Fiber Diffraction Methods - ACS Publications - American Chemical

17 Electron Diffraction and Dark Field on Ultrathin Sections of Textile Fibers R. H A G E G E

Downloaded by TUFTS UNIV on February 22, 2018 | https://pubs.acs.org Publication Date: November 17, 1980 | doi: 10.1021/bk-1980-0141.ch017

Institut Textile de France, 35 Rue des Abondances, 92100 Boulogne S/Seine, France

X-Ray d i f f r a c t i o n studies of t e x t i l e f i b e r s have led to the development of techniques to c a l c u l a t e or estimate the following f i b e r c h a r a c t e r i s t i c s : • percents crystallinity (% c r y s t a l l i n e fraction) • c r y s t a l l i n e perfection (as characterized by various indexes) • mean dimensions of c r y s t a l l i t e s • long-period as estimated by small angle X-Ray scattering, e t c . . . However, electron d i f f r a c t i o n , although frequently used for polymer single c r y s t a l s studies, has s e l dom been applied to t e x t i l e f i b e r s , and p a r t i c u l a r l y to u l t r a t h i n sections of those m a t e r i e l s . (1,2) the majority of published papers dealing with electron d i f f r a c t i o n of f i b e r s i s concerned with i s o l a t e d fibrils or fragments prepared by mechanical m i l l i n g . As far as we know, apart from a preliminary report about mercerization of cotton f i b e r s (3) and a recent paper about chemically etched PETP filaments (4), high modulus aramide fibers and carbon f i b e r s are p r a c t i c a l l y the only systems with d e t a i l e d (recently) published work on electron d i f f r a c t i o n and dark field of u l t r a - t h i n sections of t e x t i l e or p a r a t e x t i l e f i b e r s (5, 6, 7). Here we report s i m i l a r studies on 2GT polyester and 66 polyamide f i b e r s and define l o c a l order indexes.

0-8412-0589-2/80/47-141-279$05.75/0 © 1980 American Chemical Society French and Gardner; Fiber Diffraction Methods ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

280

FIBER

Material

and

DIFFRACTION

METHODS

methods

Various kinds of m u l t i f i l a m e n t coutinuous yarns o f 2GT p o l y e s t e r ( r e f e r r e d t o as PETP i n the p r e s e n t paper) were i n v e s t i g a t e d : . 1 FT t e x t u r e d c o n t i n u o u s y a r n (PETP^) . 1 m u l t i f i l a m e n t from a g e o t e x t i l e spun bond membrane made o f BIDIM ( R h o n e - P o u l e n c - T e x t i l e (RPT) - marque deposee) (PETP ) . 1 thermoset m u l t i f i l a m e n t f o r t i r e - c o r d a p p l i c a t i o n (PETP ) 2


3

V a r i o u s 66 p o l y a m i d e c o n t i n u o u s y a r n s were a l s o examined ( r e f e r r e d t o as, "type 2", "type 4" and "type 5") : t h e s e are e x p e r i m e n t a l y a r n s p r e p a r e d i n d i f f e r e n t c o n d i t i o n s and s u p p l i e d by RPT. Only transverse s e c t i o n s ( i . e . s e c t i o n s c u t as p r e c i s e l y as p o s s i b l e , normal t o the f i b e r a x i s ) were examined. The p r o d u c t i o n o f e l e c t r o n m i c r o d i f f r a c t i o n p a t t e r n s and d a r k f i e l d m i c r o g r a p h s has t o be done on very t h i n s e c t i o n s ( i f p o s s i b l e s e c t i o n s thinner than those used f o r o r d i n a r y b r i g h t f i e l d work). T h i s i s v e r y d i f f i c u l t t o do w i t h t h i s k i n d o f m a t e r i a l . S t a i ning with A g f o l l o w i n g the u s u a l method i n our l a b o r a t o r y (8) o f t e n , i f n o t always, i s u s e f u l i n improv i n g the q u a l i t y o f the s e c t i o n s , w i t h o u t d i s t u r b i n g e i t h e r the p r o d u c t i o n o f a d i f f r a c t i o n p a t t e r n c h a r a c t e r i s t i c o f the polymer s p e c i e s , or the p h o t o g r a p h i n d a r k - f i e l d c o n d i t i o n s . Ag2S s t a i n i n g p r o c e d u r e : the f i b e r s are t r e a t e d under 15 Atm a t 2 0 ° C by gazeous H S. A f t e r m i l d r i n s i n g w i t h a l c o h o l or acetone, they are immersed f o r 16 h o u r s a t 2 0 ° C i n t o an aqueous 0,1 M s o l u t i o n o f s i l v e r n i t r a t e . Sorbed H S i s t h u s t r a n s f o r m e d i n t o A g S and " i n s i t u " p r e c i p i t a t e d i n t o the a c c e s s i b l e r e g i o n s . The f i b e r s are t h e n r i n s e d by water and d r i e d b e f o r e embedding and c u t t i n g . #

s

2

2

2

2

E l e c t r o n D i f f r a c t i o n Micrographs P r o d u c t i o n o f the n e g a t i v e p r i n t s . In o r d e r t o a l l o w a q u a n t i t a t i v e t r e a t m e n t o f the m i c r o g r a p h s , the w i d t h o f the e l e c t r o n beam was c a r e f u l l y c o n t r o l l e d . The " i r r a d i a t e d a r e a " i s the a r e a o f the s e c t i o n i l l u m i n a t e d by the e l e c t r o n beam, whereas the

French and Gardner; Fiber Diffraction Methods ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


17.

