Modacrylic fibres

IARC. 1979. Acrylonitrile, acrylic and modacrylic fibres, and acrylonitrile-butadiene-styrene and styrene-acrylonitrile copolymers. IARC monographs on the evaluation of the carcinogenic risk of... 

Many brilliantly coloured and tinctorially strong basic dyes for silk and tannin-mordanted cotton were developed in the early decades of the synthetic dye industry. Most of these belonged to the acridine, azine, oxazine, triarylmethane, xanthene and related chemical classes their molecules are usually characterised by one delocalised positive charge. Thus in crystal violet (1.29) the cationic charge is shared between the three equivalent methylated p-amino nitrogen atoms. A few of these traditional basic dyes are still of some interest in the dyeing of acrylic fibres, notably as components of cheap mixture navies and blacks, but many modified basic dyes were introduced from the 1950s onwards for acrylic and modacrylic fibres, as well as for basic-dyeable variants of nylon and polyester [44] ... 

Some anthraquinone dyes with pendant cationic groups are used commercially on acrylic and modacrylic fibres [22]. Only two disclosed structures are included in the latest revision of the Colour Index, the dyes being the reddish blue Cl Basic Blue 47 (6.54) and the greenish blue Cl Basic Blue 22 (6.55). 

Methyl acrylate is used in manufacture of acrylic and modacrylic fibres, amphoteric surfactants, leather finish resins, textile and paper coatings and plastic films (United States National Libraiy of Medicine, 1997). 

The most successful approach for flame-retarding acrylic fibres is to copolymerise halogen-containing monomers into the fibre. These modacrylic fibres have excellent permanent flame retardancy and acceptable fibre properties. Some problems including reproducibility of dyeing gave rise to their substitution by flame-retardant modified polyester, for example for curtain fabrics and other decorative textiles. 

Providing flame retardancy for fibre blends has proved to be a difficult task. Fibre blends, especially blends of natural fibres with synthetic fibres, usually exhibit a flammability that is worse than that of either component alone. Natural fibres develop a great deal of char during pyrolysis, whereas synthetic fibres often melt and drip when heated. This combination of thermal properties in a fabric made from a fibre blend results in a situation where the melted synthetic material is held in the contact with the heat source by the charred natural fibre. The natural fibre char acts as a candle wick for the molten synthetic material, allowing it to bum readily. This can be demonstrated by the LOl values of cotton (18-19), polyester (20-21) and a 50/50 blend of both (LOl 18), indicating ahigher flammability of the blend as described later (Section 8.11). But a rare case of the opposite behaviour is also known (modacrylic fibres with LOl 33 and cotton in blends from 40-60 % can raise the LOl to 35). 

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. 

The modacrylic fibres have similar properties to those of acrylics and are flame resistant..Mostly this fibre is based on a 60/40 or 50/50 copolymer of acrylonitrile with vinylidine chloride (CH = CCy together with small proportion of ternary monomer to improve ionic dyeability or hydrophilicity. The better known modacrylic fibres have a ribbon-shaped or pea-nut shaped cross-section. One problem encountered with modacrylic fibre is loss of lustre at the boil [83, 84]. This fibre is used for apparel, home furnishing, wigs etc. 

Generally, scouring of modacrylic fibres is not always necessary. However, scouring and desizing may be carried out in a similar manner to that regular acrylic... 

These fibres cannot be heat-set in the conventional sense since the fibres are readily stretched or deformed at temperatures above 75 C. The degree of stability, however, can be obtained by passing these fabrics through a hot air stenter at about 120 C. Temperatures above 120 C may cause discolouration of the fabrics. For blended fabrics containing acrylic and modacrylic fibres higher heat-setting temperatures may be required. Knitted fabrics produced from a feeder blend of acrylic and textured polyester fibres, are heat-set at about 160 C for 30 sec. 

Methyl methacrylate, (MMA) N-Methylolacrylamide Modacrylic fibres 1,5-Naphthalene diisocyanate... 

Acrylics and modacrylics. Flame retarded acrylics find little application within the technical textile sector and they are usually so highly modified in terms of comonomer content that they are termed modacrylics. This latter group has been commercially available for 50 years or so but at present few manufacturers continue to produce them. The preferred comonomer is vinylidene choride and to enhance the flame retardant activity of the chlorine present, antimony III oxide (ATO) is included, although this may reduce the lustre of the fibres and resulting fabrics. Modacrylic fibres, like acrylic... 

Halogen-containing fibres, such as modacrylic fibres (e.g., Saran fibres ), are also used as flame-retardant components in blends of fire protection equipment.i ° i i Modacrylic fibres are typically copolymers of vinyl chloride or vinylidene dichloride and acrylonitrile. However, while, modacrylic fibres are non-flammable and do not melt or drip, they shrink rapidly when exposed to fire, and thus are rarely used in firefighters clothing. 

A patent from 1982 describes a treatment of acrylic and modacrylic fibres to produce a copper sulphide element that confers electrical conductivity (Gomibuchi et al., 1982). A patent from 1980 describes the use of copper iodide to produce an electrically conductive fibre without substantial colour change (Tanaka and Tsunawaki, 1981). 

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. 

The content of acrylonitrile units in modacrylic fibres is, by definition, between 35 and 85 wt%. These fibres usually have a high concentration of halogen-containing comonomers (such as vinylidene dichloride, vinyl bromide and vinyl chloride) which improve their flame resistance. Related to modacrylic fibres, but with a higher content of halogen-containing monomers, are chlorofibres, produced only in small quantities from poly(vinyl chloride), poly(vinylidene dichloride) and from their copolymers, e.g. with vinyl acetate. ... 

Until now, we were concerned with fibres made from crystallizable linear flexible-chain polymers. Acrylic and modacrylic fibres are produced from copolymers derived from atactic polyacrylonitrile, which are noncrystallizable. Yet these fibres are in many aspects similar to the semicrystalline fibres. 

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