Crystallinity and Disorder in Textile Fibers - ACS Symposium Series

11 Crystallinity and Disorder in Textile Fibers MICHEL SOTTON

Downloaded by TUFTS UNIV on November 24, 2015 | http://pubs.acs.org Publication Date: November 17, 1980 | doi: 10.1021/bk-1980-0141.ch011

Laboratory of the French Textile Institute, 35 rue des Abondances, 92100 Boulogne sur Seine, France

Crystallinity and disorder are important structural parameters for understanding relationships between structure and physical properties. Flaws and distortions are the main features that limit the ultimate properties of textile fibers. Some of these crazes, cracks and voids are revealed under the electron microscope, either on the surface or in cross sections stained with heavy metals (1,2). However, these staining techniques (that reveal the main morphological features) make it much more difficult to determine the degree of distortion of the crystalline fraction. Theoretically, line profile studies permit separation of effects due to crystalline size from those due to structural distortions. However, the lack of peaks in semicrystalline fiber x-ray patterns hinders that approach. Nevertheless, when we carry out x-ray crystallinity measurements on textile fibers, we must consider distortions that always affect crystalline material. Even in a completely crystalline material, the scattered x-ray intensity is not located exclusively in the diffraction peaks. That is because the atoms move away from their ideal positions, owing to thermal motion and distortions. Therefore, some of scattered x-rays are distributed over reciprocal space. Because of this distribution, determinations of crystallinity that separate crystalline peaks and background lead to an underestimation of the crystalline fraction of the polymer. In this paper, we attempt to calculate the real crystallinity for textile fibers from apparent values measured on the x-ray pattern. This is done by taking into account the factor of disorder following Ruland's method (3). Theoretical Review-Ruland's Method The basic equations proposed by Ruland for the calculation of the crystallinity of polymers are :

0-8412-0589-2/80/47-141-193$05.25/0 © 1980 American Chemical Society In Fiber Diffraction Methods; French, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

194

FIBER

2

s T

I

Jo

, .ds cr(s)

l

2

ST

L

(s)

s: I

.ds

Jo

DIFFRACTION

2

METHODS

2

s f ds 2

2

s f j ) ds

where x = w e i g h t f r a c t i o n o f t h e c r y s t a l l i n e m a t e r i a l i n t h e p o l y m e r ; s = 2 s i n 9/A, m a g n i t u d e o f t h e r a d i a l v e c t o r s i n t h e r e c i p r o c a l s p a c e (2 0= d i f f r a c t i o n a n g l e , X- w a v e l e n g h e x p r e s s e d i n A) ; \ = coherent scattered i n t e n s i t y ; I = p a r t of the c o h e r e n t s c a t t e r i n g w h i c h i s c o n c e n t r a t e d i n t o the c r y s t a l l i n e p e a k s ; f = mean s q u a r e o f t h e s c a t t e r i n g f a c t o r s o f t h e atoms i n the p o l y m e r ; and rj = d i s o r d e r f u n c t i o n . T h i s method u s e s t h e f a c t o r |< f o r t h e " a p p a r e n t " c r y s t a l l i n i t y , w h i c h i s , i t s e l f , a f u n c t i o n o f t h e d i s o r d e r p a r a m e t e r , J) Q


2

t

oo 2

f. /

2

s f ds 2

2

s ? D ds

D i n c l u d e s t h e d i s o r d e r r e s u l t i n g f r o m b o t h t h e r m a l m o t i o n and l a t t i c e imperfections. R u l a n d showed t h a t t h e s e two k i n d s o f d i s o r d e r c o u l d be r e p r e s e n t e d a p p r o x i m a t e l y as one and t h e same function

under the assumption of i s o t r o p i c d i s o r d e r ; t h a t i s , the average atom moves away f r o m i t s i d e a l p o s i t i o n i n a l l d i r e c t i o n s . F o r a g i v e n p o l y m e r t h a t has v a r i a b l e amounts o f c r y s t a l l i n i t y , the s c a t t e r e d i n t e n s i t y over a l a r g e range of r e c i p r o c a l s p a c e may be i n t e g r a t e d o v e r a number o f i n t e r v a l s s - s . Such i n t e r v a l s c a n be d e f i n e d e x p e r i m e n t a l l y i n s u c h a way t h a t t h e f o l l o w i n g e q u a t i o n be v e r i f i e d i n d e p e n d e n t l y f r o m t h e c r y s t a l l i n i t y o f the m a t e r i a l Q

o

p

o

s and Sp b e i n g t h e l o w e r and u p p e r l i m i t s o f i n t e g r a t i o n . On t n e s e a n g u l a r i n t e r v a l s , e q u a t i o n s c a n be u s e d f o r any s a m p l e s , under the form

In Fiber Diffraction Methods; French, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

11.