HAGEGE

Ultrathin Textile Fibers

281

" s e l e c t e d a r e a " i s i s o l a t e d from t h e i r r a d i a t e d a r e a by means o f a s e l e c t i o n a p e r t u r e which has a diameter o f 0.5 o r 1 pm, i . e . , 1/10 t o 1/5 o f t h e l a t t e r . The s e c t i o n i s searched under v e r y m i l d c o n d i t i o n s o f i r r a d i a t i o n so t h a t t h e a r e a o f i n t e r e s t does n o t d e t e r i o r a t e , the filament being g e n e r a l l y undersaturated and a l l o t h e r s e t t i n g s t o t h e minimum. In the p r e s e n t work, we have t r i e d t o examine t h e v a l i d i t y o f t h e f o l l o w i n g method f o r q u a n t i t a t i v e p u r poses : f i r s t we p h o t o g r a p h t h e " i n t a c t " d i f f r a c t i o n p a t t e r n under d e f i n e d c o n d i t i o n s , then we photograph the amorphous p a t t e r n under -bhe same c o n d i t i o n s . The amorphous p a t t e r n i s o b t a i n e d b y i n c r e a s i n g t h e r a d i a t i o n rate u n t i l the c r y s t a l l i n e d i f f r a c t i o n d i s a p p e a r s . I n o r d e r t o r e c o r d t h e " c r y s t a l l i n e " and "amorphous" p a t t e r n s o f t h e same s e l e c t e d a r e a on t h e same photographic emulsion ( t o minimize the i n f l u e n c e o f photographic processing c o n d i t i o n s ) , the f o l l o w i n g p r o c e d u r e was adopted : a) v i s u a l l y i d e n t i f y t h e " c r y s t a l l i n e " p a t t e r n i n m i l d i r r a d i a t i o n c o n d i t i o n s (those c o n d i t i o n s a r e i n a dequate f o r t h e photography) b) i n t r o d u c e an o b j e c t i v e a p e r t u r e o f 75 ym: t h i s i s o f s u f f i c i e n t s i z e so n o t t o h i d e t h e main d i f f r a c t i o n a r c s . T h i s aperture prevents the i r r a d i a t i o n o f the p h o t o g r a p h i c e m u l s i o n f a r away from t h e c e n t e r o f t h e " i n t a c t " p a t t e r n , which a l l o w s f o r o t h e r p r i n t s t o be taken on t h e same p l a t e o r f i l m c) c e n t e r t h e " d i f f r a c t i o n spot" ( i . e . t h e impact o f the u n s c a t t e r e d beam) i n a c o n v e n i e n t p o s i t i o n ( e . g. near one c o r n e r o f t h e p h o t o g r a p h i c p l a t e ) and r e c o r d t h e d i f f r a c t i o n p a t t e r n w i t h c a r e f u l l y def i n e d c o n d i t i o n s o f i r r a d i a t i o n and exposure time d) " d e s t r o y " t h e c r y s t a l l i n e o r d e r o f t h e s e l e c t e d a r e a and i t s s u r r o u n d i n g s ( c o n t r o l l i n g i t v i s u a l l y ) b y a s t r o n g i n c r e a s e o f t h e r a d i a t i o n r a t e d u r i n g adequate time e) r e c o r d t h e " d e s t r o y e d " p a t t e r n i n t h e same c o n d i t i o n s as i n c) w i t h t h e c e n t e r o f t h e d i f f r a c t i o n spot i n a d i f f e r e n t p a r t o f t h e p h o t o g r a p h i c p l a t e


282

f)


g)

FIBER

DIFFRACTION

METHODS

r e p e a t d) a n d e) t o g e t a s e c o n d e x p o s u r e o f t h e " d e s t r o y e d " p a t t e r n . T h i s i s t o check the d i s a p p e a rance o f the c r y s t a l l i n i t y r e t u r n t o "image" c o n d i t i o n s and e x p o s e t h e irrad i a t e d z o n e a n d i t s s u r r o u n d i n g s ; t h e beam s h o u l d b e f o c u s e d ( l e s s t h a n i t was f o r t h e r e c o r d i n g o f d i f f r a c t i o n p a t t e r n ) and d e f l e c t e d and t h e p r e p a r a t i o n s h i f t e d so t h a t t h i s e x p o s u r e i s n o t s u p e r i m p o sed on the p r e c e e d i n g o n e s .

