Effects of gamma- and electron-beam irradiation on semi-rigid amorphous polyethylene terephthalate copolymers

Two semi-rigid amorphous polyethylene terephthalate copolymer materials (in both sheet and powder forms) containing 3% 1,4-cyclohexane dimethanol (CHDM) and 31% CHDM were irradiated at 5, 25 and 50 kGy at ambient temperature with a ⁶⁰Co radiator or an electron-beam accelerator. After irradiation, volatiles were determined using static headspace sampling with capillary gas chromatography and mass selective detection or flame ionization detection (HS/GC/MSD or FID). Non-volatiles were extracted with 10% aqueous ethanol and 100% n-heptane food-simulating solvents, maintained at 40°C for up to 10 days. The non-volatiles in the materials and those migrating into the food-simulating solvents were determined by high-performance liquid chromatography (HPLC) with ultraviolet and/or photodiode array detection. The results obtained from the HS/GC/MSD suggest that no new chemicals were detected by either gamma- or e-beam irradiation when compared with non-irradiated specimens. The major volatiles in the copolymers were acetaldehyde and 2-methyl-1,3-dioxolane. The concentrations of acetaldehyde increased from 1.24-1.96 mg kg^-1 to 1.94-3.65, 3.52-7.23 and 5.45-15.37 mg kg^-1 after exposure to 5, 25 and 50 kGy doses, respectively. The concentrations of 2-methyl-1,3-dioxolane decreased from 2.49-5.26 mg kg^-1 to 2.07-3.13, 1.33-2.14 and 0.64-2.24 mg kg^-1 after exposure to 5, 25 and 50 kGy doses, respectively. The results of analysis of the copolymers for non-volatiles show that irradiation did not produce any new detectable non-volatile chemicals. A 5 kGy dose had no detectable effect on either copolymer. The 25 and 50 kGy doses had slightly different effects with respect to gamma- and e-beam irradiation on low MW oligomers. However, these increased doses did not significantly affect migration. The concentration of most low molecular weight oligomers migrating into 10% ethanol and 100% heptane was ≤2 ng g^-1 of each oligomer for both copolymers. The cyclic trimer migrating from the 3% CHDM copolymer was approximately 4 ng g^-1; it was 3 ng g^-1 for the 31% CHDM copolymer. The overall results suggest that irradiation significantly increased levels of acetaldehyde but had no effect on non-volatile compounds migrating into food simulants.