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The ultraviolet absorption of stretched and unstretched GR-S latex films Mayo, Eleanor Grace 1947

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of-  THE ULTRAVIOLET ABSORPTION 0? STRETCHED AND UNSTRETCHED QR-S LATEX EELMS  by s.  E l e a n o r Grace Mayo  A T h e s i s submitted i n p a r t i a l  fulfillment  of the requirements f o r t h e degree o f MASTER OP ARTS i n the department of PHYSICS  A p r i l , 1947.  ACKNOWLED G-EMEM* .  The author wishes t o express her thanks t o Di*. H. D. Smith f o r h i s generous h e l p i n the e x p e r i mental work and t o Dr. 0. Bluh f o r h i s a s s i s t a n c e i n d i s c u s s i n g and f o r m u l a t i n g the r e s u l t s .  She i s a l s o  indebted t o t h e N a t i o n a l Research C o u n c i l f o r a Grant and t o Dr. L. A. Wood o f the Rubber D i v i s i o n o f t h e United S t a t e s Bureau o f Standards f o r s u p p l y i n g the latex.  TABLE OF CONTENTS  Page Introduction  II.  Research, on S y n t h e t i c Rubbers  . . . . . . . .  2  III.  P r o p e r t i e s o f GR-S  . . . . . . . .  4  1.  . . .  1  I.  Synthetics  General D e f i n i t i o n  . . . . . .  2„ Comparison Between GR-S  and N a t u r a l  Rubbers . . .' . . . . . . 3. Chemical P r e p a r a t i o n (a) GR-S  . . . . . . . . . .  P h y s i c a l Theory o f Rubber  Vi  Theory, o f A b s o r p t i o n  VI.  Experimental  VII.  Discussion of Results  j>  2. A b s o r p t i o n  6 .  7 '9  of Light  . 11  Procedure  Observation  5 j?  Latex . . . . . . . . .  TV.  VIII.  . . . . . . . .  S y n t h e t i c s i n General  (b>) Type I I I GR-S  1.  .4  27 . . . . .  27  and S t r e s s . . . . . . . . . .  2S  o f the Styrene  Bibliography . . . . .  Band  . . . . .  30  ABSTRACT  T h i s work on the u l t r a v i o l e t a b s o r p t i o n of s t r e t c h e d and u n s t r e t c h e d Type 3 GR-S  l a t e x f i l m s , was  undertaken on  the s u g g e s t i o n o f Dr. H. D. Smith and Dr. E. Guth, w i t h  the  e x p e c t a t i o n t h a t the u l t r a v i o l e t a b s o r p t i o n c o u l d g i v e i n f o r m a t i o n on the arrangement o f the molecules  i n the s t r e t c h e d  s t a t e as compared w i t h the u n s t r e t c h e d l a t e x .  Previous i n -  v e s t i g a t o r s have found t h a t s t y r e n e has an a b s o r p t i o n band w i t h maximum a b s o r p t i o n at 28j>0 angstroms. one o f the c o n s t i t u e n t s of GR-S  Since styrene i s  l a t e x , i t was  supposed t h a t  t h i s a b s o r p t i o n band would a l s o appear i n any a n a l y s i s of the l a t e x .  spectral  To f i n d the nature o f t h i s . b a n d  i t s behavior upon s t r e t c h i n g the sample was  one o f the  and ob-  jectives of this research. The type o f s p e c t r o g r a p h used f o r t h i s work was  a  H i l g e r E496.303 w i t h a wavelength s c a l e , and Spekker photometer attachment.  Eastman Type I I - P s p e c t r o s c o p i c p l a t e s  were used f o r a l l r e a d i n g s .  A tungsten s t e e l spark w i t h  about 25,000 v o l t s a c r o s s the e l e c t r o d e s was for a l l plates.  The  used as a  u n s t r e t c h e d f i l m s were prepared  source  by  c o a t i n g a pane o f g l a s s w i t h a t e n percent s o l u t i o n o f z i n c c h l o r i d e , and when dry, the g l a s s was  coated w i t h the l a t e x .  A f t e r d r y i n g , a very t h i n f i l m of rubber was  deposited  on  the g l a s s which c o u l d be p e e l e d o f f as.needed.  By  this  method u l t r a v i o l e t t r a n s p a r e n t f i l m s o f i n i t i a l  thickness  0.020 cm.  were o b t a i n e d .  These f i l m s were s t r e t c h e d i n t o the  shape o f a s p h e r i c a l bubble by means o f n i t r o g e n gas.  By  c a l c u l a t i n g the s u r f a c e areas o f the s t r e t c h e d samples  and  assuming Poisson's  R a t i o t o be 1/2  f o r rubber, the  thicknesses  of the" s t r e t c h e d samples c o u l d be c a l c u l a t e d . A narrow a b s o r p t i o n band was t h i c k n e s s 0.00260 cm.  found f o r l a t e x o f  i n the r e g i o n of 28.50 angstroms which  d i d not appear to s h i f t w i t h f u r t h e r s t r e t c h .  A  slight  broadening e f f e c t upon s t r e t c h i n g might have been present but i t would not amount to more than 3 or 10 angstroms i n either direction.  From t h i s ifr was  concluded  t h a t the  s o r p t i o n c e n t r e s o f the styrene molecules remained during s t r e t c h i n g .  Absorption  c u l a t e d by Lambert's Law l o s s of r a d i a t i o n was  decrease i n t h i c k n e s s was  unaffected  c o e f f i c i e n t s were a l s o c a l -  on the assumption t h a t the  due  ab-  to absorption.  I t was  total  found that a  f o l l o w e d by an i n c r e a s e i n the  s o r p t i o n c o e f f i c i e n t f o r a constant wavelength.  