T h r e e d i f f r a c t i o n p a t t e r n s and one m i c r o g r a p h a r e t h u s r e c o r d e d o n t h e same p l a t e o r f i l m . I n some c a s e s , we t r i e d t o e v a l u a t e t h e d e g r a d a t i o n o f t h e c r y s t a l l i ne p a t t e r n s d u r i n g one e x p o s u r e ; t h i s i s a n a l o g o u s to an i d e a o f a p r e v i o u s w o r k o f Dobb (9) who h a s s t u d i e d the k i n e t i c s o f the disappearance o f the main i n t e r f e rences i n the e l e c t r o n d i f f r a c t i o n p a t t e r n of c e l l u l o se u n d e r c o n s t a n t i r r a d i a t i o n r a t e b y a m e t h o d o f " t i m e - l a p s e s e r i e s " . O u r a i m was t o t r y t o d e t e r m i n e a " t r u e " c r y s t a l l i n i t y b y an e x t r a p o l a t i o n t o z e r o d o s e . I n s u c h a mode, the " c r y s t a l l i n e " p a t t e r n o f t h e same s e l e c t e d a r e a i s r e c o r d e d t h r e e t i m e s ( o n t h e s a me e m u l s i o n ) t h e i r r a d i a t i o n r a t e c o r r e s p o n d i n g t o an exposure b e i n g set o n l y d u r i n g the exposure time. On t h e same p l a t e o r f i l m , 4 d i f f r a c t i o n p a t t e r n ( t h r e e "crystalline" patterns with a beginning of degradation and a n " a m o r p h o u s " o n e o b t a i n e d a s a l r e a d y e x p l a i n e d ) and o n e m o r p h o l o g i c a l v i e w a r e o b t a i n e d . F i g u r e 1 shows a n e x a m p l e o f a s l i d e w i t h 5 e x p o s u r e s o f a P A 66 f i l a m e n t (4 d i f f r a c t i o n p a t t e r n s a n d 1 m o r p h o l o g i c view) o b t a i n e d f r o m a p a r t i c u l a r zone o f the c r o s s - s e c t i o n o f an A g S - s t a i n e d f i b e r ; the 3 " c r y s t a l l i n e " p a t t e r n s show a n i n c r e a s i n g d e g r a d a t i o n ( i n t h e follow i n g way 1 , 2 , 3) a n d " A " i s t h e a m o r p h o u s p a t t e r n . 2

T h i s p r o c e s s ( u s i n g one o f t h e m o d e s p r e v i o u s l y d e s c r i b e d ) was a p p l i e d t o a s e t o f 3 t o 12 d i f f e r e n t s e l e c t e d a r e a s on t h e t r a n s v e r s e s e c t i o n o f one f i b e r . The p h o t o g r a p h i c s e r i e s i s a c o m p l e t e d r e c o r d o f t h e w h o l e f i b e r c r o s s - s e c t i o n a t an a d e q u a t e m a g n i f i c a t i o n . On t h e l a t t e r m i c r o g r a p h t h e i r r a d i a t e d a r e a s c a n b e seen because o f t h e i r l e s s e r e l e c t r o n d e n s i t y i n b r i g h t f i e l d c o n d i t i o n s . I n some c a s e s , t h e s e i r r a d i a t e d a r e a s c o u l d a l s o be seen u n d e r d a r k f i e l d c o n d i t i o n s .



HAGEGE


Figure 1.

283

A slide with 5 exposures on the same emulsion.

In the lower left corner, zone (arrowed) of the cross section of an Ag S stained PA 66 fiber, which is responsible for crystalline pattern 1. Numbers 1, 2, and 3 are three successive exposures of the same pattern with an equal radiation rate—notice progressive fading of the outer, less intense (010) arc A: amorphous pattern (photographed in the same conditions) corresponding to the same area. s



284

FIBER DIFFRACTION

METHODS

Q u a n t i t a t i v e P r o c e s s i n g . P l a t e s or f i l m w i t h the d i f f r a c t i o n p a t t e r n s were scanned w i t h a J o y c e - L o e b l m i c r o d e n s i t o m e t e r . R a d i a l (20) d e n s i t o m e t r i c p l o t s o f the c r y s t a l l i n e p a t t e r n ( e v e n t u a l l y t h r e e s u c c e s s i v e e x p o s u r e s o f the c r y s t a l l i n e p a t t e r n are analyzed) and of the c o r r e s p o n d i n g amorphous p a t t e r n were r e c o r d e d on the same c u r v e . In t h i s way, the p l o t o f the amorphous p a t t e r n was used as a r e f e r e n c e s t a n d a r d . The d e n s i t o m e t r i c r e c o r d i n g began w i t h the o p t i c a l d e n s i t y of the n o n - i r r a d i a t e d e m u l s i o n ; t h i s a l l o w e d the e v a l u a t i o n and n o r m a l i z a t i o n o f the o p t i c a l d e n s i t y o f the d i f f r a c t i o n p a t t e r n . When the a n a l y t i c a l s l i t p a s s e d t h r o u g h the image o f the b o r d e r o f the 75 ym o b j e c t i v e a p e r t u r e , the d e n s i t o m e t r i c c u r v e showed a sudden d e n s i t y r a i s e " A d . ( F i g . 6) The p l o t s o f the amorphous and c r y s t a l l i n e p a t t e r n s were thus n o r m a l i z e d t o the same r e f e r e n c e " A d" . C r y s t a l l i n i t y was determined on the n o r m a l i z e d c u r v e s by measuring the areas "C + A" and "A" under the c r y s t a l l i n e and amorphous p l o t s r e s p e c t i v e l y . In some c a s e s , an " a z i m u t a l c o r r e c t i o n " was app l i e d by the f o l l o w i n g method : an a z i m u t a l p l o t o f the d i f f r a c t e d i n t e n s i t y was o b t a i n e d u s i n g a p o l a r c o o r d i n a t e s t a b l e . The c o r r e c t i v e f a c t o r f o r "C/A" was e/e where i s the a r e a under the a z i m u t a l p l o t and e i s the a r e a o f the r e c t a n g l e h a v i n g the same base and w i t h the h e i g h t e q u a l t o the maximum d e n s i t y o f the a z i m u t a l p l o t . C o r r e c t e d o r u n c o r r e c t e d C v a l u e s were t r a n s f o r m e d t o C% v a l u e s by means o f the A C formula : % A 1 + C A M

