PSI - Issue 40

A.A. Ushkanov et al. / Procedia Structural Integrity 40 (2022) 440–444 A.A. Ushkanov, S.A. Sleptsova / Structural Integrity Procedia 00 (2022) 000 – 000

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In fig. 1, visible fibers of different nature on the friction surface of the composites. They are randomly distributed and protrude from worn surfaces. It is presented in the literature (Vasilev et al. (2019)) that PTFE undergoes destructive-structuring transformations during friction, which determine the nature of the formation of friction surfaces and the tribotechnical characteristics of a friction pair. It is possible that the fibers localized on the surface layer of the composites protect it from destruction, due to which the wear resistance increases. It is worth noting the nature of natural fibers. In the work by Mohammed Layth et al. (2015), it is described that the main disadvantage of such fibers is that the structure of the fibers allows them to absorb moisture from the environment, which causes weak bonds at the polymer-filler interface. However, we observe that the friction surface of composites with basalt fibers (Fig. 2b) is characterized by relative smoothness and no visible damage. To better clarify the effect of natural fiber at the polymer-fiber interface on the properties of composites, the supramolecular structure of the composite has been studied in more detail. Carbon fibers in the studied fluorine composite are randomly distributed. They are localized close to each other. From the analysis of the presented micrographs, it can be assumed that the wear of the material is accompanied by the removal and tearing of both polymer particles and individual fibers from the boundary regions (Fig. 2c).

Fig. 3. Basalt fiber surface morphology and su pramolecular structure of composites based on PTFE: (а) BF (x5.00k); (b) PTFE + 18 wt.% BF (x150); (c) PTFE + 18 wt.% BF (x500)

According to the literature (Fig. 3a), the original continuous fiber has a smooth surface without significant defects (Rybin (2016)). As can be seen, in the micrographs of composites with basalt fibers (Fig. 3c), there are fibrillar filaments on the surface of the fibers. We assume that the found ribbons on the fiber surface are the crystalline phase of the polymer. This assumption can be proved by an increase in the degree of crystallinity of the composites by 20% compared to the initial polymer. Generally, high crystallinity values are observed in composites with basalt fibers. This behavior of the increase in crystallinity is possibly associated with an increase in the adhesive interaction of the polymer with basalt fibers due to the natural composition of the reinforcing fibers. 4. CONCLUSIONS Analysis of the results of the degree of crystallinity, tribotechnical and structural characteristics allows us to conclude that there is an increase in the degree of crystallinity of composites by 20% in comparison with the pure polymer. This is since there is an effect of fillers on the processes of structure formation of the polymer matrix. When the polymer matrix is filled with basalt or carbon fibers, the wear resistance increases up to 500 times compared to the initial polytetrafluoroethylene, which indicates the formation of a protective film, which in turn localizes the shear deformation and protects the surface layer of the composites from destruction. Thus, composites