To  ab-  obtain  the t r u e a b s o r p t i o n c o e f f i c i e n t s , the c o e f f i c i e n t s computed, by Lambert's Law body s c a t t e r i n g .  must, be c o r r e c t e d f o r s u r f a c e r e f l e c t i o n T h i s may  a f f e c t the v a l u e s o f the  f i c i e n t s but not the p o s i t i o n of the band.  The  coef-  Increase  s c a t t e r i n g w i t h a decrease i n t h i c k n e s s i s suggested to due  and  in be  to the e x i s t e n c e o f m i c r o c r y s t a l s when the l a t e x i s under  stress.  1.  THE  ULTRAVIOLET ABSORPTION OE  STRETCHED AND GR-S  UNSTRETCHED "  LATEX FILMS  I . INTRODUCTION  I n comparison w i t h the study o f chemical, mechanic a l , thermal and e l e c t r i c a l p r o p e r t i e s o f s y n t h e t i c rubbers, v e r y l i t t l e r e s e a r c h has been c a r r i e d out on the o p t i c a l p r o p e r t i e s o f these substances.  Some work has been done  on d e t e r m i n i n g the r e f r a c t i v e i n d i c e s , s c a t t e r i n g e f f e c t s , double r e f r a c t i o n and a b s o r p t i o n i n the i n f r a r e d , but n o t h i n g on u l t r a v i o l e t a b s o r p t i o n .  The p r e s e n t work  r  almost was  undertaken on the s u g g e s t i o n o f Dr. H. D. Smith and Dr.< E. Guth.  Research on the u l t r a v i o l e t a b s o r p t i o n was  peeted to g i v e i n f o r m a t i o n on the arrangement o f the  ex-  molecules  i n the s t r e t c h e d s t a t e as compared w i t h the u n s t r e t c h e d s t a t e o f rubber.  P r e v i o u s i n v e s t i g a t o r s have found  that styrene  has an a b s o r p t i o n band w i t h maximum a b s o r p t i o n a t 2850 angstroms.  S i n c e s t y r e n e i s one o f the c o n s t i t u e n t s o f  l a t e x , which was  used i n the i n v e s t i g a t i o n , i t was  GR-S  sup-  posed t h a t t h i s a b s o r p t i o n band would a l s o appear i n anys p e c t r a l a n a l y s i s o f the l a t e x .  To f i n d the nature o f t h i s  band and i t s behavior upon s t r e t c h i n g the sample was- one o f the o b j e c t i v e s o f t h i s r e s e a r c h .  I I . RESEARCH ON SYNTHETIC RUBBERS  The  search f o r s y n t h e t i c rubbers s t a r t e d almost a t  once a f t e r C h a r l e s Goodyear i n 1839 d i s c o v e r e d t h e process of v u l c a n i z a t i o n . Faraday  A few years p r e v i o u s t o t h i s d i s c o v e r y ,  i n 1826 demonstrated t h a t rubber was e s s e n t i a l l y a  hydrocarbon  and found the e m p i r i c a l formula C^Hg.  But i t  was not u n t i l i860 t h a t anyone was s u c c e s s f u l i n b r e a k i n g down rubber i n t o i t s c o n s t i t u e n t s . W i l l i a m s found t h a t by pyrolysis  (a c r a c k i n g process) a water-white,  mobile low  b o i l i n g l i q u i d o f t h e same composition as rubber c o u l d be obtained.  T h i s substance he named i s o p r e n e .  F i f t e e n years  l a t e r , Bouchardat converted i s o p r e n e i n t o an e l a s t i c mass and p o i n t e d out the monomer polymer r e l a t i o n e x i s t i n g between t h i s m a t e r i a l and rubber. From the time o f Bouchardat on, the s e a r c h f o r a s y n t h e t i c product" gained momentum w i t h the g r e a t e s t p r o g r e s s made i n the decade p r e c e d i n g the f i r s t World War. l a r g e l y because o f o r g a n i z e d r e s e a r c h groups. t a n g i b l e accomplishments o f t h i s p e r i o d were:  T h i s was  The most  1. the development by the E n g l i s h groups i n c o l l a b o r a v  t i o n w i t h Auguste Fernbach of the P a s t e u r I n s t i t u t e of a process f o r the f e r m e n t a t i o n of s t a r c h to g i v e acetone and a s e r i e s o f h i g h e r a l c o h o l s . 2. the d i s c o v e r y by the German group o f o r g a n i c a c c e l e r a tors of vulcanization.  T h i s was  independent  o f the  d i s c o v e r y o f these compounds i n the U n i t e d S t a t e s . Both groups evolved workable processes f o r the p r o d u c t i o n o f i s o p r e n e and s e v e r a l of i t s homologs and f o r t h e i r p o l y m e r i z a t i o n induced by heat or by c a t a l y s t s such as sodium.  The  products were poor i n q u a l i t y , i n f e r i o r i n e l a s t i c i t y , and i n r e s i s t a n c e t o a g i n g and wear. A f t e r the war,  s y n t h e t i c r e s e a r c h was  virtually  g i v e n up except f o r work a t I . G. F a r b e n i n d u s t r i e i n Germany and duPont i n the U n i t e d S t a t e s .  The main r e s u l t o f t h i s  t h a t many patents were taken out i n Germany; q u a l i t y of the s y n t h e t i c m a t e r i a l s was  still  but by 1930  was the  unsatisfactory.  