Research On The Preparation And Properties Of Thermal Conductive Engineering Plastics

Thermally conductive engineering plastics obtained the widespread attention in recent years because of their excellent performance like light weight,easy to be processed,high mechanical strength and good thermostability.In this dissertation,the effect of the phase structure and filler combination on the properties of the filled thermally conductive composites was investigated.The relationships between the composition,structure and properties were discussed.Firstly,the Polybutylene terephthalate?PBT?/ Polycarbonate?PC?/ aluminium oxide?Al₂O₃?composite system was researched through the way in contral of the phase structure of PBT/PC alloy.In this system,the PBT/PC alloy was used as the matrix and the Al₂O₃ was used as the thermal conductive filler,respectively;then,the PBT/PC/Al₂O₃ composite was prepared by melt-compounding method.Triphenyl phosphite?TPPi?as an inhibitor was used to suppress the transesterification between PBT and PC.The transesterification,thermally conductive property,phase structure,crystallization parameters and mechanical properties of the materials were characterized by fourier transform infrared spectrometer?FT-IR?,laserflash thermal analyzer,scanning electron microscopy?SEM?,differential scanning calorimetry?DSC?and mechanical properties tester,respectively.Experimental results show that TPPi can effectively suppress the transesterification;by this,the phase structure of the blend changed and the distribution of the fillers also be influenced.With1.0wt% of TPPi loading in PBT/PC?1/1?,the co-continuous phase structure formed and the thermal conductivity of the blend improved effectively.After adding 33vol% of Al₂O₃ filler in the blend system,the thermal conductivity of the composite reached to 0.89w/?m·k?,which improved 13% than that of no TPPi in it.In order to improve the mechanical and flame retardant properties further,glass fiber?GF?and fire retardant were adding into the composite.Results show that with 7vol% GF and 10wt% 1,4-Bis?2-hydroxyethoxy?-2-butyne?BEO?,thermal conductivity of the composite can reach to 1.08 W/?m·k?;the tensile strength keeps 53.5MPa and the impact strength remains 11.2KJ/m2.The limiting oxygen index was 28.5%,and the flame resistance reachs to the level of V-0.So the practical application requirements at the the heat dissipation of household appliances could be achieved.In another system,polyamide 6?PA6?was used as matrix,and expanded graphite?EG?,graphite?G?,boron nitride?BN?,aluminium oxide?Al₂O₃?and tetrapod-shaped ZnO whisker?T-ZnOw?were used as fillers,and a series of composites were prepared bymelt-compounding method.Both insulation and non-insulation PA6 based thermal conductive system were researched.The relationship between micro-structure of the composite and the thermally conductive property were investigated by using SEM and laserflash thermal analyser.In the insulation thermal conductive system,the good synergistic effect between BN?17vol%?and T-ZnO?3vol%?is found,the thermal conductivity of 1.11 W/?m·k?in PA6/ BN?17vol%?/T-ZnO?3vol%?obtained,and the volume resistivity of the composite can maintain at 1013?·m.There are two kinds of heat charge carriers,the electronic and the phonon,in the non-insulation thermal conductive system.The specific flaky shape of EG had the advantages than the other spherical or amorphous fillers to form a thermal conductive network.The thermal conductivity of PA6 based composite with EG in 20vol% loading is up to 2.34 W/?m·k?.The highest thermal conductivity of 3.11 W/?m·k?achieved in PA6/Al₂O₃?5vol%?/EG?15vol%?compound system among all the investgated composites in this study,the volume resistivity of the composite can be keeped at 7.8×105 ?·m.In summary,the thermal conductivity of the composite could be improved through the controllable of the structure,or useing compound fillers with different shapes.