Damage to natural and synthetic fibers treated in supercritical carbon dioxide at 300 bar and temperatures up to 160°C

This paper examines and discusses fiber damage in cotton, viscose, polyester, polyamide 6.6, silk, and wool in supercritical carbon dioxide at 100, 120, 140, and 160degreesC for 1. and 4 hours at a pressure of 300 bar. For comparison, experiments are conducted for 4 hours at 160degreesC in nitrogen and air under atmospheric conditions. Damage is determined by fiber-specific reactions, staining tests, shrinkage, stress-strain measurements, viscosimetric molecular weight, and amino acid analyses. Shrinkage occurs only in polyamide 6.6 and polyester, and is comparable to water dyeing. During all treatments above 120degreesC in carbon dioxide, the degree of polymerization of polyamide 6.6 decreases, which is also detectable by stress-strain measurements. Polyester is. not damaged by any treatment. Damaging effects on cotton, viscose, silk, and wool are only revealed by stress-strain measurements after 4 hours at 160degreesC in carbon dioxide, but not in nitrogen and air. The degree of polymerization of cellulose fibers starts to decrease slightly after 4 hours at 120degreesC, while amino acid analyses of silk and wool indicate damage only after 4 hours at 160degreesC. Generally, the combination of heat, treatment time, and carbon dioxide seems to be responsible for the damaging effects. The results show that except for polyamide 6.6, where treatment conditions are limited to 120degreesC at 300 bar for I hour, supercritical carbon dioxide is a suitable solvent for dyeing or other treatments, even for the most sensitive textiles up to 140degreesC. The treatment time at 160degreesC should not be longer than I hour.