 2 0.04% mv NaCMC

3.0.02016 IV NaCMC 4.0.02% mv N ~ M C

5.0.01% iv NaCMC and 0.01 %

rnv NaCMC 6.0.02% iv NaCMC and 0.02% rnv NaCMC 7.0.01% iv NaCMC

8.0.01% mv NaCMC

0.9 1.3

- - - - -- - - - - -

9. - *

10.0.005% mv NaCMC

26

2 5

1

0.9

3.3

0.65 1

2.5 3.2

0.5

0.0

0.9 1 0.6 1.5

1.1

0.75

0.55

2

0.55 1.2

0.95

0.6

0.5

1.6

2.5 2.4

2.5 1.9

4.2) Resiùts of sedimentation volume investigations

The results of sedirneatation volumes (Vs) are presented in TabIes 4 2 1 to 42.3 aaà F p s

4.2.1 m 4.23. In TabIe 4.2.1, at 10 and 20 minutes after homogenization (shaking), Vs can

aot bc recorded duc to the vtrg milky-like narure of ttit suspensions. This phmornenon was

also found for some tubes afier 3 hours. As can be sem in Table 4.2.1 and F i e 42.1, the

lv NaCMC shows a stabiliwig effxt ia the whole concenmtion range. This means that the

Vs values significantiy decrmse with increasing concentration of polymer. In the case of the

mv NaCiMc, howwer, a maximum Vs appeaxs at the Iowest polyrner concentrations due to

the b d g i n g flocculation. The mv polymer cm ban bridges between the positive@ charged

edges of differcnt partides. The simuitaneous addition of the h and rnv po lpm in the

suspension Ieads to intermediate sedirncatatioa volumes, indicaàng that beside the

adsorption of IV NaGMC the bridge forming adsorption of mv NaGMC also occm (site-

blodnng effecr).

The sirndtaneous addition of NaCl and NaCMC in the kaolin suspensions resutted in

interesting obserpations. As can be seen iu Figure 4.22, the N a U rliminishes the stabrlizing

capabili ty of IV NaCMC, cspecially at the Iower concenaations of the lv polymer (also see in

Figure 4.21). This &en c m be atmbutcd to screeaiag of the eiecwstatic forces by the

sodium chioride. The NaCl can declease the adsorption capabilicy of the negatively diarged

polymers on the positivdy charged edges on the one hand; On the ottter hmd, the sodium-

ions cm &O sueen the electrustatic repuision between the polper-covered partides. An

opposite effect can be obserrred for the mv NaCMC The NaCl impmves the stabiliPng

capaàty of the polymer, supposedy due to the hindered bridge fomiing adsorption.

In F i 4.2.3 and Table 4.2.3, the results of Vs of 25% kaolin suspension in the presence

of NaU are presented. The study of sedimmtation voIumes in the presence of NaU is of

great importance because we cm get indirect infounation about the arnphoteric diatacter of

the surface charges of kaolin partides. As a n be seen in Frgure 4.23, the Vs values are

deaeasing with increasing concentration of the NaU up to 0.6 cm3, then remaining at a

constant value. The partide-particle adhesion in this case becornes weaker afitf ad@ NaCl

into kaolin suspension which can be expIained in cemis of saeening the facezdge electcic

attractions. The NaCl hinders the adsorption (saeening effect) and also saeens the

repulsion among the NaCMC-comd putides. The NaU mostly hliders the badge

forming adsorption of mv NaCMC renilring in a more stable suspensioas.

Table 4.2.1 Vs (Sedimentation Volumes) of 25% kaolin suspension wiîh the a d â i i of iv and mv NaCMC. For a totai vdume of 1OmL after shaking thoroughly. IV: low viscosity; mw medium viscosity

Unit mL

ComposiüonlSample

1

2

3

4

5

6

7

8

9

10

after 10 min.

O

O

O

O

O

O

O

O

O

O

25% Kaolin + 0.04% iv NaCMC

2.5% Kaolin + 0.04% mv NaCMC

2.5% Kaolin + 0.02% iv NaCMC

2.5% Kaolin + 0.02% mv NaCMC

2.5% Kaolin + 0.01% IV NaCMC + 0.01 %

mv NaCMC

2.5% Kaolin + 0.02% IV NaCMC + 0.02% mv NaCMC

2.5% Kaolin + 0.01% IV NaCMC

2.5% Kaolin + 0.01 % mv NaCMC

2.5% Kaolin

25%Kadn+O.O05%mvNaCMC

after 3 houn

O

O

O

3.1

3.0

O

O

3.7

2.9

3.5

shaking

20 min.

O

O

O

O

O

O

O

O

O

O

after 21 houn

0.9

1 .O

0.9

2.5

2.6

1.3

0.9

3.4

26

3.3

after 2ï ~ O W S

0.8

1.4

1.0

2 6

2.5

1 2

0.9

3.4

2.5

3.3

after 72 houn

0.9

1.3

0.9

2.6

2.5

1.0

0.9

3.3

25

3 2

Table 4 2 2 Vs (SedimentatjOn Vdumes) of 2.5% kaolin suspension with the additkm of NaCMC. For a total volume of 1 OmL after shaking thoroughly (1 % NaCl in each tube] Iv: low viscosity; mv: medium viscosity

Unit: mL

Composaion\Sample shaking 1 hours [ hours f hours 1 houm

T I l I

1

2

3

4

5

6

Table 42.3 Vs (Sedimentation Volumes) of 2.5% kaolin suspension with the a d d i i of NaCI. For a total volume of 1 OmL a* shaking thoroughly.