SOTTON

195

Crystallinity and Disorder in Textile Fibers

s X

S

^cr(s)

n

ds

St K "o,

^

s

f2

p , D' ~ > -

2

P s irs;ds

K = 2

2

s f exp

ds


o The i n t e g r a t i o n i n t e r v a l s h a v i n g b e e n d e f i n e d , t h i s s y s t e m o f e q u a t i o n s c a n be s o l v e d b y c a l c u l a t i n g t h e nomogram o f « v a l u e s t h a t m a i n t a i n as a constant t h e c r y s t a l l i n i t y , x f o r a g i v e n function of disorder rj We have u s e d t h i s a p p r o a c h f o r s e v e r a l t e x t i l e f i b e r s , b u t b e f o r e s h o w i n g r e s u l t s , t h e e x p e r i m e n t a l c o n d i t i o n s w i l l be d e s cribed. Q

(

Experimental Sample P r e p a r a t i o n . F i b e r c r y s t a l l i n i t y studies require the p r e l i m i n a r y making o f a " g l o b a l sample" i n which a l l p r e f e r e n t i a l o r i e n t a t i o n h a s b e e n removed. The g e n e r a l way i s t o g e t a "powder" made o f f i b e r c r o s s s e c t i o n s . O u r c r o s s s e c t i o n s h a v e b e e n c u t w i t h a n a u t o m a t i c m i c r o t o m e (4) made e s p e c i a l l y f o r t h i s u s e , a l l o w i n g us t o make r e g u l a r c u t t i n g s . The l e n g h t o f t h e c r o s s s e c t i o n s c a n be a d j u s t e d f r o m 20 ym t o 200 ym, and we g e n e r a l l y c h o o s e a l e n g t h o f 80 ym f o r t h e d i f f e r e n t t e x t i l e f i b e r s . C r o s s s e c t i o n s a r e t h e n s i f t e d and p e l l e t e d i n s i d e s a m p l e h o l d e r s t h a t a r e o f d i f f e r e n t s i z e s , depending on whether the t r a n s m i s s i o n o r r e f l e c t i o n mode i s u s e d . I n t h e s y m m e t r i c a l t r a n s m i s s i o n mode, where s c a n s a r e p e r f o r m e d f r o m 7° t o 75° 2 9 , t h e s a m p l e t h i c k n e s s i s l e s s t h a n 1 mm. I n t h e s y m m e t r i c a l r e f l e c t i o n mode, w i t h s c a n s f r o m 70° t o 130° 2 9 , t h e s a m p l e t h i c k n e s s i s 3 mm. C a r e f u l work i s n e c e s s a r y t o remove a l l p r e f e r r e d o r i e n t a t i o n f r o m powder s a m p l e s . F i g u r e 1 shows r e s u l t s o b t a i n e d w i t h p o l y e t h y l e n e t e r e p h t h a l a t e (PET) f i b e r s . Curve £ i s a t y p i c a l azimut h a l s c a n o f t h e 010 peak (29 = 17,5°) f o r a b u n d l e o f p a r a l l e l f i b e r s p l a c e d p e r p e n d i c u l a r l y t o t h e x - r a y beam. C u r v e b^ i s t h e same s c a n c a r r i e d o u t o n a "powder" s a m p l e , s h o w i n g t h a t a l l p r e f e r r e d o r i e n t a t i o n i s removed i n o u r c o n d i t i o n s o f m o u l d i n g (350 kg/m2). F o r e a c h k i n d o f f i b e r , i t i s n e c e s s a r y t o do p r e liminary t r i a l s t o f i n d the best experimental conditions. F o r PET f i b e r s , we show o n F i g u r e 2 t h e r e l a t i v e c r y s t a l l i n i t y i n d e x and t h e r e s i d u a l o r i e n t a t i o n p l o t t e d a g a i n s t t h e c u t - l e n g h . ( 5 ) .



196

FIBER

Figure 1.

X-ray azimuthal scans of (010)

DIFFRACTION

METHODS

peak of PET fibers.

Curve a: bundle of parallelfibersput perpendicularly to the x-ray beam; Curve b: "powder" made of cut fibers. It can be ascertained that all preferential orientation is practically removed when a powder sample made of regular small cross section is used.

Figure 2.

Effect of cross-section length on crystallinity index ( preferential orientation ( )


) and

on


11.

SOTTON


197

P r e f e r e n t i a l o r i e n t a t i o n i n c r e a s e s r a p i d l y when t h e c u t - l e n g t h i s g r e a t e r t h a n 80 ym, a n d t h e c r y s t a l l i n i t y i n d e x goes t h r o u g h a maximum a t t h e same c u t - l e n g t h . To e x p l a i n s u c h r e s u l t s we s u g gest : - the weight o f the d e c r y s t a l l i z e d m a t e r i a l which c o u l d appear a t t h e b o t h ends o f c u t s , becomes g r e a t e r and g r e a t e r a s t h e c u t length decreases. - p r e f e r e n t i a l o r i e n t a t i o n s , n o t i c e d f o r t h e l o n g e s t c u t s have f o r e f f e c t s t o r e d u c e t h e o v e r a l l c r y s t a l l i n i t y o f t h e sample (peak extinctions...) T h e r e f o r e , 80-ym c u t - l e n g t h s were u s e d f o r PET s t u d i e s . F o r o t h e r more c r y s t a l l i n e f i b e r s , e x p e r i m e n t a l c o n d i t i o n s seem l e s s c r i t i cal. T a b l e I shows t h e c r y s t a l l i n i t y i n d i c e s f o r s e v e r a l c e l l u l o s i c f i b e r s c u t a t 30ym and a t 80 ym. Those i n d i c e s do n o t seem s e n s i b l y d i f f e r e n t i n t h i s range o f c u t - l e n g t h s . Table I Polynosic F i b e r s : E f f e c t o f cut length Crystallinity

