Study On Thermal Conductivity Of Polymer/carbon Nanomaterials Composites

Carbon nanotubes（CNT）have ultrahigh thermal conductivity.Theoretically,small amount of CNT added can sharply improve the thermal conductivity of polymer matrix.In fact,thermal conductivity improved by CNT is very far below the expected value,which results from the interface thermal resistance between strengthening agentand polymer.To reduce the interfacial thermal resistance based on the modified carbon nano materials and polymer interface,there by improving the thermal conductivity of polymer composites.To design the interfacial structure or heat flow transporting in the polymer matrix,there by improving the thermal conductivity of polymer/CNT composites.Based on this idea,we carried out research on thermal conductivity of polymer / carbon nano composite material,to investigate the influence.1.First,by liquid in-suit method,the surface of carbon nanotubes coated with a layer MgO,MgO-coated carbon nanotubes was prepared（MgO@MWNT）,MgO@MWNT was well dispersed in the epoxy matrix due to good compatibility between nanotubes and epoxy matrix.The electrical-insulating layer of MgO restrained the electrontran sport properties of carbon nanotubes and kept epoxy/MgO@MWNT nanocomposites electrical insulation.With 4 wt.% MgO@MWNT loading,electrical resistivity ofepoxy/MgO@MWNT nanocomposites only decreases to 2.4×1014 ?·m from 3.8×10¹⁵ ?·m of neat epoxy.The MgO layer also promoted nanotube strong interaction with epoxy matrix and matched the modulus of MWNT and polymer matrix that improved the interfacial thermal conductivity.The epoxy nanocomposites with 2.0 wt.% r-MWNT loaded have the thermal conductivity of 0.2898 W/（m·K）.However,it is clearly observed that epoxy/MgO@MWNT nanocomposites exhibit higher thermal conductivity than epoxy/r-MWNT nanocomposites.Correspondingly,with the increase of MgO@MWNT content from 0.5 wt.% to 2.0 wt.%,the thermal conductivity of epoxy nanocomposites was increased from 34% to 89%.The thermal conductivity of 2.0 wt.% MgO@MWNT loaded epoxy reached 0.3568 W/（m·K）.2.The improved performance of epoxy was accomplished by filling the magnesium oxide coated graphenes（MgO@GR）nanomaterial into an epoxy matrix.We found that the addition of MgO intermediate layer not only improves the dispersity of graphene in the matrix and the interfacial bonding between graphene and epoxy,but also enhances the thermal conductivity of epoxy with retained electrical insulation.The thermal conductivity of neat epoxy is 0.2210 W/mk and it increased with the increase of MgO@GR content.It is worth noting that high thermal conductivity was obtained（0.3819 W/mk）with 7 wt.% of MgO@GR,corresponding to 76% increase as compared to neat epoxy.However,the improvement obtained from the GR without MgO coating was not obvious,and even lower than the neat epoxy.The volume electrical resistivity of epoxy/MgO@GR nanocomposites retained at high electrical insulation（8.66×1014Ω·m）even if the filler content was increased to 7 wt.%.3.In this experiment,poly（ethylene glycol）grafted multi-walled carbon nanotubes（PEG-MWNTs）were prepared and added into poly（L-lactide）（PLLA）/aluminum nitride（AlN）composites for obtaining PLLA/AlN/PEG-MWNTs composites.Microstructure and thermal conductivity of the composites were investigated based on the influence of PEG-MWNTs incorporated.The results showed that PEG-MWNTs were well-dispersed in the PLLA matrix and had strong interfacial adhesion with the matrix.The thermal conductivity of PLLA composites with PEG-MWNTs was higher than that with acidic MWNTs（A-MWNTs）.Meanwhile,the thermal conductivity of PLLA composites was enhanced with the increase of MWNTs or AlN loadings.The incorporation of both MWNTs and AlN improved the thermal conductivity of PLLA more significantly than either one of the two fillers used.When 2 wt.% of PEG-MWNTs and 20 wt.% of AlN were added together into the PLLA matrix,the thermal conductivity reached 0.5840 W/（m·K）with enhancement almost by 300% as compared to a neat PLLA.However,the thermal conductivity is 0.3165 W/（m·K）for the PLLA composite with 2 wt.% of PEG-MWNTs and 0.4286 W/（m·K）for the one with 50 wt.% of AlN.The mechanism maybe inferred that the hybrid filler forms a "string-bead" chain-networks structure to obtain efficient thermal conductive paths for improving the thermal conductivity of PLLA where MWNTs and AIN particles acted as strings and beads,respectively.