Petroleum-Derived Carbons - ACS Publications - American Chemical

22 Progress of Pitch-Based Carbon Fiber in Japan

Downloaded by CORNELL UNIV on July 23, 2016 | http://pubs.acs.org Publication Date: April 14, 1986 | doi: 10.1021/bk-1986-0303.ch022

Sugio Ōtani and Asao Ōya Faculty of Technology, Gunma University, Kiryu, Gunma 376, Japan

Carbon fiber technology has developed rapidly in Japan during the last decade. The origins of pitch-based fiber trace back to observations of lignin deformation during pyrolysis. Although only the low-modulus general performance carbon fiber (GPCF) made by spinning iso tropic pitch has been commercialized thus far in Japan, extensive development efforts are in progress on the high-modulus high performance carbon fiber (HPCF) pro duced by spinning mesophase pitches. Current efforts recognize two chemical factors that govern the viscous behavior and reactivity of mesophase pitch: the extent of alicyclic structure, and the hydrogen transfer between mesophase molecules. Two approaches to prepara tion of spinnable mesophase pitch are the Gundai "dormant mesophase" method, in which the pitch is hydro genated just at the point of the mesophase transforma tion, and the Kyukoshi method, which employs tetrahydro quinoline as the hydrogenating agent. P i t c h - b a s e d carbon f i b e r was i n v e n t e d i n our l a b o r a t o r y a t Gunma U n i v e r s i t y i n the summer of 1963 A t t h a t time we were a t t e m p t i n g t o prepare a c t i v e carbon from l i g n i n powder. One day we found w h i s k e r - l i k e carbon near the w a l l of a f l a s k i n which l i g n i n powder had been heated i n a i r t o 500°C; see F i g u r e 1. We s p e c u l a t e d t h a t t h e l i g n i n powder had m e l t e d i n c r e m e n t a l l y , s t a r t i n g from the w a l l of the f l a s k , and t h a t the molten l i g n i n had been s t r e t c h e d t o form f i b r o u s r e g i o n s by the s i n t e r i n g of t h e l i g n i n near the center of the f l a s k . E v e n t u a l l y the s t r e t c h e d l i g n i n became i n f u s i b l e through f u r t h e r h e a t i n g i n a i r t o h i g h e r temperature. A s p i n n i n g experiment was undertaken t o t e s t t h i s s p e c u l a tion. M o l t e n l i g n i n , produced by r a p i d h e a t i n g of the l i g n i n powder, was found t o be q u i t e s p i n n a b l e . A f t e r s p i n n i n g , the f i b e r was e a s i l y s t a b i l i z e d by h e a t i n g t o 300°C i n a i r , and then c a r b o n i z e d by h e a t i n g t o 1000°C under n i t r o g e n . Some of t h i s f i b e r i s i l l u s t r a t e d by F i g u r e 2 . 0097-6156/86/0303-0323$06.00/0 © 1986 American Chemical Society

Bacha et al.; Petroleum-Derived Carbons ACS Symposium Series; American Chemical Society: Washington, DC, 1986.


