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The thermal conductivity of natural and synthetic rubber-sulphur compounds Lang, Francis Alexander 1948

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Z*.  THE  THERMAL CONDUCTIVITY OF NATURAL AND SYNTHETIC RUBBER-SULPHUR COMPOUNDS  by  Frank Alexander  Lang  A Thesis submitted i n p a r t i a l the requirements  fulfilment of  f o r the degree o f  MASTER OF ARTS in  the department of PHYSICS  S e p t e m b e r , 1948  T or-  ABSTRACT  The  thermal  rubber-rsulphur  c o n d u c t i v i t y o f n a t u r a l and b u t y l  compounds h a s b e e n i n v e s t i g a t e d a t  temperatures  f r o m - 1 5 0 ° C. t o + 3 0 ° C. a n d e x t e n s i o n s o f  0% t o 100%.  Readings obtained  the  are p l o t t e d  o r d e r i n w h i c h t h e y were o b t a i n e d  effect.  on g r a p h s i n  t o show a l i k e l y  time  R e s u l t s o f p r e v i o u s experiments are i n c l u d e d i n the  tables. The  results  show a v e r y d e f i n i t e  change i n  c o n d u c t i v i t y due t o t h e a d d i t i o n o f s u l p h u r . definitely hysteris  prove  curve.  the e x i s t e n c e o f a completely  T h e y do n o t reproducible  ACKNOWLEDGEMENT  T h i s work was grant  t o Dr.  undertaken  0. B l u h f r o m  t h e A s s o c i a t e Committee  Rubber o f the N a t i o n a l R e s e a r c h The Dr.  w i t h the a i d o f a r e s e a r c h  author wishes  C o u n c i l .of C a n a d a .  to express h i s a p p r e c i a t i o n  0. B l u h f o r h i s c o n s t a n t h e l p f u l n e s s and  progress of t h i s  helpful  Thompson a n d  s u g g e s t i o n s and  Corporation  interest  to  i n the  work.  In a d d i t i o n , W i l l i a m B.  on S y n t h e t i c  the a u t h o r wishes Thomas M.  t o thank  C. D a u p h i n e e  the Research  f o r the s a m p l e s t h e y h a v e  Division  Messrs.  f o r many o f the  prepared.  Polymer  TABLE OF CONTENTS Page I.  INTRODUCTION 1. General Introduction 2. Thermal C o n d u c t i v i t y 3. C h o i ° o f compounds  1 2 3  e  II.  III.  IV.  APPARATUS 1. C o n d u c t i v i t y Measuring Unit 2. The H e a t i n g C i r c u i t 3. The C o o l i n g C i r c u i t \. The C o n t r o l C i r c u i t 5. The T e m p e r a t u r e M e a s u r i n g C i r c u i t . . . 6. The Cryosta.t..,. S t r e t c h e r , a n d Radiation Shield 7. The B a t t e r y C h a r g i n g C i r c u i t . ... . . . EXPERIMENTAL PROCEDURE 1. General Procedure 2. Measurement o f T h i c k n e s s 3. Guard B l o c k C o r r e c t i o n 4. Thermocouple C a l i b r a t i o n  .  RESULTS 1. C o m p o s i t i o n o f t h e Samples 2. T a b l e s and Graphs 3. Discussion of the Results (a) N a t u r a l Rubber (b) B u t y l Rubber  5 10 12 13 . 1 4 15 .17  18 21 .22 23 25 27 45 - . . . . 1^1  V.  SUMMARY  51  VI.  BIBLIOGRAPHY  52  PLATES  Page 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.  Front View Heating C i r c u i t Diagram Conductivity Measuring Unit Cooling C i r c u i t Results f o r Natural Rubber 2% S Results f o r Natural Rubber 4% S Results f o r Natural Rubber 10% S Results f o r Natural Rubber 2% S, 100% Stretch Results f o r Natural Rubber 4% S, 100% Stretch Results f o r Natural Rubber 10% S, 100% Stretch Dauphinee's Results, Natural Rubber 2% S Dauphinee's Results, Natural Rubber 2% S, 100% Stretch 13. Ivey's Results f o r G.R.S. 0% and 100% Stretch. 14. Results f o r Butyl Rubber 2% S . 15. Results f o r Butyl Rubber 4% S 16. Results f o r Butyl Rubber 10% S 17. Results f o r Butyl Rubber 2% S, 100% Stretch . 18. Results f o r Butyl Rubber 4% S, 100% Stretch . 19. Thompson's Results f o r Butyl Rubber 2% S 20. ' Thompson's Results f o r Butyl Rubber 2% S, . . 100% Stretch 21. Thompson's Results f o r Butyl Rubber 10% S. . .  7 9 9 11 36 . .. 36 37 . . 37 . . 38 . . 38 39 . . . .  .. .. . . . . . .  39 40 41 41 42 42 43 43 44 44  THE  THERMAL CONDUCTIVITY OF NATURAL AND  SYNTHETIC  RUBBER-SULPHUR COMPOUNDS  I.  1.  GENERAL INTRODUCTION The  due  INTRODUCTION  effect  upon t h e t h e r m a l  t o a change i n t e m p e r a t u r e ,  composition  amount o f s t r e t c h ,  theoretical  elastomer research.  generally applied  o f both commercial a n d  Elastomer  t o any substance  physical properties  elasticity  i s t h e name  exhibiting  o f long-range  the charac-  reversible  a n d anomalous t h e r m o e l a s t i c b e h a v i o u r .  applies regardless o f i t s chemical composition. rubber  chemical  and a g e , a n d t h e k n o w l e d g e g a i n e d t h e r e f r o m , h a s  an i m p o r t a n t b e a r i n g on many f i e l d s  teristic  c o n d u c t i v i t y of rubber  This Natural  i s t h e b e s t known e l a s t o m e r , i t s c h a r a c t e r i s t i c s  so t y p i c a l , frequently  that  the l a r g e group o f s i m i l a r  called Up  until  "synthetic"  elastomers i s  r e s e a r c h was done on  o f n a t u r a l and s y n t h e t i c  problem, a t b e s t , i s a d i f f i c u l t p r e c a u t i o n s a n d many h o u r s  being  rubber.  recent years, l i t t l e  the t h e r m a l c o n d u c t i v i t y  term  rubber.  The  one r e q u i r i n g many e l a b o r a t e  o f t e d i o u s work.  2. The  investigations  were made f o r t h e p u r p o s e  reported i n the present  of determining the effect  thermal c o n d u c t i v i t y of n a t u r a l  papers upon t h e  and b u t y l r u b b e r s o f t h e a d d i -  t i o n o f v a r i o u s amounts o f s u l p h u r , a t z e r o a n d o n e - h u n d r e d percent C. of  s t r e t c h between t h e t e m p e r a t u r e s  A knowledge o f t h e s e e f f e c t s their  because  obvious use i n t i r e  characteristics established, bute  i s important not only  manufacturing,  o f t h e i r use i n studies  the rubber molecule.  o f - 150° C and - 30°  into  because  e t c . , but a l s o  the basic  structure  of .  I f more e x p e r i m e n t a l e v i d e n c e on t h e  o f the r e l a t i v e l y  i t may be e x p e c t e d  simple rubber molecule  that  this will  were  form o r c o n t r i -  to the theory o f structure of rubber. In  correlate  t h e p r e s e n t work, a t t e m p t s  the results  investigators.  have been made t o  o b t a i n e d w i t h those obtained by e a r l i e r  Particular  emphasis was p u t on t h e o r d e r i n  w h i c h t h e r e s u l t s were o b t a i n e d i n o r d e r t o g e t some, i d e a o f t h e way i n w h i c h c o n d u c t i v i t y to due  c h a n g e s w i t h t i m e , n o t o n l y due  a g e i n g , b u t a l s o due t o a change i n t e m p e r a t u r e t o t h e r a t e o f change o f t e m p e r a t u r e ,  instance, cooling  or fast  expected rubber  r e a d i n g a t a lower cooling.  i n b u t y l rubber  temperature  Little  effect  and perhaps  i<*-e. w h e t h e r , f o r i s o b t a i n e d by slow  due t o a g e i n g  c a n be  s i n c e a g e i n g and d e t e r i o r a t i o n o f  i s l a r g e l y due t o t h e d e g r e e  o f unsaturation, which i s  small i n b u t y l rubber ( 2 ) .  2.  THERMAL  CONDUCTIVITY  Thermal  c o n d u c t i v i t y has been d e f i n e d as t h e time  rate  of transfer  ness, T  he  across unit  coefficient  the  o f h e a t , hy  conduction, through u n i t  area, f o r unit  of thermal  difference  c o n d u c t i v i t y , K,  where dQ  i s the heat  t h i c k n e s s dx  i s d e f i n e d by  temperature  T « 2  I  a c r o s s an a r e a A  T^ and  The  method u s e d required  gradient across a  3.  samples,  CHOICE OF  experiments  13,  o b t a i n e d f o r n a t u r a l and percent s t r e t c h .  the study of the e f f e c t  o f heat  used  to obtain K  tempera  composition  on c a n he u s e d  to  t h r o u g h n a t u r a l and  as an a g e n t  18) were  performed  r u b b e r s w i t h a mind t o  t i m e were b u t y l and n a t u r a l ,  further vity  hundred  butyl  (7,  aring  this  dimensions  independently of the o t h e r .  