Q

Q

1

c

0

0

=

which h o l d s f o r C% v a l u e s near b u t n o t e q u a l t o 100 because we have no f u l l y c r y s t a l l i n e s t a n d a r d .

%

Dark F i e l d M i c r o g r a p h s . Dark f i e l d m i c r o g r a p h s were o b t a i n e d by i s o l a t i n g a main d i f f r a c t i o n a r c on the m i c r o d i f f r a c t i o n p a t t e r n and, by t i l t i n g the e l e c t r o n beam a t a c o r r e c t a n g l e , r e c o r d i n g the image w i t h the d i f f r a c t e d beam o n l y . F o r the p o l y e s t e r , we have n o t been a b l e as y e t t o o b t a i n such m i c r o g r a p h s o f acceptable q u a l i t y .


17.

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F o r 66 p o l y a m i d e , we have o b t a i n e d a c c e p t a b l e r e s u l t s by s e l e c t i n g the s t r o n g e r r e f l e c t i o n , t h a t i s i n gener a l the n e a r e s t one t o t h e c e n t e r o f the p a t t e r n ( i n the t r a n s v e r s e s e c t i o n ) .


Results 2GT p o l y e s t e r . F i g u r e 2 i s a montage showing t h e c r o s s - s e c t i o n o f a t e x t u r e d p o l y g o n a l - s h a p e d PETP s t r a n d s t a i n e d w i t h Ag 2 s ; the m e t a l i s e s s e n t i a l l y p e r i p h e r i c w i t h some r a d i a l i n c l u s i o n s . The d i f f r a c t i o n p a t t e r n s o f 5 d i f f e r e n t s e l e c t e d areas a r e a l s o p r e s e n t . I r r a d i a t e d areas and s e l e c t e d areas c a n be r e s o l v e d b y t h e i r h i g h e r t r a n s m i s s i o n . There i s c o n s i d e r a b l e v a r i a t i o n i n the azimutal width o f the 3 main d i f f r a c t i o n a r c s w h i l e t h e o r i e n t a t i o n o f t h e e q u a t o r i s o n l y s l i g h t l y v a r i a b l e . On t h i s montage (as w e l l as on t h e f o l l o w i n g o n e s ) , t h e d i f f r a c t i o n p a t t e r n s have been p o s i t i o n e d i n t h e i r t r u e s p a t i a l p o s i t i o n , a f t e r c o r r e c t i o n o f t h e image r o t a t i o n depending on m a g n i f i c a t i o n and on camera l e n g t h . F i g u r e 3 i s another example on A g S s t a i n e d PETP w i t h 3 s e l e c t e d a r e a s , t h e d i f f r a c t i o n p a t t e r n s o f w h i c h have q u a s i - p a r a l l e l e q u a t o r s . F i g u r e 4 c o r r e s p o n d s t o PETP^ ( A g S s t a i n e d ) w i t h 12 d i f f e r e n t s e l e c t e d a r e a s and c o r r e s p o n d i n g d i f f r a c t i o n p a t t e r n s . One c a n see t h a t : 5 p a t t e r n s have t h e same o r i e n t a t i o n , 3 a r e p r a c t i c a l l y a t r i g h t a n g l e s from t h e l a t t e r , 2 have an i n t e r m e d i a t e o r i e n t a t i o n and t h e l a s t 2 are h i g h l y d i s o r i e n t e d , w i t h one Debye S c h e r r e r type p a t t e r n . F i g u r e 5 i s an example o f a d e n s i t o m e t r i c p l o t f o r PETP,. The s h o u l d e r c o r r e s p o n d i n g t o t h e "amorphous h a l o " o f t h e d e s t r o y e d p a t t e r n i s c l e a r l y v i s i ble. The n o r m a l i z a t i o n p r o c e d u r e i s i l l u s t r a t e d : i n t h a t s p e c i f i c c a s e , t h e amorphous p a t t e r n i s u n d e r exposed i n comparison w i t h t h e c r y s t a l l i n e p a t t e r n . Point A corresponds t o the o p t i c a l d e n s i t y d of the background o f t h e s l i d e ( t h a t i s o u t s i d e t h e image o f the b o r d e r o f t h e o b j e c t i v e a p e r t u r e ) ; p o i n t B corresponds t o the " i n i t i a l " d e n s i t y d o f the c r y s t a l l i n e p a t t e r n and B t o t h e " i n i t i a l " d e n s i t y o f t h e amorphous p a t t e r n ; i f t h e c r y s t a l l i n e p l o t i s t a k e n as t h e r e f e r e n c e , t h e amorphous p l o t d e n s i t y has t o be m u l t i p l i e d by t h e n o r m a l i z a t i o n f a c t o r e i . e . 2

2

Q

Q

1


O


286

FIBER

Figure 2.