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I n those d a y s , the mechanisms of c a r b o n i z a t i o n of p o l y v i n y l c h l o r i d e (PVC) were a l s o under study i n our l a b o r a t o r y . We found t h a t PVC t r a n s f o r m e d t o a b e a u t i f u l l u s t r o u s p i t c h upon h e a t i n g t o 400°C under n i t r o g e n . T h i s PVC p i t c h c o u l d be spun q u i t e e a s i l y , by comparison w i t h molten l i g n i n , and thus the p i t c h - b a s e d carbon f i b e r was f i r s t prepared i n e s s e n t i a l l y the same way as the l i g n i n - b a s e d carbon f i b e r . We r e c o g n i z e now t h a t we were f o r t u n a t e i n f i r s t u s i n g PVC p i t c h . We l a t e r t r i e d many o t h e r p i t c h e s as raw m a t e r i a l s f o r carbon f i b e r , but PVC p i t c h was the o n l y one t h a t c o u l d be spun w i t h o u t any p r e t r e a t m e n t . T h i s was i n 1963. We i m m e d i a t e l y a p p l i e d f o r a p a t e n t (2_), and the f u n d a mentals of p i t c h p r e p a r a t i o n and s p i n n i n g as w e l l as the s t r u c t u r e of the f i n i s h e d f i b e r s were p u b l i s h e d i n 1965 (_3). D u r i n g the e n s u i n g f i v e y e a r s , a number of p i t c h e s were developed as carbon f i b e r p r e c u r s o r s through use of v a r i o u s p r e treatment t e c h n i q u e s ( 4 - 9 ) . We e x p l o r e d four b a s i c p r e t r e a t m e n t p r o c e s s e s , sometimes i n c o m b i n a t i o n : (a) p o l y m e r i z a t i o n a n d / o r a r o m a t i z a t i o n by heat t r e a t m e n t , (b) removal of v o l a t i l e s p e c i e s by d i s t i l l a t i o n under a t m o s p h e r i c or reduced p r e s s u r e , (c) r e m o v a l of i n f u s i b l e matter by s o l v e n t f r a c t i o n a t i o n , and (d) a c c e l e r a t i o n of p o l y m e r i z a t i o n by a d d i n g a r a d i c a l i n i t i a t o r . The m e c h a n i c a l p r o p e r t i e s of the r e s u l t i n g f i b e r s were i n the ranges of 0.8 - 1.8 GPa (115 - 260 k p s i ) f o r t e n s i l e s t r e n g t h and 20 - 50 GPa ( 2 . 9 7.3 M p s i ) for Young s modulus. These methods were s u b s e q u e n t l y developed by Kureha C h e m i c a l I n d u s t r i e s Company, and f i b e r s were c o m m e r c i a l i z e d i n 1970 as the G e n e r a l Performance Carbon F i b e r s (GPCF) KCF-100 and KCF-200. At p r e s e n t these are the o n l y c o n t i n u o u s - s t r a n d low-modulus carbon f i b e r s produced c o m m e r c i a l l y from a p i t c h base. Meanwhile carbon f i b e r s d e r i v e d from p o l y a c r y l o n i t r i l e (PAN) were a l s o under development, and around 1963 methods of heat t r e a t i n g under s t r e s s were found t o enhance s h a r p l y the m e c h a n i c a l properties. T h i s success r e s u l t e d i n r a p i d growth of PAN-based carbon f i b e r t e c h n o l o g y f o r h i g h - p e r f o r m a n c e a p p l i c a t i o n s (Young's modulus g r e a t e r than 200 GPA, 30 M p s i ) . However, s i m i l a r methods were not s u i t a b l e f o r mass p r o d u c t i o n of pitch-based highperformance carbon f i b e r (HPCF), and other approaches were a g g r e s s i v e l y e x p l o r e d t o l e a r n how t o produce high-modulus carbon f i b e r s from i n e x p e n s i v e p i t c h p r e c u r s o r s . A number of o r g a n i c compounds were c a r b o n i z e d and g r a p h i t i z e d i n our l a b o r a t o r y as we sought t o r e v e a l the f a c t o r s t h a t govern the g r a p h i t i z a b i l i t y of carbon m a t e r i a l s . Among these was t e t r a benzo ( a , c , h , j ) phenazine ( a b b r e v i a t i o n : PZ) w i t h the m o l e c u l a r s t r u c t u r e shown i n F i g u r e 3. The m e l t i n g p o i n t of a l a r g e c o n densed p o l y c y c l i c compound such as PZ i s v e r y s e n s i t i v e t o t r a c e amounts of i m p u r i t y and thus depends on the p r e p a r a t i o n p r o c e dure. On h e a t i n g a t 530 t o 590°C f o r one hour under n i t r o g e n , PZ w i t h a m e l t i n g p o i n t of 465 - 485°C was c o n v e r t e d i n t o a l u s t r o u s p i t c h t h a t melted i n the range of 300 t o 380°C. On c o o l i n g , t h i s p i t c h e x h i b i t e d the s t r o n g p r e f e r r e d o r i e n t a t i o n of a me sophase p i t c h , as shown i n F i g u r e 4. I n 1961, the PZ p i t c h was used t o p r e p a r e carbon f i b e r s . As e x p e c t e d , the f i b e r d i s p l a y e d s t r o n g p r e f e r r e d o r i e n t a t i o n w i t h o u t any s p e c i a l t r e a t m e n t ( 1 0 , 1 1 ) . I n the course of GPCF development, as s t a t e d e a r l i e r , the p r e c u r s o r m a t e r i a l was changed from PVC p i t c h t o other p i t c h e s . 1



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Progress of Pitch-Based Carbon Fiber in Japan

F i g u r e 1.

Figure 2.

F i g u r e 3. (PZ).

W h i s k e r - l i k e carbon from

Carbon f i b e r

Molecular

prepared

structure

of

lignin.

by s p i n n i n g molten

tetrabenzo ( a , c , h , j )

lignin.

phenazi


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S i m i l a r l y , PZ p i t c h as p r e c u r s o r f o r HPCF was r e p l a c e d by other mesophase p i t c h e s ( 1 2 ) . A t t h i s p o i n t i n t i m e , as i s w e l l - k n o w n , Singer (13) and Lewis (14) of the Union C a r b i d e C o r p o r a t i o n developed s i m i l a r methods. Mesophase carbon f i b e r p r o g r e s s e d more r a p i d l y i n the USA than i n Japan because Japanese defense and aerospace needs were l e s s demanding. R e c e n t l y , however, the d r i v e toward h i g h e r - a d d e d - v a l u e p r o d u c t s from the heavy f r a c t i o n s of c o a l and p e t r o l e u m has i n t e n s i f i e d , and p i t c h - b a s e d carbon f i b e r s , i n c l u d i n g HPCF, a r e now the s u b j e c t s of e x t e n s i v e i n v e s t i g a t i o n i n many Japanese l a b o r a t o r i e s .


