Upcycled Wollastonite from Boric Acid Waste as a High-Performance Filler for Composites

Ultra-high molecular weight polyethylene (UHMWPE) suffers from low wear resistance and an insufficient elastic modulus, limiting its use in friction units. In this study, UHMWPE-based composites filled with wollastonite (0.5–5 wt.%) derived from boric acid production waste via alkaline treatment at room temperature and calcination at 900 °C were fabricated. Filler distribution in the subsurface layer under sliding friction was examined using XRD, FTIR, Raman spectroscopy, and SEM with energy-dispersive X-ray mapping. Concentration-dependent particle migration was observed: at 0.5–1 wt.%, wollastonite migrates toward the friction surface, while at 5 wt.%, migration is suppressed. Wollastonite agglomerates participate in the formation of secondary tribostructures that control wear resistance. The introduction of 0.5 wt.% wollastonite led to a 15% increase in tensile strength and an eightfold reduction in wear rate (from 0.57 × 10−6 to 0.07 × 10−6 mm3/(N·m)). At 5 wt.%, the elastic modulus increased by 30%. The correlation between the distribution patterns, contact-zone temperature, and wear mechanisms is discussed. Controlling filler migration and agglomeration in the subsurface layer is considered the key to producing high-quality polymer composite materials (PCMs) with predictable tribological properties.