Page 180 - Handbook of Surface Improvement and Modification

11.1 Methods and mechanisms of improvement of the coefficient of friction 175

Figure 11.13. Scanning electron microscopy images of (a) non-porous ethylene vinyl acetate (EVA) and (b)–(h)
porous EVA blocks with various porosities. [Adapted, by permission, from Yamaguchi, T; Sugawara, T; Taka-
hashi, M; Shibata, K; Moriyasu, K; Nishiwaki, T; Hokkirigawa, K, Tribology Intl., 116, 264-71, 2017.]
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glass transition temperature. Consequently, the friction coefficient and wear rate of PES/
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PTFE composite rises dramatically.
The poly(ethylene oxide)/polytetrafluoroethylene composite coating has the advan-
tages of wear resistance of PEO and a low friction coefficient and excellent corrosion
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resistance of polytetrafluoroethylene. The PTFE nanoparticles effectively seal the pores
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in the PEO coating. The potentiodynamic polarization and salt spray tests shows that the
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composite coating provides superior corrosion resistance to aluminium alloy. The fric-
tion coefficient remains steady and low during sliding, which could be attributed to the
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effect of PTFE.
The dry sliding friction characteristics of ethylene vinyl acetate blocks vary with
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porosity values, α. Figure 11.13 shows the porosity of the studied samples. The poros-
ity significantly influenced the friction coefficient (i.e., the friction coefficient decreased
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when α < 50% and increased with when α > 50%). The EVA blocks with a higher poros-
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ity (α > 80%) showed larger friction coefficients than the nonporous EVA block. An
elastic collapse at the interior part of the porous EVA blocks was observed at a higher
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porosity. The elastic collapse of porous EVA blocks via elastic buckling of the cell walls
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explained the effect of the porosity on the friction coefficient. The higher α provided
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larger contact areas thereby resulting in a high friction coefficients. The results suggest
that the soft porous polymers can be used as lightweight shoe sole materials with high
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cushioning and high grip, under dry conditions.
The effect of processing temperature on properties of polyetheretherketone has been
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studied. The processing temperature greatly influenced the hardness and the crystallin-
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ity, which, in turn, affected the tribological behavior of the polymer. Samples that were
produced at processing temperatures near or above the melting point of PEEK had a lower
coefficient of friction than the samples produced at a temperature below the melting point
but, the samples with the higher friction values had two-orders-of-magnitude lower wear
rates than the samples with the lower friction values because the samples produced below
the melting point had a distinctive plastic adhesion wear behavior, forming a transfer film,