Cellulose Textile Materials Studied by Using ... - ACS Publications

Chapter 13

Cellulose Textile Materials Studied by Using Fourier Transform Infrared Photoacoustic Spectroscopy 1

2

1

3

Charles Q. Yang , Randall R. Bresee , William G. Fateley , and Theresa A. Perenich 1

Department of Chemistry, Kansas State University, Manhattan, KS 66506 Department of Clothing, Textile, and Interior Design, Kansas State University, Manhattan, KS 66506 Department of Clothing, Textile, Furnishing and Interiors, University of Georgia, Athens, GA 30602 2

Downloaded by RUTGERS UNIV on March 7, 2016 | http://pubs.acs.org Publication Date: June 22, 1987 | doi: 10.1021/bk-1987-0340.ch013

3

A variety of cellulose textile materials, including sized cotton yarns and chemically treated cotton f a b r i c s were studied with f o u r i e r transform infrared photoacoustic spectroscopy (FT-IR/PAS) in our laboratory. The d i s t r i b u t i o n of chemical a d d i t i v e s i n t o cotton yarns and f a b r i c s was determined using FT-IR/PAS. It i s concluded that FT-IR/PAS is a non-destructive and information-rich analytical technique which is uniquely suitable to the near-surface characterization of a variety of cellulose textile materials. The fundamentals of FT-IR/PAS are also reviewed.

I n f r a r e d s p e c t r o s c o p y i s p r o b a b l y one o f t h e m o s t w i d e l y used i n s t r u m e n t a l methods by c e l l u l o s e chemists f o r i n v e s t i g a t i n g p h y s i c a l and c h e m i c a l p r o p e r t i e s . The f i r s t i n f r a r e d a b s o r p t i o n s p e c t r u m o f c o t t o n c e l l u l o s e was p u b l i s h e d by Rowen e t . a l . i n 19^7 [J_]. D u r i n g the f o l l o w i n g decade, i n f r a r e d s p e c t r o s c o p y was e x t e n s i v e l y a p p l i e d t o t h e a n a l y s i s o f c e l l u l o s e t e x t i l e s u s i n g sampling t e c h n i q u e s such as m i n e r a l o i l m u l l s [2-5] or f i l m s c a s t on g l a s s p l a t e s [6-7] . F o r many y e a r s , d i s p e r s i v e i n f r a r e d s p e c t r o s c o p y h a s been a p p l i e d t o study c h a r a c t e r i s t i c s o f c e l l u l o s e t e x t i l e m a t e r i a l s s u c h a s t h e c e l l u l o s e m o l e c u l a r o r i e n t a t i o n , hydrogen bonding, d e g r a d a t i o n and d e c o m p o s i t i o n p r o c e s s e s , and c h e m i c a l m o d i f i c a t i o n o f c o t t o n c e l l u l o s e [8-10]. T h e most commonly u s e d s a m p l i n g t e c h n i q u e f o r obtaining infrared absorption spectra of c e l l u l o s e t e x t i l e m a t e r i a l s i s t h e p o t a s s i u m bromide (KBr) p e l l e t method. T h i s t e c h n i q u e f i r s t was i n t r o d u c e d t o c e l l u l o s e a n a l y s i s i n 1 957 [ ν Π , m o d i f i e d l a t e r [12] , a n d h a s become a r o u t i n e and v e r s a t i l e procedure f o r o b t a i n i n g i n f r a r e d spectra of t e x t i l e s f o r both q u a l i t a t i v e and q u a n t i t a t i v e a n a l y s i s purposes [j_3]. A t t e n u a t e d t o t a l r e f l e c t a n c e (ATR) a l s o h a s been used t o o b t a i n i n f r a r e d a b s o r p t i o n s p e c t r a o f c e l l u l o s e t e x t i l e m a t e r i a l s [Jjl] . E v e n though t h e ATR t e c h n i q u e can be used t o study the s u r f a c e c h e m i s t r y o f t e x t i l e m a t e r i a l s , t h i s t e c h n i q u e o f t e n s u f f e r s from the poor c o n t a c t between samples and r e f l e c t i o n c r y s t a l s [15]. An a l t e r n a t i v e a p p r o a c h o f s a m p l e p r e p a r a t i o n f o r i n f r a r e d

0097-6156/87/0340-0214$06.00/0 © 1987 American Chemical Society

Atalla; The Structures of Cellulose ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


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Cellulose Textile Materials and FTIR Spectroscopy

