The Mechanical and Thermal Properties of Polyoxymethylene (POM)/Organically Modified Montmorillonite (OMMT) Engineering Nanocomposites Modified with Thermoplastic Polyurethane (TPU) Compatibilizer

摘要

In this work the effect of macromolecular polyurethane compatibilizer on the structure, mechanical and thermal properties of polyoxymethylene/organically modified montmorillonite (POM/OMMT) nanocomposites was investigated. The thermal stability of obtained systems was significantly enhanced by compatibilizer both in oxidative and inert atmosphere. The thermoanalytical methods (TG-FTIR and TG-MS) were used for identification of gaseous products of degradation. The results showed less intensive evolution of formaldehyde and formic acid during the thermal degradation of POM/TPU/OMMT nanocomposites. Both formaldehyde and formic acid had an autocatalytic effect on degradation of neat POM and POM/MMT nanocomposites, especially in the initial stage of the process. However, in the presence of TPU the monomer formed in depolymerization reaction was captured most probably by urethane linkage in a formylation process. The decreased concentration of catalytic agent is considered as a cause of the reduced rate of mass loss of POM/TPU/OMMT nanocomposites. Interestingly, during thermooxidative degradation the temperature of maximum rate of mass loss was shifted towards higher temperature more than it could be anticipated from the TGA results obtained for neat POM, POM/TPU blend and POM/OMMT nanocomposite material with corresponding contents of nanofiller and compatibilizer. It is likely that the mechanism of thermal stabilization may be also related to the physical barrier effect of layered silicate towards oxygen diffusion. Both chemical and physical mechanisms of stabilization are referred to the structure and interfacial area developed in nanocomposite materials and thus can be influenced by addition of a compatibilizer. The obtained POM/TPU/OMMT nanocomposites revealed higher impact strength as compared to POM/OMMT materials due to the presence of elastomeric domains facilitating the dissipation of impact energy.