Morphology changes during radiation-thermal degradation of polyethylene and an EPDM copolymer by C-13 NMR spectroscopy

The gamma radiation induced degradation of an EPDM copolymer was compared t o that of a C-13 enriched polyethylene at exposure temperatures of 22 and 8 0 degreesC. Morphological changes were measured by MAS C-13 NMR spectroscop y and DSC. By first examining the high quality and less complex spectra of C-13 enriched polyethylene, a protocol for the interpretation and deconvolu tion of the more complex EPDM spectra was developed. The morphological chan ges during ambient temperature gamma irradiation were similar for the two m aterials while the morphological changes during gamma irradiation at 80 deg reesC were notably different. The polyethylene exhibited a substantial incr ease in crystallinity as a function of aging time at both temperatures. The EPDM copolymer exhibited a substantial increase in crystallinity at 22 deg reesC but only a minor increase in crystallinity at 80 degreesC. The reduct ion in the growth of the crystalline phase was attributed to the melting of a significant fraction of the smaller crystallites at the 80 degreesC irra diation temperature. When the sample was returned to ambient temperature th ese crystallites were unable to reform due to the crosslinks introduced dur ing the radiation-thermal exposure. Published by Elsevier Science Ltd.