215

t r a n s m i s s i o n measurements o f c e l l u l o s e was a l s o r e p o r t e d [ V6 ] . Other s a m p l i n g t e c h n i q u e s such as p r e p a r i n g a t h i n l a y e r o f p a r a l l e l f i b e r s sandwiched between two p l a t e s o f window m a t e r i a l s a l s o have been used to o b t a i n i n f r a r e d s p e c t r a o f t e x t i l e m a t e r i a l s [ 1 7 - 1 9 ] , b u t t h e s e t e c h n i q u e s u s u a l l y r e q u i r e a h i g h d e g r e e o f s k i l l and p a t i e n c e t o o b t a i n s p e c t r a of high q u a l i t y . F o u r i e r t r a n s f o r m i n f r a r e d s p e c t r o s c o p y ( F T - I R ) has b e e n d e v e l o p i n g r a p i d l y and has become more i m p o r t a n t i n t h e f i e l d o f a n a l y t i c a l s p e c t r o s c o p y d u r i n g the p a s t decade. I t r e c e n t l y has been introduced to c e l l u l o s e r e s e a r c h f o r the i d e n t i f i c a t i o n and q u a n t i t a t i v e a n a l y s i s o f f i n i s h i n g a g e n t s on c e l l u l o s e t e x t i l e s [20,21]. With the a s s i s t a n c e o f a l a r g e c a p a c i t y d a t a s y s t e m , F T - I R spectrometers have v a r i o u s a d v a n t a g e s over d i s p e r s i v e i n f r a r e d spectrometers. The m u l t i p l e x i n g a d v a n t a g e makes i t p o s s i b l e t o m e a s u r e a l l f r e q u e n c i e s s i m u l t a n e o u s l y , so i n f r a r e d s p e c t r a can be c o l l e c t e d at a much f a s t e r speed and the s i g n a l - t o - n o i s e (S/N) ratio f o r a g i v e n r e s o l u t i o n c a n be improved by i n c r e a s i n g the number o f scan. The throughput a d v a n t a g e o f F T - I R a l l o w s a l a r g e amount o f energy to r e a c h the d e t e c t o r , so a s i g n i f i c a n t improvement i n the S/N ratio results. A l s o , t h e u s e o f a He-Ne l a s e r i n t e r f e r o m e t e r t o r e f e r e n c e t h e p o s i t i o n o f a m o v i n g m i r r o r g r e a t l y i n c r e a s e s the accuracy of frequency determination, a l l o w i n g s p e c t r a l s u b t r a c t i o n t o become p r a c t i c a l f o r i d e n t i f y i n g c h e m i c a l s p e c i e s i n a m i x t u r e [ 2 2 ] . A l t h o u g h u l t r a v i o l e t and v i s i b l e p h o t a o c o u s t i c s p e c t r o s c o p y has b e e n u s e d by a n a l y t i c a l c h e m i s t s t o i n v e s t i g a t e s o l i d samples f o r many y e a r s , the p h o t o a c o u s t i c t e c h n i q u e was a p p l i e d t o t h e i n f r a r e d r e g i o n o n l y when p h o t o a c o u s t i c d e t e c t i o n was c o m b i n e d w i t h an i n t e r f e r o m e t e r and a l a r g e c a p a c i t y d a t a s y s t e m i n t h e l a t e 1 9 7 0 s . S i n c e t h e n , FT-IR/PAS has a t t r a c t e d c o n s i d e r a b l e i n t e r e s t due t o i t s many a d v a n t a g e s [ 2 3 - 2 5 ] . The h i g h o p t i c a l t h r o u g h p u t and the m u l t i p l e x i n g c h a r a c t e r i s t i c s made F T - I R / P A S a r o u t i n e a n a l y t i c a l t e c h n i q u e f o r q u a l i t a t i v e a n a l y s i s w i t h a d e s i r a b l e S/N r a t i o . A t y p i c a l F T - I R / P A S e x p e r i m e n t i s i l l u s t r a t e d i n F i g u r e s 1 and 2. IR r a d i a t i o n p a s s i n g through an i n t e r f e r o m e t e r i s m o d u l a t e d by a moving m i r r o r . The modulated IR beam i s then f o c u s e d onto a sample which i s s e a l e d i n s i d e a s m a l l v o l u m e c e l l ( F i g u r e 1 ) . This PAS s a m p l e c e l l has an o p t i c a l window f o r t r a n s m i t t i n g IR r a d i a t i o n i n the r e g i o n of i n t e r e s t , e.g., a KBr window f o r m i d - i n f r a r e d r a d i a t i o n o r a p o l y e t h y l e n e window f o r f a r - i n f r a r e d r a d i a t i o n ( F i g u r e 2 ) . The PAS c e l l a l s o c o n t a i n s a s e n s i t i v e m i c r o p h o n e f o r p h o t o a c o u s t i c signal detection (Figure 2). An i n f r a r e d t r a n s p a r e n t gas such as h e l i u m i s used t o f i l l the PAS c e l l t o c a r r y p h o t o a c o u s t i c s i g n a l s . The IR r a d i a t i o n a b s o r b e d by t h e s a m p l e i s c o n v e r t e d t o heat by a radiationless transfer process. When t h e h e a t p r o p o g a t e s t o t h e s a m p l e s u r f a c e and t r a n s f e r s a t t h e s a m p l e - g a s i n t e r f a c e i n t o the s u r r o u n d i n g gas, p r e s s u r e v a r i a t i o n s o f the gas are g e n e r a t e d because t h e i n t e n s i t y o f the IR r a d i a t i o n i s modulated by the i n t e r f e r o m e t e r at an a u d i o f r e q u e n c y r e g i o n . T h i s p h o t o a c o u s t i c s i g n a l i s d e t e c t e d by t h e m i c r o p h o n e , and p r e a m p l i f i e d i n t h e PAS s a m p l e c e l l u n i t ( F i g u r e 2 ) . The e l e c t r i c s i g n a l i s s u b s e q u e n t l y F o u r i e r - t r a n s f o r m e d by t h e d a t a system t o y i e l d a s i n g l e beam FT-IR/PAS spectrum ( F i g u r e 1). Carbon b l a c k i s n o r m a l l y used as a r e f e r e n c e m a t e r i a l b e c a u s e a l l IR r a d i a t i o n can be a b s o r b e d by c a r b o n b l a c k and c o n v e r t e d t o photoacoustic s i g n a l s .


