A New Polyester Matrix Resin System for Carbon Fibers - ACS

24 A New Polyester Matrix Resin System for Carbon Fibers ROBERT

EDELMAN

and P A U L E. M c M A H O N

Resins for Aerospace Downloaded from pubs.acs.org by FUDAN UNIV on 11/19/16. For personal use only.

Celanese Research Company, 86 Morris Avenue, Summit, N J 07901

E p o x y resins a r e t h e p r i m a r y matrix materials u s e d in carbon fiber c o m p o s i t e s t o d a y . P r e p r e g s y s t e m s made with t h e s e resins a r e used in recreation and a e r o s p a c e applications. The e p o x i e s w e r e c h o s e n for their good handling characteristics as well as their good a m b i e n t and e l e v a t e d t e m p e r a t u r e c o m p o s i t e properties. H o w e v e r , epoxy resin s y s t e m s h a v e certain deficiencies in t h a t t h e p r e p r e g materials must b e k e p t refrigerated resulting in limited o u t t i m e . C o s t is also higher t h a n other available thermoset materials and c u r e t i m e is often l o n g . In the a e r o s p a c e industry, these deficiencies have been tolerated when high levels of p e r f o r m a n c e that c o u l d b e achieved only with epoxy materials, were desired for certain applications. However, a s additional applications for composites are considered, w h e r e l o w e r property levels are acceptable, it is likely t h a t other t y p e s of prepreg c o u l d b e u s e d in place of t h e epoxy s y s tems currently available, particularly t h e "250°F" curing epoxy systems. Polyester r e s i n prepregs s h o u l d b e considered as a pot e n t i a l a l t e r n a t i v e t o t h e s e e p o x y m a t e r i a l s , s i n c e t h e y do n o t have t h e i r n e g a t i v e f e a t u r e s . Most p o l y e s t e r systems t h a t a r e used today c o n t a i n g l a s s r e i n f o r c e m e n t and u s e s t y r e n e a s t h e r e a c t i v e monomer. S t y r e n e i s t h e most f r e q u e n t l y u s e d monomer s i n c e i t p r o v i d e s good a m b i e n t t e m p e r a t u r e p r o p e r t i e s a t low c o s t . Elevated temperature propert i e s (100 C and a b o v e ) a r e f r e q u e n t l y p o o r . S t y r e n e does have a s i g n i f i c a n t d r a w b a c k i n t h a t i t i s q u i t e v o l a t i l e a t room t e m p e r a t u r e l e a d i n g t o environmental c o n t r o l problems. In addition, s t y r e n e monomer u n d e r g o e s v e r y h i g h s h r i n k a g e and e x o t h e r m i n g o n c u r e n e c e s s i t a t i n g t h e use o f e x t e n s i v e f i l l e r a d d i t i o n t o m i n i m i z e w a r p a g e and c r a c k i n g . (1,2) T h i s u s e o f f i l l e r s f r e q u e n t l y r e s u l t s i n a d i s t i n c t l o w e r i n g o f t h e p r o p e r t i e s o f t h e system. I t i s obvious then that a s i g n i f i c a n t l y d i f f e r e n t p o l y e s t e r r e s i n s y s t e m must b e c o n s i d e r e d a s a p o s s i b l e r e p l a c e m e n t f o r a n epoxy m a t e r i a l . There are commercially a v a i l a b l e m a t e r i a l s t h a t a p p e a r t o meet t h e n e c e s s a r y r e q u i r e m e n t s . A f o r m u l a t i o n t h a t c o n t a i n s d i a l l y l p h t h a l a t e monomer and a h i g h p e r f o r m a n c e u n s a t 0-8412-0567-1/80/47-132-317$05.00/0 © 1980 A m e r i c a n C h e m i c a l Society


318

RESINS F O R A E R O S P A C E

TABLE I PROPERTIES OF D I A L L Y L ORTHOPHTHALATE (DAP) Ο II

C-OCH -CH==CH 2

2

•C-OCH - C H = C H „ Ο VAPOR PRESSURE

LOW

(0.1 T o r r a t 90 C)

11.8%

( S t y r e n e = 17%)

AT ROOM TEMPERATURE VOLUME SHRINKAGE V e r y l o n g a t t e m p e r a t u r e s up t o 82°C GELATION TIME Rapid a t temperatures greater than 149°C (1-2 m i n u t e s a t 177°C when catalyzed) EXOTHERM DURING CURE

LOW

(93°C)

Comparable s t y r e n e system t o 204°C

exotherms

THERMAL RESISTANCE

V e r y good a t t e m p e r a t u r e s up t o 121 C

MOISTURE RESISTANCE

V e r y good a t t e m p e r a t u r e s up t o 95°C


24.