The approach o f the chemists f a i l e d because the exact molecular c o n f i g u r a t i o n o f rubber, the mechanism o f p o l y m e r i z a t i o n whereby i s o p r e n e i s converted i n t o n a t u r a l rubber and the way z a t i o n has remained polymer was v e l o p new  nature i s a b l e t o p e r f e c t t h i s p o l y m e r i e s s e n t i a l l y unknown.  A truly  rubberlike  not r e a l i z e d u n t i l chemists s t r u c k out t o de-  polymers  t h a t might possess t h e , e s s e n t i a l p r o p e r -  t i e s o f the n a t u r a l product but would be d e r i v e d from monomers d i s t i n c t l y d i f f e r e n t i n t h e i r chemical  composition  4. from i s o p r e n e .  No s y n t h e t i c polymer  developed t h a t approaches  o f i s o p r e n e has y e t been  n a t u r a l rubber i n q u a l i t y o r i s  comparible w i t h the s y n t h e t i c s now b e i n g produced. The f i r s t r e a l l y s u c c e s s f u l product was developed i n 1931 and was c a l l e d p p l y c h l o r o p r e n e ( l a t e r c a l l e d duprene or neoprene). approaches  P h y s i c a l l y the s t r u c t u r e o f t h i s  synthetic  t h a t o f n a t u r a l rubber but c h e m i c a l l y i t c o n t a i n s  40 percent c h l o r i n e .  I n 1932 T h i o k a l , an a l k y l e n e p o l y -  s u l p h i d e e l a s t i c appeared  f o l l o w e d i n 1933 by K o r o s e a l , a  p l a s t i c i z e d p o l y v i n y l c h l o r i d e , and i n 1933 hy the German buna s y n t h e t i c rubbers.  The buna s y n t h e t i c s o r GR-S as they  are c a l l e d i n the U n i t e d S t a t e s a r e by f a r t h e best synthet i c s developed and as a r e s u l t were produced q u a n t i t i e s d u r i n g the second World  i n the g r e a t e s t  War.  I I I . PROPERTIES OF GR-S SYNTHETICS  1.  General D e f i n i t i o n S y n t h e t i c rubbers a r e those o r g a n i c substances  t h a t possess the p r o p e r t y o f f o r c i b l y r e t r a c t i n g t o a p p r o x i mately t h e i r o r i g i n a l s i z e and shape a f t e r being g r e a t l y distorted. "elastomer".  The above d e f i n i t i o n would a l s o cover the term  5. 2.  Comparison Between GR-S and N a t u r a l  Rubbers  GR-S which used t o be known as Buna-S i s a l s o made under the p r o p r i e t a r y names o f Butaprene-S, Chemigum I T , Hycar TT and Buton-S.  I t has the g e n e r a l  n a t u r a l rubber but i n some r e s p e c t s  properties of  i t i s superior to i t .  I t s p r o p e r t i e s can be compared i n the f o l l o w i n g t a b l e : Superior  3i  In  I n f e r i o r In  1. A b r a s i o n  1. Dynamic f l e x  2. A g e i n g  2. Heat b u i l d up  3. R e v e r s i o n on overeure  3. B r l t t l e n e s s  4. Tendency t o s c o r c h processing  4. Rate o f v u l c a n i z a t i o n  in  Chemical P r e p a r a t i o n (a) GR-S S y n t h e t i c s The  cracking  . i n General.  b a s i c m a t e r i a l f o r a l l GRrS s y n t h e t i c s i s  butadiene, a substance t h a t i s a gas above -3° C e n t i g r a d e . Butadiene i t s e l f can be prepared by f o u r main p r o c e s s e s : 1. p y r o l y s i s ( o r c r a c k i n g ) o f h i g h e r b o i l i n g components o f petroleum 2. dehydrogenation o f some o f the lower b o i l i n g components o f petroleum 3. c o n v e r s i o n  i  of a l c o h o l  2C H^0H—s>CH 2  alcohol 4. from a c e t y l e n e  2  = CH-CH = C H  2  + 2H G + Hg 2  butadiene by the s u b s t i t u t i o n o f hydrogen  6. + coke  —  +  CaO  > 0aC2  lime  calcium carbide  H 0 2  3>HC a  +  CH  CO  +  CaO  acetylene —  +  HgO  —a>CHj- -  CHO  acetaldehyde 1  CH^ - CHO -— ^ C H ^ - CHOH - C H - CHO 2  aldol 1  —  +  CH5 - CH( OH) - C H - CH OH  2H  2  2  butanediol or butylene  glycol  1  3> C H = CH - CH = C H + 2H 0 2  2  2  butadiene I t i s very d i f f i c u l t  t o o b t a i n butadiene o f h i g h  p u r i t y from petroleum products e s p e c i a l l y when they a r e products o f c r a c k i n g o p e r a t i o n s o r from a g r i c u l t u r a l p r o ducts.  The process f o r o b t a i n i n g butadiene from a c e t y l e n e  Is by f a r the best method o f o b t a i n i n g a y i e l d o f h i g h purity since i t i s free of side reactions.  GR-S i s t h e n  made from butadiene by an emulsion p o l y m e r i z a t i o n p r o c e s s w i t h 20% - 50% s t y r e n e added. o f new carbon-to-carbon  This involves the formation  linkages,  (b) Type I I I GR-S Latex Type -III GR-S l a t e x as was used i n t h e f o l l o w i n g research consists o f :  r  7. Material  P a r t s by Weight  Butadiene  30  Styrene  30  Emulsifier  3  Potassium per sulphate  (KgSgOg)  0.6  Mereaptan  0.4-3  Water The  The  140  emulsifier i t s e l f  contains:  D r e s s i n a t e 731  1  D r e s s i n a t e 212  9  c h a r a c t e r i s t i c f e a t u r e o f t h i s type o f l a t e x i s t h a t  diene and styrene e x i s t i n equal q u a n t i t i e s .  buta-  I t i s a white  l i q u i d o f about the same c o n s i s t e n c y as creamy m i l k but  has  a v e r y s t r o n g odor o f s t y r e n e .  