Toughening mechanism in polyoxymethlene/thermoplastic polyurethane blends

In order to better understand the toughening mechanism in polyoxymethylene (POM)/thermoplastic polyurethane (TPU) blends and obtain 'super-toughened' POM, we carried out an investigation on the notched impact strength, fractured surface, inter-particle distance and spherulite size of POM as a function of the TPU content. A compatibilizer, namely polystyrene-block-poly(ethylene-butylene)-block-polystyrene, grafted with maleic anhydride (SEBS-graft-MA), was used to enhance the interfacial interaction between the POM and TPU. The impact strength is found to increase in two steps as a function of TPU content, namely a linear increase at the very beginning, and then a jump of impact strength is seen when the TPU content is larger than 30 wt%. A 'supertough behavior' is not observed for POM/TPU blends at room temperature, but can be achieved after adding 5 wt% of SEBS-graft-MA as the compatibilizer. The impact strength was found to depend not only on the interparticle distance but also on the interfacial interactions between POM and TPU. The dependence of impact strength on crystal size is considered for the first time, and a single curve is constructed, regardless of the composition and interfacial interactions. Our results indicate that the crystal size of POM indeed plays a role in determining the toughness, and has to be considered when discussing the toughening mechanism. (C) 2004 Society of Chemical Industry.