G.R.S. and  one  side at  to maintain a constant  with natural, results  cold  sample o f r u b b e r o f known  e a c h one  difference  COMPOUNDS  Previous  z e r o and  through  i n t h i s work i s t o m e a s u r e  equipment t o be d e s c r i b e d f u r t h e r  m e a s u r e two  the  the  Many methods h a v e b e e n u s e d  the q u a n t i t y of heat  The  transferred  C.G.S. u n i t s , - K h a s  n  1  experimentally.  ture  dx  s i d e at temperature  cal.sec7 cm7 deg7-'1  A  i n t i m e d t , dT b e i n g t h e t e m p e r a t u r e  between the hot  and  temperature.  equation dt  is  in  thick-  synthetic The  comp-  rubber  rubbers  at  selected  and were i n v e s t i g a t e d  to  o f s u l p h u r on t h e c o n d u c t i synthetic  rubber.  i n the v u l c a n i z a t i o n process of  b u t y l rubber, hence i t s e f f e c t  upon the t h e r m a l  Sulphur natural proper-  t i e s of rubber i s important.  The effect of sulphur on the  d i e l e c t r i c properties of similar elastomers was at t h i s university  investigated  simultaneously with t h i s work ( 6 ) .  5.  II.  APPARATUS  The apparatus used was the same as that used by Thompson (18) except f o r a few changes.  It was found neces-  sary to replace a l l the large rheostats used i n the heater c i r c u i t s by f i v e small rheostats arranged f o r convenience on the front panel just above the potentiometer.  These were  found e n t i r e l y s a t i s f a c t o r y and helped to shorten the time required to obtain a balance.  Other changes included removal  of the reversing switches, etc., i n the thermocouple c i r c u i t , since they were found unnecessary and l i a b l e to error, and the construction of a radiation shield of aluminum to surround the measuring u n i t .  1.  CONDUCTIVITY MEASURING UNIT The conductivity measuring unit (Plate 3) i s const-  ructed i n f i v e parts, one a cold block, two main heating blocks and two guard blocks each of which i s surrounded by a heating block on three sides.  The.cold block i s a rectangular  piece of copper 10x4x1 cm mounted above a large tapped copper plug and connected by a triangular section of copper which conducts heat from the cold block down through the tapped plug to a c y l i n d r i c a l piece of copper threaded into the tapped plug around which i s wrapped a c o i l which carries l i q u i d nitrogen as a c o o l t . a n  The cold block contains two heaters to allow  for exact adjustments of t h e i r temperature, one of 20 ohms  resistence which may be controlled manually and another one of 700 ohms resistance which may be controlled, manually or 'automatically.  The f i r s t heater i s powered from 12 v o l t storage  batteries and the second heater i s powered by a 110 v o l t d.c. laboratory generator. The main heating blocks are also made of copper of similar width and thickness as the cold block, but are only 6 cm long. to be exact.  The measurements of length and width are machined Heat i s generated i n these through 20 ohm  heaters wound twice through equally spaced holes placed as far back i n the blocks as possible to give uniform heating over the surface.  In practice, i t was discovered that t h i s did not  work out quite as anticipated and i t i s therefore believed that some of the windings had shorted to the block.  The main  heating blocks f l o a t on f i b e r pins supported by the guard blocks.  The height of the pins can'be altered by adjusting  screws so that the surface of the main heating blocks are i n the plane of the surface of the guard blocks and p a r a l l e l to the surface of the cold blocks. The guard blocks are made from both copper and brass Copper i s used on the ends which make actual contact with the rubber and brass i s used across the back which also connects the two copper end pieces.  Brass i s used since strength here  i s important so that the unit may be properly held together. The copper blocks, and with them the brass block, can be maintained through the use of t h e i r own heaters at the temperature of the main heating block, so that the copper  7  8  blocks prevent l a t e r a l sample and  conduction of beat a l o n g the  t h e b r a s s b a c k and  the copper  a l o n g the f i b e r If,  found  by  f o r some r e a s o n , t h e  guard  b l o c k s cannot  discussed  under a s e p a r a t e  ends,  $j50  erature.  Two  b l o c k and  one  bottom o f the  a t t a c h e d to copper  the  the  plugs, are  block, a l l equidistant  sample.  A  shunt  near  each o f the guards  and  block at a point difference  just  below  couple i s l o c a t e d  the c o l d  side  and  cold  the between  sheet  heater c o n t r o l s the l o s s  of heat  found that  s h u n t w o u l d be C.  of  between  i s intended to provide  r e s i s t a n c e p a t h t o h e a t p i c k e d up by  much b e l o w - 120°  the  i t s guard.  consisting of a triangular  a l a r g e r heat  temp-  from  the top of the  e i g h t h i n c h c o p p e r wound w i t h a h e a t e r i s c o n n e c t e d  temperatures  copper  top of each h e a t i n g block,  b l o c k n e a r e s t , two  o f t h e h e a t i n g b l o c k s and  a low  be  o f t h e b l o c k s i n o r d e r t o measure t h e i r  i n the c o l d  A heat  This w i l l  term  cotton covered copel wire t w i s t e d at  are l o c a t e d near  of the c o l d  equation.  at  heading.  near the top o f each guard  side  one  double  i n each  be m a i n t a i n e d  c o n s i s t i n g o f jfj>2 o x i d e c o a t e d  d i p p e d i n s o l d e r and  inserted  negligible.  o f the main h e a t i n g b l o c k s , a c o r r e c t i o n  Thermocouples, w i r e and  cond-  conduction  c a l c u l a t i o n t o be  must be a d d e d t o t h e c o n d u c t i v i t y  two  The  p i n s was  the temperature  rubber  blocks prevent  u c t i o n from the back o f the h e a t i n g b l o c k .  -  the guards.  t h r o u g h them. required  I t has  The been  f o r work a t  9  2.,  THE  HEATING CIRCUIT The  is  heating c i r c u i t ,  shown i n P l a t e 2,  and  was  easier manipulation  c u r r e n t s and enabling  redesigned and  and  T h i s new  e n a b l i n g the  s i n c e the  through„the v o l t m e t e r  through  the l i n e .  were p u t voltage  i n s o t h a t one across e i t h e r used  main h e a t e r l i n e s . resistance  used  way,  i t has  voltmeter  been found  c o u l d be  o f the main h e a t e r s to r e a d the  resistors  and  to read  s c a l e , and  to read  one  on  the  (100  9 volts  full  selected  later  M o d e l 280  purposes  and  on meters  no  on  a  calibration  f o r p u r e l y comparative  type  exact.  and  used  The  the  Milliammeter.  auxiliary heating c i r c u i t s .  and  the  The  scale  on  from  of  ohms/volt) i n s e r i e s  used  guard  the  milli-  other.  t o be  the  any  t o r e p l a c e the meters  a Weston M o d e l &  were c a r e f u l l y  the  Switches  showed power r e a d i n g s  required  that  Resistors e x a c t l y equivalent to  resistor  standard 3 volt  used  to  current  current i n either  a Weston M o d e l 1 V o l t m e t e r ohm  quite  i s equal the  ammeters  are  These  readings  are  are  them. r h e o s t a t s a r e f o u r 25  r h e o s t a t s , one  i n each o f the  w a t t , 100 two  of  read  calculated  s u b t r a c t e d from  h e a t e r when t h e y a r e b e i n g u s e d are  the advantage t o be  the h e a t e r  o f the m e t e r s a r e u s e d  w i t h a 600  All  the h e a t e r  accurate  heater  t o l e a d r e s i s t a n c e become n e g l i g i b l e .  ammeter c o u l d be  one  has  c u r r e n t t o be  ourrent  e r r o r s due  t o make f o r more  circuit  current through  In t h i s  diagram o f which  r e a d i n g o f the main  the true v o l t a g e a c r o s s  directly, easily  voltages.  the'schematic  ohm  m a i n and  IRC  two  radio  guard  11.  Cooling  Circuit  circuitsj  and  one  25 w a t t ,  the  cold block (auxiliary)  was  left  automatic c o n t r o l  manual c i r c u i t over.  ohm  IRC  circuit.  radio  The  type r h e o s t a t  auxiliary  control circuit  c a n be e a s i l y  circuit.  