IV. PHYSICAL THEORY OP RUBBER  Elastomers  i n a d d i t i o n to t h e i r w e l l known l o n g  range r e v e r s i b i l i t y e x h i b i t other g e n e r a l  characteristics,  (a) Heat i s produced upon s t r e t c h i n g the elastomer a c o o l i n g e f f e c t i s noted upon r e l a x a t i o n . known as the J o u l e Heating  and  This i s  Effect.  (h>) S t r e s s f o r a g i v e n degree o f s t r e t c h i s a l i n e a r f u n c t i o n o f temperature.  (c)  Elastomers when c o l d harden and a t h i g h temperatures they tend t o he t h e r m o p l a s t i c . They a l s o  exhibit  both temporary and permanent p l a s t i c i t y .  They show  a c r y s t a l l i n e s t r u c t u r e a t h i g h s t r e t c h e s which may a l s o occur a t low temperatures i n the u n s t r e t c h e d state, All  x  types o f s y n t h e t i c rubber c o n s i s t o f atomic c h a i n s o f  v e r y g r e a t l e n g t h ( g i a n t molecules) t h a t a r e b u i l t up by the r e p e t i t i o n o f some u n i t c o n f i g u r a t i o n .  These l o n g c h a i n s a r e  n e a r l y always formed by the p o l y m e r i z a t i o n o f the molecules of  certain liquids.  The double bond a t t a c h e d t o a carbon  atom a t the end o f the molecule opens' t o form the n e c e s s a r y v a l e n c e bond f o r attachment  t o t h e next u n i t .  These l o n g  c h a i n molecules have f r e e l y r o t a t i n g l i n k s and weak secondary f o r c e s e x t e n d i n g around them, w i t h the r e s u l t t h a t a l o o s e three d i m e n s i o n a l network forms. From a study o f the e l a s t i c b e h a v i o r o f rubber, we can make a number o f i n f e r e n c e s about the s i z e and shape o f the  molecules.  The f a c t t h a t rubber c a n be s t r e t c h e d almost  r e v e r s i b l y up t o 1000 percent w i t h l i t t l e  change i n d e n s i t y  shows t h a t rubber must c o n t a i n s t r o n g f i l a m e n t s t h a t a r e • normally crumpled o r t w i s t e d t o l e s s than one-tenth o f t h e i r extended l e n g t h .  These f i l a m e n t s can s l i d e past one another  with very l i t t l e  f r i c t i o n over most o f t h e i r l e n g t h but a t a  few p o i n t s they a r e i n t e r l o c k e d i n a -three d i m e n s i o n a l n e t work t o l i m i t the degree o f d e f o r m a t i o n o r f l o w .  There must  a l s o be some mechanism t h a t tends t o make the f i l a m e n t s and  9. network r e t u r n s u b s t a n t i a l l y t o t h e i r o r i g i n a l a f t e r the e x t e r n a l s t r e s s i s removed.  crumpled  Recently  state  methods o f  s t a t i s t i c a l mechanics have been a p p l i e d t o t h i s problem o f e l a s t i c i t y by E. Guth.  V. THEORY OF ABSORPTION OE LIGHT  When a beam o f l i g h t either transmitted,  f a l l s on matter, the l i g h t i s  r e f l e c t e d o r absorbed by the substance.  A substance i s s a i d t o e x h i b i t " g e n e r a l a b s o r p t i o n "  if it  reduces the i n t e n s i t y o f a l l wavelengths o f l i g h t by n e a r l y the same amount. transmitted  T h i s means f o r v i s i b l e l i g h t t h a t the  l i g h t shows no marked c o l o r change.  There i s  merely a r e d u c t i o n o f the t o t a l , i n t e n s i t y o f the white l i g h t . No substance i s known t h a t absorbs a l l wavelengths  equally;  but some, such as f i l m s o f p l a t i n u m , approach t h i s  condition  over a f a i r l y wide range o f wavelengths.  A substance t h a t  absorbs c e r t a i n wavelengths o f l i g h t i n p r e f e r e n c e i s s a i d t o show " s e l e c t i v e a b s o r p t i o n " . practically  The c o l o r o f  a l l c o l o r e d substances i s due 'to the  of s e l e c t i v e absorption  to others  existence  i n some p a r t o r p a r t s o f the v i s i b l e  spectrum. When l i g h t i s absorbed, i t s energy may  be t r a n s -  f e r r e d i n three ways: 1. the energy may  be r e - e m i t t e d  as f l u o r e s c e n t  light  10. 2. the molecules t h a t have absorbed  the l i g h t b e i n g now  i n a h i g h e r energy o r e x c i t e d s t a t e may e n t e r i n t o chemical r e a c t i o n o r may d i s s o c i a t e .  Ultraviolet  r a d i a t i o n i s known t o be v e r y e f f e c t i v e i n promoting chemical changes 3. the absorbed  energy may be changed i n t o heat  energy.  Lambert's Law s t a t e s t h a t each l a y e r o f equal t h i c k n e s s absorbs an equal f r a c t i o n , o f t h e ^ l i g h t t h a t t r a v e r s e s i t . I f l a y e r s o f the t h i c k n e s s o f a s i n g l e molecule a r e c o n s i d e r e d , then each molecule absorbs an equal f r a c t i o n o f the l i g h t t h a t passes by i t .  T h i s can be s t a t e d i n the form o f an  equation. I = I where . I  0  G  e-K*  = i n t e n s i t y o f the l i g h t e n t e r i n g the l a y e r ,  x  = thickness of the l a y e r .  