CRAZE FIBRIL BREAKDOWN IN GLASSY-POLYMERS

Recent work suggests that the origin of fibril breakdown is disentanglement of polymer chains in the 'active zone' at the craze-bulk interface, where the deformation ratio of the polymer is increasing towards that of the fully formed fibril, and the polymer is in a strain-softened state (that is, the chains are relatively mobile). Since disentanglement times are expected to be strongly dependent both on temperature and on the molecular weight of the chains in the fibril, it is clear that these parameters should also strongly affect fibril stability. We have investigated craze fibril breakdown as a function of molecular weight and temperature in thin films of polystyrene and poly(ether sulphone), and have found good qualitative agreement between our results and a molecular model for fibril breakdown based on the earlier ideas of Kramer and Berger.