Fatigue behaviour of injection-moulded polymer blends of polypropylene and liquid crystalline polyester

Abstract Fatigue processes in injection-moulded blends of polypropylene (PP) and a liquid-crystalline polyester (LCP) were investigated with reference to variations in the inner microstructure and the dynamic viscoelastic properties under cyclic tensile loading. For neat PP, whitening caused by inter-spherulite and/or interlamella microcrazing was observed over a wide range within the specimen, and the storage modulus E ′ and the loss tangent than δ monotonically decreased and increased, respectively, until fracture. For the neat LCP specimen, on the other hand, the molecular orientation progressed all over the specimen during fatigue, and, as a result, E ′ remained almost constant and tan δ clearly decreased, until they were drastically reversed just before fracture. In the blends containing over 40 wt% of the LCP, the influence of LCP was so strongly reflected as to reduce tan δ during fatigue and to extend the fatigue lifetime. In addition, it was observed that the PP and the LCP phases closely attach to each other under loading. Such morphological change in the blended specimens with higher LCP content was also considered to contribute to a decrease in tan δ during fatigue and to the extension of their fatigue lifetimes.