{'fraction_non_alphanumeric': 0.024934383202099737, 'fraction_numerical': 0.010498687664041995, 'mean_word_length': 5.327800829875518, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Tribological Properties of Thermosetting Polyimide/TiO2 Nanocomposites Under Dry Sliding and Water-Lubricated Conditions

Thermosetting polyimide(PI)-based nanocomposites containing various contents of nano-TiO2 were fabricated via an in situ polymerization of monomer reactants (PMR) process. Under dry sliding and water-lubricated conditions the friction and wear behaviors of the PMR PI and its nanocomposites were evaluated and compared. The addition of nano-TiO2 in PI contributed to improving the friction and wear behavior considerably under dry sliding. The highest change ratio of wear rate was 61% with the optimum nano-TiO2 content of 3%, while the highest change of friction coefficient was 60% with the optimum nano-TiO2 content of 9%. Under water-lubricated condition, contrarily, the addition of nano-TiO2 in PI does harm to the tribological properties. Namely, the friction coefficient of the nanocomposites increased with increasing the nano-TiO2 content. These results may be caused by the following facts: the hardness of the PI matrix would be increased by adding the nano-TiO2 reducing the ability of elastic deformation of the nanocomposites; accordingly, the poor elastic deformation hindered the formation of a water-lubrication film on the surface. An investigation on the wear tracks indicated that the wear mechanism of PI/TiO2 nanocomposites under dry sliding condition proceeded from fatigue wear to a combination of fatigue wear and abrasive wear with increasing the mass fraction of nano-TiO2.