3 * 
A Study of Natural Rubber Latex - Filler Interaction 
By 
Clement Namal PERIS 
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 j c j e n c e in Polymer^Science and Technology. 
Univers i ty of M o r a t u w a 
82711 
Department of Chemical and Process Engineering, 
University of Moratuwa, 
Sri Lanka. 
April, 2004 6 2 7 I 
8 2 7 1 1 
ii 
1. Dec la ra t ion by the cand idate 
I certify that this thesis does not encompass without acknowledgement any material 
previously submitted for the consideration of a Degree or Diploma in any University. Also, to 
the best of my knowledge and belief it does not contain any material previously published, 
written or communicated by any means by another person, institution or an organization 
except where the due reference is made. 
Clement-Ntrnal PERIS 
2. A t tes ta t ion by the Superv isors 
To the very best of our knowledge, the above particulars, mentioned by the candidate are true 
and correct. 
Senior Lecturer. Senior Lecturer, 
Dept of Chemical and Process Engineering, 
University of Moratuwa, 
Dept. of Material Engineering, 
University of Moratuwa, 
Sri Lanka. Sri Lanka 
in 
Abstract of the study 
An attempt has been made to evaluate natural rubber latex - filler interaction. 180°-peel test 
of flexible to rigid joints was performed to determine the peel strength of natural rubber latex 
-kaolin joints in order to evaluate the interaction of natural rubber latex with standard rubber 
grade kaolin and activated one by ion exchange reaction with amino -functional derivatives. 
Experimented natural rubber latex compounds were pre vulcanized with sulphur and 
ionization radiation. Radiation vulcanization was performed using 6 0 Co source irradiator, 
originally designed for sterilization of medical products, with reduced gamma rays dose rate. 
Its suitability for radiation vulcanization of locally produced natural rubber latex was 
confirmed experimentally. 
Obtained results showed that the peel off test device was acceptable for evaluation of natural 
rubber latex -filler interaction irrespective of the vulcanization system used with latex 
compound. Peel test results displayed the influence of modified fillers on the peel strength 
values of tested laminates. Increased peel strength values of the samples containing modified 
kaolin were attributed to better interaction of the filler with rubber polymer. 
It was investigated, that facilitated interaction observed with natural rubber latex and modified 
kaolin resulted in improved properties of filled natural rubber latex compounds of both 
vulcanization system, and irradiated one was more susceptible within the experiment 
performed. Preference in mechanical stability time, viscosity factor and tensile was given to 
radiation vulcanization natural rubber latex (RVNRL). 
Reinforcing effect of modified filers in natural rubber latex compounds was lower of that 
observed earlier with dry rubber compounds. The reason for it could be associated with partial 
deactivation of the active centres initially brought by modification the phenomenon that have 
to be studied and overcome in the future. However, it is hoped that carried out research 
positively contributes to the understanding the mechanism of reinforcement of rubber 
polymers with fillers and development of the technologies upgrading cheap local mineral 
resources to use them more beneficially in natural rubber formulation technology. 
Another aspect covered by research related to development of radiation vulcanization 
technology that gives a definite support for introduction to local latex based manufacturing 
industries. 
iv 
Acknowledgements 
It is with a great honour and pleasure, I wish to pay my gratitude to my immediate 
supervisors, Dr. (Ms.) Olga Gunapala and Dr. P.Y. Gunapala in giving their fullest support, 
assistance, guidance and encouragement to make this study project a successful. Also, I 
mention with a great respect that the comments and suggestions given by Dr. Shantha 
Walpolage, the M. Sc. (Polymer Science and Technology) course coordinator effected greatly 
to make this project a successful up to this extent. 
It would be a difficult task if the colleagues of my working place, specially at the quality 
control (compounding) laboratory at Ansell Lanka Pvt. Ltd., where the study was done, did 
not give their fullest cooperation, express their valuable views, forward constructive critics 
and important suggestions in this connection. Thus, I honour and appreciate their friendly 
assistance.Also, I wish to offer special thanks to Comrade Nishantha S. Perera ,designer, in 
assisting me to complete the diagrams where they were necessary. 
Every emblem certifying my relative success, whatever it is, reflects the precious love of my 
parents that they showed me without any lack in all the time. 
