Study of the morphology and properties of melt-mixed polycarbonate–POSS nanocomposites

In this work, the morphology and thermo-mechanical behaviour of nanocomposites formed by a polycarbonate (PC) matrix and polyhedral oligomeric silsesquioxane with phenethyl substituents (Ph-POSS) have been studied. The Ph-POSS nanocages were added to the PC by direct melt blending at loadings between 0% and 15 wt%. Good dispersion was achieved up to 5 wt% of nanofiller. At higher loadings micron-sized aggregates were observed in the nanocomposites by scanning and transmission electron microscopy. Increasing of Ph-POSS content lead to phase separation, agglomeration and low values on the final properties. The DSC and DMA analyses showed that increasing the amount of nanocages caused a continuous decrease on the composite’s Tg. Although little increments on the polycarbonate decomposition temperature were found, the presence of Ph-POSS did not improve significantly the thermal stability. Under nitrogen atmosphere the degradation mechanism of PC was not affected by the POSS. The residual weights obtained under oxygen atmosphere were in agreement with the theoretical weights of the Ph-POSS added. With respect to the nanocomposites mechanical properties the most remarkable trend was an improvement on the composite’s yield stress having the maximum at 5 wt% of nanofiller. Higher amounts of Ph-POSS lead to a decrease on the yield stress, finding even lower values than the one corresponding to the neat matrix. This behaviour has been attributed to the presence of large POSS agglomerates with low adhesion to the polymer matrix. A continuous decrease on the strain at break was also observed, reflecting the brittle character of the formed composites.