E D E L M A N AND M^MAHON

Matrix

for Carbon

319

Fibers

u r a t e d p o l y e s t e r produces an unexpectedly h i g h l e v e l o f composite mechanical properties. D i a l l y l p h t h a l a t e i s a commonly a v a i l a b l e p r o d u c t t h a t i s used i n c r i t i c a l e l e c t r i c a l / e l e c t r o n i c a p p l i c a t i o n s r e q u i r i n g h i g h r e l i a b i l i t y under l o n g - t e r m a d v e r s e environmental conditions. (3) The r e a s o n s why d i a l l y l p h t h a l a t e was c h o s e n c a n b e s e e n i n T a b l e I w h i c h shows t h e e x c e l l e n t b a l a n c e o f 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 o f t h e m a t e r i a l . The v a p o r p r e s s u r e o f t h e monomer i s l o w c o n t r i b u t i n g t o r e d u c e d environmental hazards. Shrinkage o f the m a t e r i a l i s the lowest o f t h e commonly a v a i l a b l e monomers. T h i s t e n d s t o r e s u l t i n lower warpage i n the f i n a l p a r t . Gel time behavior i s i d e a l f o r a prepreg r e s i n . A t t e m p e r a t u r e s up t o 82°C v i r t u a l l y no c u r e w i l l occur i n the catalyzed m a t e r i a l . This important property removes t h e need f o r r e f r i g e r a t i o n w h i c h i s a n e c e s s a r y f e a t u r e w i t h t h e u s e o f epoxy p r e p r e g s . T h i s p a r t i c u l a r mode o f b e havior i s r e l a t e d t o the a c t i v i t y l e v e l o f the s t a b l e a l l y l radical. A t lower temperatures, d e s p i t e the a v a i l a b i l i t y o f f r e e r a d i c a l s from an i n i t i a t o r , t h e r e a c t i o n r a t e o f t h e a l l y l i e s p e c i e s i s s i m p l y t o o s l u g g i s h f o r s i g n i f i c a n t advancement t o occur. Thus, i t i s necessary t o use h i g h e r temperature i n i t i a t o r s t o c a t a l y z e a l l y l i c systems. I n a d d i t i o n , the exothermic h e a t r e l e a s e d d u r i n g t h e c u r e c y c l e i s low compared to o t h e r monomers, r e s u l t i n g i n s i g n i f i c a n t l y l e s s c r a c k i n g i n the cured p a r t . (4) F i n a l l y , p h y s i c a l p r o p e r t i e s s u c h a s t h e r m a l and m o i s t u r e r e s i s t a n c e a r e good b e c a u s e o f t h e t i g h t c r o s s l i n k e d n e t w o r k t h a t c a n b e d e v e l o p e d b y t h e d i f u n c t i o n a l monomer. E s t e r l i n k ages a r e n o t r e a d i l y a v a i l a b l e f o r a t t a c k b y w a t e r b e c a u s e o f the l a t t e r feature. R e s u l t s and D i s c u s s i o n A c a r b o n f i b e r p r e p r e g was p r e p a r e d f r o m a p o l y e s t e r m a t r i x r e s i n s y s t e m f o r m u l a t e d w i t h d i a l l y l p h t h a l a t e and a h i g h p e r formance u n s a t u r a t e d p o l y e s t e r . An i n i t i a l s e t o f room t e m p e r a t u r e c o m p o s i t e p r o p e r t i e s was o b t a i n e d by m o l d i n g the p r e p r e g i n a compression mold u s i n g a 177°C p r e s s . Time i n t h e m o l d was f i f t e e n m i n u t e s a t a p r e s s u r e o f 500 p s i (3.5 MPa). T h e d a t a o b t a i n e d a r e shown i n T a b l e I I . The f i b e r used i n a l l o f t h e w o r k d i s c u s s e d i s C e l a n e s e s Celion 6000 c a r b o n f i b e r . For purposes o f comparison, key p r o p e r t i e s w e r e o b t a i n e d o n some p r e p r e g s p r e p a r e d f r o m commerc i a l l y a v a i l a b l e s t y r e n e - p o l y e s t e r , v i n y l e s t e r as w e l l as an epoxy p r o d u c t . The v a l u e s o b t a i n e d a r e shown i n T a b l e I I I . I t i s apparent t h a t i n the key area o f i n t e r l a m i n a r shear s t r e n g t h , t h e d i a l l y l p h t h a l a t e s y s t e m and t h e epoxy m a t e r i a l a r e v i r t u a l ly identical. T h e o t h e r two m a t e r i a l s a r e d i s t i n c t l y i n f e r i o r . However, f l e x and t e n s i l e p r o p e r t i e s a r e q u i t e s i m i l a r f o r most o f t h e m a t e r i a l s examined. F i b e r volumes o b t a i n e d w i t h t h e v i n y l e s t e r s y s t e m w e r e q u i t e l o w and t h i s r e s u l t e d i n a r e d u c t i o n o f t e n s i l e and f l e x p r o p e r t i e s . Unfortunately, the 1