CNP 
C o n t e n t s 
Page numbers 
Chapter 1 - Introduction to the Study 1 -4 
1.1 Introduction 1 
1.2 Objective of the Research 4 
Chapter 2 - Literature Review 5 - 3 8 
2.1 Introduction to reinforcement 5 
2.2 Factors influencing reinforcement 5 -7 
2.3 Types of Fillers 7 
2.3.1 Carbon black 8 
2.3.2 Silica 8 
2.3.3 Silicate Minerals 9 
2.3.4 Kaolin and its Structural Chemistry 9-10 
2.3.5 Cation exchange of Kaolinite 10-11 
2.4 Fillers in latex formulation technology 1 2 - 2 1 
2.4.1 Filled latex compounds for carpet applications 1 4 - 1 6 
2.4.2 Fillers in latex based adhesives 1 6 - 1 8 
2.4.3 Latex based paints 1 8 - 1 9 
2.4 4 Moulded latex foams 19 
2.4.5 Moulded goods 2 0 - 2 1 
2.5 Radiation Vulcanization of Natural Rubber Latex (RVNRL) 22 - 25 
2.5.1 Absence of nitrosoamines 22 - 23 
2.5.2 Very low cytoxicity 
2.5.3 Low emission of SO2 and less formation of ashes 24-25 
2.5.4 Higher degree of transparency and softness 25 
v 2.5.5 Degradability 25 
2.6 Materials for the preparation of RVNRL 
2.6.1 Sensitisers 
2.6.2 Polyfunctional monomers 
2.6.3 Monofunctional monomers 
2.6.4 Latex 
2.7 The mechanism of RVNRL 
2.8 Radiation vulcanisation process 
Chapter 3 - Experimental methods, materials and conditions 
3.1 Experimental Objectives 38 
3.2 The materials and other conditions 
3.2.1 Latex 
3.2.2 Toluene 
3.2.3 Hydroxyetyl cellulose 
3.2.4 Fabric 
3.2.5 Sulphur dispersion 
3.2.6 Activated kaolin 
3.2.7 Sensitiser 
3.2.8 Ammonia solution 
3.3 Preperation of kaolin slurry 
3.4 Preparation of sulphur cross-linked type pre-vulcanized 
natural rubber latex compounds 
3.5 Preparation of RVNR latex 
3.6 Dosimeters 
3.7 Testing the characters of two vulcanization systems of 
kaolin and latex 
3.8 Measurement of pH 
V I I 
3.9 Measurement of MST 52 
3.10 Determination of Total Solid Content 52 
3.11 Measurement of viscosity 53-54 
3.11.1 Viscometers 53-54 
3.12 Investigating of tensile properties of the vulcanisates 55 
3.13 Measurement of swelling ratio 55 
3.14 Preparation of applicable specimens for the peel test device 56-57 
3.15 Special devices used in the study - Peel test device 57-58 
3.16 Testing of the specimen in the normal environment under static weight 58 
3.17 Evaluating the suitability of the 6 0 Co irradiator for the production 
of RVNR latex with locally produced natural rubber latex 59 
C h a p t e r 4 - Results a n d Ca l cu la t i ons 60- 72 
4.1 Test results performed to find out the suitability of 6 0 Co 
irradiation facility in the production of RVNR latex with locally produced 
natura l r u b b e r latex 60-63 
4.2 Peel - test results 64- 67 
4.3 Test results on physico-mechanical properties of 
tilled natural rubber latex 68-72 
C h a p t e r 5- Ana lys i s o f the Resul ts a n d Discussion 73-97 
5.1 Discussion of the results on the establishment of suitability of 
h
" Co irradiation facility at reduced gamma ray dose rate for 
radiation vulcanization of locally produced NRL 73 
5.1.1 Effect of irradiation dose on properties of RVNR latex 73-75 
5.1.2 Effect of concentration of sensitiser n-BA on properties of RVNR latex 75-79 
5.2 Discussion of the peel strength test results 80-85 
5.3 Effect of modified fillers on properties of irradiated and 
sulphur vulcanised natural rubber latex 86-94 
5.3.1 Percentage modulus of the RVNR latex vulcanisates 94-97 
VI11 
Chapter 6- Conclusion of the study 
6.1 Conclusions 
98-101 
98 
6.2 Conclusion on the study of possibility of use of 
low gamma ray dose rate 6 0 Co irradiator for 
radiation vulcanization of natural rubber latex 
6.3 Conclusion on evaluation of natural rubber latex - filler interaction 
based on peel test of latex - kaolin laminated samples 
98 
99-100 
6.4 Conclusion on the study of the effect of 
natural rubber latex - filler interaction on properties of 
irradiated and sulphur vulcanized natural rubber latex 100-101 
Chapter 7- Recommendations and Suggestions for Further Developments 102-105 
7.1 Ability of manufacturing the RVTMR latex barrier products 
using modified kaolin as non- reinforcing filler 102-103 
7.2 Further developments to the research 103 
7.3 Recommendations 103-105 
Appendix 1- Technical data of Kaolin 106 
Appendix 2- Measuring mechanical properties of vlkanisates 
with a tensile piece of dog bone shape. 
