Effects of gamma-ray irradiation on the change of characteristics of polyurethane

Abstract

Investigations have been carried out on the characteristic changes which occur in thermoplastic polyurethane (PU) when it is irradiated by gamma rays. The change in molecular weight as a result of irradiation and the change of absorbance of samples eluted by methanol were determined. GPC patterns, tensile strength and residual amount of radicals based on chemiluminescence were also measured. PU chain-extended with 1,4-butanediol (BU) showed degradation, while nonchain-extended PU showed mainly cross-linking by gamma-ray irradiation. G values of degradation and cross-linking were 1·1 and 0·2, respectively. A linear relationship between the irradiation dose and the residual amount of radicals was found. There was no significant difference between molecular weights determined immediately following irradiation and 6 months after irradiation. The influence of the amount of residual radical on the changes in the characteristics of PU was not significant. The elution of PU oligomers ( n = 1–10) was confirmed from the GPC pattern of the methanol extract. Changes in tensile strength correlated well with changes in molecular weight. Sequential daily methanol extract analysis showed that elution occurred semilogarithmically. The GPC pattern suggested more rapid elution of lower molecular weight compounds which were more toxic.