320

RESINS FOR

AEROSPACE

TABLE I I


MECHANICAL PROPERTIES OF CELION -, 6000/DAP-POLYESTER COMPOSITES (22°C)

Tensile

Strength, K s i

(MPa)

Modulus, M s i

(GPa)

% Elongation

222 20.3

(1531) ( 140)

1.1

Strength, K s i

(MPa)

273

(1882)

Flex (Modulus, M s i

I n t e r l a m i n a r Shear

Strength, Psi

Strength, K s i Compressive

| Modulus, M s i

(GPa)

(MPa)

(MPa) (GPa)

% Elongation

Transverse Tensile

13,600

151 17.7

(122)

(

93.8)

(1041) ( 122)

1.6

Strength, P s i

(MPa)

Modulus, M s i

(GPa)

% Elongation

17.7

5,100 1.3

( 35.2) (

8.96)

0.39

1

C o m p r e s s i o n m o l d e d c u r e a t 177 C, 500 P s i ( 3 . 5 MPa) f o r f i f t e e n minutes.

2

T e n s i l e and f l e x v a l u e s n o r m a l i z e d t o 62% f i b e r

(excluding transverse tensile) are volume.

2

Elongation

Modulus,

(GPa)

20.8

303

1.1

T e n s i l e and f l e x p r o p e r t i e s n o r m a l i z e d

49.6% f i b e r v o l u m e .

53.8% f i b e r volume.

2.

3.

4.

4

13,400

17.7

272

(92.4)

(122)

(1875)

(139)

20.2 1.1

(1517)

220

14,000

19.3

287

1.1

20.0

221

M

ester.

(96.5)

(133)

(1979)

(138)

(1524)

EPOXY

250°F"

t o 62% f i b e r volume f o r a l l systems e x c e p t v i n y l

C o m p r e s s i o n m o l d e d a t 177 °C 500 P s i (3.5 MPa)

(56.3)

(117)

(1544)

3

DAP POLYESTER

f o r f i f t e e n minutes.

16.9

224

(71.4) 8,170

(143)

(2089)

(125)

18.2 1.1

(1434)

VINYL ESTER

6000 COMPOSITES (22°C)

208

1.

Strength, P s i (MPa) 10,350

Msi

S t r e n g t h , K s i (MPa)

%

(139)

(GPa)

20.1

Msi

Modulus,

I n t e r l a m i n a r Shear

Flex

Tensile

(1579)

229

S t r e n g t h , K s i (MPa)

STYRENE POLYESTER

COMPARATIVE MECHANICAL PROPERTIES OF CELION

TABLE I I I


53.8% f i b e r volume.

8,200

3

(39.4)

239

F l e x s t r e n g t h n o r m a l i z e d t o 62% f i b e r volume f o r a l l systems except v i n y l

5,720

(1013)

2

(45.9)

147

ester.

(56.5)

(1648)

,f

n

(76.5)

(1993)

250°F EPOXY

11,100

289

(82°C)

DAP POLYESTER

C o m p r e s s i o n mold c u r e d a t 177 C, 500 P s i (3.5 MPa) f o r f i f t e e n m i n u t e s .

