Radiolysis of composite polypropylene/hemp fibers

This paper presents the results of the research on the effects of ionizing radiation on the properties of a composite material consisting of polypropylene (PP) and hemp fibers (HFs). The radiolysis effects were investigated for the composites having HF contents in the amounts of 10, 20, 30, and 40% by weight, as well as for pure PP. Particular attention was paid to the protective effects the aromatic compounds contained in the HF had on the radiolysis of PP/HF composites. This phenomenon may explain the deviations that the irradiated composites displayed upon the addition of HFs and their dependency on the HF content. Both the granules and the standardized composite specimens were subjected to radiation treatment. The gas chromatography (GC) technique was employed to determine the yield of radiolytically generated hydrogen (GH₂) and absorbed oxygen (GO₂). The oxidation phenomenon was studied during irradiation, 24 h after irradiation, and after a 40-day aging period at room temperature. Changes in the melt flow rate (MFR) and the mechanical properties were also determined. It was described how the radiation treatment of the investigated composites accelerates their degradation. It was found that this effect applies to both HF and PP. It was also demonstrated that PP not only does not enhance the resistance of HF to oxidation but, on the contrary, accelerates the processes of their post-radiation degradation. It was further observed that the phenomenon of postradiation degradation can be controlled by changing the PP content in the composite, as well as the amount of aromatic compounds present in the HF. The amount of the absorbed dose allows us to control the degradation time of the PP/HF composites. This applies in particular to the chain oxidation of the PP matrix triggered by the ionizing radiation. It was also found that composites based on PP and natural fibers susceptible to radiation degradation may have significant implications for the use of easily degradable polymer materials in the environment.