Tribological Properties of PTFE-Filled Thermoplastic Polyimide at High Load, Velocity, and Temperature

The effect of 20 wt% polytetrafluoroethylene (PTFE) fillers on the friction and wear properties of thermoplastic polyimides (TP) are investigated, under dry sliding in line contact against steel under 50 to 200 N, 0.3 to 1.2 m/s, and 60 to 260 degrees C. Besides the lubricating mechanisms of PTFE based on mechanical shear, the thermal and tribophysical interactions in the sliding interface are considered in this research by using thermoanalytical measurements, Raman spectroscopy, and calculating the maximum polymer sliding temperature T*. The effect of hydrolysis of the TP bulk material, causing high friction at 100 to 140 degrees C, is covered by PTFE. A transition at pv-values 2.2 MPa m/s (T* = 120 degrees C) is due to thermally controlled sliding of PTFE, while a transition at pv-values 3.2 MPa m/s (T* = 180 degrees C) remains controlled by degradation of the TP bulk material into monomer fractions. The reduced coefficient of friction in the presence of PTFE leads to smaller degradation and orientation of the molecular back-bone and side-chains within the TIP structure. The formation of a homogeneously mixed transfer film is only observed at 180 to 260 degrees C. The PTFE forms a fibrillar structure during wear at high sliding velocities, while they wear as separate particles at high normal loads. POLYM. COMPOS., 30:1631-1646, 2009. (c) 2009 Society of Plastics Engineers