DIFFRACTION

METHODS

Cross section of a textured polygonal-shaped PETP strain stained with Ag S. t

The photograph (positive print) of the cross section of the fiber has been cut around with scissors, leaving a small amount of embedding araldite around the fiber-end stuck on a "bristoV paper The diffraction patterns were stuck close to the corresponding areas (to which they are related by arrows) and their orientations are corrected according to the image j diagram rotation introduced by the microscope.

Figure 3.

Ag S-stained PETP with three selected areas, the diffraction patterns of which have quasi-parallel equators fsee also Figure 2) t



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Figure 4.


287

Ag S-stained PETP with 12 different selected areas and corresponding diffraction patterns (see also Figure 2) t

S

Figure 5.

Densitometric plot for PETP

t


288

d

FIBER

o

- d

DIFFRACTION

METHODS

oo

- d oo Table I.

Electron diffraction crystallinity


PETP

1

PETP, 2

X-Ray c r y s t a l l i n i t y (RULAND's Method)

28,8

%

27,0

%

33,4

%

32,0

%

66 Polyamide^ F i g u r e s 6 and 7 are montages o f 66 p o l y a m i d e . The d i f f r a c t i o n p a t t e r n s are much c l o s e r t o "powder" type t h a n were the PETP p a t t e r n s . In f i g u r e 8 the a l t o g e t h e r v i e w i s i n dark f i e l d conditions and the 5 d e s t r o y e d zones appear v e r y clearly. F i g u r e s 8 and 9 are d e n s i t o m e t r i c p l o t s o f v a r i o u s k i n d s o f p a t t e r n s . In f i g u r e 8, the p r o c e d u r e f o r the n o r m a l i z a t i o n o f the amorphous p l o t i s f u r t h e r e x p l a i n e d . In t h i s c a s e one has t o m u l t i p l y each i n d i v i d u a l d e n s i t y by the f a c t o r #

oo

. T h i s g i v e s the c o r r e c t e d curve (dashed l i n e ) and l e a d s t o t h e e v a l u a t i o n o f the - d o oo " C " and "A" v a l u e s . In f i g u r e 9, c r y s t a l l i n e p l o t s o f the same a r e a (two s u c c e s s i v e photographs) are shown. The f a d i n g o f the weaker l i n e i s v i s i b l e , b u t n e v e r t h e l e s s , t h e r e i s o n l y a minor v a r i a t i o n o f the a r e a under the whole c r y s t a l l i n e curve. F i g u r e 10 shows an example o f an a z i m u t a l scan, t o g e t h e r w i t h the e x p l a n a t i o n o f the " a z i m u t a l c o r r e c t i o n " . The s t r i p e d a r e a i s d i v i d e d by the a r e a o f the r e c t a n g l e b u i l t on the dashed l i n e s .


289



HAGEGE

Figure 6. Montage of 66 polyamide (see also Figure 2)

Figure 7.

Montage of 66 polyamide (see also Figure 2)



290

FIBER DIFFRACTION

METHODS

Figure 8. Densitometric plot of various kinds of patterns. The fiber is photographed in darkfieldconditions as opposed to other montages. (See also Figure 2.)



HAGEGE


Figure 9.

Densitometric plot of various kinds of patterns

PA 66 T y p e

4

Cross section - Azimutal scan

Figure 10.

Example of an azimuthal scan



292

FIBER

DIFFRACTION

METHODS

T a b l e I I g i v e s the c r y s t a l l i n i t y v a l u e s f o r v a r i o u s k i n d s o f p o l y a m i d e y a r n s . I n one c a s e , the o c c u r e n c e o f a r e l a t i v e l y amorphous s k i n can be d e t e c t e d . There i s a l s o an example o f t h e e f f e c t o f an a z i m u t a l c o r r e c t i o n . A b s o l u t e c r y s t a l l i n i t y v a l u e s do n o t agree w e l l w i t h X - r a y based c r y s t a l l i n i t y v a l u e s . N e v e r t h e l e s s , t h e r e i s a g e n e r a l q u a l i t a t i v e agreement i n the d i f f e r e n c e between polyamide and p o l y e s t e r y a r n s ( i t i s w e l l known t h a t c r y s t a l l i n i t y i s g e n e r a l l y h i g h e r f o r polyamide than f o r p o l y e s t e r commercial f i l a m e n t s ) . I n t a b l e I I I , the " c r y s t a l l i n i t y " v a r i a t i o n s e s t i m a t e d a f t e r m u l t i p l e i r r a d i a t i o n s are shown. In s p i t e o f t h e d e g r a d a t i o n which i s c l e a r l y n o t i c e a b l e ( g r a d u a l f a d i n g o f the weaker i n t e r f e r e n c e ) the e s t i mated c r y s t a l l i n i t y o f t e n shows v e r y l i m i t e d d e c r e a s e (the s t a n d a r d d e v i a t i o n s are a p p r o x i m a t e l y 8 % ) . F i g u r e s 11 t o 13 are d a r k f i e l d m i c r o g r a p h s o f 66 polyamide m o n o f i l a m e n t s . F i g u r e 11 show an A g S s t a i n e d f i l a m e n t . S i l v e r s u l f i d e p r e c i p i t a t e s , which appear as b l a c k areas (as t h e y d i d i n b r i g h t f i e l d images) as w e l l as polyamide c r y s t a l l i t e s ( b r i g h t spots) are v i s i b l e . F i g u r e 12 c o r r e s p o n d s t o a t y p e 4 f i b e r ( w i t h s k i n - c o r e morphology) where t h e r e i s a lower d e n s i t y o f c r y s t a l l i t e s i n the s k i n r e g i o n . F i g u r e 13 c o r r e s p o n d s t o the c a s e o f type 5 f i b e r which has s m a l l e r c r y s t a l l i t e s . 2

