Acrylic fibres, additives

In addition to the conventional dyeing of acrylic fibres, there is considerable interest in so-called gel dyeing of acrylic filaments during the manufacturing process after extrusion. From the viewpoint of auxiliary usage this is outside the scope of the present work, but a useful account of the factors involved is available [61]. 

Matama T, Vaz F, Gubitz GM et al (2006) The effect of additives and mechanical agitation in surface modification of acrylic fibres by cutinase and esterase. Biotechnol J 1 842-849... 

FACEGARD A, when used in the dyeing operation, will result in additional shrinkage and additional bulk to the acrylic fibre. 

Polyacrylonitile (PAN) is a long chain polymer containing acrylonitrile [-CHj-CH(CN)] as repeating unit in the polymeric chain and are formed by addition polymerisation. Acrylic fibre contains 15% or less copolymer. The modacrylic fibres are comprised of less than 85% but at least 35% by weight of acrylonitrile. The comonomers are added to increase the polymer thermoplasticity, solubility, dyeability, moisture regain, etc. 

In addition to solution-spun textile fibres, granular breaks are also found in some carbon fibres, which reflect their acrylic fibre origin, and in alumina fibres. Granular breaks are also shown in the natural fibres, wool and hair, in cotton at zero moisture content, and in resin-treated, cross-linked cotton at intermediate humidities. 

Polylactic acid (PLA), the structure of which is shown in Figure 7.10, is a polyester fibre in which there has been recent interest because of its environmental credentials. PLA may be derived from renewable resources, such as cornstarch, and it is biodegradable. PLA may be coloured using certain disperse dyes, although the dyes do not exhaust as well as on PET, mainly because of its aliphatic character. Acrylic fibres are synthetic fibres based essentially on the addition polymer polyacrylonitrile, the essential structure of which is illustrated in Figure 7.11. However, most acrylic fibres are rather more complex and contain within their structure anionic groups, most commonly sulfonate (-SOs ), but also carboxylate (-CO2 ) groups either as a result of the incorporation of co-polymerised monomers in... 

These hydrides can be determined by AAS. To illustrate, let us consider a method developed for the determination of trace amounts of arsenic in acrylic fibres containing antimony oxide fire-retardant additive [34]. The arsenic occurs as an impurity in the antimony oxide additive and, as such, its concentration must be controlled at a low level. 

In order to overcome this problem, the addition of levelling agents as well as flow reversal has been considered. However, in some cases, snchas the dyeing of cellulosic fibres with reactive dyes or acrylic fibres with cationic dyes, uiflevelness is still beyond the tolerance limit even with the addition of cationic retarders for cationic fibres or other auxiliaries for cellulose. Meanwhile, the question of the overall cost, which is increased by the addition of these materials into the dyebath, still remains. Moreover, these materials are not always environmentally friendly. 

Both acrylic and modacrylic fibres are based on atactic polyacrylonitrile. The generic name acrylic fibre refers to fibres made from linear copolymers that consist of not less than 85 wt % acrylonitrile units. The majority of commercial acrylic fibres contain between 5 and 8% of neutral comonomers, namely vinyl acetate, methyl acrylate or methyl methacrylate. In addition, smaller quantities of various ionic comonomers e,g, sodium styrenesulfonate) are used to provide, together with the ionic end-groups formed from sulfonate and sulfate initiators, the dye sites in the fibres. 

In addition to poly(methyl methacrylate) plastics and polyacrylonitrile fibres, acrylic polymers find widespread use. First introduced in 1946, acrylic rubbers have become established as important special purpose rubbers with a useful combination of oil and heat resistance. Acrylic paints have become widely accepted particularly in the car industry whilst very interesting reactive adhesives, including the well-known super-glues are also made from acrylic polymers. 

Whatever the approach, the result is a difficult-to-analyse system. Such options suit polymer producers better than additive suppliers. Aromatic polymers (PPO) have been mentioned as char-forming FRs. Polymeric UV absorbers, blended in proper proportions with commercial plastics, have potential use as stabilisers for fibres, films and coatings. Several monomeric stabilisers containing a vinyl group were homopolymerised and used as stabilisers for PE, PVC, acrylates, polystyrene, cellulose acetate and several vinyl polymers [55]. 

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