engleski

DSC analysis and morphology of gamma-irradiatied poly(ethylene oxide)

Polyethylene oxide, (PEO) is a semicrystaline polymer of increasing importance, particularly for preparation of polyelectrolytes and hydrogels. The ionizing radiation can improve many of PEO’ s important properties but, because PEO crosslinks or degrades depending on irradiation conditions, deterioration of other properties can occur. Ionizing radiation influences the degree of crystallinity that is easily and quickly assessed using differential scanning calorimetry (DSC). The shapes of thermograms and heats of phase transformations are very sensitive to the changes brought into the polymers by irradiation. Although DSC is frequently used to determine properties of PEO-based polyelectrolytes, to our best knowledge the systematic analysis of radiation effects on pure PEO by DSC was not performed. Because of that, we present part of the results collected on PEO samples of different molecular masses in various forms (powder, pellets) irradiated by 60Co  -radiation to selected doses, in air or in nitrogen. The heats of melting and fusion decrease with the dose, the changes are sometimes accompanied by the changes of trace shapes implying the influence of crosslinking on crystallization mechanism. Microscopy enables correlating the morphology to the changes of thermal properties. The molecular mass and sample form have less significant effect on thermal properties of irradiated PEO samples. The post-irradiation effects are often neglected although may have considerable influence on properties of the irradiated polymer. In the PEO samples under the consideration, the post-irradiation changes of both temperature and heats of phase transformations are greater in the samples irradiated in air and increase with dose, being considerable above 100 kGy. The irradiation in air increases the extent of postirradiation changes implying the need of further analysis of the underlying reaction mechanisms.

multiple transitions; degradation; crosslinking; heat of crystallization; crystallization temperature; post-irradiation; DSC; morphology

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