I f , f o r any  should break and  in  rheostat  d i s c o n n e c t e d from the a u x i l i a r y h e a t i n g c i r c u i t  f a v o r o f the automatic the  500  in  reason,  down, t h e n  the  q u i c k l y c o n n e c t e d up t o t a k e  A l l o f t h e s e r h e o s t a t s have c u r r e n t l i m i t i n g  resistors  c o n n e c t e d i n s e r i e s w i t h them.  5.  THE  COOLING CIRCUIT C o o l i n g i s a c c o m p l i s h e d a s shown by t h e  s k e t c h e d i n P l a t e 4.  This  circuit  n o t i c e a b l y e x c e p t f o r the r e m o v a l (carboys) which  was  n i t r o g e n through f l u c t u a t i o n s do Essentially, compressor or  o f one  changed  o f the b i g f l a s k s  u s e d t o smooth o u t t h e f l o w o f  the c o o l i n g  coils.  liquid  Although small  o c c u r , they have n e v e r been found  the c o o l i n g arrangements  troublesome*  a r e as f o l l o w s .  i s u s e d a s a s u c t i o n pump t o s u c k l i q u i d  i t s vapour  through  t h r o u g h warming c o i l s , air.  has not been  apparatus  The n e e d l e  the c o o l i n g c o i l s  o f the  c a r b o y , v a l v e , e t c . and  v a l v e i s used  and  the c a r b o y smooths i t o u t .  for  at l e a s t  a h a l f hour  to control The  A  nitrogen  cold block, out i n t o  the f l o w o f n i t r o g e n  compressor  s h o u l d be  with dry a i r before using  water  vapour  very e f f e c t i v e temperature  i n the l i n e s .  This  system  of cooling  a t t e m p e r a t u r e s much b e l o w - 1 5 0 ° C ,  the q u a n t i t y o f l i q u i d  run  liquid  n i t r o g e n i n i t t o p r e v e n t the c o o l i n g c o i l from f r e e z i n g to  the  nitrogen required  due  i s not at  which  becomes  13. v e r y g r e a t and the c o s t o f o p e r a t i n g t h e apparatus It  i s believed this  after the  c o u l d be i m p r o v e d b y r e t u r n i n g t h e c o o l a n t  i t has l e f t the c o o l i n g c o i l t o another  liquid  encircles  n i t r o g e n and thence the f i r s t  prohibitive.  c o i l located i n  back t o a t h i r d  one, t h e r e b y  coil  which  creating a regenerative  process.  4.  THE CONTROL CIRCUIT Two a u t o m a t i c  temperature e  electric  circuits  t o c o n t r o l the  o f the c o l d b l o c k and to c o n t r o l the temperature  d i f f e r e n c e between one o f t h e m a i n h e a t i n g b l o c k s a.nd i t s guard  was b u i l t  readings circuit  b y Thompson  b y one p e r s o n .  They a r e a d . c . p h o t o - c e l l - b i a s  and a r e used i n c o n j u n c t i o n with  a constant balanced  impedance p o t e n t i o m e t e r .  by the constant  E.M.F. g e n e r a t e d block.  (18) t o f a c i l i t a t e the t a k i n g o f  two g a l v a n o m e t e r s a n d  One g a l v a n o m e t e r i s  impedance p o t e n t i o m e t e r  against the  i n the thermocouple l o c a t e d i n the c o l d  The o t h e r  galvanometer i s balanced  a g a i n s t t h e E.M.E.  from the d i f f e r e n c e c o u p l e . The follows.  automatic  A light  control  on t h e c o l d -side works a s  beam f r o m t h e g a l v a n o m e t e r i s c e n t e r e d  s c a l e between two p h o t o - c e l l s .  I f the l i g h t  on one p h o t o - c e l l , c u r r e n t i s a l l o w e d in  the b l o c k .  in  E.M.F. w h i c h u n b a l a n c e s  the  light  i s made t o f a l l  t o pass through  T h i s i n t u r n warms t h e b l o c k  a heater  c a u s i n g a change  the galvanometer thereby  causing  beam t o move t o w a r d s a n d u l t i m a t e l y t o f a l l  second p h o t e - c e l l .  on a  The s e c o n d p h o t o - c e l l s h u t s  on t h e  o f f the  current  allowing  where t h e c y c l e  the block  to cool to i t s o r i g i n a l  i s repeated.  In  practice,  the output  may be v a r i e d b y t h e u s e o f o u t p u t r e s i s t o r s obtain small o s c i l l a t i o n s  about  When c o m p l e t e  i s desired,  be  the d e s i r e d  c o r r e c t e d m a n u a l l y by d e c r e a s i n g  atic  5.  equilibrium  circuit  and i n c r e a s i n g  temperature current  i n order t o temperature.  these o s c i l l a t i o n s  the current  the current  may  i n t h e autom-  i n the manual  circuit.  T E E TEMPERATURE MEASURING CIRCUIT I n o r d e r t o measure the temperature  parts  of the c o n d u c t i v i t y u n i t ,  thermocouples l o c a t e d thermocouples arrive  of the various  there are ten copper-copel  as d e s c r i b e d p r e v i o u s l y .  i n each b l o c k .  These  a t t h e mean t e m p e r a t u r e  T h e r e a r e two  are necessary i n order to  o f the b l o c k which  i s the  t e m p e r a t u r e w h i c h must, be u s e d i n a l l c a l c u l a t i o n s . junction which  o f these thermocouples  i s located  i s immersed i n c r u s h e d i c e a n d w a t e r  Dewar f l a s k . difference  The o t h e r  i n a glass  tube  a l l contained  ina  The t h e r m a l E.M.3F. t h u s g e n e r a t e d due t o t h e  i n temperature  o f t h e two j u n c t i o n s  is' b a l a n c e d  by means o f a- White D o u b l e P o t e n t i o m e t e r d e s i g n e d f o r t h e r m o couple pyrometry used i n c o n j u n c t i o n with a (<©.l m.v./mm.) junctions  Leeds  sensitive  and Northrup galvanometer.  i n the measuring u n i t  are introduced  The t h o r m o -  into a constant  t e m p e r a t u r e zone b o x where t h e y a r e c o n n e c t e d t o l a r g e  copper  l e a d s which  switch  a r e made  to pass through a twelve p o s i t i o n  with a l l copper c o n t a c t s and thence t o the p o t e n t i o m e t e r . reversing  switch i s also  included  t o reverse  A  the thermocouple  15. E.M.F. g e n e r a t e d b e l o w o r above White Double P o t e n t i o m e t e r micro-volt  or, since  per degree, found  that  charts  one  used  this  cannot  one-tenth it,  one  be  scale  four hundredth  the o t h e r Q.  the temperature  scale  to  A  calibration  In p r a c t i c e , o f the  two  the o t h e r .  scales  c o l d b l o c k and  The  i t s s e n s i t i v i t y may  THE  since  be  that  the  decreased switch For  used.  RADIATION SHIELD  w i t h a minimum o f e r r o r s  convection o f heat, the c o n d u c t i v i t y box  ( c r y o s t a t ) w h i c h c a n be The  cryostat  sealed at a l l joints.  unit  due  a  to  i s placed i n a  large  evacuated.  i s c o n s t r u c t e d o f heavy b r a s s The  A  circuit  I n o r d e r t o p r o p e r l y o p e r a t e t h e equipment a t temperature  is  c u r r e n t drawn i s n o t e x c e s s i v e .  CRYBSTAT, STRETCHER AND  s u i t a b l e low  to  w h i c h power t h e p o t e n t i o m e t e r have  ammeter i s p l a c e d i n t h e b a t t e r y  to i n d i c a t e  P  the  same g a l v a n o m e t e r  t u r n e d on s e v e r a l h o u r s b e f o r e t h e y a r e t o be  s m a l l M o d e l 280  on  the Q, s c a l e i s  a l s o mounted on t h e p o t e n t i o m e t e r .  p r o p e r usage, the b a t t e r i e s  merely  than  d i s c o n n e c t e d e n t i r e l y by means o f a n o t h e r  with four p o s i t i o n s  6.  as t h e  switch i s conveniently located  f o r a l l measurements and  t o be  However, i t was  t o measure a l l t h e o t h e r t e m p e r a t u r e s  change f r o m one  be  of a degree.  T h i s p o t e n t i o m e t e r has  t h e same.  o r i t may  of a  c o n s i d e r e d t o be r e a d more a c c u r a t e l y  they are almost  used  read to one-tenth  a c c u r a c y i s not u t i l i z e d  l a b e l e d P,  i s used  c a n be  The  there i s approximately f o r t y m i c r o - v o l t s  of a degree.  t o measure  the i c e p o i n t a t 0 ° C .  t o p p i e d e may  tightly  be removed a t w i l l  to  . replace  samples  o s t a t may  in'the measuring  be v i e w e d  unit.  Neoprene g a s k e t s t h r o u g h w h i c h a l l thermocouple  and t o t h e box w i t h g a s k e t between t h e i r  two  inside  c a n be  to the-end  c o n n e c t e d by  string  "specially b u i l t  ric  w h i c h work a g a i n s t  A radiation i s made i n s u c h a way measuring this  unit,  s h i e l d was  ostat  that  blocks blocks,  that  remained  These  a flat  plat  built  i t almost  and y e t i s e a s i l y  a r e two  clamps  a  pulleys  from  on  have e c c e n t -  t o clamp  the  samples.  