P i t c h Chemistry The p r i n c i p a l problem i n p i t c h - b a s e d carbon f i b e r i s the c o n t r o l of the p r o p e r t i e s of the p r e c u r s o r p i t c h . S t u d i e s of p i t c h c h e m i s t r y have c o n t r i b u t e d s i g n i f i c a n t l y t o the development of pitch-based carbon f i b e r , i n c l u d i n g some i n v e s t i g a t i o n s whose p r a c t i c a l purpose was u n r e l a t e d to carbon f i b e r . S i n c e about 1969, a b a s i c u n d e r s t a n d i n g of p i t c h c h e m i s t r y has been pursued a g g r e s s i v e l y i n J a p a n , and t h r e e s t u d i e s of p a r t i c u l a r s i g n i f i cance t o carbon f i b e r are summarized h e r e . Mesophase Model and the Importance of A l i c y c l i c S t r u c t u r e . The r e s e a r c h group a t Kyushu U n i v e r s i t y l e d by T a k e s h i t a and Mochida has sought t o c o n t r o l the p r o p e r t i e s of p i t c h m a t e r i a l s by c a t a l y t i c and c o - c a r b o n i z a t i o n t e c h n i q u e s . T h e i r p r o g r e s s i n these a r e a s may be summarized as f o l l o w s : ( i ) In e a r l i e r work by the p r e s e n t a u t h o r s ( 1 5 ) , AICI3 a d d i t i o n s were found t o be e f f e c t i v e i n i n c r e a s i n g the~~carbon y i e l d of p i t c h w i t h o u t l o s s of g r a p h i tizability. I n s y s t e m a t i c s t u d i e s of the use of the AICI3 c a t a l y s t , the Kyushu group found t h a t t h i s c a t a l y s t can i n t r o d u c e a l i c y c l i c s t r u c t u r e i n t o the p i t c h m o l e c u l e s , l e a d i n g t o e x t e n s i o n of the l i q u i d s t a t e to h i g h e r temperature ( 1 6 , 1 7 ) . ( i i ) This group a l s o works e n e r g e t i c a l l y on c o - c a r b o n i z a t i o n by u s i n g u s i n g o r g a n i c compounds, c o a l s , and p i t c h m a t e r i a l s . The most i n t e r e s t ing c o n c l u s i o n i s t h a t p a r t i a l l y hydrogenated pyrene i s more reactive t h a n non-hydrogenated pyrene (18). (iii) Through e x t e n s i v e a n a l y t i c a l work, the Kyushu group a l s o developed the s o c a l l e d " s p i d e r web" model f o r mesophase m o l e c u l e s ( 1 9 ) ; see F i g u r e 5. T h i s model p r o v i d e s c l e a r w o r k i n g concepts for the t y p i c a l c o n s t i t u e n t m o l e c u l e s of the mesophase. Carbonization i n Molten Salt Media. "Ôta and Ôtani (20) of Gunma University developed a novel c a r b o n i z a t i o n method i n which a r o m a t i c compounds, such as n a p h t h a l e n e , are c a r b o n i z e d homo geneously i n m o l t e n s a l t s w i t h the c a t a l y t i c a c t i o n of A l C l ^ . The molten s a l t f i r s t used was A l C ^ - N a C l - K C l ( 6 0 : 2 6 : 1 4 i n molar r a t i o ) , w h i c h has a m e l t i n g p o i n t of 95°C. More r e c e n t l y A l C l ^ C6H5NC2H5Br ( 6 7 : 3 3 i n molar r a t i o ) has been u s e d ; t h i s m i x t u r e i s l i q u i d a t room t e m p e r a t u r e . When t h i s c a r b o n i z a t i o n t e c h n i q u e i s u s e d , p o l y m e r i z a t i o n i n i t i a t e s below 100°C, and mesophase p i t c h w i t h much a l i c y c l i c s t r u c t u r e forms a t temperatures as low as 230°C. Semicoke forms a t j u s t 300°C. By u s i n g v a r i o u s c h l o r o a l kanes as c o u p l i n g r e a g e n t s , p o l y m e r i c compounds can be o b t a i n e d a t temperatures as low as 80°C. By v a r y i n g the n a t u r e and amount of



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F i g u r e 4.

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P o l a r i z e d - l i g h t m i c r o g r a p h of PZ p i t c h .

