Friday, November 15, 2019

ACRYLIC FIBRE PRODUCTION, FLOW CHART OF PRODUCTION OF ACRYLIC FIBRE, POLYACRILONITRILE.

PRODUCTION OF ACRYLIC FIBRES:

The acrylic fibre production gets completed in the following steps:

Raw Material:

Acrylonitrile is used as a monomer to produce acrylic fibres. The polymer of acrylic can be produced by using various methods. The various methods of production of acrylic monomers are given below:

1st Method

In one commercial method, hydrogen cyanide is treated with acetylene:

Acetylene+Hydrogencyanide --> Acrilonitrile

In this method of producing hydrogen cyanide reacts with acetylene gas and the acrylonitrile results after the reaction. 

2nd Method:

In this method of production of acrylonitrile, the ethylene gas gets oxidized with atmospheric air and ethylene oxide results after the reaction. Now, this resulted in ethylene oxide reacting with hydrogen cyanide.  The ethylene cyanohydrin gets formed after the reaction. The ethylene cyanohydrin is heated at 300°C in the presence of a catalyst. This acrylonitrile results after the reaction. This reaction follows below chemical equations:



After the production of the acrylonitrile, acrylic fibre  production completes in the following steps

Polymerization in solution

Direct feeding of the dope to spinning

Wet spinning

Dimethyl formamide as a solvent for both polymerization and spinning

The production method of acrylic fibre follows below process chart:



Polymerisation: 

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 H2SO4 (2.5 Parts) are fed into the reaction vessel at 52 °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 The slurry is continuously withdrawn, filtered and washed till it is free from salts and dried.

Dry spinning:

The dry spinning method is used to produce acrylic filaments. The polyacrylonitrile polymer is dissolved in an organic solvent (dimethylformamide). It is heated and extruded into heated spinnerets. As fibre comes out from the spinneret, it comes in contact with hot air or steam. The solvent ( dimethylformamide) is evaporated and is sent to a recovery unit. Now, these newly formed filaments are hot and dried. The filaments are hot stretched at 100 °C to 250 °C depending on the time of contact in the drying assembly to several times of their original length.

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