sheet aluminum  completely surrounds  removable.  The  t o prevent heating of the i n s i d e from the o u t s i d e  a t low t e m p e r a t u r e s .  p i c k e d up,  A Cenco Megavac  to a p u l l e y held f i r m l y  clamps.  s h i e l d was  through r a d i a t i o n  ularly  cover  vacuum o f  i n order to obtain  of the cryostat  e a c h o f two rollers  to the  low p r e s s u r e .  Bolted which  and h e a t e r l e  since a s u f f i c i e n t  pump i s u s e d t o e v a c u a t e t h e c r y o s t a t  new  grease i s used  1 cm Hg p r e s s u r e c a n be o b t a i n e d w i t h o u t i t .  sufficiently  Two  They a r e h e l d  g r e a s e , but no  surfaces  .. _. 16.  Contents of the c r y -  t h r o u g h a window i n t h e t o p .  l e a d s p a s s were made f o r t h e c o v e r .  ..  Previously,  purpose of the  the of  cry-  surroundings, p a r t i c so much h e a t  a t t e m p e r a t u r e s much b e l o w - 9 0 ° C, at a h i g h e r temperature  and  was  the  guard  than the main h e a t i n g  e v e n when t h e a u x i l i a r y h e a t i n g c o i l s were d i s c o n n e c t e d .  In p r a c t i c e ,  s m a l l l e a k s o c c u r which prevent the guard b l o c k s  from  sufficiently.  cooling  This  i s c o r r e c t e d f o r by h e a t i n g  t h e m a i n b l o c k s up t o t h e t e m p e r a t u r e  o f the guard b l o c k s  w h i l e a t t h e same t i m e m a i n t a i n i n g t h e t e m p e r a t u r e o  n  t h e cold'-.side,: w h i c h .-of, c o u r s e -gives;, a; l a r g e r  constant temperature  17across the rubber  sample, b u t i s n o t t h e c a u s e  f o r most s a m p l e s ,  the c o n d u c t i v i t y curve  low  temperatures.  I f there i s s t i l l  of error,  i s nearly linear at  a difference  i n tempera-  t u r e between t h e main h e a t i n g b l o c k and i t s guard, corrected  7.-  f o r by a n o t h e r  since  method w h i c h w i l l  this  may be  be d i s c u s s e d  later.  THE BATTERY. CHARGING CIRCUIT A battery charging c i r c u i t  facilitate  was made i n o r d e r t o •  the recharging which i s f r e q u e n t l y required o f a l l  the b a t t e r i e s n e c e s s a r y  t o power t h e h e a t e r  circuits.  This  circuit  a l l o w s o n l y one b a t t e r y t o be c h a r g e d  a t one t i m e  through  a Tungar R e c t i f i e r .  the b a t t e r i e s  A t any time  that  a r e n o t i n u s e t h e y s h o u l d be s e t on c h a r g e . conditions,  the batteries  main s w i t c h e s  f o r powering  remained  Under  i n good c o n d i t i o n .  the heater  circuits  power t h e p o t e n t i o m e t e r .  The  a r e below a  l a r g e r o t a r y b a t t e r y c h a r g i n g s w i t c h a n d two s m a l l to the r i g h t  these  switches  18.  I I I . EXPERIMENTAL PROCEDURE  1.  GENERAL PROCEDURE  -  - ...  Samples o f r u b b e r measuring damped  unit,  s t r e t c h e d i f r e q u i r e d and  i n positon.  thickness  At  and  t h e vacuum pump i s p u t  Finally,  junction  then s e c u r e l y  the u n i t  t h e t o p p l a c e d on  i n o p e r a t i o n and t h e  s u p p l y t u r n e d on and  Meanwhile, crushed  i c e and  water are and coils  the  cooling  w a t e r i n them.  The  c o m p r e s s o r n e e d n o t be  f o r t y minutes b e f o r e r e a d i n g s are  w a t e r may  b l o c k the l i q u i d  liquid  conductivity  different  best r e s u l t s  ature  the  force  than  i t is freezing  f o r the d r y i n g tower.  of  and  the  Readings  ways t o o b t a i n the change i n ' upon w h e t h e r t h e r u n i s t o  of d e c r e a s i n g or i n c r e a s i n g  were o b t a i n e d b y  as p o s s i b l e ,  to  traces of  taken, but  first  then i n c r e a s i n g  be  temperature.  d e c r e a s i n g the  i n steps of twenty t o t w e n t y - f i v e degrees  temperature  hours.  cold  i s adjusted to balance  o c c u r i n g , depending  made as a f u n c t i o n  two  nitrogen circulation.  the p o t e n t i o m e t e r  i n two  Then  r u n much more  l e n g t h o f t i m e , as  nitrogen i s substituted  are taken  The  this  with  potentiometer  t o remove any  t o be  the  cryostat.  compressor r u n  the  to maintain  the  o b t a i n e d f o r the  dry a i r through  important  i s covered  allowed to run at l e a s t  o f the thermocouples  Now  p l a c e d i n the  t h i s p o i n t i t i s b e s t t o measure  of the sample.  the r a d i a t i o n s h i e l d  current  are. cut to width,  temper-  t o as l o w  the temperature  a by  19.  equal steps but at different intervals u n t i l a temperature s l i g h t l y above room temperature has been reached.  To obtain a  reading at a lower temperature, a l l heaters are turned o f f and the  unit i s made to cool as fast as possible by increasing the  flow of l i q u i d nitrogen through the cooling c o i l , u n t i l the cold block i s a few degrees below the desired temperature. The a u x i l i a r y heater i n the cold block i s then turned on and the  cold side i s heated to the desired temperature, at which  point, i f the automatic c i r c u i t i s used, the control c i r c u i t potentiometer i s balanced and the automatic control c i r c u i t i s adjusted to hold the temperature constant. When the main heating and guard blocks have reached a temperature some s i x to ten degrees above the cold block, the heaters are turned on and adjusted u n t i l the temperature remains constant and u n t i l the mean temperature of the guard block i s equal to the mean temperature of i t s main heating block.  There i s an automatic c i r c u i t on one of the guards  which can be used to maintain i t s temperature.equal to some temperature i n i t s main heating block.  When equilibrium has  been reached, i . e . , when the d r i f t i n temperature i s negl i g i b l e , the temperatures.of a l l blocks are recorded.and the currents and voltages i n the main heaters are read. for increasing temperature are obtained i n a s l i g h t l y rent manner, but w i l l not be discussed here.  Readings diffe-  Further i n f o r -  mation on procedure was discussed i n theses by Thompson (18) and Ivey (13). Once a reading has been obtained, the conductivity  .2.0. o f t h e two unit  r u b b e r samples  i s being heated The  a solid  be  or cooled  calculated  o f t h i c k n e s s " d " and  to a d i f f e r e n t  measuring  temperature.  a r e a "AV  K  "T  i s made t o p a s s f ,  a  T " 1  " i s g i v e n by  the d i m e n s i o n s  c o n d u c t i v i t y K i s u s u a l l y thought  (cal.secT^cmT^degT^). o f as c o n s i s t i n g  a power f a c t o r QL , a d i m e n s i o n f a c t o r A t d factor - — i  a temperature  of  Q,.d, 1 t A (Tj-Tg)  B  In c . g . s . u n i t s , K has  factors;  which  i n time " t " from a h i g h temperature  to a lower temperature  three  w h i l e the  g e n e r a l e q u a t i o n f o r the thermal c o n d u c t i v i t y  q u a n t i t y o f h e a t "Q,"  The  may  r  of , and  .  (T;L-T ) 2  To f i n d  the power f a c t o r ,  measure the h e a t e r v o l t a g e VJJ a n d this, IMA  t  a  IJJ may  the h e a t e r c u r r e n t e  current  which  i t i s necessary only  the l i n e  be  current  f o u n d by  1^.  From  subtracting  flows through the v o l t m e t e r .  to  The  from power  factor i s  where  i s given i n milliamperes. The  dimension f a c t o r  is e a s i l y  found from  the  measurements t a k e n p r e v i o u s l y o f the t h i c k n e s s "d" o f the sample and  t h e a r e a "A"  c o u r s e i s c o n s t a n t and The temperatures  of the main h e a t i n g b l o c k s which i s e q u a l t o 24 s q .  temperature  factor  cms.  i s o b t a i n e d by l o c a t i n g  c o r r e s p o n d i n g t o the r e a d i n g s i n m i c r o v o l t s  t h e p o t e n t i o m e t e r on a l a r g e  graph which  aid  the Bureau  o f a d e v i a t i o n g r a p h and  of  was  the from  drawn w i t h the  of Standards  copper-  21. constantan  tables, Using  correction  then merely t a k i n g t h e i r  these  v a l u e s and  i s not necessary  the  difference.  