6,600

I n t e r l a m i n a r S h e a r S t r e n g t h , P s i (MPa)

(1110)

VINYL ESTER

1

161

F l e x S t r e n g t h , K s i (MPa)'

STYRENE POLYESTER

COMPARATIVE MECHANICAL PROPERTIES OF CELION 6000 COMPOSITES

TABLE I V


24.

E D E L M A N AND M ° M A H O N

Matrix

for Carbon

Fibers

323


p o l y e s t e r used i n t h e s t y r e n e and d i a l l y l p h t h a l a t e s y s t e m s i s n o t t h e same. The p o l y e s t e r i n t h e f o r m e r s y s t e m c o n t a i n s s i g n i f i c a n t l e v e l s o f a d i p i c a c i d w h i c h would tend t o have an a d v e r s e a f f e c t o n f l e x and s h e a r s t r e n g t h , p a r t i c u l a r l y a t e l e vated temperatures. I n T a b l e I V , we s e e a c o m p a r i s o n o f k e y p r o p e r t i e s a t e l e vated temperatures. H e r e , t h e f l e x and s h e a r s t r e n g t h s show a g r e a t e r s p r e a d o f v a l u e s b e t w e e n t h e D A P / p o l y e s t e r s y s t e m and t h e epoxy. Out Time Of T h e D A P - P o l y e s t e r S y s t e m . C a r b o n f i b e r p r e p r e g p r e p a r e d w i t h t h e D A P - P o l y e s t e r s y s t e m was s t o r e d i n a p o l y e t h y l e n e b a g a t room t e m p e r a t u r e f o r a s e v e n and a h a l f month period. A t t h e end o f t h i s p e r i o d t h e p r e p r e g h a d a d e q u a t e t a c k and drape. P a n e l s prepared from t h e m a t e r i a l u s i n g a s h o r t c u r e c y c l e o f two m i n u t e s a t 163°C i n a c o m p r e s s i o n m o l d f o l l o w e d b y a f r e e s t a n d i n g f i f t e e n m i n u t e p o s t c u r e a t 177°C gave v e r y good m e c h a n i c a l p r o p e r t i e s . T h e s e a r e shown i n T a b l e V. The epoxy p r e p r e g s y s t e m used i n t h i s w o r k f o r comp a r a t i v e p u r p o s e s h a s a maximum o u t t i m e o f o n e month. D A P - P o l y e s t e r S h o r t C u r e C y c l e s . The p r e v i o u s d a t a r e l a t i n g t o t h e new p o l y e s t e r p r e p r e g was g e n e r a t e d u s i n g a f i f t e e n m i n u t e c o m p r e s s i o n m o l d i n g c u r e c y c l e a t 177°C a n d 500 p s i (3.5 MPa). I n T a b l e V I , c o m p o s i t e p r o p e r t i e s a r e shown a s a f u n c t i o n o f cure cycle. The t o p row shows t h e p r o p e r t i e s o b tained using a long cure cycle. The n e x t two rows show t h a t a two t o f i v e m i n u t e c u r e a t t e m p e r a t u r e s o f 138-163°C f o l l o w e d by a s h o r t " o f f t h e t o o l " p o s t c u r e r e s u l t s i n v i r t u a l l y o p t i mum p r o p e r t i e s . T h e l a s t two rows i n d i c a t e t h a t a s h o r t c u r e o f one o r two m i n u t e s a t 177°C w i t h o u t a n y p o s t c u r e g i v e s q u i t e acceptable properties. DAP-Polyester Temperature Performance. I n a separate set of e x p e r i m e n t s , t h e performance o f C e l i o n 6000/DAP-polyester c o m p o s i t e s was c h a r a c t e r i z e d a s a f u n c t i o n o f t e m p e r a t u r e ( t h e l o n g e r c u r e c y c l e was e m p l o y e d ) . I t c a n be seen (Table V I I ) t h a t t h e s h e a r s t r e n g t h a t 82°C i s r e d u c e d t o 6 0 % o f i t s a m b i e n t value. However, t h e h i g h i n i t i a l v a l u e s t i l l k e e p s t h i s parame t e r r e a s o n a b l e a t 82°C. A t 121°C, a f u r t h e r d e c r e a s e i n s h e a r s t r e n g t h h a s o c c u r r e d and t h e f l e x s t r e n g t h h a s a l s o d e c a y e d t o 60% o f i t s i n i t i a l l e v e l . I n a new f o r m u l a t i o n t h a t we h a v e r e c e n t l y e v a l u a t e d , e l e v a t e d t e m p e r a t u r e p e r f o r m a n c e h a s b e e n i m p r o v e d compared t o t h e o r i g i n a l system. I n T a b l e V I I I , p r o p e r t i e s a r e shown a s a f u n c t i o n o f p o s t c u r e t i m e and t e m p e r a t u r e . A short cure cycle o f two m i n u t e s f o l l o w e d b y b r i e f f r e e s t a n d i n g p o s t c u r e s o f f i v e and t w e n t y m i n u t e s a t 177°C r e s u l t i n h i g h l e v e l s o f f l e x and shear p r o p e r t i e s . In T a b l e I X , p r o p e r t i e s o b t a i n e d as a f u n c t i o n o f tempera-

