Selective Distribution Of Inorganic Nano-particles And Thermal Conductivity Of Composites

Polymer based nanocomposites have been widely concerned due to theobviou improvement of mechanical and thermal properties of polymers bynanoparticles. In this dissertation, thermal conductive composites were preparedby adding boron nitride (BN) and nano-aluminium oxide (Al2O3) as thermallyconductive fillers into polyethylene (PE) and ethylene-vinyl acetate copolymer(EVA) as the matrix resins via melt-blending. The inversion point of PE/EVAwas theoretically calculated to prepare co-continuous blends by the equation ofphase inversion. The phase structure of PE/EVA blends and the selectivelocalization of BN or Al2O3in PE/EVA blends were investigated by selectivesolvent extraction and scanning electron microscopy (SEM). The thermalproperties of the composites were evaluated by thermal conductivity. Theinfluences of the selective localization and the loading levels of BN and Al2O3onthe thermal conductivity of PE/EVA/BN composites and PE/EVA/Al2O3wereinvestigated.The result showed that the phase structure of PE/EVA blends showsdependence on the mass ratio of PE and EVA. A co-continuous blends can beobtained at the PE/EVA mass ratio of1/1. Thermally conductive fillers tend toshow a selective distribution in co-continuous blends. BN and Al2O3wereobserved to mainly selectively localize in PE phase. The selective distribution offillers and the co-continuous structure of the composites were helpful inimproving the thermal conductivity of the composites, leading to a15.4%increase of thermal conductivity of PE/EVA/BN composites in comparison tothat of PE/BN composites at the same BN loading of30wt.%and a20.9%increase of thermal conductivity of PE/EVA/Al2O3composites in comparison tothat of PE/Al2O3composites at the same Al2O3loading of50wt.%. Due to theformation of continuous PE/BN phase in the PE/EVA/BN composites, the tensile strength tends to be similar to that of PE/BN composites as the loading of BNincreased to50wt.%. The elongation at break of PE/EVA/BN composites arealso improved due to the toughing effect of EVA phase.