Postmortem raman spectroscopy explaining friction and wear behavior of sintered polyimide at high temperature

With their thermal stability and high strength, polyimides are an aromatic type of polymers that are used in sliding equipment functioning under high loads and elevated temperatures. However, their tribological behaviors under high temperature and atmospheric conditions are not fully understood. It has been reported that a transition from high to lower friction occurs “somewhere” between 100 and 200 °C; however, correlation with changes in the polyimide molecular structure remains difficult to illustrate, and it is not certain whether this transition is correlated to lower wear. In the present work, sliding experiments under controlled bulk temperatures between 100 and 260 °C are performed. A transition in both friction and wear at 180 °C is observed that is further examined with microscopic analysis of the transfer film on the steel counterface and Raman spectroscopy of the worn polymer surfaces. Close examination of the spectra reveals transitions in the relative intensities of certain absorption bands, which suggests different orientation effects of the molecular conformation at the polymer sliding surface at 180 °C.