To examine the effect of bromination of carbon fibers on the coefficient of thermal expansion (CTE) of carbon fiber epoxy composites, several pristine and brominated carbon fiber-epoxy composite samples were subjected to thermomechanical analysis. The CTE's of these samples were measured in the uniaxial and transverse directions. The CTE was dominated by the fibers in the uniaxial direction, while it was dominated by the matrix in the transverse directions. Bromination had no effect on the CTE of any of the composites. In addition, the CTE of fiber tow was measured in the absence of a polymer matrix, using an extension probe. The results from this technique were inconclusive

Jaworske, D. A.

Maciag, C.

English

NASA Technical Reports Server

4,  . 
.* 
NASA Technical Memorandum 100536 
The Effect of Bromination of Carbon Fibers 
on the Coefficient of Thermal Expansion of 
Graphite Fiber-Epoxy Composites 
(AASA-Tfl-lb0236) T H E  EFFECT OF B R O I Y I I A T I O N  U 88- 10899 
OF CARBON FIBERS 08 THE COEPPICIEMT OF 
THERHAL E X P A N S I O N  OF GRAPHITE FIBER-EPOXY 
AO2/XP AD? CSCL 11D G3/28 0706494 
COnPOSITES {BASR) 6 p a v a i l :  HTIS HC Undlas 
D.A. Jaw& 
Lewis Research Center 
czeveland, Ohio 
and 
c. luhiciag 
C k M  SWZ University 
c l e w ,  CXiQ 
November 1987 
\ 
https://ntrs.nasa.gov/search.jsp?R=19880001517 2020-03-20T08:53:03+00:00Z
THE EFFECT OF BROMINATION OF CARBON FIBERS ON THE COEFFICIENT OF THERMAL 
EXPANSION OF GRAPHITE F IBER - EPOXY COMPOSITES 
D.A .  Jaworske 
N a t i o n a l  Ae ronau t i cs  and Space A d m i n i s t r a t i o n  
Lewis Research Center  
Cleveland,  Ohio 44135 
and 
C.  Maciag 
C leve land  S t a t e  U n i v e r s i t y  
Cleveland,  Ohio 44115 
SUMMARY 
To examine t h e  e f f e c t  o f  b r o m i n a t i o n  o f  carbon f i b e r s  on t h e  c o e f f i c i e n t  
o f  thermal expansion (CTE) o f  carbon f i b e r  epoxy composi t e s ,  seve ra l  p r i  s t i  ne 
and brominated carbon f i b e r  - epoxy composite samples w e r e  s u b j e c t e d  t o  thermo- 
I mechanical a n a l y s i s .  The CTE's o f  these samples w e r e  measured i n  t h e  u n i a x i a l  
a and t ransve rse  d i r e c t i o n s .  The CTE was dominated by t h e  f i b e r s  i n  t h e  u n i a x i a l  
Pa d i r e c t i o n ,  w h i l e  i t  was dominated by t h e  m a t r i x  i n  t h e  t r a n s v e r s e  d i r e c t i o n s .  
B romina t ion  had no e f f e c t  on t h e  CTE o f  any o f  t h e  composi tes.  
t h e  CTE of  f i b e r  tow was measured i n  t h e  absence o f  a polymer m a t r i x ,  u s i n g  an 
e x t e n s i o n  probe. The r e s u l t s  from t h i s  technique were  i n c o n c l u s i v e .  
4 
In 
m 
I 
W I n  a d d i t i o n ,  
INTRODUCTION 
A s  an e n g i n e e r i n g  parameter,  t h e  c o e f f i c i e n t  o f  thermal expansion p l a y s  
an i m p o r t a n t  r o l e  i n  p o s i t i o n  s e n s i t i v e  s t r u c t u r a l  components t h a t  a r e  exposed 
to  temperature extremes, such as o r b i t i n g  s a t e l l i t e  antenna d i shes  and s o l a r  
dynamic power systems. I n  o r d e r  t o  l i m i t  t h e  i n f l u e n c e  o f  temperature 
extremes, much of t h e  proposed space s t a t i o n  w i l l  be composed o f  g r a p h i t e  
epoxy composites designed t o  y i e l d  near-zero C T E ' s .  I n  composi te m a t e r i a l s ,  
t h e  o v e r a l l  CTE o f  t h e  p roduc t  i s  i n f l u e n c e d  by t h e  CTE's o f  i t s  c o n s t i t u -  
e n t s .  Hence, i t  i s  i m p o r t a n t  to  understand t h e  thermal p r o p e r t i e s  of any new 
m a t e r i a l  be ing  considered for  composite a p p l i c a t i o n s .  One such m a t e r i a l  t h a t  
i s  b e i n g  considered f o r  conduc t i ve  c o f u n c t i o n a l  space s t r u c t u r e s  i s  brominated 
p i tch-based carbon f i b e r s  ( r e f .  1 ) .  
