Preparation And Properties Of PA6/AlN Thermal Conductive Polymer Composites

With the rapid development of industry and information technology, the high demands for thermal conductive materials have promoted the research and development of thermal conductive materials. The traditional metal materials far cannot meet the widely application because of its defect. Because of good chemical corrosion resistance and insulation, easyforming, excellent anti-fatigue performance, the research of making polymer materials with good heat dissipation function had become a hotspot, PA6 had low thermal conductivity as engineering plastics. PA6/AlN thermal conductive composites had prepared by using the high thermal conductivity of AlN, the effect of filler content, particle sizes, mixed filling, coupling agent modification, processing methods were investigated on the thermal conductivity and mechanical properties of composite materials, The material systems of AlN/CF mixed and two-phase incompatible system PA6/PP was selected to study the influence of percolation theory and synergistic effects by the observation of thermodynamics and microstructure.The research showed that the thermal conductivity of PA6/AlN composites had increased with the adding of AlN content, the thermal conductivity was 1.498W/(m?K) when the percolation threshold of AlN(10μm) content was 50wt%, which was 6.51 times of PA6. The enhancement of mechanical properties was obvious when the AlN content was 30-50wt%, the right amount of coupling agent modification could improve the compatibility of various components, the mix of different AlN sizes helped to form thermal conductivity net chain structure throughout the material.On the basis of PA6/AlN system, it helped to improve the PA6/AlN/CF material’s thermal conductivity and mechanical properties because of mixed effect and synergistic effect of AlN/CF two-phase packing system. When AlN/CF total content is 40wt% and the ratio of AlN/CF was 25/15, the thermal conductivity was 1.395W/(m ? K) which was increased by 39% than PA6/AlN system filled with same content, When the ratio of AlN/CF was 20/20, the tensile strength and flexural strength composites was 97.8MPa and 135.2MPa, which was increased by 17.8% and 32.3% than single aluminum nitride filled with same content.The choice of the ways of processing was related to the kinds and content of filler. Three-screw extrusion processing ways of strong shearing action and secondary shear extrusion helped AlN with the high dispersivity, when CF content is high in AlN/CF mixed system, open mill products has the highest thermal conductivity due to small damage of CF, which kept the advantage of length-diameter ratio. In two-steps of three screw extrusion, the AlN filler has a homogeneous distribution with the process of two melting, the thermal conductivity increased by 16%, it could effectively improve the mechanical properties of composite material with high filling.On the basis of PA6/AlN system, the addition of PP phase reduces the material mechanics performance, but the percolation threshold of AlN content was reduced to 40wt% and its thermal conductivity was 1.302W/(m ? K), the content of filler had decreased because of double percolation threshold effect. The best proportion of PA6/PP was 70/30. The sea island structure and selective dispersion of AlN had observed through the microstructure.The analysis of thermodynamic showed that the addition of AlN had promoted the PA6 crystallization rate and became a heterogeneous nucleation role and increased the crystallinity of materials. But high filling and mixed packing destroyed the perfection crystallization of PA6 with the molten bimodal appered. The addition of inorganic filler AlN improved the thermal stability of composites. By using coupling agent modification and way of three screw extrusion processing, it could help ease the decline performance of process flowing property when composite materials with high filling of AlN.