Monday, 1 June 2009
Acrylic- Manufacturing Process and Properties
Polyacrilonitrile ( Acrylic)
vinyl Cyanide, more commonly known as acrylonitrile, can under go addition polymerisation to form polyacrylonitrile.
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:
acetylene + Hydrogen cyanide --> Acrilonitrile
Ethylene--Air Oxidation--> Ethylene oxide + HCN--> Ethylene cyanahydrin--Dehydration at 300 deg C (catalyst)--> Acrylonitrile
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 The slurry is continuously withdrawn, filtered and washed till it is free from salts and dried.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 Fibres
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.
1. Knit Jersey, Sweater, blankets
2. Wrinkle resistant fabrics.
3. Pile and Fleece fabrics
4. Carpets and rugs.