PHYSICO-MECHANICAL PROPERTIES OF MODIFIED KAOLIN CLAY FILLED RUBBER COMPOUNDS M.Sc (Polymer Technology) A.R.M.W.W.K.Ranasinghe University of Moratuwa October, 2001 Phys ico-mechanica l propert ies of modif ied kaol in c lay filled rubber c o m p o u n d s By A.R.M.W.W.K.Ranasinghe This thesis was submitted to the Department of Chemical and Process Engineering of the University of Moratuwa in partial fulfillment of the Degree of Master of Science in Polymer Technology eSftOQ© S H a Surges. § -i (=®)OQS. ' Department of Chemical and Process Engineering, University of Moratuwa, Sri Lanka. October, 2001 _ ^ 074446 6 6 " O V IJIIIIIIIIIIIIIIIIffllllilll 6 1 6 - 4 1 University of Moratuwa 1'IJ-IF-LL-G 74446 " I certify th;il this thesis docs not incorporate without acknowledgement any material previously submitted for a degree or diploma in any University and to the best of my knowledge and belief it does not contain any material previously published, written or orally communicated by another person except where due reference is made in the text" Signature of the candidate ( Miss A KM WW Is. Kanasinghe) " To the best of my knowledge, the above particulars are correct" l)r ( Mrs )0lga Gunapala Department o f Chemical Superv isors Dr l \Y. Gunapala Department o f Materials l.-ingineerinu and Process Kiigineering ABSTRACT A n attempt has made to activate the inert structure ol Rubber grade kaol in clays through ion-exchange process. Counter ions absorbed by unsa l i s l l ed s i l i con , oxygen and hydroxy l ions at the edges o f planar surfaces o f kaol in i tc mineral to preserve electrical neutral i ty were replaced wi th complex organic ions containing active functional groups (amine, hyd roxy l , carboxyl ) in their organic radicals. S t rong ly attached to the clay surface Ihese complex ions project their organic aryl or a lky l radicals outwards to suspending medium rubber matr ix making inorganic kaol in surface effectively organic and therefore hydrophobic one. Such change in kaol in surface facilitated rubber- f i l ler interaction owing to better wetting o f the filler surface wi th organic rubber polymer and formation o f suf f ic ient density grafted polymer layer bonding the rubber matr ix to filler. Carried out physico-mcchanical testing o f filled rubber compounds showed that modif ication o f kaol in wi th chosen basic electrolytes ionized in aqueous medium was effective. Increase in strength characteristics has made possible in commercial practicability o f rubber formulat ion technology the subst i tu t ion o f expensive reinforcing fillers w i th lowest in cost appropriately modif ied kaol in Clay. A c k n o w l e d g e m e n t s I am very much grateful to my supervisors Dr ( Mrs) Olga Gunapala and Dr P.Y Gunapala for their encouragement, guidance, and their patience paid through out my research. Also a special word of thanks to Dr ( Mrs ) B.M.W.P.K .Amarasinghe,the head of the department and Mr S.A. Perera former head of the department and all other academic staff of the Chemical and Process Engineering and the Materials Engineering departments. My special thanks are due to Mr K Subramanium, head of the Polymer division, Mrs Shantha Maduwage , Mr P. Weragoda for their great support given me through out my research. Also I would like to thank technical and technical assistant staff of the Polymer Processing laboratory, Latex and Testing laboratories, Ceramic laboratory and all laboratories of Materials Engineering department. My thanks are due to the officers of Polymer department of ITI providing me the facilities to get the rheographs. My special thanks are due to Miss Duminda Liyanage, Mrs Samadara Jayarathne, Mr Nalin Gangodavilage and other colleagues for their great support and the encouragement given me to complete my research successfully. My heartiest gratitude is for my family members for their great support given me through out the research. Finally, I would like to thank the Asian Development Bank (ADB) for granting me the financial assistance to cany out my research successfully. 2 CONTENTS CHAPTER 1 : Introduct ion 1.0 Introduction 10 CHAPTER 2 : L i te ra ture review 2.1 Types of fillers and their properties 13 2.2 Structural chemistry and processing 19 2 .3 Chemical modification of china clay 20 2.4 . Physical modification of kaolin 24 CHAPTER 3 : Mater ia ls and Experimental methods 3.1 Materials used for the experiment 33 3.2 Experimental procedures 38 CHAPTER 4 : Results and c a l c u l a t e s 4.1 Results obtained from the Kjeldahl experiment 46 4.2 Results obtained from the Mooney Viscometer and Monsanto Rheometer 50 4.3 Tensile properties of vulcanized samples 53 4.4 Abrasion resistance test Results 56 4.5 Flex cracking and crack growth lest Results 57 4.6 Bound rubber content test Results 58 4.7 Swelling test Results 59 C H A P T E R 5 : Discussion and conclusions 5. I D i s c u s s i o n 5.2 C o n c l u s i o n s C H A P T E R 6 : Suggestions and recommendations 6.1 Sugges t ions 6.2 Future R e c o m m e n d a t i o n s R E F E R E N C E S A P P E N D I X I ( T e c h n i c a l data o f k a o l i n ) A P P E N D I X I I ( C h a r a c t e r i s t i c C u r i n g c u r v e ) A P P E N D I X I l l ( E q u i p m e n t s used for s a m p l e tes t ing) LIST OF TABLES CHAPTER 3 Table I : Properties of RSS I Rubber 34 Table 2 : The standard formulation of 111 led natural rubber based compounds 37 Tabic 3 : The mixing schedule for mixes on an open two roll mill 41 Table 4 : Required amount of 0.1 I IC'I lor the titration 46 CHAPTER 4 fable 5 : Results obtained from the Mooney Viscometer 50 fable 6 : Results obtained from the Monsanto Rheometcr 50 fable 7.1 : Tensile properties of mixes, extended with modified and standard kaolin before aging 54 fable 7.11 :Tensile properties of the mixes extended with Modified and standard kaolin after aging 54 Table 8 : Abrasion resistance test results 56 fable 9 : Results of De-Mattia flex cracking test 57 fable 10: Results of bound rubber content test 58 Table I I : Results of swelling test 59 5 LIST O F ( IRAPUS CHAPTER 4 6 Graph ! : Curing curves obtained from Mooney Viscometer 5 I Graph 2 : Kheographs obtained from the Monsanto Rheometer 52 Graph 3 : Comparison of tensile properties before aging 55 Graph 4 : Comparison of tensile properties after aging 55 Graph 5 : Comparison of abrasion test results 56 Graph 6 : Comparison of De-Mattia Ilex cracking and crack growth tests results 57 Graph 7 : Comparison of bound rubber content test results 58 Graph 8 : Comparison of swelling test results 59 Graph 9 : Differential thermal analysis (DTA) of raw rubber filled with kaolin treated with monoethanolamine 60 Graph 10: Differential thermal analysis of kaolin sample treated with monoethanolamine 61 LIST OF FIGURES CHAPTER 2 Figure I I I b - Sketch of a Din-Abrader used lo measure abrasion resistance Figure I I I c - A Pendulum/general type tensile strength tester, for measuring force and elongation at specified time or at break Figure.I l l d - The mechanism of the De-Mattia flexing machine used to find the crack initiation and the rate of cracks growth Figure I.a - Structure of Kaolinilc Layer Figure l.b - Micropliotograpli showing Book-shaped arrangements of hexagonal plates in kaolin Figure 2.a - S i lane coupling agents Figure 2. b - Diagram showing polymer strand bound lo kaolin through Sikine coupling agents Figure 3 - Diagram illustrating the Mechanism of adsorption and modification APPENDIX II Figure 4 - Characteristic Curing cure APPENDIX III Figure I l i a - Sketch of an Oscillating Disk Rheometer used lo monitor the cure characteristics NOMENCLATURE DTA -. Differencial thermal analysis MEA - Monoethanol amine PVA - Polyvinyl alcohol UF - Urea formaldehyde NMR - Nuclear Magnetic Resonance Mix N° - Mix Number N - Newton MPa - MegaPascal Q - Toluene uptake per gram of Rubber hydrocarbon u - Microns RSS - Ribbed Smoked Sheet rubber FICI - Hydrochloric acid DPG - Diphenyl guanidine. MBTS - 2,2, Dithiobis benzothiozole ZnO - Zinc Oxide DEG - Diethyleneglycol PEG - Polyethyleneglycol H 3 B O 3 - Boric acid NIL) Ac - Ammonium acetate Nl l . iCI - Ammonium chloride Nm - Newton meter Outl ine of the Thesis T h e Miosis cons is ts ol" l ive chapters. Chapter one i s composed wi th the introduction and the objectives o f the research. Chapter two describes the ex is t i ng background o f the f i l l e r s , properties o f kaol in and i ts modi f icat ions, also jus t i f i ca t ion o f the present work . Chapter three describes the materials, experimental techniques and tests used in analyzing the prepared test samples. T h e resu l ts obtained from the research are given in chapter four ,chapter l i ve cons is ts o f I he d iscuss ion o l ' l l io obtained resu l ts , and dual chapter cons is ts o f suggest ions, future recommendations and recommendations for the indust ry . 9 CHAPTER 1 L 1. INTRODUCTION A wide variety o f particulate f i l l e r s are used in the rubber industry to improve the performance o f rubber compounds. A general d i v i s i on o f f i l l e r classes i s based on the effect o f f i l l e r on physico-mechanical properties o f rubber. Part icular ly the f i l l e r s , increasing the hardness, s t i f f ness and strength characteristics o f vulcanized rubber are called reinforc ing f i l l e r s . W h i l e f i l l e r s , which effect on those properties ins ign i f icant ly and act merely as di luents and extenders arc referred to non-reinforcing f i l l e r s . Carbon blacks belong to h ighly reinforcing f i l l e r s because they contain many active functional groups on the surface, which are capable o f reacting wi th polymer molecules to form grafts dur ing processing and vu lcaniz ing. T h i s resu l ts in the highest degree o f reinforcement coming through high values o f tensi le strength, tear strength, abrasion resistance and other properties. A number o f mineral f i l l e r s are also used in rubber industry to extend or reinforce elastomers, including carbonates, clays, s i l icates and talc. A s compared to carbon blacks non-blacks or mineral fillers are lower in reinforcing effect. Among those mineral f i l l e r s kaol in clays are the cheapest and most versat i le. T h e y are second on ly to carbon blacks in t h i s respect. Kao l i n clays are unusual ly inert, temperature stable and disperse wel l in polymer sys tems. Because o f i ts inert nature kaol in i s not able lo form strong interfacial bonds wi th hydrophobic polymer rubber matr ix and can be added in large quantit