Degradation by ultraviolet light of wool and other textile fibres

Physical and chemical changes occuring in wool as a result of exposure to ultra-violet light have been investigated. The methods used included the determination of strength, extensibility and reduction in work of rupture, the measurement of density, refractive index, urea-bisulphite solubility, alkali solubility, water imbibition, specific surface area, dye absorption and X-ray diffraction. There is a progressive decrease in strength and extensibility and hence an increase in the reduction in the work of rupture of the wool fibre after successive doses of ultraviolet radiation. Increases in density and refractive indices of the wool fibre were observed, which indicated an increase in crystalline - amorphous ratio, probably due to molecular chain readjustment effected by ultra-violet energy. The imbibition value and the specific surface area of exposed wool fibres was reduced, showing that accessibility to certain reagents was lowered after exposure or that the structure became more compact in the molecular sense. No appreciable changes in X-ray if photograph were however observed to confirm these effects. That the exposure of wool resulted in degradation of main-chains and disulphide linkages was shown by the increase in urea-bisulphite solubility and alkali solubility after irradiation, The rate of dye uptake of wool fibres was enhanced after exposure. The dyeing rates of unexposed and exposed descaled wool were apparently equal. One of the main effects of irradiation on intact wool was therefore modification of the cuticle. The examination of degradation by ultra-violet light was extended to other fibres. Losses in strength, extensibility and reduction in work after exposure were recorded for matt and bright M 95, viscose rayon, Acrilan, Matt Courtelle, Fibrolane a and nylon 66. The light stability of acrylonitrile fibres seems to be very good, followed by nylon, viscose and Fibrolane DX in that order. The results of strength tests showed that the presence of a delustring agent increased the degree of fibre degradation. Ultra-violet exposure resulted in an increase in fluidity of viscose rayon, and a diminution of the viscosity and molecular weight of nylon. This suggests that in both viscose rayon and nylon rupture of the main chain molecules has occured