Molecular dynamics study on the thermal, mechanical and tribological properties of PBI/PI composites

Temperature resistance of polymer determined their service life as frictional materials. In order to improve the glass transition temperature (Tg), mechanical strength and wear resistance of polyimide (PI), the polybenzimidazole (PBI) with high temperature resistance was introduced for blends. However, research on the blending mechanism of PBI/PI composites were still not fully understood at the atomic level owing to the difficulty in situ experiments. Therefore, molecular dynamics simulation was employed to predict their thermal, mechanical and tribological performance of PBI/PI composites. Results indicated that the glass transition temperature, Young’s modulus and shear modulus of PI increased with an increase of PBI contents, while the friction coefficient of PBI/PI composites sliding against copper decreased. 50%PBI/PI composite had the highest Tg of 575 K increased by 11.2%, Young’s modulus of 8.64 GPa increased over three times and the smallest friction coefficient decreased from 0.16 to 0.11. The thermal expansion ratio of 50%PBI/PI composite also decreased compared to pure PI. The inherent mechanism was explored by analyzing the intermolecular forces. The fractional free volume (FFV) and mean square displacement (MSD) decreased after filling PBI because of strong adsorption effect between PI and PBI molecular, which restricted the movement of PI. Therefore, the thermal resistance and mechanical properties were improved after filling PBI.