Index %

Samples Cut

l e n g t h 30 ym

Cut

l e n g t h 80 ym

Polynosic ref. A

68 %

72 %

Polynosic ref. B

62 %

62 %

Polynosic ref. C

58 %

60 %

T r e a t m e n t o f E x p e r i m e n t a l V a l u e s . The e x p e r i m e n t a l v a l u e s a r e c o r r e c t e d f o r a i r s c a t t e r i n g , p o l a r i z a t i o n , but a b s o r b t i o n - geom e t r i c ( L o r e n t z ) c o r r e c t i o n s a r e n o t made. A f t e r t h e v a r i a b l e 28 i s transformed i n t o s = 2 s i n 8 , the e x p e r i m e n t a l curves are n o r m a l i z e d , i n e l e c t r o n i c u n i t s , by adjustment t o a t h e o r e t i c a l curve. T h e o r e t i c a l c u r v e s ( t o t a l s c a t t e r i n g power, summing up c o h e r e n t and i n c o h e r e n t s c a t t e r i n g s ) a r e c a l c u l a t e d f r o m t h e s t o i c h i o m e t r i c composition o f polymers. I n o r d e r t o o b t a i n good a d j u s t e m e n t b e t w e e n e x p e r i m e n t a l a n d t h e o r e t i c a l c u r v e s , we c o r r e c t f o r t h e a b s o r b t i o n d i s c r e p a n c y b e t ween t h e c o h e r e n t and i n c o h e r e n t s c a t t e r i n g , w h i c h becomes l a r g e r at wide s c a t t e r i n g a n g l e s . Because o f t h i s d i s c r e p a n c y , c o r r e c t i o n s a r e s u c c e s s i v e l y made t o t h e r a t i o I ( i n c o h ) (3) f o r t h e I (coh) a b s o r b t i o n e f f e c t s i n t h e sample i n r e f l e c t i o n mode, t h e a i r p a t h , and t h e R o s s f i l t e r s . A f t e r a l l c o r r e c t i o n s are completed, the diagrams o f s I ^ v s . s a r e drawn. C o n v e n i e n t i n t e g r a t i o n i n t e r v a l s a r e d e t e r mined f o r c a l c u l a t i n g t h e nomogram o f K v a l u e s . F o r i n s t a n c e , 2



198

FIBER DIFFRACTION

METHODS

INTENSITY (ELECTRONIC UNIT)

Figure 3.

Theoretical curves of scattered intensity by PET and experimental normalized intensity by PET fibers


11.

SOTTON


199

F i g u r e 4 c o r r e s p o n d s t o a p o l y p r o p y l e n e sample and F i g u r e 5 t o a w e l l - c r y s t a l l i z e d PET s a m p l e . F o u r i n t e g r a t i o n i n t e r v a l s c h o s e n f o r the diagrams o f the main t e x t i l e f i b e r s . F o r PET f i b e r s , t h e y are : s

to s °

P

= 0.1 t o 0.4 0.1 t o 0.67

0.1 0.1

t o 1.0 t o 1.2

I t i s t h e r e f o r e p o s s i b l e t o c a l c u l a t e the K v a l u e s over these i n t e r v a l s w i t h d i f f e r e n t k v a l u e s . The r e s u l t s f o r PET a r e shown on F i g u r e 6. I t c a n be a s c e r t a i n e d , a s R u l a n d has a l r e a d y shown f o r p o l y e t h y l e n e , t h a t s t a r t i n g from a d i s o r d e r f u n c t i o n w i t h s p h e r i c a l symmetry, t h e p l o t s o f K v s . s ( t h e u p p e r l i m i t s o f i n t e g r a t i o n ) c a n be r e d u c e d t o a s e t o f s t r a i g h t l i n e s f o r t h e d i f ferent k values. F i n a l l y , b e f o r e c a r r y i n g out the c a l c u l a t i o n , i t i s n e c e s s a r y to s k e t c h t h e b o u n d a r y b e t w e e n t h e c r y s t a l l i n e p e a k s a n d t h e amorphous b a c k g r o u n d . T h i s l i n e c a n be c a l c u l a t e d i f a n amorphous sample has b e e n u s e d a s a r e f e r e n c e , s u c h a s f o r PET and c e l l u l o s e fibers. I f no amorphous s t a n d a r d s a r e a v a i l a b l e , t h e b a c k g r o u n d i s drawn m a n u a l l y , f o l l o w i n g a l i n e p a r a l l e l t o t h e t h e o r e t i c a l c u r v e (4,5) ( t o t a l s c a t t e r i n g power summing up c o h e r e n t a n d i n c o herent s c a t t e r i n g ) . T a b l e I I shows e f f e c t s o f t h e d i s o r d e r p a r a m e t e r o n t h e c a l c u l a t e d c r y s t a l l i n i t y o f c o t t o n , n y l o n 66 (PA 66) and PET f i b e r s a m p l e s . When k = 0, no c o r r e c t i o n f o r d i s t o r t i o n i s made d u r i n g calculation of crystallinity. A c c o r d i n g l y , v a l u e s o f X become s m a l l e r a s t h e i n t e g r a t i o n i n t e r v a l s i n c r e a s e . On t h e nomogram of K v a l u e s , i t i s p o s s i b l e t o determine the d i s o r d e r parameter v a l u e t h a t m a i n t a i n s as a p p r o x i m a t e l y c o n s t a n t t h i s c r y s t a l l i n i t y when u s i n g t h e d i f f e r e n t i n t e r v a l s : t h e d e v i a t i o n f r o m t h e c o n s tancy i s used, i n the computing program t o determine the b e s t v a l u e o f k and t o e s t i m a t e t h e e r r o r s o f t h e s e a n a l y s e s . The d i s o r d e r p a r a m e t e r k i s h i g h e r i n c o t t o n and PA 66 t h a n i n a l l PET f i bers. B e s i d e s , one c a n see t h a t a p p a r e n t c r y s t a l l i n i t y v a l u e s ( d i s o r d e r parameter not considered) are lower than the t r u e ones.