2.5% Kaolin + 0.01 % mv NaCMC

2.5% Kaolin + 0.02% mv NaCMC

2.5% Kaolin + 0.04% mv NaCMC

2.5% Kaolin + 0.01 % iv NaCMC

2.5% Kaolin + 0.02% IV NaCMC

25% Kaolin + 0.04% IV NaCMC

4 2.5% Kaolin + 0.6% NaCl 1

CompositionSample

5 1 25% Kaolin + 0.8% NaCl I

1

2

3

16 1 25% Kaolin + 1 a% NaCl

2.5% Kaolin

2.5% Kaolin + 02% NaCl

2.5% Kaolin + 0.4% NaCl

I . 1 m 1 . 1 . I . I . io (3

9 m

'f? N

9 CU

'f? P

9 P

4.3) Reauita of rheological investigations

The d t s of rheologicai investigations in tbis s t u d y were e x h e d for the aqumus

NaCMC sohtions and for the 40% and WO kaolin suspensions. E v q investigated sarnple

showed non-Nmonian, mosdy plastic behaviour. The viscosity m e s and flow m e s for

the aqueous NaCMC solutions can be seen in Ergures 4.3.1.1 and 4.3.2.4. The viscosiy

c w e s and flow curves for the Wh kaolin samplcs can be sccn in Figures 4.3.1.2 and 4.3.2.5.

And the viscosity eumes and fiow curves for the 50% kaoih samples can be seen in Figures

4.3.1.3 and 4.3.1 A. The determined rhco1ogia.i parameters (the range of apparent viscosiaes,

plastic viscosity, Hadiel-Buildey and Bingham fieid stress, a m of the hysteresis loop for

thixotropy and elasticity ratio for creep-recovery tests) for both the 4û% and Sû?! kaolin

suspensions are given in Tables 4.1 and 42, respecckeiy. n e yidd stresses of samples

prepared fiom 40°/o and 50% kaoh suspensions arc shown in TabIes 43.21 and 4 3 2 2

The characreristic results of tbixompy measuremenrs appear in F'gures 433.1 (for the 40%

kaoiin suspensions) and Figures 4.33.2 - 4.3.3.4 (for the 50% kaolin suspensions). in the

meantirne, the characterisac aeeprecovery fünctions are given in Figures 4.3.4.1 - 4.3.4.4

(for the 40% kaoh suspensions) and Fies 43.4.5 - 43.4.7 (for the 50% kaolin

Smpemioas).

The viscosity cuves for &m)v NaCMC (0-m)v: Iow and medium viscosity} are shown in

Figure 43.1.1. As can be seen, there is an iacreasc in viscosity with the inacase of the

concentration of rnv NaCMC. Corn- the viscosiy of 1% mv NaCMC ~4th 1% NaCi

added 1% mv NaCMC solution, the addition of 1% NaCl results in approximateiy IO%

decrease, supposedly due to the screening effect It can screen the repulsion belareen the

chains of segments of (Chic-> macromoIcculcs. Hence, the mac~omolecuies become srnalier

(reaching a more coiled co&xmation) in the solution l a h g to the dccrease of viscosiy.

The Ostwaidde-Waele patameters for the invesùgated aqueous NaCMC soIuaons are givm

in Tablc 4.3.1.1. AU the dopes of the smight liaes in &e flow m e s indiate the degree of

deviaaon h m Newtonian behavior, and all the samples show pseudoplastic (shear-thuuitng)

behavior with n < 1. 1% mv NaGMC has the largest value of n among al of them, it shows

the rnost Newtonian-like behavior. 1% mv NaCMC and 1% NaU together also has the

largest value of n among aii of dicm; it shows almost Newtonian behvior as weli. 5% mv

NaGMC has the smdest value of n among ail of thun showing a very shear-thinning

behavior. The iiow behavior cuves of the above solutions axe presmted in Figure 43.1.4.

As cari be seen in Figure 43.12, the curve of 40% kaolin suspension p m t e d the highest

viscosity value cocresponding to the shear rate. 1% NaCl added sarnple presented the lowest

vatue. 1% NaCi was a bettu thinning agent than 1% mv NaCMC in this casa The viscosirp

for the 1% mv NaCMC and 1% NaCI added togeher sample was aise lower chan just the

40% kaolin suspension; chey act as thhnhg agents here as weiL

NaCMC is a polyelectrolyte, it can dissociate in watcr. The negativeiy char@ (CMC)

molecules can adsorb on the positbeiy charged surface of kaolin partides: the card-pack

senicnire breaks down. At a &ùmt level of polymer concentration, the adsorption resuits

in the steric and elastic stabilization of suspension (viscosiy deaease). When NaCl is added

to the aqueous kaolin suspension, the eiectrostatic interaction (attraction) between the

oppositely charged partide surfaces is reduced (screening effea). This results in a weaker

structure i.e. i t deaeased the viscosiy of the sample. The results can be supported by the

sedimenmtion volumes study (see Tables 421 and 42.3)). When the two additions are put

into the kaolin suspension together, the viscosity deaeased as weii ( i i F i e 4.3.1.2

compacing to the 40% kaolin suspension). In the sedimentacion voIume study, you can see

the obvious deaease in the Vs value Fable 4.22). The eiectrolyte decreases the eiemstatic

repulsion between the maaomolecule covered partides (saeening effect). Thac is, the

addition (Na3 can deaease the stabrlizing effea of (CMC) in cornparison with the viscosity

of the 1% mv NaCMC-added kaolin suspension. The flow pmperty of these ames are

presented in Figures 43.1.5 and 4.3.1.6. The flow parameters for the samples with 40°/o

kaolin content are shown in Tables 4.3.1.2 and 4.3.13 accordmg to the Herschel-Bulkley and

Bingham approximation. Sirnilar to the analpis of NaCMC solutions, the smder the a value

(Iess than l), the mages the deviacion fiom the Newtonian behavior. The plastic viscosity

of each sample is shown in Table 4.3.13.

