11 Shrink-Resist Polymers for Wool: A Comparative
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Study of Reactive Poly(Alkylene Oxides) for Pad Application DAVID J. KILPATRICK, JOHN A. RIPPON, MICHAEL A. RUSHFORTH, and TREVOR SHAW IWS Technical Centre, Valley Drive, Ilkley, West Yorkshire, LS29 8PB, England In recent years the commercial importance of polymer shrink-resist processes for wool has increased considerably, until, at the time of writing, approximately half the world production of SR wool is polymer treated, the remainder being treated by the older and less effective oxidative processes. Shrink-resist polymers may be applied to wool at any stage of manufacture, from loose stock to garments, but treatment of tops or slivers, fabrics and garments ace of most commercial significance. The polymer treatments which are in industrial use may be divided into two types - those in which prechlorination of the wool is a necessary part of the process (1) and those in which prechlorination is not required (2-7). There are fundamental differences between these two types of process with regard to the polymers used and the mechanism by which shrink-resistance is conferred on the treated goods. From the practical point of view, the chlorination/resin processes have the disadvantages mainly associated with the chlorination step, which degrades and therefore weakens the wool fibre and makes dyeing to high standards of wet-fastness more difficult. But the overriding advantage of these processes is that they are applicable to a wider range of substrates by convenient processing techniques. Thus chlorination/resin processes are effective on tops or slivers, but no polymer has yet been discovered which gives shrink-resistance when applied to unchlorinated tops. Again, long-liquor batch-exhaust processes of the chlorination/resin type have been in commercial use for the treatment of knitted garments for some years (l), whilst the development of a technology by which polymers may be exhausted from long liquor on to unchlorinated wool is still in its infancy (8). For these reasons chlorination/resin processes have been more successful in terms of weight of wool treated than the alternative processes by which polymers can be applied by padding techniques to unchlorinated woven or knitted fabrics, or to knitted garments in modified dry cleaning machines by dip176
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e x t r a c t - d r y methods. However, s i g n i f i c a n t developments have occurred i n recent years i n the technology o f the a p p l i c a t i o n o f prepolymers to u n c h l o r i n a t e d wool s u b s t r a t e s and i n the design and s y n t h e s i s o f polymers f o r t h i s purpose, typically, these prepolymers c o n s i s t o f a polymeric backbone w i t h t e r m i n a l r e a c t i v e groups. A f t e r a p p l i c a t i o n to the wool the products can be polymerised through these groups. I t i s the o b j e c t o f t h i s paper t o d i s c u s s these developments, and to attempt t o demonstrate how the p r o p e r t i e s o f the t r e a t e d wool, the s t a b i l i t y o f a p p l i c a t i o n baths, the c u r i n g c o n d i t i o n s r e q u i r e d and the s h e l f l i f e o f the polymer depend on i t s f u n c t i o n a l groups and other aspects o f i t s chemical s t r u c t u r e . Experimental M a t e r i a l s Wool F a b r i c s . The k n i t t e d f a b r i c used was s i n g l e j e r s e y , k n i t t e d from R74/2 tex 100% wool y a m to a t i g h t n e s s f a c t o r o f 13· The f a b r i c was scoured i n an aqueous s o l u t i o n o f L i s s a p o l IT (ICI, 1 g / l ) and sodium bicarbonate ( l g / l ) , at a liquor:goods r a t i o o f 40:1 f o r 20 min a t 40°C, f o l l o w e d by thorough r i n s i n g with water. The f a b r i c pH was 8. The woven f a b r i c was undyed, a l l - w o r s t e d , 2 X 2 t w i l l o f weight 192 g m-2 ( S a l t s o f S a l t a i r e L t d . , UK). The f a b r i c pH was 7·5· Polymers. These were s