MORPHOLOGY AND PROPERTIES OF BLENDS WITH DIFFERENT THERMOPLASTIC POLYURETHANES AND POLYOLEFINS

Unmodified blends of two thermoplastic polyurethanes (TPU) and six pol yolefines were used to study the influence of the component viscositie s on the blend morphology and mechanical properties. Blends were produ ced by melt mixing using a twin screw extruder. Interactions between t he blend components could not be detected by DSC, DMA, selective extra ction, and SEM micrographs of cryofractures. The variation in tensile strength with blend composition produce a U-shaped curve with the mini mum between 40 and 60 wt % of polyolefine. At similar viscosity ratios (eta(d)/eta(m)), blends with polyether based TPU(TPU-eth) have a fine r morphology than blends with polyester based TPU (TPU-est). This is d ue to the lower surface free energy of the polyether soft segments com pared to the polyester soft segments. Different morphologies also lead to changes in mechanical behavior. Blends with TPU-eth show a lower d ecrease in tensile strength with blend composition than blends with TP U-est. The viscosity ratio between TPU and polyolefines can be directl y correlated to the blend morphology obtained under similar blending c onditions. TPU/PE blends show a lower dispersity than TPU/PP blends, d ue to the higher viscosity ratios of TPU/PE blends. This results in a greater reduction in tensile strength with the disperse phase content. (C) 1997 John Wiley & Sons, Inc.