Th i s  paper addresses t h e  e f f e c t  of b r o m i n a t i o n  of carbon f i b e r s  on t h e  CTE 
o f  t h e i r  composites. I n  a d d i t i o n ,  t h e  CTE o f  t h e  f i b e r s  a lone  was measured. 
MATERIALS AND METHODS 
The u n i d i r e c t i o n a l  composite samples were  f a b r i c a t e d  u s i n g  e i t h e r  PAN- 
based T-300 f i b e r s ,  p i  tch-based P-75, or p i  tch-based P-100 f i b e r s  manufactured 
by Amoco. 
process may be found elsewhere ( r e f .  1 ) .  
7 p e r c e n t  Br2 by weight ,  w h i l e  the  P-75 and P-100 f i b e r s  were a p p r o x i m a t e l y  
15 pe rcen t  Br2 by weight .  
P r i s t i n e  f i b e r s  were  used as-received.  D e t a i l s  o f  t h e  b r o m i n a t i o n  
The T-300 f i b e r s  were a p p r o x i m a t e l y  
The MY720 epoxy was used w i t h  DDS hardener  ( r e f .  2 ) .  
A f t e r  t he  composite was f a b r i c a t e d ,  f ou r  sample cubes were c u t  from each lam i -  
na te  u s i n g  a diamond saw, and t h e i r  d imensions were measured t o  t h e  n e a r e s t  
0.01 mm w i t h  d i g i t a l  c a l l i p e r s .  Care was taken t o  c u t  t h e  samples as o r thogo-  
n a l l y  as p o s s i b l e .  
L i n e a r  expansion d a t a  were c o l l e c t e d  on a Perkin-Elmer TMS-2 thermomechan- 
i c a l  ana lyze r  i n  t h e  temperature range o f  30 t o  130 O C ,  a t  a scan r a t e  o f  
20 OC/min. The CTE was c a l c u l a t e d  o v e r  t h i s  range u s i n g  a two p o i n t  method. 
A l though t h e r e  was c u r v a t u r e  i n  some o f  t h e  da ta ,  t h i s  method y i e l d e d  an aver-  
age expansion ove r  t h i s  temperature range. 
u s i n g  an aluminum standard.  On t h e  f i r s t  sample, t r i p l i c a t e  measurements o f  
t h e  CTE i n  t h e  a - d i r e c t i o n  were ob ta ined ,  f o l l owed  by t r i p l i c a t e  measurements 
i n  t h e  b - d i r e c t i o n  and t h e  c - d i r e c t i o n  ( f i g .  1 ) .  T h i s  p r o v i d e d  a measure o f  
t h e  v a r i a t i o n  w i t h i n  t h e  technique.  On t h e  n e x t  t h r e e  samples, t h e  CTE was 
measured once i n  each d i r e c t i o n .  T h i s  p r o v i d e d  a measure o f  sample to  sample 
v a r i a t i o n .  Since t h e  v a r i a t i o n  w i t h i n  t h e  technique was s m a l l e r  t han  t h e  v a r i -  
a t i o n  w i t h i n  the  samples, t h e  r e s u l t s  r e p o r t e d  for  each composi te a r e  t h e  aver-  
age o f  t h e  f o u r  samples. 
The i n s t r u m e n t  was c a l i b r a t e d  
A s p e c i a l  e x t e n s i o n  probe was used t o  measure t h e  CTE o f  seve ra l  carbon 
f i b e r  tows ( r e f .  3). T h i s  was accompl ished by c lamping t h e  carbon f i b e r  tow 
between two copper c l i p s  and mount ing t h e  c l i p s  between t h e  q u a r t z  sample 
probes. A smal l  drop of  epoxy was used t o  secure each copper- to-carbon j o i n t .  
