Study On Preparation And Properties Of Poly(m-phenylene Isophthalamide)composite With Enhanced Thermal Conductivity

With the development of science and technology,the demand of high-power,and high-centralized electronic integrated systems are increasing.There are tens of billions of transistors in the centimeter size?10.3 billion transistors in Huawei 5G chip?on a microelectronic chip.Considering the electrical resistance of transistors,a large amount of waste heat can be generated during operating,and the temperature of device will rise rapidly,the high temperature will deteriorate working efficiency of device.For traditionally electronic packaging materials,thermal interface materials,thermally conductive electronic substrates and gap filler materials,the operating temperature are always below 100°C.When they are employed in electronic field under high-temperature for a long time,the internal structure of corresponding materials will deteriorate,which can decline the ability of heat dissipation as well as performance of device.In order to meet the requirements of advanced electronics and high-technology industries,it is necessary to fabricate high-performance polymer-based electronic materials.The high-temperature polymers are available to be used in electronic field are mainly including polyimide?PI?,poly?m-phenylene isophthalamide??PMIA?,polyetheretherketone?PEEK?,etc.Although these high-performance polymers can meet the requirements of high-temperature,due to their special chemical structures,the thermal conductivities are less than 0.3 W/?m·K?,leading to the waste heat can't be dissipated timely.For now,adding fillers with high thermal conductivities into polymer matrix is a versatile approach for preparing high-performance thermally conductive composites.In addition,it is worth noting that the thermally conductive fillers also have some influences on other properties of polymer matrix,such as dielectric properties,mechanical properties,and breakdown strengths.Therefore,it is paramount to investigate other related properties of fabricated composites.In this paper,PMIA was used as polymer matrix to prepare high-performance electronic materials.However,considering the low thermal conductivity of PMIA?0.23 W/?m·K??,the heat dissipation is too poor to meet the requirements of electronic materials.According to previous research,it is known that the hybrid particles display better effect than single-system particles on improving heat dissipation.Consequently,graphene,carbon nanotubes?CNTs?,boron nitride?BN?,boron nitride nanosheets?BNNSs?and spherical alumina?Al₂O₃?were used to prepare hybrid fillers to enhance thermal conductivity of PMIA matrix.Furthermore,considering the high breakdown strength,high temperature stability as well as high toughness of PMIA matrix,barium titanate nanowires?BTW?was utilized as high dielectric fillers to improve the dielectric properties of PMIA matrix and explore the application of high-dielectric PMIA composites in field of energy storage.Due to the highly thermal conductivity of carbon-based fillers,GO was firstly prepared via modified Hummers method,the oligomer polyisophthalamide?OPIA?was synthesized and then grafted onto surface of GO,the functionalized GO was then reduced by hydrazine and named as frGO.After that,frGO and MWCNTs were mixed in solvent.according to?-?interaction,MWCNTs was adhered onto the surface of frGO to generate frGO-MWCNTs?FGC?nanoparticles.Then FGC fillers were added into PMIA slurry to manufacture FGC/PMIA nanocomposite.The results indicated that,due to the synergistic effect of FGC fillers,the thermal conductivity of FGC/PMIA composite was significantly improved.For example,the in-plane thermal conductivity and through-plane thermal conductivity of PMIA nanocomposite with 3 wt%FGC fillers were increased to 7.38 and 0.81 W/?m·K?,respectively.However,owing to the two-dimensional structure of frGO as well as one-dimensional structure of MWCNTs,the FGC fillers tended to be aligned and formed thermal conduction networks in in-plane direction,resulting in the thermal conductivity of in-plane direction was much better than that of through-direction.The dielectric constant of FGC/PMIA nanocomposite was also increased with increasing content of FGC fillers.For PMIA nanocomposite with 3 wt%FGC fillers,the dielectric constant was increased to 9.8 at 10³ Hz,the enhanced dielectric constant could increase delay time of electronic signals.In addition,it is worth pointing out that,although the carbon-based fillers can significantly improve the thermal conductivity of polymer matrix,the electrical conductivity can decline the insulation properties and limit the applications in insulative field of electronic devices.Considering the carbon-based fillers have negative effect on insulating properties of polymer matrix,the enhanced dielectric constant can increase the delay of electronic signal and decrease the efficiency of transmission of electronic signals.Consequently,hexagonal boron nitride?hBN?particles with high thermal conductivity and outstandingly electric insulation were used to prepare hBN/PMIA composites with excellently insulating properties,improved thermal conductivities and low dielectric constants.Initially,in order to improve the compatibility between hBN fillers and PMIA matrix.hBN particles were modified at high temperature to graft hydroxyls,and then functionalized by silane coupling agent?KH-550?.What's more,for the purpose of further improving the thermal conductivity of PMIA matrix,micro/nano-sized hBN hybrid particles were utilized to form more heat dissipation paths in hBN/PMIA composite on account of synergistic effect among micro/nano-sized hBN hybrid particles.For instance,the through-plane thermal conductivity of PMIA composite with 30 wt%m/n-hBN particles was increased to 0.94 W/?m·K?,which was 3times higher than that of pure PMIA.Due to