y n t h e s i s e d i n the l a b o r a t o r y , w i t h the exception o f the p o l y a c r y l a t e , Acramin SLN (Bayer), and Hercosett 57 (Hercules Powder Co). The s y n t h e t i c methods can be found i n the l i t e r a t u r e , as f o l l o w s : polythiomalate (2), polycarbamoyl sulphonate (p), p o l y i s o c y a n a t e (4) « p o l y t h i o s u l p h a t e (5)* p o l y t h i o g l y c o l l a t e (6) and polysulphonium bromide (7)* Other Reagents. The wetting agent used was T i n o v e t i n LB (Ciba-Geigy) and the e m u l s i f y i n g agent was L i s s a p o l NX ( I C I ) ; a l l other reagents were l a b o r a t o r y grade. Experimental Methods A p p l i c a t i o n o f Prepolymers to F a b r i c . Polymers IV and VI were e m u l s i f i e d w i t h L i s s a p o l IT (20% on weight o f polymer), and stock emulsions used to make up padding-strength emulsions w i t h other a d d i t i o n s (Table I I ) as r e q u i r e d . The remaining polymers were s o l u b l e i n the padding l i q u o r , and s o l u t i o n s were prepared immediately p r i o r to padding. S o l u t i o n s o r emulsions were padded onto weighed p i e c e s o f f a b r i c , u s i n g a l a b o r a t o r y padmangle, and the p i e c e s were subsequently reweighed to enable c a l c u l a t i o n o f the wet pick-up. They were then d r i e d i n a f o r c e d - a i r oven and steamed where necessary (see Table I I ) . H a l f o f each t r e a t e d sample was subjected to a simulated afterwash process c o n s i s t i n g o f 2 X 10 min c y c l e s i n 25 1 o f water i n an I n t e r n a t i o n a l Cubex wash
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t e s t i n g machine. The f a b r i c s were r e d r i e d at 100°C and f i n a l l y semi-decated (5 min steam). Test Methods. The f a b r i c s were wash t e s t e d 7 days a f t e r treatment. The f e l t i n g shrinkage t e s t c o n s i s t e d o f 180 min a g i t a t i o n i n the Cubex washing machine i n 15 l i t r e s o f pH 7 phosphate b u f f e r a t 40°C w i t h a 1 k g l o a d . A f t e r washing, samples were s p i n d r i e d , then l i n e d r i e d . Area shrinkage was determined by measuring p r e v i o u s l y a p p l i e d bench marks. Durable Press r a t i n g was assessed by comparison o f the f a b r i c s w i t h the AATCC r e p l i c a s (9) (D.P. r a t i n g s 1-5)· F l e x u r a l r i g i d i t y was measured by the c a n t i l e v e r bending l e n g t h method a c c o r d i n g to B r i t i s h Standard
3356:1961.
R e s u l t s and D i s c u s s i o n P r o p e r t i e s Required i n S h r i n k - R e s i s t Polymers. I t i s not d i f f i c u l t t o l i s t the c r i t e r i a which an i d e a l s h r i n k - r e s i s t polymer should s a t i s f y . T h i s l i s t c o n s i s t s o f two s e t s o f a t t r i b u t e s : one concerned w i t h the ease o f a p p l i c a t i o n o f the polymer and the other w i t h the performance and p r o p e r t i e s o f the treated f a b r i c . Since i t i s intended to d i s c u s s the polymers examined i n t h i s paper i n terms o f how n e a r l y they s a t i s f y these c r i t e r i a , i t i s as w e l l , a t t h i s stage, to c o n s i d e r i n f u l l the points i n this l i s t . Application c r i t e r i a : (i) The s h e l f l i f e o f the prepolymer concentrate, s t o r e d under normal c o n d i t i o n s , should exceed a c e r t a i n minimum, and s i x months i s probably the minimum a c c e p t a b l e . ( i i ) P r e p a r a t i o n o f the padding l i q u o r should be simple and should not r e q u i r e s p e c i a l equipment. F o r example, a prepolymer which i s i n s o l u b l e i n water may be a p p l i e d to wool f a b r i c from an aqueous emulsion, but the chemistry o f the polymer should be such t h a t i t i s p o s s i b l e f o r a s t a b l e emulsion t o be prepared by the chemical manufacturer s i n c e t h i s r e q u i r e s s p e c i a l equipment not n o r m a l l y found i n t e x t i l e f i n i s h i n g p l a