SURFACE NATURE OF UV DETERIORATION IN PROPERTIES OF SOLID POLY(ETHYLENE-TEREPHTHALATE)

We investigated the changes in the molecular weight and also in the me chanical properties with the distance to the exposed surface of the ir radiated stacked poly(ethylene terephthalate) (PET) film samples. A re lation between the molecular weight and the mechanical properties of t he irradiated PET was established. The relation demonstrates that the decrease in molecular weight is one of the main origins causing the de terioration in the mechanical properties. The photodegradation process developing in PET was quantitatively studied by investigating the deg radation kinetics of stacked PET film samples. Our results show that t he strongest degradation takes place at the exposed surface, and the d egradation rate decreases with increasing the distance. This further i mplies that the capability to bear a tensile stress in the area near t he exposed surface is much lower than that in bulk. Therefore, irradia ted PET may be fractured in a lower stress. These results indicate the surface nature of ultraviolet deterioration in the physical propertie s of PET. (C) 1996 John Wiley & Sons, Inc.