Acrylic Fiber Introduction and SPG Process

July 10, 2022

Introduction

FTC (Federal Trade Commission) defines acrylic fibers as those containing at least 85% by weight of acrylonitrile co-monomer.
Modacrylic is a modified acrylic containing at least 35% but less than 5% by weight of the acrylonitrile co-monomer
Produced from solutions either by wet or dry SPG system
Co-monomers are used (at 10:90) rationally

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Acrylic Comonomer

|Vinyl Acetate||Methyl Acrylate|

C2H4O (Ethylene oxide) + HCN (Hydrogen cyanide) → HO-CH2-CH2-CN (Ethylene chlorohydrin)

HO-CH2-CH2-CN (Ethylene chlorohydrin) + KCN (Potassium cyanide) → CH2=CHCN (Acrylonitrile)

n.CH2=CHCN (Polyacrylonitrate)

n = 2000 -5000 nm long.

Most acrylic fibers are wet spun (about 85%)
Sodium thiocyanate + PAN containing methyl acrylate
A solution in dimethyl acetamide with PAN containing vinyl acetate as a comonomer
During the dry SPG (15%) solution is dimethylformamide and the co-monomer is methyl acrylate.

Spinneret holes 10,000 -60,000
Spinneret holes dia 0.05 - 0.38 mm
The individual filaments emerging from each hole are drawn from the bath together as large filaments tow
After extrusion, all acrylic fibers are washed thoroughly to remove solvents, drawn to increase orientation, dried, and relaxed in either water or steam to improve abrasion resistance and resistance to fibrillation.

The adjacent polymer chain is strongly Hydrogen bonded between the electronegative nitrogen atoms and the hydrogen atoms on the polymer backbone
The strong dipole-dipole interaction between them
CN group of adjacent polymer chains.

PAN Structure