p

Q

Experimental

Results

P o l y e s t e r F i b e r s . The f i r s t example i n v o l v e s two i n d u s t r i a l PET y a r n s . The f i r s t y a r n has a r e s i d u a l s h r i n k a g e o f 8 % ( F i g u r e 7) a n d t h e s e c o n d y a r n has u n d e r g o n e i n d u s t r i a l s t a b i l i z i n g h e a t t r e a t m e n t and has a l m o s t no r e s i d u a l s h r i n k a g e (0,6 % ) . We see t h a t t h e s e c o n d sample i s , o f c o u r s e , more c r y s t a l l i n e t h a n t h e f o r m e r b u t t h a t i t has a h i g h e r d i s o r d e r p a r a m e t e r ( g i v e n i n brackets). B o t h s a m p l e s were a n n e a l e d f o r 1 h o u r a t 220°C i n a s l a c k s t a t e ( s h r i n k a g e d u r i n g a n n e a l i n g was a l l o w e d ) . The sample t h a t s h r i n k s 8 % c r y s t a l l i z e s a t a l e v e l c l o s e t o t h a t o f the i n d u s t r i a l l y s t a b i l i z e d y a r n . But s i m u l t a n e o u s l y w i t h




to o o


2

Figure 5. Is vs. s diagram for a well-crystallized PETfiber( ) and an amorphousfibersample ( ). The amorphous background has been calculated in the ranges A-B, B-C, C-D . . . from the amorphous curve and a factor of proportionality.


to Ο

S

* > • .

S'

ι

1'

§

S*

î

H H Ο

8


202

FIBER

DIFFRACTION

2

METHODS

Figure 6. Nomogram of K (s k) values for PET fibers in the hypothetical ideal case where an isotropic disorder exists in the crystalline fraction of those fibers and calculated for the chemical composition (C O H ) and s = 0.1 p

10

4

8

n

0



: s -s o p

: s -s o p

2nd

3rd

X

c

|

CV % 5,8

0,41

0,434

0,401

0,381

0,422

C.V.

!

j

!

I

I

|

Crystallinity

0,08

0,100

0,146

0,204

Coefficient

Crystallinity

: Variation

T.C. : T r u e

A.C. : A p p a r e n t

i

!

!

0,122

0,101

!

!

0,184

0,317

2,3

0,236

0,239

0,231

0,232

0,242

P o l y e s t e r Y a r n (PET) A.C. i T.C. k = 0 | k = 2,5

as F u n c t i o n o f k and I n t e g r a t i o n

Cotton Fibers A.C. | T.C. k = 0 ! k = 4

Fraction X

Average

4 t h : s -s o p

: s -s o p

1st

- s o p Intervals

s

Crystalline

Table II

0,161

0,191

0,260

0,474

1

j

I

i

!

!

7 , 3

0,563

0,601

0,555

0,508

0,586

P o l y a m i d e Y a r n (66) A.C. i T.C. k = 0 I k = 3,3

Intervals


204

FIBER

DIFFRACTION

METHODS

a 0,40 annealed

sample

4

level

(2,8)


0,30

i n i t i a l sample (2,5) level

0,20^

IQ

50

0,40

4

annealed

. yg c

3

l e s

100

sample

level

[ _ . — : = = — „ . . , T

i n i t i a l sample l e v e l !

L

0,30

(2,1)

4— (2,9)

(2,4)

(1,7)

0,20 j

1.0 50

Figure 7.

ycles

100

Effect of annealing treatment and mechanical fatigue on crystallinity and disorder for two samples of PET fiber.

(a) PET singlefilamentyarn (industrial sample): 110 tex f 220 S 28 tpm (Tergal 5 dtex), shrinkage capacity 8%; (b) PET singlefilamentyarn (industrial sample): 116 tex f 220 S 32 tpm (Tergal 5,25 dtex), stabilized sample (conditions of stabilization are unknown), residual shrinkage 0.6%. The values of k appear between brackets. Annealing treatment (1 hr at 220°C) produces an increasing of crystallinity: the range of this change is represented by arrows on the figures for the two samples of PET fibers. Mechanical fatigue produces an increase in crystallinity for the less crystallized sample—8% shrinkage (Figure 7a), and a decrease in crystallinity for the stabilized, well crystallized sample—0.6% shrinkage (Figure 7b). In both cases fatigue produces a decrease in the disorder parameter.



11.

