Page 182 - Handbook of Surface Improvement and Modification

11.1 Methods and mechanisms of improvement of the coefficient of friction 177

Figure 11.18. SEM images of a typical woven polyester fabric subjected to (a–c) hydrophobic treatment with
metal soap particles, and (D–f) treatment with the cationic surfactant at different magnifications. [Adapted, by
permission, from Mondal, S; Reddy, V; Sarkar, A; Aravindakshan, P; Ghatak, A, Tribology Intl., 97, 38-48,
2016.]

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rics. The friction values measured in the palm of the hand displayed a marked effect of
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the gender. Wool produced the highest friction coefficient in both body regions for men
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and women.
Measuring the tribological attributes of human skin is of limited value when it comes
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to haptic perception. The subjective perception of grip and slipperiness shows the poor
correlation between the coefficient of dynamic friction and the perceived gliding quality
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of a surface. Figure 11.16 shows the texture of 3 different polymers with two of them
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typically considered soft (EPDM/ABS and PU). The EPDM/ABS has the highest fric-
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tion coefficient of the three samples and its ranking agrees with human perception. The
remaining two materials (PC and TPU) do not differ significantly in respect to their fric-
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tion coefficients but they do so in the perception of their gliding properties. In addition,
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skin moisture and age influenced the grip perception.
Characterization of frictional characteristics of textile fabrics is difficult because of
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the surface heterogeneity in both topography and the surface chemistry. Aqueous disper-
sions of hydrophobic metal-soap particles and long-chain cationic surfactant were used to
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modify frictional properties of polyester fabrics (Figure 11.18). The surfaces can be
characterized by the distribution of friction coefficient and the amplitude of the dominant
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mode of the fluctuations. These parameters distinguish between different fabrics and
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quantify the extent of the treatment.
Various friction test set-ups were compared with respect to the measured coefficients
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of friction (Figure 11.19). A fabric of commingled yarns of glass and polypropylene fila-
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ments and a metal surface were used in determination of friction. Tests at ambient tem-
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perature and above the melting point of polypropylene were carried out. Systematic
differences were observed between the measurements obtained by the different set-ups. 20