Polyimide Prepreg

34 Effect of Room-Temperature Aging on Graphite/ Polyimide Prepreg Materials H. C. NASH, C. F. PORANSKI, JR., and R. Y. TING

Downloaded by PEPPERDINE UNIV on September 26, 2017 | http://pubs.acs.org Publication Date: August 28, 1980 | doi: 10.1021/bk-1980-0132.ch034

Chemistry Division, Naval Research Laboratory, Washington, D C 20375

Fiber-reinforced composite materials are of increasing i m p o r t a n c e in many a e r o s p a c e applications. The driving force b e h i n d this t r e n d is t h e r e q u i r e m e n tforlighter-weightstructural materials for advanced vehicles. Fiber c o m p o s i t e s seem t o satisfy this need by offering a very high strength to w e i g h t ratio when compared with conventional metallic structural materials. This weight consideration is especially important to the successful development of vertical and short-take-off and landing (V/STOL) aircrafts i n o r d e r t o c o m p e n s a t e for t h e large and h e a v y e n g i n e s required for vertical lift. S i n c e many epoxy resins only h a v e a maximum u s e t e m p e r a t u r e a r o u n d 135°C (275°F), a number o f high t e m p e r a t u r e resin s y s t e m s a r e b e i n g e v a l u a t e d a s possible candidates for t h e resin matrix material in graphite reinforced c o m p o s i t e s on future V/STOL aircraft. A resin is being s o u g h t w h i c h will meet operational r e q u i r e m e n t s at t e m p e r a t u r e s in e x c e s s o f 204°C (400°F), b u t will be relatively insensitive to moisture and will h a v e t h e e a s e o f fabrication of state-of-the-art e p o x i e s . One o f t h e p r o m i s i n g s y s t e m s u n d e r consideration is an addition polyimide, Hexcel's F-178 resin (1). A m a j o r d i f f i c u l t y i n h a n d l i n g many p r e p r e g s i s t h a t t h e m a t e r i a l must be s t o r e d a t v e r y l o w t e m p e r a t u r e s ( i . e . -20 C ) . The s h e l f l i f e o f t h e s e p r e p r e g s i s g e n e r a l l y o n l y a few weeks a t room t e m p e r a t u r e and o n l y a few months a t f r e e z e r t e m p e r a t u r e s . P r e s u m a b l y , c o n t i n u a l B - s t a g i n g o c c u r s a t room t e m p e r a t u r e a n d , a t t h e same t i m e , t h e r e s i n may d e g r a d e by a b s o r b i n g m o i s t u r e from t h e atmosphere. Also, since before lay-up f o r f a b r i c a t i o n t h e p r e p r e g must warm up t o room t e m p e r a t u r e , i t c o u l d a b s o r b moisture through condensation. We t h e r e f o r e c a r r i e d o u t an a g i n g s t u d y t o e x a m i n e t h e e f f e c t s o f o u t - t i m e and h u m i d i t y a t room t e m p e r a t u r e on t h e p r o p e r t i e s o f F - 1 7 8 / g r a p h i t e p r e p r e g . We f a b r i c a t e d l a m i n a t e s f r o m m a t e r i a l w h i c h had b e e n exposed t o v a r i o u s h u m i d i t i e s a t room t e m p e r a t u r e and e v a l u a t e d t h e m e c h a n i c a l p r o p e r t i e s a s a f u n c t i o n o f p r e p r e g o u t - t i m e . We a l s o a n a l y z e d e x t r a c t s o f t h e aged p r e p r e g u s i n g p r o t o n nmr s p e c t r o s c o p y t o s e e i f t h i s t e c h n i q u e c o u l d r e v e a l a n y t h i n g about the c h e m i s t r y of the a g i n g p r o c e s s . This chapter not subject to U . S . copyright. Published 1980 American Chemical Society May; Resins for Aerospace ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


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

Figure 1. Top: ultrasonic C-scan results for F-178/T300 laminates, (showing voids); bottom: ultrasonic C-scan results for F-178/T300 laminates, (void free)

May; Resins for Aerospace ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

34.

NASH E T AL.