SOTTON

205


t h i s n e o c r y s t a l l i z a t i o n , the d i s o r d e r parameter i n c r e a s e s from k = 2.5 t o k = 2.8. A l s o , t h e a n n e a l i n g t r e a t m e n t does n o t g r e a t l y i m p r o v e t h e c r y s t a l l i n i t y o f t h e s t a b i l i z e d sample b u t does a l l o w d i s t o r t i o n t o b e removed ( k d e c r e a s e s f r o m 2.9 t o 2 . 6 ) . These two s a m p l e s h a v e a l s o u n d e r g o n e m e c h a n i c a l f a t i g u e ( t h o u s a n d s o f c y c l e s o f e x t e n s i o n i n t h e Hooke's Law zone b e t w e e n two l e v e l s o f s t r e s s ) . The c u r v e s ( F i g u r e 7) show changes o f c r y s t a l l i n i t y and changes o f t h e d i s o r d e r p a r a m e t e r when p l o t t e d a g a i n s t t h e number o f c y c l e s . The s a m p l e t h a t was i n i t i a l l y l e s s c r y s t a l l i n e r e g i s t e r e d a n i n c r e a s e i n c r y s t a l l i n i t y and a r e d u c t i o n i n d i s t o r t i o n s a f t e r the f a t i g u e t r e a t m e n t . T h i s r e s u l t i s u n u s u a l . F o r most c r y s t a l l i n e m a t e r i a l s , f a t i g u e r e d u c e s t h e c r y s t a l l i n e f r a c t i o n and t h e amount o f d i s t o r t i o n . P a r a d o x i c a l l y , such a m e c h a n i c a l f a t i g u e a p p a r e n t l y a c t s as a t r e a t m e n t f o r r e l a x a t i o n o f s t r e s s and a l l o w s f l a w s , l o c a t e d a t the s t r e s s a r e a s t o be p a r t l y d i s s i p a t e d . A l s o , m e c h a n i c a l f a t i g u e t r e a t m e n t s can e l i m i n a t e e f f e c t s o f a p r e v i o u s t h e r m a l t r e a t m e n t . Two s a m p l e s t h a t were i n i t i a l l y d i f f e r e n t became more s i m i l a r w i t h r e g a r d t o t h e i r c r y s t a l l i n i t y a f t e r 50 x 1 0 c y c l e s . They had a medium l e v e l o f c r y s t a l l i n i t y c h a r a c t e r i z e d b y d i s o r d e r p a r a m e t e r v a l u e s t h a t a r e p a r t i c u l a r l y low. F i g u r e 7 a l s o shows t h a t t h e two s a m p l e s c o u l d become i d e n t i c a l a f t e r the a n n e a l i n g treatments, t h i s time a t a h i g h l e v e l o f c r y s t a l l i n i t y and c h a r a c t e r i z e d b y s t r o n g d i s t o r t i o n s . I t seems d i f f i c u l t t o remove, b y a n n e a l i n g , t h e s e d i s t o r t i o n s ( c h a i n f o l d i n g s ) t h a t a p p e a r d u r i n g a t h e r m a l t r e a t m e n t w i t h t h e sample allowed t o shrink. I n t h e c a s e o f a n amorphous sample a n n e a l e d s e v e r a l hours t o get a c r y s t a l l i n e s t a n d a r d , r e a l c r y s t a l l i n i t y was a s h i g h a s 0.66 b u t k r e m a i n e d a s h i g h a s 2.6 (_5). These r e s u l t s a r e n o t t h e o n l y ones t h a t c o u l d be r e g i s t e r e d , and e x t e n s i v e changes o c c u r i n the amorphous f r a c t i o n . For i n s t a n c e , t h e o r i e n t a t i o n f u n c t i o n o f t h e m o l e c u l e s i n t h e amorphous zone changes s t r o n g l y a f t e r e a c h t r e a t m e n t . The r e s u l t s i n T a b l e I I I a n d I V w i l l n o t be d i s c u s s e d h e r e i n d e t a i l , b u t s i m u l t a n e o u s d e t e r m i n a t i o n s o f t h e amorphous m o r p h o l o g y and c r y s t a l l i n e perfection could lead t oa better understanding o f f i b e r properties. They c o u l d g i v e a b e t t e r u n d e r s t a n d i n g o f SAXS p a t t e r n s , the i n t e n s i t y d i f f e r e n c e s o f w h i c h are d i f f i c u l t t o e x p l a i n on t h e b a s i s o f changes i n c r y s t a l l i n i t y . T a b l e V shows r e s u l t s o b t a i n e d o n t e t r a m e t h y l e n e t e r e p h t h a l a t e f i b e r s , h e a t t r e a t e d a t 220°C f o r d i f f e r e n t t i m e s i n a r e l a x e d s t a t e . T h e r e a g a i n , we o b s e r v e a g r e a t improvement i n t h e amount o f t h e c r y s t a l l i n e m a t e r i a l b u t a l s o i n c r e a s i n g d i s t o r tions . 3



initial

-

f am

c S A X

2,4

2,1

1,7

2,0

2,6

2,9

k

V c

193

203

216

203

217

189

10

3

A

Crystallinity 3

R x 3,6

R x 2,9

-

R x 2,3

R x 6,9

R x 3.6

S A X S

2

Parameters L

A x

0,839 0,843

0,984 0,982

150 152

0,831

0,745

0,790

^ am

0,840

0,985

0,984

0,984

f

L

Amorphous

0,985

-

150

143

150

P

o

: 0 ,6 %

a

o

87

81

-

78

75

82

A

Amorphous

length.