In F i e 43.13,05% IV NaCMC-added 50% kaolin suspension shows the lowest viscosity

in the whole investigated shear rate range. The most effective stabrlipng agent for 50%

kaolin suspension was 0.5% b NaCMC. Adding a small amount of mv N a m (0.01% or

0.25Yo) kt0 this sample, the viscosïy is Wer due to the bridging flocculation effect The

presence of the low viscosity (and low mol& weight) polyrner, by the site-blodang

mechanism (Aksberg and Qdberg, 1990) [101, enhances the bridge flocculation capabiiity of

the medium viscosity &her molecular weight) polper. In the meantime, the highest

viscosity is found for the sample of &m)v NaCMC: 0.1% - 0.002°/0 and 0.5% NaU added to

the kaolin suspension. In this situation, 05% NaCl increased the viscosity value at each shear

rate investigated. Besides, it is very interesting to note that 1% NaU deaeased the stabiliy

of the 50% kaolin suspension, while it inacased the stability of the 4û% kaolin suspension.

The reason for this effca is aot yet k n o m The inorganic electrolyte in this case a m as a

"salting-our" agent causing destabilization of the suspension. Therefore, the observed

behaviour can be atmbuted to cwo opposite effccts: sçrcening of the face-edge attraction and

saitingsut. The salting-out cffca c m be rdated to the dimiaished hydration repulsion

(Dq-aguin and Churaev, 1989) [5fI between the panides. In the work of Ghannam and

Esmaii, the? explained the effect of elecaoiyte on the flow of coating pigments as foliows.

They indicated that due to the process of NaCl adsorption &om solution onto the surface of

the pigment partides, the number of aggiegates and floc bulkiness in the suspension

inaeased. This lads to an increase in the volume of immobied wacer, and eventualiy the

viscosity inaeases [52]. In the dense suspension, the addition of NaU drastically deaeased

the amount of fiee water molecules onginally at a tower level. Where kaolin solid content is

up to 50%, the m a i . role to stabiIize the suspensions was the 05% low viscosity NaCMC. Et

correiates w d with the rcsult of the sedimentation volume investigations. (also see the result

(T) of sedimentation volumes smdy).

The flow cumes of 50% kaolin suspensions are presented in F i 43.1.6. The flow

parameters of samples with the 9% kaolin content according to the Herschel-Bulkley and

Bingham approximation, and plastic viscosiy of samples measured at higher shear rate are

&en in Tables 4.3.1.4 and 4.3.1.5.

Table 4.3.1.1 Effect of sarnples of NaCMC aqueous solutions on kand n accotding to the Ostwaldae- Waele equation.

5% mv NaCMC 1 134.4 0.33 I

Iv: low viscosity; mv: medium viscosity.

sam~le

1 % mv NaCMC

2% mv NaCMC

3% mv NaCMC

4% mv NaCMC

Table 4.3.1.2 Effect of sarnples of 4O0h M i n suspensions on kand n according to the Herschel-Bulkiey equation in a skady-state condition.

5% iv NaCMC

1 % mv NaCMC + 1 % NaCl

k[Pa. s]

0.1 1

2.89

13.99

35

Table 4.3.1.3 Effect of samples of 40Qh kaolin suspensions on zB and I J ~ acc0rding to the BRigham equation.

n

0.87

0.66

0.52

0.45

0.27

0.09

THE: Herschel-Bulkley yield stress; mv: medium viscosity.

0.86

0.88

Sample

40% K suspension

40% K with 1% mv NaCMC

40% K with 1% NaCl

40%Kwith l%NaCl+l%mvNaCMC

TB: Bingham yield stress: mv: medium viscosity.

I -

I - - - -

WO Kwith l%NaCl+l%mvNaCMC 1672 1 32

?ne Pa1 209.3

81 35

101.2

167.2

Sampte

40% K suspension

40% K with 1 % mv NaCMC

40% K wiîh 1% NaCl

k [Pa- s]

29.45

16.28

13.93

1929

o Fa1

209.3

81 -35

1012

n

0.5

0.5

0.5

0.5

t7p [Pa. 4 2.64

1.1 1

1.25

TaMe 4.3.1.4 Effect of -les of M i n suspensions on kand n accotding to the Herschei-Bulidey equation in a skdysbte amdii. Herschel-Bulkley yieid stress k low viscosity; rnv: medium viscosity.