assuming t h a t a guard  block  conductivity equation  now  becomes K r 0.239 £ A S  However, i f the  necessary  2  guard  to introduce a correction and  the  final  "dt"  i s the a b s o l u t e  between the guard  transfer  coefficient  negative  as d e t e r m i n e d  2.  MEASUREMENT OF Before  1 (  approximately  ADT  T  different  by  the  c o l d b l o c k and  becomes  the  conductiis  )  o f the  temperature  diffe-  the m a i n b l o c k s , " a " i s the and  is positive  heat  or  "dt".  THICKNESS  any m e a s u r e m e n t s o f the  properly adjusted  with  A  -  i n watts/degree,  parallel  same t h i c k n e s s a s  b e t w e e n t h e b l o c k s and  t h i s had  term i n t o  I>H±  value  and  s a m p l e s were made, a p l a n e  the  i s at a  form o f the e q u a t i o n  K = 0.239  rence  block  from the main h e a t i n g b l o c k , i t t h e n  v i t y equation,  where  T  T T]_-T .  where B g i s i n w a t t s a n d  temperature  3|  t o be  clamped certain  i n the plane  b e e n done, the r u b b e r  piece  of metal  a rubber  tight.  of the  Then t h e  of placed  s c r e w s were parallel  auxiliary blocks.  s a m p l e s were f i r s t  microscope.  rubber  sample was  t h a t t h e b l o c k was  a s o f t m a t e r i a l s micrometer, then  measured w i t h a t r a v e l l i n g  thickness of  to  When  measured  clamped i n t o p l a c e  and  82 • Many m e a s u r e m e n t s were t a k e n and a l l v a l u e s o f t h i c k n e s s u s e d were t h e a v e r a g e . scope  S i n c e the t r a v e l l i n g  c o u l d n o t he r e a d a c c u r a t e l y  m i l l i m e t e r , and s i n c e  to better  the t h i c k n e s s  than  one-tenth  o f t h e r u b b e r sample i s  e x p e c t e d t o be  slightly  different  it  that  t h i c k n e s s measurements cannot  i s believed  any  when clamped  c o n s i d e r e d a n y more a c c u r a t e t h a n 6%. t o be  s l i g h t l y greater f o r stretched  shows t h a t  the r e l a t i v e  temperature  3.  range  never exceeds  be  T h i s e r r o r would samples.  i n thickness  2%,  t h a n when n o t ,  tend  Thompson  (18)  o v e r the  h e n c e c a n be n e g l e c t e d .  GUARD BLOCK CORRECTION At  the  variation  micro-  low  temperature  temperaturesj i t i s very d i f f i c u l t o f t h e g u a r d b l o c k s down t o t h e  o f the m a i n b l o c k s e v e n by a r a d i a t i o n  s h i e l d and  means o f a h e a t s h u n t . increase  though  i n e m i s s i v i t y due  partially  due  the guard b l o c k s are  to f r o s t  temperature  sary to account  f o r the power t r a n s m i t t e d  higher temperatures.  difference,  i n which  difference,  versa  as  i s neces-  t o the h e a t e r b l o c k  to a f i r s t on t h e  c a s e , the power i n p u t may  where "a'' i s the t r a n s f e r  t o an  shield.  a correction  depends l i n e a r l y  PJJ -± a d t  by  i s sometimes t h e c a s e a t  I t i s assumed t h a t  the heat t r a n s f e r  sink  on the b l o c k s and  to n e c e s s a r y l e a k s i n the r a d i a t i o n  from the guard b l o c k or v i c e  protected  i s b e l i e v e d p a r t i a l l y due  Because o f t h i s  mation,  temperature  are connected t o the c o l d  This  to lower  be  approxi-  temperature written  watts  coefficient  i n watts/degree  and " d t "  23. is  the temperature  difference.  e x p e r i m e n t a l l y by comparing without  The c o e f f i c i e n t  the n e c e s s a r y heat  the guard b l o c k s balanced*  at a given  Values  o f " a " a t v a r i o u s temperatures  guards  i s given i n the f o l l o w i n g  " a " i s found i n p u t , w i t h and  temperature.  and f o r each  o f the  table.  TABLE I  Guard B l o c k T r a n s f e r Coefficient "a" Watts/Degree . Side 1 Side 2  Temperature °C  4.  0.06 0.06 0*06 0.09 0.09 0.11 0.11 0.12 0.12  0.10 0.10 0.10 0.15 0.15 0.20 0.20 0-25 0.25  20 0 -20 -40 -60 -80 -100 ^120 -140  THERMOCOUPLE CALIBRATION C a l i b r a t i o n o f the thermocouples  carried  out by Ivey  who f o u n d  very close  shortly after  ( 1 3 ) a n d was l a t e r agreement.  was  checked  originally b y Thompson (18)  S i n c e t h i s work was t a k e n up  Thompson, i t was c o n s i d e r e d u n n e c e s s a r y t o  perform  further  c a l i b r a t i o n , b u t t h e c a l i b r a t i o n was a g a i n  checked  a t the f r e e z i n g point  o f water,  o f Carbon D i o x i d e and the b o i l i n g s h o w i n g a change s i n c e  the l a s t  point  the s u b l i m a t i o n p o i n t o f Oxygen, w i t h o u t  calibration.  A further  check  24. was  made a t room t e m p e r a t u r e  mercury thermometers i n the  by  inserting  c r y o s t a t and  three very taking their  accurate average.  IV.  1.  RESULTS  COMPOSITION OF THE SAMPLES - TABLE I I (a)  Cure:  Natural  Rubber  50 m i n a t 2 9 6 ° F 2M-83456  P a r t s by Weight 4M-317  Smoked S h e e t Total Sulphur Combined S u l p h u r Free Sulphur Z i n c Oxide Zinc Dibutyldithocarbamate  100* 2.0 1.8 0.2 1.0  100 4.0 2.0 2.0 1.0  100 10.0 3.9 6.1 1.0  0.1  0.1  0.1  T o t a l P a r t s by Weight  103.1  105.1  COMPOSITION  (b)  Cure:  Butyl  4M-318  111.1  Rubber  60 m i n a t 3 0 7 ° F  COMPOSITION  8 0 3  .  A  PTt.^ I t f *  8 0 s  _  c  Butyl Total Sulphur Combined S u l p h u r Free Sulphur Z i n c Oxide Te trame t h y l h i u r a m Disulphide  100 2.0 1.6 0.4 1.0  100 4.0 3.0 1*0 1.0  100 10.0 4.4 5.6 1.0  1.0  1.0  1.0  Total Parts  104.0  106.0  112.0  by W e i g h t  The above  i s the c o m p o s i t i o n o f the samplesinves-  26, tigated  over the past year.  include  d a t a on t h e c o m p o s i t i o n o f t h e s a m p l e s u s e d  (a)  F o r comparative  T. M. C. D a u p h i n e e  (7)  purposes,  we  previously.  N a t u r a l Rubber  o  Cure:  120 m i n a t 2 7 4 ° F  .  COMPOSITION  P a r t s by W e i g h t  Pure L a t e x Carbon B l a c k Z i n c Oxide Stearic Acid Pine Tar Sulphur Antioxidant Captax  100  T o t a l P a r t s by Weight  114.1  —  3 4 2 2.7 1.5 0.9  *  (b)  Cure:  D. G-. I v e y  (13)  60 m i n a t 2 9 8 ° F  G.R.S.  (Optimum)  COMPOSITION  P a r t s by Weight  -  G.R.S. Carbon Blaok Z i n c Oxide Sulphur Captax Bardol B  100  T o t a l P a r t s by W e i g h t  113.5  (c)  W. B. Thompson The  with those  5 2 1.5 5  (18)  B u t y l Rubber  samples i n v e s t i g a t e d  investigated  this  b y Thompson were  y e a r by the a u t h o r .  identical  A l l the  27. samples  u s e d b y m y s e l f were p r e p a r e d b y t h e R e s e a r c h  of the Polymer been  Corporation at Sarnia,  c a r e f u l l y molded  o f the approximate was  cut i n half,  measuring  unit.  t o ensure plane p a r a l l e l  Their  width  The p h y s i c a l  and c h e m i c a l p r o p e r t i e s  b y H. B a r r o n i n h i s book (2)  The a n a l y s i s  o f these  entitled  of free sulphur  made b y Mr. C o d r i n g t o n a n d t h e R e s e a r c h D i v i s i o n o f t h e  Polymer  Corporation with s a t i s f a c t o r y  TABLES AND  which  agreement.  GRAPHS  -The in  f a c e s a n d were  a p p r o x i m a t e l y , f o r use i n t h e c o n d u c t i v i t y  "Modern S y n t h e t i c R u b b e r s . "  2.  The samples h a d  d i m e n s i o n s 8" x 6" x 1/16".  rubbers i s given i n f u l l  was  Ontario.  Division  results  a r e shown i n t h e t a b l e s  t h e y were o b t a i n e d .  are  connected by l i n e s  are  drawn t o t h e same s c a l e .  Points plotted  i n chronological  i n the o r d e r  from the r e a d i n g s  order.  A l l graphs  There i s an i n d i c a t i o n  change w i t h age a n d p r e v i o u s h i s t o r y o f t h e s a m p l e s  that a takes  place. The T  m  a b b r e v i a t i o n s used  - temperature o f main h e a t i n g b l o c k , side  T  M2  T  G1 -  T  G2 ~  n  tt  ^  tt  " guard  "  "  ,  »  tt  tt  ti  ^  tt  ti  "  " AT-j_ -r t e m p e r a t u r e £rp  i n the t a b l e s a r e as f o l l o w s .  „  •  M  tt  tt  cold  #1  block  difference tt  #1  between h o t s i d e 1 and c o l d tt  tt  "  2  "  "  side "  28.  