216

THE STRUCTURES OF CELLULOSE

IR S O U R C E

DATA

ι—>

SYSTEM

electrical signal

Î

RECORDER

electrical signal


_

u

η

m o d u l a t e d IR beam

I NTERFEROMETER

F i g u r e 1. Schematic spectrometer.

PAS SAMPLE

of a Fourier

CELL

transform

infrared

KBr WINDOW!

•

XI

GAS

MODULATED IR

BEAM T O DATA SYSTEM

-0 PRE MICROPHONE

AMPLIFIER

PHOTOACOUSTIC SIGNAL

P O W E R SUPPLY

F i g u r e 2.

S c h e m a t i c o f a p h o t o a c o u s t i c sample c e l l

unit.



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From t h e a b o v e PAS s i g n a l g e n e r a t i o n sequence, i t can be seen t h a t opaque m a t e r i a l s or h i g h l y s c a t t e r i n g s a m p l e s c a n be m e a s u r e d u s i n g F T - I R / P A S w i t h o u t sample p r e p a r a t i o n and the sample i n t e g r i t y i s maintained d u r i n g the e x p e r i m e n t . This i s impossible for c o n v e n t i o n a l i n f r a r e d sampling techniques. D i f f i c u l t i e s due t o poor c o n t a c t b e t w e e n s a m p l e s and r e f l e c t i o n e l e m e n t s common t o ATR experiments i s no l o n g e r a problem f o r FT-IR/PAS because p h o t o a c o u s t i c s i g n a l s a r e d i r e c t l y d e t e c t e d by a m i c r o p h o n e w i t h o u t u s i n g any r e f l e c t i o n elements and p h o t o d e t e c t o r . For thermally t h i c k s a m p l e s , i . e . , when s a m p l e t h i c k n e s s i s g r e a t e r t h a n thermal d i f f u s i o n l e n g t h , o n l y t h e h e a t g e n e r a t e d w i t h i n the f i r s t t h e r m a l d i f f u s i o n l e n g t h can propogate t o the heat t r a n s f e r s u r f a c e and cause p h o t o a c o u s t i c s i g n a l s . C o n s e q u e n t l y , FT-IR/PAS can be used t o study the chemistry of s o l i d s u r f a c e l a y e r s . T h i s i s another major a d v a n t a g e of FT-IR/PAS o v e r c o n v e n t i o n a l i n f r a r e d techniques. The t h e r m a l d i f f u s i o n l e n g t h (y ) i n cm c a n be c a l c u l a t e d as f o l l o w s [26]; 3

y

-

(-^-)

