Ultraviolet radiation-induced degradation

Fortin, J. B. Lu, T. M., Ultraviolet radiation induced degradation of poly para xylylene (parylene) thin films, Thin Solid Films 2001, 397, 223 228... 

Carbon loadings are used in extruded cable screens in concentrations up to almost 40%, to give appreciable electrical conductivity for management of electric fields so that measurement of carbon content is of some interest. Carbon is also incorporated into polyethylene sheathing for protection against ultraviolet (UV)-radiation-induced degradation, but at much lower levels around 2.5%. 

Photolysis Reactors and Ultraviolet Sources. For 253.7-m/ irradiation, a modified irradiation apparatus purchased from Delmar Co. was used. The reactor was a 2-necked, 500-ml., round-bottomed flask. One neck was an O-ring joint, and the other was a 24/40 joint. A 4- X 1-inch coiled low pressure mercury quartz lamp was placed inside the flask through the O-ring neck, and the joint was sealed with removable O-rings. The reactor was connected directly to the mass spectrometer by the 24/40 joint. The samples were placed inside the flask and irradiated internally. The O-ring was shielded from direct radiation so as not to induce degradation. The estimated output of the lamp was 30 watts, and the ambient temperature within the reactor during irradiation was 70°C. 

Photodegradation Degradation induced by exposure to ultraviolet radiation. 

A process of cracking under induced mechanical stress. Stress cracking generally starts with microscopic surface cracks, caused by chemical attack or other degrading influence such as ultraviolet radiation. Under mechanical stress, the microcracks propagate eventually producing a localized failure. 

Ultraviolet stabilisers for epoxies. The function of ultraviolet (UV) stabilisers is to retard light-induced polymer degradation which is caused by electromagnetic radiation emitted by the sun. Commonly used UV stabilisers for epoxy systems are given in Table 2.6 (Dexter, 1982). Only chemical names along with chemical abstracts services (CAS) registry numbers are mentioned commercially they are known by trade names. 

Photolysis. Chemical reaction (synthesis or degradation) induced by absorption of ultraviolet or visible radiation. 

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