51 
POSSIBL : ROLE OF SOAP STRENGTH ON MECHANICAL 
STABILI1 Y AND OTHER PROPERTIES OF LOW QUALITY 
LA-T2 NATURAL RUBBER LATEX CONCENTRATE 
by 
Kodikara Manjula Dilkushi Silva 
This dissertatioi was submitted to Department of Chemical and Process Engineering 
of the University of Moratuwa in partial fulfillment of the requirement for the Degree 
of Master of Science in Polymer Technology 
Department of Chemical and Process Engineering MM TfieS'S colj. 
University of Moratuwa 
Sri Lanka 
November, 2003 
University of Moratuwa 
79562 I! IlIIIIIIIII 
79562 
DECLARATION 
I hereby declare that this submission is a result of a work carried out by me and to the 
best of my knowledge, it contain no material previously written or published by 
another person nor material which has been accepted for the award of any degree or 
acceptable qualification of a university, or other Institute of higher learning, except 
where the due reference to the material is made. 
K.M.D.Silva 
November 2003 
I 
ABSTRACT 
Ever-growing impact of rubber and its products form an inseparable and integral part 
in human life. But today, rubber industries suffer from lack of quality latex for 
production. Over the last few decades, various efforts have been carried out to study 
the ability of Fatty Acid soaps to enhance stability of latex upon mechanical forces. 
However, an investigation has never been carried out in Sri Lanka on property 
variation of low quality latex upon soap addition. This study was undertaken with the 
view to fulfill this requirement. Current study consists of determination of MST and 
other properties of low quality latex and brief investigation on anti foaming 
behaviour of phenol on latex base. 
Latex was obtained with absence of added soap on a special request from centrifuge 
plant of Lalan group. They were collected from small holders of Matale, which 
represents the non-specific climatic conditions for latex production. Soap was added 
in different strengths at different maturity times. Following properties were 
investigated at intervals: MST, KOH number, Viscosity. Foaming Height, and 
Conductivity. Anti-foaming behaviour of phenol on latex base was determined. 
Results of this study provide information of low quality latex upon soap addition and 
aging. Out of entire investigated properties response to the soap was remarkable in 
MST and Foaming Height upon aging. Viscosity showed great variation within 3 
weeks maturation. Prevalence of soap was critical between soap levels of4.2xl0" 4 and 
5.0x10"4 moles per lOOg of latex. Results suggest that the system attain to critical 
micelle concentration within this range. 
Minimum soap level that is necessary to create observable change in MST and 
Foaming Height lies between 0.5x10"4 and 0.84x10"4 moles perlOOg latex. Soap level 
of 0.5x10"4 makes great variations in Viscosity, Conductivity and KOH No. Effect of 
soap on Conductivity and KOH No diminishes after 8.41x1 0"'1 moles of soap. Both 
I I 
properties are responsible for the total molecules that are present in the ionized form 
and not the total molecules in the medium. Since, the soap effect upon KOH No 
diminishes after certain soap level it cannot be used as an identification of soap 
addition to latex. However added soap can be identified by variation in the Foaming 
Height. Significant relationship between soap addition and foaming height reveals 
that the foreign soap molecules increase the froth formation in latex. 
Phenol addition can reduce the foaming in latex. But it reduces the MST of the latex 
and hence detrimental for the quality of latex. 
Variation in MST and Viscosity by deliberate soap addition primarily causes by Fatty 
Acid soap ions that are adsorbed at the particle surfaces. Variations in KOH No, 
Conductivity and Foaming Height has brought about by consequent changes taking 
place in the medium. 
Ill 
ACKNOWLEDGEMENT 
I wish to express my deepest gratitude to my supervisor, to whom I am deeply 
indebted, Dr Shantha Walpolage, the Head of Polymer Division, Department of 
Chemical and Process Engineering, University of Moratuwa. His attentiveness and 
interest in this study, creditable assistance, advice and criticism have motivated me 
immensely and guided me on the pathway to the successful completion of this work 
within specified time period. 
I would like to express my deep gratitude to staff members of the Lalan group and 
profoundly extend my appreciation to Dr. Kithsiri Dissanayaka, Head of the Earth 
Resources, University of Moratuwa, for his kind assistance in granting me to carryout 
certain practical in his departmental premises. 
I would like to acknowledge Dr. Gamini Senevirathna, Deputy Director General, 
Rubber research Institute for granting permission to carryout this project in their 
institute premises and to the staff members and technical officers of Rubber Research 
Institute Ratmalana for their kind corporation. 