Discussion L o c a l O r i e n t a t i o n . The most s t r i k i n g o b s e r v a t i o n o f t h i s work i s t h a t the s e l e c t e d a r e a d i f f r a c t i o n p a t t e r n s are not i n g e n e r a l o f a Debye-Scherrer t y p e . Among t h e v a r i o u s h y p o t h e s e s which can be drawn t o u n d e r s t a n d such a f a c t , the most p r o b a b l e one i s t h a t the s e c t i o n s are n o t t r u l y t r a n s v e r s e ones ; i n d e e d , i f one supposes the e x i s t e n c e o f a c y l i n d r i c a l symmet r y a t the l e v e l o f each s e l e c t e d a r e a , 0.5 t o 1 ym i n d i a m e t e r (the symmetry a x i s b e i n g always p a r a l l e l t o the f i b e r a x i s ) the " d e t e c t a b l e " network main p l a n e s have t o be p a r a l l e l t o the " c " a x i s o f the i n d i v i d u a l


17.

HAGEGE


Table II.

Type* 4

293

Crystallinity of PA 66-C%

Type 4 (+Ag S) 2

Type 5

Type 2 (+Ag S) 2

Core

Without Skin azimutal corr.


o n

With azimutal corr. o n

%

%

%

%

38,5

32,3

51,6

36,4

6,2

8,2

4,4

6

Table III.

%

°/o

44,1

57,6

Mean

9,7

7,8

Standard deviation

Type 2 Polyamide Degradation of the Diffraction Pattern

N° of the C r i s t a l l i n i t y % after selected the 1st i r s a d . the 3rd i r r a d . the 2nd i r r a d . area 68,9

66,3

56,2

55,3

53,3

63,4

61,5

62,7

65,0

63,8

65,4

63,5

61,3

58,8

55,5

46,7

45,4

45,1



294

FIBER

Figure 11.

DIFFRACTION

METHODS

Dark field micrograph of 66 polyamide microfilaments

Figure 12. Dark-field micrograph of the cross section of an Ag S-stained Type 2 (see text) PA 66 fiber. Notice black deposits of silver sulfide in the periphery and white dots in the whole section, corresponding to crystallites in Bragg position. 2



17.

HAGEGE


295

Figure 13. Dark-field micrograpn oj tne cross section of a Type 4 PA 66 fiber. No silver sulfide deposits; notice the skin-core effect and the dimensions of the crystallites (white dots).



296

FIBER

DIFFRACTION

METHODS

c r y s t a l l i t e s , and t h e i r angle w i t h the i n c i d e n t beam has t o be e q u a l t o the Bragg angle 0. F o r a rough e s t i m a t e , one can n e g l e c t t h i s Bragg angle ( t h i s i n f a c t i s v e r y s m a l l because o f the low v a l u e o f the wavelength a s s o c i a t e d t o the e l e c t r o n s ) and a l s o the mean o r i e n t a t i o n angle o f the c - a x i s o f the i n d i v i d u a l c r y s t a l l i t e s ( p e r f e c t o r i e n t a t i o n ) . In such a s i t u a t i o n the " v i s i b l e " network p l a n e s have a c o n s t a n t o r i e n t a t i o n i n space ; t h e y must be p a r a l l e l t o the i n c i d e n t beam and t o the f i b e r - a x i s . The e q u a t o r o f the r e s u l t i n g d i f f r a c t i o n p a t t e r n i s normal t o these p l a n e s , i . e . , normal t o t h e l o n g a x i s o f the t h e o r e t i c a l l y e l l i p t i c s e c t i o n . As a s u p p o r t t o t h i s h y p o t h e s i s , the e q u a t o r s o f v a r i o u s l o c a l d i f f r a c t i o n p a t t e r n s are most f r e q u e n t l y p a r a l l e l t o one a n o t h e r . T h i s i s n o t o n l y t r u e f o r the same c r o s s s e c t i o n b u t a l s o i n d i f f e r e n t f i b e r s which have been s e c t i o n e d as an embedded bundle o f p a r a l l e l f i b e r s . N e v e r t h e l e s s , we were n o t a b l e t o f i n d any r e l a t i o n s h i p b e t ween the o r i e n t a t i o n o f the l o n g a x i s o f the pseudo e l l i p t i c a l s e c t i o n and t h a t o f the e q u a t o r o f the d i f f r a c t i o n pattern. F i g u r e 14 i s a scheme o f the s e c t i o n (S) t h a t was c u t s l i g h t l y o b l i q u e t o the f i b e r a x i s ( A Q ) • the beam a x i s (I) impinges n o r m a l l y i n the c e n t e r o f the s e l e c t e d a r e a (S) ; a cone o f r e v o l u t i o n (C) has been drawn round the a x i s ( A ) , p a r a l l e l t o ( A Q ) and i s supposed t o be a l o c a l r e v o l u t i o n symmetry a x i s . The angle 0 o f t h i s cone c o r r e s p o n d s t o the mean o r i e n t a t i o n o f the c - a x i s o f t h e i n d i v i d u a l c r y s t a l l i t e s ; another r e v o l u t i o n cone ( e ) i s centered around (I) : i t s angle 0 i s one o f the main Bragg a n g l e s (0 i s g e n e r a l l y much s m a l l e r than 0}. "DetectabJe" network p l a n e s show two main f e a t u r e s : they are t a n g e n t t o ( e ) and t h e y c o n t a i n one g e n e r a t o r o f the cone ( C ) . A p l a n e normal t o (I) i n t e r c e p t s on (C) as an e l l i p s a (E) and on ( e ) a s a s m a l l c i r c l e Q

