Investigating the tribological properties of thermoplastic polymer composite materials based on local raw materials

Abstract

This study investigates the tribological and physicomechanical properties of a thermoplastic polymer composite material based on polypropylene, modified with walnut shell pyrolysis residue as a local raw material. The composite's composition consists of 65 wt.% polypropylene, 15 wt.% fine-fraction walnut shell pyrolysis residue, 4 wt.% glycerol monostearate, 1 wt.% zinc oxide, and 15 wt.% R-grade glass fiber. The scientific concept of the research is to reduce the coefficient of friction, increase surface hardness, and ensure the dimensional stability of the material through the synergistic effect of a carbon-rich natural waste-based filler, a glass fiber reinforcing component, and an anti-friction additive within the polypropylene matrix. Composite samples were prepared via the extrusion method. Tribological tests were performed under dry sliding conditions with a contact pressure of 2 MPa and a sliding speed of 0.5 m/s. Furthermore, the material's hardness was assessed using the Shore D method, and its mechanical strength was evaluated by its ultimate tensile strength. The results revealed that the composite with the optimal composition had a coefficient of friction of 0.08, which was significantly lower than that of the comparative sample. For this composition, the ultimate tensile strength was 48.6 MPa, and the coefficient of linear thermal expansion was 0.0001 mm/ (m·°C). The findings indicate that walnut shell pyrolysis residue is significant not only as a simple, low-cost filler in the polypropylene matrix but also as a tribologically active carbon component. Glycerol monostearate, as an additive that reduces friction and facilitates the processing stage, and zinc oxide, as a functional modifier, enhance the operational properties of the composite. R-grade glass fiber increases the load-bearing capacity, hardness, and dimensional stability. The proposed composite material is recommended as a promising material for polymer pipes, protective coatings, and sliding elements that operate in contact with abrasive particles.