## 1 Introduction
In this case, hydrophobic radicals can bind to polymer molecules, and hydrophilic ones are able to joint with molecules of inorganic fillers. Samples have been tested using an abrasive wear tester with a rotating disc and silica sand as an abrasive. It has been shown that wear of the composites has depended on the fiber content, aspect ratio, sizes of abrasive particles, and sliding speed. Loading with wollastonite fibers at their content 5-20 wt. % has improved abrasion resistance of the UHMWPE-based composites. The maximum abrasion resistance has been found at a content of 10 wt. % and an aspect ratio of 20:1. For comparison, volumetric wear has been 102 mm\({}^{3}\) for neat UHMWPE, 73 mm\({}^{3}\) for one loaded with 10 wt. % untreated fibers, and 62 mm\({}^{3}\) for the polymer filled with the functionalized ones. An increase in the fiber aspect ratio has been the most important factor in improving abrasion resistance. Additionally, abrasive wear of the composites has been mainly due to plastic strains, micro-ploughing, micro-cutting, and the formation of micro-cracks. In [40], wollastonite particles have been loaded in porous alumina and UHMWPE by electrophoretic deposition (EPD) to fabricate the alumina-wollastonite and UHMWPE-wollastonite composites. They have been impregnated with simulated body fluid (SBF) to evaluate their apatite-forming ability. Apatite has been induced from wollastonite particles deposited on the composite surfaces. The apatite-forming ability in SBF has been used as an indicator of biological activity. Adhesion strength of the apatite layer with the substrates has reached 8.9 MPa for alumina and 5.2 MPa for UHMWPE. Thus, the designed alumina-wollastonite and UHMWPE-wollastonite composites can be used as bone substitutes. In recent years, fibrous wollastonite, as an inexpensive natural biocompatible mineral filler composed of calcium and silicon oxides (metasilicate CaSiO\({}_{3}\)), has become a common alternative to fiberglass. It is used in the form of needle-shaped particles with sizes (lengths) from 2 up to 40 \(\upmu\)m [41]. Also, it is often applied as a reinforcing filler, which improves both tensile strength and bending strength of the composites. The wollastonite acicular (fibrous) shape provides characteristics comparable to those of fiberglass [42]. As reinforcing additives, wollastonite is typically loaded in an amount up to 20 wt. % for hardening polyethylene and polypropylene. This improves tensile strength by \(\sim\)30%, bending strength by \(\sim\)20%, as well as impact toughness and the elastic modulus by \(\sim\)60% [43]. As in the case of other silicate minerals (for example, fiberglass), the freshly milled surfaces of wollastonite particles attract hydroxyl groups (from water), ensuring adhesion to non-polar polymers [44]. However, it is believed that wollastonite treatment with silane-containing coupling agents improves both adhesion and dispersion [45; 46; 47]. It has been shown in [42] that the fiberglass silarization significantly increases wear resistance and mechanical properties of the UHMWPE composites. In the present paper, the tasks have been solved to design of the UHMWPE-based composites with improved mechanical and tribological properties (compared to neat polymer), and to evaluate the role of increasing interfacial adhesion due to the silarization of wollastonite fibers with various silane-containing coupling agents. The composites are intended to be operated in the metal-polymer tribological units under conditions of dry sliding friction at different load-speed parameters.