Liquid Ammonia Treatment of Cotton Fabrics

4 Liquid Ammonia Treatment of Cotton Fabrics

Downloaded by MONASH UNIV on April 23, 2017 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0049.ch004

S. ALLAN HEAP International Institute for Cotton, Manchester, England

The last few years have seen the development and commercial introduction of a brandnewfinishing technology in the use of anhydrous liquefied ammonia as a setting agent for cotton fabrics. IIC has been sponsoring background research on several aspects of this process, mainly at the University of Stuttgart and the Norwegian Textile Institute, and I would like to discuss two topics from this programme today:1. The influence of the ammonia content of the fabric upon its deformability, 2. Easy-care finishing of ammonia treated fabrics; a comparison of the low-add-on crosslinking technique with the normal padding method. But first, bywayof introduction, a few data which have already been published in the German language but may not have been seen here, and which draw some comparisons between NH3 and caustic soda treatments. Figure 1 illustrates the swelling (change in thickness) of an unrestrained poplin fabric as a function of time and the concentration of ammonia. Two points are immediately obvious; the very rapid rate of the reaction and the sensitivity to the presence of moisture, When we expand the time scale by speeding up the chart, it is clear that for anhydrous ammonia, essentially all the swelling takes place within the first fifteen seconds. Figure 2 shows a comparison between anhydrous ammonia and caustic soda in the yarn untwisting test. Ammonia shows a clearly faster rate of swelling, but a lower equilibrium value. Although the equilibrium swelling of the fibres is less in NH3 than in NaOH, fabric shrinkage tends to be about the same when little or no restraint is applied. The actual difference depends upon the fabric construction and presumably can be explained by assuming that fibres are prevented from reaching their maximum degree of swelling, especially in caustic soda. Indeed, the caustic swollen fabric is much more easily prevented from shrinking by the application of a restraining force (Figure 3). 63

Arthur; Textile and Paper Chemistry and Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

TEXTILE AND PAPER CHEMISTRY AND TECHNOLOGY

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NH /Ç%H 0 3

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S 10 min TIME Of SWELLING Figure

1.

Swelling of bleached liquid ammonia/water

cotton poplin (~ —40°C)

fabric

in



4.

HEAP

Liquid

Ammonia

Treatment

of Cotton

Fabrics

65

When the f a b r i c i s held to constant dimensions, the f o r c e generated by ammonia s w e l l i n g i s g e n e r a l l y much l a r g e r than that caused by c a u s t i c soda (Figure 4 ) . Furthermore, the a p p l i c a t i o n of a pretension to the f a b r i c , before contact with the s w e l l i n g agent produces a marked reduction i n the s w e l l i n g f o r c e generated by NaOH, but has apparently almost no i n f l u e n c e on the NH3 system (Figure 5 ) . The l a r g e i n f l u e n c e of tension upon the degree o f s w e l l i n g of cotton f i b r e s i n c a u s t i c soda i s , of course, w e l l documented, so the apparent i n s e n s i t i v i t y of the ammonia system to tension was rather s u r p r i s i n g . I t has l e d us p r o v i s i o n a l l y to conclude that the ammonia c e l l u l o s e complex i s rather d i f f e r e n t from a l k a l i c e l l u l o s e , e s p e c i a l l y i n i t s mechanical p r o p e r t i e s , with l i t t l e c a p a b i l i t y f o r s t r e s s decay. The p r a c t i c a l consequence of t h i s behaviour i s that i t i s somewhat more d i f f i c u l t to c o n t r o l the dimensions of a f a b r i c i n the ammonia process than i n mercerising. Figures 6 and 7 , which p i c t u r e the length changes during t y p i c a l s w e l l i n g c y c l e s w i l l serve to i l l u s t r a t e the point a l i t t l e further. Figure 6 i s supposed to model a s l a c k s w e l l i n g and r e s t r e t c h ing c y c l e . Note the s i m i l a r degree of shrinkage with a f a s t e r r a t e f o r N H 3 . The f a b r i c was then loaded with lKg per cm. bef o r e removal of the s w e l l i n g agent. The c a u s t i c - s w o l l e n sample immediately s t r e t c h e d s i g n i f i c a n t l y , with a f u r t h e r r e s t r e t c h i n g as soon as the water r i n s i n g bath was a p p l i e d . The ammonia swollen sample, however, extended f a r l e s s on f i r s t applying the l o a d , and there was a c l e a r delay a f t e r the s t a r t of evaporation before r e s t r e t c h i n g began. In Figure 7 , the c y c l e i l l u s t r a t e d i s one where a pretension i s a p p l i e d before s w e l l i n g . This tension was s u f f i c i e n t to more or l e s s eliminate shrinkage i n NaOH, but there was s t i l l a f a i r degree of shrinkage i n N H 3 . Once again, during evaporation of NH3 there was a delay period during which no extension occurred. Concentration

Of NH3 On The F a b r i c .

