Mechanical property and molecular weight distribution changes with photo- and chemical-degradation on LDPE films

摘要

In order to clarify the effect of photo- and chemical-degradation on the structure of polyethylene materials, the change in molecular weight distribution and mechanical properties of photo- and chemical-degraded LDPE films were investigated. The molecular weight distribution was significantly changed with photo-exposing times, and the drastic change appeared especially for 8 days-exposed samples where the molecular weight of the high molecular weight fraction increased. However, the molecular weight of the lower molecular weight fraction was almost the same for all the photo-exposed films, irrespective of irradiation time, and also for chemical-degraded films. It is suggested that the molecular chains with a certain length, which consist of a crystal lamellae in spherulites, cannot be broken by photo-irradiation. Consequently, there would be threshold for the molecular weight in terms of photo-degradation process, and almost the same threshold can be observed for the chemical-etching films. Stress—strain curves were measured for photo-degraded films and their "quenched films after remolding" and "annealed films after remolding", and chemical-degraded films.