I  = i n t e n s i t y o f t h e l i g h t a f t e r p a s s i n g throught the l a y e r .  E  = a b s o r p t i o n c o e f f i c i e n t s i n c e i t i s a measure o f the r a t e o f l o s s o f l i g h t from the d i r e c t beam.  T h i s e q u a t i o n may be r e w r i t t e n as . I_  T o-  where  log  1 0  log  1 0  _ „-Kx « e  I _ = -0.4343 Kx -|- = 0.4343 Kx = E  T  = t r a n s m i s s i o n = l o g ^_  E  = e x t i n c t i o n o r o p t i c a l d e n s i t y = l o g Jo_ . I  . . log  1 0  E = log  O.4343 K + l o g  1 0  1 0  x.  Since the a b s o r p t i o n c o e f f i c i e n t K v a r i e s w i t h the wavelength and t h i c k n e s s x, the shape of the a b s o r p t i o n or t r a n s m i s s i o n curve depends upon the term l o g the curve upon the term l o g ^  x 0  1 G  0.4343 k and the h e i g h t o f  •  I n a s o l u t i o n the a b s o r p t i o n depends upon c e n t r a t i o n and t h i c k n e s s o f the l a y e r t r a v e r s e d . be expressed  where  T h i s may-  by an equation which i s known as Beer's I = I  0  e-  the.con-  Law.  a c x  a  = a b s o r p t i o n c o e f f i c i e n t of u n i t c o n c e n t r a t i o n ,  x  = thickness,  c  = concentration.  I  0  I  = e n t e r i n g i n t e n s i t y o f l i g h t beam. = i n t e n s i t y o f l i g h t a f t e r p a s s i n g through the solution.  No  exceptions have ever been found t o Lambert's Law,  Beer's Law  but  holds o n l y f o r c e r t a i n ranges o f c o n c e n t r a t i o n ;  i . e . the absorbing power of a molecule i s i n f l u e n c e d by  the  p r o x i m i t y of i t s neighbors.  71. EXPERIMENTAL PROCEDURE  The type of spectrograph  used f o r t h i s work was  H i l g e r E496.303 w i t h a wavelength s c a l e and Spekker photometer attachment.  Eastman Type I I - F s p e c t r o s c o p i c p l a t e s  a  12. were used f o r a l l r e a d i n g s .  ..A tungsten s t e e l spark w i t h about  35,000 v o l t s a c r o s s the e l e c t r o d e s was a l l plates. w i t h a 110  T h i s source was  used as a source f o r  o b t a i n e d by u s i n g a t r a n s f o r m e r  v o l t primary and 20,000 v o l t secondary winding i n  p a r a l l e l w i t h f o u r Leyden j a r condensers hookup.  I t was  i n a series  parallel  found t h a t t h i s gave a v e r y i n t e n s e s o u r c e .  1 «  Fig. P r e l i m i n a r y experiments  1. were conducted  on  sheets o f f a i r l y t r a n s p a r e n t V u l c a n i z e d X-224 GR-S ness 0.0635 cm.  t o determine  w i t h a one way  the b e s t  I t i s known f o r v i s i b l e l i g h t t h a t  s t r e t c h the rubber sample becomes cloudy or  "milky" and t r a n s m i t s o n l y a s m a l l p o r t i o n o f the l i g h t beam.  of thick-  the amount o f s t r e t c h t h a t c o u l d  be expected from such a sheet and to determine method o f s t r e t c h i n g .  thin  However, i f s t r e s s e s are a p p l i e d both  incident longi-  t u d i n a l l y and l a t e r a l l y s i m u l t a n e o u s l y , the rubber remains transparent.  A s u r f a c e e f f e c t r e s s e m b l i n g o x i d a t i o n was  a l s o noted on the s u r f a c e of the rubber c l o s e s t t o the  spark  source but on the o p p o s i t e s u r f a c e no such e f f e c t c o u l d be detected.  So i t was  expected  t h a t i f the experiments  were  Rubber Sample  Quartz Window  Section A-A  FIG  conducted  i n an oxygen f r e e atmosphere such an e f f e c t c o u l d  be e l i m i n a t e d .  I t was  decided to use a n i t r o g e n atmosphere  which c o u l d a l s o serve as the s t r e t c h i n g f o r c e . A s u i t a b l e clamp f o r the rubber was  b u i l t which  a l l o w e d . e q u i l a t e r a l s t r e s s and a n i t r o g e n atmosphere.  The  h o l d e r ( f i g . 2) c o n s i s t e d of a p i e c e o f brass s t o c k d r i l l e d to a l l o w a beam of l i g h t one pass through.  square  A quartz window was  c e n t i m e t e r i n area t o glued onto one  end and  brass p l a t e f i t t e d onto i t t o make a s t r o n g w a l l . sample was  rubber  p l a c e d on the o t h e r end and h e l d r i g i d l y i n p o s i -  t i o n by means of another cut.  The  a  brass p l a t e i n t o which grooves were  S i m i l a r grooves were cut i n t o the main p a r t o f the  h o l d e r and i n t o these the rubber was the p l a t e was  t i g h t e n e d up.  l e a d f o r the n i t r o g e n was  supposed t o "flow" when  I n t o the hollow c e n t r a l p a r t a  d r i l l e d and a l s o one  n e c t i o n to a mercury manometer.  By simply i n c r e a s i n g the  n i t r o g e n p r e s s u r e the rubber sample was the form o f a sphere  made to s t r e t c h  or b a l l o o n and i n t h i s way  f o r c e i n a l l d i r e c t i o n s was  f o r a con-  into  an,equal  e x e r t e d on the sample.  