Technology For Pre-Textile Cotton Cleaning - ACS Publications

2 T e c h n o l o g y For P r e - T e x t i l e C o t t o n

Cleaning

Downloaded by YORK UNIV on June 3, 2018 | https://pubs.acs.org Publication Date: July 1, 1982 | doi: 10.1021/bk-1982-0189.ch002

WILLIAM F. LALOR Cotton Incorporated, Raleigh, NC 27612

When cotton bolls open, the production phase is over and the processing phase begins. At boll opening, the fiber is virtually free of visible foreign matter. Like many natural products, cotton becomes contaminated during the preharvest and harvest periods and has to be cleaned during the processing phase before marketing. This paper is a review of how cotton becomes con taminated, nature of the foreign matter found in cotton, and importance of clean cotton with respect to textile performance of the fiber. Strategies to prevent contamination of cotton during harvesting w i l l be examined. Currently used cleaning techniques w i l l be reviewed and current research to clean cotton w i l l be dis cussed briefly. Regulations promulgated by OSHA (1) t o l i m i t the amount o f cotton dust t o which t e x t i l e workers are exposed, c o n s t i t u t e the p r i n c i p a l new aspect of c o t t o n c l e a n i n g i n the 1980s. I t should be emphasized, however, that even though high dust l e v e l s i n m i l l s are a s s o c i a t e d w i t h high f o r e i g n matter l e v e l s i n l i n t ( 2 ) , i t i s u n l i k e l y that any g i n - a p p l i e d c l e a n i n g measure w i l l alone permit f u l l compliance w i t h current OSHA standards ( 3 ) . This leaves researchers w i t h the c o n c l u s i o n that compliance w i t h the OSHA standards w i l l l i k e l y be the r e s u l t of a p p l y i n g s e v e r a l proven d u s t - c o n t r o l measures during f i b e r processing ^4)• Furthermore, a recent p u b l i c a t i o n by F i s c h e r , Morey, and Sasser (_5) presents data showing a very poor r e l a t i o n s h i p between v i s u a l t r a s h r a t i n g of f i b e r samples and the presence of gram-negative o r g a n i s m s — a p o s s i b l e causative agent of b y s s i n o s i s . L i n t c l e a n i n g per se i s not t h e r e f o r e l i k e l y t o solve h e a l t h problems a r i s i n g out of cotton-dust exposure but l i n t c l e a n i n g w i l l

©

0097-6156/82/0189-0011 $6.00/0 1982 American Chemical Society

Montalvo; Cotton Dust ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

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nevertheless play a prominent r o l l i n the p r e p a r a t i o n of c o t t o n f o r markets of the 1980s and beyond.


Trash C o n s t i t u e n t s Morey, Sasser, Bethea, and Kopetzky (6) examined and c l a s s i f i e d the p l a n t p a r t s i n S h i r l e y analyzer waste from s i x raw cottons that had been processed through the model card room at North C a r o l i n a State U n i v e r s i t y . B r a c t , l e a f , weeds, veins and endocarp were the major p l a n t parts present. Bract and l e a f c o n s t i t u t e d up to 52 percent of the f o r e i g n matter i n the cottons they examined. There was evidence that using g i n l i n t cleaners reduced the t o t a l t r a s h content but increased the p r o p o r t i o n of bract r e l a t i v e to other foreign-matter p a r t i c l e s remaining i n the fiber. The l e a f - l i k e m a t e r i a l i n other samples examined was 58 percent b r a c t , 22 percent c o t t o n l e a f and 20 percent weed l e a f (7)• Morey c a l c u l a t e d that a bale of c o t t o n could c o n t a i n the e q u i v a l e n t of up to 50,000 b r a c t s , depending on grade. At harvest time, about three m i l l i o n b r a c t s were found on the p l a n t s that would y i e l d harvested m a t e r i a l f o r one b a l e . The b r a c t removal e f f i c i e n c y of commerical h a r v e s t i n g and g i n n i n g i s t h e r e f o r e extremely h i g h . L e a f l i k e t r a s h , e s p e c i a l l y the b r a c t , was shown to be e a s i l y subdivided i n t o p a r t i c l e s l e s s than 10 microns i n s i z e by processing i n a l a b o r a t o r y m i l l (_8) • Equipment i n gins and i n t e x t i l e m i l l s can be expected to produce the same g r i n d i n g e f f e c t . P a r t i c l e s l e s s than 15 microns i n s i z e are the target of cotton-dust r e g u l a t i o n s a p p l i c a b l e to areas where c o t t o n i s being processed. Preventing processing equipment from c r e a t i n g r e s p i r a b l e - s i z e p a r t i c l e s from b i g p a r t i c l e s i s , t h e r e f o r e , very important. Preventing Contamination Because mechanical c l e a n i n g of f i b e r almost always r e s u l t s i n some f i b e r damage, prevention of contamination by f o r e i g n matter i s p r e f e r a b l e to u s i n g machines subsequently to remove the contaminants. Preventive c u l t u r a l p r a c t i c e s are t h e r e f o r e of great importance because they have a bearing on the l e a f content of harvested m a t e r i a l . Approximately one-fourth of the s m a l l e r t r a s h p a r t i c l e s s i f t e d from S h i r l e y - a n a l y z e r waste was found to be monootyledonous and dicotyledonous weed p a r t s ( 7_, 8_, 9) • Leaf p a r t i c l e s are very d i f f i c u l t to remove from the f i b e r e s p e c i a l l y i f they are from h a i r y l e a v e s — t h e l e a f h a i r s become entangled w i t h the c o t t o n f i b e r s . Bract p a r t i c l e s are h a i r y , and they become entangled w i t h f i b e r f o r the same reason. Apart from w o r k p l a c e - r e l a t e d problems l i k e c o t t o n dust, the presence of g r a s s , bark, sand, seeds and seed p a r t s i n l i n t causes grade r e d u c t i o n and a s s o c i a t e d reductions i n the market value of the f i b e r (10). For i n s t a n c e , unbleachable grass-seed



