Blocked isocyanate silane modified Al2O3/polyamide 6 thermally conductive and electrical insulation composites with outstanding mechanical properties

Abstract

The surface of alumina (Al₂O₃) particles was modified by a blocked isocyanate silane coupling agent, which was synthesized by using methylethyl ketoxime (MEKO) to block isocyanate-propyltriethoxy silane via nucleophilic reactions. For comparison, the surface of Al₂O₃ particles was also modified by propyltrimethoxy silane (KH-331). The thermally conductive and electrical insulating Al₂O₃/polyamide 6 composites were prepared by dispersing modified Al₂O₃ in polyamide 6 (PA6) using a twin-screw extruder. The X-ray photoelectron spectroscopy (XPS) results revealed that blocked isocyanate-propyltriethoxy silane and KH-331 were successfully attached to the surface of Al₂O₃ particles with chemical bonds. The blocked isocyanate silane modified Al₂O₃ were well dispersed in PA6 as revealed by scanning electron microscopy (SEM). When the Al₂O₃ content was 70 wt%, the tensile strength (85.2 MPa) and flexural strength (136.4 MPa) of blocked isocyanate silane modified Al₂O₃/PA6 composites were higher than those of KH-331 modified Al₂O₃/PA6 composites (52.5 MPa, 77.8 MPa), respectively. The thermal conductivity and impact strength of blocked isocyanate silane modified Al₂O₃/PA6 composites were also higher than that of KH-331 modified Al₂O₃/PA6 composites at the same content of Al₂O₃. The volume electrical resistivity of modified Al₂O₃/PA6 composites decreased with increasing Al₂O₃ content, but they still were good electrical insulating materials.