+ It was not reproducible

Table 4.3.1.5 Effect of samples d 50% kdin suspensions on r , and vp according to the Bingham

n

0.16 7

2

3

4

5

6

7

8

9

10

equaüon. 'te: Bingharn yield stress

Sample

220.2

80.1

9.54

2.52

173.6

7.92

125.4

130.1

303.8

-- - - - - - -

50%kwithl%NaCI

50% K mth 0.5% mv NaCMC

50% K with 0.25% IV NaCMC and 0.25% mv NaCMC

50% K with 0.5% IV NaCMC

K with 0.1% iv NaCMC

50% K wiîh (1-m)v NaCMC: 0.5% - 0.01%

50% K with 0.5% h NaCMC and 1% NaCl

50% K with (Cm)v NaCMC: 0.1 % - 0.002%

50% K with (t-m)v NaCMC: 0.1% - 0.002%, and 0.5%

NaCl - - - - - - . .

rm [Pa]

221.4 1

k (Pa- s] 15.02 50% kaolin ' 25.34

8.1 7

2.15

1 2 4

12.21

2.25

6.53

16.31

18.39

IV: low viscosity; mv: medium viscosity.

1 1 NaC1 1 1 It was not reproducible

0.01

0.37

0.67

0.44

0.22

0.71

0.09

0.01

0.14

VP [Pa. 4 0.55

1.91

0.31

0.1 1

0.03

6

7

8

9

10

re Pal 221.4

220.2

80.1

9.54

2.52

Sample

173.6

7.92

125.4

130.1

303.8

.

50%Kwith0.1%hrNaCMC

50% K with (1-m)v NaCMC: 0.5% - 0.01 %

50% K with 0.5% hr NaCMC and 1% NaCl

W h K with (I-m)v NaCMC: 0.1 % - 0.002%

50% K with (1-m)v NaCMC : 0.1% - 0.002%, and 0.5%

1

2

3

4

5

0.45

0.08

024

0.33

0.67

50% kaolin ' 50% k with 1 % NaCl

50% K with 0.5% mv NaCMC

50% K with 025% hr NaCMC and 0.25% mv NaCMC

50% K with 0.5% h, NaCMC

a m b + a m . +

+ a m . + a m , +

a m . + a m . +

Figure 4.3.1.3. Vhicosity cuves of 50% kaolin suspensions. IV: low viscosity; mv: medium vlscosity.

100 7 i Kaolin 0 K + 0.1% IV NaCMC + O.Q02% mv NaCMC + 0.5% NaCi

9

g

I

3

A K + 0.5% IV NaCMC r K + 0.5% mv W C

1 K + 0.25% IV NaCMC + 0.25% mv NaCMC I

10 7 I - - . I

r

- - 1

+ K * 0.5% IV NaCMC + 1% NaCl x K * 0.5% IV NaCMC + 0.01% rnv NaCMC m K + 0.1% IV NaCMC

O K + 0.1% IV NaCMC + 0.002% mv NaCMC m - i

4- * rn r n *

O

v + + v +

V)

tu a. *

- .- 8 .

. R 9 R

f i x a 0.1 : I

* ' mmM6s~rupirrUII - A

7 A A L

I

0.01

A A A A A ~ & ~ ~ A -

w 1 I I w - 1 m w 1 1 1 w . I l w

10 100 Io00 Shear rate [SI]

50% K + 0.5% IV NaCMC + 0.01% mv NaCMC A 50% K + 0.1% NaCMC r 50% K + 0.1 % IV NaCMC + 0.002% mv NaCMC + 50% K + 0.1% IV NaCMC + 0.002% mv NaCMC + 0.5% NaCl + 50% K * 0.5% IV NaCMC x 50% K + 0.5% mv NaCMC m 50% K + 0.25% IV NaCMC + 0.25% mv NaCMC - 50% K + 0.5% IV NaCMC + 1 % NaCl

100000

.1

10000

. . I

1000 3 3 I

I I

I - I O O ?

0 I - I

VI I

l! - I

U1 10

a 3

1

. I

I

0.1 1 1 1 1 I I 1 ,

I O 1 I I 1 1 1 1 ,

100 1 O00 Shear rate [SI)

Figure 4.3.1 .B. Flow curves of 50% kaolin suspenslais. IV: low viscoslty; mv: medium viscosily.

43.2) 2)esuits of pieId stress anal*^

As shown in Table 432.1, 40% kaoh swpeasion bas the largest yield stress (using

Herschel-Bulkiey & Bingham approximation) among the samples. Adding polymer or

inorganic salt, decreased the yield s u c s s ~ , 1% rnv NaCbiC-added kaolin suspension has the

smallest value among the samples. The kaolin partides aggregate in the suspension, they

fom the 'md-house' stnicturt, and the suspension is not stable. The negatively charged

(CMC) chahs of the dissolved NaCiMC can adsorb onto the positively chargcd surface of

kaolin parcides: the card-house m a u r e breaks down. The stcric and electrostatic

stabilizarion of the suspension is fomed (viscosity decreases). The yield stress in the

stabilized suspension is Iower or duninished. Sice the viscosity of suspension wirh the

addition of 1% NaCl deaeased due to the mb*iliwng ability of NaCi, the yield stress also

becomes lower.