ies to many formulat ions in order to reduce production cost due to di luent effect and s l i gh t l y improve some performance propert ies o f rubber compounds. In accordance wi th general pr inciples o f rubber compounding, kaol in i s t radi t ional ly added wi th a more expensive active reinforcing filler, thai increases also tensi le, shear strength, max imum strength at break, impact resistance, in order to keep balance between performance and compound cost. New developments in rubber formulat ion technology aim to increase the replacement value o f reinforcing I IHe rs wi th non-reinforcing ones on score o f cost and avai labi l i ty, keeping the performance properties unchanged by means o f appropriate activation o f the inert fillers. Surface modif ied clay f i l l e r s that are approaching the performance o f h igh ly reinforcing fillers such as carbon black and precipitated s i l i ca are most ly due to the var ious types o f s i lane treatments. It has been reported prev ious ly , that increase in performance o f interfaces in mineral filled polymers could be achieved wi th si lane based coupling agents. Even after s i l an iza t ion , wett ing properties can be further enhanced by treatment w i th amine or functional addit ives. T h e better interaction between surface treated clays and var ious types o f r es i ns which are added to rubber compound (eg. Coumaronc indene res in ) lb enhance composite properties, manifested i t s e l f i n : • easier d ispers ion , leading to higher filler loading and reduced cost. • improved process abi l i ty • improved un i fo rmi ty o f physical properties. • higher tensi le l lexura l strength, w i th greater scratch and impact resistance. • reduced degradation o f physical and electrical properties by reduction o f mois ture absorbed . However these modif icat ions are s t i l l costly exercised due to high price o f s i lanes , making modif icat ions economically not worth the properties improvement. L o o k i n g at the structural features o f kao l in , it cons is ts o f crysta ls o f kaol in i te. T h e s e kaol in i tes are thin hexagonal plates. In these plates some oxygen and hydroxy l valences are not balanced, and these unbalanced valences are sat isf ied in practice by external ions that do not form a part o f the structure but merely act as 1 I counter ions , that contribute for retaining electrical neutral i ty o f the kao l in i le structure. T h e s e counter ions , most ly cations , are capable o f being exchanged w i th other cations. In the disordered ko l i n i t cs , additional balancing cations arc present because o f the lattice subst i tu t ions . These additional cations also contribute to cation exchange that occurs wi th the disordered kaol in i tes. Replacing the counter and balancing cations wi th appropriately selected compounds, can change chemical structure o f kaol in surface, making it active towards rubber polymer. In (h i s connection it was thought thai properties o f f i l led rubber compounds could be improved through modif ication o f kaol in by exchanging sonic cations associated in kaol ini te wi th organic cations containing some active functional groups capable o f formation o f physical or chemical bonds wi th rubber polymer Opposite the s i lan iza l ion the ion exchange process employs electrolytes readily d isso lved in water so that they do not need another solvent for ion dissociat ion that resu l t s in modif ication and product being cost effective. There fore the study o f activation o f inert kaol in clays though ion-exchange process gives r i se to interest in both, the development o f fundamental invest igat ions in the reinforcement o f polymers w i th f i l l e r s and so l v ing a practical task connected wi th opt imizat ion o f rubber compound formulat ion technology. T h e aim o f the research could be formulated as f o l l ows : • f i n d i n g the ion exchange capacity o f rubber grade kaol in • Introduction o f the functional groups active towards rubber polymer through ion exchange process to kaol in clay • Car ry ing out the ser ies o f chemical and physico-mechanical tests and procedures in order to investigate the effect o f structure o f kaol in on the performance properties o f f i l led rubber compounds 12 CHAPTER 2 L1TRATURE REVIEW 2.1 Types ol' fillers and their properties Fillers or extenders are finely divided solids added to polymer systems lo improve properties or reduce cost. Fillers can be minerals, metallic powders , organic-by products, or synthetic inorganic compounds. They cover a broad range of particle sizes and shapes and may be under gone surface treatments. Although most fillers are solids, a lew silicate types contain air voids to reduce effective filler density .( Barlow, 1989 ) In classifying the dry fillers used in rubber lo increase its usefulness or make a cost effective product; it is convenient to divide them into black and non black IIHers or mineral fillers. These non-black fillers are chosen over one or more of three reasons: 1. 'fhe product has to be white or light coloured. 2. Certain unique properties are required like thermal conductivity by using of zinc oxide 3.It is hard to gel less cost materials than natural products in good supply like clay or ground lime stone Non-black fillers have certain features in common compared to carbon blacks. They have higher specific gravities from 1.95 for a precipitated hydrated silica lo 5.6 for zinc oxide. At the same loading by weight they have lower tensile values than blacks. For example, in a 50 part loaded nilrile slock with 25 parts of plastici/.er, the highest tensile for the most reinforcing non black filler . silica, would probably be 1800-2000 psi; carbon black would range from 1900 to 3000. There is simply not the chemical and physical interaction between filler and polymer that exists with carbon black. For the same reason modulus is lower at the same hardness. High tensile and modulus are considered as vital components ol'abrasion resistance. Non black fillers are less abrasion resistant. Certain differences are shown up in process as well. There is more chance that natural non black fillers wi l l have more oversize particles than blacks. Such particles can easily lower tensile or tear strength as they can well be the points of initial rupture. Normally carbon blacks are aggregates of particles; most non- black fillers are not, they consist of circular, platy, or blocky particles. This difference can be shown up in shrinkage with or cross the grain or calendered or extruded stocks. There are many ways to classify non black fillers considering the variety of natural sources and various treatments now being used. Mineral fillers usually have low refractive indexes (1.4 -1.6), in the range of most polymers and binders. Such fillers show little i f any hiding power, but are extremely useful in a formulated coating to increase colorant effect, adjust gloss, imparl adhesion or other properties, and increase solids content at low cost. In plastics , fillers increase stiffness, affect of electrical properties, improve chemical resistance, and reduce cost. In rubber, reinforcing fillers improve rigidity and tear strength. In liquid systems, such as caulks, sealants, and adhesives, functional fillers control thixotropy, sag, and shrinkage. (Barlow.F.W, 1989 ) With the development of polymers in the early 1900s, fillers were needed to meet key functional requirements. Among the all fillers carbon blacks and mineral fillers play the main roll in rubber compounding. Their industrial uses vary with the required properly of the rubber product. Compared with carbon blacks mineral fillers show some interesting characters based on the final rubber product. Some comparative properties of mineral fillers are given bellow. 14 2.1.a. Calcium carbonate Tillers Calcium carbonate is in many ways a direct contrast to carbon black. In its natural form ground lime stone and ground chalk ( Whiting), the particles are coarse , ( ol'the order of().5-30um for limestone and 0.2-IOum lor chalk), off-white (lime stone ) or while (chalk) and confer very litlle, if any reinforcing effect. These carbonates do give some increase in hardness and provide a useful base for light coloured goods. Because of their low cost they are frequently used in non-black compounds of only modest strength specifications. Some what superior materials may be obtained by calcining the raw chalk to give calcium oxide, slaking it in water, filtering off impurities and bubbling in carbon dioxide to reform calcium carbonate, which is precipitated. Such precipitated calcium carbonates are of liner particle size and give compounds of improved properties compared with those based on ground whiting. The precipitated calcium carbonates may be treated with up to 3% of stearic acid or a stearate to aid dispersion. Such activated calcium carbonates are some times used in higher- grade coloured compounds. It is now recognized that the presence of many small molecules, including stearales, on the particle and rubber molecule surface may interfere with the interaction between filler particle and rubber molecule and thus prevent calcium carbonates from reaching its true potential as a reinforcing filler. In contrast to the silicas and silicates, little success has been achieved by the use of coupling agents as the si lane and litanate types ( Barlow.F.W.,1989) 2.1.b.Silicas and silicates Silicas are used as extenders; they are grouped into crystalline silica, precipitated silica, pyrogenic silica, diatomaceous earth, and silica gel. Compared with carbon blacks the following features of silicas should be noted. • The surface of the silica particle is hydrophilic and much absorbed water is present. This causes difficulties in achieving rapid wetting and dispersion. The 15 longer mixing times may cause excessive heat generation and in the case of IR and NR, polymer break down. The particle surface is acidic and active- 011 groups on the surface lend to bond and deactivate accelerator molecules. As a result of these effects cure is retarded, and in order lo maintain a given cure rate. It is necessary lo use a higher level of accelerators than in corresponding black formulations. A l one time it was common practice to add a substance which was preferentially absorbed on to the surface of the filler particle at an early stage in the mixing process and before the addition of the accelerator. Silicas generally have a greater surface area than a carbon black of the same particle size, thus indicating a greater porosity. This can lead to a greater stiffness for uncured stocks at a given filler loading. Additional plasticizer is therefore required lo achieve parity of stock viscosity with the corresponding black compound. High levels of reinforcement may be achieved with silica fillers, particularly where silane coupling agents are used. Most studies reported concur that the tensile strength of a silica- filled compound is comparable with a reinforcing black (Barlow.F.W, 1989) Some workers ( eg Stewart, 1977 ) stated that replacement of carbon black with a fine silica wil l adversely affect abrasion resistance and lower the 300% modulus. On the other hand.