S

1 / 2

(1)

pCU)

Whierj* k _js the sample 's t h e r m a l conductivity in cal*cm -s -°C , ρ i s t h e s a m p l e ' s d e n s i t y i n g-cm , c i s the s a m p l e ' s s p e c i f i c h e a t i n CJLI · g -°C a n d ω i s the angular modulation frequency i n r a d i a n - s . The a n g u l a r m o d u l a t i o n f r e q u e n c y ω can be c a l c u l a t e d from the m o d u l a t i o n f r e q u e n c y f i n H e r t z , as the following: ω = 2*f

(2)

f

(3)

= vel-v 1

w h e r e v e l i s the o p t i c a l v e l o c i t y o f an i n t e r f e r o m e t e r i n ^ m - s and ν i s t h e f r e q u e n c y o f IR r a d i a t i o n i n wavenumbers (cm ). In a G e n z e l d e s i g n i n t e r f e r o m e t e r , which was used i n our e x p e r i m e n t s , the o p t i c a l v e l o c i t y i s e q u i v a l e n t t o f o u r t i m e s the m i r r o r v e l o c i t y . By c o m b i n i n g E q u a t i o n s 1-3, i t c a n be s e e n t h a t t h e r m a l d i f f u s i o n l e n g t h i s i n v e r s e l y p r o p o r t i o n a l t o the s q u a r e r o o t o f t h e product o f o p t i c a l v e l o c i t y a n d w a v e n u m b e r o f IR r a d i a t i o n . T h e r e f o r e , t h e r m a l d i f f u s i o n l e n g t h can be v a r i e d by c h a n g i n g t h e o p t i c a l v e l o c i t y o f the i n t e r f e r o m e t e r . F o r o p t i c a l l y opaque and t h e r m a l l y t h i c k samples, i . e . , when b o t h o p t i c a l p e n e t r a t i o n l e n g t h and t h e r m a l d i f f u s i o n l e n g t h a r e s m a l l e r than the sample t h i c k n e s s , the PAS e f f e c t i v e s a m p l i n g depth can be changed by a p p l y i n g d i f f e r e n t m i r r o r v e l o c i t i e s i f the o p t i c a l p e n e t r a t i o n l e n g t h i s g r e a t e r than the thermal d i f f u s i o n l e n g t h . T h e r e f o r e , sample s u r f a c e l a y e r s w i t h d i f f e r e n t t h i c k n e s s e s can be examined by PAS, and the p e n e t r a t i o n o f c h e m i c a l a d d i t i v e s i n the s u r f a c e l a y e r s o f c e l l u l o s e textile m a t e r i a l s can be i n v e s t i g a t e d by t h i s depth p r o f i l i n g t e c h n i q u e [ 2 7 ] . T h i s i n f o r m a t i o n i s of i n t e r e s t i n t e x t i l e r e s e a r c h , but i t i s d i f f i c u l t t o o b t a i n by o t h e r n o n - d e s t r u c t i v e a n a l y t i c a l t e c h n i q u e s . A v a r i e t y o f c e l l u l o s e t e x t i l e m a t e r i a l s were s t u d i e d u s i n g FTIR/PAS i n our l a b o r a t o r y . The d i s t r i b u t i o n o f s i z i n g agents and f i n i s h i n g agents i n c o t t o n y a r n s and f a b r i c s was determined. The r e s u l t s o f these i n v e s t i g a t i o n s a r e p r e s e n t e d here.


218


Experimental An IBM IR-98 s p e c t r o m e t e r was used f o r a l l FT-IR/PAS measurements. The p h o t o a c o u s t i c c e l l used was b u i l t ^ a t Ames L a b o r a t o r y . Resolution for a l l PAS m e a s u r e m e n t s was 8 cm , and no smoothing f u n c t i o n was used. Helium p a s s i n g t h r o u g h a l i q u i d n i t r o g e n t r a p was u s e d t o p u r g e t h e s a m p l e chamber and as c o n d u c t i n g gas i n s i d e the PAS c e l l . Carbon b l a c k was used as a r e f e r e n c e m a t e r i a l . O p t i c a l v e l o c i t i e s c o r r e s p o n d i n g t o v a r i o u s m i r r o r v e l o c i t i e s o f the i n t e r f e r o m e t e r are presented in Table I .


Table

Velocity 0 1 2 3 4

I.