I express my deep gratitude to Mrs.Shantha Maduwage, Department of Chemical and 
Process Engineering, University of Moratuwa, for her kind corporation. I further 
extend my deep gratitude to Dr. (Mrs.) Padma Amarasinghe, Head of the Department 
of Chemical and Process Engineering, University of Moratuwa, all academic staff and 
the laboratory staff of the department for their support in numerous ways, for which I 
will always be thankful. I will indebted to Asian Development Bank for granting 
financial assistance for the course of study. ' 
Last but not least I acknowledge with heartiest gratitude to my husband Manoj 
Kumara, my parents, sister, brother and friends who supported me in numerous ways. 
IV 
TABLE OF CONTENTS 
Declaration 
Abstract 
Acknowledgement 
Table of contents 
List of Tables 
List of Figures 
List of Abbreviations 
CHAPTER 1 - INTRODUCTION 
1.1 Background Motivation 
1.2 Aims and Objectives 
CHAPTER 2 - LITERATURE REVIEW 
2.1 Historical background of Latex Production 
2.2 Natural Rubber Latex 
2.2.1 NRL is a living pharmaceutical factory 
2.2.2 NRL and the greenhouse effect 
2.2.3 Significance of NRL in other areas 
2.3 Definition of latex 
2.3.1 Constituents in NRL 
2.4 Stability of a colloidal system 
2.4.1 Destabilization 
2.4.2 Mechanisms of destabilization 
2.4.2.1 Chemical destabilization 
2.4.2.2 Physical destabilization 
2.5 Characteristic properties of NRL 
2.5.1 Mechanical Stability of Natural Rubber Latex 
2.5.2 KOH No of natural rubber latex 
2.5.3 VFA No of natural rubber latex 
2.5.4 Conductivity of NR latex 
2.5.5 Viscosity of NR latex 
2.6 Preservation 
2.6.1 Superiority of LATZ system as a preservative 
2.7 Concentration of NRL 
2.8 Stabilizing additives 
2.9 Possible role of Soap on NRL 
CHAPTER 3 - METHODOLOGY 
3.1 Determination, organization and preparation of principal requirements 
3.1.1 Selection of Latex Type 
3.1.2 Preparation of ammonium laurate soap solution and other 
chemicals 
3.1.3 Preparation of latex samples by varying concenlration 
and length of maturation 
3.2 Study of the role of ammonium laurate soap on the property 
variation in latex with aging and concentration 
3.2.1 Determination of MST 
3.2.2 Determination of KOH No 
3.2.3 Determination of Viscosity 
3.2.4 Determination of Foaming Height 
3.2.5 Determination of Conductivity 
CHAPTER 4 - RESULTS AND DISCUSSION 
4.1 Role of fatty acid soap on the properties upon aging 
4.1.1 Response to the MST 
4.1.2 Response to the KOH No 
4.1.3 Response to the Viscosity 
4.1.4 Response to the Foaming height 
4.1.5 Response to the Conductivity 
4.2 Prevalence of properties over strength of soap 
4.2.1 Prevalence of MST 
4.2.2 Prevalence of KOH No 
4.2.3 Prevalence of Viscosity 
4.2.4 Prevalence of Foaming Height 
4.2.5 Prevalence of Conductivity 
4.3 Variation in MST with soap addition over varying length of 
maturation time 
4.3.1 Soap addition after one week maturation 
4.3.2 Soap addition after Two weeks maturation 
4.3.3 Soap addition after Four weeks maturation 
4.4 Behaviour of phenol on latex base 
4.4.1 Influence upon MST 
4.4.2 Influence upon Conductivity 
4.4.3 Influence upon Foaming Height 
4.5 Effect of phenol in highly concentrated soap added latex on MST 
CHAPTER 5 - CONCLUSION 
5.1 Conclusion 
5.2 Future recommendations 
APENDICES 
Appendix A Working Plan 
Appendix B Role of fatty acid soap on the properties 
upon aging 
Appendix C Prevalence of properties over strength o f soap 
Appendix D Variation in MST with soap addition over 
varying length of maturation time 
Appendix E Behaviour of phenol on latex base 
REFERENCES 
LIST OF TABLES 
Page No. 
