Blends of thermoplastic polyurethane and maleic-anhydride grafted polyethylene. I: Morphology and mechanical properties

Thermoplastic polyurethane elastomers (TPU) and polyethylene (PE) form immi scible blends with an extremely low compatibility. In order to improve the dispersion, stability, and properties of these blends, polyethylene was gra fted with maleic anhydride (PE-g-MA). Subsequently, it was blended with a c ommercial polyester type TPU in a twin-screw extruder. With PE-g-MA as blen d component, the particle size was dramatically reduced in comparison with PE. Coalescence was significantly reduced and the increase in particle size with composition was less pronounced than in blends with PE. In addition, the phase adhesion and the mechanical properties were improved by using PE- g-MA as minor component. Grafting of the MA onto the PE leads to a decrease of the molecular weight, the melt viscosity, and the mechanical. propertie s of the pure PE. Hence, the reactive blend system exhibits a lower viscosi ty ratio. Comparison of these results with those from uncompatibilized blen ds with different viscosity ratios revealed that the reduction in viscosity ratio has a big influence on the blend morphology and because of that on t he mechanical properties. In addition, there is a further effect on morphol ogy and properties caused by the reduction in interfacial tension, which re sults from the compatibilizer formed at the interface.