## 4 Discussion
Therefore, in addition to the factors mentioned above, this gave the following effects:* prevented debris removal and reduced abrasive wear of the components due to better retention of fibers in the polymer matrix;
* reduced wearing the polymer matrix and breaking fibers by tensile loads due to higher strength and less strains of the composites;
* decreased stress gradients at the interface between the filler and the polymer due to the formation of a transition layer between them; and
* deteriorated the polymer matrix and, accordingly, the mechanical and tribological properties of the composites due to the complex chemical structure. The results of the analysis of the mechanical test data (Tables 1-4) were consistent with the latest statement. Loading with the \"OTS\" coupling agent reduced yield strength of the \"UHMWPE + 23% wollastonite\" composite compared to that of the untreated one. It could also be the cause of the ambiguous change in wear resistance as a function of the silanization efficiency. Despite the fact that the \"UHMWPE + 23 wt. % wollastonite + KH-500\" and \"UHMWPE + 15 wt. % wollastonite\" composites were recommended according to Sections 3.3 and 3.4 for use under the moderate and severe conditions of tribological loading, respectively, these compositions had been designed by summarizing all the tribological, mechanical, and physical properties considered by the computer algorithm. It should be noted that the designed composite really possessed the minimal wear rate under the moderate conditions of tribological loading, while the \"UHMWPE + 23 wt.% wollastonite + Penta-1006\" and \"UHMWPE + 23 wt. % wollastonite + OTS\" composites were the best ones for the severe conditions. They were not characterized by the maximum yield strength (compared to that of the \"UHMWPE + 23 wt. % wollastonite + KH-500\" composite). In most cases of the moderate and severe tribological conditions, loading with the \"OTS\" coupling agent was accompanied by the minimal wear rate at almost all filling degrees. This conclusion was based on the results of the comparison of the data presented in Figure 7.  
However, in addition to the contribution of each coupling agent to the interfacial adhesion value, their different chemical nature also affected the polymer matrix structure. Therefore, it was impossible to unambiguously interpret the \"adhesion-wear resistance\" correlation according to the obtained results. Moreover, this relationship was not the same under the moderate and severe conditions of tribological loading. Further, the authors stated that the maximum wollastonite content had to be 23 wt. % as the key condition for the summarized interpretation of the tribological test data (first of all, according to the criterion of the maximum increase in the strength properties without considering the decrease in impact strength). In the framework of this formulation, loading with all the studied coupling agents made it possible to improve wear resistance under the moderate conditions of tribological testing with respect to untreated wollastonite fibers (Figure 7a). The minimal wear rate was characteristic of the most effective \"KH-550\" coupling agent (although these composites and neat UHMWPE possessed close wear rate values of approximately \(0.49\times 10^{-6}\) mm\({}^{3}\cdot\)N\({}^{-1}\cdot\)m\({}^{-1}\)). In this case, wear rate was calculated considering the elastic recovery, namely, 24 h after the end of the tribological tests (it was equal to approximately \(1.34\times 10^{-6}\) mm\({}^{3}\cdot\)N\({}^{-1}\cdot\)m\({}^{-1}\) immediately after the tests). It should be noted that wear rate was slightly higher than \(0.57\times 10^{-6}\) mm\({}^{3}\cdot\)N\({}^{-1}\cdot\)m\({}^{-1}\) for the least active \"OTS\" coupling agent. It follows from the analysis of the photographs in Figure 10 that the minimal wear rate was accompanied by the formation of the smoother wear track surfaces (Figure 10c,e) with such significant wollastonite content (23 wt.%) in UHMWPE compared with that of neat polymer (Figure 10a).