DEPOLYMERISATION OF NR L A T g X AND ITS APPLICATIONS by M a n a w a c h a n d r a B o p i t l y a A d i s s e r t a t i o n s u b m i t t e d a s p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r t h e a w a r d o f P o s t g r a d u a t e D e g r e e in P o l y m e r T e c h n o l o g y a t t h e U n i v e r s i t y o f Mora tuwa , S r i L a n k a . P o l y m e r T e c h n o l o g y D i v i s i o n D e p a r t m e n t o f C h e m i c a l E n g i n e e r i n g U n i v e r s i t y of Mora tuwa Sr.t L a n k a . May 1 9 8 9 . - CONTENT - Page * A c k n o w l e d g e m e n t ( i ) * A b s t r a c t ( ( i i ) CHAPTER ONE - I n t r o d u c t i o n 1 1 . 1 G e n e r a l 1 1 1 . 2 C o m p o s i t i o n o f NR l a t e x and s t a b i l i z a t i o n 4 1 .3 M o d i f i c a t i o n r e a c t i o n s 11 1 . 3 . 1 D e p o l y m e r i z a t i o n 12 1 . 3 . 1 . 1 S i n g l e t o x y g e n f o r m o d i f i c a t i o n r e a c t i o n s 14 1 . 3 . 1 . 2 C h e m i c a l s o u r c e s o f S i n g l e t O x y g e n 15 1 . 3 . 1 . 3 O x y g e n a t i o n b y S i n g l e t o x y g e n 17 1 . 4 O b j e c t i v e o f t h e p r e s e n t w o r k 2 0 1 . 4 . 1 A d h e s i v e s 2 0 1 . 4 . 2 Na tu r a l r u b b e r l a t e x f o r p r e s s u r e s e n s i t i v e a d h e s i v e s 2 1 1 . 4 . 2 . 1 T a c k y f i n g r e s i n f o r a d h e s i v e s 2 4 CHAPTER TWO - A n a l y t i c a l t e c h n i q u e s ' 26 2 . 1 P r e p a r a t i o n o f l a t e x 27 2 . 1 . 1 P r e p a r a t i o n o f c e n t r i f u g e d c a t o n i c l a t e x 27 2 . 2 D e t e r m i n a t i o n o f t o t a l s o l i d c o n t e n t ( T S C ) 29 2 . 3 D e t e r m i n a t i o n o f d r y r u b b e r c o n t e n t ( D R C ) 30 2 . 4 D e t e r m i n a t i o n o f m o l e c u l a r w e i g h t b y s o l u t i o n v i s c o s i t y m e a s u r e m e n t s 32 ' 2 . 5 D e t e r m i n a t i o n o f Hydrogen p e r o x i d e s t r e n g t h b y I o d o m e t r i c m e t h o d 35 2 . 6 D e t e r m i n a t i o n o f sod ium h y p o c h l o r i t e s t r e n g t h b y I o d o m e t r i c m e t h o d 37 2 . 7 I n v e s t i g a t e d p r o p e r t i e s 38 CHAPTER THREE - D e p o l y m e r i s a t i o n o f NR l a t e x 39 3 . 1 I n f l u e n c e o f l a t e x p r e s e r v a t i v e on d e p o l y m e r i s a t i o n 42 3 . 2 I n f l u e n c e o f pH^on"depolymer i f f l t ion 43 3 . 3 I n f l u e n c e o f c h e m i c a l d o s a g e on d e p o l y m e r i s a t i o n 4 4 CHAPTER FOUR - T h e i n v e s t i g a t i o n s o f t h e s u i t a b i l i t y . o f d e p o l y m e r i s e d l a t e x in p r e s s u r e s e n s i t i v e a d h e s i v e 4 ^ 4 . 1 T a c k y f i n g r e s i n to i m p r o v e t a c k 49 4 . 1 . 1 P r e p a r a t i o n o f e s t e r i f i e d r o s i n 49 4 . 1 . 2 D e t e r m i n a t i o n o f a c i d v a l u e 50 4-»-1.3"".Ireparatlon-- o^r«sln" dispersion 52 4 . 2 P r e p a r a t i o n o f a d h e s i v e and d e t e r m i n a t i o n o f p e e l s t r e n g t h 53 > 4 . 2 . 1 P r e p a r a t i o n o f a d h e s i v e f i l m s 53 4 . 2 . 2 T e s t i n g 54 4 . 3 R e s u l t s 54 CHAPTER F I V E - D i s c u s s i o n 5 . 1 S u g g e s t i o n s f o r f u r t h e r w o r k 68 R E F E R E N C E S 69 APPENDIX i - ACKN3WL0DGEN13NT - I am deeply indebted to my supervisor Dr. A. Coornarasamy for the active, ready and willing assistance and guidance given to me in the fulfilment of this project. A special word of thanks to Dr.(Mrs.) L. Sivagurunathan, Head of Polymer Technology Division and Lecturer Mr. K.P. Fernando. It must be placed on record the appreciation I owe to Mr. H.N.K.K. Chandralal for the suggestions and advice willingly given. I wish to thank Mr. Earny Silva, Mr. Wasantha Ranatunga and Mr. Nihal Wickramasinghe. I would also wish to thank Mr. Kirthi Silva, Mr. Dekumpitiya and Technical staff of Polymer Chemistry Section for their valuable assistance in carrying out the laboratory work. I w i s h t o e x p r e s s my s i n c e r e g r a t i t u d e t o S u n e e t h a La thpandura f o r t y p i n g t h e r e p o r t . F i n a l l y I o f f e r my s i n c e r e t h a n k s t o a l l p e r s o n n e l f o r the a s s i s t a n c e and f o r b e i n g s o k i n d and c o n s i d e r a t e towards me a t a l l t i m e s . Manawachandra Bopltlya (iii) ABSTRACT The c o n t r o l l e d molecu lar weight reduc t ion of NR i n la tex phase had been c a r r i e d out by t reat ing NR la tex w i th s ing le t molecular oxygen generated from i n e x p e n s i v e and nontoxic reagents 'Hydrogen p e r o x i d e and sodium h y p o c h l o r i t e ' . The extent of degradat ion was s t u d i e d b y v i s c o s i t y measurements. The extent to w h i c h v i s c o s i t y i s r e d u c e d can be c o n t r o l l e d to a l a r g e extent b y the amount of reagents used and the pH of the l a t e x . In a c i d i c medium extent of degradat ion was h i g h e r . The mechanism of s c i s s i o n i s i n v e s t i g a t e d . The r e s u l t s obta ined a re more in favour w i th the mode of s c i s s i o n p r o p o s e d b y Hock . Potent ia l a p p l i c a t i o n s of the p r o c e s s can be grouped in to th ree genera l a reas c o r r e s p o n d i n g to low, in termedia te and h i g h l e v e l of treatment. Low l e v e l of treatment g i v e r u b b e r of r e d u c e d v i s c o s i t y w i t h i n the normal range for b u l k r u b b e r . In termediate l e v e l s g i v e s o f t , s t i c k y r u b b e r s pa le i n co lour and showing good p r e s s u r e s e n s i t i v e tack and pee l s t rength even without the use of t a c k y f i n g r e s i n s . High l e v e l s of treatment g i v e v e r y v i s c o u s l i q u i d r u b b e r .