(Wagner, 1977) stated that these properties were comparable with the two types of fillers. He has suggested that the difference was due to the choice, level and point of addition of the coupling agent. The major use of synthetic silicas is in shoe sole manufacture. There has been some increased use in tyre applications where tear resistance was more important than abrasion resistance, such as in olT-lhc-road earthmovcr and truck lyres. Hydrated calcium and Aluminium silicates are semi reinforcing fillers which may have a slight retarding effect on cure. In recent times these materials have tended to be replaced by the less expensive mixtures of silica and china clay. 16 2.I.e. Kaolin ( China clay ) The china clays are hydrated aluminium silicates resulting from the weathering of feldspars. Like the calcium carbonates they are often considered as low cost inert fillers but grades are available that provide a fair measure of reinforcement at low cost. Compared with calcium carbonates the basic grades of china clay show the following vulcanizate characteristics: • Low pigmenting powder; • Slight reinforcing at low levels; • I ,owcr resilience; • The plate like particles can lead to anisotropy in products and also to poor tear resistance; • Good electrical insulation properties; • Good resistance to mineral acids. The china clays are frequently classified into the following groups. 1. Soft clays with particle size greater than 2 urn. They have a marginal reinforcing effect and are used mainly in mechanical goods. 2. Hard clays of finer particle size ( less than 2um) confer a significant reinforcing effect to the rubber. As with other fine particle-size slilcates they may have a retarding effect on cure, particularly which at loading; 3. Calcined clays . These are hard clays calcined to remove water and which confer higher (ensile strength, hardness and electrical resistivity as well as a good white colour. They may be used where colour and good electrical insulation are particularly important. They may have a less retarding effect on cure 4. Treated clays . They may be of many types . At one time such diverse material as amines and polyglycols were used but are no longer of much importance. The silanc coupling agents, particularly the mercapto- terminated silanc which arc particularly effective with the calcined clays much more significantly. They function by providing a link between filler and rubber molecule ( Brydson, 1988 ) 17 i, 2.2 Structural chemis try and process ing 2.2.1 Characteristics of china clay Kaolin is a hydrated Aluminium silicate mineral of definite chemical composition having the general formula Al2O3.2SiO2.2H2O. It is most common of the four polymorfs in the phylosilicate subclass and applies the same chemistry of other silicates and silica as a filler.(Sutton.D,1998) The surface of kaolin is highly polar and hydrophilic as a result of its polysiloxane structure as the presence of numerous silanol groups. The chemically active silanoles on the surface of clays ( silicates ) contain active hydrogen atoms that can react with various chemical groups. If the surface area is high then surface activity is high and this can have a dramatic effect on in-compound reactions, specially sulfur vulcanization. The silanol groups are acidic in nature and reactive. Silanols show similarities to carboxilic acid groups in their reaction with amine, alcohol and metal ions. At elevated temperatures silanol groups on the surface of the silicates will react with a number of chemical groups present in rubber compounds. If ZnO and stearic acid are added earlier, form zinc stearate and subsequently reacts with silicates or silanol groups and reduce cure properties. (Byers.J.T., 1998) 18 <»®>oge. (F'ig 1 .a) Structure of Kaolinite Layer ( Fig l.b.) Micropliotograpli showing Book-shaped arrangements of hexagonal plates in kaolin (Velde B, 1992) 2 .3 . C h e m i c a l modi f i ca t ion of ch ina c lay China clay used in many industries for several purposes and required properties can be obtained through some physical and chemical treatments . Some of those treatments are given bel ovv 7 4 4 4 6 2.3.1 Calcination Calcination, the operation of heating or roasting, is useful to pre react materials and provide stable product as improved raw materials. By heating at a suitable temperature, four hours at 800 °C the water of hydration can be removed from kaolinite. (Worral.W.E.,1986 ) Al2O3.2SiO2.2H2O = A l 2 0 3 . 2 S i 0 2 + 2 H 2 0 2.3.2 Oxime treatment 8-Hydroxy quinoline (oxime ) is an almost colourless crystalline solid, with melting point in a range 75-76 °C. It is almost insoluble in water. The reagent is prepared for use in following way to be treated with required metal ion in aqueous medium. Two grams of oxime were dissolved in 100 ml of 2N acetic acid and ammonium solution was added drop wise until a turbidity began to form. Oxime having both a phenolic hydroxy] group and a basic nitrogen atom , is amphoteric in aqueous solution. Oxime ( C 9 H 7 O N ) forms sparingly soluble derivatives with metallic ions, which have the composition M ( C Q H 6 0 N ) 4 If the co ordination number is six. (eg: Aluminium, Iron , Bismuth, Gallium ) The usefulness of this sensitive reagent has been extended by the use of masking agent ( eg: EDTA, Citrate, Cyanade, Tartarate ect.) and by control of PH ( Vogel. A, 1989 ) 2.3.3 Polar polymer grafting Kaolin can react with long chain or short chain polar polymers due to the high polarity of silica or silane particles. Reacting or grafting polymer can be tailored for required properties such as better dispersion, reinforcement, whiteness, ect.. Clay can be de watered by flocculating with organic flocculants such as polyacrylamides. This method is more effective than using electrolytes. These organic flocculants may act in several ways by entering the stem layer, by rending the surface of the clay hydrophobic or by linking clay particles via-chain molecules.. ( Mark.J.E, 1994 ). 20 2 .3 .4 .Sur face deact ivat ion by Es tcr i f ica t ion process Moisture is readily attached to the silica/silicate surface through hydrogen bonding. Absorbed water on the surface of filler particles reduce the activity ol" the silanols. I f diethylene glycol (DEG) or polyethylene glycol (PEG) is present in the recipe, it can replace the volatilised water and reduce the reactivity of the filler surface with moisture thereby increasing the cure characteristics in sulfur vulcani/.ation.( BycrsJ.T, 1998 ) As in (he same way by reacting (silica/silicalcs) wilh a polyol such as he.xadecanol or ethyl methyl alcohol, it was found that wilh these products the relaxation modulus or stiffness of uncured mixes of chlorosulphonaled rubber decreases with decrease of surface activity due to the reaction between polyol present and silanol groups on the filler surface . Thus esterificalion treatment seems lo function as dispersing aid for such elastomers and deactivating agent between polar polymer and the filler ( Roychoudhuri.A,l995 ) 2 . 3 . 5 S i l a n c coupl ing Several coupling agents arc commonly used in sulfur cured compounds filled with non-black fillers . Some of them are Mercaplo silanc. Thyocyanato silanc. Tetrasulphidc silanc. ( Pig 2.a ) The melhoxy or ethoxy groups react during mixing with the silanol groups on the structure of silica, silicate or clay particles and give strong bonds. The sulfur containing group of each structure reacts during vulcanization to give bonding to the polymer. Al l these silanes probably yield similar final structures for the coupled linkage between the filler and the polymer. ( BycrsJ.T, 1998 ). 21 CH3 O CH3-0-Si-CH rCH2-S-H O CHj C 2H 5 O C2H5-0-Si-CH2-CH2-CH2-SCN O C2H. Mcrcapto silanc Thiocyannto silanc C2H5 C 2H 3 O O C2H5-0-Si-CH2-CH2-CH2-S-S-S-S-CH2-CH2-CH2-Si-0-H5C2 O O C2H5 C2Hj Tctrasulphide silanc Fig. ( 2.a ) Silane coupling agents Fig (2.b) Diagram showing polymer strand bound to kaolin through silane coupling agent Investigations obtained using NMR spectroscopic analysis give models for these reaction systems. A single siloxane bond is first formed with the silica/silicate surface (primary reaction) it is followed by condensation reactions between silanol groups of silane molecules which are already bound to the silica surface 22 ( secondary reaction ). Primary reaction faster than secondary reaction and both become rapid in acidic and alkaline PI I ranges. Primary reaction accelerates up to a particular water content after which the rate is constant. But secondary reaction keeps on accelerating with rising water content ( Gocrl.Udo. 19°7 ). The silane loading to a particulate mineral 111 lor depends on the surface area of the filler and the coverage of the specific silane. The level of silane varies from 2-1 I by weight for the particular silica/ silicate filer depending on the properties of the final product (Byers.J.T,l998 ). 