A Study of Some Factors Affecting the Photodegradation of Textile Yarns Part II: Nylon 66 and Polyethylene Terephthalate Yarns

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Abstract
A study has been made of the effect of relative humidity, anatase titanium dioxide content, and uv-stabilizer on the photodegradation of nylon 66 and polyethyleneterephthalate yarns exposed to pyrex/clear glass filtered xenon-arc radia tion, at 20, 50, and 80% RH, in the Weather-Ometer, and to sunlight behind single, strength-window glass at approxi mately 20% RH. Analysis of loss of tensile properties has shown that a high relative humidity level in the Weather- Ometer has significantly accelerated photodegradation of both fibers. X-ray diffraction analysis, performed on several nylon yarns, has indicated a higher degree of crystalline perfection after irradiation at 80% RH, giving a possible ex planation for accelerated loss of tensile properties. Results of xenon arc and filtered sunlight irradiations at comparable RH levels (20%) have shown that a difference in RH does not contribute to the poor correlation found between Weather- Ometer and outdoor exposures. Titanium dioxide significantly accelerated photodegradation of nylon and was the main cause of breakdown of polyester exposed to filtered sunlight. Photosensitization of titanium dioxide was less apparent in the Weather-Ometer. The protective effect of the uv-stabilizer added to several nylon yarns was more apparent during outdoor exposure than during xenon-arc irradiation.