抄録
It is well known that sunlight induces the ultraviolet (UV) degradation of polymers. This paper describes the effects of UV irradiation on the change of mechanical properties of polypropylene (PP)and polycarbonate (PC) films. After the specimens were exposed to UV light from the fluorescent UV apparatus, some specimens were subjected to a dead load afterwards the exposures. Tensile tests and dynamic viscoelastic mechanical tests were conducted. In addition, infrared spectrum and molecular weight were measured in order to investigate changes in chemical properties. (1) The degradation of mechanical properties due to UV irradiation is divided into two periods, i. e., the degradation-incubation period and degradation-development period. The failure strain does not change in the first period, and gradually decreases with increase of the integrated UV irradiation energy. The applied stress during irradiation has a tendency to accelerate degradation. (2) The temperature during exposure influences degradation considerably when it is greater than the glass transition temperature. (3) The reason for the existence of the incubation period is different for two materials. PP has no active bases originally for light-induced chemical reaction, and thus a certain period is necessary to initiate scission of main chains. On the other hand, PC has active bases but the second conjugation is strong. Therefore a certain number of main chain scissions are required to decrease the failure strain.