2.3.6 A d d i t i o n of A m i n e of Aminof i ine t io i ia l der ivat ives Amino functional derivatives (Diamine salts of fatty acids) or Amines improve the mechanical properties of silica/silicate filled compounds. From swelling it has been shown thai amine or amino functional derivatives improve filler dispersion and also have some effect on cross link density. These amines or amino functional groups give optimum properties with silane coupling agents and can be observed through computer aided image analysis or micro photographs. ( Ismail.11 ) Most of the accelerators used in sulfur cure systems contain an amine group . Strong adsorption or reaction with filler particles can decrease the amount of accelerator available for vulcanization reaction. This can give slower cure rates and reduced slate of cure, therefore addition of amine or amino functional derivatives gives rise to faster cure rates and dispersion properties. (Ism i Ie. II ). Polar oils or aromatic rosins generally improve dispersion properties of compounds containing silicates. ( Byers.J.T, 1998) ) 2.4 .Phys ica l modi f ica t ion of Kaol in Kaolin has a low cation exchange capacity ranging from about 2 to I Meg/lOOg and the chief exchangeable ions are H+, Ca 2 + , Mg 2 + , Na+, and K+ . Due to their low ion exchange capacity, china clay requires less amount of dellocculant than sedimentary clay. For kaolin group minerals Na' ions favor the stability of dellocculation whilst IT1 and Ca 2 1 ions cause llocculation. In the dellocculation 23 process. Poly phosphates are said to be more effective and high zeta potential accompanied by deflocculalion, can be reduced when only a fraction of the total cation sites have been replaced by sodium. Hence "Calgon" sodium llexamela phosphate is more effective in dellocculation of china clay (Mark..1.1'.. I c)94 ) As mentioned above kaolin can be modified chemically or physically through several processes. The possibilities of such modifications are mainly due to the structural features of the kaolinite particle. 2.4.1.Cause of cation exchange In the kaolin minerals ihe oxygen ;inil hydroxyl valences at the planer surfaces of the structure and completely satisfied. At the edges, however there are aluminium, silicon, oxygen and hydroxyl ions that are not satisfied because the lattice is capable of extension indefinitely in the ab plane. These unsatisfied valences . or broken bonds as they are often called, are satisfied in practice by external ions that do not form part of the structure, but merely act as counter ions, preserving electrical neutrality. These counter ions , particularly the cations , are capable of being exchanged for other ions and are one possible cause of cation exchange in clay minerals. ' broken bonds' however arc not the only cause ol'cation exchange in disordered kaoliites, as mentioned previously additional balancing cations are present because of the lattice substitutions. These additional cations probably account for the greater part of the cation exchange that occurs with the disordered kaolinilcs. Another possible cause of cation exchange in clays, often quoted in the past is ionization of basal hydrogen groups . to produce a negative charge on the oxygen and a hydrogen ion that is exchangeable for other cations i f this were so, one would expect the cation exchange capacity to be strongly dependent on PH, which is certainly not the ease. Ionization of hydroxyl groups is of course an important factor in oxides (Worral.W.E,l9986 ) 2.4.2.Cation exchange capacity For a given eiay, the maximum amount of any cations thai can be taken up is constant and is known as the cation exchange capacity (Worral.W.F, 1986), often abbreviated to c.e.c. In principle, the c.e.c is determined by leaching the clay with a chosen electrolyte , so as to replace all existing cations by one particular cation . The clay is then filtered, washed free of excess of electrolyte ( often with alcohol rather than water, to avoid hydrolysis) and the amount of chosen cation is determined. Ammonium acetate is the electrolyte frequently chosen for this purpose, since ammonium can readily be determined by distillation. Instead of an electrolyte, an exchange resin in the ammonium form may be employed. Other electrolytes, in which the relevant cations can be readily determined by chemically, have also been used, such as acetates, sulphates or chlorides of manganese, lithium and sodium. On the whole, values of c.e.c. obtained with different monovalent cations agree reasonably well, but discrepancies has been found when comparing monovalent with polyvalent cations. This discrepancy has been ascribed to the formation of complex ions of type M-OFI by polyvalcnls ions; with calcium for example, it is conceivable that one monovalent ( Ca-OITJ ion could be attached to every exchange site , resulting in an apparent c.e.c of twice the normal value if the latter is calculated as Ca 2 ' rather than Ca-()ll . Alcoholic solutions of polyvalent cations are said to give normal values of c.e.c. presumably because the complex ions cannot be formed in alcohol. ( Woiral.W.i:,l ()86 ) 2.4.3. Values of cation exchange capacity For well crystallized kaolinites the c.e.c. is small, being approximately 2-5 meq/IOOg. The amount of c.e.c. contributed by broken bonds is probably small, since the crystals are relatively large ; moreover , the degree of substitution is small. For the disordered kaolinites, however, the c.e.c is high, and of the order ol 30-40 meq/IOOg, due to lattice substitution. Many workers have reported that 25 c.e.c increases with specific surface area. This would indeed but true if c.e.c were associated entirely with broken bonds al the edges, and many authorities have found a linear relationship between c.e.c and surface area for well- crystallized kaolinites (Worral.W.E., 1986 ) 2 .4 .4 .Ca t ion exchange react ions If a clay is placed in a solution of a given electrolyte, an exchange occurs between the ions of the clay and those of the electrolyte: X - C l a y + Y + *" Y - C l a y + X + As indicated, the reaction is a balanced one and the extent to which the reaction proceeds from left to right depends on the nature of the ions X and Y. their relative concentrations , the nature of clay , and on any secondary reactions. Even for equivalent concentrations , some cations are adsorbed better. One obtained the lyotropic or I lofmeister scries: I-l > Al > Ba > Sr > Ca > Mg > N H 4 > K > Na > Li ( Worral.W.E ) 2 . 4 . 5 . C a t i o n exchange react ions with o rgan ic ions It had been investigated that the organic cations also can be exchanged with the associated cations in kaolinite structure as inorganic cations . As might be expected, basic organic compounds that ionize in aqueous solution may also replace other cations on clay surfaces. Amines for example, may react with calcium clays: R.NlV' + Ca-Clay *- R. NH3 Clay + Ca 2 + In the above equation, R stands for an alkyl or aryl group. Whatever the nature of the original counter ions, replacement of the latter with amine invariably results, in aqueous suspensions, in the clay being strongly flocculated, possibly because the amine is strongly attracted to the stern layer. Another explanation may be that since the amine is adsorbed with the Nl 1 / group close to the surface, the alkyl or aryl group projecting outwards, the surface is therefore hydrophobic; thus, the 26 solvation energy of the composite clay particle is drastically reduced. Conversely, if the amine-clad clay is dispersed in organic medium, the solvation energy is very high and this alone may account lor the delTlocculalion that occurs. Because of their organophilic properties, amine-clad clay have many industrial applications. Their compatibility with organic media enables them lo be used as paint-thickeners, in polishes, and in treatment of effluents. It is common experience that when clay is shaken and dispersed in water, the resulting suspension remains cloudy on standing and frequently may be not clear for days or even for weeks. This is because a colloidal solution of clay in water has been formed, the particles of clay are so small that they settle extreme slowly. The stability of this colloidal suspension depends primarily on the nature and concentration of the counter ions So counter ions favor stability and complete dellocculation, whilst hydrogen and calcium ions cause flocculation to occur. Dcllocculated clay suspensions are required for casting slips and in the determination of particle size; flocculated clays, on the other hand may be required for various devvatering processes such as liller pressing. Deflocculatcd clays have a characteristically lower viscosity than flocculated clays ( Worral.W.E ,1986 ). One method of achieving dellocculation is the precipitation and replacement mechanism, in which the displacement is removed from solution by precipitation or sequestration. Thus calcium clays may be deflocculatcd wilh sodium carbonate, sodium oxalate, sodium phosphate; hydrogen clays may be dcllocculated with sodium hydroxide. There is a class of dcflocculants, however, that appears to function differently. Sodium silicate, for instance is a very powerful detlocculant for the majority of natural clays. The mechanism of this instance is not simply the replacement of other ions by sodium, followed by the precipitation of the displaced cations as silicates. Simple measurements have shown that a high Z.eta- polential. accompanied by dellocculation, can be produced when only a fraction of the total cation sites have been replaced by sodium Similar results are observed wilh other polyelectrolytes such as 'calgon' ( sodium hexameta phosphate ) and 27 V 'Dipex' ( sodium polyacrylale ). These observations suggest that the anion plays an important roll in dellocculation. Large polyanions such as silicate, polyphosphate and polyacrylate are adsorbed by clay surfaces, in addition to sodium ion. It is not quite clear how this adsorption produces a high-zeta (potential, but it would seem likely (hat the adsorbed polyanions provide extra negative sites that are strongly ionized, so that the associated cations are al a relatively great distance form the surface. Polyanions are likely to be repelled by the negative planer faces of clay crystals, and it is therefore probable that they are absorbed onto the edges, either by anion exchange or by physical adsorption. Another characteristic of polyclcclrolyle deflocculants is that considerable excess can be tolerated without offsetting the dcllocculating effect.( Worral. W.L. 1986 ) According lo G. Pctzold and H.M. Buchhammer adsorption of polycalion as well as the modification with oppositely charged polyelectrolytes is a useful tool for surface modification. A strong enhancement of the attainable specific calionic surface charge was observed with eg., with poly (diallyl-dimethylammonium chloride) as the polycation and maleic acid-co-methyl styrene) as the polyanion, at a ratio of anionic to calionic charges of n7n+ = 0.6..0.7 28 1. Adsorption of polycation 2. Addition of polyanion PEL surface complex PECwith excess of free polycation Fig ( 3 )Mechanism of adsorption and modification (Petzold.G, 2000) According to their study it was concluded the formation of positively charged surfaces is influenced by the adsorption polycation on clay as well as the formation of a non stoicheometric polyelectrolyte complex, with polycation in excess, and reversible interaction , with polyanion in the surrounding solution. ( Petzold.G,2000) 29 11 2.4.6.Tlic effect of edge charges 30 • The edges of clay crystals may behave differently from the planer surfaces in having an atmospheric character. It is clearly possible for the edges to carry a net positive charge over a wide range of I'll, whilst (he laces are permanently negative. In these circumstances, the edges and faces will mutually attract, giving rise to a so-called 'edge-to-face1 llocculation, even though the zcta potential may be moderately high. Because of the comparatively small magnitude of the edge charges, they can be neutralized or reversed by small additions of a suitable electrolyte.