C r y s t a l Volume c a l c u l a t e d f r o m t h e 010 - 100 and 105 l i n e - b r e a d t h (5) I n t e n s i t y o f t h e S A X S d i a g r a m s , i n a r b i t r a r y u n i t s , and e x p r e s s e d compared to the i n t e n s i t y R o f the i n i t i a l (8% shrinkage) f i b e r diagram. L o n g P e r i o d by S A X S. O r i e n t a t i o n f u n c t i o n of the c r y s t a l l i n e f r a c t i o n ( 1 2 ) . O r i e n t a t i o n f u n c t i o n o f t h e amorphous f r a c t i o n c a l c u l a t e d f o l l o w i n g D u m b l e t o n ' s method ( J . P o l y m . S c i . A V o l . 6 7 9 5 ) , 1968.

0,33

110.000

V

0,32

57.000

0,35

0,39

0,30

cycles

c

0,35

X

26.000

fatigue 4.500

- a n n e a l e d 220°C

-

S a m p l e

POLYESTER Y a r n - 2 GT - R e s i d u a l S h r i n k a g e

Changes i n c r y s t a l l i n e and amorphous f r a c t i o n s o f PET f i b e r s a f t e r a n n e a l i n g t r e a t m e n t and m e c h a n i c a l f a t i g u e .

Table I I I


to o

C5/

D

§

W H

O H O

m

03

ON


initial

-

c

0,25 0,28 0,31 0,25

0,37

0,24

X

L

am

c S A X S

V

fatigue 4.500 c y c l e s 25.000 63.800 82.000

- a n n e a l e d 220°C

-

S a m p l e 3

au

S A X S

109 99 96 119 R x 2

R x 1,9 R x 1 ,5

L

137 138 137 137

131

138

A P

: 8 %

0,987 0,985 0,985 0,991

0,854

0,854 0,832

o

A

Amorphous

length.

2

O r i e n t a t i o n f u n c t i o n o f t h e amorphous f r a c t i o n c a l c u l a t e d D u m b l e t o n ' s method ( J . P o l y m . S c i . A V o l . 6 795) 1968.

O r i e n t a t i o n f u n c t i o n o f t h e c r y s t a l l i n e f r a c t i o n (12) following

I n t e n s i t y o f t h e S A X S d i a g r a m s , i n a r b i t r a r y u n i t s , and e x p r e s s e d compared t o t h e i n t e n s i t y R o f t h e i n i t i a l (8 % s h r i n k a g e ) f i b e r d i a g r a m . L o n g P e r i o d by S A X S.

(5)

76 81 77 76

70

0,690

0,976

a 77

am

L

0,832

x

f

0,987

f

Amorphous

C r y s t a l v o l u m e c a l c u l a t e d f r o m t h e 010 - 100 a n d 105 l i n e - b r e a d t h

2 2,4 1,9 2

R x 5,4

A

181

3

2,8

10 R

c 111

V

Parameters

2,5

k

Crystallinity

POLYESTER Y a r n - 2 GT - R e s i d u a l S h r i n k a g e

Changes i n c r y s t a l l i n e and amorphous f r a c t i o n s o f PET f i b e r s a f t e r a n n e a l i n g t r e a t m e n t and m e c h a n i c a l f a t i g u e .

T a b l e IV


208

FIBER

DIFFRACTION

METHODS

Table V

POLYESTER 4 GT x

Sample -

Yam

initial

c

k

0.22

1.9

f

0.43

2.6

15'

0.41

2.8

30'

0.43

2.6

- a n n e a l e d 220°C


shrink time

: 30 :

2

%

N y l o n F i b e r s . T a b l e V I shows t h a t PA 66 f i b e r s a r e d i f f e r e n t , t h a t h e a t t r e a t m e n t s o f 2 s e c o n d s a t 220°C, w i t h s h r i n k a g e a l l o w e d , do n o t m o d i f y t h e c r y s t a l l i n i t y . Such m o d i f i c a t i o n r e quires annealing f o r 3 minutes, with shrinkage allowed. The r e a l c r y s t a l l i n i t y o f PA 66 f i b e r s i s h i g h e r t h a n t h a t o f PET f i b e r s , b u t i n c o n t r a s t w i t h r e s u l t s o b t a i n e d w i t h PET f i b e r s , h e a t t r e a t ments d e c r e a s e t h e k p a r a m e t e r . V a r i a t i o n s o f k must be compared w i t h v a r i a t i o n s i n a P e r f e c t i o n C r y s t a l l i n e Index ( I P ) obtained a c c o r d i n g to D u m b l e t o n ' s method, f r o m t h e 010 and 100 p e a k s ( 7 ) . I P increases r a p i d l y a f t e r heat treatments. An i n c r e a s e o f t h i s i n d e x i s p r o o f of a p r o g r e s s i v e t r a n s f o r m a t i o n from a pseudohexagonal phase i n t h e i n i t i a l sample ( d i s t u r b e d as s e e n f r o m t h e k v a l u e ) d e c r e a s i n g to g i v e a l e s s d i s t u r b e d t r i c l i n i c phase a f t e r thermal treatment^ We a l s o n o t i c e a c o n s i d e r a b l e i n c r e a s e o f t h e SAXS i n t e n s i t y t h a t c o u l d n o t be e x p l a i n e d by t h e change o f c r y s t a l l i n i t y ( w h i c h r e m a i n s p r a c t i c a l l y c o n s t a n t ) b u t c o u l d p a r t l y be e x p l a i n e d by a d e c r e a s e d k. C

