Basic Studies on the Stability of Filtration Fabrics

Abstract

Synthetic fabrics used as filters for removing particles from industrial smoke are liable to deteriorate under operating conditions, i.e., the presence of moisture, relatively high temperatures, and aggressive gases like SO₂ and NO₂. This paper (the first in a series) describes the deterioration of polyacrylonitrile (PAN) fibers under laboratory-simulated conditions by Fourier transform infrared spectroscopy, differential scanning calorimetry, scanning electron microscopy, and tensile strength measurements. The results indicate that the fibers are subject to oxidative degradation (chain scission, formation of —CO—, —COOH, etc.), cyclization via the nitrile side chains, and a slight introduction of SO₂ and SO₃ groups to the polymer chain. All these primary and secondary reactions are basically related to thermal or alkaline degradation of PAN, and both SO₂ and NO₂ appear to play a catalytic role in the oxidation process. Mechanically, the fibers become unworkably brittle after treatment with the pollutant gases. Increasing the water content of the NO₂ gas substantially reduces the damage to the fiber. PAN is relatively unaffected by calcium hydroxide, which is often used to neutralize acid gases.