Volatile and non-volatile compounds in irradiated semi-rigid crystalline poly(ethylene terephthalate) polymers

Abstract

In this study two diVerent semi-rigid crystalline and oriented polyethylene terephthalate materials were used and were irradiated at 25-kGy dose at room temperature by using a caesium¹³⁷ radiator. Volatile and nonvolatile compounds present in the irradiated materials were identified and quantified. The qualitative results obtained from HS/GC/TCD/FID analysis at room temperature showed volatiles could not be identified. The HS/GC/MSD analysis performed at 106°C showed that the irradiation generated 668-742 μg/kg formic acid, 868–922 μg/kg acetic acid, 17–32 μg/kg 1,3-dioxolane, and 47–71 μg/kg 2-methyl-1, 3-dioxolane based on PET weight. The results obtained from the thermal desorption and GC/MSD performed at 200°C showed that 10–12mg/kg acetaldehyde, 479–975 μg/kg 1,3-dioxolane, and 6.6–11.2mg/kg methyl-1, 3-dioxolane were detected after irradiation. The concentrations of the two dioxolanes found from thermal desorption were much higher than those observed in the HS, although formic and acetic acids were not detected. It is possible that the formic and acetic acids produced by irradiation underwent further reactions with ethylene glycol during thermal desorption to form the dioxolanes. The soluble solid extracted from various PET specimens before and after irradiation were in a range of 0.67–0.78%. PET cyclic trimer is the major component and is present at 0.41–0.50%, accounting for more than 50% of the percent total solid in PET. Statistically, irradiation did not increase the soluble solid and cyclic trimer. The overall results suggest that 25-kGy irradiation had a significant eVect on increasing the volatile but not the non-volatile compounds detected in the PET specimens.