C

A c r y l i c F i b e r s . T a b l e V I I shows t h a t c r y s t a l l i n i t y o f p o l y a c r y l o n i t r i l e i s o n l y s l i g h t l y m o d i f i e d by h e a t t r e a t m e n t s . The f r a c t i o n o f c r y s t a l l i n e m a t e r i a l seems r a t h e r d i s t o r t e d , as j u d g e d by t h e k v a l u e s . Wet t r e a t m e n t s a l o n e a l l o w s u b s t a n t i a l amounts o f d i s t o r t i o n s t o be removed. W a t e r m o l e c u l e s c o u l d e n t e r t h e o r d e r e d r e g i o n s and r e l a x d i p o l e - d i p o l e i n t e r a c t i o n s , a l l o w i n g some m o l e c u l a r m o t i o n .


11.

SOTTON


209

Table V I

PA 66 Y a r n - 78 d t e x Sample

k

c

SAXS Integrated intensity

PI

%

0.56

3.3

47

164 a.u.

+ 2 %

0.56

2.5

69

235

0 %

0.59

2.9

67

350

- 2 %

0.55

2.9

66

545

- 4 %

0.56

2.8

67

473

- 6 %

0.56

2.6

72

493

- a n n e a l e d - 3'

0.61

2.7

80

-

-

initial


- heat t r . 220°O2"

220°C - 10 %

Table V I I

CRYLOR

(homopolymer)

Sample

X

k c

-

initial

- d r y heat

3.8

0.37 0.39

3.6 3.6

0.33 0.38

3.3 3.3

treated

140°C 170°C - wet h e a t

0.34

treated

130°C 180°C



210

FIBER DIFFRACTION

METHODS

C o t t o n F i b e r s . F i g u r e 8 shows t h e way t h e b a c k g r o u n d was drawn on t h e x - r a y d i a g r a m , i n r e f e r e n c e t o a s t a n d a r d amorphous p a t t e r n . As w i t h PAN f i b e r s , t h e c r y s t a l l i n e f r a c t i o n i n c o t t o n seems r a t h e r d i s t u r b e d by d i s t o r t i o n s , j u d g e d by t h e h i g h k v a l u e s (Table V I I I ) . A m e r c e r i z i n g treatment w i t h c a u s t i c soda s o l u t i o n , which transforms c e l l u l o s e I to C e l l u l o s e I I , produces a reduct i o n o f the o v e r a l l c r y s t a l l i n i t y , w i t h a r e l a x a t i o n o f t h e i n i t i a l crystalline distortions. P e r c e n t a g e s o f c e l l u l o s e I and c e l l u l o s e I I , as w e l l as t h e o v e r a l l c r y s t a l l i n i t y d e t e r m i n e d a c c o r d i n g t o a r e l a t i v e method ( 5 ) , a r e shown i n t h e r i g h t p a r t o f Table V I I I . We c o u l d assume t h a t t h e d e c r e a s e o f k t h r o u g h merc e r i z a t i o n c o u l d be a c c o u n t e d f o r by t h e f o l l o w i n g simultaneous effects. The f i r s t e f f e c t i s t h e r e m o v a l o f t h e most d i s t u r b e d f r a c t i o n of the i n i t i a l l y c r y s t a l l i n e , f i b r i l l a r s u r f a c e of the cellulose. The s e c o n d e f f e c t i s a r e g e n e r a t i o n o f a l e s s d i s t u r b e d p h a s e . I f we r e c a l l t h a t c h a i n - f o l d i n g c a u s e d d i s o r d e r i n PET, t h e r e g e n e r a t i o n o f a l e s s d i s o r d e r e d p h a s e s u g g e s t s t h a t t h e f o r m a t i o n of c e l l u l o s e I I occurs without c h a i n - f o l d i n g . Table V I I I

COTTON 53/2 Sample

X

- Menoufi

k

Cell.I

%

Cell.II %

Cr.

%

c -

initial

0.41

4

80

-

80

-

mercerized

0.27

3.1

29

48

77

K e v l a r F i b e r s . T a b l e I X shows r e s u l t s o b t a i n e d w i t h K e v l a r 950 f i b e r s . The c r y s t a l l i n i t y o f t h i s a r o m a t i c p o l y a m i d e i s o n l y s l i g h t l y h i g h e r than t h a t f o r the a l i p h a t i c polyamide samples t h a t we s t u d i e d ( T a b l e V I ) . But i n K e v l a r , as f o r PET f i b e r s , t h e d i s o r d e r p a r a m e t e r k i s s m a l l e r t h a n i n PA 66 f i b e r s . Thermal t r e a t m e n t a t 220°C f o r 1 h o u r i n s l a c k c o n d i t i o n s does n o t s u b s t a n t i a l l y i n c r e a s e t h e a v e r a g e c r y s t a l l i n i t y o f t h e K e v l a r 950 f i b e r s and p r o d u c e s more d i s t o r t i o n s . C o n s e q u e n t l y , we c o n c l u d e t h a t the b e h a v i o r o f t h i s A r a m i d f i b e r d u r i n g our a n n e a l i n g t r e a t m e n t i s s i m i l a r t o PA 66 as f a r as c r y s t a l l i n i t y i s c o n c e r n e d K e v l a r 950 i s a l s o s i m i l a r t o PET f i b e r w i t h r e g a r d t o t h e b e h a v i o r o f the d i s o r d e r p a r a m e t e r .



