Recycling Automotive Plastic Waste: Residual Polyvinyl Butyral (rPVB) as Solid Lubricant in Polyoxymethylene (POM) Blends

Abstract

Polyoxymethylene (POM) is an engineering thermoplastic commonly used in tribological applications due to its low friction and auto-lubrication properties. To improve its performance further and broaden its applications to higher sliding speeds and loads, it is commonly reinforced with different particles, fibers, or solid lubricants. In this study, the effect of adding residual polyvinyl butyral (rPVB) from automotive windshields production lines on the tribological performance of POM during pin-on-disk wear tests at different loads (12, 15, and 18 N) and sliding speeds (0.25, 0.50, and 0.75 m/s) is investigated. It was found that rPVB acts as a solid lubricant, reducing the coefficient of friction (CoF) up to 50%. It is suggested that the formation of a protective layer of adhered material on the wear track is the mechanism behind CoF reduction. Melt flow index, Shore D hardness and elastic properties decrease linearly with rPVB content. However, the reduction in tensile strength, and thus shear strength of the blends, seems to be more significant on their CoF behavior than the reduction in hardness. No trend was found for wear resistance. Under certain sliding conditions rPVB decreased volume loss, but in other cases it increased it. It is suggested that, for the conditions analyzed in this study, adding 10 wt% of rPVB to a POM matrix results in the best balance of tribological performance, with an overall CoF reduction of 36%, and an average volume loss increase of only 1%.