Silvia Illescas

The morphology and properties of melt-mixed polyoxymethylene/ monosilanolisobutyl-POSS composites

In this study, the morphology and thermo-mechanical behavior of composites formed by a polyoxymethylene (POM) matrix and monosilanolisobutyl polyhedral oligomeric silsesquioxane (msib-POSS) filler have been studied. The msib-POSS molecules were added to the POM by direct melt blending at loadings between 0 and 10 wt.%. Hydrogen bonding interactions were detected between POM and msib-POSS Si-OH groups, increasing their mutual compatibility and leading to nanometer-size dispersion of some msib-POSS molecules. These interactions do not prevent POSS aggregation during blending, but lead to micron-scale msib-POSS domains. The thermal decomposition temperature of the composites remained practically constant under inert and oxidative conditions. The low temperature thermal transition (γ) and glass transition temperature (Tg) of POM were found to move to higher temperatures only when 2.5 wt.% of msib-POSS was added, indicating that POSS is physically linked to the POM chains, restricting their motion under those conditions. Low content (2.5 wt.%) of msib-POSS results in antiplastization, whereas higher levels of POSS lead to a decrease in the storage modulus of the polymer. The relationships among these effects and the morphological characteristics of the systems will be discussed herein.

Thermal Degradation of Polyoxymethylene Evaluated with FTIR and Spectrophotometry

Thermooxidative degradation at and beyond processing temperatures of a polyoxymethylene copolymer has been progressively accelerated to carbonisation through oven-storage aging. The quantification of such degradation was carried out through FTIR spectrography and colour spectrophotometry methods. The state of thermo-oxidation was monitored through the FTIR spectra corresponding to the carbonyl aldehyde group (O=CH) and methylene bending (–CH2), as well as the chromaticity changes experienced on the sample surface. The results showed that the FTIR bands suggested are a reliable indicator during the initial conditions of degradation, however, the spectrophotometry becomes more appropriate method for more aggressive conditions leading to carbonisation.

Influence of polyhedral oligomeric silsesquioxanes on thermal and mechanical properties of melt-mixed poly(methyl methacrylate)/polyhedral oligomeric silsesquioxanes composites

In this study, the influence of the functionalization of fully or incomplete condensed polyhedral oligomeric silsesquioxanes composites (POSS) nanoparticles on the properties of poly(methyl methacrylate) (PMMA)-based composites has been studied. POSS with different organic substituents (methacryl, methacrylateisooctyl and trisilanolphenyl) are taken into account and added to the PMMA matrix by direct melt blending at loadings between 0 and 5 wt%. Significant differences in compatibility were observed depending on the structure of nanoparticles. POSS aggregation occurred during blending producing micron-sized aggregates in the composites. The thermal decomposition temperature of the composites with good dispersion of POSS aggregates increased under oxidative conditions. There were no significant changes in other thermal and mechanical properties of the composites. The relationships among these effects and the morphological characteristics of the systems were analysed.

Properties of POSS blends with pCBT, PMMA, PC and POM thermoplastics

The influence of the functionalisation of fully or partially condensed POSS cages on the properties of engineering thermoplastic-based nanocomposites is studied. POSS with different organic substituents were selected in accordance with the structure and chemical composition of the host polymer and melt mixed with the corresponding matrix. In general, good dispersion at the nanoscale level was achieved upon the addition of some functionalised POSS, leading to a remarkable increase on the thermal decomposition temperature under nitrogen atmosphere. However, for the polymers having high decomposition temperatures, there were no significant changes on the thermal properties of the nanocomposites. On the other hand, the dispersion of the POSS, whatever its functionalisation was, led to the presence of micron-sized aggregates. The relationships among these effects and the morphological characteristics of the systems were analysed.