( Worral.W.E, 1986 ) It has been observed that when a hydrogen clay is treated with successive small additions of NaOH, the degree of llocculation, and therefore the viscosity, at first begins to increase markedly until just before the equivalence point, after which dellocculation suddenly occurs and the viscosity drops sharply. This is because the sodium ions first replace H + on the faces only, increasing their negative potential without influencing the edges; this results in an increased attraction between edges and faces. On further addition of NaOI-l, the I'll rises sufficiently to reverse the edge charges, so that the clay particles become negatively charged overall and the system is therefore dcllocculatccl. It has been suggested that the remarkably small additions of polyeleclrolyle required to deflocculate clays. It can be explained by supposing that the polyanions are absorbed on to the crystal edges and thus ' mask ' any positive charge on these sites. This explanation cannot be regarded as satisfactory, however, since it does not account for the very high zela potential that is observed when clays are dellocculaled in this way 2.4.7.Other causes of flocculutioii Calcium is a predominant exchangeable cation ol natural clay that is normally llocculated. The degree of llocculalion is in all cases increased by the addition of any electrolyte in sufficient quantity, due lo 'crowding" of the stern layer. Sails of polyvalent cations are more effective flocculants than those of monovalent cations. Thus, the deflocculalion of natural clay may be inhibited in the presence of soluble salts, notably sulfates of calcium, magnesium or iron. If the clay processing involves filter pressing, much of the soluble salt wil l be removed; there by otherwise, careful addition of the stoichiometric amount of barium carbonate may effectively remove the sulfates: CaSO., + BilCO.? * (a ( ( ) , + BaSO., The net effect of this treatment, as indicated by equation, is lo produce two sparingly soluble substances, the effect of which is thus minimized. Dellocculation can often subsequently be achieved by the addition of sodium carbonate, sodium silicate or bolh.( Worral.W.T:, 1986) CHAPTER 3 M A T E R I A L S A N D M E T H O D S 3.1 M A T E R I A L S U S E D F O R T H E E X P E R I M E N T (a) Kaolin Rubber grade kaoiln processed in Moralesgamuwa rellnary was used for the experiment as a I]Her. Kaolin is a rock or aggregate composed of asscnlially of clay minerals of kaolinile group. The kaolin minerals consist essentially of a hydrous aluminium silicate having the general formula A l 2 0 : ! . 2Si0 2 . l l : 0 Used grade had following characteristics: -the ion exchange capacity was 4.1 milli equivalents per 100 grams -IM I value was 5.2 -particle size ranged from 0.2 to 1.0 u -moisture content was 2.3% ( Other technical data are given in appendix I ) (b) Urea (Carbamide) -Analar grade urea having Chemical formula NIT- CO - NIT in granular form with 99% degree of purity was used in experiment, 'fhe impurities are given below -Sulfated ash content did not exceed 0 .1% -Chloride content did not exceed 0.002% -Sulfate cotent did not exceed 0.05% -Melting point was in a range of 13 I -134°C (c) Polyvinyl alcohol ( PVA) Commercial grade granular form polyvinyl alcohol ,having molecular weight of 1000 gram , readily water soluble was used. Degree of purity corresponded to 95% and degree of acetyl group substitution corresponded to 12 % Chemical structure is given bellow. - CH—CH O C=0 CH 3 -CH—C- OH n (d) Monoethanol amine (MEA) Commercial grade monoethanolamine in a liquid form having Chemical formula NH2--CH2-- CH 2 OH with 96% degree of purity , 1.07 g/cm ? specific gravity and 170°C boiling point was used for the experiment. (e) Rubber and additives All experimental procedures were carried out using ribbed smoked natural rubber of grade I (RSS I) The typical characteristics of raw rubber and black filled vulcanizate properties are given in table I. Table I: Properties of natural rubber Type Source Dirt content % Weight Mooney Viscosity Tensile Strengh (mN/m 2) RSS I Co-agulated field Latex 0.0-0.08 60-100 2.1 -2.8 33 V u l k u i i i z i n g agent Su11 iir was used as a vulkanizing agent in its elemental form as finely ground rhombic crystals with 99.5% degree of purity and ash content of 0.5 % Activators Zinc oxide ( ZnO ) : Zinc Oxide was used as an activator being coarse white in colour with degree of purity 9*).')%,. Particle size of used zinc oxide did not exceed 1.0 u Product contained impurities as follows: I ,ead (Pb) content did not exceed 0.005% Sulfur (S) compounds content did not exceed 0.01% Calcium (Ca) content did not exceed ().05%> Potacium ( K) content did not exceed 0.01%) Iron ( Fc) content did not exceed 0.001 % Sodium (Na) content did not exceed 0.05% Magnesium (Mg) content did not exceed 0.005%) Stearic acid A fatly acid having chemical formula Cn I f s COOII was used in a powder)' form as a dispersing and activating agent, present in the non hydrocarbon constituents of natural rubber . In standard practice stearic acid is added to compound for a precausion against possible deficiencies of the accelerators of vulkanization in the raw rubber. I Ised stearic acid was of 95%) degree of purity with melting point in a range of67-69 "C 34 Accelerators Diphcnyl Guanidine ( PPG ) : DPG is a typical amine type accelerator, that acted as a secondary accelerator in natural rubber compounds. -The chemical structure is given bellow. N i l . <^Oy>- N H -c -NH —(^Oy Product was of 97% degree of purity with melting point in a range of 177-180 °C 2.2 Pithio bis benzothiozole (MBTS ) : MBTS belongs to thiozole type accelerators .It was used in a powdery form, being of light yellow colour. MBTS acted as a primary accelerator and scorch modifying secondary accelerator in natural rubber compounds . The chemical structure is given bellow: Used MBTS had degree of purity - 99.0% with melting point ranging from 159°C to 170 °C and density of 1.51- 0.3 Mg / m 3 35 3 .1.1 Rubber compounding The standard formula used for compounding of the rubber is given in tabic 2. fable 2 : T h e s t a n d a r d formulat ion of fi l led na tura l r u b b e r based c o m p o u n d Ingredients We igh t , g W e i g h t , Rubber 100.0 70..S2 Zinc oxide 5.0 3.54 Stearic acid 2.0 1.41 f i l ler 30.0 21.24 MBTS 1.5 1.06 DI'G 0.2 0.16 Sul I'u r 2.5 1.77 f ive compounds were prepared according to given formula, so as formula N I included standard rubber grade kaolin as a filler, while in formulae N N 2-5. standard kaolin was completely replaced with kaolin modified respectively with carbamide ( urea), polyvinyl alcohol, monoethanol amine and urea formaldehyde resin. Modification procedure was developed and described in an experimental 3.2 EXI'UIMENTAL PROCEDURES 3.2.1 (a )F in t l ing the ion e x c h a n g e capac i ty In order I D determine llic ion exchange capacilv. i.e the lumiher ol valence siles available in kaolin structure . kjcldahl method was proceeded . The method included following steps. Weighed portion of rubber grade kaolin of approximately 10.0 g was mixed with 200.0 ml of 0.1 N ammonium acetate solution in order lo replace all counler cations attached to the kaolin surface with ammonium cations. Then this portion was distilled with 2.0 g of Magnesium Oxide powder (MgO). so as to replace ammonium ions with magnesium ions Mg" 1 from kaolin . The ammonium liberated al high temperature in the gassious form was trapped in to the Boric acid . Complex containing boric acid and ammonia was titrated with 0.1 M hydrochloric acid ( IICI ) using Bromocresol green as an idicator to Unci ammonium acetate concentration. The results obtained from the titration were used to calculate the number of equivalents that participated in cation exchange reaction. 3 . 2 . 1 . ( b ) T r c a t m c n t of kaol in Water soluble amines were selected for modification of kaolin on account of their capability of being exchanged with cations associated with kaolin and on economical reason, as they did not require expensive solvent for dissociation. (a ) T r c a t c m c n t o f k a o l i n w i t h u r e a The relevenl concenlralion needed for ireatment of kaolin ,\vas calculated using the value of ion exchange capacity of kaolin obtained experimentally. A portion of kaolin weighed about 100.0 g was treated with 200 ml of 0.025 mol / dm 3 carbamide (urea) solution by keeping them in contact for 12 his while stirring ,lo ensure better ion exchange. Then the mixture was filtered off. precipitated suspension was dried tinder normal atmosphere untill permanent weight was achieved. ( h ) T r e a t m e n t o f k a o l i n w i t h P o l y v i n y l a l c o h o l ( P V A ) It was difficult lo find equivalent number of PVA as it belongs to polyclcclrolyte compounds. In this connection the optimum concentration of PVA. needed for Ireatment of kaolin was determined experimentally as described bellow. The samples treated with PVA solutions of following concentrations 1.0 g/dnr . 4.0 g/dm"3 , 8.0 g/dm"3 ,12.0 g/dm"3, 16.0 g/dm"3 were ground easier. The PVA solution of highest concentration that corresponded to 16.0 g/dnv was selected for further experiment Other procedures were carried out similar to those, developed for treatment of carbamide described earlier. 