Scan V e l o c i t y

Mirror Velocity (cm* s ) 0.059 0.070 0.083 0.099 0.118

o f IBM

Optical Velocity (cm*s ) 0.235 0.280

IR-98 FT-IR

Velocity 5 6 7 8 9

0.333 0.396 0.470

Spectrometer

Mirror Velocity (cm·s ) 0.140 0.166 0.198 0.236 0.280

Optical Velocity (cm*s ) 0.559 0.665 0.791 0.9^1 1.119

The c o t t o n yarns s i z e d w i t h v a r i o u s p o l y m e r i c s i z i n g agents were p r o v i d e d by S o u t h e r n R e g i o n a l R e s e a r c h C e n t e r , U.S. Department o f Agriculture. These yarns had been s i z e d on a l a b o r a t o r y s i n g l e - e n d slasher. P o r t i o n s o f t h e s i z e d y a r n s a l s o had been s u b j e c t e d t o a d e s i z i n g p r o c e s s i n v o l v i n g a b o i l - o f f w i t h 0.5% sodium h y d r o x i d e . The c o t t o n f a b r i c s were t r e a t e d u s i n g c o n v e n t i o n a l p a d d i n g and f o a m - f i n i s h i n g t e c h n i q u e s by U n i t e d Merchants and M a n u f a c t u r e r s . The two f i n i s h i n g a g e n t s u s e d h a v e t h e t r a d e n a m e s o f V a l r e z 248 and V a l r e z ULF. V a l r e z 248 i s d i m e t h y l o l d i h y d r o x y e t h y l e n e u r e a (DMDHEU) w i t h the f o l l o w i n g s t r u c t u r e :

Ο

, ι

HO-CHo-N ι

>J-CH -OH 2

ι

HO-C-C-OH

The hydroxymethyl g r o u p s i n DMDHEU w e r e m e t h y l a t e d t o f o r m V a l r e z ULF. F i b e r s w i t h a c e l l u l o s e t r i a c e t a t e c o r e and a c e l l u l o s e s k i n w e r e p r e p a r e d by p a r t i a l l y s a p o n i f y i n g c e l l u l o s e t r i a c e t a t e f i b e r s f o l l o w i n g a c o n v e n t i o n a l p r o c e d u r e by the use o f a hot, s t r o n g sodium hydroxide s o l u t i o n [28]. To d e t e r m i n e the t h i c k n e s s e s o f the s k i n and the c o r e , t h e f i b e r s were d y e d w i t h C. I . D i r e c t G r e e n 26 so c e l l u l o s e was d y e d more d e e p l y t h a n t r i a c e t a t e . T h i c k n e s s o f the c e l l u l o s e s k i n was measured by o p t i c a l m i c r o s c o p y a f t e r f i b e r c r o s s


13.