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glumes have been found as a disfigurement i n f i n i s h e d f a b r i c . The presence of grass causes d e t e r i o r a t i o n i n yarn q u a l i t l y and an i n c r e a s e i n ends down during s p i n n i n g (11)• Because of the importance of weed p a r t s as a t r a s h component, weed and grass c o n t r o l during the production phase i s extremely important. I t may be concluded (12) that i f there i s grass i n the f i e l d , there i s l i k e l y to be grass i n the f i b e r . Broad-leaf-weed and grass c o n t r o l i n the f i e l d p r o v i d e , t h e r e f o r e , the f i r s t e f f e c t i v e o p p o r t u n i t y a v a i l a b l e to reduce the f o r e i g n matter content of ginned f i b e r . The design of production systems f o r c o t t o n i s being re-examined a t t h i s time w i t h the o b j e c t i v e of ensuring maximum p r o d u c t i v i t y . System-related f a c t o r s can p l a y important r o l e s i n determining the cleanness of c o t t o n . Wanjura and Baker (13) found that row spacing a f f e c t s the s t i c k content of s t r i p p e r harvested c o t t o n — s t i c k content was lower f o r narrower rows. V a r i e t a l c h a r a c t e r i s t i c s have a l s o been shown to be important. Morey, Sasser, Bethea, and Kopetzky (6) showed that v a r i e t i e s , h a r v e s t i n g methods and g i n n i n g procedures a f f e c t the type and amount o f t r a s h i n l i n t c o t t o n . Some v a r i e t i e s are h a i r y and l i n t becomes entangled i n l e a f h a i r s , g r e a t l y i n c r e a s i n g the d i f f i c u l t y of s e p a r a t i n g the f i b e r from f o r e i g n matter. Openboll types tend to have more s m a l l p a r t i c l e s e n t r a i n e d i n the f i b e r than do the more storm-proof types which have less-open b o l l s (14)• Because bract content of the f o r e i g n matter seems so important, the development of caducous-bract c o t t o n types i s r e c e i v i n g p a r t i c u l a r a t t e n t i o n (15). I r r i g a t i o n i s a f a c t o r i n c u l t u r a l p r a c t i c e s that are used i n the Southwest and West. I r r i g a t i o n i s beginning to be used i n other areas. Because i r r i g a t e d crops tend to have higher moisture content than n o n - i r r i g a t e d crops, the f o r e i g n matter content of f i b e r could be a f f e c t e d . Cleaning e f f i c i e n c y i s reduced when moisture contents of seed c o t t o n and f i b e r are e l e v a t e d d u r i n g g i n n i n g and c l e a n i n g (see l a t e r ) . Whether the crop i s i r r i g a t e d or r a i n grown i s a l s o important i n determining the preharvest p r e p a r a t i o n that leads to lowest t r a s h content i n ginned l i n t . P r o f i t i s the m o t i v a t i o n f o r c o t t o n p r o d u c t i o n . Production p r a c t i c e s w i l l t h e r e f o r e be responses to market c o n d i t i o n s . The extent to which there are premiums f o r c l e a n c o t t o n and f o r c o t t o n that i s u n l i k e l y to produce a l o t of dust w i l l determine the production and h a r v e s t i n g p r a c t i c e s used. P r i c e w i l l a l s o a f f e c t the amount of processing to which the c o t t o n w i l l be subm i t t e d before shipment to m i l l s . Because of c o s t / p r o f i t r e l a t i o n s h i p s , f o r example, h a r v e s t i n g methods vary w i t h c u l t u r a l p r a c t i c e s . About 30 percent of the U. S. cotton crop i s s t r i p p e r - h a r v e s t e d . In Texas, more than 80 percent of the c o t t o n i s s t r i p p e r - h a r v e s t e d because of crop c u l t u r e , low h a r v e s t i n g c o s t , and high h a r v e s t i n g capacity associated with strippers.



