Oxidative stabilization of acrylic fibres

Abstract

The mechanism of oxidative stabilization of acrylic fibres is characterized by two limiting cases which are determined by the fibre chemistry, the reaction conditions, and the diameter of the filament. These limiting cases correspond to diffusion-limited and reaction-limited kinetic processes. Although the chemistry of stabilization is too complex to specify, the various reactions are separated into two categories: those which occur prior to or concurrently with polymerization of the nitrile groups, called “prefatory reactions”; and those which occur subsequent to nitrile polymerization, called “sequent reactions”. Under conditions which allow the prefatory reactions to occur significantly before the sequent reactions, the diffusion of oxygen to reactive sites is limited by previously oxidized material; and the fibre shows a typical two-zone morphology. Under conditions where the prefatory and sequent reactions occur sequentially, the overall stabilization process is limited by the rate of the prefatory reactions; but a skin is established at the fibre surface which acts as an oxygen barrier. Data from a variety of sources, including oxygen analysis, microscopic examination, fibre residue after etching, tension developed in fibres held at constant length, and small-angle X-ray patterns, are cited as evidence for the two limiting cases.