F i g u r e 5. The " s p i d e r web" model f o r the c o n s t i t u e n t of mesophase, a f t e r Mochida e t a l . ( 1 9 ) .

molecules


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the c o u p l i n g r e a g e n t , the g r a p h i t i z a b i l i t y of t h e r e s u l t i n g coke can be c o n t r o l l e d t o a l a r g e e x t e n t . A l t h o u g h some problems r e m a i n t o be s o l v e d (such as t h e s e p a r a t i o n of p i t c h from m o l t e n s a l t ) , these n o v e l methods a r e expected t o c o n t r i b u t e s i g n i f i c a n t l y t o t h e development of p i t c h - b a s e d carbon f i b e r s as w e l l as other a p p l i c a t i o n s i n the near f u t u r e . C h a r a c t e r i z a t i o n Techniques f o r P i t c h M a t e r i a l s . Among a number of c h a r a c t e r i z a t i o n t e c h n i q u e s developed i n J a p a n , t h e t e c h n i q u e due t o t h e members of t h e S o c i e t y of Heavy O i l , l e d by K u n u g i , stands out as p a r t i c u l a r l y u s e f u l . The a n a l y t i c a l d a t a a r e t r e a t e d by computer methods t o c o n s t r u c t average m o l e c u l a r s t r u c t u r e s f o r t h e carbonaceous m a t e r i a l s . Sanada's group i n Hokkaido U n i v e r s i t y used h i g h - t e m p e r a t u r e NMR and ESR d a t a o b t a i n e d by i n s i t u measurements of p i t c h m a t e r i a l s i n molten s a l t ( 2 1 ) . Much information on mesophase behavior during the heat-treatment p r o c e s s was o b t a i n e d i n t h i s way. Another s i g n i f i c a n t t e c h n i q u e developed by Sanada's group i s the c h a r a c t e r i z a t i o n of p i t c h f o r i t s e l e c t r o n donor ability, w h i c h i s e s t i m a t e d by the amount of hydrogen t r a n s f e r r e d from p i t c h t o anthracene a f t e r the m i x t u r e has been heated t o 400°C (22). The p r e s e n t a u t h o r s l a t e r showed t h a t t h e e l e c t r o n a c c e p t o r a b i l i t y of p i t c h can be e s t i m a t e d i n a s i m i l a r manner by u s i n g a m i x t u r e of p i t c h and d i h y d r o a n t h r a c e n e ( 2 3 ) . The d e t a i l s of hydrogen t r a n s f e r between p i t c h m o l e c u l e s i s an i m p o r t a n t t o p i c f o r study t o u n d e r s t a n d t h e i n i t i a l s t a g e s of c a r b o n i z a t i o n p r o cesses. Recent Developments of P i t c h - B a s e d Carbon F i b e r i n J a p a n A number of i n v e s t i g a t i o n s of the p r e p a r a t i o n of p i t c h - b a s e d carbon f i b e r are i n progress i n industrial laboratories i n Japan. However, a s i d e from p a t e n t s , only t h e developments by Honda and Yamada's group a t t h e Kyushu I n d u s t r i a l R e s e a r c h I n s t i t u t e and by the p r e s e n t a u t h o r s a t Gunma U n i v e r s i t y have been published. P i t c h - B a s e d G e n e r a l Performance Carbon F i b e r ( G P C F ) . As d e s c r i b e d i n t h e i n t r o d u c t i o n , c o n t i n u o u s - s t r a n d GPCF has been produced c o m m e r c i a l l y only by the Kureha C h e m i c a l I n d u s t r i e s Company. P u b l i c a t t e n t i o n has r e c e n t l y been a t t r a c t e d t o t h i s type o f carbon f i b e r by the s u c c e s s i n u s i n g carbon-fiber-reinforced c o n c r e t e i n the c o n s t r u c t i o n of the Arsasheed Monument i n I r a q (24) by the Kashima C o n s t r u c t i o n (Kashima K e n s e t s u ) C o . F u t u r e c o n s t r u c t i o n p r o j e c t s i n Japan p l a n t o u t i l i z e f u r t h e r t h i s type of f i b e r - r e i n f o r c e d c o n c r e t e . Such a p p l i c a t i o n s may l e a d t o mass consumption of f i b e r i f i t s p r i c e can be brought below $ 9 / k g ($4/lb). The a u t h o r s b e l i e v e t h a t some s u b s t a n t i a l r e d u c t i o n s i n the p r i c e of the g e n e r a l - p e r f o r m a n c e f i b e r , perhaps t o $ 6 . 5 / k g ( $ 3 / l b ) , may occur i n t h e near f u t u r e .



