engleski

Radiation effects in solid, molten and dissolved poly(ethylene oxide)

Poly(ethylene oxide), PEO, is semicrystalline polymer that mostly degrades if irradiated in air while crosslinks in the inert atmosphere. The reduction of the degree of crystallinity of PEO brought in by both degradation and crosslinking is preferred for some applications. The first goal of this study is to determine the influence of less studied factors like aggregate state and sample form on the outcome of irradiation. Samples of solid, molten PEO and its aqueous solutions were irradiated by 60Co gamma -radiation in air and in nitrogen to selected doses. The changes brought into PEO by radiation were investigated by differential scanning calorimetry (DSC), FTIR spectroscopy, microscopy and X-ray diffraction (WAXD). The greatest changes were observed in PEO samples irradiated as aqueous solutions, most likely because of higher crosslinking extent. The DSC peaks of solid samples broadened, while diffraction maxima showed increase of crystallite size at lower doses. The WAXD was not able to detect any shifts of maxima that would indicate the structural changes. Another goal was to find how much information on radiation effects can be obtained by FTIR spectroscopy. In FTIR spectra recorded on erasing the thermal history by heating-cooling cycles, the absorption intensities of – C– O– C– vibration (triplet at around 1100 cm-1) showed the most prominent changes on irradiation. In the samples irradiated in solid state the intensities of those absorptions changed similarly to changes in the heats of crystallization determined by DSC: an increase at lower doses due to crystallization of shorter polymer chains formed on degradation in more radiation-sensitive amorphous part followed by the decrease at higher doses as a result of further degradation1. On the other hand the intensities of free – OH increased with almost identical trend as decrease of the crystallization temperatures. At higher doses triplet broadens and vibrations characteristic of crystalline PEO at 1342 cm-1 and 1360 cm-1 merge into a single absorption that is typical for melt indicating amorphization due to significant degradation. Oxidative degradation in air caused appearance of carbonyl absorptions and vinyl absorptions in FTIR spectra of solid samples. The results indicate that degradation prevails in PEO irradiated in molten and in solid state especially in contact with air, while similar decrease in crystallinity in aqueous solution without oxidative changes suggest crosslinking.

poly(ethylene oxide); gamma irradiation; degradation; crosslinking; FTIR; DSC; XRD

nije evidentirano