38 (c)Treatment of kaolin with Monoethanolamine ( MEA ) The relevent concentration of MEA needed for the activation of kaolin was calculated in order to keep equality of equivalent number to cation exchange capacity of kaolin obtained experimentally Weighed portion of 100.Og kaolin was immersed in 200.0 ml of 0.025 mol/ dm"3 monoethanolamine solution. Few drops of 0.1 M HC1 solution were added to ensure the stability of formed cations . Composition was left for 12 hours to provide better ion-exchange. It was stirred time to time The rest of experiment was proceeded similar to that of treatment of kaolin with carbamide. (d) Treatment of kaolin with urea formaldehyde resin Synthesis of urea formaldehyde in a water soluble form A pyrex glass beaker was filled with 270 ml of 37 % formalin .The PH was adjusted to 4.6-5.3 using aqueous solution of NaOH. Then 100 g of urea was added to formalin , by portions while heating , At time all urea had been introduced, reaction mixture was brought to boiling at 90-100 0 C. In 30 minutes heating was stopped and reaction mixture was cooled.The PH of the reaction mixture was increased to 7-8 using ammonium hydroxide. Freshly prepared resin was used for treatment of kaolin according to the procedures discribed earlier. 3.2.2 Rubber compounding The compounds were prepared on an open two- roll mill of laboratory size, having circumference milling speed 5 rpm and friction ratio 1.4 at a temperature ranging between 40 °C and 60 °C. Formulae N N 1-5 were performed according to mixing cycle given in table 3 39 able3 : The mixing schedule lor 5 mixes on an open two -roll mi Ingredients Rubber ZnC) Stearic acid Filler (kaolin) M U T S J ) I , ( Time on mill (min 24 Unload 3.2.3 Determination of vulcanization characteristics (JI) Viilkunizution charactcries This lest was carried out to determine the vulkanization characteristics of rubber compounds. The effect of heat on compound caused changes in the viscosity and scorch characteristics were determined from initial portion of the curve of torque versus time. The vulcanization limes of all prepared compounds for determination of tensile properties and tear resistance were found from theological or cure curves obtained with Mooncy Viscometer and Monsanto Rheometer Mooney Viscometer test was carried out according to ASTM 2084 - 95. A specimen of a specified shape was sheared by a rotor having diameter corresponding to 1.5 inches. Speed developed by rotor was 2 rpm and .temperature was maintained at I60°C 40 Monsanto Rheometer test was carried out according to ASTM 5289-95. A standard shape specimen was shcard by the rheometcr disk making 30 rounds per minute.Temperature was maintained at 16()"C The following standardized values were taken from the obtained rheological curves and used lo calculate cure lime: Minimum torque in Nm Maximum torque where curve plateaus in Nm Minutes lo one Ibf inches rise above minimum torque used with l" arc, minutes lo two Ibf inches rise above minimum torque used wilh 3 "arc Minutes lo 90 % of maximum torque 3.2.4 Phys ico- m e c h a n i c a l tests 3.2.4 (b) Tensile test Tensile properties of vulkanized rubber were determined according lo ASTM I) 412- l>2. using "\T type dumb bell lest specimens of about 2 mm thickness. Standard mould was used for press curing of test samples under temperature of 140 °C for period of lime, determined for each compound from rheological curves. Dumb bell test specimens were tested with a tensometer at 28°C lo lake following readings: I .Modulus at 100% elongation 2. Modulus at 300% elongation 3. Tensile strength al break 4. Elongation al break 41 3.2.4 (c) Ageing test The dumb bell test pieces were kept ul 100° C for 72 hours and tested with tensometer to find the tensile strength values and elongation al break.Testing procedures were carried out at 28°C 3.2.4 (il) Ahration resistance test This test was performed according to ASTM D 1630- 94 standard using ihe instrument called " Din Abrador " .The test specimen of 16 mm diameter and 8 mm height was subjected to wearing by rubbing with the abrasive held on the rubber Three lest specimens were run in order to obtain average value of abration resistance 3.2.4 (e) Flex cracking test This lesl was done according to ASTM 4482-85 standard by De Matlia Ilex cracking experiment .The flexing machine provided 300 bending cycles per minute. The number of cycles at crack initiation was measured. for crack growth a single cut of I mm was introduced using a razor blade .The direction of the cut growth followed in groove along the specimen centreline.The cut length and number of cycles were recorded . The results reported were the average of three samples tested. 3.2.4 (I) Bound rubber content 'fhis test was performed on filled raw rubber compounds to find the bound rubber or gel content corresponding to the amount of rubber sufficiently strongly attached onto the filler surface. This test was carried out to establish certain correlation between bound rubber content and strength characteristics of filled rubber compounds. .k Several samples of approximate dimensions 10 xl() mm were prepared from rubber compounds N N 1-5, loosely packed each in its own prior washed and dried pure cotton bag of approximate dimensions 30x 35 mm. The open ends of the bags were stiched . In a such manner prepared bags were immersed in lo 100 mi of toluene for 96 hours at room temperature. To intensify the extraction of rubber from a specimen , toluene was replaced with a fresh portion in every 24 hours. After extraction, bags were taken out of toluene and dried al ambient temperature untill constant weight of residue was achieved. The bound rubber content was calculatrd as a percentage of insoluble polymer 3.2.4.(|4) Swelling test The swelling lest was performed with vulcanized rubber, in order lo get some useful information about density of cross links of chemical bonds, from each vulcanized compound the specimens having approximate volume of 0.2 cm' were prepared and weighed.The weight of each specimen was recorded using an electronic balance having 0.0001 g accuracy. In this study the weight of toluene uptake per gram of rubber hydrocarbon (Q) was calculated according to the expression derived by Park and Brown as shown bellow Swollen weight - Deswollen weight Q = Dry weight X 100 /•'ormii/ti wcig/il Where formulation weight was the total weight of the rubber plus compounding ingredients based on 100 parts of rubber. Dry weight was the original weight of the sample 3.2.3 Differential Thermal Analysis (DTA) This test provides the information about enthalpy changes reflecting a chemical or physical changes occuring under heating or cooling of tested samples at permanent rate. Two specimens were tested: 1. A sample of kaolin treated with MEA 2. A sample of rubber compound, filled with kaolin treated with MEA 44 C H A P T E R 4 RESULTS AND CALCULATIONS 4.1 Results obtained from the Kjcldahl cxparimcnl Amount ol' I TCI required for titration of ammonium cations ( Nl I./ ) removed from kaolin structure is given in table 4. Table 4 :Required amount ofO.I N IICI Trial Required amount of NCI.ml 1 3.8 2 4.1 3 4.1 Average 4.0 F i n d i n g the ion exchange capac i ty Average amount of the 0.1 M IICI for the titration is , 4.0 ml Number of moles of IICI required to neutralize NM.iOTI is. _0J x 4.0 1000 - 4.0 x 10"' niol I ICI + NI-UOH > N I I 4 C I + H 2 0 1 : 1 1 : 1 According to the stoicheometry; number of Ammonium moles present in the titration medium is equal to number of MCI moles required for the titration, that is 4.0 x I0" 4 mol Hence the number of mill i equivalents per 100 grams is - 4.0 45 Number of moles of each chemical required lor the treatment of 100.0 g of kaolin was equal lo (he number of mil 1 i equivalents of exchangeable cations present in 100 .0 g of kaolin Obtained value of cation ion exchange capacity was used in further calculations, required for preparation of the solutions for the Ireatment ol kaolin. Calculat ion of modif iers' concentrat ions, required for treatment of kaolin. . Carbamide According to ( Morrison & Boid ) dissociation of carbamide is given by reaction: () () I U ) t l l 2 N-C-NH 2 [ H 2 N - C - N l V ] ' + O f f So the amount of carbamide that could be involved in ion exchange reaction with lOOg portion of kaolin was equal to , ( \ition exchange capacity of kaolin in equivalence X molecular weight of carbamide; 4 x 10 ' X 60 - 0.24 g Amount of carbamide obtained from ihe above calculation was dissolved in 100.0 ml of water to get the final concentration . To prepare the solution for Ireatment of kaolin an excess of carbamide was taken to obtain 2.5 g / d n r . Urea Formaldehyde Water soluble resin of the second stage polymerization is a linear polymer with a structure O I I - [ N H - C - N H - C H 2 j „ - O H Where; n - 6-8 46 Number of moles of each chemical required for the treatment of 100.0 g of kaolin was equal to the number of milli equivalents of exchangeable cations present in 100 .0 g of kaolin Obtained value of cation ion exchange capacity was used in further calculations, required for preparation of the solutions for the treatment of kaolin. Calculat ion of modi f i ers ' concentrat ions , required for t rea tment of kaol in. 1. C a r b a m i d e According to ( Morrison & Boid,1996 ) dissociation of carbamide in acidic medium is given by reaction: ? r ? H + + H 2N-C-NH 2 < - [ H 2 N — C - — N H 3 J + So the amount of carbamide that could be involved in ion exchange reaction with 100 g portion of kaolin was equal to , Cation exchange capacity of kaolin in equivalence X molecular weight of carbamide; 4 x 10 " 3 X 60= 0.24 g Amount of carbamide obtained from the above calculation was dissolved in 100.0 ml of water to get the final concentration . To prepare the solution for treatment of kaolin an excess of carbamide was taken to obtain 2.5 g /dm" 3 . 2. U r e a F o r m a l d e h y d e Water soluble resin of the second stage polymerization is a linear polymer with a structure O H- [ NH-C-NH-CH 2 ] n -OH Where; n = 6-8 Approximate amount of urea formaldehyde resin for kaolin treatment was calculated as follows: Assume, that 100 g of urea was reacted I-l NH-. O 7 H - C = ( ) + 7 (p=0 H [ NH-C-NH -CH2 ] 7 O H N H 2 l()o/ 60 = 1.67 moles of urea reacted Amount of formaldehyde reacted has to he 1.67 moles loo 1.67 x 30 = 50 g of formaldehyde reacted Approximate weight of resin produced would be : 100 + 50 =150 g Total weight of solution ( determined experimentally) was 400 g, so approximate resin content ratio is , ( I S()/400 ) x 100%- 37%, Proceeding from a common mechanism ol dissociation of amines I-l1 | NH-C-NH-CH 2 ] 7 O H * H + | N H - C - N H - C H 2 | 7 + O H at least 4 x I0"3 moles of resin participated in cation exchange reaction with 100 got"kaolin. 4 x 10" x molar weight of resin = 4 x 10 x 548 = 2.2 g of resin involved in ion exchange reaction with 100 g of kaolin. Minimum amount of 37 %> resin solution required for treatment of 100 g kaolin is calculated as: 2.2 x 100 — = 6 g 37 This amount was diluted with water to get 100 ml of resin solution. 