Page 179 - Handbook of Surface Improvement and Modification

174 The Coefficient of Friction

Figure 11.11. Schematic diagram of the interactions (van der Waals and acid-base origins) between a silicon
nitride tip and macromolecules of (A) a polystyrene with high molecular weight, (B) a polystyrene with low
molecular weight. Capillary bridges between the tip and the polystyrene surface are represented. [Adapted, by
permission, from Ghorbal, A; Brahim, AB, Polym. Testing, 32, 1174-80, 2013.]

adhesion, a higher friction coefficient is
expected for larger macromolecular
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chains. Figure 11.12 shows the relation-
ship between the molecular weight of poly-
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styrene and the friction force.
The influence of the material pairs
configuration on tribological properties of
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polyamide-6 has been examined. The
moving body defines the efficiency of heat
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removal resulting from a friction. It is,
therefore, important to make moving body
from a more thermally conductive material
(stainless steel pin was more effective in
heat removal from PA-6 disc than PA-6 pin
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from stainless steel disc). The self-mated
Figure 11.12. Molecular weight of polystyrene vs. fric- PA-6/PA6 contact exhibited the worst tribo-
tion force. Velocity = 10 mm/s. [Data from Ghorbal, A; logical properties because of inability to
Brahim, AB, Polym. Testing, 32, 1174-80, 2013.]
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remove the heat from the contacting parts.
Polyethersulfone was blended with polytetrafluoroethylene to improve its tribologi-
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cal properties. The performance of anti-friction and wear resistance of the PES/PTFE
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composites were far better than that of the virgin PTFE. The tribological behavior of the
PES/PTFE composite is governed by the interaction between the PTFE transfer film and
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the PES layer. The 40 wt% of PES gave the best tribological properties, attributed to the
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coexistence of the uniform PTFE transfer film and the continuous PES layer. The heat
accumulated during the friction may be the primary reason for critical values of load,
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velocity, and ambient temperature. When the sliding parameters are higher than the crit-
ical values, PES can be easily deformed because the interfacial temperature reaches its