As c m be seen in Table 43.2.2, the samples of 50% kaolin suspension with 1% NaCi and

50% kaolin suspension with 0.1% hr as weii as 0.002% mv NaCMC as well as with 0.5%

NaU show the Iargest yield vaiues (using Herschel-Bulkley & Bingham approxhaaon). The

addition of inorganic salt d c e d in a d e r yield stress compared with that of just 50% kaoiia

suspension. 0.5% IV NaCMC-added kaolin suspension shows the smallest field vahe among

these samples, whiie 0.1% IV NaCMC-added kaolin suspension shows a much larger yieId

d u e than the 05% addcd sample. When 1% NaCl is added to the sampie with 0.5% hT

NaCMC content, the yield stress caused much higher. in the same tirne, putting srna11

amount (0.01% or 0.25%) of mv NaCMC into the 0.5% iv NaGMC-added kaolin suspension

simultaneously, the yield smss becomes greater. The low viscosity (and low mol&

weight) polymer, enhances the bridging floccuiation capabiiity of the medium viscosity

Olghtx mole& weight) polymer by a site-blodung mechanism [IO].

Table 4.3.2.1 Herschel-Bulkîey and Bingham yieid sbesses of m e s of 40% kaolin suspensions in a non steady-state condition. rnv: medium vimsity. tris: Herschei-Bulkley yidd stress TB: Bingharn yield stress

1 40% K with 1°C mv NaCMC and 1 % NaCl 40 21 2 1

-

40% Kwith 1% NaCl

Table 4.322 The Herschel-Bulkley and Bingham yield &esses of sarnples of 50% M i n suspensions in a non steady-state condition. 7 ~ 8 : Herschel-üulkley yield stress TB: Bingham yield stress

re (Pa)

240

110

- p b

40% Kaolin

40% Kwith 1% mv NaCMC

(Pa)

60

1 O

I I

22

50% K with 0.1% IV NaCMC 140 225

50% K with 0.5% IV NaCMC and 0.01% mv NaCMC 1 O 15

50% K with 0.5% iv NaCMC and 1 % NaCl 120 1 22

50% K with 0.1% IV NaCMC and 0.002% mv NaCMC 130 151

50% K with 0.1% hr NaCMC and 0.002% mv NaCMC, 250 41 9

125

K low viscosity; mv: medium viscosity.

* It was unmeasurably high

Sample ~ H B (Pa)

305

100

11

2.2

1

2

3

4

5

%(Pa)

330

390

116

16

2.4

50% Kaolin '

50%Kwithl%NaCl

50% K with 0.5% mv NaCMC

50% K with 0.25% IV NaCMC and 025% mv NaCMC

50% K with 0.5% IV NaCMC

The simultaneously added 1% NaU and 1% mv NaCMC cause the most sigdicant

thixotropy @gue 4.3.3.1). Ad- 1% NaU only, the system does not show significant

thixotropy. Thixotropy is a v q tirnedependent property of samples as the structure

changes. 1% mv NaCMC-added sampIe &O shows more significant thixotropy than 40%

kaolin suspension. 1% mv NaCMC increases the thixotmpy of 40% kaolin suspension, A

modest thixotropy was obsenred for the 40% kaolin suspension indicarhg the preseace of a

weakiy aggregated structure due to the hce-edge amcàon of partides (card-house

structure). The hysteresis loop area d u e s of the samples are shown in Table 433.1. As is

weli known, the condition of thixompy is a weakly ffocculated state of the samples

(flocculation to the secondary minimum in the interpaflde potential energy m e ) . The mv

NaCMC increases the area of the thkotropy loop that can be interpreted in tenns of

NaCMC initiated flocculation of maaomoIecules. It means that small arnounts of mv

NaCMC polymer takes part in bridge formation. The added NaU screens the repulsion of

the NaGMC-added particies by meam of the secoridarg energy minimum in the pair-

potentiai enugy function becoming deeper, manifesàng itseif in a more significant

thixompy.

In F i 433.5 0.1% Iv NaCMC, 0.002% mv NaCMC and 0.5% NaCI together cause the

most sigdcant tlixotropic behavior. 0.5% mv NaCMC-added 50% kaolin suspension does

not show more thixompy, c o m p d to 1% mv NaCMC-added 40% kaolin suspension (see

the explanaaon below). In Figute 4.3.33, putting a small amount of mv NaCMC (0.01% or

025%) into the iv NaCMC-added kaolin suspension results in more impoctaat thixotropy

due to the bridging fioccuiation effen. in Figure 4.3.3.4, O.lO/o IV NaCMC-added kaolin

suspension, and 0.5% lv NaCMC with 1% NaU simuitaneously added kaolin suspension,

present not too sipficanc anci-thixotropy behavior, especiaiiy at the lowm shear rate. The

reason for this behavior is not yet known; it maybe due CO oniy a vuy weak (repulsion)

intaactions among the panides. The "area" of hysteresis Ioop was significaatly higher for

thc m e of the more concentratcd (5Po) kaoh suspension compared to the results of the

less (40%) concenaated ones. Table 4.332 prese~rs the hysteresis Ioop area values for the

sampIes.

There are s d possibIe reasons for sampIes KI show thixotropic property. Fmt, it

happens in dense suspensions, composed of anisometrical solid particies; Second, the

suspension has to be in a weakly floccuiated state (see the detinition in the introduction),

which can be sheared easiiy and b d t up again afier removing the applied force. It means

chat there shouid be an optimum meqh structure in the suspension, The IV NaGMC-added

kaolin suspension, does not show ~ o m p y because the 1ow viscosiy polymer stabilizes the

suspension; but this is not a gel structure, the @cies in d i s case repuIse cach orher. The

mv NaMC stabilizes (adsorbing on the &des) and destabilizes (fonning bridges between

tbe partides) at the sarnc time which resuits in sig&cant thixotmpy (also see the

explanacion for the mv NaCMC-added 40% kaolin). The IV NaCMC-added samples in the

presence ol mv NaCMC show a weakly flocculated suspension. The bridging floccuiation

occurs by the site-blodring medianism. The reIativeIy sipiflcaut ciiixotropy of 50% kaolin

suspension in the presence of 1% NaU may be atmiuted to the high kaoh content The

rhixotropic behavior becomes more signifiant for the kaolin suspension after ad* the

NaU and CiMC simultaneously. The addition of NaU may cause many different interactions

between the kaolin suspension as foiiows: 1) partide-partide interaction; 2) the

hydrodynarnic size of maaomolecules; 3) the adsorpaon capability of macromolenJes on

the same partide; and 4) the bridge fonning adsorption.