Q

( Y

o>-

In f i g u r e 15, examples o f these two g e o m e t r i e s are shown. T r a c e s o f the d e t e c t a b l e network p l a n e s must have an o r i e n t a t i o n comprised between the two i n t e r n a l common t a n g e n t s t o ( Y ) and (E) ? i t i s t h u s p o s s i b l e t o b u i l d g e o m e t r i c a l l y (as the f i g u r e shows)




HAGEGE

Figure 14. Similar to Figure 13, but with Type 5 PA 66 fiber (the cross sections have been thermally treated; notice very tiny, well-defined crystallites)



298

FIBER

DIFFRACTION

METHODS

Figure 15. (Lett) Case of PETP: constant local orientation and variable local rotation axis; (right) case of PA 66; variable local orientation and constant local rotation axis



17.

HAGEGE


299

the a z i m u t a l opening o f t h e i n t e r f e r e n c e c o r r e s p o n d i n g to t h e Bragg angle 0 . There a r e two d i f f e r e n t ways t o g e t l o c a l d i f f r a c t i o n p a t t e r n s "Debye-Scherrer" type (such p a t t e r n s a r e o b t a i n e d i f ( y ) i s found w i t h i n (E) . I n t h e f i r s t case ( f i g u r e 15? the o r i e n t a t i o n o f the l o c a l symmetry a x i s ( A ) i s v e r y c l o s e t o t h a t o f (I) w i t h the c o n s e quence triat the whole cone ( e ) i s l o c a t e d w i t h i n t h e cone (C) even i f the l o c a l o r i e n t a t i o n i s r e l a t i v e l y good, i . e . , angle 0 i s s m a l l . I n the second case, the l o c a l o r i e n t a t i o n i s poorer, i . e . , 0 i s f a i r l y l a r g e . As a r e s u l t 0 and a) (angle between ( A ) and ( I ) ) have e q u i v a l e n t v a l u e s and a g a i n cone (C) surrounds cone ( e ) . The f i r s t case may c o r r e s p o n d t o PETP i n which t h e r e would be a n o t i c e a b l e d i s p e r s i o n o f t h e l o c a l symmetry a x i s around f i b e r a x i s . T h i s c o u l d e x p l a i n the r e l a t i v e l y f r e q u e n t v a r i a t i o n s i n t h e o r i e n t a t i o n of the d i f f r a c t i o n p a t t e r n i n t h e s p e c i f i c case o f PETP. The second case would c o r r e s p o n d t o 66 polyamide which h a s l o c a l v a r i a t i o n s o f o r i e n t a t i o n and l e s s o v e r a l l o r i e n t a t i o n t h a n i n PETP. The two c a s e s a r e p r e s e n t e d i n f i g u r e 15. Local C r y s t a l l i n i t y . The " a z i m u t a l c o r r e c t i o n " p r e v i o u s l y mentioned s h o u l d be a p p l i e d o n l y i n t h e second case d i s c u s s e d above, i . e . , when t h e v a r i a t i o n of the l o c a l o r i e n t a t i o n i s the main f a c t o r i n a f f e c t i n g t h e observed d i f f r a c t i o n p a t t e r n . I n t h i s s p e c i f i c c a s e , t h e d i f f r a c t e d i n t e n s i t y i s spread over t h e whole i n t e r f e r e n c e . As a r e s u l t , t h e c o r r e c t i o n s h o u l d be made f o r 66 polyamide and n o t f o r PETP. T h i s c o r r e c t i o n c o u l d have a l a r g e e f f e c t and would r e s u l t i n l o w e r i n g the c r y s t a l l i n i t y d i f f e r e n c e s between the two kinds o f f i b e r s . This azimutal c o r r e c t i o n gives a bett e r account o f the whole a z i m u t a l i n t e n s i t y than t h e n o r m a l i z a t i o n o f t h e h a l f - h e i g h t w i d t h v a l u e as p r o p o sed i n another paper ( 1 0 ) . Nevertheless, numerical values obtained i n the p r e s e n t work are p r e l i m i n a r y r e s u l t s and f u r t h e r exp e r i m e n t s are underway. A t the moment, we are unable t o say whether s e c t i o n t h i c k n e s s c a n i n f l u e n c e t h e c r y s t a l l i n i t y v a l u e s o b t a i n e d even t h r o u g h the use of "c" t e c h n i q u e . A