The next problem encountered the t h i c k n e s s o f the sample when i t was  was  how  t o measure  stretched.  decided to use an o p t i c a l d e v i c e to measure t h i s by  It  was  simply  o b t a i n i n g r e f l e c t i o n s o f a l i g h t beam o f f both s u r f a c e s o f the rubber  sample.  15.  V  F i g . 3. The rubber sample was s e t i n such a p o s i t i o n t h a t the l i g h t beam was i n c i d e n t upon the s u r f a c e at an angle o f 45° and the r e f l e c t i o n s from both the upper and lower s u r f a c e s were then r e f l e c t e d up i n t o a microscope.  By measuring the d i s t a n c e  between these beams and knowing the m a g n i f i c a t i o n o f the microscope, the t h i c k n e s s o f the sample c o u l d be determined. I t was found t h a t t h i s was a v e r y e f f i c i e n t method f o r obt a i n i n g the t h i c k n e s s o f an u n s t r e t c h e d  sample but when the  sample was s t r e t c h e d i t s t h i c k n e s s was so reduced t h a t the r e f l e c t i o n s from the two s u r f a c e s appeared i n the microscope as a s i n g l e l i n e .  Thus t h i s method was not a p p l i c a b l e .  The method o f measurement t h a t was f i n a l l y  used  was t o photograph the bubble a g a i n s t a white background and thus o b t a i n a s i l h o u e t t e o f i t s o u t l i n e on a photographic plate.  By having the camera s e t up a t such a d i s t a n c e t h a t  the s i l h o u e t t e obtained was i n a r a t i o o f one t o one w i t h the bubble, the r a d i u s o f the s p h e r i c a l s u r f a c e c o u l d be measured d i r e c t l y from the p l a t e .  With the r a d i u s known t h e  s u r f a c e area o f the f i l m c o u l d be c a l c u l a t e d .  By assuming  16. Poisson's R a t i o f o r rubber to be 1/2,  t h a t i s , t h a t the volume  o f the u n s t r e t c h e d rubber i s the same as the volume o f the s t r e t c h e d rubber, the t h i c k n e s s o f the s t r e t c h e d f i l m c o u l d be determined.  °It was  o r i g i n a l l y intended to make  determina-  t i o n s o f the s i z e of the bubble as a f u n c t i o n o f the p r e s s u r e e x e r t e d upon i t by the n i t r o g e n gas.  Then by simply r e a d i n g  the p r e s s u r e from the mercury manometer when the s p e c t r o graphic p l a t e s were being taken, the bubble s i z e c o u l d be read d i r e c t l y from the predetermined such a f u n c t i o n was  graphs.  But i t was  not always reproduceable  found  that  s i n c e many f a c t o r s  entered i n such as the r a t e a t which the n i t r o g e n gas was a l lowed to f l o w i n t o the h o l d e r . be determined  Thus the bubble s i z e had  to  at the same time as the s p e c t r a l a n a l y s i s was  done. A b s o r p t i o n curves were o b t a i n e d f o r v u l c a n i z e d £-224 GR-S  samples of i n i t i a l t h i c k n e s s 0.06j55 cm.  but i t was  found t h a t w i t h maximum s t r e t c h f o r these samples, r e a d i n g s could not be obtained below about 3200 angstroms.  These  >  samples then, were not of much v a l u e s i n c e knowledge o f the a b s o r p t i o n was  d e s i r e d p a r t i c u l a r l y i n the r e g i o n o f  2800 - 2900 angstroms.  As these were the t h i n n e s t t r a n s -  parent samples t h a t c o u l d be o b t a i n e d from the U n i t e d S t a t e s Bureau o f Standards from Type I I I GR-S The  i t was  decided to make v e r y t h i n f i l m s  latex.  u n s t r e t c h e d f i l m s were prepared by c o a t i n g a  pane o f g l a s s w i t h a t e n percent s o l u t i o n of z i n c When t h i s was  dry the g l a s s was  chloride.  coated w i t h the l a t e x .  Upon  17. d r y i n g a very t h i n f i l m o f rubber was d e p o s i t e d on the g l a s s which c o u l d be p e e l e d o f f as needed. ;  I t was found t h a t w i t h  p r a c t i c e f i l m s o f a v e r y u n i f o r m t h i c k n e s s c o u l d be made. By t h i s method u l t r a v i o l e t t r a n s p a r e n t f i l m s o f i n i t i a l t h i c k n e s s 0.020 cm. were o b t a i n e d which gave the p o s s i b i l i t y of o b t a i n i n g experimental r e s u l t s i n the u l t r a v i o l e t r e g i o n .  TABLE I Readings and C a l c u l a t i o n s Unstretched Sample Thickness = 0.020 cm Surface A r e a = 1.432 cm Volume * .0286 cm? 2  Wavelength A (Angstroms)  Extinction Coefficient E  6700 5800 5100 4750 4360 4220 4060 3980 3880 3800 3740 3670 3650 3630 3600 3585  .7 .8 .9 1.0 1.1 1.2 1.3 1.4 1.5 1*6 1.7 1.8 1.85 1.9 1.95 2.0  .  Percent Transmission 20.0 15.9 12.6 10.0 7.95 6.32 5.02 3.99 3.16 2.52 2.00 1.59 1.43 1.26 1.12 1.0  Log Percent Transmission 1.301 1.201 1.100 1.000 .900 .801 .701 .601 .500 .401 .301 .201 .154 .100 .049 0.0  Total Absorption C o e f f i c i e n t  s  .80 x 10 .92 1.04 1.16 1.27 1.38 1.50 1.61 1.73 1.84 1.96 2.08 2.13 2.19 2.25 2.31  2  cm"  1  TABU! I I Radius o f bubble «* 1.00 cm 'b = 2* Surface Area  1  4  *L dx  1/2  ^ (1.0  A  -  = 2*(1.0)(1.0 + .75)= 11.00 cm  dx 2tf I r dx P o i s s o n ' s R a t i o g i v e s f i n a l volume = i n i t i a l volume. J -.75 . ' . 