2

Figure 8. Is vs. s diagram for cottonfibers( ) and amorphous cellulose ( ). The amor phous background has been calculated from the amorphous curve and a factor of proportionality. ( ) Experimental curve; (·---) amorphous cellulose sample; (· · -) amorphous background.


ι—*

Κ)

a

S*

I

Î

Ο Η Η Ο

212

FIBER DIFFRACTION

METHODS

Table IX

Intervals

Kevlar

s

t y p e 950


o

- s p

1st i n t s -s o p 2nd i n t s - s o p 3rd i n t s -s o p 4th i n t s -s o p Moy. X

q

CV %

K e v l a r t y p e 950 annealed 220°C - 1 h (slack)

C.A. k=0

C.V. k = l ,8

C.A. k=0

C.V. k=2

0,486

0,564

0,514

0,606

0,409

0,593

0,401

0,604

0,328

0,591

0,294

0,560

0,235

0,561

0,240

0,615

0,577

0,596

2,9 %

4,1 %

Conclusion These e x a m p l e s i l l u s t r a t e how t o o b t a i n r e s u l t s a b o u t c r y s t a l l i n i t y and d i s o r d e r f o r a b e t t e r u n d e r s t a n d i n g o f t h e r e l a t i o n s h i p s b e t w e e n s t r u c t u r e and p r o p e r t i e s . The r e a d e r i s , h o w e v e r , c a u t i o n e d t h a t c r y s t a l l i n i t y and d i s o r d e r p a r a m e t e r s d e t e r m i n e d by x - r a y d i f f r a c t o m e t r y a r e a v e r a g e v a l u e s and t h a t t h e y s h o u l d be c a r e f u l l y compared w i t h l o c a l o r d e r measured b y e l e c t r o n d i f f r a c t i o n on u l t r a - t h i n c r o s s s e c t i o n s o f t e x t i l e f i b e r s ( 9 ) w i t h d i f f e r i n g c r y s t a l l i t e s i z e s (10,11).

Abstract Corrections of the apparent crystallinity values of fibers materials have been carried out by taking into account a disorder parameter k, following Ruland's method. Peculiar care was taken about samples preparation (cutting and pelleting of fibers), data collection and reduction, which will be briefly described. Cryst a l l i n i t y and disorder parameter measurements have been performed on main textile fibers (polyester, polyamide, aramid, polypropylene, cellulosic fibers) and the results w i l l be discussed comparatively, with those got by more conventional x-ray crystallinity determinations. The complementarities of these different approaches w i l l be illustrated with several examples. For instance,



11.

SOTTON


213

polyester fibers exhibit, after heat treatments in the slack state, higher crystallinity but also higher disorder parameter, and after mechanical fatigue, an increasing of the crystalline fraction with this time a reduction of the k value. For example, after 65,000 cycles of extension between two levels of stress choosen in the Hooke's zone - the crystallinity in a Poly(ethylene terephthalate) fibers increases from 23 % to 30 % and k decreases from 2.5 to 1.9. On the contrary in 66 polyamide fibers, after heat treatments, the crystalline fraction does not increase a lot, but a significant decrease of the k parameter is registered simultaneously with greater percentage of the gamma to alpha phase transformation. As far as cotton fibers are concerned,mercerizing treatments in caustic soda, produce a significant decrease of the overall crystallinity and a removing of distortions, in proportion as transformation c e l l . I to c e l l . I I increases. Literature Cited 1. SOTTON, M. C.R. Acad. Sc. Paris, 1970, 270, série B, 1261. 2. SOTTON, M. Textile Research Journal, 1971, 41, 834. 3. RULAND, W. Acta Crystallogr., 1961, 14, 1180. 4. SOTTON, M. ; ARNIAUD, A.M. ; RABOURDIN, C. J . Appl. Polym. S c i . , 1978, 22, 2585. 5. SOTTON, M. ; ARNIAUD, A.M. ; RABOURDIN, C. Bulletin Scientifique ITF, 1978, 7, 265. 6. ALEXANDER, L.E. "X-Ray Diffraction Methods In Polymer Science"; Wiley, 1969. 7. DUMBLETON, J.H. J. Appl. Polym. S c i . , 1968, A 2, 2067. 8. RHÔNE POULENC TEXTILE - Private Communication. 9. HAGEGE, R. "Diffraction Methods for Structural Determination of Fibrous Polymers" ; American Chemical Society : Washington, 1979, in Press. 10. HINDELEH, A.M. ; JOHNSON, D.J. Polym. 1972, 13, 27. 11. JOHNSON, D.J. ; "Diffraction Methods for Structural Determination of Fibrous Polymers" ; American Chemical Society : Washington, 1979, in Press. 12. URBANCZYK, G.W. ; Kolloid Z . , 1960, 2, 128. RECEIVED May

21,

1980.


Crystallinity and Disorder in Textile Fibers - ACS Symposium Series

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