n t s . ( i i i ) The prepared padding l i q u o r should be s t a b l e and usable f o r at l e a s t 8 h (a f u l l s h i f t ) a f t e r p r e p a r a t i o n , and p r e f e r a b l y f o r l o n g e r than t h i s . Of course, the padding l i q u o r must c o n t a i n any c u r i n g c a t a l y s t s which are used and t h i s tends to make i t l e s s c h e m i c a l l y s t a b l e than a l i q u o r c o n t a i n i n g the prepolymer alone. A d d i t i o n a l l y , d i l u t e emulsions may have a g r e a t e r tendency to separate o r "cream" than concentrates, ( i v ) A f t e r a p p l i c a t i o n t o the f a b r i c , the prepolymer must cure r e a d i l y , and under r e l a t i v e l y m i l d c o n d i t i o n s . I d e a l l y , d r y i n g the t r e a t e d f a b r i c i n the c o n d i t i o n s normally used f o r d r y i n g wool should be s u f f i c i e n t . Any n e c e s s i t y f o r heat c u r i n g a t e l e v a t e d temperatures i s a d i s t i n c t disadvantage because wool f i n i s h e r s o f t e n do not have f a c i l i t i e s f o r t h i s type o f treatment,
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and i n any case, i t may damage the wool o r cause i t to yellow, p a r t i c u l a r l y i f the c l o t h i s i n an a l k a l i n e c o n d i t i o n . (v) I n the i d e a l system, afterwashing, e i t h e r to improve the f a b r i c hand o r to remove excess c a t a l y s t s or wetting agents e t c . should not be necessary. ( v i ) The c r o s s - l i n k e d polymer should have minimal e f f e c t s on the dyeing p r o p e r t i e s o f t r e a t e d wool, so t h a t u n l e v e l polymer a p p l i c a t i o n w i l l not l e a d to u n l e v e l dyeing when dyeing succeeds the s h r i n k - r e s i s t treatment. Performance c r i t e r i a : (yil) The f e l t i n g r e s i s t a n c e o f t r e a t e d f a b r i c s should enable them to survive a severe wash t e s t , at l e a s t equivalent to the maximum amount o f washing a garment w i l l r e c e i v e d u r i n g i t s a n t i c i p a t e d wear l i f e . ( v i i i ) The t r e a t e d f a b r i c should have good wash and wear (minimum i r o n ) p r o p e r t i e s , equivalent at l e a s t to a DP3 r a t i n g a f t e r severe machine washing. K n i t t e d f a b r i c s should r e t a i n good s t i t c h c l a r i t y through the machine wash. ( i x ) The cost o f the polymer and the r e q u i r e d add-on must be such that c r i t e r i a ( v i i ) and ( v i i i ) can be s a t i s f i e d a t reasonable cost. (x) The a e s t h e t i c p r o p e r t i e s o f the f i n i s h e d f a b r i c must be v i r t u a l l y i n d i s t i n g u i s h a b l e from untreated wool. In p a r t i c u l a r the process must not n o t i c e a b l y i n c r e a s e the s t i f f n e s s o r harshness of the f a b r i c , nor cause i t s hand to become greasy o r tacky. With such a l i s t of c r i t e r i a to s a t i s f y , i t i s h a r d l y s u r p r i s i n g that the i d e a l s h r i n k - r e s i s t polymer f i n i s h has yet to be found. I t i s p a r t i c u l a r l y d i f f i c u l t to f i n d polymers which have good s h e l f l i f e and a p p l i c a t i o n - b a t h s t a b i l i t y , and yet cure under m i l d c o n d i t i o n s a f t e r a p p l i c a t i o n to the f a b r i c ; the reasons f o r t h i s c o n f l i c t i n p r o p e r t i e s are q u i t e obvious. I t i s a l s o very d i f f i c u l t to produce a h i g h l e v e l of s h r i n k re s i stance combined w i t h good f a b r i c a e s t h e t i c s without washingo f f a f t e r polymer a p p l i c a t i o n to improve the f a b r i c ' s hand. Polymer S t r u c t u r e . (Table i ) . The polymers d i s c u s s e d i n t h i s paper are more a c c u r a t e l y described as r e a c t i v e , s e l f c r o s s l i n k i n g oligomers. T y p i c a l l y , they c o n s i s t e d o f a s o f t backbone s t r u c t u r e , o f t e n a p o l y ( a l k y l e n e oxide) o f molecular weight Λ
