Effect of tensile stress on chain scission and crosslinking during photo-oxidation of polypropylene

Scission and crosslink concentrations have been determined in polypropylene samples using gel permeation chromatography molecular weight distributions and computer simulations. Measurements have been made at different depths within injection moulded bars 3 mm thick after 4 weeks ultraviolet (UV) exposure. The scission and crosslink concentrations were found to be 0.025 and 0.006 mol/kg respectively at the surface and 0.004 and 0.001 mol/kg respectively at the centre. The values at the unexposed face were similar to those at the exposed face. Samples exposed to UV while loaded in uniaxial tension (10 MN/m(2)) showed markedly increased chain scission but little change in the crosslinking rate. (C) 2001 Elsevier Science Ltd. All rights reserved.