Effect of Gamma Radiation on the Chemical Structure and Physical Properties of Poly(butylene terephthalate) (PBT).

This study presents the effect of gamma rays of up to 2000 kGy on the chemical structure and the physical properties of a poly(butylene terephthalate) (PBT). PBT is an important engineering polymer, tougher than PET, that can be upgraded by radiation crosslinking with the addition of crosslinkers. Previous studies found in the literature provided very limited data about the effect of ionizing radiation on pure PBT. No gel was produced, and the changes in molecular weight with the increase in dose were in agreement with the results found in the literature, with a decrease until 1000 kGy dose when chain scission predominated and a slight increase at higher doses when crosslinking became significant. Proton NMR analysis was used for the first time in PBT to determine the changes in chemical species, mainly the appearance of terminal butyl groups and aromatic carboxylic groups coming from the rupture of the ester linkage. Both thermal and mechanical properties were explained by the scission of the chains in the amorphous phase and at the boundaries of the crystallites, and the crosslinking in the amorphous phase. The thermal parameter most affected by irradiation was the crystallization temperature, which increased when chain scission was predominant up to a 1000 kGy dose and decreased at higher doses when crosslinking became significant. Stress and strain at break suffered a continuous decrease with dose until PBT became fragile at high dose, with a faster decrease in strain at break from the 1000 kGy dose, when crosslinking became significant.