0 2 8 6 cm3 = 11.00 x t t  =• .00260 cm = t h i c k n e s s o f sample.  Amount o f s t r e t c h = 11-00 - 1.4?2 = 688f, 1.452 Wavelength A (Angstroms) 6800 " 5600 • 5070 2990 2915 2885 2865 2850 2855 2820 2800 2775 2760 2750 2745 2730 2720 2710  Extinction Coefficient E .2 .4 .6 •1 .8 .9 1.0 1.0 1.0 1.2 1.3 1.4 1.3 1.6 1.7 1.8 1.9 2.0  Percent Transmission 63.2 39.9 25-2 20.0 15.9 12.6 10.0 10.0 10.0 6.32 5.02 3.99 3.16 2.52 2.00 1.59 1.26 1.0  Log Percent Transmission  Total Absorption C o e f f i c i e n t  1.801 1.601 1.401 1.301 1.201 1.100 1.000 1.000 1.000 .801 .701 .601 .500 .401 .301 .201 .100 0.0  1.77 x-102 cm-1 3.55 5.32 6.20 7.09 7.98 8.86 8.86 8.86 10.63 11.52 12.41 13.30 14.20 15.07 15.96 16.83 17.72  2  TABLE I I I Radius o f Bubble • 1.25 cm S u r f a c e Area '17.55 cm Thickness = .OOI65 cm Amount o f S t r e t c h »• 1110$  2  Wavelength A .< (Angstroms)  Extinction .Coefficient E  5700 3500 5050 2990 2970 2950 2925 2915 2910 2900 2890 2880 2880 2880 2875 2870 2865 2850 2849 2847 2845 2840 2830 2830 2810  .2 .4 .6 .7 . .75 .8 .82 .84 .86 .90. .92 .96 .98 1.00 1.05 1.10 1.15 1.15 1.10 1.05 1.05 1.10 1.15 . 1.20 1.30  •  Percent Transmission :  63.2 39.9 25.2 20.0 17.8 15.9 15.2 14.5 13.8 12.6 12.0 11.0 10.5 10.0 8.92 7..95 7.08 7.08 7.95 8.92 8.92 7.95 7.08 .6.32 5.02  Log Percent Transmission 1.801 1.601 1.401 1.301 1.250 1.201 1.182 1.161 1.140 1.100 1.079 1.041 1.021 1.000 .950 .900 .850 .850 .900 .930 .950 . 900 .850 .801 .701  Total Absorption Coefficient 2.80 x 10 5.59 . 8.37 9.76 11.0 11.15 11.44 11.72 12.0 12.56 12.83 13.39 13.67 13.95 14.7 15.3 16.1 16.1 15.3 14.7 14.7 15.3 16.1 16.7 18.2 V  2  cm-  1  TABLE IV Surface Area = 2 4 . 8 6 em^ Thickness = .00115 cm Amount o f S t r e t c h = 1635% Wavelength A (Angstroms) 3600 3070 2890 2880 2875 2870 2870 2865 2860 2850 2849 2848 2847 2845 2840 2840 2857 2855 2830 2815 2800 2790  Extinction Coefficient E .2 .4 .7 .74 .8 .82 .84 .86 .9 .9 .86 .84 .82 .8 .8 .82 .84 .86 ,9 1.0 1.1 1.2  Percent Transmission *  63i2 39.9 20.0 18.4 15.9 15.2 14.5 13.8 12.6 12.6 13.8 14.5 15.2 15.9 15.9 15.2 14.5 13.8 12.6 10.0 7.95 6.32  Log Percent Transmission 1.801 1. 601 1.301 1.265 1.201 1.182 1.161 1.140 1.110 1.110 1.140 1.161 1.182 1.201 1.201 1.182 1.161 1.140 1.110 1.000 .900 .801  Total Absorption Coefficient 4.0 x 10 8.0 14.0 14.8 16.0 16.4 16.8 17.2 18.0 18.0 17.2 16.8 16.4 16.0 16.0 16.4 16.8 17.2 18.0 20.0 22.0 24.0  2  cm  - 1  -  22.  l  (1-  20  r  — i  l  \  o  o  V  \ \  G  \  —  o u_  U_ LU O O,.o  V\ OJ )20 cm.  O hO  -  pes  X LU  ^ > •  0 . 0 ) 2 6 0 cm.  0.0016! i c m . 0.00115 cr i .  2500  3000  3500  WAVE  4000  •,.  LENGTH  4500  5000  A.U.  5500  23.  24.  80  2500  3000  3500  4000  4500  5000  ' , WAVE LENGTH A.U.  25  27.  V I I . DISCUSSION OF RESULTS  A  1,  Observation  o f the Styrene  I t may  Band  be n o t i c e d t h a t there i s a l a r g e d i f f e r e n c e  between the t h i c k n e s s o f the u n s t r e t c h e d t h i c k n e s s e s o f ihe  s t r e t c h e d samples.  sample and  The  t a i n i n g t h i c k n e s s e s between 0.020 cm.  and  the  d i f f i c u l t y of 0.00260 cm.  to the f a c t t h a t l a t e x , e x h i b i t s a tendency to flow; when under pressure f a c e area i n a way pressure had all;  ob-  i s due i.e.  the l a t e x f i l m tended to i n c r e a s e i n s u r out of our c o n t r o l .  A c e r t a i n minimum  to be a p p l i e d i n o r d e r to s t r e t c h the f i l m s a t  however, i t was  nesses 0.0026 cm.,  p o s s i b l e to produce f i l m s o f t h i c k -  O.OOI65 cm.  and  0.00115 cm.  Although  the range of t h i c k n e s s e s f o r s t r e t c h e d samples was narrow, the accuracy  relatively  of the method used seemed to be  high  enough to d i s c l o s e any p o s s i b l e d i f f e r e n c e i n a b s o r p t i o n e f fects. A narrow a b s o r p t i o n band was 0.00260 cm.  found f o r l a t e x o f  t h i c k n e s s i n the r e g i o n of 2850 angstroms;,  a t a wavelength where p r e v i o u s band i n s t y r e n e . i n unstretched  As i t was  i.e.  i n v e s t i g a t o r s have found a  impossible  t o observe t h i s band  l a t e x (because of the i m p o s s i b i l i t y o f p r e -  paring s u f f i c i e n t l y t h i n unstretched  f i l m s o f l a t e x ) we  o n l y compare the a b s o r p t i o n e f f e c t s r e l a t i v e to v a r y i n g >  can  28. stretch.  The a b s o r p t i o n band does not appear to s h i f t  f u r t h e r s t r e t c h but we s l i g h t broadening broadening  must not exclude  with  the p o s s i b i l i t y o f a  e f f e c t being p r e s e n t .  