抄録
To examine the heating condition to prepare a flame-proofed fiber, polyacrylonitrile fiber was heat-treated in air at temperatures in excess of 180°C and tensile properties of the heat-treated ones were measured. Since polyacrylonitrile fiber was observed to decompose rapidly at around 250°C and yield a brittle residue, the fiber preheated at 240°C (or 230°C) was used for heat-tre-atment at temperatures above 250°C. Measurements were also carried out on weight, fiber length, elementary analysis, X-ray and density.
In the range of 180_??_240°C, weight, tensile strength and breaking elongation decrease with increasing of heating time and of heating temperature. However, the tensile properties of the flameproofed fibers obtained are almost same since flame-proofness appears with a shorter heating time at a higher temperature.
Changes in tensile properties with elevation of heat-treatment temperature show different behaviours depending on temperture range. Namely, both tenacity and elongation decrease in the range of 180_??_250°C, but turn to increase from 250°C to 300°C and then decrease again above 300°C. It is observed moreover that on each curve of the weight-loss vs. temperature and the shrinkage vs. temperature, an inflection point is present the values increasing with a larger rate above 260_??_280°C, These phenomena are discussed with the results on X-ray, elementary analysis and density.