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High-Performance Carbon Fiber (HPCF) from Non-Hydrogenated Pitch, P i t c h - b a s e d h i g h - p e r f o r m a n c e f i b e r s from c o m m e r c i a l l y a v a i l a b l e p i t c h e s were f i r s t prepared from mesophase pitches d e r i v e d from n a p h t h a - c r a c k i n g p i t c h e s ( 1 2 ) . I n g e n e r a l these mesophase p i t c h e s have q u i t e h i g h s o f t e n i n g p o i n t s and a r e n o t s u i t a b l e f o r smooth s p i n n i n g . P r i o r t o 1970, the mesophase c o n t e n t i n such p i t c h e s was thought t o be e q u a l t o t h e q u i n o l i n e i n s o l u b l e (QI) c o n t e n t . I n 1976 we found t h a t , i n p i t c h e s d e r i v e d from naphthalene and anthracene w i t h the use of A l C l q c a t a l y s t , the o p t i c a l l y a n i s o t r o p i c r e g i o n s were f a r l a r g e r than the QI content ( 2 5 ) . By h e a t i n g n a p h t h a - t a r p i t c h e s or a t m o s p h e r i c r e d u c e d p i t c h e s w i t h A 1 C 1 - , Yoshimura (26) p r e p a r e d mesophase p i t c h e s w i t h good s p i n n a b i l i t y and w i t h s o f t e n i n g p o i n t s as low as 200 t o 300°C. In those d a y s , p i t c h c h e m i s t r y had n o t advanced s u f f i c i e n t l y t o u n d e r s t a n d f u n d a m e n t a l l y the f o r e g o i n g phenomena. The p r e p a r a t i o n of mesophase p i t c h w i t h low s o f t e n i n g p o i n t ( t h e s o - c a l l e d " s o f t mesophase p i t c h " ) was based on d i r e c t e x p e r i m e n t . N e v e r t h e l e s s through e x t e n s i v e and s e r i o u s e f f o r t s , i t became p o s s i b l e t o prepare s o f t mesophase p i t c h e s from naphtha t a r s , decant o i l s from fluidized c a t a l y t i c crackers (FCC), atmospheric-reduced crude o i l s , and other p i t c h - l i k e m a t e r i a l s . A t y p i c a l example of these p r e p a r a t i o n procedures i s the f o l l o w i n g . A p u r i f i e d FCC or naphtha p i t c h i s heated a t 400°C f o r one hour under methane t o c o n v e r t the p i t c h t o a mesophase c o n t e n t of 23.6% ( 2 7 , 2 8 ) . The mesophase s e p a r a t e d by s e d i m e n t a t i o n has a s o f t e n i n g p o i n t of 226°C; i t i s spun a t 320°C, and the f i b e r i s s t a b i l i z e d i n a i r and f i n a l l y c a r b o n i z e d by r a p i d h e a t i n g a t 100 t o 1600°C/min ( 2 9 ) . H i g h - P e r f o r m a n c e Carbon F i b e r (HPCF) from Hydrogenated P i t c h . A l i c y c l i c m o l e c u l a r s t r u c t u r e and the e x t e n t of hydrogen t r a n s f e r between m o l e c u l e s have been p r o g r e s s i v e l y r e c o g n i z e d as i m p o r t a n t f a c t o r s t o c o n t r o l t h e p r o p e r t i e s of t h e p r e c u r s o r p i t c h f o r f i b e r spinning. Three e x p e r i m e n t a l methods of p i t c h p r e p a r a t i o n were e x p l o r e d as our u n d e r s t a n d i n g of p i t c h c h e m i s t r y was d e v e l o p e d . The f i r s t method i s the s o - c a l l e d "dormant mesophase" or Gunma U n i v e r s i t y (Gundai) method ( 3 0 , 3 1 ) i n w h i c h the mesophase p i t c h i s i n i t i a l l y p r e p a r e d from p e t r o l e u m a s p h a l t by o r d i n a r y p y r o l y s i s p r o c e d u r e s ; t h i s p i t c h i s then hydrogenated t o c o n v e r t i t t o an i s o t r o p i c p i t c h under c o n d i t i o n s t h a t a v o i d d e c o m p o s i t i o n r e a c t i o n s , and f i n a l l y c o n v e r t e d a g a i n t o mesophase p i t c h by another t h e r m a l t r e a t m e n t . The dormant mesophase method ( a l s o known as the Gundai method) i s o u t l i n e d and compared i n F i g u r e 6 w i t h the second method, known as t h e K y u k o s h i method (32) because the p r o c e s s was developed by the Kyushu I n d u s t r i a l R e s e a r c h I n s t i t u t e ( K y u k o s h i ) . I n t h i s second method, naphtha or c o a l - t a r pitches are hydrogenated by u s i n g t e t r a h y d r o q u i n o l i n e (THQ) s o l v e n t and then c o n v e r t e d t o mesophase p i t c h by r a p i d h e a t i n g t o 450 t o 500°C. The t h i r d method uses p r e c u r s o r p i t c h e s p r e p a r e d from hydrogenated c o a l - t a r p i t c h or an SRC ( s o l v e n t - r e f i n e d c o a l ) p i t c h subjected to a hydrocracking technique. A f e a t u r e of the Gundai p r e p a r a t i o n method i s shown i n F i g u r e 7. The mesophase p i t c h e s i n d i c a t e d by DA240(A) were o b t a i n e d by r e h e a t i n g a hydrogenated p i t c h d e r i v e d from a p i t c h c o n t a i n i n g 3% mesophase; the DA240(B) p i t c h e s were similarly


