The effect of morphology on the melting and crystallization of irradiated poly(ethylene) in a solvent

The melting and crystallization of irradiated isotropic highly oriented (dr awing ratio, 25-30) bulk and powdered linear PE samples dissolved in decali n were studied by DSC. A significant difference in behavior of the samples had been observed during the first heating in the solvent, which was even i ncreased in the subsequent heating-cooling cycles. Variation of the supermo lecular structure (morphology) not only leads to different relative yields of the cross-linking and degradation processes, but results in the differen t ability of the PE samples to dissolve on heating and crystallize on cooli ng in the solution as well. There are two melting peaks in the DSC curves o f both block and powdered PE samples, irradiated upon dissolution followed by slow cooling, which correspond to the melting of sol and gel fractions s eparated from the samples. It is suggested that these fractions represent P E crystallites of two different types. The single peaks of melting and crys tallization observed in irradiated oriented samples are apparently an evide nce of a single type of crystallites having a large number of defects, espe cially upon the irradiation to high doses.