Elevated-Temperature Oxidative Curing, Friction and Wear of Polyphenylene Sulfide (PPS) and its Composites



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Every day more high-performance polymers composites overcome demanding dynamic sealing conditions in industrial applications, like rotary and reciprocating machinery. Low friction and wear, especially at elevated temperatures, are the dominating selection criteria in these applications. Compared with other polymers in this category, Polyphenylene Sulfide (PPS) shows an impressive set of characteristics such as superior resistance to solvents, good mechanical properties, versatile processing, and lower price. However, the lack of understanding of its complex processing, which involved curing reactions, and the effect of those reactions on its mechanical properties had hindered its development as a matrix for self-lubricated polymer composites. Moreover, little is known about its friction and wear behavior at high temperatures and the role of conventional fillers like PTFE, graphite, and carbon fiber on its performance. In this study, thermal colorimetry was used to describe the influence of processing parameters on PPS morphology due to its oxidative curing reaction. Then a set of PPS composites with different weight fractions of PTFE, short carbon fiber, and graphite were obtained by compression molding. Its mechanical response as a function of temperature was evaluated, and its tribological behavior was analyzed on a Pin-on-disk tester to understand the role of surface temperature, transfer film and individual fillers. An experimental method to qualify the degree of curing was developed, and its relationship with crystallization kinetics was established. The tribological test results show that both PPS and PTFE friction and wear are affected by sliding speed (0.05 to 0.5 m/s) but not significantly by the normal load (0.25 to 2 MPa). In the case of the PPS/PTFE composites, there is a significant decrease in the friction coefficient and specific wear rate, with the addition of PTFE up to 19% in weight. Moreover, the addition of short carbon fiber dramatically improves both frictions and wear behavior. A special emphasis was taken on the changes of the transfer film characteristics with the different fillers and contact surface temperature during the tribological testing, proving that the transfer film played a significant role in determining the friction and wear characteristics of PPS, PTFE/PPS blend, and its composites.



Polyphenylene Sulfide, Composites, Tribology, Friction, Wear