47 3 . M o n o c t h a n o l a m i n e The amount of Monocthanol amine that could be involved in ion exchange reaction with 10()g of kaolin was equal to; Molecular weight of monocthanol amine X ('ation exchange capacity of kaolin in milli-equivalcnts As monocthanol amine was available in a liquid form at market, volume required for treatment was calculated as: / II eignl / Density Since the specific gravity of monocthanol amine is 1.07 g / dm . required volume containing 59 g was taken as 60 ml lo ensure belter ion-exchange reaction. The calculations were done as follows; 60.0 ml X 4.0x 10 ~3 = 2.4 x 10 " 1 g / dm"3 4. Polyvinyl a lcohol On the reasons given in experimental part 16 v of polyvinyl alcohol were dissolved in 100.0 g of water to get a solution wilh 16 g / dm"3 concc'iiration. 4 S 4 .2 Results obtained from the Mooncy Viscometer and Monsanto Rhcomctcr Values of scorch lime and cure time ol"all samples were calculated from the rheographs obtained from the Mooncy Viscometer ( fable 5 . Graph I ). fable 5 : Results obtained from the Mooncy Viscometer Mix N " Scorch lime, Min Cure time, Min 1 6.0 1 1.5 1 (..(> 1 1.0 6.0 10.5 4 4.0 7.0 5 6.0 10.75 Scorch lime and cure time values for all live samples were obtained from rheographs obtained from the Monsanto Rhcomctcr ( fable 6.Graph 2 ) fable 6: Results obtained from the Monsanto Rhcomctcr Mix N 0 Scorch time. Min Cure lime. Min 1 6.0 1 1.0 2 6.5 1 1.0 i 6.0 10.5 4 3.0 6.0 5 5.5 1 1.5 49 Graph 1 :Curing curves obtained from the Mooney Viscometer 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Time (Min) Curing curve of Mix 1 Curing curve of Mix 2 Curing curve of Mix 3 Curing curve of Mix 4 Curing curve of Mix 5 50 G r a p h 1 : R h c o £ r a j > p h o b t a i n e d f r o m M o n s a n t o r h c o m c t c r 4.3 Tensi le properties of vulcanized samples Obtained results were the average of 5 trials lor each sample .The tensile strength and the modulii are given in M I'a ,and calculated as follows; Tensile strength - Required force to break the ilttinh hell sample Surface area of surface to that force applied Eg: for specimen N I Obtained force at breakage - 83.6 N Surface area that force applied to - 4x1 mm 2 = 4x10"''m~ Tensile strength - 83.6 N = 20.4 Ml'a 4x 10"6 n r Force required lo elongate the sample Modulus 100% - by 100 % of its original length Surface area of the surface to that force was applied Modulus 300% Force required to elongate the sample by 300 "/<> of its original length Surface area of the surface lo that force was applied Fable 7 I: Tensile properties of mixes extended with modified and standard kaolin before aging. Properties Mix N° 1 2 4 5 Modulus at 100%. M Pa 2.03 2.86 2.24 3.78 3.26 Modulus at 300% ,M Pa 4.33 5.31 5.51 7.98 6.08 Tensile strength, MPa 14.6 22.5 21.7 26.3 24.97 Elongation at break. %. 1649 1540 1440 1352 1401 Tensile strength and elongation at break of aged specimens were calculated as it was shown in previous test Table 7 11: Tensile properties of the mixes, extended with modified and standard kaolin after aging Tensile properties after heat Mix N aging at 100 °C during72 hours 1 2 J) 4 1 .'Tensile strength, M Pa 6.25 9.91 1 i .04 15.25 16.12 2. Elongation at break % 401.5 421.8 461.0 282.0 273.4 53 Graph 3 : Graphical comparison of Tensile properties obtained for vulcanized samples 30 25 E 20 CO 15 c' 10 T e n s i l e p r o p e r t i e s of m i x e s I 2 3 4 M i x n u m b e r • M o d u l u s a t 1 0 0 % • M o d u l u s a t 3 0 0 % • T e n s i l e s t r e n g t h b e f o r e a g i n g • T e n s i l e s t r e n g t h a f t e r a g i n g Graph 4 : Graphical comparison of results, obtained for elongation at break. E l o n g a t i o n a t b r e a k 2 3 4 5 M i x N u m b e r • E l o n g a t i o n a t b r e a k b e f o r e a g i n g n E l o n g a t i o n d t b r e a k a f t e r a g i n g 54 4.4 Abrasion resistance test results Finalized results were the average of five trials for each samples and the result were expressed as weight loss after abrasion in grams. Table 8: Abrasion resistance test results Mix N° Initial weight, g Weight after abrasion, g Weight loss ,g 1 1.25 1.10 0.15 2 1.51 1.43 0.08 ~> 1.43 1.34 0.09 4 1.52 1.43 0.09 5 1.46 1.39 0.07 Weight loss = Initial weight of sample - weight of the same sample after wearing Graph 5: Graphical comparison of abrasion resistance test results Abrasion resistance test results 0.2 lo ss 0.15 lu m e 0.1 V ol 0.05 2 3 4 Mix number 4.5 T h e Flex c r a c k i n g a n d c r a c k g r o w t h test resu l t s Obtained results were the average of four trials done for each samples. Results were expressed as the number of cycles passed to the appearance of first crack and the number of cycles required lo increase the crack width by I mm. fable 9 : Results of De-Mattia flex cracking test Mix N 0 Number of cycles to the first crack appearance. Number of cycles to that crack has increased by 1 mm in w idth 1 5872 6501 2 7218 8313 3 7881 9017 4 9125 1 1337 ' 5 9579 1 1864 Graph 6 : Graphical comparison of flex cracking and crack growth test results De-Mat t i a flex c r a c k i n g t e s t r e s u l t s m Number of cycles to the first crack appeared • umber of cycles to that crack has increased by 1mm in width 1 2 3 4 5 M i x number 56 4. Bound rubber content test Results Mix N° Initial wcight.g Final weight,g Bound rubber content % 1 0.98 0.033 3.4 2 0.95 0.044 4.6 3 1.00 0.121 12.1 4 0.96 0.279 29. r 5 0.98 0.375 32.4 • Graph 7 : Graphical comparison of the results obtained from bound rubber content test Bound rubber content test results Results were expressed as a percentage of remaining rubber to the initial weight. Obtained results were the average of two trials. fable 10 : Results of Bound rubber content test 4.7 Results obtained from the swelling test Results obtained from this test were expressed as the percentage increment of weight of samples after keeping them in toluene. The finalized results were the average o f lwo trials carried out for each sample, fable I 1: Results of swelling test Vulcanizate ( Compound Number) Increased weight % 1 253.9 2 246.1 3 161.2 4 1 17.7 5 133.0 Graph 8 : Graphical comparison of the results obtained from the swelling test of raw rubber 300 250 x : cn (i> 200 1 a; 150 ai M CD ^~ 100 o c 50 Swelling test results • Increased weight 2 4 6 Mix number 58 I BO 5ai 37 * 2 ^ s 15 E: i S9a < ( i | ASSISE! <5 :1e 2 tf $0 a 5 50 Hi i I i 3S i _ i _ L -30^- 3; 20 i i i , : 1 i i _1_L U 4 1! - U - xu 1 I :S ' I i i i i i i - Graph 9 : D T A of raw rubber filled with kaolin treated with MEA CHAPTER 5 5.1 DISCUSSION I lie modifications of kaolin in this study were based on the ion exchange capacity and the adsorption ability of kaolin surface. Ammonium cations were introduced using Kjeldahl method to occupy the equivalence points on the clay surface through an ion exchange process . This was done in order to determine the exact amount of the chemical concentrations needed for the treatment and verify whether the ion exchange process could be practically applicable for the modification procedure, i.e. to confirm whether the ion exchange would take place. The reactions carried out by the Kjeldahl method are shown in a simple schematic diagram bellow. M £ r Treated wilh K 1 - 0.1 N Nil,AC I f Kaolinile hexagonal plate Distilled with MgO > NH., + HjBO.," Libera'ed NH, Trapped int llj lJO, N H 3 + H 3 B O 3 itrated with TIG using Bromocresol green indicator I f BO," -1- I f H»BO» The solution contained Hd30t and NTfC'l al the equivalence point. The PH of (he solution was in a range of 5-6 61 Il was found thai the ion exchange phenomena could be applied lo kaolin modifications. Concentrations required for treatments were calculated keeping equality of modifying cations to ion exchange capacity. A slight excess of each chemical was taken to ensure a better ion exchange. The benefit of modification of kaolin with basic organic compounds, dissociated in water medium, gave evidence, when comparing physical properties of filled rubber vulcanizales. Tensile test results given in table 2 showed higher (al leasl by I 1%) tensile strengths as well as moduli at 100% and 300% elongation for all specimens containing modified kaolin (N° N° 2-5) i f compared lo strength value specified for specimen filled with non-activated standard kaolin (N° I) Aging test followed the same trends, indicating that modification had developed certain resistance of rubber to prolonged action of high temperature (72 hours al 100 °C). Thermal degradation of course brought down tensile strength for all specimens, but standard one was affected to a greater extent. Increase in strength characteristics could be related directly to rubber-filler interaction that was promoted by active functional sites introduced lo the inert kaolin structure by ion-exchange process. Reinforcing effect came according to generally accepted theoretical conception through a particular attraction between these active sites and reactive points on the rubber-polymer chains, stemmed from weak double olefin bonds and broken under mechanical action of shear force paraffin bonds. Polymer chains even rubber fragments attached to the filler surface formed a grafted layer, held on the kaolin surface by various types of physical, hydrogen and chemical bonds with a wide range of magnitude of their respective bond energy from 0.08 K.l/mol to 1000 K.l/mol. Examination of flexibility of tested specimens did not reveal within the experimental errors any significant change in elongation at break. However a Molecular-mechanical or adhesion-deformalional hypothesis ol friction ol polymers suggested the reduction in energy of adhesive bonds as a measure against intensive wearing. From this point of view physical or so-called secondary Van-der Waals bonds, which prevailed in a spectrum of adhesion bonds, established across rubber-filler inter face, were of a great importance. Being of low energy by nature they could be easily destroyed under force action, permitting chains desorbed and slipped on the IIHer surface, so that break of a polymer chain did nol occur. Such aim of physical bonds was efficient lo a certain extent, but did not fully guard against seizure. Constant stresses and heal finally destroyed interface and weared a specimen out. Analogous behavior was exhibited by the specimens in Ilex cracking test. Results obtained from DE- Mattia Hexing machine are given in table l) Vulcanizates wilh modified filler displayed better Ilex resistance, than