Hysteresis "arean (Pals) 04 sampies of 40% W i n suspensioris.

1 40% K with 1% mv N ~ M C + 1% N~CI

mv: medium viscosity

Table 4.3.32 Hysteresis "arean (Pals) of sarnples of 50% kaolin suspensions.

s a m ~ k 40% Kaolin

40% K with 1 % mv NaCMC

Hysteresis area (Pals)

1810

3 . 1 W

IV: low viscosity; mv: medium viscosity

It is not reproducible

40% Kwith 1% NaCl 41 80

Hysteresis area (Pals)

4 . 2 W

Sample

3 . 2 ~ 0 4

1 . M

3040

750

-9960

2590

3460

-4630

7 . W

2

3

4

5

6

7

8

9

10

1 ~

50%Kwithl%NaCl

50% K with 0.5% mv NaCMC

50% K with 025% IV NaCMC and 0.25% mv NaCMC

K with 0.5% IV NaCMC

50% K with 0.1 O h hr NaCMC

50% K with 0.5% iv NaCMC and 0.41% mv NaCMC

50% K with 0.5% hr NaCMC and 1 % NaCl

50% K with 0.1% IV NaCMC and 0.002% mv NaCMC

50% K with 0.1% hr NaCMC and 0.002% mv NaCMC,

50% Kaolin '

-x- M i n + 1% mv NaCMC + 1% NaCl -O- Kaolin + 1 % NaCl -m- W i n + 1% mv NaCMC -r- Kaolin

x-x-x-x-

-Mc--*

T I I v I . I I

O 200 400 600 800 Shear rate [s-11

Figure 4.3.3.1. Thixotropy curves of 40% kaolin suspension wiîh additions of NaCMC and NaCI. mv: medium viscosity.

+ Kaolin + 0.5% IV NaCMC -#- Kaolin + 0.5% IV NaCMC + 0.01 % mv NaCMC -7- Kaolin + 0.25% IV NaCMC + 0.25% rnv NaCMC

J 1 w 1 1 I w I 1 I O 200 400 600 800

Shear rate [s-1)

Figure 4.3.3.3. Thixotropy curves of 50% kaolin suspension with additions of NaCMC. IV: low viscosity; rnv: medium viscosity. [2]

-v- Kaolin + 0.1 % IV NaCMC -x- W i n + 0.1 % IV + 0.002% mv NaCMC

I I 1 I I m

O I I I

200 1-

400 600 800 Shear rate [s-11

Figure 4.3.3.4. Anti-thixotropy curves of 50% kaolin suspension with additions of NaCMC. IV: low viscosity; mv: medium viscosity. 131

In order to get information about the eiasticiy of the prepared samples, the aeeprecovery

behavior was studied using the CS mode of the RS100. In the same period of observation

(300 seconds for the creep c - e ) and (300 seconds for the recovery curve), prepated

sarnples of 40% and 50% kaolin suspaxions were investigated. Different shear stresses

below the yield stress were applied. At certain stresses, the cornpliance oc) inaeased with

tirne in a nodinear manner showing &tic behavior of the samples. At the other stresses,

the compliance (Jc) inaeased with time in a linear manner showing viscous behavior of the

samples. For the detennination of the sampIes dasticity, the eIasticity ratio (the ratio of the

elastic and maximum compliance) for e v q sample was examined. The eiastic compliance

was determined from the aeep m e fitting a straight line to the near linear (viscous) part of

the curve. The intersection of the fitted Iine and the verticai axis provided the &tic

cornpliance. The maximum compliance was given directly frorn the aeep m e (at the

highest value).

4.3.4.1) C~ncpncovtty tedjr tbe 40% kaah Npcmons

The creeprecovery functions for 40% kaolin sampies were &en at the same shear stress (T

= 50Pa) in Figutes 43.4.1 - 43.4.4. In order to characterize the elastiaty of the prepared

samples, the calcuiated eiastiay ratios are given in Table 4.1. Despite the hi& eiastic ratio

showed in Table 4.1, some systems were not reaI e M c because there was no entire recovery

d u k g the o b s m a o n time (see Frgures 4.3.4.1 and 4.3.43)). Real eiastic behavior was not

obsemed for the kaolin suspensions ( F i i 43.4.1). The relativdy high eIasticity ratio (I'able

4.1) d u n o m t e s @diy rather tfian eiasticiy. There is no ugnificant recovery aftm ceasing

the stress. For the 1% mv NaCMC-added sampIc, the cum showed iiquid-like b&vior at

this shear stress (see Figure 4.3.4.2). As cari be seen in Figure 4.3.4.4, the 1% mv NaCMC &

1% NaCl together show really dasàc behavior.