324

RESINS F O R

AEROSPACE


TABLE V

COMPOSITE MECHANICAL PROPERTIES OF CELION 6000/DAP-POLYESTER AFTER 7% MONTHS OF ROOM TEMPERATURE AGING'

INTERLAMINAR SHEAR STRENGTH

TEST TEMPERATURE

FLEXURAL STRENGTH MODULUS

(°C)

K S I (MPa)

MSI (GPa)

P S I (MPa)

22

294 (2027)

20.6 (142)

13,400

(92.4)

82

270 (1862)

—

9,900

(68.3)

121

198 (1365)

—

6,800

(46.9)

1

F l e x v a l u e s a r e n o r m a l i z e d t o 6 2 % f r o m 56.9%.

2

Samples w e r e c o m p r e s s i o n m o l d c u r e d a t 163°C and 500 P S I (3.5 MPa) f o r two m i n u t e s . P o s t c u r e was done f r e e s t a n d i n g a t 177 C f o r f i f t e e n m i n u t e s .

3

P r e p r e g was k e p t i n a p o l y e t h y l e n e b a g d u r i n g t h i s

period.

12,900(88.9)

12,800(88.3)

17.9(123) 18.3(126)

18.0(124)

17.7(122)

281(1937) 274(1889)

276(1903)

263(1813)

22 22

22

22

F I V E MINUTES AT 325°F

NONE F I F T E E N MINUTES AT 350°F

NONE

NONE

AND 500 P S I (3.5 MPa)

F I V E MINUTES AT 138°C AND 500 P S I (3.5 M P )

TWO MINUTES AT 177°C AND 500 P S I (3.5 MPa)

ONE MINUTE AT 177°C AND 500 P S I (3.5 MPa)

Flex values normalized

t o 62% f i b e r volume.

12,500(86.2) 13,300(91.7)

17.4(120) 16.2(112) 17.7(122)

262(1806) 287(1979) 247(1703)

22 82 22

NONE

TWO MINUTES AT 163°C

1

12,900(88.9) 8,300(57.2) 13,200(91.0)

17.7(122)

273(1882)

22

NONE

FIFTEEN MINUTES AT 177°C AND 500 P S I (3.5 MPa)

a

13,600(93.8)

MODULUS MSI (GPa)

STRENGTH KSI(MPa)

POST CURE

INTERLAMINAR SHEAR STRENGTH P S I (MPa)

COMPRESSION MOLD CURE CYCLE

FLEX

TABLE V I 6000/DAP-POLYESTER COMPOSITE PROPERTIES AS A FUNCTION OF CURE CYCLE TEST TEMPERATURE (°C)

CELION


RESINS F O R


326

AEROSPACE

TABLE V I I

PROPERTIES OF CELION 6000/DAP-POLYESTER COMPOSITES AS A FUNCTION OF TEMPERATURE

TEST TEMPERATURE (°C)

STRENGTH K s i (MPa)

MODULUS M s i (GPa)

INTERLAMINAR SHEAR STRENGTH P s i (MPa)

22

247 (1703)

17.6 ( 1 2 1 )

13,400 (92.4)

82

240 (1655)

15.9 (110)

8,200 (56.5)

121

155 (1069)

16.3 (113)

5,000 (34.5)

FLEX

1

C u r e d a t 177°C, 500 p s i (3.5 MPa) f o r f i f t e e n m i n u t e s .

