Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives

15 Use of Fiber and Chemical Microscopy in Applied Woven and Nonwoven Technology ARTHUR DRELICH Absorbent Technology, Johnson & Johnson, c/o Ethicon, Inc., Somerville, N.J. 08876

Downloaded by TUFTS UNIV on June 3, 2018 | https://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0058.ch015

DAVID ONEY Research Div., Chicopee Manuf. Co., Milltown, N.J. 08850

Chemists traditionally use structural formulas and mathematical expressions to understand and to figuratively see technical problems and scientific phenomena. There are many technical areas where i t is valuable to l i t e r a l l y see materials and the changes they undergo as a result of chemical or physical processes. Understanding through seeing is especially useful in fiber and textile technologies. This seeing is carried out using optical and electron microscopy. The experimenter must understand the capabilities and the limitations of his equipment, and develop a good level of competence in using i t . Otherwise, his visual evidence w i l l be, at best, incomplete and at worst, unreliable or even incorrect. In practice he must also develop adequate s k i l l s in scientific photography. The modern history of textile microscopy started with a book by Prof. Schwarz (MIT), Textiles & the Microscope (1934). Other important early contributors include George Royer and Charles Maresh of Cyanamid, and Mary Rollins of the Southern Regional Lab of the USDA. Woven Fabrics In defining woven fabrics, two of the most important parameters are the geometry of the yarns in the overall structure, and of the fibers within the yarns. Figure 1 shows an 88 χ 88 count cotton fabric, original magnification of 20X, illuminated from below by the bright field method. The informa tion obtainable from this picture includes thread 233

Turbak; Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives ACS Symposium Series; American Chemical Society: Washington, DC, 1977.


SOLVENT SPUN RAYON, MODIFIED CELLULOSE

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c o u n t , u n i f o r m i t y o f weave and o f y a r n t h i c k n e s s , and d i m e n s i o n s o f open a r e a s . F i g u r e 2 shows t h e same a r e a o f t h i s f a b r i c i l l u m i n a t e d from above by i n c i d e n t l i g h t s a t an a n g l e about 4 5 ° . Here we can see t h e s u r f a c e t e x t u r e o r roughness, and an i n d i c a t i o n o f f i b e r s t r u c t u r e . T h i s i s t h e u s u a l way t h a t f a b r i c s a r e p i c t u r e d .

Figure 3

F i g u r e 3, s t i l l showing t h e same a r e a o f t h e same f a b r i c , h i g h l i g h t s t h e f i b e r s which make up t h e yarns. I n d i v i d u a l f i b e r s a r e c l e a r l y r e s o l v e d , even though t h e i r a c t u a l d i a m e t e r s a r e o n l y about 15 micrometers ( m i c r o n s ) . The d i r e c t i o n and a n g l e o f t w i s t can r e a d i l y be measured. F i g u r e 4 shows a h i g h e r m a g n i f i c a t i o n (of #3) f o r ease o f s e e i n g d e t a i l . L i t e r a l l y every s u r f a c e f i b e r o f every yarn i s c l e a r l y v i s i b l e . The f o l l o w i n g two F i g u r e s (#5 and #6) a r e o f f a b r i c s w i t h more complex weaves. The p r e c i s e weave and s p i n n i n g s t r u c t u r e s a r e v i s i b l e and can be q u a n t i t a t i v e l y measured.



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SOLVENT SPUN RAYON, MODIFIED CELLULOSE FIBERS

Figure 4

The t e c h n i q u e f o r making t h e s u r f a c e f i b e r s so c l e a r l y v i s i b l e (as i n F i g u r e s 2 through 6, and F i g u r e 10) r e q u i r e s t h e f o l l o w i n g two s t e p s : 1.

The f i b e r s t r u c t u r e i s l i g h t l y coated with gold o r other s u i t a b l e m e t a l i n a vacuum e v a p o r a t o r o r DC s p u t t e r e r , and

2.

The specimen i s i l l u m i n a t e d i n a substage d a r k f i e l d mode f o r v i e w i n g and photography.

C r o s s - s e c t i o n i n g o f f a b r i c s i s now w e l l known. Some o f t h e p i o n e e r work i n t h i s f i e l d was done by George Royer and o t h e r s o f American Cyanamid from about 1942 t o 1950, and p u b l i s h e d i n t h e T e x t i l e R e s e a r c h J o u r n a l and t h e J o u r n a l o f t h e S o c i e t y o f Dyers and C o l o r i s t s . They demonstrated t h e d y e i n g and f i n i s h i n g o f f a b r i c s by p e n e t r a t i o n o f t h e s e r e a g e n t s i n t o y a r n s and f i b e r s u s i n g c r o s s - s e c t i o n s which were t r e a t e d by d i f f e r e n t i a l s t a i n i n g t e c h niques. These were p a t t e r n e d a f t e r t h e methods b i o l o g i s t s use t o show t i s s u e s t r u c t u r e .