107-108 
Appendix 3 -Irradiation process 109-111 
Appendix 4 - Recommended antioxidants to use in RVNRL process 112 
Appendix 5 - Viscosity measurements 113 
References 114-116 
List of Figures 
C h a p t e r 1- nil 
C h a p t e r 2 
Figure 2 .1 : A model representing kaolinite crystals 10 
Figure 2.2: Schematics of kaolin platelet 11 
Figure 2.3: Comparison of sensitizing efficiency of various sensitizers 29 
Figure 2.4: Sensitizing effect of MFM 30 
Figure 2.5: Sensitizing efficiency of n - BA on R V N R L 31 
Figure 2.6: A Structure of cross- l inks of N R with n- BA 35 
Figure 2.7: Rate of hydrolysis of n- BA 36 
Figure 2.8: Effect of the rate of radiation on Dv and maximum Tb 37 
C h a p t e r 3 
Figure 3.1 : Line diagram of the laboratory scale ball mil l 43 
Figure 3.2: The setup and the electrical circuit diagram of the heat supplier 47 
Figure 3.3: Diagram of showing the basic components of Brookfield viscometer 54 
Figure 3.4: Line diagram of Zahn cup viscometer 54 
Figure 3.5: Test specimen of lax - kaolin laminate 56 
Figure 3. 6: Peel off test device used in the study 57 
C h a p t e r 4 - nil 
C h a p t e r 5 
Figure 5.1.1 : Effect of irradiation dose on tensile strength of irradiated samples 73 
Figure 5.1.2 : Effect of irradiation dose on elongation at break of R V N R latex 74 
Figure 5.1.3: Effect of irradiation dose on swelling index of irradiated samples 74 
Figure 5.1.4: Effect of concentration of n-BA on tensile strength of R V N R latex 75 
Figure 5.1.5 : Effect of concentration of n-BA on elongation at break of R V N R latex 76 
X 
Figure 5.1.6: Effect of concentration of n- BA on swelling index of 
irradiated samples 76 
Figure 5.1.7: Tensile strength of sulphur vulcanised and irradiated samples 77 
Figure 5.1.8: Elongation at breaks of irradiated and sulphur vulcanised samples 77 
Figure 5.1.9: 300 % modules of irradiated and sulphur vulcanised samples 78 
Figure 5.1.10: 500% Modules of irradiated and sulphur vulcanised samples 78 
Figure 5.1.11: Swelling index of irradiated and sulphur vulcanised samples 79 
Figure 5.2.1: Peel stress versus peel speed for RVNR latex -unmodified 
kaolin laminated units 80 
Figure 5.2.2: Peel stress versus peel speed for RVNR latex -modified 
kaolin laminated units 81 
Figure 5.2.3: Peel stress versus peel speed for the sulphur vulcanized 
natural rubber latex -unmodified kaolin laminated units 82 
Figure 5.2.4: Peel stress versus peel speed for sulphur vulcanized 
natural rubber latex - kaolin laminated units 83 
Figure 5.3.1: Viscosity of sulphur vulcanised natural rubber latex 
compounds filled with modified and unmodified kaolin 86 
Figure 5.3.2: Viscosity of the RVNR latex tilled with modified 
and unmodified kaolin 88 
Figure 5.3.3: Mechanical stability time of natural rubber latex 88 
Figure 5.3.4: Tensile strength of sulphur vulcanized natural rubber latex samples 90 
Figure 5.3.5: The column graph showing the elongation at break of 
sulphur vulcanised natural rubber latex samples 90 
Figure 5.3. 6: A graph of showing 300 % modulus of sulphur vulcanised samples 91 
Figure 5.3.7: A graph showing 500 % modulus of sulphur vulcanised 
natural rubber latex samples 91 
Figure 5.3.8: Swelling index values of natural rubber latex vulkanisates 92 
Figure 5.3.9: Tensile strength of irradiated samples 93 
Figure 5.3.10: Elongation at break of unfilled and filled RVNR latex 94 
Figure 5.3.11: 300 % modules of RVNR latex samples 94 
Figure 5.3.12: 500 % modules of RVNR latex samples 95 
Figure 5.3.13: Swelling index values of RVNR latex vulkanisates 95 
Chapter 6 - nil 
« Chapter 7 - nil 
Appendix 2: Figure A- 2.1: Illustration of a typical dog bone sample 107 
Appendix 3: Figure A-3.1: Irradiator set up 110 
Figure A-3.2: Irradiator plan 111 
> 
X l l 
List of Tables 
C h a p t e r 1 - N i l 
C h a p t e r 2 
Table 2. I: Clay slurry composition 12 
Table 2.2: Pyrophyllite slurry composition 13 