Room-Temperature

Aging

471


Experimental Material. The p o l y i m i d e / g r a p h i t e p r e p r e g (F-178/T300) was o b t a i n e d d i r e c t l y f r o m t h e m a n u f a c t u r e r , H e x c e l . The r e s i n i s described as a bismaleimide type of polyimide which cures through a f r e e - r a d i c a l a d d i t i o n mechanism. The p r e p r e g h a d b e e n i n c l u d e d f o r t e s t i n g i n t h e NRL V/STOL p r o g r a m b e c a u s e i t a p p e a r e d t o h a v e a number o f d e s i r e d f e a t u r e s : h i g h o p e r a t i o n a l t e m p e r a t u r e , 500 h r s a t 246 C (475 F ) ; i t c o n t a i n s no s o l v e n t s ; no v o l a t i l e p r o d u c t s a r e formed d u r i n g c u r e ; and i t can be p r o c e s s e d l i k e s t a t e - o f - t h e - a r t e p o x i e s . Recent work a t t h i s L a b o r a t o r y has shown t h a t t h i s r e s i n s y s t e m h a s a h i g h e r f r a c t u r e t o u g h n e s s t h a n h i g h t e m p e r a t u r e epoxy s y s t e m s . The g l a s s t r a n s i t i o n t e m p e r a t u r e , d e t e r m i n e d b y t o r s i o n a l pendulum m e a s u r e m e n t s , was 360 C f o r t h i s r e s i n compared t o 260 C f o r a n epoxy ( 2 ) . A g i n g and F a b r i c a t i o n . F r e s h p r e p r e g m a t e r i a l was c u t , p a c k e d i n k i t s and s t o r e d a t room t e m p e r a t u r e i n t h r e e e n v i r o n m e n t a l chambers c o n t r o l l e d a t 16%, 5 0 % a n d 9 5 % r e l a t i v e h u m i d i t y , respectively. The k i t s w e r e e s s e n t i a l l y s m a l l a l u m i n u m s h e l v e s w i t h 17 o p e n s l o t s . Each k i t t h e r e f o r e c o n t a i n e d seventeen p i e c e s o f p r e p r e g , 15 cm χ 15 cm i n s i z e w i t h o n e p i e c e i n e a c h slot. A g i n g extended over a p e r i o d o f t w e n t y - e i g h t weeks. At t h e end o f e v e r y f o u r - w e e k p e r i o d , a k i t was removed f r o m s t o r a g e a n d a 1 6 - p l y l a m i n a t e p r e p a r e d o n t h e same day. The e x t r a s h e e t o f aged p r e p r e g f r o m e a c h k i t was u s e d f o r p r o t o n nmr analysis. U n i d i r e c t i o n a l 1 6 - p l y l a m i n a t e s w e r e f a b r i c a t e d i n a Wabash P r e s s u s i n g c o n v e n t i o n a l vacuum b a g t e c h n i q u e s . The s a m p l e l a y up i n c l u d e d o n e g l a s s b l e e d e r p l y p e r e v e r y f o u r p l i e s o f p r e p r e g w i t h t o p b l e e d i n g o n l y . A p o r o u s f e l t m a t e r i a l was u s e d a r o u n d t h e s a m p l e t o f o r m a dam t o p r e v e n t o v e r b l e e d i n g f r o m t h e edge o f t h e s a m p l e . I n i t i a l l y t h e p r o c e s s i n g i n t h e p r e s s was b a s e d on a m a n u f a c t u r e r recommended c u r e c y c l e o r i g i n a l l y d e s i g n e d f o r a u t o - c l a v e o p e r a t i o n . The r e s u l t i n g l a m i n a t e s , h o w e v e r , h a d h i g h v o i d c o n t e n t s a s e v i d e n t from the r e s u l t o f a n u l t r a s o n i c C-scan study o f t h e l a m i n a t e s (see F i g . l a ) . V a r i a t i o n s from t h a t c u r e c y c l e w e r e made t o a d j u s t f o r t h e p r e s s o p e r a t i o n . P r o c e s s i n g parameters such as d w e l l t i m e , temperature and time of p r e s s u r e a p p l i c a t i o n were v a r i e d u n t i l h i g h q u a l i t y , r e p r o d u c i b l e laminates could be f a b r i c a t e d . These l a m i n a t e s had a v o i d c o n t e n t o f l e s s t h a n 0.5%, a n d a t y p i c a l C - s c a n r e s u l t i s shown i n F i g . l b . T h i s m o d i f i e d c u r e c y c l e , w h i c h i s g i v e n g r a p h i c a l l y i n F i g . 2, e s s e n t i a l l y i n c l u d e d a f u l l vacuum c y c l e a t 121°C (250°F) a n d a p r e s s u r e c y c l e a t 177°C (350°F) a n d a p r e s s u r e o f 6.9 χ 10 P a (100 p s i ) . P o s t - c u r e r e q u i r e m e n t was 10 h o u r s a t 249 C (480 F ) . T h i s c u r e c y c l e was t h e n k e p t t h e same f o r p r o c e s s i n g a l l a g e d s a m p l e s i n o r d e r t o d e t e c t a n y c h a n g e of p r o c e s s a b i l i t y i n t h e m a t e r i a l due t o a g i n g . 5