2


t o 62% f i b e r

volume.


P o s t c u r e i s d o n e f r e e s t a n d i n g a t 177°C.

(2)

(3)


C o m p r e s s i o n m o l d c u r e d a t 163°C, 500 p s i ( 3 . 5 M P a ) f o r two m i n u t e s .

12,800(88.3) 9,300(64.1) 8,000(55.2)

19.2(132) 19.0(131) 18.7(129)

250(1724) 206(1420) 182(1255)

22 82 121

20

(1)

12,700(87.6) 9,400(64.8) 7,200(49.6)

11,000(75.8) 4,800(33.1) 3,100(21.4)

Inter laminar Shear Strengt P s i (MPa)

19.2(132) 18.8(130) 18.2(125)

Modulus M s i (GPa)

258(1779) 192(1324) 184(1269)

2

22 82 121

Strength K s i (MPa)

Flex

5

Test Temperature (°C)

1

22 82 121

ο

6000/DAP-POLYESTER COMPOSITE PROPERTIES AS A FUNCTION OF POST CURE T I M E

0

Post Cure Time (min. )

CELION

TABLE V I I I


RESINS FOR


328

AEROSPACE

TABLE I X COMPARATIVE COMPOSITE PROPERTIES OF CELION 6000/DAP-POLYESTER AND CELION 6000/EPOXY TEST TEMPERATURE (°C)

FLEXURAL"

DAP POLYESTER

"250°F" EPOXY

STRENGTH

22

258(1779)

284(1958)

K S I (MPa)

121

184(1269)

142(979)

22

19.2(132)

19.8(137)

121

18.2(125)

MODULUS MSI (GPa)

INTERLAMINAR SHEAR STRENGTH

22

12,700(87.6)

14,100(97.2)

121

7,200(49.6)

7,300(50.3)

P S I (MPa)

(1)

C o m p r e s s i o n m o l d c u r e d a t 163°C, 500 P S I ( 3 . 5 MPa) f o r two minutes f o l l o w e d by a f i v e minute f r e e s t a n d i n g post cure a t 177°C.

(2)

C o m p r e s s i o n m o l d c u r e d a t 154°C, 500 P S I (3.5 MPa) f o r f i f t e e n minutes. No p o s t c u r e was done.

(3)

F l e x v a l u e s a r e n o r m a l i z e d t o 62%.

24.

