Modacrylics polymerization

Fig. 3. An aqueous dispersion polymerization process used in the manufacture of acrylic and modacrylic fibers.

Residual acrylonitrile monomer may also occur in commercially-made polymeric materials used in rugs and other products. Estimated levels include acrylic and modacrylic fibers (less than 1 mg acrylonitrile/kg polymeric material), acrylonitrile-based resins (15 to 50 mg/kg), and nitrile rubber and latex (0 to 750 mg/kg) (IARC 1979 Miller and Villaume 1978). It is possible that acrylonitrile may evaporate into air or leach into water from these products, but no data on this topic were located. 

Uses Copolymerized with methyl acrylate, methyl methacrylate, vinyl acetate, vinyl chloride, or 1,1-dichloroethylene to produce acrylic and modacrylic fibers and high-strength fibers ABS (acrylonitrile-butadiene-styrene) and acrylonitrile-styrene copolymers nitrile rubber cyano-ethylation of cotton synthetic soil block (acrylonitrile polymerized in wood pulp) manufacture of adhesives organic synthesis grain fumigant pesticide monomer for a semi-conductive polymer that can be used similar to inorganic oxide catalysts in dehydrogenation of tert-butyl alcohol to isobutylene and water pharmaceuticals antioxidants dyes and surfactants. 

Polymerization Methods. Acrylonitrile and its comonomers can he polymerized by any of the well-known free-radical methods. Bulk polyntenzaiion is the most fundamental of these, but its commercial use is limned by ns aulocutalyiie nature. Aqueous dispersion polymerization is the itiosi common commercial method, whereas solution polymerization is used in cases where the spinning dope can he prepared directly from the polymerization reaction product. Emulsion polymerization is used primarily for modacrylic compositions where a high level of a water insoluble monomer is used or where the monomer mixture is relatively slow reacting. 

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. 

Acrylics and Modacrylics Polybenzimidazole and Carbon Fibers Polymerization Process Technology Fiber Formation... 

Of the fibers listed in Table II only the polyesters, polyamides, spandexes, acetates, and rayon are discussed in this chapter. While the acrylics and modacrylics are the third most important class of commercial fibers because their polymerization chemistry is also discussed in other chapters concerned with vinyl addition emulsion polymerizations, it will only be briefly summarized here. For the same reason polypropylene polymerization chemistry is also not covered in this section. However, two additional topics, carbon fiber formation and polybenzimidazoles have been included on the basis of the current Interest in high-performance fibers for composite materials. 

ORIGIN/INDUSTRY SOURCES/USES production of acrylic and modacrylic fibers plastics rubber elastomers solvents polymeric minerals dyes pharmaceuticals insecticides nylon fumigant formation of high-impact resins... 

An example of a commercial semibatch polymerization process is the early Union Carbide process for Dynel, one of the first flame-retardant modacrylic fibers [14,15]. Dynel, a staple fiber, which was wet-spun from acetone, was introduced in 1951. The polymer is made up of 40% acrylonitrile and 60% vinyl chloride. The reactivity ratios for this monomer pair are 3.7 and 0.074 for acrylonitrile and vinyl chloride in solution at 60°C. Thus, acrylonitrile is mueh more reactive than vinyl chloride in this copolymerization. In addition, vinyl chloride is a strong chain transfer agent. 

Emulsion polymerization generally restricted to modacrylics and not relevant for a carbon fiber precursor ... 

Polyacrylonitrile pa-le- a-kr9-lo- nl-troh n (1935) (PAN) Made by free-radi polymerization of acrylonitrile (CH2=CHCN) in solution or suspension, this highly polar polymer is the basis of large-volume acrylic and modacrylic fibers. 

Dynel, a modacrylic fiber, is a wet-spun fiber. Two chemicals, i.e. acrylonitrile and vinyl chloride, are co-polymerized in the ratio of 2 3 and the copolymer is dissolved to a 21% solution in acetone. The acetone solution is de-aerated, filtered, and then extruded by the usual wet spinning technique into a water bath, where it coagulates to form continuous strands of filaments. 

The first two modacrylic fibers ever introduced in the United States were Dynel (by Union Carbide) in 1949 and Verel (by Tennessee Eastman) in 1956. The former was a copolymer of 60 percent vinyl chloride and 40 percent acrylonitrile, and the latter was said to be a 50-50 copolymer of vinylidene chloride and acrylonitrile with perhaps a third component graft-co-polymerized onto the primary material to secure dyeability. SEF and its version for wigs, Elura , were introduced by Monsanto Fibers in 1972. A few foreign manufacturers are making modacrylic fibers, but the only modacrylic fiber currently in production in the United States is SEF . 

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