Tensile failure of weathered polycarbonate

Abstract

AbstractWeatherability of several UV stabilized and unstabilized grades of LEXAN® polycarbonate (PC) was studied by exposure in a xenon arc lamp weather‐o‐meter. The tensile properties of thin (0.2 to 0.3 mm) compression molded and thick (3.4 mm) injection molded samples were investigated as a function of exposure time and correlated with the changes in fracture morphology and molecular weight by scanning electron microscopy (SEM) and gel permeation chromatography (GPC). The elongation at failure was the essential mechanical property influenced by exposure. An initial decrease in elongation at failure, followed by a slight increase before the materials turned completely brittle (i.e.; failure without yielding), was correlated with a change in the fracture mechanism starting from the exposed surface of the samples. The initial decrease was caused by penetrating surface cracks, while the later increase in ultimate elongation resulted from the flaking off of the brittle surface layer. The UV stabilized grade remained more ductile, since its molecular weight remains fairly constant up to 1500 h of exposure, while the unstabilized grades decrease in molecular weight continuously from the start of exposure. The useful lifetime of the samples, defined by the complete loss of ductility, is approximately 1500‐2000 h of accelerated exposure, which corresponds approximately to 1 year outdoor exposure under Israeli conditions.