E D E L M A N AND M ° M A H O N

Matrix

for Carbon

329

Fibers

ff

fl


t u r e a r e compared w i t h t h o s e o b t a i n e d u s i n g a 250°F curing epoxy s y s t e m . T h e p o l y e s t e r a n d epoxy p r e p r e g m a t e r i a l s o f f e r s i m i l a r performance. The c o m p o s i t e s p r e p a r e d f r o m t h e D A P - P o l y e s t e r s y s t e m c a n be u s e d a t t e m p e r a t u r e s a s h i g h a s 150°C f o r s h o r t e x c u r s i o n s . An e x t e n d e d p o s t c u r e o f a t l e a s t two h o u r s s h o u l d b e done i f t h i s l e v e l o f temperature w i l l be experienced. A l o n g e r post c u r e o f about f i v e h o u r s i s p r e f e r r e d . I n T a b l e X, ambient a n d 150°C p r o p e r t i e s a r e compared a f t e r a two h o u r p o s t c u r e . M o i s t u r e R e s i s t a n c e o f t h e D A P - P o l y e s t e r System. A n o t h e r s e t o f s a m p l e s h a s b e e n used t o c h e c k J^he m o i s t u r e s e n s i t i v i t y of the mechanical properties o f C e l i o n 6 0 0 0 / D A P - P o l y e s t e r composites. The r e s u l t s o b t a i n e d a r e s u m m a r i z e d i n T a b l e X I , w h e r e i n t h e e x c e l l e n t r e t e n t i o n o f d r y "as i s " p r o p e r t i e s i s seen a f t e r a 24 h o u r s o a k i n 71°C w a t e r . F l e x and s h e a r s t r e n g t h s a r e r e g a r d e d a s t h e k e y p r o p e r t i e s s i n c e t h e y a r e most s e n s i t i v e t o changes a t t h e i n t e r f a c e . Vacuum B a g - A u t o c l a v e M o l d i n g O f The D A P - P o l y e s t e r P r e p r e g . F o r a e r o s p a c e a p p l i c a t i o n s , t h e p r e f e r r e d t e c h n i q u e used t o p r e p a r e c o m p o s i t e p a r t s w o u l d b e vacuum b a g a u t o c l a v e m o l d i n g . A p o l y e s t e r p r e p r e g c o n t a i n i n g t h e new f o r m u l a t i o n r e f e r r e d t o a b o v e was u s e d i n t h i s w o r k . P a n e l s w e r e p r e p a r e d u s i n g a t o t a l cure c y c l e o f seventy minutes. The l a y up was c o n s o l i d a t e d u s i n g a vacuum b a g u n d e r 7-14 K P a (2-4 i n . Hg) vacuum f o r f i f t e e n m i n u t e s a t room t e m p e r a t u r e . T h e b a g was t h e n p l a c e d i n an a u t o c l a v e , and a p r e s s u r e o f 85 p s i ( 0 . 5 9 MPa) was a p p l i e d . Vacuum was m a i n t a i n e d t h r o u g h o u t t h e e n t i r e c u r e . H e a t i n g was done a t a r a t e o f 2.2°C/minute u n t i l a t e m p e r a t u r e o f 65.6°C was r e a c h e d . D w e l l t i m e a t t h i s t e m p e r a t u r e was t e n m i n u t e s . H e a t i n g was t h e n c o n t i n u e d a t a r a t e o f 3.9°C/minute u n t i l a t e m p e r a t u r e o f 163°C was r e a c h e d . D w e l l t i m e a t t h i s t e m p e r a t u r e was f i f t e e n m i n u t e s . The p a r t was t h e n q u i c k l y c o o l e d u n d e r f u l l p r e s s u r e and vacuum. The c u r e c y c l e u s e d i s shown g r a p h i c a l l y i n F i g u r e 1. C o m p o s i t e p r o p e r t i e s o b t a i n e d o n t h e p a n e l s a r e shown i n T a b l e X I I . I t s h o u l d b e m e n t i o n e d t h a t i t i s v e r y l i k e l y t h a t a s t r a i g h t up c u r e c y c l e c o u l d a l s o b e u s e d w i t h t h i s system. Conclusions The p r o p e r t i e s shown f o r t h e c o m p o s i t e s made f r o m t h e DAPP o l y e s t e r carbon f i b e r p r e p r e g system a r e s i m i l a r t o those obt a i n e d w i t h a 250°F c u r i n g epoxy s y s t e m . The m a t e r i a l c a n b e c u r e d r a p i d l y u s i n g c o m p r e s s i o n m o l d i n g p r o c e d u r e s o r b y vacuum bag a u t o c l a v e m o l d i n g . T h e r m a l and m o i s t u r e r e s i s t a n c e a r e v e r y good. C o s t o f t h e r e s i n s y s t e m i s l o w and r e f r i g e r a t i o n i s n o t n e c e s s a r y . Out t i m e o f t h e p r o d u c t i s i n e x c e s s o f s i x months. P r e p r e g h a n d l e a b i l i t y i s e x c e l l e n t a s e v i d e n c e d b y ff

ff

RESINS FOR


330

AEROSPACE

TABLE X COMPOSITE MECHANICAL PROPERTIES OF CELION 6000/DAP-POLYESTER AFTER EXTENDED POST CURE

TEST TEMPERATURE (°C) STRENGTH

22

K S I (MPa)

150

292(2013) 107(738)

FLEXURAL MODULUS MSI(GPa) INTERLAMINAR SHEAR STRENGTH P S I (MPa)

are normalized

22

20.2(139)

150

17.4(120)

22

13,200(91.0)

150

4,500(31.0)

(1)

Flex values

t o 6 2 % f r o m 53.5%.

(2)

Samples w e r e c o m p r e s s i o n m o l d c u r e d a t 163°C, 500 P S I (3.5 M P a ) f o r two m i n u t e s . P o s t c u r e was f r e e s t a n d i n g i n a 177°C c i r c u l a t i n g a i r o v e n f o r two h o u r s .

