Use of Gamma-Irradiated Polypropylene to Control the Degradation of Some Polyolefinic Blends

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This work was concerned with the use of gamma irradiated polypropylene (PP) to control the degradation of some polyolefin blends. Six samples of PP/PE blends were prepared and irradiated with gamma rays from 2.5 Mrads to 12.5 Mrads. Data showed that PP content in the blends and irradiation level could play a great role in controlling the degradability of the PP/ PE blends. The mechanical properties, like tensile strength and elongation and other physical properties were observed as measures of the degradability of these PP/PE blends. These blends were exposed to accelerated weathering and natural weathering under Kuwait climate and a correlation was found. Results showed that PE got cross-linked upon irradiation, and its tensile strength increased as irradiation dose increased from 0.0 to 12.5 Mrads. The presence of PP in the PP/PE blend drastically reduced the elongation percentage of the blend with and without irradiation. Increase in PP content in the blend drastically decreased tensile strength after only 5.0 Mrads of irradiation dose. The presence of PP in the blend increased the blends tensile strength with the irradiation dose similar to pure PE. The presence of PP in the PP/PE blend 20/80 accelerated the degradation process where 50% reduction in tensile strength occurred in 8 d compared to 16 d in the absence of PP in the blend under the same accelerated weathering conditions and for all irradiated samples. PE irradiated with a dose of 12.5 Mrads lost 50% of its tensile strength after 24 d of accelerated weathering compared to PP/PE blend 20/80 where the same loss of 50% took place after only 4 d of accelerated weathering. Un-irradiated PP/PE blends 0/100 and 20/80 lost 50% of original tensile strength after exposure to natural weathering for 2 and 1.3 mo respectively, indicating that PP accelerated degradation with and without irradiation. The tensile strength of irradiated PP/PE blend 0/100 exposed to 16 d at accelerated weathering was equivalent to exposure to 2.0 mo at natural weathering in Kuwait. Melt flow Index (MFI) was found to be a good measure of degradability where a reduction in molecular weight took place upon aging. Color density increased as the time of exposure increased for both irradiated and un-irradiated PP/PE blends, and as the irradiation dose increased. The hazed change decreased as the time of exposure and as PP percentage in the blend increased. Blends containing 0.0%, 20%, 40%, 60%, 80% and 100% of PP lost 50% of their original tensile strength in about 16 d, 8 d, 5 d, 4 d, 2 d, and 4 d, respectively of accelerated weathering (QUV) exposure time for all irradiation doses (0.0 Mrads – 12.5 Mrads). The same drop of 50% of tensile strength for the same blends exposed to natural weathering took place in 2.0 mo, 1.0 mo, 1.9 mo, 1.0 mo, 0.5 mo and 1.0 respectively.