472

RESINS

AEROSPACE

6 .9 χ 1 0 Pa PRESSURE 5

FULL VACUUM


FOR

JL 2

3 TIME

Figure 2.

(hour)

Cure schedule for fabricating F-178/T300 laminates in press

2,8

Λ

2.6

ho

6

Ο

Χ Ο

2.0

1.8

ο

ο

ο

χ

JL 8

12 A g i n g

Figure 3.

9

P e r i o d

16

20

24

28

( w e e k )

Laminate flexural strength as a function of aging period; F-178/T300, room-temperature aging; R.H.: (O) 16%, (χ) 50Ψο, (Q) 9 5 %



34.

NASH E T AL.

Room-Temperature

Aging

473

M e c h a n i c a l T e s t i n g , Samples w e r e c u t f r o m t h e l a m i n a t e a n d t e s t s were c a r r i e d out t o d e t e r m i n e i f any change o c c u r r e d i n t h e i r mechanical p r o p e r t i e s r e l a t i v e t o composites prepared from unaged p r e p r e g . The s h o r t - b e a m s h e a r t e s t was c h o s e n t o d e t e r m i n e t h e 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 , a r e s i n - d o m i n a t e d p r o p e r t y . The t e s t was c a r r i e d o u t a c c o r d i n g t o t h e ASTM s t a n d a r d D2344. The d i m e n s i o n s o f t h e s h e a r s p e c i m e n s w e r e 0.5" χ 0.16" χ 0.28", a n d 20 s p e c i m e n s w e r e t e s t e d f o r e a c h l a m i n a t e s a m p l e . On t h e o t h e r h a n d , t h e f l e x u r a l t e s t was s e l e c t e d t o m e a s u r e t h e l a m i n a t e f l e x u r a l s t r e n g t h and modulus, which a r e f i b e r - d o m i n a t e d properties. The f l e x u r a l s p e c i m e n s w e r e 2" χ 1" χ 0.08", s a t i s f y i n g t h e r e q u i r e m e n t i n ASTM s t a n d a r d D790. S i x s p e c i m e n s were t e s t e d i n t h i s case f o r each l a m i n a t e sample. Both mechani c a l t e s t s w e r e c a r r i e d o u t on a n INSTRON t e s t i n g m a c h i n e a t a c r o s s h e a d s p e e d o f 0.05 i n / m i n . P r o t o n NMR. Weighed 2 cm χ 2 cm s a m p l e s o f aged p r e p r e g w e r e p l a c e d i n t a r e d v i a l s ; 1 gram o f a c e t o n e - d ^ was added t o e a c h v i a l . The s a m p l e s w e r e e x t r a c t e d f o r ~2 h o u r s a t room t e m p e r a t u r e w h i l e b e i n g s t i r r e d on a magnetic s t i r r e r . The r e s u l t i n g s o l u t i o n s w e r e f i l t e r e d d i r e c t l y i n t o d r y nmr s a m p l e t u b e s . The r e s i d u e s w e r e d r i e d a n d w e i g h e d . The s p e c t r a w e r e o b t a i n e d o n a JEOL FX60Q spectrometer system w i t h t h e f o l l o w i n g parameters: f r e q u e n c y , 59.75 MHz ; 90° p u l s e ( 8 s e c ) ; 600 Hz s p e c t r a l w i d t h ; 500 H z , 4p o l e B u t t e r w o r t h f i l t e r ; q u a d r a t u r e phase d e t e c t i o n ; 8 sec p u l s e r e p e t i t i o n r a t e ; 100 p u l s e s ; 8192 d a t a p o i n t s . The i n t e r n a l d e u t e r i u m l o c k was p r o v i d e d b y t h e s o l v e n t . The s p e c t r a w e r e r u n a t 25 C. M

