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

摘要

The γ radiation induced degradation of an EPDM copolymer was compared to that of a ~13C enriched polyethylene at exposure temperatures of 22 and 80℃. Morphological changes were measured by MAS ~13C NMR spectroscopy and DSC. By first examining the high quality and less complex spectra of ~13C enriched polyethylene, a protocol for the interpretation and deconvolution of the more complex EPDM spectra was developed. The morphological changes during ambient temperature γ irradiation were similar for the two materials while the morphological changes during y irradiation at 80℃ were notably different. The polyethylene exhibited a substantial increase in crystallinity as a function of aging time at both temperatures. The EPDM copolymer exhibited a substantial increase in crystallinity at 22℃ but only a minor increase in crystallinity at 80℃. The reduction in the growth of the crystalline phase was attributed to the melting of a significant fraction of the smaller crystallites at the 80℃ irradiation temperature. When the sample was returned to ambient temperature these crystallites were unable to reform due to the crosslinks introduced during the radiation-thermal exposure.