Introduction of Acrylic Fiber | Properties of Acrylic Fiber | Production Process of Acrylic Fiber | Uses of Acrylic Fiber

Acrylic Fiber:
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 [-CH2-CH(CN)-] (FTC definition). Acrylic fibers are produced by two basic methods of spinning (extrusion), dry and wet. In the dry spinning method, material to be spun is dissolved is a solvent. After extrusion through the spinneret, the solvent is evaporated, producing continuous filaments which later may be cut into staple, if desired. In wet spinning, the spinning solution is extruded into a liquid coagulating bath to form filaments, which are drawn, dried, and processed.

Acrylic fibers are synthetic fibers made from a polymer (polyacrylonitrile) with an average molecular weight of ~100,000, about 1900 monomer units. To be called acrylic in the U.S, the polymer must contain at least 85% acrylonitrile monomer. Typical comonomers are vinyl acetate or methyl acrylate. The Dupont Corporation created the first acrylic fibers in 1941 and trademarked them under the name "Orlon".

Raw Material

Acrilonitrile is the main main raw material for the manufacture of acrylic fibres. It is made by different methods. In one commercial method, hydrogen cyanide is treated with acetylene: 

1st Method
Acetylene + Hydrogen cyanide --> Acrilonitrile

2nd Method
Ethylene--Air Oxidation--> Ethylene oxide + HCN--> Ethylene cyanahydrin--Dehydration at 300 deg C (catalyst)--> Acrylonitrile

Production Process of Acrylic Fiber
The acrylic process is a "one step technology", with the following main characteristics:
  1. Polymerization in solution
  2. Direct feeding of the dope to spinning
  3. Wet spinning
  4. DMF as solvent for both polymerization and spinning
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Production Process of Acrylic Fiber
In a continuous polymerisation process, 95% acrylonitrile and 6% methyl acrylate (400 parts) 0.25% aqueous solution of K2S2O8(600 parts), 0.50 % Na2S2O5 solution ( 600 Parts) and 2N sulphuric acid (2.5 Parts) are fed into the reaction vessel at 52 deg C under nitrogen atmosphere giving a slurry with 67% polymer. The slurry is continuously withdrawn, filtered and washed till it is free from salts and dried.

Acrilonitrile is dry spun. The material is dissolved in dimethyl formamide, the solution contains 10-20 polymers. It is heated and extruded into a heated spinning cell. A heated evaporating medium such as air, nitrogen or steam moves counter current to the travel of filaments and removes the solvent to take it to a recovery unit. The filaments are hot stretched at 100 to 250 C depending on the time of contact in the hot zone, to several times their original length.

Properties of Acrylic Fibers
  1. Acrylic has a warm and dry hand like wool. Its density is 1.17 g/cc as compared to 1.32 g/cc of wool. It is about 30% bulkier than wool. It has about 20% greater insulating power than wool.
  2. Acrylic has a moisture regain of 1.5-2% at 65% RH and 70 deg F.
  3. It has a tenacity of 5 gpd in dry state and 4-8 gpd in wet state.
  4. Breaking elongation is 15% ( both states)
  5. It has a elastic recovery of 85% after 4% extension when the load is released immediately.
  6. It has a good thermal stability. When exposed to temperatures above 175 deg C for prolonged periods some discolouration takes place.
  7. Acrylic shrinks by about 1.5% when treated with boiling water for 30 min. 
  8. It has a good resistance to mineral acids. The resistance to weak alkalies is fairly good, while hot strong alkalies rapidly attack acrylic.
  9. Moths, Mildew and insects do not attack Acrylic.
  10. It has an outstanding stability towards commonly bleaching agents.
Uses of Acrylic Fiber
  1. Knit Jersey, Sweater, blankets
  2. Wrinkle resistant fabrics.
  3. Pile and Fleece fabrics
  4. Carpets and rugs.
Precaution of Acrylic Fiber 
  • Wash delicate items by hand in warm water. Static electricity may be reduced by using a fabric softener in every third or fourth washing. Gently squeeze out water, smooth or shake out garment and let dry on a non-rust hanger. (Sweaters, however, should be dried flat.) 
  • When machine washing, use warm water and add a fabric softener during the final rinse cycle. 
  • Machine dry at a low temperature setting. Remove garments from dryer as soon as tumbling cycle is completed. 
  • If ironing is required, use a moderately warm iron. (For specific instructions, refer to garment's sewn-in care label.)
 

9 comments:

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Anonymous said...

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