Enhanced crosslinking of polypropylene in γ-irradiation via Copper(Ⅱ) doping

Crosslinked Polypropylene (PP) has a greater application prospect due to its excellent properties, hence, how to improve the crosslinking of PP is significant. In our research, the effects of γ-irradiation on the crosslinking of PP blended with copper(Ⅱ) acetate monohydrate were investigated. Firstly, PP was melt-blended with a crosslinking agent (1,2-Polybutadiene (PB) or Trimethylolpropane triacrylate (TMPTA)) and copper(Ⅱ) acetate monohydrate in a twin-screw extruder, then treated with various γ-irradiation dose. The influence of copper(Ⅱ) content and radiation dose on crosslinking of PP was characterized by gel content, melt flow index measurement (MFI), rheological analysis measurement, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The results of gel content, MFI, and Rheological analysis indicated that the copper(Ⅱ) could enhance the crosslinking of both PP/PB and PP/TMPTA at all ranges of radiation dose, more particularly, the enhanced effect was much prominent at low radiation dose, and of which is more obvious in the latter system. The crosslinking effect based on the mechanism of copper(Ⅱ) catalysis enhanced was also discussed, which is assumed as the promotion of free radical production during irradiation processing. In addition, the copper(Ⅱ) would also enhance the thermal stability of the γ-irradiation treated PP/PB and PP/TMPTA blends, and decrease the crystallinity and the melting point. This paper provided a novel method to increase the irradiated crosslinking of PP at a lower irradiation dose, which was expected to expand its application field.