Acrylic and modacrylic fibers

Acrylic fibers are a major synthetic fiber class developed about the same time as polyesters. Modacrylic fibers are copolymers containing between 35-85% acrylonitrile. Acrylic fibers contain at least 85% acrylonitrile. Orion is an acrylic fiber developed by DuPont in 1949 Dynel is a modacrylic fiber developed by Union Carbide in 1951. 

Polyacrylics are produced by copolymerizing acrylonitrile with other monomers such as vinyl acetate, vinyl chloride, and acrylamide. Solution polymerization may be used where water is the solvent in the presence of a redox catalyst. Free radical or anionic initiators may also be used. The produced polymer is insoluble in water and precipitates. Precipitation polymerization, whether self nucleation or aggregate nucleation, has been reviewed by Juba. The following equation is for an acrylonitrile polymer initiated by a free radical  

Copolymers of acrylonitrile are sensitive to heat, and melt spinning is not used. Solution spinning (wet or dry) is the preferred process where a polar solvent such as dimethyl form amide is used. In dry spinning the solvent is evaporated and recovered. 

a modacrylic fiber, is produced by copolymerizing vinyl chloride with acrylonitrile. Solution spinning is also used where the polymer is dissolved in a solvent such as acetone. After the solvent is evaporated, the fibers are washed and subjected to stretching, which extends the fiber 4-10 times of the original length. 

Acrylic fibers are characterized by having properties similar to wool and have replaced wool in many markets such as blankets, carpets, and sweaters. Important properties of acrylics are resistance to solvents and sunlight, resistance to creasing, and quick drying. 

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

Acrylonitrile is mainly used to produce acrylic fibers, resins, and elastomers. Copolymers of acrylonitrile with butadiene and styrene are the ABS resins and those with styrene are the styrene-acrylonitrile resins SAN that are important plastics. The 1998 U.S. production of acrylonitrile was approximately 3.1 billion pounds. Most of the production was used for ABS resins and acrylic and modacrylic fibers. Acrylonitrile is also a precursor for acrylic acid (by hydrolysis) and for adiponitrile (by an electrodimerization). 

The primary use of acrylonitrile is as the raw material for the manufacture of acrylic and modacrylic fibers. Other Major uses include the production of plastics (acrylonitrile-butadiene- styrene (ABS) and styrene-acrylonitrile (SAN), nitrile rubbers, nitrile barrier resins, adiponitrile and acrylamide (EPA 1984). 

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. 

Acrylic and modacrylic fibers have a wool-like appearance and feel, and excellent resistance to heat, ultraviolet radiation, and chemicals [Bajaj and Kumari, 1987]. These fibers have replaced wool in many applications, such as socks, pullovers, sweaters, and craft yams. Other applications include tenting, awning fabric, and sandbags for rivershore stabilization. The use of acrylic and modacrylic fibers in carpets is low since these materials do not hold up well to recycling through hot-humid conditions. This also prevents its use in the easy-care garment market. 

An example of this type of a safer chemical is methacrylonitrile (1) compared with acrylonitrile (2) (Figure 1.1). Both compounds are a, 3-unsaturated aliphatic nitriles, and structurally very similar, but 2 causes cancer whereas 1 does not appear to do so. Among other applications, 2 is used in the production of acrylic and modacrylic fibers, elastomers, acrylonitrile-butadiene-styrene and styrene-acrylonitrile resins, nitrile rubbers, and gas barrier resins. In a study conducted by the US National Toxicology Program (NTP) in which 2 was administered orally to mice for 2 years, there was clear evidence that it caused cancer in the treated mice (in addition to causing other toxic effects), and is classified by the NTP as a probable human carcinogen [26]. 

Acrylic and modacrylic fibers are sold mainly as staple and tow products with small amounts ofconltnunus filament liber sold in Europe and Japan. 

Disperse dyes can be used to produce light to medium deep shades on acrylic and modacrylic fibers [96, p. 639], The dyeing mechanism and process correspond to those used on PES and CA fibers (see Section 4.12). However, dyeing can be performed below 100°C. Addition of carriers is not required. The good migration properties of disperse dyes result in problem-free level dyeing. 

Acrylonitrile resembles VC, a carcinogen, in structure. It is a flammable, explosive liquid (b.p. 77 C, V.P. 80 mm at 20°C). AN is a component of acrylic and modacrylic fibers produced by copolymerization with other monomers, e.g., with methyl acrylate, Me-methacrylate, vinyl acetate, VC and VDC. Other major uses of AN include copolymerizations with butadiene and styrene to produce ABS polymers, and with styrene to yield SAN resins which are used in the manufacture of plastics. Nitrile elastomers and latexes are also made with AN, as are a number of other chemicals, e.g. acrylamide and adiponitrile. Acrylonitrile is also used as a fumigant. 

Acrylic and modacrylic fibers are produced by either dry or wet spinning. As a result of the strong interraolecular attractions present in the acrylics, the only solvents that are suitable are those that are very polar and thus capable of disrupting these secondary valence bonds. These include Af.AT-dimethylformamide, dimethyl sulfone, dimethyl sulfoxide and dimethyl acetamide. Modacrylics, however, are soluble in more volatile, lower polarity solvents such as acetone. After spinning the residual solvent in acrylics must be removed by washing, and the fibers are drawn either dry (in a hot air oven or over-heated rolls at 80-110 °C) or wet (in steam or hot water at 70-100 °C). Finally the yarns must be dried... 

