Moulding And Properties Of Co-Continuous Phase Thermal Conductive Composites

In this article, the extrude-prilling process and the injection moulding process were used to prepare the crosslinking, the co-continuous phase, and the crosslinking/co-continuous phase thermal conductive composites, which had high thermal conductivity and good mechanical properties. The effects of crosslinking and the formation of co-continuous phase on all of the properties of the composites were mainly researched:(1) The effects of the graft-crosslinking, particle size of MgO, the content of silane coupling agent modifying MgO, the content of MgO and the addition of flow additives on the properties of the thermal conductive composites of the crosslinking high density polyethylene (HDPE)/MgO were researched. (2) The effects of the characterization of co-continuous phase, the formation of co-continuous phase, the amount of matrix resins, the content of the flake graphite (LG), the ratio of HDPE/nylon 6 (PA6), and the addition of carbon fiber (CF) on the properties of co-continuous phase HDPE/PA6/LG thermal conductive composites were studied. (3) The synergy of the two means (crosslinking and co-continuous phase) on the properties of the thermal conductive composites HDPE/PA6/LG were studied.The results were as follows:1. On the basis of ensuring the high thermal conductivity of the HDPE/MgO composites, graft-crosslinking could improve the tensile strength and heat resistance, especially promoting the impact strength to a great extent. The composites filled with MgO having an average particle size of 55.0?m had the best properties. For example, the crystallinity was 70.3%, and the heat deflection temperature (HDT) was 83.5?, and the thermal conductivity was 0.447 W·(m·K)-1. When the content of silane coupling agent modifying MgO was 1.0%, the phase interfaces between MgO and HDPE were largely improved, and the properties of the composites was better. With the increase of the MgO amount, the tensile strength of the composites increased significantly and the impact strength was very good. For example, when the filled amount of MgO was 70%, the thermal conductivity was 1.065 W·(m·K)-1, and the HDT was 100.0?, and the tensile strength was 35.64 MPa, and the impact strength was 9.375kJ/m2. The compatibility between HDPE and MgO was better than the un-crosslinking composites from the SEM images of the brittle fracture faces of the graft-crosslinking ones.2. The co-continuous phase was characterized by the method of etching PA6 in formic acid. The results showed that when the proportion of HDPE/PA6 was 90/10 (the LG content was 50 to 65%), the co-continuous phases between HDPE and PA6 were informed in the composites. The processing of the composites was easier, and the SEM images showed less brittle section effects. The thermal conductivity of the material was greatly enhanced (when the filled amount of LG was 65%, the thermal conductivity of the material was 1.964 W·(m·K)-1). What's more, when the filled amount of LG was 60% and the proportion of HDPE/PA6 was 10/8,9/9,8/10, the co-continuous phases could also be formed, and the thermal conductivity was 2.463 W·(m·K)-1 when HDPE/PA6 was 8/10. Taking the HDPE/PA6 rate of 8/10, the filled amount of LG was 60% and the filled content of CF was 3%. The properties of the composites of HDPE/PA6/LG/CF were improved largely, such as the tensile strength was 42.68 MPa, and the bending strength was 66.00 MPa, and the impact toughness was very good. The HDT was 163.4?, which was 139.94% higher than the pure HDPE, and the thermal conductivity was 2.737 W·(m·K)-1, which was 7.92 times more than the pure HDPE.3. The experimental results showed that the overall performance of the co-continuous phase composites could be improved by the method of crosslinking. Compared with the un-crosslinking composites, the tensile strength (37.20 MPa), the elastic modulus (1594.77 MPa) and the bending strength (67.46 MPa) of the crosslinking composites HDPE/PA6/LG had increased 3.56%,46.63% and 7.40% respectively. And the impact strength (5.23 kJ/m2) and the HDT (129.0?) of the crosslinking ones were very excellent. The crosslinking and co-continuous phase composites had the better thermal conductivity (2.634 W·(m·K)-1) than the un-crosslinking ones.In a word, it could be achieved that keeping the thermal conductivity of the composites filled with high content of fillers and improving the mechanical properties of composites to the most extent by the methods of crosslinking, the formation of the co-continuous phase, crosslinking/ co-continuous phase and addition with various fillers, at the same time. Finally, the elastic modulus, the tensile strength, the bending strength, the elongation at break, the impact strength, the HDT and thermal conductivity of the crosslinking and co-continuous phase thermal conductive composites were 2472.55 MPa,45.73 MPa,72.75 MPa,1.75%,3.40 kJ/m2,176.3? and 3.214 W·(m·K)-1,respectively, which could meet the cooling needs of market LED lamps.