Effects of Light on the ESR Spectra of Dyed Cottons

Abstract

It was demonstrated, by using electron spin resonance (ESR) 'methods, that free radicals are produced in purified and dyed cotton celluloses by the action of light. Cottons were dyed with 24 different dyestuffs selected from eight broad classifications: direct dyes (either low or high in light-fastness; after-treated with CuSO ₄ or diazotized and developed), soluble ester vat dyes, and vat dyes applied by the hot-pigment method, sulfur dyes, and naphthols. Some of the copper-containing dyestuffs and cottons dyed with these materials gave EPR signals with broad line widths. Most of the other dyestuffs used and dyed cottons gave narrow singlet ESR spectra before irradiation with the intense source of light; this indicated that the natural light interacted with the dyestuffs and with dyed cottons to form free radicals.

On irradiation of the dyed cottons with the intense source of light, narrow singlet ESR spectra were also obtained; the signal strengths of these spectra were greater than those which resulted from the interaction of natural light with the dyed cottons. In most cases, the increases in the signal strengths of the spectra observed for the dyed cottons on irradiation were several times greater than the increase observed for purified cotton on irradiation. There was no obvious correlation between the interaction of light with the dyed cottons, as indicated by changes in their ESR spectra and the weather resistances of 'these cottons. This indicated that the energy absorbed by the dyed cottons from both natural and intense sources of light was not necessarily localized, so as to cause depolymerization of the cellulose molecule and consecluent loss in breaking strength of the yarn.