The role of polyhedral oligomeric silsesquioxane on the thermo-mechanical properties of polyoxymethylene copolymer based nanocomposites.

Hybrid nanocomposites formed with polyoxymethylene copolymer (POM) and different types of polyhedral oligomeric silsesquioxane (POSS) nanoparticles have been investigated. Four types of POSS have been studied in contents of 2.5% and 5% wt. The POSS were incorporated by direct melt-mixing. Traditionally copolymerization has been the preferred approach used to form polymer-POSS nanocomposites because the possibility of immiscibility with the polymer matrix is reduced. However, melt-blended POSS nanoparticles can also improve the thermo-mechanical properties of some polymers. Different morphologies were obtained depending on the type of POSS used. GI-POSS and O-POSS exhibit sub-micron or micron-sized inclusions which size increased with increasing percentages of POSS added. On the other hand, both G-POSS and T-POSS appeared to be uniformly dispersed in the POM matrix probably at a molecular level. This is a clear indication of miscibility between these systems and also that POSS solubility in POM is higher than 5 wt%. G-POSS improved the thermal stability of the systems. However, the melting temperature and the modulus of elasticity were found to slightly decrease. On the other hand, the O-POSS produced the opposite effect in the matrix. Finally T-POSS filled systems do not yield important variations in regard to polymethylene oxide properties although interaction between T-POSS and the matrix was detected.