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Figure 5

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A f u r t h e r method not o f t e n used i s the p l a n a r s e c t i o n i n g o f f a b r i c s t o r e v e a l and d e f i n e i n t e r i o r s t r u c t u r e , where the s e c t i o n s a r e c u t p a r a l l e l t o the major p l a n e o f the f a b r i c . An example i s shown i n F i g u r e 7. T h i s i s a composite s t r u c t u r e o f two woven f a b r i c s bonded t o g e t h e r by f u s e d n y l o n powder a t the i n t e r f a c e . T h i s photomacrograph i s one o f a s e r i e s showing the depth of p e n e t r a t i o n o f the f u s e d powder i n t o the two f a b r i c s . T h i s photograph was t a k e n by p o l a r i z e d l i g h t which a c t e d t o e f f e c t i v e l y d i f f e r e n t i a l l y s t a i n the f i b e r s and a d h e s i v e .

Figure 7

Non-Woven F a b r i c s The s t r u c t u r e o f non-woven f a b r i c s d e f i n e s , t o a considerable extent, t h e i r p r o p e r t i e s . The d i s t r i b u t i o n and o r i e n t a t i o n o f the f i b e r s can e x p l a i n r e l a t i v e l o n g and c r o s s t e n s i l e p r o p e r t i e s ( F i g u r e 8, an o r i e n t e d c a r d web). A photomacrograph o f a nonwoven c o n t a i n i n g b u n d l e d f i b e r s ( F i g u r e 9) can e x p l a i n w i c k i n g and a b r a s i o n r e s i s t a n c e . Obvious t a n g l i n g o f f i b e r s , as shown i n F i g u r e 10 can e x p l a i n t e n s i l e p r o p e r t i e s .



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Figure 10

Where the non-woven i s bonded by c h e m i c a l a d h e s i v e s , the d i s t r i b u t i o n and l o c a l c o n c e n t r a t i o n o f b i n d e r h e l p s t o u n d e r s t a n d and e x p l a i n p e r f o r mance. O v e r a l l i m p r e g n a t i o n , F i g u r e 11, produces numerous bond s i t e s . T h i s p r e v e n t s movement of f i b e r s and e x p l a i n s why the f a b r i c i s s t i f f . I n t e r m i t t e n t bonding produces f a b r i c s w i t h many h i n g e p o i n t s , hence a more f l e x i b l e hand. For example, c o n s i d e r a non-woven f a b r i c bonded w i t h p o l y v i n y l acetate i n a fine l i n e pattern. PVAc i s s t a i n e d by I ~ i n t e n s e brown o r blue-brown color. Bonded a r e a s , as w e l l as unbonded a r e a s , a r e c l e a r l y shown i n F i g u r e 12. This c o l o r i s f u g i t i v e , r e q u i r i n g t h a t the p h o t o g r a p h i c s u b j e c t be immersed i n a d i l u t e I ~ during observ a t i o n o r photography. F i g u r e 13 i s an SEM m i c r o g r a p h o f a rayon nonwoven f a b r i c , bonded by v i s c o s e which was regenerated t o c e l l u l o s e i n s i t u a f t e r i t was a p p l i e d t o the fabric. Note the l i g h t u n i f o r m c e l l u l o s e d e p o s i t i n the bond a r e a . K

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Figure 13

The f a b r i c shown on t h e l e f t s i d e i n F i g u r e 14 i s a non-woven f a b r i c , p r i n t - b o n d e d w i t h an a c r y l i c l a t e x by t h e c o n v e n t i o n a l method. T h i s a l l o w s t h e binder t o spread l a t e r a l l y , t h a t i s , t o migrate. The f a b r i c shown on t h e r i g h t was p r i n t - b o n d e d under p h y s i c o - c h e m i c a l c o n d i t i o n s which r e s t r i c t e d b i n d e r m i g r a t i o n p r o d u c i n g s h a r p e r , narrower b i n d e r l i n e s . The l a t t e r f a b r i c has a more f l e x i b l e , more t e x t i l e l i k e hand. C r o s s - s e c t i o n i n g f u r t h e r shows f i b e r / b i n d e r morphology. F i g u r e 15 shows a l a t e x - b o n d e d f a b r i c where c a p i l l a r y f o r c e s a p p a r e n t l y c o n t r o l l e d b i n d e r placement. The f i b e r s e v i d e n t l y p r o v i d e d t h e c a p i l l a r y s t r u c t u r e f o r the l a t e x binder t o run i n t o . On t h e o t h e r hand, F i g u r e 16, a l s o a c r o s s - s e c t i o n , shows t h e e f f e c t o f a sudden c o a g u l a t i o n o f t h e l a t e x ; t h e f i b e r s d i d n o t have time t o f u l l y f u n c t i o n as c a p i l l a r i e s because t h e l a t e x was r a p i d l y c o n v e r t e d t o a s e m i - s o l i d . Under t h e s e c o n d i t i o n s , more f i b e r s a r e embedded w i t h i n t h e s o l i d i f i e d b i n d e r .



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The m i c r o s c o p i c a l approach has p i t f a l l s . It r e q u i r e s a more t h a n average s k i l l i n u s i n g equipment and i n t e r p r e t i n g the images seen. The m i c r o s c o p i s t must n e v e r f o r g e t t h a t he has a s e v e r e sampling problem. He examines m i c r o a r e a s , but makes macro interpretations. As w i t h a l l a n a l y t i c a l t o o l s , i t needs t o be used w i t h c a r e , and i n c o n j u n c t i o n w i t h o t h e r a n a l y t i c a l methods.


Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives

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