I n  a d d l t i o n  t o  t h e  s u i t e  of carbon f i b e r s ,  seve ra l  m a t e r i a l s  o f  known CTE were 
prepared i n  a s i m i l a r  fash ion,  and these d a t a  were used t o  generate a s tandard 
curve for  comparison. 
RESULTS AND DISCUSSION 
O f  t h e  two methods chosen t o  s tudy  CTE, t h e  use o f  composite cubes was 
much more r e l i a b l e  than  t h e  use o f  f i b e r  tows. The f i b e r  tow work s u f f e r e d  
from a l a r g e  spread i n  t h e  da ta ,  as i n d i c a t e d  by t h e  nonuni form r e s u l t s  
o b t a i n e d  from metal  w i r e  s tandards.  T h i s  was a t t r i b u t e d  to  nonuni form prepara- 
t i o n  o f  t h e  f i b e r  tow or w i r e  samples, compared to  t h e  composite cubes. Hence, 
o n l y  t h e  composite d a t a  w i l l  be presented.  
There was l i t t l e  d i f f e r e n c e  i n  t h e  observed va lues o f  CTE b e f o r e  and 
a f t e r  b r o m i n a t i o n  i n  t h e  u n i a x i a l  a - d i r e c t i o n ,  as shown i n  t a b l e  I. For exam- 
p l e ,  t h e  p r i s t i n e  P-75 composi te had a va lue  of -1.520.1 ppm/K w h i l e  t h e  bro- 
minated composite had a va lue  o f  -1.750.5 ppm/K. L i kew ise ,  t h e r e  was l i t t l e  
d i f f e rence  i n  the  t r a n s v e r s e  b- and c - d i r e c t i o n s .  The p r i s t i n e  and brominated 
P-75 composites had CTE va lues i n  the  b - d i r e c t i o n  o f  3222 and 3422 ppm/K, 
r e s p e c t i v e l y ;  w h i l e  they  had va lues i n  t h e  c - d i r e c t i o n  o f  3025 and 3624 ppm/K, 
r e s p e c t i v e l y .  Th i s  r e s u l t  i s  n o t  s u r p r i s i n g  when one cons ide rs  t h a t  t h e  CTE 
i n  t h e  a - d i r e c t i o n  i s  c o n t r o l l e d  by t h e  a-ax is  expansion of t h e  g r a p h i t e  l a t -  
t i c e  w i t h i n  the  f i b e r ,  w h i l e  t h e  CTE's i n  the  t r a n s v e r s e  d i r e c t i o n s  a r e  con- 
t r o l l e d  by b o t h  the  c-ax is  expansion of t h e  g r a p h i t e  l a t t i c e  w i t h i n  t h e  f i b e r s  
and t h e  expansion o f  t h e  m a t r i x .  
Whether t h e  b r o m i n a t i o n  r e a c t i o n  i s  a d s o r p t i o n  or i n t e r c a l a t i o n ,  bromina- 
t i o n  does n o t  seem to  a l t e r  t h e  g r a p h i t e  l a t t i c e  s i g n i f i c a n t l y .  
b romina t ion  does a l t e r  t he  surface c h a r a c t e r i s t i c s  o f  the  f i b e r  to  an e x t e n t  
measurable by i n t e r l a m i n a r  shear s t r e n g t h  ( r e f .  l), t h i s  a l t e r a t i o n  goes 
unno t i ced  i n  terms o f  CTE. 
A l though  
2 
The observed CTE va lues  i n  t h e  u n i a x i a l  d i r e c t i o n  w e r e  o f  t h e  same 
o r d e r  o f  magnitude as va lues  o f  p y r o l y t i c  g r a p h i t e ,  and showed a t r e n d  w i t h  
i n c r e a s i n g  g r a p h i t i z a t i o n  s i m i l a r  to  t h e  t r e n d  i n d i c a t e d  by t h e  manufacturer .  
P y r o l y t i c  g r a p h i t e  has a CTE va lue  o f  -0.6 ppm/K p a r a l l e l  t o  t h e  p lane  o f  depo- 
s i t i o n ,  and Amoco i n d i c a t e s  t h a t  t h e  CTE va lues o f  t h e  p r i s t i n e  T-300, P-75, 
and P-100 f i b e r s  a re  -0.5, -1.3, and -1.6 ppm/K, r e s p e c t i v e l y  ( r e f s .  4 and 51. 
