Correlation between rotational molding process temperature and degradation changes of polyethylene and composites containing coffee spent grounds used as an active filler

Apart from developing novel polymeric compositions, industrially oriented research should consider the critical impact of processing parameters on the structure and properties of final products. It is of vital importance, especially in the case of multithreaded processing, taking into account both the influence of individual raw materials and the process parameters, which may noticeably affect them in situ. Herein, the presented work quantifies the impact of rotational molding (RM) conditions on degradation mechanisms in low-density polyethylene (LDPE) and LDPE-based composites. The experimental technological tests were performed at 200, 225, and 250 °C temperature sets. The influence of different conditions affecting the outer layers of the product (overheating) and inner walls (thermo-oxidation) was analyzed. The polymeric composite was produced using coffee spent grounds (CSG), a waste-based filler rich in active antioxidant compounds, which makes the final material a potential self-stabilizing composite. After processing, samples taken from rotational molded parts were exposed to UV light on the external and internal walls of the product to intensify selected groups of degradation phenomena and to separate the effects resulting from the degradation of the lignocellulosic filler itself, the polymer matrix, and the passivation of active compounds contained in the CSG. Studies have shown that the introduction of 5 wt% CSG, regardless of the degree of degradation of the filler's lignocellulosic structure, did not significantly affect the limitations of stabilization efficiency resulting from the passivation of polyphenolic active compounds. The protection factor (PF), calculated based on oxidation induction time (OIT), decreased by 5 to 23 %, depending on the sample mass, as a result of using a maximum temperature set of 250 °C.