I N C O R P O R A T I O N O F A C T I V A T E D C A R B O N 
IN N A T U R A L R U B B E R L A T E X F O A M 
F O R I M P R O V E M E N T IN S O R P T I O N P R O P E R T Y 
A dissertation submitted as partial fulfillment of the requirements for the 
award of the degree of MASTER OF SCIENCE in Polymer Technology, 
University of Moratuwa. 
Department of Chemical and Process Engineering 
University of Moratuwa 
Sri Lanka. 
BY 
A. R. M. RAJAKAR UNA 
May 2006 
87134 
8 7 1 3 4 
DECLARATION 
I certify that this dissertation does not incorporate without any acknowledgement any 
material previously submitted for a Degree or a Diploma in any University or Institution 
and to the best of my knowledge and belief it does not contain any material previously 
published or written by another person except where due references are made in the text. 
A. R. M. Rajakaruna 
Approved for submission 
Dr. Shantha Walpolage 
Course Coordinator - M.Sc in Polymer Technology, 
Senior Lecturer, 
Department of Chemical and Process Engineering, 
Faculty of Engineering, 
University of Moratuwa. 
ii 
ACKNOWLEDGEMENT 
I wish to express my heartfelt gratitude to Dr. Shantha Walpolage, the Course 
Coordinator - MSc in Polymer Technology, University of Moratuwa, as well as my 
project supervisor, for providing me the guidelines and the necessary facilities to carry 
out this research study. I acknowledge with deepest gratitude for his constant guidance, 
timely advice and consultative encouragement extended to me throughout the study. 
I am indebted to my employer, Mr. Rohana Silva, former General Manager - Richard 
Pieris Natural Foams Ltd, Biyagama and Arpico Natural Latexfoams Ltd, Avissawella, 
sanctioning me leave and providing facilities to follow the M S c in Polymer Technology 
course. 
I owe a sense of gratitude to Mr. Wasantha Abeysirigunawardena, General 
Manager - Group Research and Development, R & D Centre, Richard Pieris and 
Company, for providing me the opportunity to carry out this research study successfully 
and backing me up with advice, suggestions and assistance whenever I needed. 
My sincere thanks should also go to Manjula, Susantha and Chandika at Arpico Natural 
Latexfoams Ltd for their kind assistance given to me to carry out laboratory testing and 
experimental work. I would also like to thank Lelwela, Indika and the technical staff of 
R & D Centre, who helped me in many ways. 
I wish to record my sincere appreciation for the assistance given by Mr. Sisira de Silva, 
Mr. Hemachandra and the technical staff of Latex laboratory of Chemical and Process 
Engineering department, University of Moratuwa. 
I wish to thank J.B Activators, Silvermill Group and Heycarb International for providing 
me with samples of activated carbon free of charge to carry out this study. 
Last but not least, I would like to dedicate a very special word of thanks to my late father, 
my mother, my husband Rasika and my parents-in-law for being with me throughout the 
study. 
iii 
ABSTRACT 
Natural Rubber (NR) latex is a colloidal dispersion of N R polymer which is 
predominantly cis 1,4 -Polyisoprene in an aqueous medium. Various chemicals are added 
to N R latex mainly as dispersions, at compounding stage to enhance processing 
characteristics and to obtain desired properties of the final product. The properties of 
chemicals in dry form or as dispersions are critical for latex compounding for 
maintaining the overall colloidal stability of the latex mix. Addition of chemical 
dispersions into latex for compounding are basically governed by particle or droplet size, 
physical nature, viscosity, pH and stability of the dispersion. Hence, properties of raw 
materials (compounding chemicals) are very important for making good dispersions for 
latex compounding and producing desired latex products. 
In this study, an attempt was made to use activated carbon as a compounding ingredient 
to enhance the sorption properties of N R latex foam product. From this study it was 
found that activated carbon powder which had particle size below lOp. and pH (in 1% 
solution) having a basic pH or a p H towards neutrality can be made to a stable dispersion 
of 3 6 % Total Solids Content by ball milling for 18 hours in the presence of a dispersing 
agent. This dispersion had proper dispersion characteristics such as low particle size (3p.), 
a p H greater than 7 and low viscosity value. From mechanical and chemical stability 
studies on latex compound, it was found that up to 2 .0% (on dry weight of latex) of 
activated carbon, the latex compound had good mechanical and chemical stability. At 
2 .0% activated carbon, the cellular structure of the foam was satisfactory. From physical 
property testing of foam with activated carbon on compression set and tensile strength, it 
was found that good foam properties were obtained with the chemical formula for 
opt imum vulcanizing condition consisting of phr 2.55 Sulphur, 1.10 ZDC and 0.85 
Z M B T . 
