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Gamma irradiation of poly(ethylene oxide) and nano-silica in aqueous solution

Poly(ethylene oxide), PEO, is a versatile semicrystalline polymer. The reduction of the degree of crystallinity is preferred for some applications and can be achieved by irradiation in appropriate conditions. This presentation is a part of the study on the outcome of interactions of various factors on irradiation effects in PEO and its nanocomposites. If irradiated dry, the PEO chains are directly affected so in presence of oxygen PEO generally degrades, while the changes observed on irradiation in the inert atmosphere are consistent with partial crosslinking. In aqueous solution radiation produces reactive species in water and the reaction of these species with PEO chains is supposed to lead to crosslinking. We prepared aqueous solutions of PEO with nano-silica and without it. The solutions were irradiated by γ-radiation to various doses at different dose rates. The dried samples were investigated by differential scanning calorimetry (DSC), FTIR spectroscopy and X-ray diffraction (WAXD). The DSC peaks broadened and shifted to significantly lower temperatures compared to unirradiated PEO. The diffractograms display either small maxima (no shifts that would indicate the structural changes were observed) or are fully amorphous at higher doses. The greatest changes in FTIR spectra were observed in the shape and the absorption intensities of –C–O–C– triplet at around 1100 cm-1. The vibrations characteristic of crystalline PEO at 1342 cm-1 and 1360 cm-1 merged into a single absorption that is typical for melt and indicates amorphization. The significant decrease in crystallinity appeared at much lower doses that would cause degradation. Those results suggest crosslinking of PEO irradiated in aqueous solution occurred but specific spectral changes have yet to be found. The concentration of aqueous solution was significant for the outcome while radiation dose rate and the molecular mass of PEO had minor influence. The nano-silica contributed to the effects of irradiation implying synergism.

poly(ethylene oxside); radiation chemistry; aqueos solution; silica; nanocomposite; crosslinking

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