300

FIBER

DIFFRACTION

METHODS

( T h i s method p a r t i a l l y e l i m i n a t e s the i n f l u e n c e o f t h e t r a n s m i s s i o n o f the sample " y t " f a c t o r ) . Moreover, i t seems r e a s o n a b l e t h a t the s e c t i o n s l a c k p l a n a r i t y and have a t i l t i n g a r t i f a c t i n a t l e a s t p a r t o f the c r y s t a l l i t e s due t o the a c t i o n o f the k n i f e . These f a c t o r s might have a l a r g e i n f l u e n c e on the v a r i a t i o n s o f o r i e n t a t i o n and i n t e n s i t y o f the l o c a l d i f f r a c t i o n p a t t e r n s .


Conclusion We have p r e s e n t e d p r e l i m i n a r y r e s u l t s on s e l e c t e d area e l e c t r o n d i f f r a c t i o n of "pseudotransverse" u l t r a t h i n s e c t i o n s o f PETP and PA66 f i l a m e n t s . These r e s u l t s suggest t h a t the c l a s s i c a l h y p o t h e s i s o f r e g u l a r c y l i n d r i c a l symmetry i n c i r c u l a r - s h a p e d s y n t h e t i c f i l a m e n t s i s i n c o r r e c t . A l t h o u g h the b e s t way t o study l o c a l v a r i a t i o n s o f o r i e n t a t i o n i s t o work on l o n g i t u d i n a l s e c t i o n s , our r e s u l t s s t r o n g l y s u g g e s t t h a t the c y l i n d r i c a l symmetry has t o be c o n s i d e r e d a t the l e v e l o f a s m a l l a r e a o f l e s s than 1 ym i n d i a m e t e r (and p r o b a b l y much l e s s ) and not a t the l e v e l o f the whole f i l a m e n t , as X - r a y d i f f r a c t o m e t r y has s u g g e s t e d . However, i n PETP, a p o s s i b l e d i s p e r s i o n i n the o r i e n t a t i o n o f l o c a l symmetry a x i s , around the f i l a m e n t a x i s , i s t o be c o n s i dered. The c r y s t a l l i n i t y i n d e x , as o b t a i n e d u s i n g the "amorphous" d i f f r a c t i o n p a t t e r n (by d e s t r u c t i o n o f l o c a l o r d e r under the e l e c t r o n beam) g i v e s r e l i a b l e i n f o r m a t i o n , i . e . , i n agreement w i t h dark f i e l d images. I t should be emphasised t h a t the s e a r c h and p h o t o graphy o f the d i f f r a c t i o n p a t t e r n ( u s i n g the p r o c e d u r e s o u t l i n e d above) does n o t b r i n g about major d e g r a d a t i o n o f the o r i g i n a l c r y s t a l l i n i t y . T h i s i s p o s s i b l y i n p a r t due t o our use o f a h i g h vacuum e l e c t r o n m i c r o s c o p e , i n which the r a t e o f c o n t a m i n a t i o n o f the sample i s small. Acknowledgments The author wishes t o thank the workers o f the l a b o r a t o r y f o r t e c h n i c a l a s s i s t a n c e and the "RHONE POULENC TEXTILE" S o c i e t y f o r f i n a n c i a l s u p p o r t o f p a r t o f the p r e s e n t work.


17.

HAGEGE


301

Literature cited 1. HARRIS, P . H . , 5th i n t e r n , Acad. Press. N.Y. (1962)

cong.

for E l e c . Micr. BB-8

2. SCOTT, R . G . , Symposium on resinographic methods s p e c i a l t e c h n i c a l p u b l i c a t i o n N 60348 ASTM (1963)


3. BULEON, A . , CHANZY, H., HAGEGE, R . , B u l l . 4, 229-233 (1975)

Scien.ITF

4. MURRAY, R., DAVIS, H . A . , TUCKER, P . , J. Appl. Sci., 33, 177-196 (1978)

Polym.

5. Brevet, Francais, DU PONT, n ° 2, 134, 582, Enregistrement n ° 15,014 (1972) 6. DOBB, M . C . , JOHNSON, D.J., SAVILLE, B.P., J. Polym. S c i . Polym. Phys., 15, 2201 (1977) 7. DOBB, M . C . , JOHNSON, D.J., SAVILLE, B . P . , J. Polym. S c i . Polym. Symp., 58, 237-251 (1977) 8. SOTTON, M . , C . R. Acad. S c i . Paris 270B (1970) 9. DOBB, M . C . , MURRAY, R . , J. Micros. 101, 299-309 (1974) 10.

SOTTON, M . , ARNIAUD, A . M . , RABOURDIN, C., J. Appl. Polym. Sci., 22, 2585-2608 (1978).

RECEIVED May 21,

1980.


Fiber Diffraction Methods - ACS Publications - American Chemical

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