The results of sorption property investigations of this study reveal that N R latex foam 
with 2 .0% activated carbon has a significantly higher sorption property compared to 
standard N R latex foam. Therefore, activated carbon can be incorporated to a N R latex 
compound in dispersion form at 2 .0% dosage to produce a latex foam pil low having 
higher sorption property. 
iv 
CONTENTS 
Page 
Declaration ii 
Acknowledgement iii 
Abstract iv 
List of tables viii 
List of figures xi 
List of abbreviations xiii 
I N T R O D U C T I O N 
1.1 Natural Rubber (NR) latex foam 1 
1.2 Activated carbon and latex foam 3 
1.3 Objectives of the project 3 
L I T E R A T U R E R E V I E W 
2.1 Latex 5 
2.2 N R Latex 5 
2.3 Manufacture of N R latex foam 7 
2.4 Activated carbon 25 
2.5 Method of approach for developing N R latex foam with 
activated carbon 32 
2.6 Method of incorporation of activated carbon into N R latex 
compound 33 
2.7 Uses of activated carbon in N R latex foam 33 
3.0 E X P E R I M E N T A L D E S I G N 
3.1 An outline of the proposed experimental design 35 
3.2 Testing of activated carbon powder 36 
3.3 Methods of preparation of activated carbon dispersion 37 
3.4 Preparation of activated carbon dispersion with max imum 
T.S .C% and investigation of dispersion properties 38 
3.5 Determination of the best activated carbon dispersion for 
making a stable N R latex compound 41 
3.6 Determination of the effect of dosage of activated carbon 
dispersion for making a stable foam from N R latex 45 
3.7 Optimizing the vulcanizing system 48 
3.8 Production of pil lows with activated carbon 50 
3.9 Investigation of sorption property of N R latex foam 
having activated carbon 52 
4.0 R E S U L T S A N D DISCUSSION 
4.1 Selection of activated carbon powder 54 
4.2 Preparation of activated carbon dispersion 55 
4.3 Properties of activated carbon dispersion with maximum 
T.S.C % 60 
4.4 Selection of best activated carbon dispersion at 3 6 % 
T.S.C in N R latex compound 63 
4.5 Effect of dosage of activated carbon for making a stable 
foam of N R latex 68 
vi 
4.6 Optimizing the vulcanizing system- chemical formulation 73 
4.7 Compression set and tensile strength values for pil lows with 
activated carbon 77 
4.8 Measurement of sorption property of N R latex foam having 
activated carbon 78 
5.0 C O N C L U S I O N S A N D S U G G E S T I O N S F OR F U T U R E W O R K 
5.1 Conclusions 80 
5.2 Suggestions for future work 80 
Appendix I 81 
Appendix II 82 
Appendix III 83 
Appendix IV 84 
List of references 
vii 
LIST OF TABLES 
Table No. Page 
2.1 A typical composition of field latex 6 
2.2 Composition of centrifuged latex concentrate 7 
2.3 A typical formulation for initial latex compound 16 
2.4 Formulation for second stage addition of chemicals for latex compound 16 
2.5 Formulation for addition of gelling agents for latex compound 17 
2.6 Solubilities and equilibrium pH values of various silicofluoride salts 20 
3.1 Different preparation methods of AC dispersion 3 8 
3.2 Formula for activated carbon dispersion preparation 39 
3.3 Formula for preparation of chemical dispersions for latex compounding 41 
3.4 Formula for 20% soap (potassium oleate) solution preparation 42 
3.5 A basic formulation for white latex compound 42 
3.6 Formula for latex compounds with varying AC dosages from S2-D 
dispersion 46 
3.7 Formulation for compound preparation with varying sulphur 48 
3.8 Formulation for compound preparation with varying ZDC 48 
3.9 Formulation for compound preparation with varying ZMBT 48 
3.10 Formulation for production of pillows with activated carbon 51 
3.11 Dimensions of foam pieces for sorption test 52 
4.1 Results related to raw material testing of different activated 
carbon samples 54 
viii 
4.2 Data related to different dispersion preparation methods for 
sample ID S-2 56 
4.3 Data related to different dispersion preparation methods for 
sample ID S-3 57 
4.4 Data related to different dispersion preparation methods for 
sample ID S-5 57 