Table 2.3: Typical composition of talc slurry 13 
Table 2.4: Typical composition of Natural latex based adhesive 16 
Table 2 5: Composition for fixing ceramic tiles 17 
Table 2.6: Effect of filler addition 17 
Table 2.7: Effect of different polymer/polymer/filler ratios 19 
on some foam properties 
Table 2.8: Typical composition for casting the rigid model in plaster moulds 20 
Table 2.9: Composition for making flexible casting 21 
Table 2.10: Heat sensitive composition. 21 
Table 2.1 1 :Combustion analysis of 
latex gloves vulcanized under different conditions 25 
C h a p t e r 3 
Table 3.1: Specifications of the latex used for the study 39 
Table 3.2: Specifications of toluene used 40 
Table 3.3: Technical and physical data of sulphur dispersion used 41 
Table 3.4: Formulation of the control sample 45 
Table 3.5: Formulation of NR latex compound filled with unmodified kaolin 45 
Table 3.6: Formulation of natural rubber latex compound 
filled with modified kaolin 46 
Table 3.7: Formulation of the test ample for the preparation of RVNR latex 49 
Table 3.8: Formulation for RVNRL with unmodified kaolin 50 
Table 3.9: Formulation for RVNRL with modified kaolin 50 
X l l ! 
Table 3.10: The types of latex -kaolin laminates 57 
Table 3.11: Components of the laminated test samples 
for peel-off experiment 58 
C h a p t e r 4 
Table 4.1.1: Properties of RVNR latex compounds 60 
Table 4.1.2: Properties of control sulphur vulcanization natural rubber latex 61 
Table 4.1.3: Effect of concentration of n-BA on tensile properties of 
RVNR latex films 61 
Table 4.1.4: Effect of concentration of n-BA on 
percentage swell of RVNR latex films 62 
Table 4.1.5: Effect of absorbed dose rate on tensile properties of 
RVNR latex 62 
Table 4 .1.6: Effect of absorbed dose rate on percentage swell of 
RVNR latex films 63 
Table 4.1.7: Properties of controlled sulphur vulcanized 
natural rubber latex sample 63 
Table: 4.2.1 Results of peel-test of 
RVNR latex film-unmodified kaolin laminated units 64 
Table 4.2.2: Results of peel-test of 
RVNR latex film - modified kaolin laminated unit 64 
Table 4.2.3: Results of peel-test of sulphur vulcanized 
natural rubber latex film -unmodified kaolin laminated units 65 
Table 4.2.4: Results of peel-test of sulphur vulcanized 
natural rubber latex film - modified kaolin laminated units 65 
Table 4.2.5:Peel stress and peel speed, at which RVNR latex film 
was peeled off from unmodified kaolin ground 66 
Table. 4.2.6:Peel stress and peel speed, at which RVNR latex 
film was peeled off from modified kaolin ground 66 
Table 4.2.7:Peel stress and peel speed, at which sulphur vulcanized 
natural rubber latex film was peeled off from 
unmodified kaolin ground 67 
Tables 4.2.8:Peel stress and peel speed, at which sulphur vulcanized 
natural rubber latex film was peeled off from 
modified kaolin ground 67 
X I V 
Table 4.3.1:Properties of RVNR latex compounds, 
tilled with unmodified kaolin 68 
Table 4.3.2:Properties of RVNR latex compounds, 
filled with modified kaolin 69 
Table 4.3.3:Properties of sulphur vulcanization natural rubber 
latex compounds, filled with unmodified kaolin 69 
Table 4.3.4:Properties of sulphur vulcanisation natural rubber 
latex compounds filled with modified kaolin 70 
Table 4.3.5:Results of Tensile test of RVNR latex films 
filled with unmodified and modified kaolin samples 71 
Table 4.3.6:Results of tensile test of sulphur vulcanized 
natural rubber films filled with unmodified and modified kaolin 71 
Table 4.3.7:Swelling index values of RVNR latex films 
tilled with unmodified and modified kaolin 72 
Table 4.3.8:Swelling index values of sulphur vulcanized natural rubber latex 
films filled with unmodified and modified kaolin 72 
C h a p t e r 5 -
Table 5.1 : Peel strength values of natural rubber latex - kaolin laminated units 
C h a p t e r 6 -Ni l 
C h a p t e r 7 -Nil