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Characterization of blends of PP with vitamins "c" and "e" exposed to gamma radiation at sterilization dose

Abstract:

In this study, the influence of two vitamins (C and E) on the properties of isotactic polypropylene (PP) exposed to gamma radiation at the minimal sterilization dose of 25 kGy was evaluated. To do so, PP was blended in solution with the vitamins at varying concentrations. These formulations were irradiated with gamma rays at a dose of 25 kGy from a 60Co source and then characterized using different techniques such as FTIR, GPC, DSC, TGA, and tensile testing. The incorporation of the different vitamins, either individually or combined, did not avoid the formation of carbonyl groups in the PP after irradiation. Moreover, the average molecular weight of the polypropylene decreased significantly, even in those samples where the additives were present. Tensile tests unfolded an increased stiffness in those samples with individual additives, whereas a decrease was detected in those systems with a combination of them. A decrease in both tensile strength and elongation at break was displayed by the compounds when compared to irradiated PP. An increase in the crystallization temperature was detected when Vitamins C and E were incorporated into the PP, which demonstrated a nucleating effect of these compounds. The highest nucleating effect was found for concentrations of 0.3% of Vitamin E and 0.5% of Vitamin C. For these formulations, more homogeneous melting endotherms and narrower crystallization exotherms were obtained. An increase in the nucleating density in PP was observed as well, when a combination of Vitamins E/C (0.5/0.5%) was employed. © 2010 Springer-Verlag.