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219

s e c t i o n s were p r e p a r e d from the dyed f i b e r s . The f i b e r s were found t o h a v e d i a m e t e r o f a p p r o x i m a t e l y 18 ym and s k i n t h i c k n e s s e s o f a p p r o x i m a t e l y 2 ym. R e s u l t s and D i s c u s s i o n Near S u r f a c e A n a l y s i s . A c e l l u l o s e f i b e r , a c e l l u l o s e t r i a c e t a t e f i b e r and a f i b e r w i t h a c e l l u l o s e s k i n and a t r i a c e t a t e c o r e w e r e s t u d i e d u s i n g FT-IR/PAS ( F i g u r e 3). The s p e c t r a l c h a r a c t e r i s t i c s o f b o t h the c e l l u l o s e and the c e l l u l o s e t r i a c e t a t e f i b e r s ( F i g u r e s 3A and 3 B ) a r e r e v e a l e d i n the spectrum of the c e l l u l o s e s k i n - c e l l u l o s e t r i a c e t a t e core f i b e r ( F i g u r e 3 θ where the s t r o n g h y d r o g e n - b o n d e d OH s t r e t c h i n g peak around 3300 cm i s due t o the c e l l u l o s e s k i n , and t h e s t r o n g c a r b o n y l s t r e t c h i n g peak a t 1730 cm i s due t o t h e c e l l u l o s e t r i a c e t a t e underneath the s k i n . S i n c e the thermal d i f f u s i o n l e n g t h o f c e l l u l o s e at scan v e l o c i t y 0 i s a p p r o x i m a t e l y 412 urn i n t h e mid i n f r a r e d f r e q u e n c y range (4000-400 cm ), which i s l a r g e r than the s k i n t h i c k n e s s (2 ym), b o t h t h e c e l l u l o s e s k i n and the c e l l u l o s e t r i a c e t a t e c o r e can be d e t e c t e d by FTj-IR/PAS. However, the i n t e n s i t y o f t h e c a r b o n y l peak a t 173.9 r e l a t i v e t o the i n t e n s i t y o f t h e s t r o n g e s t peak a t 1045 cm i n the spectrum o f the s k i n - c o r e sample ( F i g u r e 3C) i s lower t h a n t h a t i n t h e s p e c t r u m of p u r e c e l l u l o s e t r i a c e t a t e ( F i g u r e 3 B ) , because l e s s c e l l u l o s e t r i a c e t a t e was d e t e c t e d by PAS i n the s k i n - c o r e sample. I n t h e t e x t i l e i n d u s t r y , s i z i n g agents are g e n e r a l l y a p p l i e d t o warp yarns t o i n c r e a s e t h e i r a b r a s i o n r e s i s t a n c e d u r i n g w e a v i n g . A f t e r weaving i s completed, s i z i n g agents a r e removed t h r o u g h a d e s i z i n g p r o c e s s t o o b t a i n d e s i r e d y a r n p r o p e r t i e s . In our r e s e a r c h , a p u r e c o t t o n y a r n and a c o t t o n y a r n s i z e d w i t h a p o l y u r e t h a n e were examined by^PAS a t v e l o c i t y 0 ( F i g u r e s 4A and 4 B ) . An i n t e n s e peak a t 1730 cm o b s e r v e d i n F i g u r e 4B was due t o the c a r b o n y l s t r e t c h i n g o f the p o l y u r e t h a n e s i z i n g a g e n t . The s i z e d c o t t o n y a r n was then g r o u n d i n t o a powder t o pass a 40-mesh s c r e e n and re-examined by FTIR/PAS a t v e l o c i t y 0 ( F i g u r e 4 C ) . I t can be seen t h a t the i n t e n s i t y o f t h e c a r b o n y l p e a k o f t h e powder s a m p l e ( F i g u r e 4C) was g r e a t l y r e d u c e d compared w i t h t h a t o f t h e w h o l e y a r n s a m p l e ( F i g u r e 4 B ) . S i n c e p h o t o a c o u s t i c s i g n a l s a r e g e n e r a t e d o n l y from the s u b s t a n c e s w i t h i n one thermal d i f f u s i o n l e n g t h t h i c k n e s s , the i n f r a r e d spectrum o f t h e s i z e d y a r n ( F i g u r e 4B) p r o v i d e s i n f o r m a t i o n o f the c h e m i c a l c o m p o s i t i o n o f the s u b s t a n c e s w i t h i n a few m i c r o n s s u r f a c e l a y e r . Upon g r i n d i n g t h e s a m p l e , h o w e v e r , t h e s u r f a c e l a y e r and the bulk were mixed and averaged. Because the diameter o f the c o t t o n y a r n i s a p p r o x i m a t e l y 350 ym, the amount o f s u b s t a n c e s w i t h i n a few microns s u r f a c e l a y e r i s v e r y s m a l l compared t o the amount o f s u b s t a n c e s i n t h e b u l k ; t h e r e f o r e , t h e i n f r a r e d s p e c t r u m o f t h e powder sample ( F i g u r e 4C) r e p r e s e n t s m a i n l y the c h e m i c a l c o m p o s i t i o n o f t h e b u l k . The o b s e r v a t i o n t h a t the c a r b o n y l peak f o r the y a r n sample i n F i g u r e 4B was much more i n t e n s e than the same peak f o r the powder s a m p l e i n F i g u r e 4C d e m o n s t r a t e s a h i g h e r c o n c e n t r a t i o n o f the p o l y u r e t h a n e s i z i n g agent i n the s u r f a c e l a y e r o f the y a r n than i n the b u l k . This suggests t h a t the s i z i n g p r o c e s s d i d not r e s u l t i n uniform d i s t r i b u t i o n o f the p o l y u r e t h a n e s i z i n g a g e n t i n t o t h e y a r n b u l k . S i n c e t h e w e a v i n g p e r f o r m a n c e o f s i z e d yarns i s g r e a t l y a f f e c t e d by s i z e p e n e t r a t i o n , F T - I R / P A S a p p e a r s t o be a v a l u a b l e t o o l f o r studying s i z i n g processes.


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