Preparation And Properties Of Thermally Conductive Poly (Methyl Methacrylate) Composites

Polymer matrix materials have the advantages of improved corrosion resistance, goodprocessability and excellent electrical resistivity, and are widely used in the field ofaerospace, microelectronics packaging, heat engineering, and solar energy utilization andso on. The vast majorities of the polymer are insulator, with excellent electrical insulatingproperties but poor thermal conductivity. Generally the thermal conductivity of polymerscan be improved incorporating inorganic fillers into the polymer matrix. The inorganicparticles with high thermal conductivity and low dielectric constant have proved to be goodcandidates for improving the thermal conductivity property of the polymeric electronicmaterials. So we are interested in the proper addition of high thermally conductive fillers tothe polymer matrix.Poly(methyl methacrylate)(PMMA) is a kind of important thermoplastic, which is ahard and stiff material with high abrasion resistance. Boron nitride (BN) is widely usedceramic filler, displaying very high thermal conductivity while being electrically insulating.Thus, one promising application of BN is as fillers in polymer composites to provideenhanced thermal conductivity properties while preserving electrically insulating propertiesof the polymer matrix. Nano-silica (SiO2) is one of the common oxide fillers, it can be alsoused to improve the thermal conductivity of polymer materials. In this study, PMMA/BNand PMMMA/SiO2composites were prepared by dispersing BN and SiO2particles intomethyl methacrylate (MMA) monomer phase via a bulk polymerization method,respectively. To enhance the interface thermal conductance effect and improve theinterfacial adherence of the matrix and the filler, a silane coupling agent,γ-methacryloxypropyl trimethoxy silane (CH2=C(CH3)COOC3H6Si(OCH3)3, γ-MPS), wasused as the surface modification agent of the BN and SiO2particles. The surface treatmentand the effects of fillers content on the thermal conductivity, electrical insulation,mechanical properties and thermal properties of composites were discussed detailed byFTIR, TGA, thermal tester, high insulation resistance meters, mechanical testing machine,DMA, SEM, and TEM and so on.PMMA/BN composites with different BN contents were successfully fabricated via abulk polymerization. Silane coupling agent γ-MPS has been successfully grafted to the surface of BN particles. The thermal conductivity of the composites increased with a rise inthe BN contents, and the highest thermal conductivity of0.67W/(m·K) was obtained forthe loading level of20wt%of BN, representing a value3.5times of pure PMMA(0.19W/(m·K)). SEM, EDX and TEM microstructure observation revealed BN particles withuniform dispersion in the matrix, and the BN particles connected with each other well toform a continuous thermal conductive pathway in the composite; electrical propertiestesting displayed the surface resistivity continuously and slightly declined, while thevolume resistivity hardly changed with increasing BN concentration; the impact strengthand tensile strength all showed a downward trend after the first increase compared to thepure PMMA, the composites exhibited relatively good mechanical properties especiallywith2wt%of BN; Tgs of the PMMA/BN composites were higher than that of the purePMMA, TGA analysis showed the thermal decomposition temperature of compositesincreased, indicating the thermal stability of PMMA could be improved increasing the BNcontents.For PMMA/SiO2composites, silane coupling agent γ-MPS has also been successfullygrafted to the surface of SiO2; the thermal conductivity, electric insulation performance andthermal stability of the composites all showed good results, but the impact strength andtensile strength with the content increase of SiO2showed a downward trend, from the SEMand TEM, SiO2particles were uniformly distributed in matrix, and there was reunionphenomenon of some particles in high content.