**3.1.1 Historical background**

The first commercial fibre-forming polyester was developed by Dickson and Whinfield working at the Calico Printers' Association in England in 1941. It was produced by condensation of ethylene glycol and terephthalic acid. Rights to manufacture this product were bought by ICI and DuPont. The ICI product was named Terylene and the DuPont product Dacron (A. D. Broadbent).

Polyester fibres are produced as medium- and high-tenacity filament yarns and as staple fibres of various lengths and fibre colour to suit the kinds of spinning machinery found in the textile trade. Polyester fibre not only offers the typical features of a synthetic fibre, such as high chemical resistance, high moth-proofness, excellent wash and wear and permanent press characteristics, but also, when blended with cotton and wool, gives rise to fabrics of high quality. These unique properties make it the largest commodity fibre in the synthetic fibre world, in 1990, polyester production exceeded the total production of both polyamide and polyacrylic fibres (Brunnschweiler & Hearle, 1993).

Recent developments include new polymer compositions, physical characteristics improvement, enhanced aesthetic quality and improved dyeability (Fig. 13). Developments in physical characteristics include decreasing the fibre's intensity so as to facilitate the rupture and removal of objectable 'fuzz balls' (pilling-resistant fibre) and anti-static finishing through the application of the hydrophilic finish which creates capillarity in the interfibre spaces (Brunnschweiler & Hearle, 1993). As for improvements in dyeing properties, modified polyester has been introduced that contains ionic sites to facilitate ionic

Dyeing with Disperse Dyes 207

of 15%, 6% and 8%, respectively, after treatment at 80C for 72 hours, but dilute solutions of

Polyester fibres can be treated with dilute alkalis at temperatures up to 100C and can withstand the strongly alkaline conditions used in vat-dyeing and or in mercerizing. However, solutions of caustic alkalis do, in fact, attack and hydrolyze the polymer, but at temperatures up to the boil, such attack is confined to the surface of the fibre; this particular

Polyester polymers display the typical reactions of ester and can be hydrolyzed in the presence of dilute alkali or acid or by water alone. No serious change can be expected to be observable in the textile-processing properties of fibres and yarns dyed for one to two hours at 130C, so long as the pH of the bath has been maintained close to 7. However, in an acidic bath of pH substantially less than 4 or in an alkaline bath, more rapid attack will occur Above pH 8, high-temperature dyebaths can induce serious degradation of polyester fibres

Cellulose acetates are esters of cellulose in which a large fraction or even all the hydroxyl groups have been esterified using acetic anhydride. The two major types of cellulose acetate have about 55 and 62% of combined acetic acid. These values correspond to cellulose with degree of substitution of 2.48 and 3.00, respectively. The latter is called cellulose triacetate,

Acetate fibres belong to the class of man-made cellulosic fibres and are manufactured by treating cellulose in the form of pure wood pulp or, less frequently, cotton linters, with a mixture of glacial acetic acid and acetic anhydride at low temperature in the presence of an activation catalyst such as sulphuric acid, perchloric acid, zinc chloride or similar salts (Rouette, 2000). Cooling prevents an increase in temperature of the mixture that will promote excessive hydrolysis of the cellulose. This initial product is cellulose triacetate (primary cellulose acetate) and cellulose diacetate (secondary cellulose acetate) is obtained

Cellulose diacetate, once widely known by its producer's company name, Celanese, can be written and drawn in a similar manner to cellulose, except that between 77-80% of the hydroxyl groups have been acetylated by reaction with acetic acid, to give cellulose acetate

Acetate was the first hydrophobic man-made fibre, and when it appeared on the market, knowledge about the mechanism of dyeing and of molecular structure of fibres was limited. Because acetylation makes the fibre hydrophobic, resistant to swelling, and endows it with a

characteristic has been utilized in the production of silk-like polyester.

and the former is called cellulose diacetate (Fig. 14) (Broadbent, 2001).

directly from the triacetate by partial hydrolysis (Broadbent, 2001).

mineral acids are resisted, even at 100C.

if treatment is prolonged (Nunn, 1979).

Fig. 14. Chemical structures of acetate fibres

**3.2 Acetate fibres** 

esters (Trotman, 1984).

**3.2.1 Historical background** 

dye attachment as well as the use of a copolymer that lowers the compact structure of polyester (Moncriff, 1970). To increase the aesthetic quality of textured yarns, high refractive index inorganic particles have been incorporated into fibres and silk-like polyester fibre have been developed (Brunnschweiler & Hearle, 1993). However, although these modifications enhanced the lustre of polyester, softness in handle was lacking. During the 1970's and 1980's, the 'touch' of polyester fibre was enhanced; alkali deweighting treatments were used to make the fibre more delicate and a wrinkle finish imparted it to an appearance similar to that of silk. In addition, there have been many other activities in fibre development, such as polymer modification, fibre blending, surface treatment, the mixture of various fibre cross sections, special spinneret design and fine denier spinning for polyester and silk-like fibre developments (Brunnschweiler & Hearle, 1993).

Fig. 13. Modified polyester dyeable with cationic dyes.