Results Mechanical Properties. F i g u r e 3 shows t h e f l e x u r a l s t r e n g t h of t h e g r a p h i t e / p o l y i m i d e composite p l o t t e d as a f u n c t i o n o f p r e p r e g a g i n g p e r i o d i n weeks. I t can be seen t h a t l a m i n a t e f l e x u r a l p r o p e r t y s t e a d i l y d e c r e a s e s a s a g i n g c o n t i n u e s . The e f f e c t i s more p r o n o u n c e d a t h i g h e r h u m i d i t y l e v e l s . A f t e r t w e n t y weeks o f a g i n g a t 9 5 % r e l a t i v e h u m i d i t y , t h e f l e x u r a l s t r e n g t h i s reduced by n e a r l y 25% from t h a t o f t h e o r i g i n a l c o n t r o l sample. The same t r e n d i s f o l l o w e d b y t h e f l e x u r a l m o d u l u s d a t a . F i g u r e 4 presents the i n t e r l a m i n a r shear s t r e n g t h data as a f u n c t i o n o f p r e p r e g a g i n g p e r i o d . I n t h i s c a s e , t h e r e s u l t s show a r a p i d i n c r e a s e i n shear s t r e n g t h i n i t i a l l y as aging proceeds. Then i t becomes c o n s t a n t a t a l e v e l a p p r o x i m a t e l y 5 5 % h i g h e r t h a n that of the i n i t i a l c o n t r o l . The i n c r e a s e seems t o b e i n d e p e n d e n t of t h e h u m i d i t y l e v e l a t w h i c h p r e p r e g s a m p l e s w e r e a g e d . A t f i r s t g l a n c e t h e s e r e s u l t s seemed s u r p r i s i n g b e c a u s e a n y r e s i n degradation t a k i n g p l a c e due t o moisture a b s o r p t i o n i n t h e prepreg would l e a d t o poorer resin-dominated p r o p e r t y such as 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 . The f a c t t h a t 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 was i m p r o v e d a n d f l e x u r a l p r o p e r t i e s d e t e r i o r a t e d may b e


474


h

20

8 * 16

Γ

θ

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ΙΟ

8

μ

1

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ι

ι

ι

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4

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28

Aging Period

(week)

Figure 4.

InteAaminar shear strength of aged samples; F-178/T300, room-tem perature aging; R.H.: (O) 16%, (X) 50%, (Q) 95%

Figure 5.

Laminate density as a function of aging period; F-178/T300, temperature aging; R.H.: (O) 16%,(X)50%, (0)95%


room-


34.

NASH E T AL.

