The Photochemistry of Dyes. IV—The Role of Singlet Oxygen and Hydrogen Peroxide in Photosensitised Degradation of Polymers

Abstract

The effect of sensitising dyes on the photochemical degradation of textile fibres is discussed. The degradation is dependent upon the presence of oxygen, and is accelerated by water vapour and rise in temperature. The study of simple model photochemical systems intended to simulate the dyed fibre system indicates that there are significant differences between the two systems. The sensitising effect of dyes in the textile systems seems to be due to the formation of excited singlet oxygen and hydrogen peroxide. The latter is not formed in the absence of water vapour.

Effect of Lignin on the Heat and Light Resistance of Lignocellulosic Fibers

“…The effects of light on the properties of lignin and other lignocellulosic materials have been studied by many researchers under various conditions 12, 24, 25. The reduction in the breaking tenacity of the kenaf, cornhusk and cotton fibers exposed to xenon light should be due to the damage to the interactions between the cellulose, lignin and hemicellulose and also due to the degradation of these polymers themselves.…”

“…The reduction in the breaking tenacity of the kenaf, cornhusk and cotton fibers exposed to xenon light should be due to the damage to the interactions between the cellulose, lignin and hemicellulose and also due to the degradation of these polymers themselves. It has been shown that exposure to light degrades cellulose and reduces the degree of polymerization of cellulose leading to lower breaking tenacity 12, 24, 25. In addition, lignin is more sensitive to light, absorbs light readily and transfers the energy to cellulose thereby accelerating the photochemical degradation of lignocellulosic materials 25.…”

II—Evidence for the Formation of Singlet Oxygen by Phototendering Vat Dyes

“…The evidence in favour of the singlet-oxygen theory has been extensively reviewed [6], but there are two main assumptions of this theory which have yet to receive experimental verification, namely:…”

“…There is a certain amount of indirect evidence in favour of assumption (a) [6]. In case (b) the only evidence available concerns strictly non-vat dyes, although the parent system, anthraquinone, is known to be a sensitiser of singlet oxygen [6].…”

“…There is a certain amount of indirect evidence in favour of assumption (a) [6]. In case (b) the only evidence available concerns strictly non-vat dyes, although the parent system, anthraquinone, is known to be a sensitiser of singlet oxygen [6]. Because of the critical importance of the second assumption to the singlet-oxygen theory of phototendering, we have attempted to obtain direct evidence for the ability of the phototendering vat dyes to behave as photochemical sensitisers for singlet oxygen, both in solution and in the solid state.…”