4 W a s h i n g M e t h o d s for C o t t o n
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Effects on Fiber, Processing Qualities, and Dust Generation HENRY H. PERKINS, JR. and JOSEPH B. COCKE U.S. Department of Agriculture, Agricultural Research Service, Cotton Quality Research Station, Clemson, SC 29631 Thoroughly washed cotton generates less dust in pro cessing and is biologically less active than un washed cotton and has been exempted from the OSHA cotton dust standard. Cottons washed under differ ent conditions of time, temperature, detergency, and fiber finish were evaluated for effects on noncellulosic constituents, fiber properties, dust genera tion, and processing and yarn qualities. The more severe washing treatments adversely affected fiber properties and caused removal of large percentages of the natural waxes. The milder washing treatments did not affect fiber properties and left the natu ral waxes intact. A l l washing treatments reduced dust levels generated in processing. The effects of washing on processing and yarn qualities were vari able and generally somewhat adverse, but the yarns produced were of acceptable commercial quality. Washed c o t t o n i s b i o l o g i c a l l y l e s s a c t i v e and generates l e s s dust i n p r o c e s s i n g than unwashed c o t t o n ( 1 ) . Thoroughly washed cotton has been exempted from coverage by the OSHA c o t t o n dust standard ( 2 ) . The washing c o n d i t i o n s s p e c i f i e d i n the dust standard are vague and i n c l u d e statements such as: (1) "Washed cotton means cotton which has been thoroughly washed i n hot water and i s known i n the cotton trade as p u r i f i e d or dyed," and (2) "The washing process can be as simple as the water washing of baled cotton w i t h w e t t i n g agent as described by Merchant e t a l . (1), o r as elaborate as b l e a c h i n g and p u r i f y i n g processes commonl y p r a c t i c e d i n the h e a l t h products i n d u s t r y " . The wash c o n d i t i o n s described by Merchant are 30 minutes a t the b o i l a t pH 12. Any c o n d i t i o n s l e s s severe than t h i s r e q u i r e v e r i f i c a t i o n f o r e f f e c t i v e n e s s . The c o n d i t i o n s mentioned i n the standard are more severe than are e i t h e r economically o r t e c h n i c a l l y acceptable t o the t e x t i l e i n d u s t r y . Research i s a c t i v e to determine whether economically and t e c h n i c a l l y f e a s i b l e washing This chapter not subject to U.S. copyright. Published 1982 American Chemical Society.
Montalvo; Cotton Dust ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
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c o n d i t i o n s l e s s severe than those s t a t e d can be e f f e c t i v e i n p u r i f y i n g c o t t o n to an acceptable l e v e l of b i o l o g i c a l a c t i v i t y and dust generation p o t e n t i a l . I f acceptable washing c o n d i t i o n s can be achieved, then proc e s s i n g washed c o t t o n may be a r e a l i s t i c long term method f o r d e a l i n g w i t h the dust standard and f o r i n s u r i n g worker s a f e t y and h e a l t h , f o r a t l e a s t some segments of the t e x t i l e i n d u s t r y . Both independently and i n c o n j u n c t i o n w i t h Cotton Incorpor a t e d and i n d u s t r y , USDA has conducted l a b o r a t o r y , p i l o t - s c a l e , and p r o d u c t i o n - s c a l e washing t r i a l s to determine the e f f e c t s of washing on: (1) the l e v e l s of n o n c e l l u l o s i c c o n s t i t u e n t s removed from the c o t t o n , (2) f i b e r p r o p e r t i e s , (3) dust l e v e l s , and (4) p r o c e s s i n g q u a l i t y . Some r e s u l t s have been reported p r e v i o u s l y (3). The washing methods and s i g n i f i c a n t f i n d i n g s a r e d e s c r i b e d and summarized i n t h i s r e p o r t and represent our understanding of the current s t a t e - o f - t h e - a r t of c o t t o n washing. Cotton has been washed by d i f f e r e n t processes or methods as follows: •Laboratory •Rayon washing l i n e , r a i n pan w e t t i n g of a b a t t of cotton - p i l o t - s c a l e . •Batch process - production k i e r s . •Wool scouring process - c o t t o n submerged. Laboratory Washing Conditions F i f t y g c o t t o n samples were washed w i t h vigorous s t i r r i n g f o r 5 minutes i n a 0.1% s o l u t i o n of a n o n i o n i c w e t t i n g agent a t 38°, 60°, 80°, and 100°C. W a t e r - t o - f i b e r r a t i o was 50/1. Each sample was r i n s e d i n two changes of water a t the same temperature as the wash and a i r - d r i e d . Contents of reducing sugars, wax (as determined by 1,1,1-trichloroethane e x t r a c t i o n ) , and e t h y l a l c o h o l - e x t r a c t a b l e s were determined f o r the washed cottons and the unwashed c o n t r o l (4_). Reducing sugar content decreased from 0.31% f o r the unwashed c o t t o n to 0.02% f o r a l l washing treatments. As washing temperature i n c r e a s e d , the l e v e l of wax remaining on the f i b e r s t e a d i l y decreased from 0.5% f o r the c o n t r o l to l e s s than 0.2% f o r the cottons washed a t 100C (Figure 1 ) . The mechani c a l a c t i o n and enhanced e m u l s i f i c a t i o n c o n d i t i o n s created by the s t i r r i n g apparently were p a r t l y r e s p o n s i b l e f o r the decreases i n wax content, because i n other washing t r i a l s i n v o l v i n g h i g h temperatures but minimal mechanical a c t i o n , decreases i n wax content were not l a r g e . The l e v e l of a l c o h o l - e x t r a c t a b l e s remaining on the f i b e r a l s o decreased as washing temperature increased (Figure 2 ) . However, the q u a n t i t y of m a t e r i a l removed a t the lowest wash temperature was s i g n i f i c a n t and d i d not i n c r e a s e markedly w i t h i n c r e a s e s i n wash temperature. Apparently, l i t t l e would be gained i n u s i n g the higher temperatures to remove these types of e x t r a c t a b l e s . Washing temperatures above 60°C tended to lower f i b e r l e n g t h
Montalvo; Cotton Dust ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
PERKINS
A N D COCKE
0.5
Washing Methods for Cotton
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WASH TEMPERATURE (°C) Figure 1.
Plot of wax content vs. wash temperature. Laboratory washing conditions. Key: O unwashed; #, washed.
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