Specific features of creep and tribological behavior of polyimide-carbon nanotubes nanocomposite films: Effect of the nanotubes functionalization

The nanocomposite films were synthesized based on the thermally stable benzoxazole-containing aromatic polyimide. The multi-walled carbon nanotubes in the concentrations from 0.25 to 1.0 wt.% were introduced in the matrix polymer as a nanofiller. Two types of nanotubes were used: the pristine nanotubes and those containing COOH-groups attached to the nanotubes' surface. The impacts of the nanoparticles on the mechanical properties of the films in both single extension and creep conditions, and on the tribological properties of the material in the polymer/steel friction couple were tested. The positive actions of the COOH-containing nanotubes on both the mechanical properties and the tribological behavior of the studied materials were evidenced. These effects can be caused by the formation of the tightly packed nanocomposite structure in which the H-bonds are formed between CO- groups of the imide cycles of the polymer chains and COOH-groups of the nanotubes. The COOH-pretreatment hinders the aggregation processes of the nanotubes if their concentration in the composite films is less than ~1 wt. %.