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Large d i f f e r e n c e s i n the amount of harvested m a t e r i a l r e q u i r e d to y i e l d a bale of f i b e r c o n s t i t u t e the main d i f f e r e n c e between the two h a r v e s t i n g methods. During s p i n d l e - p i c k i n g , about 680 kg of harvested m a t e r i a l are gathered to produce one 218-kg bale of f i b e r . Most of the burs, penducles and stem m a t e r i a l are l e f t on the p l a n t . This method of h a r v e s t i n g i s the more commonly used i n the i r r i g a t e d west and i n the r a i n b e l t areas of the south and southeast. Harvesting by means of s t r i p p e r s i s p r a c t i c e d mainly i n West Texas and the a d j o i n i n g areas of Oklahoma and New Mexico. This method has a l s o gained great importance i n the C o a s t a l Bend area of Texas. Because a s t r i p p e r h a r v e s t e r (whether a f i n g e r s t r i p p e r or a brush s t r i p p e r ) removes almost a l l v e g e t a t i v e m a t e r i a l from the p l a n t (except f o r the c e n t r a l stem and major branches), about 1100 kg of harvested m a t e r i a l are brought to the gin to y i e l d one 218-kg bale of l i n t . The l i n t t h e r e f o r e i s approximately o n e - t h i r d of the harvested m a t e r i a l i n s p i n d l e picked c o t t o n and can be as l i t t l e as o n e - f i f t h i n s t r i p p e r harvested c o t t o n . Because of the cost advantages of s t r i p p e r h a r v e s t i n g , i t s use i s l i k e l y to i n c r e a s e . In M i s s i s s i p p i , approximately 25 percent of the t o t a l c o t t o n - p r o d u c t i o n cost was a t t r i b u t a b l e to s p i n d l e - p i c k e r h a r v e s t i n g i n 1979 ( 1 6 ) . Cost advantages i n f a v o r of s t r i p p e r h a r v e s t i n g and the c u l t u r a l system that accompanies i t are estimated to range from eleven to eighteen cents per k i l o of l i n t (17). The extent of the l i k e l y spread of s t r i p p e r h a r v e s t i n g w i l l depend upon the success achieved by p l a n t breeders and agronomists i n developing p l a n t types and c u l t u r a l systems a p p r o p r i a t e f o r s t r i p p e r h a r v e s t i n g . T r a n s p l a n t i n g c u l t u r a l p r a c t i c e s and h a r v e s t i n g methods from one geographic area to another i s not always s u c c e s s f u l . I t i s f o r t h i s reason that there are many r e p o r t s of s t r i p p e r - h a r v e s t e d c o t t o n having more t r a s h , more neps, more m i l l waste and more dust than c o t t o n from the same f i e l d s harvested w i t h a s p i n d l e p i c k e r . When used i n the a p p r o p r i a t e production system, however, s t r i p p e r h a r v e s t i n g i s an acceptable s t r a t e g y . The work by K i r k , C o r l e y , Kummer, Brashears, Hudspeth, L a i r d , and Baker (18-22) should be c a r e f u l l y reviewed i n s t u d y i n g a p p l i c a b i l i t y of s t r i p p e r - h a r v e s t i n g techniques to the r a i n b e l t areas. Regardless of h a r v e s t i n g method, s k i l l f u l management of the crop during the harvest season i s e s s e n t i a l to keep f o r e i g n matter content at a minimum. Using seed c o t t o n storage i s one way f o r farmers to a v a i l themselves of the very best h a r v e s t i n g c o n d i t i o n s . Harvesting when the crop i s ready i s extremely important. The h a r v e s t i n g - g i n n i n g system should be such that no producer f e e l s the need to harvest the crop under compromising circumstances i n order to g a i n a place i n the queue at the g i n . High moisture content i s the s i n g l e biggest problem that a r i s e s because of improper h a r v e s t i n g . Cocke (23) concluded that cotton harvested at high moisture content was extremely d i f f i c u l t