330


GUNDAI METHOD

KYUKOSHI METHOD

Raw

Raw P i t c h J Coal o r naphtha

Pitch A240

Heat Treatment ( I ) ~~J 440°C 2 h r

Hydrogénation 1 38ΊΓ TUTT°C

Mesophase

Hydrogenated. P i t c h

Pitch

ι

Heat T r e a t m e n t

Hydrogénation


pitch

"~J 450°C, s h o r t Mesophase P i t c h

Heat Treatment ( H ) "~J 350 - 400°C

time

Dormant Mesophase P i t c h DA240-400 H e a t T r e a t m e n t (HE) 400

480°C

Mesophase P i t c h DA240-480 F i g u r e 6. Flow c h a r t s f o r t h e p r e p a r a t i o n of f i b e r - s p i n n i n g p i t c h e s by the Gundai (dormant mesophase) and K y u k o s h i methods.

320

Usual method : Kyukoshi method = Gundai method ο

300|

100, ο

280

.''A240 260h ο ° 95 ^ 95 ^ ° ^ > 6 0 J, Sî 240| ° ^ A 2 4 0 ( ^ o

220h 200Ό

2

° 10

6

0

20 30

6

4

0

(

B

)

0

-Ι 40 50 Ql(%)

60 70 80

F i g u r e 7. R e l a t i o n s between s o f t e n i n g p o i n t s , q u i n o l i n e - i n s o l u b l e c o n t e n t s , and mesophase c o n t e n t s of p r e c u r s o r p i t c h e s p r e pared by the Gundai and K y u k o s h i methods. The volume percentage of mesophase i s i n d i c a t e d by the numbers a d j a c e n t t o some points.



22.

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p r e p a r e d from a 5% mesophase p i t c h . I n both c a s e s , the i n i t i a l mesophase p i t c h e s were o b t a i n e d from A s h l a n d A240 p e t r o l e u m p i t c h by h e a t i n g a t 400°C. The numbers a d j a c e n t t o some symbols i n F i g u r e 7 r e f e r to the mesophase c o n t e n t s measured o p t i c a l l y and e x p r e s s e d i n volume-%. The DA240 mesophase p i t c h e s have lower QI contents and lower s o f t e n i n g p o i n t s than those of mesophase p i t c h e s p r e p a r e d by the u s u a l p y r o l y s i s p r o c e d u r e s , and F i g u r e 7 shows t h a t the s o f t e n i n g p o i n t s a l s o tend t o be lower than f o r p i t c h e s p r e p a r e d by the K y u k o s h i method. Thus the Gundai method p i t c h e s are c h a r a c t e r i z e d by low s o f t e n i n g p o i n t s d e s p i t e t h e i r h i g h QI c o n t e n t s . To r e v e a l the hydrogénation e f f e c t s more c l e a r l y , measure ments of r a d i c a l c o n c e n t r a t i o n and the amount of t r a n s f e r r e d hydrogen were compared f o r p i t c h e s p r e p a r e d by the Gundai method and by o r d i n a r y p y r o l y s i s ; see T a b l e I . Mesophase appears a t n e a r l y the same temperature i n b o t h methods. For measurements made j u s t b e f o r e the mesophase a p p e a r s , the p i t c h prepared by the Gundai method e x h i b i t s a l a r g e r amount of t r a n s f e r r e d hydrogen and a lower r a d i c a l c o n c e n t r a t i o n . These c h a r a c t e r i s t i c s must cause the lower s o f t e n i n g p o i n t s a t h i g h QI c o n t e n t s . These d i f f e r e n c e s d i s a p p e a r upon t h e r m a l t r e a t m e n t t o 480°C. Table I· Comparison of Transferred Hydrogen and Radical Concentrations i n Dormant and Ordinary Mesophase P i t c h Radical Concentration (/g)

Transferred Hydr ogen (mg/g) O r d i n a r y Mesophase P i t c h

(A240)

A f t e r 400°C f o r 2 hr A f t e r 480°C f o r 20 min Dormant Mesophase P i t c h

3.88 χ 1 0 " 2.30 χ 1 0 "

2 2

97.4 22.7

χ 1θ} χ 10

2.9 21.9

χ 1018 χ 10

8

1 8

(DA240)

A f t e r 400°C f o r 2 hr A f t e r 480°C f o r 30 min

42.6 χ 1 0 " 2.52 χ 10-2 2

1 8

Three p o i n t s are noteworthy f o r the K y u k o s h i method. (i) Rapid h e a t i n g of the hydrogenated p i t c h t o above 450°C produces a p i t c h s u i t a b l e f o r smooth s p i n n i n g . ( i i ) T h i s p i t c h appears t o be i s o t r o p i c a t the s p i n n i n g temperature of 370°C. ( i i i ) The v i s c o s i t y - t e m p e r a t u r e r e l a t i o n s h i p , p l o t t e d i n F i g u r e 8 i n terms of the Andrade e q u a t i o n A η = Ae