The CTE va lues i n  t h e  t r a n s v e r s e  d i r e c t i o n s  were l e s s  than t h e  52 ppm/K o f  t h e  
neat  r e s i n  and more than t h e  23 ppm/K of p y r o l y t i c  g r a p h i t e  measured perpendic-  
u l a r  to  the  p lane  o f  d e p o s i t i o n ,  i n d i c a t i n g  t h a t  t h e  t h e  c -ax i s  expansion o f  
t h e  composite has c o n t r i b u t i o n s  from b o t h  f i b e r s  and m a t r i x  ( r e f s .  2 and 4) .  
The somewhat l a r g e r  v a r i a t i o n  i n  t h e  t r a n s v e r s e  d i r e c t i o n  CTE r e s u l t s  can 
p robab ly  be a t t r i b u t e d  to  a nonhomogeneous f i b e r  d i s t r i b u t i o n  w i t h i n  each com- 
p o s i t e  as w e l l  as d i f f e r e n c e s  i n  f i b e r  l o a d i n g  from composi te t o  composi te.  
The es t ima ted  f i b e r  volume pe rcen t ,  as determined from mass, volume, and f i b e r  
d e n s i t y  data,  v a r i e d  from 51 to  76 pe rcen t .  
made. 
No e s t i m a t e  o f  v o i d  c o n t e n t  was 
I t  i s  i n t e r e s t i n g  t o  n o t e  t h a t  t h e  f i b e r s  have a n e g a t i v e  CTE i n  t h e  
a-ax is  d i r e c t i o n ,  which becomes more n e g a t i v e  w i t h  an i n c r e a s i n g  degree o f  
g r a p h i t i z a t i o n .  
m a t r i x ,  makes these f i b e r s  u s e f u l  i n  t a i l o r i n g  a near-zero CTE f o r  o r b i t i n g  
space s t r u c t u r e s .  
t h e  way fo r  c o f u n c t i o n a l  s t r u c t u r e s  made from h i g h l y  e l e c t r i c a l l y  conduc t i ve  
brominated p i  tch-based f i b e r s .  
Th is  unusual p r o p e r t y ,  combined w i t h  t h e  p o s i t i v e  CTE o f  t h e  
The f a c t  t h a t  b r o m i n a t i o n  does n o t  a l t e r  t h i s  p r o p e r t y  paves 
CONCLUSIONS 
The b r o m i n a t i o n  o f  carbon f i b e r s  has l i t t l e  e f f e c t  on t h e  c o e f f i c i e n t  o f  
thermal expansion o f  carbon f i b e r  - epoxy composites. The CTE i n  t h e  u n i a x i a l  
d i r e c t i o n  i s  dominated by t h e  a-ax is  expansion o f  t h e  carbon f i b e r s  w h i l e  t h e  
CTE's i n  t h e  t ransve rse  d i r e c t i o n s  a re  dominated by b o t h  t h e  c -ax i s  expansion 
o f  t h e  carbon f i b e r s  and t h e  m a t r i x .  The n e g a t i v e  CTE o f  t h e  brominated 
f i b e r s  combined w i t h  t h e  p o s i t i v e  CTE o f  the  m a t r i x  make these m a t e r i a l s  s u i t a -  
b l e  for  t a i l o r i n g  c o f u n c t i o n a l  composite space s t r u c t u r e s  w i t h  near-zero t h e r -  
mal expansion. 
REFERENCES 
1 .  D.A. Jaworske, J.R. Ga ie r ,  C.C. Hung, and B.A. Banks, SAMPE Q., (1986) 9. 
2 .  D.A.  Scola,  and R.H. Pa te r ,  " Imide M o d i f i e d  Epoxy M a t r i x  Resins,"  NASA 
CR-165229 ( 1  981 1. 
3. Technica l  B u l l e t i n  990-9719, Perkin-Elmer,  Norwalk, CT (19701. 
4. " P r o v i s i o n a l  Values f o r  Thermal L i n e a r  Expansion o f  P y r o l y t i c  Graph i te , "  i n  
Thermophysical P r o p e r t i e s  o f  M a t t e r ,  Vol . ' 13 - Thermal Expansion,' Nonmetal- 
l i c  S o l i d s ,  e d i t e d  by Y.S.  Toulouk ian,  R.K. K i r b y ,  R.E.  T a y l o r ,  and T.Y.R. 