Room-Temperature

Aging

475

r e s o l v e d b y c o n s i d e r i n g some p h y s i c a l c h a n g e s t o t h e p r e p r e g s which occurred d u r i n g aging. F i r s t of a l l , during the aging period the prepreg m a t e r i a l c l e a r l y showed a s t e a d y l o s s o f t a c k i n e s s . A s a g i n g c o n t i n u e d , t h e p r e p r e g g r a d u a l l y became d r y a n d b r i t t l e , m a k i n g i t d i f f i c u l t to keep a l l p l i e s p r o p e r l y a l i g n e d and adhered d u r i n g l a y - u p . S e c o n d l y , t h e b l e e d i n g d u r i n g c u r i n g was g r e a t l y r e d u c e d f o r aged s a m p l e s . W e t t i n g o f t h e b l e e d e r p l i e s became l e s s a n d l e s s , p a r t i c u l a r l y around the c o r n e r s o f the square p l i e s , a s aging c o n t i n u e d . T h e s e c h a n g e s seem t o s u g g e s t t h a t t h e amount o f r e s i n f l o w was g r e a t l y r e d u c e d d u e t o a g i n g . These o b s e r v a t i o n s suggest t h a t exposure t o h i g h h u m i d i t y c a u s e d l i t t l e o r no c h e m i c a l d e g r a d a t i o n i n t h e r e s i n s y s t e m . B u t room t e m p e r a t u r e s t o r a g e p r o d u c e d a p r e p r e g m a t e r i a l t h a t was e x c e s s i v e l y B-staged. The aged p r e p r e g s e s s e n t i a l l y h a d a h i g h e r degree o f c r o s s l i n k i n g than a f r e s h sample a t t h e b e g i n n i n g o f the f a b r i c a t i o n p r o c e s s . T h i s change i n degree o f c r o s s l i n k i n g was n o t d e t e c t e d b y p r o t o n NMR, b u t t h e m a t e r i a l was e s s e n t i a l l y one w i t h h i g h e r m o l e c u l a r w e i g h t s h a v i n g g r e a t e r m e l t v i s c o s i t i e s . T h i s , t h e r e f o r e , l o w e r e d t h e f l o w when t h e s a m p l e was s u b j e c t e d to the p r o c e s s i n g c y c l e o r i g i n a l l y designed f o r the c o n t r o l s a m p l e . The r e s u l t was a c o m p o s i t e l a m i n a t e h a v i n g h i g h e r r e s i n content, b u t poorer f l e x u r a l p r o p e r t i e s . Laminate d e n s i t y measurements a n d f i b e r / m a t r i x v o l u m e d e t e r m i n a t i o n c o n f i r m e d t h i s . The r e s u l t s , shown i n F i g s . 5 a n d 6, i n d i c a t e d t h a t t h e r e s i n content i n the l a m i n a t e s i n c r e a s e d w i t h i n c r e a s e d age o f t h e prepreg, r e s u l t i n g i n decreased laminate d e n s i t y . P r o t o n NMR. The two m a j o r components o f t h e F-178 r e s i n s y s t e m w e r e i d e n t i f i e d t h r o u g h p r o t o n a n d c a r b o n - 1 3 nmr. In the p r o t o n s p e c t r u m , F i g u r e 7, t h e l i n e s a t 4.2, 7.1 a n d 7.4 ppm a r i s e from the methylene, o l e f i n i c and a r o m a t i c p r o t o n s o f t h e bismaleimide of methylene d i a n i l i n e , I . A l l o f the l i n e s i n t h e 4.4 t o 6.3 ppm r e g i o n a r e d u e t o t h e a l l y l p r o t o n s o f t r i a l l y l i s o c y a n u r a t e , I I . T h e r e a r e a number o f l o w i n t e n s i t y l i n e s w h i c h we h a v e n o t a t t e m p t e d t o i d e n t i f y .

I

II




476

12

16

Aging P e r i o d Figure 6.

20

24

(week)

Volumetric fractions of fiber and matrix vs. aging period in weeks; F-178/T300, room-temperature aging at 95% R.H.

j y

Figure 7. 60-MHz proton NMR spectrum of material extracted from unaged F-178/T300 prepreg. The line at 0 ppm is that of the reference, tetramethylsihne. The multiplet at 2 ppm is attributable to the residual protons in the solvent, acetone —d«.


34.

NASH E T AL.

Room-Temperature

Aging

477

The a g i n g i n t h e F-178 r e s i n s y s t e m i s a c o n t i n u a t i o n o f t h e c u r i n g r e a c t i o n s i n i t i a t e d during the manufacture o f t h e prepreg. The s y s t e m c u r e s t h r o u g h f r e e r a d i c a l p o l y m e r i z a t i o n o f t h e o l e f i n i c b o n d s . Some t y p i c a l r e a c t i o n s a r e shown b e l o w . R e a c t i o n s ( 1 ) a n d ( 2 ) a r e two o f t h e c h a i n p r o p a g a t i n g r e a c t i o n s f o r t h i s s y s t e m w h e r e R« a n d R * a r e a n y f r e e r a d i c a l s .


