Papers by Author: João M. Maia

Abstract: The effect of the dispersion state of carbon nanotubes in polycarbonate on the rheological, mechanical and electrical properties of melt-extruded compounds is presented. The dispersion state was monitored by means of grey values distribution histograms of optical micrographs of the composites. Increasing the processing residence time, and hence the deformation induced by the surrounding polymer, increased the level of dispersion of CNTs in the matrix. This, in turn, resulted in a large improvement of the CNTs reinforcement effect and decreased composite electrical resistivity. Rheological behaviour is in agreement with these observations.

Abstract: In this work the transient shear behaviour, in terms of both flow and stress relaxation, were measured for several blends of PA6/EPM/EPM-g-MA. The results indicate that there is a competition between slip at the interface due to the non-compatibility between the PA6 and the EPM and the action of the compatibilizer. In flow experiments, at low total strains it was observed that the behaviour is characteristic of immiscible polymer blends and gradually changes to that typical of compatible blends. This suggests that initially the action of the compatibilizer (especially for low compatibilizer contents) is not enough to prevent the lower viscosity PA matrix from slipping around the high viscosity EPM droplets. However, as the droplets are deformed and oriented, the increase in interfacial area enhances the performance of the compatibilizer, thus resulting in a much better interaction between the two phases across the interface.