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Gamma-irradiation of solid, molten and dissolved poly(ethylene oxide) and its nanocomposites

Poly(ethylene oxide), (PEO), is a semicrystalline polymer with a numerous applications (hydrogels, polyelectrolytes, etc.). Its degree of crystallinity can be reduced by both degradation and crosslinking. Gamma irradiation is a suitable method widely used to achieve modification of PEO for specific applications. The outcome can be influenced by different factors like PEO characteristics and irradiation conditions, even though some of them are rarely implicated. Namely, effect of PEO molecular mass, sample form, state of aggregation, total dose and dose rate can be assessed only through systematic approach. A part of the ongoing systematic study on interactions of PEO characteristics (aggregate state, molecular mass, sample form) and irradiation conditions (atmosphere, total dose, dose rate) will be presented. A number of experimental techniques like DSC, WAXD, FTIR etc. were applied, DSC being the most sensitive. It has been found that the gamma-irradiation dose and the state of aggregation of PEO samples are the most important factors determining the outcome. The influence of atmosphere, molecular mass and form of PEO sample (for those irradiated in the solid state) cannot be neglected. Chain scission dominated in PEO irradiated in the presence of oxygen especially in solid state and resulted in an increase in crystallinity and crystallite size at small doses. The increase in crystallinity did not occur on irradiating PEO at temperatures above its melting point or in aqueous solution. The lowest degree of crystallinity and phase transformation temperatures with preserved mechanical properties were obtained on irradiation of aqueous solution in an inert atmosphere and was probably due to crosslinking. The protective effect of solvent seems to be questionable since also degradation was observed in PEO samples irradiated as aqeous solutions in presence of oxygen. The results of the extensive study help in ongoing optimization of radiation preparation of PEO nanocomposites.

poly(ethylene oxide); gamma-irradiation; hydrogels; nanocomposites; degradation; crosslinking; crystallinity; DSC; XRD; aggregate state; crystallite size; crystallite orientation

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