The mv NaCMC smbilized the W/o kaolin suspension, as the macromolecules adsorbeci

onto the kaolin partides. Under h&er shear stress (T = SOPa), the suspension was very

liquid-like, there aras no &orneration which muid cause elasaciy in i t The partides

repeiied each other. When 1% NaCl was added into the above sample, somc aggregates

couid forni due to the screening effect of (Na3 manifesthg itselfin more elastic behavior.

4.3.4.2) Cncp-nco-y t e ~ j r tbc 50% k a o h mpemon~

The creeprecovery functions for 50% kaolin samples are given at the shear stress (t = 05Pa

and 5Pa) in Figures 43.4.5 - 4.3.4.7. In order to characterize the elasücity of the prepared

sampies, the caicuiated elasticiy ratios u,/Ja are @en in Table 42. As can be seen in

Figure 43.4.6, 0.5% mv NaCMC causes the most elastic behavior; thc elastiatp ratio was

0.92. The 0.25% iv NaCMC and 0.25Yo mv NaCMC together caused the most viscous

bcfiavior at this stress (the elastiaty ratio was 026). The 0.5% IV NaCMC at even lower (T

=O5 Pa) sheat stress showed rattier viscous behavior (the eiastiay ratio was 039). It should

be noted rhat the elastiaty measürements were found to be non-reprodua3le for rhe denser

kaolin suspension, Ail the data for dis section can be seen in Table 4.2.

As can be seen in Table 4.3.4.1 the eIastiaty ratio for 0.5% mv NaCMC-added kaolin

suspension was Iarger than that for the 0.25% IV NaCMC and 0.25% mv NaCMC

simuItaneously added sample at the same shear stress (r = 5Pa). It showed that 0.5% mv

NaCMC individuaiiy can cause the more eIastic behavior. With inaeasing shear stress, the

ratios for (1-m)v NaGMC-added sample decnased: it showed more and more viscous

behavior as cxpeaed. The mv NaCMC-added sample, however did not show this result due

to more elastiaty (rigidity). The higher the shear stress, the lower the elasticity ratio was

found due to the structurai breakdom. Btsides, the sample with the 0.5% mv NaCMC

showed more elasticiy even at higher shear stress (T = SOPa).

Accordmg to the data in TabIe 43.42, 0.5% IV NaCMC has the most stabilizing ability. It

shows viscous properties even at very srna11 shear stresses. Putting a smaü amount of mv

NaCMC (0.01Yo) into this sampte, it shows higher elastiaty ratio values; the elastia ty itseIf is

significant men at iarger shear stresses. The addition of 0.01% mv NaCMC a n cause the

elastic behavior. As cm be seen in TabIe 4.3.43, the ciasticity ratio value of 0.5% mv

NaCMC-added susp-on is laitger at h@ shear stress, cornparhg with that of 0.5% IV

NaCMC-added sample, whidi lead to more sigdicant ciastic property due to the bridging

tloccuiation.

Table 4.3.42 ElasWty rati*os of two Mferent samples: 50% K + 0.5% iv NaCMC and 50% K + 0.5% k NaCMC + 0.01% mv NaCMC. IV: low viscositv

Table 4.3.4.1 Bsücty ratios of two different sampk: 50% K + 0.5% mv NaCMC and 50% K + 0.25% k NaCMC + 025% rnv NaCMC. mv: medium viscagity

50% kaolin suspension with

0.5% mv NaCMC

50% kaolin suspension with

0.25% IV NaCMC and 0.25%

mv NaCMC

0.5% IV NaCMC

50% kaolin suspension with

Shear stress [Pal

t= 5Pa

t = 10 Pa

t=20 Pa

t= 50 Pa

t= 1 Pa

t= 2Pa

t= 3Pa

t= 4Pa

t= 5Pa

Elastici IWO (JJJmir)

0.92

0.95

0.93

0.92

0.93

0.92

0.93

0.56

0.26

Shear stress [Pa]

r = 0.088 Pa

5û% kadin suspension with

Elasticity ratio (JJJm$

0.79

0.5% IV NaCMC and 0.01 % mv

r=1 Pa 1

r = 2 Pa 1 0.93 1 NaCMC

0.90

I

r = 3 Pa 0.95

TaMe 4.3.4.3 aasnicity ratios of two different sampies: 50% K + 0.5% iv NaCMC and 50% K + 0.5% mv NaCMC. hr: low viscosity; mv: medium viscosity

5û% kaolin suspension with

0.5% iv NaCMC

50% kaolin suspension with

0.5% mv NaCMC

Shear stress (Pa]

7 = 0.088 Pa

5= 0.5 Pa

r = 5 Pa

Eiastif:iîy raüo (J,JJ,,,J

0.79

0.39

0.92

O 100 200 300 400 500 600 Time [s]

Figure 4.3.4.2. Creep-recovery curve of 40% kaolin suspension with addition of mv NaCMC (t = 50Pa). mv: medium viscosity.

4- W i n * 0.25% IV NaCMC * 0.25% rnv NaCMC

1 I 1 I m I w I v I . I . 1

O 1 O0 200 300 400 500 600 Time [s]

Figure 4.3.4.5. Crsep-recovery curve of 50% kaollri suspension with additions of NaCMC. IV: low viscosity; mv: medium viscosity. (o = 5Pa)

43.5) Summarv of rheoloacal HI * . . .

v-ons of kaoh sam

For comparison, the co11ected rheological parameters in Table 4.1 (for the 40% kaolin

samples) and Table 4.2 (for the 50% kaolin samples) are given here.