ones with non-modified filler. Similarly the crack growth became slower. Behavior of a polymer that was repeatedly bent lo a double position agreed well wilh previously considered hypothesis of disorption of the polymer chains from the filler surface and "stress softening effect". Vulcanized rubber always contained micro irregularities of its structure in the form of cracks, mechanical inclusions. Density of cross-links was also not even through out the rubber matrix, because of snarls and entanglements of macromolecules. These irregularities experienced higher stresses, than the average one in a specimen, facilitated mechanical destruction and a specimen failed under the effect of stress lower than ultimate strength. As chains desorbed from the filler surface, they regrouped themselves such a way to pass over into the most 64 slightly expressed tendency to reduction ol' flexibility was observed in the row- unmodified kaolin, kaolin modified with urea, kaolin modified with polyvinylalcohol, kaolin modified with monoethanolamine and ureaformaldehyde, that could be associated wilh restriction of chain mobility owing lo the increase of the cross link density in the same sequence. Another aspect involved in reinforcing mechanism of modified filler referred lo some degree of ordering or orientation of the chain portions close lo the filler surface due lo physical adsorption. Active centers, which are believed, amine, carboxyl and hydroxyl groups in organic radicals ol" exchangeable cations being strongly attached to the filler surface, influenced the electron density of double bonds of rubber polymer caused them displaced, so as arisen inductive dipole interaction culminated in crystallization. Crystallization on the filler surface functioning in that case as crystallization nuclei, could reduce degree of crystal I inily in rubber matrix, but no serious negative effects on the strength of rubber were reported, because of cross links density generally increased Abrasion resistance lesl results given in table 8 favoured also the compounds, filled with modified kaolin. These compounds lost weight on wearing, but much slower, than standard ones filled with non modified kaolin. Abrasion resistance of vulcanized rubber according to "eneral laws of wear in friction depends on the nature of adhesive bonds formed across contact /.one (interface). In abrasion test under periodical action of external force these bonds deformed repeatedly, strained, hardened and softened again. Process normally involved heal, oxidation and structural changes (reorientation, recrystallization) that together vvcared a specimen out. probable slate with minimum free energy, reducing the stress concentration level. Structure of vulcanization network became more even and stronger each time alter a repeated load applied, so number ol" cycles to first crack appeared and achieved 3/4 inch in width increased significantly. Non-activated kaolin also held certain amount of polymer owing to mechanical interlocking of the rubber in the micro irregularities on the porous structure of kaolin or absorption to the active sites on the planar surfaces of kaolinite mineral. Suggested reinforcing mechanism of activated kaolin, thai came through facilitated absorption of rubber polymer to the filler surface was confirmed by bound rubber content lest results [fable 10 |. The amount of rubber strongly attached lo the filler, was significantly .more for mixers containing modified kaolin ( N"N° 2 - 4 ). As ion-exchange process touched only upon chemistry of kaolin keeping unchanged its surface geometry, obtained increment in bound rubber content attributed just to intensified attraction of rubber polymer lo filler wilh establishment of sufficiently strong intermolecular bonds capable lo withstand prolonged action of solvent. The claim of improved interfacial activity with polyvinylalcohol as modifying agent was based on enhanced compatibility of inorganic filler wilh organic rubber. Polyvinylalcohol an amphipalhie agent by nature, being applied lo ihe filler surface prior to compounding promoted intrinsically welling, increased adhesion, dispersion and distribution of kaolin particles through out the rubber matrix. Comparing the efficiency of chosen basic organic electrolytes, mix N° 4. containing kaolin modified with monoethanolamine attracted attention in virtue of exceptionally high strength characteristics obtained by all lest procedures and 65 hound rubber content. The beneficial effect of monoethanolamine as modifying agent related in all probability to following: • The discrepancy in the degree of substitution due to large si/.e of polyvinylalcohol molecule leading In sleric hindrance, when arranged on ihe silica sheel was nol concerned wilh monoclhanolaininc • Even for equivalent concentrations, monoethanolamine ions could be absorbed more strongly, than carbamide ions, because of their higher activity in the lyolropic or I lofmeiler series • It could not also be ignored, (hat monoetanolaminc effected on vulcanization of rubber, acting as accelerating agent. Analysis of rheographs showed the reduction in scorch lime and cure lime nearly I wo times. It would be too early to stale about the formation of additional crosslinks in the network of chemical bonds, because high bound rubber content could be originated from chemical as well as physical adhesion bonds, established across rubber-filler interface. However clearly expressed endothermal peak on the thermograph curves obtained by DTA al 142 °C' gave definite support to chemical reaction occurred between rubber and modified kaolin with evolution of low molecular weight byproducts. 5.2 CONCLUSION Inert structure of rubber grade kaolin was activated through an ion-exchange reaction to match active tillers in their reinforcing capability. It was suggested that treatment of kaolin with basic organic compounds dissociated into complex ions containing amine, carboxyl and hydroxyl functional groups in aqueous medium, facilitated rubber-tiller interaction owing to better compatibility and grafting of rubber polymer to the tiller surface. Physico-mechanical properties of rubber compounds extended with activated kaolin showed definite improvement in performance characteristics, confirming that modification of kaolin with selected compounds was effective. 67 C H A P T E R 6 6. SUGGESTIONS AND FUTURE RECOMMENDATIONS 1. As Monoethanol amine performed the ability of accelerating the curing rate and reducing the cure time, it can be tested as an accelerator for room temperature vulcanization 2. The filler concentration was only 30 parts per 100 parts of rubber in this study. It wil l be useful to continue this study to investigate the effect of modified filler concentration on properties of fdled rubber compounds and compare the variation in properties with properties of carbon black loaded compounds. 3. In addition kaolin has some sites occupied with anions, that can be involved in ion-exchange process also. So ion-exchange capacity of kaolin could be increased and investigation of this increment on properties of rubber would be interesting 4. Since Urea in water medium can be introduced to the kaolin surface it wil l be useful to study whether there is a possibility of any chemical synthesis, starting from urea, attached to kaolin surface so as to bind rubber to kaolin particles as well as kaolin particles distributed through rubber matrix in to continuous network of chemical bonds 5. Melamine formaldehyde, in its water soluble form can be used to treat kaolin also. It may display some useful effect on filled rubber compounds by means of carefully selected curing system. 68 6. Activity of Carbon black is normally attributed to large amount of COOH groups on its surface and if there is a possibility to introduce -CN groups to kaolin , that can be converted further chemically in to -COOH acting as pendent groups present in carbon black, activity of inert kaolin could be increased 7. As monoethanol amine being attached to kaolin surface accelerated cross linking the filled rubber, this fact is worth to be studied in details too. 8. Cation exchange capacity of kaolin varies, depending on physical modification. In this connection it would be useful to investigate effect of modified kaolins, of various cation exchange capacities on physico- mechanical properties of rubber. In spite of preliminary nature of obtained results the certain recommendations to rubber processing industry can be given from carried out research 1. As treatment of kaolin with selected compounds improves its distribution through out the rubber matrix, mixing cycle on two roll mills or in an internal mixer can be reduced significantly. 2. Treatment of kaolin improves tensile strength, abrasion resistance, flex cracking, and thermal stability of natural rubber based compounds. 3. Replacement value of kaolin to carbon black can be increased as some reinforcement will be brought by modification, that is of low cost. So introduction of modified kaolin will reduce cost of rubber compound. 69 V REFERENCES 70 1. Abstracts, Rubber chemistry and technology, Vol-70,1997. 2. Bikales..M&Menges,.0, Encyclopedia of polymer science and engineering. 1997.Vol 7 P.53-54.199-200 3. Billmeyer.P. W. Text book of polymer science 2 nd Ed: . Wiley- inter science : Division of John Wiley and sons .Inc. 1962 4. Blow. C M . & I lcpbur,.C, Rubber technology and manufacture 2 "'' Ed.. l ')87 5. Brown. R.P Physical testing of rubber. London : Applied rubber publishers Ltd. 1979. 6. Byers John, T." Silane coupling agent for enhanced silica performance" Rubber world. VolSl , 1998. P.38-42. 7. Chow ,T.S , "Tensile strength of filled polymers1'. Journal of polymer science and polymer physics Ed;20 1982 P. 2103-2109 S. Dai.J.C & HuangJ.T. "Surface modification of clay and clay rubber composite". Applied clay science. Vol. 15,1999,p.51 -65. (>. Danneberg, E.M " I he effect of surface chemical interaction on the properties of lillcr-rcin forced rubbers". Rubber chemistry and technology. Vol 48.1975 P 434- 442. 10. Goerl Udo, Hunschc Andrea, Mueller Arndt & Koban I l.g." Invcsigations into the silica/Silane Reaction system1' Rubber chemistry and tcchnology.Vo\ 70 1997.P.608-623. 11. (irim.R.E. Clay mineralogy. Mc Ciraw-Mill. 1968 12. .Ismail. I I , Ishiku ,U.S, Ishak .Z.A.M &. Freakley .P.K,"Thc effect o fa calionic surfactant ( Patty Diamine) and a commercial silane coupling agenl on the properties ol'a Silica III loci Natural rubber compound," /-,'///•*>/><•