High Temperature Tribological Properties of Thermosetting Polyimide

Thermosetting polyimide oligomers with different diamines (isomers) was synthesized with 3,3’, 4,4’-biphenyltetracarboxylic dianhydride (s-BPDA), 4,4’-diaminodiphenyl ether (4,4’-ODA), 3,4’-diaminodiphenyl ether (3,4’-ODA) and 4-phenylethynylphthalide (4-PEPA). Furthermore, dry sliding tests were performed at 25 ℃, 100 ℃, 200 ℃, 250 ℃, 300 ℃ and 350 ℃ on a ball-on-disk wear tester. Mechanisms of friction and wear were studied in detail by scanning electron microscope and energy dispersive X-ray spectroscopy. At elevated temperature, experimental results demonstrated that the wear rate increased first, then decreased and finally increased. However, average coefficient of friction showed a tendency to plummet with temperature range from 25 ℃ to 350 ℃. This trend was attributed to changes in the mechanical properties of the polymer surface. The wear mechanisms at elevated temperatures were different. At 25 and 100 ℃, fatigue wear and abrasive wear prevailed. From 100 ℃ to 200 ℃, a dense of transfer film generated and the thickness increased due to adequate shearing motion of molecular chain. Hence, mild abrasive wear played a major role. Above 250 ℃, wear rate rapidly increased with damage of interaction between the molecular chain and polyimide was peeled on worn surface under the lasted load, adhesive wear was dominant. As a general guideline, higher ambient temperature rendered a greater wear rate.