B

/

T

shows a change i n s l o p e a t a t r a n s i t i o n temperature T , w h i c h i s dependent on the p i t c h . F i b e r spun near T e x h i b i t s r a d i a l s t r u c t u r e , but w i t h o u t an open wedge. F i b e r spun a t lower temperatures develops the open-wedge r a d i a l s t r u c t u r e , w h i l e f i b e r spun a t h i g h e r temperature d i s p l a y s e i t h e r random or o n i o n - s k i n s t r u c t u r e s , as s k e t c h e d s c h e m a t i c a l l y i n F i g u r e 8. I n r e s p e c t t o p r o c e s s e s of o x i d a t i o n s t a b i l i z a t i o n and c a r b o n i z a t i o n of the spun mesophase f i b e r s , we are aware of no g

s


332



f u r t h e r developments except f o r the r a p i d c a r b o n i z a t i o n t e c h n i q u e p r e v i o u s l y noted ( 2 9 ) . The m e c h a n i c a l p r o p e r t i e s as a f u n c t i o n of heat treatment temperature are shown i n F i g u r e 9 f o r f i b e r s prepared by the K y u k o s h i method. F i b e r h e a t - t r e a t e d t o 2000°C or h i g h e r have s t r e n g t h s above 3GPa (435 k p s i ) and t e n s i l e m o d u l i of the order of 500 GPa (72 M p s i ) . The p r e s e n t a u t h o r s now b e l i e v e t h a t , i n the near f u t u r e , i t w i l l be p o s s i b l e t o produce carbon f i b e r of e q u i v a l e n t p r o p e r t i e s by s e l e c t i o n of s u i t a b l e raw p i t c h m a t e r i a l s and by development of s p e c i a l i z e d p r e t r e a t m e n t procedures for the p i t c h t o r e p l a c e the e x t e n s i v e hydrogénation t e c h n i q u e d e s c r i b e d here.

The F u t u r e of P i t c h - B a s e d Carbon F i b e r

I n comparison w i t h the USA, the aerospace and defense i n d u s t r i e s of Japan are q u i t e s m a l l . T h i s i s the p r i n c i p a l r e a s o n f o r the r e l a t i v e l y slow c o m m e r c i a l i z a t i o n of p i t c h - b a s e d h i g h - p e r f o r m a n c e carbon f i b e r (HPCF) i n J a p a n . As i n c e n t i v e f o r the HPCF i n d u s t r y , o t h e r f i e l d s of a p p l i c a t i o n s must be sought. I n g e n e r a l , the automotive i n d u s t r y i s thought t o be the most p r o m i s i n g f i e l d , but s e v e r a l w e l l - k n o w n c o n d i t i o n s must be s a t i s f i e d . The c o s t of f i b e r must be d e c r e a s e d , mass p r o d u c t i o n p r o c e s s i n g of f i b e r must be e s t a b l i s h e d , and improved m o l d i n g t e c h n i q u e s f o r the composites s h o u l d be d e v e l o p e d . F u r t h e r m o r e , new types of applications s h o u l d be c o n s i d e r e d ; f o r example, a GPCF c l o t h r e i n f o r c e m e n t f o r p h e n o l i c r e s i n has been used f o r s e v e r a l y e a r s as a wear r i n g i n the s u s p e n s i o n of a dump t r u c k . Such a p p l i c a t i o n s suggest t h a t carbon f i b e r can be extended beyond p r i m a r y s t r u c t u r e s t o s u c h a r e a s as f i l l e r f o r e n g i n e e r i n g p l a s t i c s , e l e c t r o m a g n e t i c s h i e l d s , and so o n . I n the case of g e n e r a l performance carbon f i b e r (GPCF), carbon-fiber-reinforced concrete i s a very promising a p p l i c a tion. As shown i n F i g u r e 10, Akihama e t a l . (33) a c c o m p l i s h e d r e m a r k a b l e improvements i n the m e c h a n i c a l p r o p e r t i e s of c o n c r e t e by a d d i n g chopped GPCF. By s k i l l f u l u n i d i r e c t i o n a l a l i g n m e n t of GPCF i n the cement m o r t a r , Furukawa e t a l . (34) o b t a i n e d i n c r e a s e s i n m e c h a n i c a l s t r e n g t h by f a c t o r s of 2 t o 3 f o r f i b e r a d d i t i o n s of one p e r c e n t or l e s s . As n o t e d e a r l i e r , new a p p l i c a t i o n s of f i b e r s i n the c o n s t r u c t i o n i n d u s t r y a r e i n c r e a s i n g . These s h o u l d b r i n g about mass consumption of the g e n e r a l performance f i b e r , but lower c o s t s f o r a l l types of f i b e r must be a c h i e v e d . In t h i s r e s p e c t , the p i t c h - b a s e d f i b e r i s i n a more f a v o r a b l e s i t u a t i o n than P A N based f i b e r . Through e s t a b l i s h m e n t of mass p r o d u c t i o n f a c i l i t i e s , GPCF s h o u l d p l a y a r o l e as n a t u r a l l e a d e r t o HPCF, w i t h f a v o r a b l e e f f e c t s i n c o s t r e d u c t i o n s of not o n l y GPCF but a l s o HPCF.