E-L  - v o l t a g e a c r o s s main h e a t e r  E  - v  2  1-^  "  ti  current  Ig -  »  T-^ - a v e r a g e  "  - conductivity  Kg  -  " The  " average  two.  2  1  . 2 between h o t  o f sample  which i s not  with T j except degree or  "  temperature  K^  s i d e , Tg,  «  tt  i n supply l i n e  "  1  "  i n side "  "  temperature included  i n a v e r y few  side  1 and  cold  side  1 2  between h o t  i n the  tables,  side is  r e a d i n g s where i t may  2 and  cold  identical v a r y by  a  TABLE I I I  1. 2.  Natural: Natural: M1  S, d=0.195 cm 1% S, d=0.200 cm G1  T  T  °C  °C  13.3 - 6.0 - 29.0 --65.1 - 50.0 - 4-2.1 -124.9 - 99.9 - 93-4 - 82.5 -107.0 - 67.1 - 48-6 - 42.0 - 33.0 - 66.8 - 24.5 - 19.8 - 15.1 - 23.9 - 21.3 - 14-4 - 6.2  13-3 - 6.0 - 29.0 - 64.3 - 50.2 - 42.O -125.0 - 99.5 - 93.4 - 82.4 -105.5 - 63.9 - 45.9 - 39.9 - 33.6 - 65.3 - 26.0 - 20.3 - H.8 - 24.3 - 21.7 - 14.5 - 6.2  T  M2  °C 11.9 - 6.6 - 27.7 - 60.9 - 46.5 - 38.8 -126.0 - 99.7 - 93.5 - 82.5 -106.3 - 67.6 - 48.5 -.42.6 - 32.6 - 69.1 - .25.8 - 22.1 - 16.3 - 24.2 - 21.7 - 14.7 - 6.3  ZERO STRETCH  . G2 T  °C ir.9 - 6.5 - 27.7 - 59.8 - 46.6 - 38.7 -125.8 - 99.7 - 93-4 - 82.4 -104.5 -.'63:5 - 44.6 - 38.2 - 32.5 - 63.9 - 24.8 - 22.2 - 16.5 - 23.8 - 21.4 - 14.7 - 6.7  T  AT  C  °c  °c  4.6 8.7 - 13 '.6 7.6 - 38.6 • 9.6 - 80.8 15.7 - 65.1 15.1 - 53.6 _ 11.7 -151.8 26.9 18.5 -118.4 -110.0 16.6 14.8 - 97.3 28.5 -135.5 11.2 -'78.3 6.0 - 54.6 -47.4 5-4 6.1 - 39.1 11.0 - 77.8 5.8 - 30.3 - 27.2 7.4 6.6 - 21.7 - 30.2 6.3 5.8 - 27.1 - 19.8 5.4 4.7 - 10.9  l  *1  °c  volts  ma  volts  ma  °c  xio4  xl04  7.3 7.0 10.9 19.9 18.6 14.8 25.8 18.7 16.5 14.8 29.2 10.7 6.1 4.8 5.5 8.7 4.5 .5.1 5-4 6.0 5.4 5.1 ' 4.6  5.88 4.46 5-73 7.32 7.14 6.66 9.21 7.83 7.44 7.11 9.18 5.52 3.90 2.28 3.81 3.42 4.40 4.83 4.14 3.75 3-75 3.75 3.75  322 ,245 314 402 392 366 515 432 411 392 500 305 215 126 210 189 242 265 229 208 208 208 208  4-98 4.86 6.21 8.19 7.95 7.11 8.88 7.80 7.23 6.93 9.18 5.34 3.72 2.31 4.02 3.36 3.45 4.17 3.99 4.02 4.02 4.02 4.02  269 9 261 - 10 333 - 34 - 73 441 428 - 58 384 - 48 -138 483 423 -109 -102 392 376 - 90 500 -121 288 - 73 202 - 52 125 - 45 218 • - 36 182 - 73 186 - 28 210 - 2L - 18 215 217 - 27 217 - 24 217 - 17 217 - 9  4.15 2.73 3.56 3.38 3.52 3-96 3.34 3.47 3.51 3.58 3.20 1.70 3-96 2.13 2.22 2.80 2.98 3.15 2.81 2.26 2.42 2.75 3.16  3.60 3.53 3.71 3.42 3.56 3.59 3.24 3.45 3.36 3.44 3.30  2  E  E  2  J  2  T  l  K  l  K  2  3.42 2.63 3.10 2.54 3.20 3.30 3.03 2.98 3.26 3.36 3.56  TABLE III - CONTINUED  M1  T  T  °C  2.0  18.9 32.7 ?/:..!  -  M2  °c  °C  2.2 IS. 8 32.2  - 1.8  13.9  18.0 31.8 33.2  '  T  AT!  G2  °C  -  1.3 18.0 31.0 33.1  °C  -  6.3  12.0 27.1 28.5  AT  II  2  °C  °C  4.3 6.9 5.6 5.6  1.5 6.0  4.7 4.7  volts  3.75 5.25 5.25 5.25  ma  208 288 289 289  E . J2 2  volts  4.02 . A. 6 2 4.65 4-65  ma  217  250 251 251  Tl o C  - 4 15 30 31  Kl  K  2  xlO^  xio4  3.36  3.81  Z..14 A. 99  A. 5 0  5.10  3.77 /..7«J  TABLE IV 1 . Natural": 2. "Natural':  -  ?/../  - n.6 - 26.6 - 1Z .6 - 6.4 -113.0 - 92.6 13.0 -  32.3  - 6Z...5 - LI . 3 -  17.4  -  ?.5' • ~, t f  -  95.6 92.1 40.3 5.3 10.3 34.3 - 31.0 ' - 26.3 - 1Z.3 - 6.5 -111.5 -' 9 3 . 4 12.8 - 32.0 - 64.5  - urn -  -  17.2 ?.5 29 o7  M2  .  °c  °c 94..490.3 /I.? 5.4 11.2  T „  T„ Gl  T  -  2% S, d=0.125 cm L$ S, d = 0 . 1 3 0 cm  :  G2  . - 99.2 '• - 93.7 - 41.0 • ' - 4-5 - 10.3 - ??.9 ' - 31.0 •- 26.6 - 14.5 - 6.5 -113.4 - 92.4 12.3 - 81.9  - 65.6 •- /6.0 16.? ~.r\  0  °c  °c  -  100% STRETCH  1  - 99.2 - 9/.5 - 40.3 - 4-2 - 10.0 - 33.9 - 31.1 - 26.9 - 14.4, - 6.4 -112.5 - 92.3 12.7 - 32.2. -  > j. »<->  Z6.3 16.2 - ^.2 30.1 -  c c  -125.3 -112.6 -'4-8.0 - 9.4 -  16.1  - Z2.4 - 38.9 - 34.2 - 20.7 - 12.0 -133.0 -111.6 9.6 -102.7 - a . o - 53.5 -  26.3  - 10.0. °5 ,1  dT., 1  AT„  °c 31:4 22.3 6.7 4.0 '...9 3.0 7.9 7.6 6.1 5.6 23.0 19.0 i ~n, '  0 . .  16.5 ' 14.2 9.46.5 '.6  E-, 1  In 1  2  I„ 2  T, 1  K, 1  °c  volts  ma  volts  ma.  °c  xlO^  xlO  26.6 18.9 7.0 Z..9 5-3 3.5 7.9 7.6 6.2 5.5 24.6 19.2 3-2 20.3 ' 15.4 12.5 10.5 6.8  8.40 7.56  464  1.91 2.16  Z..26 3.42  230 189 191 254 254 254 24.6 2/3  1.42 I.4.8 2.05 2.00 1.74 1.79 1.80  2  3.45 4-59 Z.59 4.59 4.45 Z.41 5-94 6.33 4-02 ^.54 6.80 6.60  5.945.06 '  <* i  413  327  350 221 °60 375 364 ?27 *-/V  8.58 7.33 3.50 4.03 4.08 5.22 5.22 5.22  467  425 194 220 221  -110 -101 _  n  281 231  ~ -  15 33 35 ?0  4-70  252.  -  18  4.41 8.4.0 7-92 3.72 7.9 7.23 6 .75 6.33  233  - 9 -126 -101 11 - 92 - 7?  7  5«07 4.62  281  458 429 202 4?/ ?5 363 345 OC  252.  -  51  - 22 27  1.34  2.14 2.31 1.12 1.31 3.13 1.54 1.36 2.02 2.54 ' ^.64 3.44  2 z  1.3? 2.°7 2.0/. ?. 13  2.32  2.?8 2.44. 2./5 2.0? 2.25 2.94 2.03 r.?5 2.51 5.64 2.95  VO H  TABLE V 1. .2.  Natural: Butyl: TjH °C  -117.0 -103.2 - 90.2 - 74.6 - 60.1 - 44-5 - 30.3 - 22.1 3.8 8.7 18.7 - 27.0 - 49.3 - 69.0 -126.9 - 38.0  10% S, l& S,  -T ,. G  d=0.195 d 0.174  ramTOln  ZERO STRETCH  =  T  h  2  T  G  2  °C  °C  °C  -117.0 -103.5 - 90.2 - 7/.6 - 60.2 - 44.5 - 30.2 - 22.1 3.8 8.7 13.7 - 27.1 - 49.3 - 68.9 -126.6 - 38.0 '  -117.7 -3-03.3 - 90.3 - 79.0 , - 64.5 • - 47.4 - 34-1 - 25.1 - 10,0 8.3 18.4 - 28.7 - 49.5 - 69.0 -128.6 - 39.3  -117.7 -103.6 - 90.3 - 79.0 - 6A.5 - 47./ - 34.1 - 25.2 - 10.0 8.3 18.4 . - 23.6 - 49.5 - 68.9 -128.5 - 89.3  T  C  °C  ^ volts  -141.0 5.39. -122.5 A . 93 4.92 -106.5 - 91.6 5,94 5.64 - 74.7 - 56.I 5.0/ 5.04 - AO.3 - 31.7 5.01 - 15.7 - 4 . 5 4 0.7 5.16 4.53 12.9 - 35.0 A . 20 4.00 - 58.5 - 30.8 4.21 -153.2 6.27 -105.0 5.16  I X  E  2  i  2  ma  volts  326 302 272 ?26 311 273 278 277 243 235 250 232 215 233 347 285  423 7.33 7.24 ^39 6 . 7 7 • 368 290 277 245 245 230 272 233 229 276 312 386 366  f  T]  ma  °2?  5.37 5.13 4-55 4.55 4-27 5.01 4.29 4.23 5.00 5.73 7.11 6.77  4 _ °C  °C  24.0 19.3 16.3 17.0 14.6 11.6 10.5 9.6 6.9 3.0 5.8 8.0 9.2 11.8 26.3' 17.0  23.3 19.2 16.2 12.6 10.2 3.7 6.7 6.6 5.7 7.6 5.5 6.3 9.0 11.8 24.6 15.7  «  x  °C -129 -113 - 93 - 33 - 67 - 50 - 35 - 27 - 12 5 16 - 31 - 54 - 75 -140 - 97  ^  %  xlO 1  1.53 1.55 1.57 2.13 2.29 2.31 2.57 2.77 3.12 3.52 ' 3.74 2.32 1.78 1.62. 1.63 1.66  ±LQ l  2.A6 2.5A 1.62 -.61 2.62 2.7° 2.34 '2.36 2.97 3.06 °..ll 2.66 2.62 2.60 1.95 2.66  TABLE VI Natural:. 10% S d=0.1J2 cm 2. Butyl: 4-% S, d = 0 . 1 3 3 cm G1 °c  T M2 °C  T G2 °C  - 22.6 - 45.6 - 74-1 -110.4 -1T3-1 - 90.9 - 65.5 - 35.1  - 22.7 - 46.4 - 74-0 -111.0 -135.0 - 93.1 - 66.6 - 36.3 - 3.8  - 22.8 - 46.3 - 73-9 -111.0 -135.2 - 93.0 - 66.6 - 36.3 - 3.8  T  T  °c - 22.7 - 4-5.7 - 74.1 -110.4 -133.1 - 90.9 - 65.5 - 35.1 - 3.8  -  3.8  10Qf ' STRETCH  "  1.  T  C  °c - 29.2 - 53.0 - 84.0 -127.0 -153.4 -105.1 - 76.4 - 43.1 - 8.3  o  l  h  volts  ma  h volts : ma  4.26 3.51 3.81 4.33 5.4.7 5.03 4-78 4.64 4.02  235 195 211 263 304 ' 278 265 257 222  5-03 4.74 5.87 6.97 7.38 6.30 5.38. 5.63 4.75  E  E  2  271 257 319 380 4.03 343 319 305 258  * 1 °C T  6.5' 7.3 9.9 16.6 20.3 14.2 10.9 3.0 5.0  G°C  h xlO^  6.5 — 2 6 6.6 -49 10.0 - 79 16.0 -119 13.4 -1Z3 12.0 - 98 9.8 - 71 6.8 - 39 5-0 - 6  2.16 1.32 1.12 1.08 1.17 1.37 1.61 2.07 2.49  * 2 °C T  T  l  K  2  x!0  A  2.71 2.41 2.49 2.20 2.09 2.^5 2.43 3.30  3.18  VO  TABLE V I I 1. 2.  B u t y l : 2% S, d=0.183 cm B u t y l : 10% S, d=0.180 cm T Gl °c  T M1 °c 1  - 3.0 - 21.4 - 35.2 - 45.0 - 95.7 -124.4 - 82.5 - 64.O - 35-4 - 14.7 18.8  - 3.0 — 21.4 - ?5.2 -  44M?  - 95-7 -I24.4 - 82.5 - 64.O - 35.4 - 14.7 18.8  T M2 °c - 3.3 - 22.3 - 35.4 - AA.9 - 94-9 -123.9 - 81.0 - 62.2. - 36.0 - 12.3 20.0  ZERO STRETCH T G2 °c  - 3.3 - 22.3 - 35-4 - 44.-9 - 94.9 -123.9 - 31.2 .- 62.2 - 36.0 - 12.3 20.0  T c °c' - 9.2 - 29.3 - 44.8 - 55.0 -106.9 -151.1 - 97.A - 75.1 - 45.2 - 19-4 14.5  2  l  V  volts  ma  volts  4.12 4.2.6 4.25 4.20 4.30 6.75 4-50 4.44 4-17 2.94 .3.84  226 236 235 231 252 341 250 239 231 164, 214  4.20 A.A7 5.03 5.22 5.56 8.40 6 . A2 5.36 5.10 4.38 4-26  E  E  -  ma  T 1 °C  T 2 °C  229 2A6 275 287 306 457 354 315 281 240 235  6.2 8.4 9.6 - 10.0. 11.2 26.7 14.9 11.1 9.8 4.7 • 4.3  •5-9 7.5 9.4 10.1 12.0 27.2 - 16.4. 12.9 9.2 7.1 5.5  X  2  T 1 °C  xlO^  xlO^  - 6 - 26 - 40 - 50 -100 -138 - 90 - 69 - 4-0 - 17 17  2.66 2.1/ 1.86 1.75 1.73 1.57 1.^5 1.70 1.81 1.36 3. A3  2.79 2.53 2.57 2.56 2.A9 2.46 2.44 2.52 2.73 2.60 3.19  K  l  K  2  TABLE V I I I 1. 