Influence of phase morphology on the rheology and thermal conductivity of HDPE/PA6 immiscible blends with alumina whiskers

The thermal conductivity (TC) of HDPE/PA6/alumina whisker composites was measured as a function of the whisker amount and HDPE/PA6 ratio and related to their composite morphology and rheological properties. The preparation of the composites, in two extrusion steps, encouraged filler localization in the HDPE phase. The addition of the whiskers produced a morphological refinement in composites with 60/40 and 50/50 HDPE/PA6 ratios, resulting in a sea-island morphology with smaller domains of polyamide (dispersed phase). For the 40/60 HDPE/PA6 ratio, a sea-island microstructure with dispersed polyethylene domains filled with alumina was observed. The best TC data was measured in composites with a 50/50 HDPE/PA6 ratio, which was associated with an increase in the effective filler amount in the host phase, in agreement with the rheological data. Induced flow at low shears produced an increase in TC, which was associated with conductive network strengthening for the 40/60 and 60/40 HDPE/PA6 ratios.