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The effect of input doses of 60Co γ-radiation from 80 to 12,000 kGy on the thermophysical properties and thermal stability of samples of polypropylene granules and powder obtained by high temperature shear grinding of irradiated granules, as well as on the tensile strength properties of a plate made from irradiated granules and their corresponding powders, was studied. The thermophysical properties of the powder are determined by the changes introduced by radiation into the initial polymer granules. The effects of radiation in air (environments with oxygen) were studied. Grinding redistributes oxygen-containing functional groups from the surface layer of irradiated granules throughout the entire volume of the obtained powder leading to the destruction of polymer chains as there is a component due to thermal destruction of radiolyzed polymer chains. High-temperature shear grinding of irradiated granules has a significant effect on the product powder, reducing its thermal stability but increasing the tensile strength of plates pressed from it at low absorbed doses. The current work shows that radiation treatment coupled with high temperature shear grinding could be a method for modifying the properties of polymers so that polypropylene waste can be processed for other applications. 

The effect of γ-irradiation in vacuum and air followed by HTSG of polypropylene (PP) is studied using both infrared (IR) spectroscopy and computational chemistry at the correlated G3(MP2)B3 molecular orbital theory level. γ-irradiation of PP in vacuum was found to primarily induce unsaturation and hydroxyl formation from residual system water whereas γ-irradiation of PP in air oxidizes the polymer and degrades the backbone in a thin layer due to oxygen permeability limitations as supported by the computational thermodynamics results. HTSG of the irradiated PP produced smaller particles than un-irradiated PP. HTSG of the irradiated PP led to a decrease in the IR band intensity from degradation due to a nominal homogenization of the pellet. HTSG of air irradiated PP led to a reduction in IR vibrational band intensity from oxidation due to thermal degradation. High-temperature shear grinding of γ-irradiated PP produces variable chemical and physical composition depending on irradiation input dose and environmental conditions. The combination of γ-irradiation and HTSG may be of benefit in recycling polypropylene.