2.  Butyl:2 2% S, B u t y l : 2% S, T ML o C  '9.1 - H.9  -36.8 - 55.0 - 85.1 -11/.. 5 27.5 8.3 - 35.9 - 65.2 - 92.9  -  d=0.131 cm, dzO.180 cm, T M2 o C  G1 o C T  9.2 - 1/..8 - 36.8 -  55-0  - 85.1 -114.5 27.5  -  8.3  35.9 65.2 - 92.9  15-4  - 35-8 - 53.6 - 79.8 . -108.4 29.1 • —  T  G2  l  0  -  15.5  - 35.8 - 53-6  l  h  c  volts  3.2 21.4  4.71 4.18 4.03  0  C  9.7  9-7 -  100% s t r e t c h zero s t r e t c h  -  - 43.9  - 63.9 - 96.7 -131.0 -108.4 23.6 29-1 . - 13.8 - 44.1 - 74.6 -103.0 -  79.8  E  4.26  3.98 4.29 4.26 4.31  5.66 5.08 4-/8  2  h  ma  volts  na  261 230  4.32  254 225 253 291 384 427  224  237 221 238 236 240 313 280 248  E  4.06 4.73 5.2.8 6.95 7.74 4.39  2/4  * 2 T  0  C  6.0 6.5  7.1  8.9 11.6 16.5 3.9 5.5  8.2  9.4  10.1  0  C  6.5  6.0 8.1 10.3 16.9 22.6 5.5  T  0  l C  6 - 18 - 40 - 59 - 91  -123 26 - 11 - 40  - 70 -98  .  l  K  xlO  4  2.63 1.91 1.63 1.45  0.97 0.79 3.31 2.39 2.27 1.93 l./l  K  2  4  xlO ' 2.98 2.66  2.60 2.61 2.77 2.57 3.43  36.  Results  f o r N a t u r a l R u b b e r J$  S  37.  r  N.«„,.l  .10"/.$  A B C  AUS » > • II  A  i -200  160  120  80  40  0  10  *40  PLATE 7 Results  f o r N a t u r a l Rubber 10% S  N.tur.l < 27. S 100 7. Stre»«h  -200  160  120  80  A JULY 19 B " 20 C •• 2J| 0 - z\ E AUG 4  40  0  + 40  PLATE 8 Results  f o r Natural  Rubber 2% S, 100% S t r e t c h  38.  ^1 A B C D E  PLATE Results  f o r Natural  Results  f o r Natural  9  Rubber 4%  PLATE  J U L Y 19 •• 20, 23 24 AUG 4  S, 100%  Stretch  10  Rubber 10%  S, 100%  Stretch  39.  PLATE 12 D a u p h i n e e ' s R e s u l t s f o r N a t u r a l Rubber 2% Refer  (7)  S, 100%  Stretch  4-0.  PLATE  13  I v e y ' s R e s u l t s f o r G.R.S. 0%  Refer  (13)  and  100$  Stretch  P L A T E 15 R e s u l t s f o r B u t y l Rubber )&  S  4-2.  PLATE 16 Results  f o r B u t y l R u b b e r 10%  PLATE  S  17  R e s u l t s f o r B u t y l R u b b e r 2$  S, 100$  Stretch  4-3.  r  BUTYL 100 7.  -200  160  4 •/. S  A U G 18  Stretch  120  80  40  0  +40  A  P L A T E 18 Results  f o r B u t y l R u b b e r J$  S, 100%  Stretch  P L A T E 19' Thompson's R e s u l t s  f o r B u t y l R u b b e r 2% S  Refer  (18)  4-4-•  -PLATE 20 Thompson's R e s u l t s  f o r B u t y l Rubber 2$ S, 100$  PLATE 21 Thompson's R e s u l t s Refer  (18)  f o r B u t y l R u b b e r 10$ S  Stretch  5.  DISCUSSION OF THE (a)  Natural  RESULTS  Rubber  With. 2fo S u l p h u r c o n t e n t i n the r u b b e r sample 5)  a l a r g e r e g i o n o c c u r s between t e m p e r a t u r e s  and  2 0 ° C b e t w e e n w h i c h no  has been measured. in  two  branches  relatively latter  v a l u e o f the t h e r m a l  B, and  D, E , A, F*  together  case * the t h e r m a l c o n d u c t i v i t y drops s h a r p l y temperature.  The  f r o m a p p r o x i m a t e l y 3.3  x 10  1 oal.sec.  x 10""  —1 ' —1 cm.  deg.  a t 2 0 ° C.  4  branch  at  No r e a d i n g  o b t a i n e d i n the l o w e r b r a n c h b e l o w - 8 0 ° C where t h e  uctivity join  i s n e a r 1.6 the upper  x 1 0 " * K.  u n i t s , and  branch around  below - 80° C appeared  on  2 0 ° C.  the u p p e r  change was  branch.  the temperature  which  t h e r e a d i n g s were t a k e n , a p p e a r e d  Dauphinee  Comparison  effected,  The and  t o have  (Plate  spontaneous  11)  changes  by D a u p h i n e e p r e s e n t work.  be  i n the upper  of the curve w i t h that shows f a i r  c o n d u c t i v i t y a t 0 ° C,  prepared  rapidly  direction  in  the o r d e r i n little  on t h e a b s o l u t e amount-of the c o n d u c t i v i t y , i . e .  w h e t h e r t h e c o n d u c t i v i t y would branch.  increases  cond-  A l l readings taken  which  influence  a  with  c o n d u c t i v i t y i n the upper  - 1 4 0 ° C t o a p p r o x i m a t e l y 4.3  to  conductivity  the former showing  Q  was  C  s m a l l change w i t h t e m p e r a t u r e , whereas i n t h e ':•>-. .  decreasing  goes  below - 140°  The m e a s u r e d p o i n t s a r e g r o u p e d  C, D,  (Plate  and  agreement  i n part  or lower  o b t a i n e d by i n the v a l u e f o r  o f the branch E.  b e t w e e n t h e two  branches  which  The were  have n o t b e e n o b s e r v e d t o t h e same d e g r e e However, t h e  with d i f f e r e n t  samples  fillers  u s e d by D a u p h i n e e  under  different  many found i n the  were  conditions  and  46.  p r o b a b l y c o n t a i n a d i f f e r e n t amount o f combined s u l p h u r as w e l l as b e i n g o f d i f f e r e n t age.  Dauphinee f r e q u e n t l y n o t e d a  change from one b r a n c h t o t h e o t h e r w h i l e r e a d i n g s were a c t u a l l y b e i n g made.  Upon s t r e t c h i n g h i s sample, he found t h e num-  ber o f t h e s e changes t o i n c r e a s e , w h i c h he e x p l a i n s as  indica-  t i n g a s m a l l energy d i f f e r e n c e between t h e two branches w h i c h on s t r e t c h i n g • i s made even  smaller.  Upon s t r e t c h i n g o f my sample t h e r e a r e s t i l l  two  branches Ay E, D, and C, B, n o t i c e a b l e ( P l a t e $) but t h e d i s t ance between them was  g r e a t l y reduced and t h e r e was a  ced d e c r e a s e i n c o n d u c t i v i t y a t low t e m p e r a t u r e . ous changes a r e o b s e r v e d .  No  pronounspontane-  These r e s u l t s conform more t o r e a d -  i n g s o b t a i n e d by I v e y on G.R.S. ( P l a t e 13) where no changes were o b s e r v e d between t h e two branches and where a 100$ s i o n caused a n o t i c e a b l e d e c r e a s e i n c o n d u c t i v i t y .  exten-  They d i f -  f e r i n so f a r as I v e y ' s v a l u e s show a n e g l i g i b l e change i n t h e d i f f e r e n c e i n t h e r m a l c o n d u c t i v i t y between t h e two b r a n c h e s , whereas mine show an a p p r e c i a b l e d i f f e r e n c e .  Ivey's curves  a l l o w one t o o b s e r v e the d i f f e r e n c e w h i c h o c c u r s i n t h e t h e r mal c o n d u c t i v i t y o f rubber when r e a d i n g s a r e made oh d i f f e r e n t days, and when t h e y a r e a l l o b t a i n e d i n one c o n t i n u o u s s e r i e s of observations. The i n v e s t i g a t i o n o f change o f t h e r m a l . c o n d u c t i v i t y w i t h t h e amount o f s u l p h u r was the main i n t e r e s t i n t h e p r e s ent work.  The a d d i t i o n o f s u l p h u r t o t h e samples used t e n d e d  t o decrease the c o n d u c t i v i t y i n a l l c a s e s , t h e decrease i n c o n d u c t i v i t y i n the u n s t r e t c h e d r u b b e r b e i n g g r e a t e r t h a n i n  the  stretched  conductivity The  rubber.  At least  curve, but t h e i r  conductivity  of natural  combined s u l p h u r i n c r e a s e s - 8 0 ° C t o 3.8 x 1 0 In  9  two b r a n c h e s  range  - 1 4 0 ° C.  K. u n i t s  Upon 1 0 0 % e l o n g a t i o n ,  conductivity degT  the  1  a t - 3 0 ° C t o 1.65 x 1 0 ~ fairly  c o n s t a n t down t o  i t was f o u n d t h a t  4  fairly  c o n s t a n t down t o - 1 4 0 ° C.  from t h i s p o i n t ,  a t 0 ° G.  now t h e  I t c a n be n o t e d t h a t  temperature  practically  ing  temperature  a t - 2 5 ° C.  Butyl  a t - 6 5 ° C where Upon  was  t o n e a r 2.5 x 10 the curve f o r i n c r e a s -  i n t e r s e c t s the curve f o r decreas-  Rubber  the temperature  graph the r e s u l t s of the thermal  c o n d u c t i v i t y measurements w i t h u n s t r e t c h e d B u t y l 2% added s u l p h u r show t h e e x i s t e n c e C, e a c h w i t h a d i f f e r e n t  conductivity.  I n the upper  rubber with  o f two b r a n c h e s , AJ3, a n d A and B a r e b e l i e v e d  t o be i n t h e same b r a n c h a n d t h e d i f f e r e n c e a time e f f e c t .  increasing  the thermal c o n d u c t i v i t y  almost l i n e a r l y  ing  In  K.  4  o b s e r v e d t o be i n c r e a s e d  (b)  9  d e c r e a s e s r a p i d l y f r o m 2.2 x 10"" c a l . s e c T ^ - c m r ^  temperature  K. u n i t s  b r a n c h B.  decreases at f i r s t  a t - 2 5 ° 0 t o n e a r 1.2 x 10"* K. u n i t s  remains  units at  a t 20° 0 i n the upper  t h e l o w e r b r a n c h G, A, t h e c o n d u c t i v i t y 4  i s smaller.  