Dry sliding friction and Wear behavior of thermoplastic polyurethane against abrasive paper

Thermoplastic polyurethane (TPU) is attractive as the outer sole of running shoes because of its excellent mechanical properties and ease of processing. This study investigated the friction and wear of TPU block against counterpart materials with different surface roughness (Ra). The results indicated that the friction coefficient values of TPU exceeded 1.0 regardless of Ra of counterpart material, and were greater than those of conventional rubber materials; butadiene rubber (BR) and styrene butadiene rubber (SBR). The specific wear rate for all materials tended to increase with Ra. In addition, although the specific wear rate for TPU was higher than that of BR, TPU showed better wear resistance than that of SBR. On the basis of observation of worn surfaces of TPU and rubber specimens with scanning electron microscopy (SEM), the wear modes could be classified into three types; pattern wear, abrasive wear, and mixed wear mode consisting of both pattern wear and abrasive wear. The wear modes for TPU, BR, and SBR block specimens changed with increase in Ra of the counterpart material. For discussion, when Ra of the counterpart material was small, TPU provided large adhesion friction, resulting in a large friction coefficient compared with those of conventional rubber materials. When Ra of the counterpart material was large, TPU provided large deformation friction, which resulted in a large friction coefficient compared with those of rubber materials. These results demonstrated the applicability of TPU as the outer sole of sports shoes in terms of its higher friction and similar wear resistance compared with those of conventional materials.