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... 

OTHER COMMENTS utilized as a monomer, polymer, or eopolymer the monomer in the manufacture of leather finish resins, textile and paper eoatings, and plastic films primary use in production of acrylic and modacrylic fibers produces the hardest resin of the acrylate ester series. 

FIGURE 12.28 Tow processing of acrylic and modacrylic fibers. (From Hobson, P.H. and McPeters, A.L., Kirk-Othmer Encyclopedia of Science and Technology, 3rd ed., Vol. I, Wiley, New York, 1978.)... 

Methods and Instruments for Analysis of Acrylic and Modacrylic Fibers... 

A summary of the methods and equipment used for evaluating acrylic and modacrylic fiber properties in Table 12.31. 

Metalized and semiconducting fibers have also been discussed [585-587]. Another key industrial application for acrylic fibers is for asbestos replacement, especially for concrete reinforcement and friction surfaces. An example of a concrete and mortar reinforcement fiber is Dolanit acrylic from Faserwerk Kelheim GmbH [588]. The subject has been reviewed by a number of authors [589-591]. Other acrylic fiber modifications and reviews of acrylic fiber modifications, in general, have been published by several authors [592-596]. A comprehensive summary of specialized acrylic and modacrylic fibers is given in Table 12.35. The major types. 

Uses Copolymer intermediate for acrylic and modacrylic fibers resins and dispersions for paints, varnishes, inks, papers, adhesives, and glues aq. disp. for nonwoven fabrics, textiles, and paper cleaning and waxing prrxfs. plastics and syn. resins syn. mbber and latexes org. synthesis Properties APHA 10 max. clear liq. m.w. 86 sp.gr. 0.950 vise. 0.461 mPa s vapor pressure 91 mbar (20 C) f.p. - 75 C b.p. 80 C ( 1013 mbar) flash pt. (OC) 3 C ref. index 1.400 Precairtirm Highly flamm. 

Hazardous Decomp. Prods. CO, CO2, NO, hydrogen cyanide NFPA Flealth 4, Flammability 3, Reactivity 2 Uses Monomer for acrylic and modacrylic fibers, paints in prod, of ABS and SAN copolymers, nitrile rubber, surfactants, adhesives, polyols, barrier resins, carbon fibers organic synthesis formerly as pesticide fumigant... 

This method of analysis is suitable for fiber identification, as well as for characterization of any chemical differences between two fibers of the same class. For instance, acrylic and modacrylic fibers containing copolymers of varying constitution and proportion may be identified. Identification depends on matching the additional bands with those in the IR spectrum of a fiber whose identity is already known. Both the wavelength and intensity differences of bands in each spectrum must be taken into account. Fiber samples may be prepared in the form of a pressed disk, where very finely divided particles of the fiber are uniformly distributed in powdered po-tassiiun bromide. The mixture is pressed into a small disk of about 1 mm thickness in a vacuum die vmder... 

There have been reviews of flammability (70-74), methods that can be used to enhance the flame resistance of acrylic and modacrylic fibers (75), and the mechanism of flame-retardant additives (76). 

Acrylonitrile in Polymers. The very low amount of residual acrylonitrile in finished resins or products (ca 1 ppm in acrylic and modacrylic fibers, 20-50 ppm in ABS and SAN) does not pose the threat of acrylonitrile migration or release imder normal intended use and handling conditions. Materials made from acrylonitrile are exempt fi om OSHA regulations, provided they are not capable of releasing acrylonitrile in airborne concentrations in excess of 1 ppm as a 9-h time-weighted... 

Who Employees occupationally exposed to acrylonitrile (AN). The standard does not apply to processing, use, and handling of finished polymers (and products made from polymers) of ABS resins, SAN resins, nitrile barrier resins, solid nitrile elastomers, acrylic and modacrylic fibers, and solids made from or containing AN that will not be heated above 170 degrees F. (Also exempt are other AN materials that are not capable of releasing specified amounts of airborne I AN.) Also, this standard incorporates by reference 1910.132 and 1910.134,... 

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. 

Acrylic and Modacrylic Fibers Acrylic Modaciyl ic Other acryl ics... 

The nature and distribution of acrylonitrile and comonomer or comonomers in the acrylic fibers affect the overall dyeability and the classes of dyes that may be used in dyeing these fibers. Both acrylic and modacrylic fibers can be dyed using disperse dyes, with the more hydrophobic and less crystalline modacrylic being more dyeable with this dye class. The polar cyanide groups in the acrylonitrile unit of these fibers have some affinity for acid dyes and particularly mordanted systems containing copper or chromium ions. Addition of an acid or basic comonomer such as acrylic acid or vinyl pyridine as comonomer imparts improved dyeability with basic and acid dyes, respectively, for these fibers. Vat dyes can be used on acrylic fibers to a limited extent. 

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