## 1 Introduction
%, while it has been almost linearly increased by more than 1.5 times (up to 3.7 GPa) with a filling degree of 8 wt. %. In [29], epoxy resin composites loaded with UHMWPE fibers have been designed. They have possessed high adhesive properties due to forming interfacial membranes on the surfaces of UHMWPE fibers. The membranes have been polymerized by aldol condensation between glutaraldehyde and polyvinyl alcohol (PVA). According to energy dispersive spectral analysis and X-ray photoelectron spectroscopy, fibers treated with the \"Corona-PG-2S\" agent have shown an oxygen content on their surfaces of 17.3 wt. % more compared to untreated ones. Thus, the adhesive properties have been improved due to the increase in the surface polarity. Flexural strength, ultimate cohesive force, tensile strength, and peel strength of the composites have been significantly enhanced up to 262.8%, 166.9%, 139.7%, and 200.6%, respectively, compared to the samples loaded with untreated fibers. In [30; 31], polyethylene-based composites loaded with heenquen fibers modified with a silane-containing coupling agent have been studied. The results have shown that silane improved the adhesion of fibers to the matrix. Consequently, their strength increased from 71.8 MPa for untreated fibers up to 79.3 MPa for silanized ones. However, it has been found that the resulting strength and stiffness of the composites have depended on the amount of the coupling agent deposited on fibers. The threshold value of the silane concentration has been revealed, above which tensile strength of the composites has not been improved. The efficiency of treatment with silane has been also shown in [32] by an example of epoxy composites loaded with heenquen fibers. The composites loaded with silane-treated fibers have possessed a greater tensile strength than untreated ones. It has been shown that the silane concentration of 1 wt. % has been the optimum for improving the mechanical properties. [PERSON] et. al. [33] have grafted cellulose on the surface of a UHMWPE film by ultraviolet irradiation. Benzophenone has been applied as a coupling agent (this fact has been proved by Fourier-transform infrared spectroscopy). The best results have been obtained after one hour of preliminary treatment with mixed acids and grafted cellulose. An increase in tensile strength of 1400% has been observed, as well as a decrease in tensile strength of oriented UHMWPE films by 10%. Data on contact angles have showed that treated UHMWPE films have been hydrophobic, but hydrophobicity has decreased by 17% compared to untreated ones. In [34], the possibility of designing a coupling agent between UHMWPE and nanoparticles has been evaluated through UHMWPE powder bromination in carbon tetrachloride. Atomic force microscopy (AFM) has showed that adhesion of aluminum nitride (AlN) nanoparticles to brominated particles (Br-UHMWPE) has been higher than that of untreated polymer particles. The enhanced interaction between nanoparticles and UHMWPE has been also proved by the results of mechanical tests. Adhesion strength of AlN particles to Br-UHMWPE ones has been 3.6 times higher than that of untreated mixture. The average values were 1.26 and 4.56 \(\upmu\)N, respectively. Adhesion strength increased by 45% and 260% in the cases of SiC and AlN, respectively. The design of the UHMWPE-based composites with improved mechanical and tribological properties for operating in friction units under dry sliding conditions is an industrially demanded task. The efficiency of the use of fibrous fillers, primarily to improve the mechanical properties of UHMWPE, has been shown in [35; 36; 37; 38; 39]. In [39], the UHMWPE-based composites loaded with wollastonite fibers (aspect ratios of 10:1, 15:1, and 20:1) have been studied. The fibers have been treated by the combined modification with a silane-titanate agent. This is a proper modifier to improve the bond between polymers and inorganic materials, because they contain both hydrophobic and hydrophilic radicals.