Table 1-Typical composition of field latex 10 
Table 2- Properties of the latex 25 
Table 3- Samples prepared to investigate property variation with 
storage time. 28 
Table 4- Samples prepared to investigate properties with varying soap 
concentrations. 29 
Table 5- Samples investigated for MST, KOH No, Viscosity, Foaming 
Height and Conductivity upon maturation. 29 
Table 6- Samples investigated for effect of soap concentration upon MST, 
KOH No, Viscosity, Foaming Height and Conductivity 30 
Table 7- Samples investigated for MST with soap addition over varying 
maturation time 30 
Table 8- Samples investigated for effect of phenol addition upon MST, 
Foaming Height and Conductivity with soap and phenol 
and soap concentration 31 
Table 9- Samples investigated for effect of phenol addition 
upon MST 31 
VIII 
LIST OF FIGURES 
Page No. 
Figure 1. Effect of fatty acid soap addition on Mechanical Stability 
Time upon maturation of LA-TZ latex ' 36 
Figure 2. Effect of fatty acid soap addition on KOH number 
upon maturation of LA-TZ latex 40 
Figure 3. Effect of fatty acid soap addition on Viscosity 
upon maturation of LA-TZ latex 43 
Figure 4a. Effect of fatty acid soap addition on Foaming Height 
upon maturation of to LA-TZ latex 45 
(Measurements taken at 25 seconds) 
Figure 4b. Effect of fatty acid soap addition on Foaming Height 
upon maturation of LA-TZ latex 45 
(Measurements taken at 60 seconds) 
Figure 5. Effect of fatty acid soap addition on Conductivity 
upon maturation of LA-TZ latex 47 
Figure 6. Effect of level of fatty acid soap addition after two weeks of 
collection upon mechanical stability of LA-TZ latex 49 
Figure 7. Effect of level of fatty acid soap addition after two weeks of 
collection upon KOH Number of LA-TZ latex 52 
Figure 8. Effect olTevelof fatty acid soap addition after two weeks of 
collection upon Viscosity of LA-TZ latex 54 
Figure 9. Effect of level of fatty acid soap addition after two weeks of 
collection upon Foaming Height of LA-TZ latex 56 
Figure 10. Effect of level of fatty acid soap addition after two weeks of 
collection upon Conductivity of LA-TZ latex 57 
Figure 11. Fatty acid soap addition to one week matured LA-TZ latex 
and its effect on mechanical stability 59 
Figure 12. Fatty acid soap addition to four weeks matured LA-TZ latex 
and its effect on mechanical stability 61 
Figure 13. Influence of phenol and combination of phenol and soap 
addition on MST of LA-TZ latex upon maturation 62 
IX 
Figure 14a. Influence of phenol and combination of phenol and 
soap addition on Foaming I lcight of LA-TZ hi lex 
upon maturation (Measurements taken at 25 seconds) 
Figure 14b. Influence of phenol and combination of phenol and soap 
addition on Foaming Height of LA-TZ latex upon 
maturation (Measurements taken at 25 seconds) 
Figure 15. Influence of phenol and combination of phenol and soap 
addition on Conductivity of LA-TZ latex upon maturation 
LIST OF ABBREVIATIONS 
Ca - Calcium 
C 0 2 - Carbon Dioxide 
C0 3 " 2 - Carbonate ion 
cp(s) - Centipoises 
DRC - Dry Rubber Content 
FA(s) - Fatty Acid(s) 
F.H - Foaming Height 
HA - High Ammonia 
HCO3" - Bicarbonate ion 
HFA - Higher Fatty Acid(s) 
Int'l - International 
IRSG - International Rubber Study Group 
LA - Low Ammonia 
LATZ - Low ammonia latex preserved with ZnO a n d TMTD 
K/K + - Potassium/Potassium ion 
KOH No - Potassium Hydroxide number 
Mg/Mg 2 + - Magnesium/Magnesium ion 
MRPRA - Malaysian Rubber Producers Research Association 
MST - Mechanical Stability Time 
MS - Mechanical Stability 
mS - Milliseiman 
No - Number 
Na/Na + - Sodium/Sodium ion 
NCRT - National College of Rubber Technology 
NH4OH - Ammonium Hydroxide 
NRL - Natural Rubber Latex 
0 2 - Oxygen 
RRIM - Rubber Research Institute of Malaysia 
VFA - Volatile Fatty Acid 
TMTD - Tetra Methyl Thiuram Disulphide 
TSC - Total Solid Content 
ZnO - Zinc Oxide 
XI