r a p i d l y f r o m 2.2 x 10"  u n i t s a t - 7 0 ° G where i t r e m a i n s  it  o f temperature  i n the  rubber a t z e r o s t r e t c h w i t h 10%  K. u n i t s  r a p i d l y f r o m 2.35 x 1 0 ~  appear  i s perhaps  branch, the c o n d u c t i v i t y  due t o decreas-  e s r a p i d l y f r o m a p p r o x i m a t e l y 3.0 x 10"" K. u n i t s a t 5 ° 0 down 4  t o a p p r o x i m a t e l y 2.65 x 1 0 ~  4  K. u n i t s a t - 1 5 ° C where i t  remains constant  down t o - 1 2 0 ° C.  In the lower r a p i d l y from 1.7 x I O "  4  branch,  a b o u t 3.4 x I O "  K. u n i t s  constant at l e a s t  the c o n d u c t i v i t y decreases a t 2 0 ° c down t o  4  a t - 5 0 ° C where i t t o o r e m a i n s n e a r l y  t o as l o w a s - 1 4 0 ° C, b e l o w w h i c h t h e  c o n d u c t i v i t y was n o t m e a s u r e d . w i t h Thompson's c u r v e effect dered  approximately  A comparison o f t h i s  which a l s o d i s c l o s e s  - i f the average  value  a likely  of the p o i n t s alone  curve time  i s consi-  ( P l a t e 19) - shows q u i t e good agreement i n t h a t t h e  d i s t a n c e between t h e b r a n c h e s  i s similar,  over  i s c o n s t a n t , and the r a t e o f  p o r t i o n s o f each branch  decrease.of nearly  c o n d u c t i v i t y from  t h e same.  I t i s noted  the c o n d u c t i v i t y  2 0 ° C down t o a r o u n d t h a t the v a l u e s  - 20° C i s  of conductivity  o b t a i n e d b y Thompson a r e h i g h e r by a b o u t 0.6 x 1 0 ~  K.  units.  A n i n c r e a s e i n t h e amount of. s u l p h u r p r e s e n t  i n the  B u t y l rubber  sample  B u t y l rubber  w i t h 2% s u l p h u r  lessen that  one o f t h e two b r a n c h e s o b s e r v e d i n to disappear  t o such  i t c a n a l s o be e x p l a i n e d a s a d i f f e r e n c e The v a l u e  w i t h 4% t o t a l obtained  o f the t h e r m a l  sulphur  content  f o r the upper branch  2% s u l p h u r .  due t o a  i s very s i m i l a r C i n the curve  when i t a g a i n d e c r e a s e s .  time  constant  Similarly,  of Butyl  rubber  3.15 x 1 0 ~ 4  4  at  K. u n i t s a t  to near  B u t y l rubber  s u l p h u r added shows t h e same c o n s t a n t  rubber  t o the value  s l o w l y t o 2.6 - 2.9 x 1 0 ~  - 3 0 ° C where i t r e m a i n s f a i r l y  an e x t e n t  conductivity of Butyl  I t s t a r t s at approximately  2 0 ° C and d e c r e a s e s  total  or, at l e a s t , to  the d i f f e r e n c e between the branches  effect.  with  causes  4  - 120^ C, with 10%  thermal  conducti-  4-9. vity  over the range  a p p r o x i m a t e l y 2.6 u n i t s a t 2 0 ° G.  x 10~ Two  10% S-sample, b o t h erature, in  the  - 10° G to - 140° K.  4  series  on d i f f e r e n t  (Plate  are about vity  o f the  0.5  21)  x 10~  curve.  days,  one  K.  The  average  u n i t s lower.  ture.  However, a l a r g e  v i t y was  noted  just  the c o n d u c t i v i t y a t 1 0 ° G and  x 10"  I n the upper  f r o m 3.3 K.  4  The  x 10"*  units  stretch,  perhaps  for a slight  tures.  The  during this t h e end Values stretch  K.  w i t h 2%  they  sulphur i n i t  temperature  x 10~  t o 0.65  the t h e r m a l  tempera-  conducti-  K.  4  x 10""  units K.  4  units  conductivity  C  decrease  of b u t y l rubber no  w i t h 4%  change w h a t e v e r  i n c o n d u c t i v i t y at low  sample u n d e r i n v e s t i g a t i o n  t o r e i n the  S,  except tempera-  cryostat  t h e r e f o r e the v a l u e s o b t a i n e d a t  o f t h e m e a s u r e m e n t s seem t o be  c o u l d n o t be  that  u n i t s a t 25° G t o approximately  shows p r a c t i c a l l y  f o r b u t y l rubber  dif-  found.  i s 2.60  linearly  conductivity  o b s e r v a t i o n and  to a  of n a t u r a l rubber. . Here,  branch  branch,  at -100°  thermal  a t 100%  4  attributed  P o i n t s of high conducti-  i n low  as i n t h e c a s e  i n the lower  difference  c o n d u c t i v i t y n e a r room  decrease  decreases almost  - 1 4 0 ° G.  decreases  the  this  v a l u e s o b t a i n e d by  elongation of b u t y l rubber  d i d not a p p r e c i a b l y e f f e c t  Any  agreement e x c e p t  shown on Thompson*s c u r v e were n o t 100%  K.  4  w i t h d e c r e a s i n g temp-  temperature.  a g a i n show f a i r 4  x 10""  o f measurements were made w i t h  c o n d u c t i v i t y i s n o t g r e a t enough t o be  Thompson  1.4  I t i n c r e a s e s from  u n i t s a t - 1 0 ° G t o 3.2  other with i n c r e a s i n g  ferent-branch  at  C.  w i t h 10%  doubtful (Plate  s u l p h u r added and  obtained since  at  the r u b b e r would  18). 100%  not  s t r e t c h s u f f i c i e n t l y without  tearing.  Readings o f the thermal b e r a r e somewhat a  s  to the absolute values.  values and or  s i m i l a r to those  conductivity  of butyl  o b t a i n e d by Thompson  The d i f f e r e n c e  except  i n the absolute  i s t o o g r e a t t o be a t t r i b u t e d t o e x p e r i m e n t a l  i s more l i k e l y due t o unknown d i f f e r e n c e s to ageing.  rub-  errors,  i n t h e samples  5L\.  Y.  The values  of thermal  rubbers. content effeot  values  The a t 0%  t o be  obtained are  conductivity  vulcanization and  100%  the  investigated  difference  branches o f the noticeable  i n g o o d agreement w i t h known  i n natural  of rubber  i n the p r e s e n t the  thermal  between the  conductivity  curve.  and  with  s t r e t c h , w h i c h was  general r e s u l t of lowering lessening  SUMMARY  synthetic  increasing  sulphur  the p a r t i c u l a r paper,  has  the  c o n d u c t i v i t y and  of  v a l u e s f o r the  two  A d e f i n i t e time  effect is  p a r t i c u l a r l y i n s a m p l e s w h i c h were i n v e s t i g a t e d  narrow temperature considerable  time  r e g i o n s on d i f f e r e n t d a y s , i n t e r v a l between.  with  a  in  52.  VI.  BIBLIOGRAPHY  1.  Allen  2.  B a r r o n , H., Modern S y n t h e t i c and H a l l  3.  and Maxwell, A Textbook 'Maxmillan  o f H e a t , P t s . 1 a n d 2, 1944 Rubbers,  Chapman 194-3  B e k k e d a h l , N., J . o f R e s e a r c h , N a t . B u r . o f Standards 13, 4-H, B e k k e d a h l , N., a n d M a t h e s o n , ' Research  1934-  J . , J .of 15, 503,  1935  5.  Carslaw,  6.  C o d r i n g t o n , R. S., D i e l e c t r i c P r o p e r t i e s o f N a t u r a l and S y n t h e t i c R u b b e l r - S u l p h u r Compounds, M. A. T h e s i s , U. B. C 194-8  7.  Dauphinee,  8.  Frumkin,  9.  Introduction t o t h e Mathematical Theory o f t h e C o n d u c t i o n o f H e a t , P t s . 1 a n d 2, Maxmillan 194-4  T. M c C , Heat C o n d u c t i v i t y o f R u b b e r a t Low T e m p e r a t u r e s , M. A. T h e s i s , U. B. C. 194-5  L . , a n d D u b i n k e r , Y., Tech  F r u m k i n , L . , a n d D u b i n k e r , Y.,  Rubber Chem. 11, 359,  1938  Rubber Chem. 13, 361, 194-0  Tech 10.  Guth, E., Kantchuk  13, 201,  11.  G u t h , E . , a n d Mark, H., M o n a t s c h  12. 13.  Handbook o f Chem. and P h y s . , Chem. Rubber Pub. Co. I v e y , D.- G., Heat C o n d u c t i v i t y o f S y n t h e t i c Rubber a t Low T e m p e r a t u r e s , M. A. T h e s i s , U.B.C. 194-6  14-.  James, H. M., a n d Guth, E . , P h y s . Rev.. . 59, 111,  15.  S c h a l l a m a c k , A., P r o c . P h y s .  16.  S c h a l l a m a c k , A., N a t u r e  f . Chem.  1937  65, 93, 1934-  194-1  S o c , Landau,53, 2 1 4 , 194-1 1 4 5 , 67,  1940  53. 17.  " T e m p e r a t u r e , I t s Measurement a n d C o n t r o l i n S c i e n c e and I n d u s t r y " A Symposium p u b l i s h e d by t h e A m e r i c a n I n s t i t u t e of Physics. Articles: (a) R e p r o d u c i b i l i t y o f the Ice Point, Thomas, J . L . (b) C a l i b r a t i o n o f T h e r m o c o u p l e s a t Low Temperatures, S c o t t , R. B.  18.  Thompson, ¥ . B., The T h e r m a l C o n d u c t i v i t y o f B u t y l R u b b e r a t Lov; T e m p e r a t u r e s , M. A. T h e s i s , U. B. C 1947  

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