Microstructure and Tribological Properties of TPU/Fluoropolymer Composites

Abstract A network of poly(tetrafluoroethylene) (PTFE) microfibers in a thermoplastic polyurethane (TPU) was prepared by melt mixing the TPU with solid PTFE particles. The effect of rotor speed on the fiber dimensions was investigated. Higher shear stress was found to be the critical parameter for producing thinner PTFE fibers, rather than the shear rate imposed by the mixer. Shear stress transfer from the melt to the PTFE crystal results in solid phase plastic deformation, and the efficiency of the deformation depends on the shear stress in the matrix. All of the PTFE fiber/TPU composites show lower coefficients of friction compared with the neat TPU. The magnitude of the coefficient of friction was found to correlate with the interfacial area between PTFE and TPU generated by the microfiber network. However, for macroscale PTFE agglomerates, the reduction in the coefficient of friction is mostly affected by the uneven distribution of PTFE in the bulk and on the molded part surface.