Acrylic fiber Acrylic is defined as a manufactured fiber in which the fiber forming substance is any long chain synthetic polymer composed of at least 85% by weight of acrylonitrile units. Acrylonitrile Modacrylic fiber ➢The long chain polymer, which fiber forming substance composed of less than 85% but at least 35% by weight of acrylonitrile units, is known as modacrylic fiber. ➢They are a wet or dry spun halogen-substituted hydrocarbon made primarily, from acrylonitrile (CH2=CHCN) / vinyl chloride (CH2=CHCl) or vinylidene chloride (CH2=CCl2) copolymer. ➢Modacrylic fibers are intended primarily for applications where superior flame resistance property is required. Modacrylic fiber ➢Fibers with 40 -60 % copolymerized vinyl chloride and fibers with 30 45% copolymerized vinylidene chloride are commercially important because of their flame –retardant characteristics. Acrylic fiber Acrylic fibers take third position among the synthetic fibers considering the annual quantity of commercial production in the world, which is attributed to a number of their comparable properties like superior moisture management or wick ability, quick drying time (75% faster than cotton), easy care, good shape retention capability, excellent light fastness, sunlight resistance and an attractive shining of the color dyeing with cationic dyestuffs. Acrylics found an increased use approximately by 23% in 1969 due to their introduction as an alternative to wool because of higher price of wool fiber. PRODUCTION FLOW Ethylene Cyanhydrin Dehydration Acetylene and HCN Monomer Synthesis (Acrylonitrile) Propylene Route Acetaldehyde Route Manufacturing Acrylic Fiber Polymerization Wet Spinning Spinning Dry Spinning Drawing Washing Drying Stabilizing Crimping Physical properties of Acrylic fibers Acrylic fibers have a wool-like hand. Tensile strength staple : 4.0 g/den Filament : 5 – 7 g/den Tensile strength is higher than that of wool and about the same as cotton, although it is considerably lower than other synthetic fibers. Elongation Staple : 20 – 55 % Filament: 30 – 36 % Elastic recovery Acrylic fibers have a high elastic recovery from small extensions, e.g. 90-95 % at 1% extension. The recovery from higher extensions is moderate, e.g. 50-60 % at 10% extension. In general, recovery characteristics resemble those of wool. Physical properties of Acrylic fibers Average stiffness Staple fiber: 7 -10 g/den Filament: 16 – 41 g/den Specific gravity: 1.16 – 1.18 The density of acrylic fibers is low that enables to produce a bulky fabric of lighter weight with good warmth retention and covering power. Effect of moisture Regain: 1.0 – 3.0 % Water absorption at 200C, and 95 % RH: 2.0 – 5.0 Performance of various fibers Properties Acrylic Nylon Polyester Polypropylene Sunlight resistance Excellent Poor Good Poor Chemical resistance Excellent Good Good Excellent Static electricity build up Moderate Low High High Moisture regain 1.5 – 2.0 % 4 – 5% 0.1 – 0.2 % 0% Action of sunlight and weathering ➢Due to outstanding resistance properties of acrylic fibers to sunlight and weathering, the outdoor exposure does not cause any degradation to the acrylic fibers. ➢Even in hot climates, where the sunlight, particularly the ultra-violet radiation and other degrading agents are strong, the acrylic fibers withstand excellently. ➢Compared with natural and synthetic fibers, their resistance to the attack of sunlight in retention of strength is five times better than cotton or wool and almost four times higher than nylon. Figure : Loss of tenacity of fibers after 200 hrs exposure to sunlight Action of Heat ➢ Acrylic fibers exhibit good heat stability at temperatures less than 1200C. ➢ It has been reported that even after 2 days exposure at this temperature there is no loss of strength occurred. ➢ Acrylic fibers discolored and decompose rather than melt when heated. ➢ Yellowing of the fibers may occur to a little extent, if they are subjected to a heat treatment at elevated temperatures for a ling time. ➢ Drastic heat treatment causes progressively yellowing and the fiber turns into quite black if the heating is continued. This is due to the fact that upon continuous heating at higher temperature (above 1800C), the long molecular chain of acrylic polymer does not break down extensively, but some molecular rearrangements occur and the polymers undergo autocatalytic cyclization through the nitrile groups as well as decomposition of gaseous products such as hydrogen cyanide. Action of Acids ➢Acrylic fibers are unaffected by dilute solutions of strong mineral acids, but they tend to be attacked on prolonged immersion in concentrated solution. Due to their superior resistance to acids, acrylic fibers from 100% acrylonitrile are used for filtration purpose under acidic conditions. The advantages of such filter media are no rotting under constant moist conditions, easy removal of the filter cake and scouring /cleaning at large intervals. Actions of alkalis Dilute solutions of caustic soda and all solutions of sodium carbonate and bicarbonate have no effect on the mechanical properties of acrylic fibers. Strong alkalis attack the fiber. Effect of Organic Solvents Insects Acrylic fibres generally have a good resistance to common Acrylic fibres are not attacked by moth larvae or other organic solvents, including those normally used in dry insects. cleaning. Micro-organisms Acrylic fibres are not attacked by micro-organisms. USES OF ACRYLIC Acrylic in apparel includes sweaters, shocks, blankets , and fleece or high-pile fabrics. Acrylic is also used to create fur substitutes. Acrylic in furnishings include upholstery fabrics and carpet. Acrylic resists the sun, draperies and outdoor items such as awnings, tarpaulins, tents and outdoor furniture. Other applications, sportswear, socks, shoe liners, and industrial filter USES OF MODACRYLIC Fur fabrics with both long and short fibres It is used for wigs, hairpieces, and paint-roller covers. It is flame retardant characteristics make it suitable for use in children’s pajamas and robes and some work cloths. Other uses : wall coverings, industrial filters , Window treatments, and blanket , upholstery fabrics for the home. Sometimes used in awnings and boat covers. Fiber Identification Burn Test Acrylics burn readily forming a black bead that is easily crushed in the fingers. A match or cigarette dropped on an acrylic blanket can ignite the fabric, which will burn rapidly unless extinguished. Fiber Identification Solubility test Acrylic fibers are insoluble in methanol, acetone and ethylene chloride, but they go into solution by dimethylformamide, dimethylacetamide and diethylsulfoxide at room temperature.