4.5 Properties of AC dispersions with varying T.S.C% for sample ID S- 2 60 
4.6 Properties of AC dispersions prepared from selected raw material samples 62 
4.7 Data related to T.S.C% of basic latex compound (white) 63 
4.8 Data related to MST and pH of basic latex compound (white) 63 
4.9 Results related to coagulum formation test at 1% AC dosage 64 
4.10 Results related to MST test of latex compounds with different AC 
dispersions at 1 % dosage 64 
4.11 Results related to pH test of latex compounds with different AC 
dispersions at 1% dosage 65 
4.12 Results related to chemical stability test (gel time) of latex compounds 
with different AC dispersions at 1% dosage 65 
4.13 Data related to foaming height of latex compounds at partially foamed 
stage for different AC dosages 68 
4.14 Gel times of latex compounds having different AC dosages 69 
4.15 Data related to structure analysis of foam with varying dosages of AC 70 
4.16 Compression s e t % for each sample and average compression set % 
values for IS- 3S, ID- 3D, 1M - 3M and 1C-2C 74 
IX 
4.17 Average tensile strength values of foam of 1S-3S, 1D-3D, 1M-3M and C 75 
4.18 Compression set and tensile strength of 60D black pillows 77 
4.19 Weight of normal and black foam samples with time, in ammonia 
environment 78 
4.20 Percentage sorption values of normal white foam and black foam 78 
LIST OF FIGURES 
Figure No. Page 
2.1 Structure of isoprene (2-methyl-1, 3-butadiene) 5 
2.2 A rubber tree at tapping stage 5 
2.3 Various products of latex foam rubber (Mattress/ Pillow/ Sheet) 8 
2.4 Structure of Ss ring 12 
2.5 Chemical structure of ZDC 13 
2.6 Chemical structure of ZMBT 13 
2.7 Chemical structure of Ralox 14 
2.8 Chemical structure of DPG 15 
2.9 Oakes continuous mixer 18 
2.10 Foam filling into a mould 19 
2.11 Mattress washing 23 
2.12 Horizontal slitting of foam to produce sheets 24 
2.13 Schematic flow chart of Dunlop process of N R latex foam manufacture 24 
2.14 Schematic flow chart of activated carbon manufacturing process 26 
2.15 A view of pore structure of activated carbon - SEM view 1 28 
2.16 Pore structure of activated carbon under SEM view 2 28 
2.17 Surface chemistry of activated carbon - A summary of production 
methods of different activated carbon surfaces 29 
xi 
2.18 Carbon surface chemistry; Heteroatoms and groups commonly found in 
activated carbons 30 
2.19 Applications of activated carbons; (a) A water filter, (b) A cross section 
through a water filter, ( c ) A filter mask having activated carbon filters 3 1 , 3 2 
3.1 Dial type Brookfield viscometer 41 
3.2 Mechanical stability tester 44 
3.3 Test pieces for compression set test 49 
3.4 Test piece for tensile strength test 50 
3.5 Black foam test pieces for sorption test 52 
3.6 A simple set up for measuring the sorption ability of foam to ammonia 53 
4.1 Results related to viscosity variation of AC dispersions from sample 
ID S-2 at different target T.S.C% 60 
4.2 Results related to MST variation of latex compounds with different AC 
dispersions at 1% dosage 64 
4.3 Variation of chemical stability (gel times) in latex compounds with 
different AC dispersions at 1% dosage 65 
4.4 Variation of gel times with different AC dosages 69 
4.5 Photographs of different foam structures for black foam and 
standard white foam 70, 71 
4.6 Average compression set % for different sulphur/ accelerator systems 74 
4.7 Average tensile strength values of compounds IS to C 75 
4.8 A photograph of a complete pillow with activated carbon 75 
4.9 Variation of sorption percentages of normal and black foam 79 
xn 
LIST OF ABBREVIATIONS 
N R - Natural Rubber 
A C - Activated Carbon 
T.S.C - Total Solids Content 
S - Sulphur 
ZDC - Zinc diethyl dithiocarbamate 
Z M B T - Zinc mercaptobenzothiozole 
ZnO - Zinc Oxide 
SSF - Soldium Silico Fluoride 
KC1 - Potassium Chloride 
DPG - Diphenylguanidine 
Ralox - A sterically hindered phenolic type 
antioxidant which is a butylated reaction 
product of p-cresol and dicyclopentadiene 
FS 4 A non ionic foam stabilizer 
CaC03 - Calcium carbonate 
NH3 - Ammonia 
Xl l l