Degradation depth profiles and fracture of UV exposed polycarbonate

Photodegradation depth profiles have been determined in 3 mm thick polycarbonate injection moulded bars using molecular mass measurements and an attempt made to relate the results to the fracture behaviour in uniaxial tensile tests. Unstabilised samples were compared with similar bars containing a commercial stabilising system. Although the presence of stabiliser restricted molecular mass degradation to a thin surface layer, with little degradation indicated beyond 0-1 mm from the exposed surface, the bars made from stabilised polymer embrittled at least as quickly as those made from unstabilised material, for which molecular mass degradation was evident at least up to 0-4 mm from the exposed surface. The as moulded compressive residual stresses near the surface of unstabilised polycarbonate bars increased in magnitude on UV exposure during the period in which embrittlement developed and may have partially countered the effects of molecular degradation, whereas little varition in the residual stress distribution with exposure was observed in stabilised polycarbonate.