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F i g u r e 8. V i s c o s i t y of mesophase p i t c h e s prepared by t h e K y u k o s h i method, w i t h schematic m i c r o s t r u c t u r e s of f i b e r s spun a t temperatures i n the range of 300 t o 400°C.

600 500 400 |300 200 100 1000

2000 HTT (t)

0 3000

J

0

F i g u r e 9. M e c h a n i c a l p r o p e r t i e s , as a f u n c t i o n of heat t r e a t ment t e m p e r a t u r e , of carbon f i b e r s spun from mesophase p i t c h prepared by the K y u k o s h i method.

F i g u r e 10. F l e x u r a l performance of carbon-fiber-reinforced c o n c r e t e . V i s the volume f r a c t i o n of carbon f i b e r . ç


334


Literature Cited 1. 2. 3. 4. 5. 6.


7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34.

Ō t a n i , S. Mol. Cryst. L i q . Cryst. 1981, 63, 249. Ōtani, S. Japanese Patent 1966-15728. Ōtani, S. Carbon 1965, 3, 31. Ōtani, S. Carbon 1965, 3, 213. Ōtani, S.; Yamada, K. J. Chem. Soc. Japan, Ind. Section 1966, 69, 626. Ōtani, S.; Yamada, K.; Koitabashi, T.; Yokoyama, A. Carbon 1966, 4, 425. Ōtani, S. Carbon 1967, 5, 219. Ōtani, S.; Yokoyama, A. Bull. Chem. Soc. Japan 1969, 42, 1417. Ōtani, S. Japanese Patent 1969-2511. Ōtani, S.; Watanabe, S.; Ogino, H. Bull. Chem. Soc. Japan 1972, 45, 3715. Ō t a n i , S. Japanese Patent 1979-8634. Fujimaki, H.; Kodama, F . ; Sakaguchi, T.; Okuda, K. Tansο 1975, No. 80, 3. Singer, L. S. Carbon 1978, 16, 408. Lewis, I. C.; McHenry, E. R.; Singer, L. S. U.S. Patent 3 976 729, 1976. Ōtani, S.; Ōya, A. J. Chem. Soc. Japan, Ind. Section 1970, 73, 493. Mochida, I.; Nakamura, E . ; Maeda, K.; Takeshita, K. Carbon 1975, 13, 489. Mochida, I.; Nakamura, E . ; Maeda, K.; Takeshita, K. Carbon 1976, 14, 123. Mochida, I.; Tamura, K.; Korai, Y.; Fujitsu, H.; Takeshita, K. Carbon 1982, 20, 231. Mochida, I.; Maeda, K.; Takeshita, L. Carbon 1978, 16, 459. Ō t a , E . ; Ōtani, S. Ext. Abstr. 4th Int. Symp. on Molten Salts No. 755. 1983. Miyazawa, K.; Yokono, T . ; Sanada, Y. Carbon 1979, 17, 223. Obara, T.; Yokono, T; Miyazawa, K.; Sanada, Y. Carbon 1981, 19, 263. Park, D. Y.; Ōya, Α . , Ō t a n i , S. Fuel 1983, 62, 1499. Tatsuhana, M.; Hirata, J.; Matsui, J. J. Chem. Phys. 1984, 81, 711. Ōtani, S.; Endo, T . ;Ō t a ,E.;Ōya,A. Tanso 1976, No. 87. Yoshimura, S.; et a l . Japanese Patent 1978-7533. Watanabe, S. Japan Patent 1983-156020. Watanabe, S. Japan Patent 1983-154701. Watanabe, S. Japan Patent 1983-156022. Ōtani, S.; Kikuchi, A. Japan Soc. for Promotion of Science, 117-163-A-2. Ō t a n i , S. Japan Patent 1982-100186. Imamura, T.; Shibata, M.; Yamada, Y.; Arita, S.; Honda, H. Proc. 10th Mtg. Carbon Soc. Japan, A-8 ~ A-11, 1-3 Dec. 1983, Tokyo. Akihama, S.; Suenaga, T.; Sakano, T. Concrete Journal 1982, 20, 75. Furukawa, S.; Ō t a n i , S.; Kojima, A. Proc. 10th Mtg. Carbon Soc. Japan, D-9, 1-3 Dec. 1983, Tokyo.

RECEIVED November 19, 1985


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