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to c l e a n and was put a t a permanent disadvantage by having been harvested damp. This disadvantage could not be e l i m i n a t e d by use of g i n d r y e r s . Dampness a t harvest r e s u l t s from r a i n , or from humidity from dew, or from moisture content of green m a t e r i a l harvested w i t h the f i b e r . The s k i l l f u l use of preharvest chemicals can reduce green-material content d r a m a t i c a l l y . Freezing a l s o causes p l a n t t i s s u e s t o d r y out. Unusually dry p l a n t s become b r i t t l e , however, and l e a d t o other c l e a n i n g problems ( 2A, _25) . Some s t r i p p e r harvesters are equipped w i t h onboard cleaners that have c l e a n i n g e f f e c t i v e n e s s of up t o 50 percent. Their c l e a n i n g e f f e c t i v e n e s s depends, however, on machine adjustment and on other f a c t o r s not y e t i d e n t i f i e d . In one t e s t , b i g d i f f e r e n c e s i n c l e a n i n g performance have been shown t o e x i s t between i d e n t i c a l harvesters operating under i d e n t i c a l f i e l d c o n d i t i o n s (26). This study i s c o n t i n u i n g and should lead t o improved stripper-mounted cleaner performance. In summary, good management and the a p p l i c a t i o n of e x i s t i n g technology t o h a r v e s t i n g and handling p r i o r t o g i n n i n g are the keys t o ensuring that the g i n n i n g process i s given every opport u n i t y to produce the highest q u a l i t y l i n t p o s s i b l e . Ginning Ginning per se i s the process of removing the f i b e r from the seed. The f o r c e r e q u i r e d t o remove an i n d i v i d u a l f i b e r from a seed depends on the v a r i e t y . I n t e r s p e c i f i c d i f f e r e n c e s e x i s t a l s o — t h e l i n t on pima c o t t o n has lower attachment s t r e n g t h r e l a t i v e t o f i b e r s t r e n g t h than do the upland types examined by Moore and G r i f f i n (27). This c h a r a c t e r i s t i c makes pima c o t t o n w e l l s u i t e d t o r o l l e r g i n n i n g , which i s a method of ginning p a r t i c u l a r l y appropriate f o r p r e s e r v i n g the e x t r a - l o n g - s t a p l e f i b e r p r o p e r t i e s of pima c o t t o n s . V i r t u a l l y a l l of the upland c o t t o n i n the United States i s ginned by saw g i n s . In saw g i n n i n g , the f i b e r s are engaged by the t e e t h of the saw and p u l l e d between c l o s e l y - s p a c e d r i b s . The seed i s too b i g t o pass between the r i b s , and the f i b e r i s consequently p u l l e d from the seed. This i s c l e a r l y a point a t which f i b e r damage could take p l a c e . The graph i n Figure 1 (27) shows the r e l a t i o n s h i p between moisture content and the f o r c e s r e q u i r e d to detach the f i b e r from the seed and to break the f i b e r . The height d i f f e r e n c e between the two curves i s the margin of s a f e t y between the f o r c e that must be a p p l i e d t o detach the f i b e r and the f o r c e that would r e s u l t i n breaking the f i b e r . This margin of s a f e t y can be seen to d i m i n i s h as moisture content decreases. In the d i s c u s s i o n s that f o l l o w , reference w i l l be made t o the d e s i r a b i l i t y of o b t a i n i n g the optimum d r y i n g e f f e c t . One f a c t o r i n the concept of "optimum d r y i n g " i s that of r e t a i n i n g the greatest margin of s a f e t y p o s s i b l e between f i b e r breakage f o r c e and f i b e r s e p a r a t i o n f o r c e .



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Technology For Pre-Textile Cotton Cleaning - ACS Publications

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