f

The new f r e e r a d i c a l s f o r m e d i n ( 1 ) and ( 2 ) may c o n t i n u e t o s i m i l a r l y a t t a c k o t h e r d o u b l e bonds o r t h e y may c o m b i n e i n a c h a i n t e r m i n a t i n g r e a c t i o n a s shown i n ( 3 ) . T h u s , a s t h e c u r e p r o c e e d s t h e d o u b l e bonds a r e consumed and t h e s y s t e m becomes more " a l i p h a t i c " . E i t h e r carbon-13 o r p r o t o n nmr c o u l d b e e x p e c t e d t o m o n i t o r t h e c h a n g e s o c c u r r i n g i n t h e s y s t e m . We d e c i d e d t o u s e p r o t o n nmr b e c a u s e i t i s f a s t e r , r e q u i r e s l e s s s a m p l e a n d i s e a s i e r t o q u a n t i f y . We l o o k e d f o r new p r o t o n l i n e s g r o w i n g i n t h e 2 t o 4 ppm r e g i o n s i m i l a r t o those observed by C r i v e l l o from p o l y a s p a r t i m i d e s which he h a d p r e p a r e d f r o m b i s - m a l e i m i d e s ( 3 ) . We d i d n o t d e t e c t a n y n o t a b l e d i f f e r e n c e i n t h i s r e g i o n o f t h e s p e c t r a o f t h e aged s a m p l e s compared t o t h a t o f t h e c o n t r o l s a m p l e . We a l s o m e a s u r e d t h e r a t i o s o f t h e i n t e n s i t y o f t h e o l e f i n i c peak o f I (7 ppm) t o t h o s e o f t h e a r o m a t i c p e a k o f I (7.4 ppm) a n d t h e CH ~N p e a k (4.6 ppm) o f I I . Changes i n t h e 7 ppm/7.4 ppm r a t i o would i n d i c a t e m o l e c u l a r change i n t h e e x t r a c t e d m a l e i m i d e . Changes i n t h e 7.0 ppm/4.6 ppm r a t i o w o u l d i n d i c a t e c h a n g e s i n t h e composition of the extracted r e s i n . I n each case, t h e v a l u e o f t h e r a t i o showed n o s i g n i f i c a n t v a r i a t i o n s f r o m t h e o n e m e a s u r e d on t h e c o n t r o l s a m p l e . 2



478

RESINS

FOR

AEROSPACE

The f a i l u r e o f p r o t o n nmr t o r e v e a l any a g i n g e f f e c t s i n t h i s study i s probably because t h e i n i t i a l products of t h e r e a c t i o n s a r e n o t s o l u b l e i n a c e t o n e o r t h a t t h e y do n o t r e a c h a detectable concentration before reacting further. The e x t r a c t i o n p r o c e d u r e was d e s i g n e d t o h a v e t h e l e a s t p u r t u r b a t i o n on t h e s y s tem. The c o n t a c t t i m e h a d t o b e s h o r t , f o r we h a d p r e v i o u s l y f o u n d t h a t a c e t o n e s o l u t i o n s o f t h e F-178 r e s i n d e g r a d e r a p i d l y , e v e n o v e r n i g h t . E x t r a c t i o n w i t h h o t a c e t o n e was n o t a t t e m p t e d b e c a u s e o f p o s s i b l e s i d e r e a c t i o n s . A c e t o n e - d ^ was c h o s e n o v e r d i m e t h y l s u i f o x i d e - d ^ (DMSO) a n d d i m e t h y l f o r m a m i d e - d ^ (DMF) b e c a u s e i t s r e s i d u a l p r o t o n a b s o r p t i o n o c c u r s a t 2 ppm, w h e r e a s t h a t o f DMSO o c c u r s a t 2.5 ppm and DMF h a s two a b s o r p t i o n s , 2.7 a n d 2.9 ppm, w h i c h w o u l d s t a r t o b s c u r i n g t h e r e g i o n o f interest. References 1.

Reference t o a specific p r o d u c t d o e s n o t imply a p p r o v a l o f o r r e c o m m e n d a t i o n b y the U. S. D e p a r t m e n t o f D e f e n s e .

2.

W. D. Bascom, J. L . Bitner ACS O r g a n i c C o a t i n g s a n d

3.

a n d R. L . Cottington, Plastics, 3 8 , 477 ( 1 9 7 8 ) .

J. V. Crivello, P o l y m . Prepr., A m e r i c a n C h e m i c a l Div. o f P o l y m . Chem., 1 4 ( 1 ) , 294 ( 1 9 7 3 ) .

RECEIVED

Preprint, Society,

January 22, 1980.


Polyimide Prepreg

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