Preparation And Characterization Of Flame Retardant And Thermal Conductive Highly Filled Polymer Composites

Gradually, Polymer has begun to replace traditional materials in many fields due to its excellent characteristics such as outstanding processing properties, insulation performance and so on. However, polymeric materials also have some disadvantages such as poor flame resistance and thermal conductivity. Flame retardancy and thermal conductivity are regarded as key factors in many applications, the work efficiency and service life of electronic components would be affected if the heat can not be eliminated on time. It is suggested that an ideal flame retardant and thermal conductive material should quickly release the heat under working condition,and exhibit flame retardancy under high temperature.In this research, different fillers were used to improve thermal conductivity and flame retardancy of three polymers. The influence of flame and thermal fillers on flammability, thermal conductivity and thermal stability property was fully studied, as well as the synergistic effects between fillers. The main research work is as follows:Silicon carbide (SiC) and magnesium hydroxide (Mg(OH)2) with different sizes in combination were introduced to epoxy (EP) to prepare thermally conductive and flame retarded polymer composites, the fillers was modified by silane coupling agent KH 560 to improve the dispersibility and compatibility. The high filling composites with different content and different ratio was prepared by thermosetting method. Further research indicated that the limiting oxygen index (LOI) value could reach 47.3% and UL-94 rating could achieve V-0 level at the presence of 70% fillers. Cone calorimeter (CONE) data demonstrated that peak heat release rate was significantly reduced 68.3% compared to neat epoxy. The thermal conductivity was 1.03 W/m·K when the filler load was 70% and the ratio of SiC to Mg(OH)2 was 3:2.In the second section, low density polyethylene and ethylene-vinyl acetate copolymer were chosen as matrix, while the aluminium oxide (Al2O3) and magnesium hydroxide [Mg(OH)2] were selected as fillers to prepare LDPE-EVA composite. The results showed that the thermal conductivity reached 1.21W/m·K at the presence of 25% Al2O3 and 25% Mg(OH)2 and the LDPE/EVA mass ratio of 1:1; the introduction of EVA into composites apparently increased the LOI from 27.0% to 31.5%, and the UL-94 level was improved from no rating to V-0, the residual char increased from 46.5% to 57.7% in TG at 800?. The SEM and thermal conductivity test showed blends structure was favor of the selective distribution of Al2O3, so as to make the local concentration of thermal fillers increase in polymer, promote the formation of the thermal network and improve thermal conductivity of composites. EVA as compatibilizing phase in the blends make Mg(OH)2 can play a role of flame retardant more efficiently, improve the flame retardancy and thermal stability.In the third section, EVA was chosen as matrix and graphite as flame retardant and thermal conductivity filler. Hexachlorocyclo triphosphazene (HCTP) grafted on GO to improve the flame retardancy. The grafting process and the structure of the product (M-GO) was characterized by X-ray photoelectron spectroscopy (XPS), FTIR and TGA.The thermal conductivity was reduced because of the introduction of polar groups, so a small amount of multi-walled carbon nanotube (MWNT) were introduced into as thermal conductivity compensation. LOI, UL-94 and CONE results showed that the M-GO exhibited improved flame-retardant effect, and the effect was further enhanced by replacement M-GO with a small amount of MWNTs. FTIR of residue char at different temperature showed M-GO could play a better role in the protection for substrate. Thermal conductivity tests demonstrated that the thermal conductivity of composites containing M-GO was lower than that of the composite containing pure graphite, while thermal conductivity increased when MWNTs was introduced. It is proposed that the combination of thermally conductive fillers with different dimensionalities would improve the thermal conductivity.