Gamma-radiation-induced changes in the chemical and physical structure of poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) film was irradiated with {dollar}gamma{dollar}-rays in air at doses from 0 to 620 Mrad, and at the rate of 0.8 to 1.0 Mrad/hr. Radiation-induced chemical structure changes were studied by using FT-NMR, FT-IR, UV/visible and fluorescence emission spectroscopy. Radiation-induced physical structure changes were studied by DMA and DSC measurements. Tensile properties were measured to find interrelationships with chemical and physical structure changes.; Below 100 Mrad, PET shows little change in NMR and IR spectra. Fluorescence emission spectra, however, show the presence and increase of monohydroxy-substituted phenylene groups. This hydroxylation appears to stabilize the polymer. The phenylene group in PET also contributes to radiation-resistance. The amorphous-crystalline interfaces impede the penetration of oxygen and slow the oxidative chain scission.; Between 100 and 215 Mrad, UV studies reveal that the rates of reaction begin to change rapidly. Chain scission appears to take place first in the interspherulitic amorphous regions and then in the intraspherulitic (interlamella) regions. {dollar}gamma{dollar}-Radiation-induced oxidative degradation shows aspects of both photolysis and of thermooxidative degradation (proton and carbon-13 NMR, and IR studies).; Several of the speculations offered by Turner (1973) were experimentally verified, others discounted and still others not offered by Turner were established.; The secondary transition temperature (DMA) and the melting temperature (DSC) decreased with increasing dosage. The melting peaks became broader; but the degree of crystallinity increased. It was concluded that the crystalline phase breaks down into smaller crystallites, and these smaller crystallites grow in size by acting as nucleating sites. Another reason for the apparent increase in crystallinity is that the weight ratio of the amorphous phase is decreased because it is in the amorphous phase that the decomposition reactions leading to the release of small molecules of CO, CO{dollar}sb2{dollar}, H{dollar}sb2{dollar}, CH{dollar}sb4{dollar}, etc. first begin to take place.; Tensile measurements show that throughout the range of irradiation studied the tensile strength at break and the percent elongation decrease. The tensile strength decreases uniformly and the percent elongation exhibits a more rapid decrease above 100 Mrad.; The results of this study lead to the conclusion that {dollar}gamma{dollar}-radiation-induced oxidative degradation of PET involves products that are seen in both photolysis and thermooxidation.