A study of the crystallization of γ-irradiated polyethylene terephthalate using differential scanning calorimetry

Abstract

The crystallization ofγ-irradiated polyethylene terephthalate, crystallized over a wide range of temperatures, has been studied by differential scanning calorimetry. It was found that the difference between theAvrami exponents for the low temperature and pre-melt crystallization processes was not as pronounced as it was for the unirradiated polymer. The superposability of the low temperature crystallization isotherms along the log time axis and the inability of the pre-melt isotherms to do this suggest that the crystallization mechanisms are different. The rates of crystallization and the crystallinity are affected by irradiation, the former being first retarded and then speeded-up with dosage increase, whilst the latter is a minimum at 2 mrad. The differing rates and crystallinities are discussed with respect to chain scission and crosslinking. The relationship between the crystalline melting points and the crystallization temperatures for the premelt process is as predicted by theory. The melting points of the low temperature crystallization process are higher than those predicted by theory, annealing or further recrystallization being thought to have occurred.