(3)

Three p o i n t modulus v a l u e s . Flexural strength a r e f o u r p o i n t measurements.

values


24.

E D E L M A N AND M M A H O N C

Matrix

for

Carbon

331

Fibers

TABLE X I EFFECT OF MOISTURE ON MECHANICAL PROPERTIES OF CELION 6000/DAP-POLYESTER COMPOSITES

SAMPLE CONDITIONING

TEST TEMPERATURE (°C)

FLEX STRENGTH K s i (MPa)

MODULUS Msi(GPa)

INTERLAMINAR SHEAR STRENGTH P s i (MPa)

22

263(1813)

18.3(126)

13,700(94.5)

82

240(1655)

15.7(109)

8,300(57.2)

22

272(1875)

17.7(122)

13,200(91.0)

82

248(1710)

16.6(114)

7,300(50.3)

CONTROL

AGED 24 HOURS IN 160°F WATER TESTED WET

(1)

C o m p r e s s i o n m o l d c u r e d a t 177°C, 500 p s i (3.5MPa) f o r f i f t e e n minutes.

(2)

F l e x v a l u e s n o r m a l i z e d t o 62% f i b e r volume.

RESINS F O R

332

AEROSPACE

170

140


>110

80

S H

50

Apply 7-14 KPa (2-4 in.) .Vacuum

20

Apply 0.59 MPa(85psi)

1

10

1

i

20

30

ι

1

40

50

1—

60

70

80

90

TIME, MINUTES Figure I.

Cure cycle for DAP polyester

TABLE X I I MECHANICAL PROPERTIES OF CELION 6000/DAP-POLYESTER COMPOSITES - VACUUM BAG AUTOCLAVE MOLDED

FLEX

INTERLAMINAR SHEAR STRENGTH PSI(MPa)

TEST TEMPERATURE

STRENGTH KSI(MPa)

MODULUS MSI(GPa)

22

259(1786)

18.4(127)

12,500(86.2)

82

228(1572)

16.6(114)

9,300(64.1)

(1)



24.

E D E L M A N AND M M A H O N C

Matrix

for Carbon

Fibers

333

good t a c k and d r a p e a b i l i t y . Environmental hazards are minimal b e c a u s e o f t h e a b s e n c e o f v o l a t i l e monomers. F o r t h e s e r e a s o n s t h e m a t e r i a l s h o u l d be c o n s i d e r e d f o r c e r t a i n a p p l i c a t i o n s where e p o x i e s a r e now c u r r e n t l y b e i n g u s e d .


A c k n o w l e d gment s We w o u l d l i k e t o a c k n o w l e d g e t h e e x t r e m e l y v a l u a b l e a s s i s t a n c e o f H e c t o r Z a b a l e t a who f a b r i c a t e d t h e p a n e l s used i n t h i s work. R a y S t e e l e a b l y a s s i s t e d i n t h i s e f f o r t . H o w e l l P e t e r s o n and V a l S t a n t o n p r e p a r e d a l l o f t h e p r e p r e g materials. P h y s i c a l t e s t i n g measurements w e r e c a r r i e d o u t b y G e o r g e B r e n n , S t a n U r b a n s k i and J o e Cabanas. D i c k D z e j a k a s s i s t e d i n f o r m u l a t i o n p r e p a r a t i o n and i n o b t a i n i n g v i s c o s i t y data.

Literature Cited 1. 2. lishing 3. 4.

B o e n i g , H. V., " U n s a t u r a t e d Polyesters," Elsevier Publish ing Co., New Y o r k , N.Y., 1964, p. 1 4 0 . R a e c h Jr., Η., "Allylic R e s i n s and Monomers," Reinhold Pub Corporation, New Y o r k , N.Y., 1965, p. 28. Thomas, J. L. in "Modern Plastics Encyclopedia," Volume 5 5 , McGraw Hill and Co., New Y o r k , N.Y., 1978-79, p. 9. R a e c h Jr., Η., "Allylic R e s i n s and Monomers," Reinhold Pub lishing Corporation, New Y o r k , N.Y., 1965, p. 7.

RECEIVED January 8, 1980.

A New Polyester Matrix Resin System for Carbon Fibers - ACS

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