I f there i s a 10  of the band, i t w i l l not be g r e a t e r than j> or  angstroms i n e i t h e r d i r e c t i o n over a change o f t h i c k n e s s o f 100  percent.  From t h i s i t can be concluded  t h a t the  absorp-  t i o n c e n t r e of the s t y r e n e molecule remains u n a f f e c t e d when the molecule i s s t r e t c h e d .  The .general shape of the t r a n s -  m i s s i o n curve seems t o be o f the same form as those found f o r n a t u r a l rubber o f s i m i l a r t h i c k n e s s e s ; i n c r e a s e i n a b s o r p t i o n w i t h a decrease  2.  A b s o r p t i o n and  there i s a  gradual  i n wavelength^".  Stress  The a b s o r p t i o n c o e f f i c i e n t f o r a range o f wavel e n g t h s was  c a l c u l a t e d by Lambert's Law  o f r a d i a t i o n was  due.to t r u e a b s o r p t i o n .  c o e f f i c i e n t s are entered i n Tables I to  as i f the t o t a l  loss  These a b s o r p t i o n IV.  When l i g h t passes through a medium i t i s r e f l e c t e d and  s c a t t e r e d as w e l l as being absorbed.  The  t r u e absorption!  c o e f f i c i e n t s can be c a l c u l a t e d o n l y i f the amount o f l i g h t l o s t by r e f l e c t i o n and  s c a t t e r i n g i s known.  i n t e n s i t i e s o f r e f l e c t e d and i s equal to latex.  is^_z_il^ (n + l )  d  The  r a t i o o f the  i n c i d e n t beams at each s u r f a c e  where n i s the r e f r a c t i v e index o f the  As l a t e x has a r e f r a c t i v e index of approximately  i n the u l t r a v i o l e t r e g i o n , the l o s s of i n t e n s i t y due 1  L . A. Wood, "The O p t i c a l P r o p e r t i e s o f Rubber", J . App. Phys. 12, 119-126, 1941. -  1.6  to r e -  29. f l e c t i o n on both s u r f a c e s w i l l be about IG t o 12  percent.  I n the graph o f a b s o r p t i o n c o e f f i c i e n t versus wavel e n g t h i t w i l l be n o t i c e d t h a t a decrease I n t h i c k n e s s i s f o l l o w e d by an i n c r e a s e i n t h e a b s o r p t i o n c o e f f i c i e n t f o r constant wavelength.  As the d i f f e r e n t t h i c k n e s s e s a r e p r o -  duced by d i f f e r e n t s t r e t c h , we must assume t h a t the change i n the a b s o r p t i o n c o e f f i c i e n t i s due t o the changed s t r e s s s i n c e the a b s o r p t i o n c o e f f i c i e n t f o r a uniform m a t e r i a l be constant  should  f o r a g i v e n wavelength r e g a r d l e s s o f the t h i c k n e s s  o f the m a t e r i a l .  T h i s apparent i n c r e a s e i n a b s o r p t i o n  could  be due t o a g r e a t e r s c a t t e r i n g o f l i g h t i n the l a t e x w i t h i n creased  stress.  I t i s w e l l known t h a t rubber tends t o be  c r y s t a l l i n e a t h i g h degrees o f s t r e t c h which would r e s u l t i n greater s c a t t e r i n g . Dale  2  W i l l i a m s and T a s c h e k  1  and W i l l i a m s and  found s i m i l a r changes i n the a b s o r p t i o n c o e f f i c i e n t i n  the i n f r a r e d r e g i o n which they e x p l a i n e d i n the same way.  «f, App. Phys., 8, 497-505 (1937). App. Phys., 15, 585, (1944)/  30,  V T I I . BIBLIOGRAPHY  1.  Jenkins and White, "Fundamentals o f P h y s i c a l  2.  Wood, " P h y s i c a l O p t i c s "  3.  Brode, "Chemical Spectroscopy"  4.  Desha, "Organic Chemistry"  5.  Barron, "Modern S y n t h e t i c Rubbers"  6.  Memmler, "Science o f Rubber".•  7.  M. Kroger and H. Staude, "The L i g h t A b s o r p t i o n o f S t r e t c h e d and Unstretched Rubber and o f Isoprene", Gummi-Ztg. 4 3 , 22 (1928)  Optics"  1  8.  L. A. Wood, "The O p t i c a l P r o p e r t i e s o f Rubber", J.App. Phys. 12, 119-126 (1941)  9.  L. A. Wood, " S y n t h e t i c Rubbers: a Review o f T h e i r Comp o s i t i o n s , P r o p e r t i e s and Uses", Nat.Bur.Stand. C i r c u l a r , C427  10.  J . Crabtree and A. R. Kemp, "Weathering o f S o f t V u l c a n i zed Rubber", Ind.and Eng.Chem. 38, 278-296 (1944)  11.  H. I . Cramer, " I n d u s t r i a l P r o g r e s s i n S y n t h e t i c Rubberl i k e Polymers", Ind.and Eng.Chem. 34, 243 (1944)  12.  H. A. Schwarzenbach, " L i g h t S c a t t e r i n g i n S t r e t c h e d Rubber", Rubber Chem. Tech. 1 3 , 285 (1940)  13.  W. W i t t s t a d t , ^ E x t e r n a l I n f l u e n c e and the I n t e r n a l S t a t e of Rubber'', Rubber Chem. Tech. 12, 488 (1939)  14.  E. Guth, "The Problem o f the E l a s t i c i t y o f Rubber and o f R u b b e r l i k e M a t e r i a l s " , Am. Assn. f o r Advancement o f S c i e n c e , No. 21, pp. 103-127.  15.  D. W i l l i a m s and R. Taschek, "The E f f e c t s o f E l a s t i c S t r e t c h on the I n f r a Red Spectrum o f Rubber", J.App. Phys. 8, 497-505 (1937)  16.  D. W i l l i a m s and B. Dale, "Further S t u d i e s o f t h e I n f r a Red-Absorption o f Rubber", J.App. Phys. 15, 585  (1944)  

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