Studies On Preparation And Properties Of Thermal Conductive/Flame-Retardant Polypropylene Composites

Polymer materials have been widely used with advantages such as light quality, ease of processing, good resistant to wearing and easy industrialization. While the vast majority of polymer materials are extremely restricted in application due to their low thermal conductivity. To further broaden the application fields, high thermal conductivity is necessary to be given. For improving the accuracy of electrical and microelectronic devices, extending their lives and meeting the demands of thermal conductive/insulation occasions in reality, it is of great significance to ensure a high insulation while the polymer composites having got a good thermal conductivity.Even though highly filled polymer composite shows high thermal conductivity, its mechanical behaviors degrade significantly. On the other hand, flammability becomes the greatest hidden danger in the application of high performance plastics. To abstain the arises of fire and its losing, the flame-retardant property of polymer composites becomes one of the most important criterions which measures their value in use. Therefore, it is significant to prepare a multi-function composite with high thermal conductivity, excellent insulation, good fire retardancy and mechanical properties. The specific research content as follows:1. Magnesium hydroxide/polypropylene composites had been prepared by melt extrusion and their morphology, thermal, electrical, mechanical and flame-retardant properties were characterized. The results indicate that thermal conductivity of the composites is 0.92 W/(m*k) when the filled quantity of Mg(OH)2 is 70 wt%, which is 5.1 times that of pure polypropylene resin. Vertical flame test grade of the composites is UL94 V-0 when the content of Mg(OH)2 is above 60 wt%. The composites keep excellent insulation as Mg(OH)2 is added. Scanning electron micrographs show that Mg(OH)2 distributes uniformly in the matrix without any agglomerations. The mechanical tests show that flexural properties of the composites increase by a slight at high filler content, while the tensile strength, elongation at break and notched impact strength decrease significantly.2. Magnesium hydroxide/polypropylene/graphene nanoplatelets composites had been prepared and their morphology, thermal, electrical, mechanical and flame-retardant properties were characterized. The results indicate that replacing a small amount of Mg(OH)2 with GNPs can observably improve the thermal conductivity of the composites. For example, the thermal conductivity of PP/Mg(OH)2 composites is 0.92 W/(m*k) when the filled quantity of Mg(OH)2 is 70 wt%, while it is raised to 1.5 W/(m*k) with filling content of 61 wt% Mg(OH)2 and 9 wt% GNPs. The composites keep excellent insulation when GNPs content is no more than 9 wt%. Tensile properties and anti-impact properties of the composites are improved in small increments as GNPs is added, and the flame resistance effect of the composites is satisfactory.3. Flexible Kevlar fiber and polyethylene-octene copolymer were used to toughen flame-retardant polypropylene composites highly filled with magnesium hydroxide in order to solve the problem of increased brittleness. The PP/Mg(OH)2/POE composites and PP/Mg(OH)2/KF composites were prepared by melt extrusion and their morphology, mechanical and flame-retardant properties were characterized. The results indicate that the composites are well toughened by both Kevlar fiber and POE and also exhibit satisfactory flame-retardant, thermal conductive and insulating properties. The toughening process significantly improves the practicability of PP/Mg(OH)2 composites.