Lee, ( IFI /P lenum, New York, 1977) p.  79. 
5. Technica l  B u l l e t i n s  F-4311, F-5817, and F-7007, Union Carb ide,  Danbury, CT 
(1983). 
3 
TABLE I .  - COEFFICIENT OF THERHAL EXPANSION ( i n  ppm/K) OF 
PRISTINE AND B W I N A T E D  CARBON FIBER - EPOXY COnPOSITES, 
AS HEASURED I N  THE TEHPERATURE RANGE OF 30 t o  130 O C  
a-Di rect ion 
-1.633.4 
-1.k1.2 
Pr is t ine T-300 
Bmni nated T-300 
b-Di rect ion c-Di rection 
25+3 25+1 
32+_ 1 29t 1 
Pr is t ine P-75 
Bromi nated P-75 
Pr is t ine P-100 
Brominated P-100 
-1.5io. 1 32+2 3Q5 
-1.733.5 34*2 36*4 
-2.133.8 52*2 41t2 
-1.833.3 42+2 41+1 
I 
C 
FIGURE 1. - SCHEMATIC DIAGRAM OF A UNIAXIAL CARBON FIBER - EPOXY 
COMPOSITE SHOWING THE A-. B-. AND C- DIRECTIONS. 
4 
Nalmnal Aeronautics and 
1. Report No. 
Report Documentation Page 
2. Government Accession No. 3. Recipient's Catalog No. 
NASA TM- 1 002 3 6 
4. Title and Subtitle 
The E f f e c t  of Brominat ion o f  Carbon F ibers  on the  
F ibe r  - Epoxy Composi t es  
C o e f f i c i e n t  o f  Thermal Expansion o f  Graphi te  
7. Author@) 
D.A. Jaworske and C. Maciag 
5. Report Date 
November 1987 
6. Performing Organization Code 
8. Performing Organization Report No. 
E-3665- 1 
10. Work Unit No. 
506-41 -46 
9. Performing Organization Name and Address 
11. Contract or Grant No. Nat ional  Aeronaut ics  and Space Admin i s t ra t i on  
Lewis Research Center 
Cleveland, Ohio 44135-3191 13. Type of Report and Period Covered 
9. Security Classif. (of this report) 
U n c l a s s i f i e d  
12. Sponsoring Agency Name and Address 
Nat iona l  Aeronaut ics and Space Admin i s t ra t i on  
Washington, D.C. 20546-0001 
22. Price' 20. Security Classif. (of this page) 21. No of pages 
Uncl a s s i  f led 5 A02 
Technical  Memorandum 
15. Supplementary Notes 
D.A. Jaworske, NASA Lewis Research Center; C. Maciag, Cleveland Sta te  
U n i v e r s i t y ,  Cleveland, Ohio 44115. 
16. Abstract 
To examine the e f f e c t  o f  brominat ion o f  carbon f i b e r s  on the  c o e f f i c i e n t  o f  
thermal expansion (CTE) of carbon f i b e r  epoxy composites, several  p r i s t i n e  and 
brominated carbon f i b e r  - epoxy composite samples were subjected t o  thermomechan- 
i c a l  ana lys is .  The C T E ' s  of these samples were measured i n  the u n i a x i a l  and 
t ransverse d i r e c t i o n s .  The CTE was dominated by the f i b e r s  i n  the u n i a x i a l  
d i r e c t i o n ,  w h i l e  i t  was dominated by the  m a t r i x  i n  the  t ransverse d i r e c t i o n s .  
Brominat ion had no e f f e c t  on the CTE o f  any of  the  composites. 
CTE o f  f i b e r  tow was measured i n  the absence o f  a polymer ma t r i x ,  us ing  an exten- 
s ion  probe. The r e s u l t s  from t h i s  technique were inconc lus ive .  
I n  a d d i t i o n ,  t he  
17. Key Words (Suggested by Author(s)) 
Graphi te  f i b e r s  
C o e f f i c i e n t  o f  thermal expansion 
Graph1 t e  f i b e r  - epoxy composites 
I 18. Distribution Statement 
Unc lass i f i ed  - Un l im i ted  
Subject  Category 24 


The effect of bromination of carbon fibers on the coefficient of thermal expansion of graphite fiber-epoxy composites

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