The thought n a t u r a l l y a r i s e s that t h i s block to the extens i b i l i t y of ammonia swollen f a b r i c should be r e l a t e d to the conc e n t r a t i o n of ammonia remaining i n the f i b r e s . Figure 8 shows the values obtained from the instantaneous elongation experienced by s l a c k swollen samples, as a f u n c t i o n of the load a p p l i e d and the ammonia content at the i n s t a n t of a p p l i c a t i o n of the l o a d . Three l e v e l s of ammonia are shown to i l l u s t r a t e the extremes and an intermediate i n the family of curves. C l e a r l y , the highl y swollen m a t e r i a l i s very r e s i s t a n t to elongation, and t h i s must be a b a s i c f i b r e property s i n c e the f a b r i c s t r u c t u r e w i l l be jammed at f u l l s w e l l i n g . Only when the f i b r e s w e l l i n g i s reduced s u f f i c i e n t l y to create space i n the f a b r i c w i l l elongat-




TIME OF TREATMENT Figure

3. Shrinkage of bleached cotton poplin fabric, (left) in liquid monia (~ —40° C); (right) in 20% aqueous NaOH (20°C)

TIME Of TREATMENT Figure 4.

Development

of tension during

swelling


am-

Liquid

HEAP

Ammonia

Treatment

of Cotton

67

Fabrics


4.

Figure

6.

Shrinkage and elongation

of cotton poplin fabric during NH and treatments 3


NaOH

68



(warp)

TENSION



4.

HEAP

Liquid

Ammonia

Treatment

of Cotton

69

Fabrics

ion become p o s s i b l e at reasonable l o a d s . There i s also the p o s s i b i l i t y that at some intermediate ammonia content the f i b r e i t s e l f becomes capable of easy elongation as the ammonia c e l l ulose complex i s broken down. Both mechanisms ( f a b r i c jamming and f i b r e e x t e n s i b i l i t y ) w i l l presumably be a f f e c t e d by the manner of ammonia removal - i n p a r t i c u l a r , one might expect d i f f e r e n c e s between the cases where ammonia i s removed by "dry" evaporation on the one hand, or by replacement with water on the other. Up to now, we have studied only the evaporation systems i n t h i s respect. Figure 9 shows a t y p i c a l r e s u l t when one a p p l i e s a constant load during evaporation of the ammonia. R e s t r e t c h i n g begins at an ammonia concentration of about 55%, and one can suppose t h i s f i g u r e to i n d i c a t e approximately the point at which one i s begi n n i n g to remove ammonia from within the f i b r e s rather than simply evaporating i n t e r s t i t i a l l i q u i d . We have other c i r c u m s t a n t i a l evidence p o i n t i n g to a f i g u r e i n the region of SQ% f o r the within fibre liquid. This 50% NH3 f i g u r e does not correspond to the c r i t i c a l point as c o n v e n t i o n a l l y defined during drying processes, when the r a t e of drying and the f a b r i c temperature changes abruptly due to the greater d i f f i c u l t y of removing more t i g h t l y bound liquid. Figure 10 shows t h a t , f o r one set of circumstances, we found t h i s c r i t i c a l point to be i n the region of 35% N H 3 . This l a t t e r value happens to agree p r e t t y w e l l with a c a l c u l a t e d three moles of NH3 per glucose r e s i d u e . Recently, we have been c o n s i d e r i n g the p o s s i b i l i t y that a 50-60JÎ l e v e l of add-on may be a l l that i s t e c h n i c a l l y needed to produce the d e s i r a b l e e f f e c t s of ammonia treatment and we have made a f a i r l y l a r g e number of s t u d i e s i n t h i s area. So f a r , the r e s u l t s are i n c o n c l u s i v e and not p a r t i c u l a r l y encouraging. Easy-Care-Finishing. A range of samples was prepared on continuous p i l o t s c a l e equipment by applying i n c r e a s i n g l e v e l s of DHDI lEU/l lgCl2 to ammonia t r e a t e d , mercerised, and c o n t r o l f a b r i c s . On the one hand, the usual padding technique was used to apply the c r o s s l i n k i n g l i q u o r , and on the other hand, the new Low-Add-On (LAO) system was used. In the LAO system, the amount of l i q u o r appl i e d can be c o n t r o l l e d at such a l e v e l ( 3 D - 3 5 ^ ) that e s s e n t i a l l y no migration ensues during drying and a more uniform d i s t r i bution of c r o s s l i n k i n g i s obtained i n the f i n a l f a b r i c . A wide range of q u a l i t i e s were processed which a l l gave s i m i l a r r e s u l t s , t h e r e f o r e , j u s t one set of r e s u l t s i s presented here today. The mercerised samples gave r e s u l t s very s i m i l a r to those of the c o n t r o l s and t h e r e f o r e , these are not i n c l u d e d . Generally speaking, the use of the LAO system gave b e t t e r crease recovery angles and/or b e t t e r abrasion r e s i s t a n c e f o r v

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TEXTILE

my

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A N D PAPER

CHEMISTRY

I ι I ι I ι I ZO 60 40 20 AMMONIA ON FABRIC

1

A N D TECHNOLOGY

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Figure 9. Degree of restretching of cotton poplin as a function of ammonia concentration on the fabric

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Figure 10.

Fabric temperature

during

drying


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71

Liquid Ammonia Treatment of Cotton Fabrics

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Liquid Ammonia Treatment of Cotton Fabrics

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