Table 4.1 The calculated rheological properties for the 40% W i n samples. The apparent viscosities are measured at 750s'' and54s", respectively. The fhe &viadeviation of averaged values was found to be fi% in most cases. nv: medium viscosit

Sample

mv NaCMC

4 40%Kwith1% mv NaCMC

I and 1% NaCl

aasticii 1 viscosity [pas1 I ~t~ixotropy Yield stress r [Pa]

Sarnpie

1

3

q

5

6

7

8

g

50% Kaolin

* wia, 14; NaCl

Wh K with 0.5% mv NaCMC

SO%Kwith 025% IV NaCMC and 025% mv NaCMC

50% K ~ i m 0.5% fv NaCMC

K M O . ' % iv NaCMC

50% K with O.5Xiv NaCMC and0.01% mv NaCMC

0.5% IV NaCMC and t % NaCl

SO%Kwiai

Oast ic ' i 'BNO

(JdJniJ

(cl-)

- (&Pa) (-1OPa) (eOPa)

(r=5ûPa) (~=iPa)

(&Pa) (.F=3Pa) (&Pa) (&Pa)

130

250

Vbcosity A4paient v i s d t y range

0.5582

0.6-10.6

0.340

0.08-0.4

0.03-0.09

0.47426

0.08-0.3

024-4.82

t O

' It

0.79

0.92 0.95 0.93 0.92 0.93 0.92

0.56 0.26

ThiwboW

w (P.ls)

4.2-

3 . 2 ~ 0 4

1.-

3040

750

-9960

271 4

3461

151

41 9

[Pa-s] -- q

0.10

0.096

0.16

0.06

0.03

0.18

0.06

0.07

0.13

0.11

t m

(&.Spa)

(=75pa]

(r=lPa) . , ( d P a )

(-Pa)

(-lm)

-4630

7.-

Meld stress

~ k m w = ~ BU"k@ (%al -*

305

IO0

11

22

140

10

120

0.79

0.39

0.99

0.9

0.93

0.95

0.99

0.1% Iv NaCMC and 0.002% mv NaCMC sorcK*ax hrm,a00~16 nnrNaCMCad 05%Fla#

r [Pa]

(%Il

330

390

116

16

2.4

225

15

122

is iaot very reproducible

=1

=l

0.87

(.E=30Pa) . (.E=soPa)

(T=lmPr)

@=125Pa)

(~=150Pa)

(dopa)

0.3243

0.5-113

=1

=1

0.92

CHAPTFR 5

SUMMARY

The rheological behaviors of aqueous kaolin suspensions @H = 5-6) were studied in this

work In order to get a better understandkg of the rheological results, the sedimentation

volume experiments with saaiples prepared h m 2.5% kaolin suspensions wae also

performed. The compositions were prepared fiom NaCi, and NaCMC with diffaent

viscosity molenilar weights. Fmt, the e f f i of the preparation technique on the rheological

behavior was cxamined; the suspensions having kaolin contents of 40% and 5û% h m

powdas (NaCMC, NaCl, kaolin and distilled water) and h m smch solutions (NaCMC,

NaCI, as weii) were made. Regardhg the prrpatation technique, the rheological prop&

showed eimedependence for samples prepared h m powden. Time-dependence was not

observed if the samples were prepared fiom solutions. The sedimentatïon volumes however,

aiways showed tirnedependencc The sedimenration volume investigations revealed that at

the lowest concentration (0.005% - 0.0l0/) of rnv NaCMC, the polymer initiated budging

flocculation. Using the mixture of IV and mv NaCMC, the budging flocculation couId &O

take place aithrough the sedimmtation volumes showed the sigdlcant adsorpaon of Iv

NaCMC, which means chat the bridging fiocdation occurred by a site-blocking mechanism.

The NaCl oppositely affected the sedimentation volumes of the different viscosity NaCMCs.

The stabdkbg capabiiïy of the iv polymer was deaeascd by adding NaCi, wMc the

stabiüiq capabitity of the mv polymu was impmved with inmashg the concentration O€

NaCI. These effects can be atmbuted to the elecaostatic screening of NaU chat e s p d y

hindered the bridge-fonning adsorption of rnv NaCMC. The rheological resuits wece in

good agreement to the Vs results conceming the stabilizing ability of different viscosity

polymas. Tbc b d g h g kculation enhanccd by n site--blocking mechanism was also

revded. lv NaCMC was a bcttcr s t a b ' i and t)iinning agent chaa mv NaCMC. But the

NaU inçreased the viscosiy of CMC added suspensions. Conceming ttiis effeq there is a

good conelauon benmen sedimenation volumes and visc~sity for IV NaCiMC. But there was

a contradiction as mv NaCMC. 0.1% IV NaCMC, 0.002% mv NaCMC and 0.5% NaCf

togettier caused the most sig&cant thiirotropy; without of NaCl, it shows anti-sbltotropy.

Accordmg to the results, the effect of N a U in the 20 - 25 cimes denser kaolin suspensions is

even more complicated. Supposedly, the saeening of the interpartide tepulsion is of great

importance; the particies cm Çonn aggregates resulting in a viscosity inaease of such

suspensions. Reai-eiasticiy due to bridge-forming was only found in the presence of mv

NaCMC. The saniples, prepared b m the mixture of Iow and medium viscosity CMCs, were

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