the low dielectric constant of hBN particles,the dielectric constant of hBN/PMIA composite was maintained at a low level,which is conducive to the transmission of electronic signals;What's more,with increase content of hBN particles,the insulative performance of hBN/PMIA composite was also enhanced.However,with increasing content of hBN particles,the tensile strength of hBN/PMIA composite obviously decreased,this can be ascribed to that,in order to make the hBN particles contact with each other to form heat conduction paths in PMIA matrix,the high content of hBN particles are always necessary,which leads to decrease of mechanical properties of composite,this consequence inhibits the prepared PMIA composite to be employed in flexible electronic devices;In consideration of above reasons,solvent-assisted ultrasonic stripping method was chose to exfoliate hBN particles to manufacture boron nitride nanosheets?BNNSs?,and BNNSs was further modified by octadecyl isocyanate to prepare fBNNSs to improve the compatibility between BNNSs and PMIA matrix.The obtained result showed that fBNNSs can significantly improve thermal conductivity of PMIA matrix at low content;When fBNNSs content was 12 wt%,the thermal conductivity of in-plane direction of fBNNSs/PMIA nanocomposite was increased to 8.06 W/?m·K?,which was 35 times than that of pure PMIA;In addition,the breakdown strength and insulation properties of PMIA matrix was also enhanced.When the content of fBNNSs increased from 0 wt%to 12 wt%,the breakdown strength of fBNNSs/PMIA nanocomposite was increased from 79.1 MV/m to 105.6 MV/m,which can meet the requirement of high voltage and insulation applications;For the mechanical properties of fBNNSs/PMIA nanocomposites,since the fBNNSs particles were uniformly dispersed in PMIA matrix and could transfer stress effectively,the prepared nanocomposites maintained outstanding mechanical properties.When the fBNNSs content was 12 wt%,the corresponding tensile strength of nanocomposite was 94 MPa,which is still higher than that of pure PMIA.It is worth mentioning that,due to the prepared BNNSs were two-dimensional particles,they tend to be aligned in in-plane direction in polymer matrix,which resulted in a significant anisotropy in the thermal conductivity of prepared fBNNSs/PMIA nanocomposites.In view of the two-dimensional structures of GO and BNNSs particles,the heat dissipation paths are inclined to be generated along in-plane direction,and the thermal conductivity of polymer composite only obviously increase in in-plane direction.Consequently,this method on enhancing thermal conductivity is lower than that polymer composite with three-dimensional heat dissipation networks.In order to prepare PMIA composite with three-dimensional heat dissipation networks,high-temperature treated boron nitride nanoparticles were adhered onto surface of polydopamine-coated spherical alumina particles,and Hexamethylene Diisocyanate?HDI?was chose as“bridging agent”to fabricate double-core-shell structured BN@PDA@Al₂O₃?F-BA?particles.The results indicated that,with increasing content of F-BA particles,F-BA particles began to contact with each other to form three-dimensional heat dissipation networks,and improving the thermal conductivity in in-plane direction and through-plane direction simultaneously.For instance,the in-plane thermal conductivity of F-BA-25 composites was increased to 6.07 W/?m·K?,and the through-plane thermal conductivity was increased to 1.38 W/?m·K?,which were 25.4 times and 5 times higher than that of pure PMIA,respectively.Additionally,the breakdown strength of F-BA/PMIA composites were also enhanced,e.g.the breakdown strength of F-BA-25 increased to 146.3 MV/m,showing an increment of 68.5%in comparison with that of pure PMIA;What's more,the dielectric constant and loss of all F-BA/PMIA composites were less than 3.5 and 0.02 in whole frequency,respectively,indicating the little delay and loss of electronic signal.Polymer film capacitor is a new type of energy storage device that can release stored electrical energy in short time to generate high power pulses.Currently,film capacitors are mainly manufactured by biaxially oriented polypropylene?BOPP?.However,due to the poor heat-resistance of BOPP,it can no longer meet the requirements of new technologies,such as high-end oil and gas extraction equipment,advanced propulsion systems as well as hybrid vehicles.It is necessary to develop special film capacitors for high temperature applications.On account of the particularity of polymers,their dielectric constants are usually very low,which is not conducive to improving the energy storage density of film capacitors.In order to increase the dielectric constant,a common method is adding inorganic fillers with high dielectric constant into polymer matrix.It is pointed out that inorganic fillers can increase dielectric constant of polymer matrix,but the dielectric loss of materials also increase;and the dielectric loss can convert electrical energy into thermal energy,this will improve the temperature of the film capacitor and affect the efficiency of device.Therefore,it is necessary to improve the heat dissipation performance of film capacitors and reduce the impact of temperature on device.Barium titanate nanowires?BTW?possesses high intrinsic dielectric constant,which can effectively improve the dielectric properties of polymer matrix.In this paper,barium titanate nanowire?BTW?was synthesized by nano titanium dioxide?TiO₂?via hydrothermal method.Considering polydopamine?PDA?can improve the compatibility between BTW and PMIA matrix.Polydopamine?PDA?was coated onto surface of barium titanate nanowire to prepare polypopamine@barium titanate nanowire?D@BTW?.But previous research demonstrates that BTW can weaken the breakdown strength of polymer matrix,while BNNSs can increase the breakdown strength of polymer matrix.Consequently,D@BTW and octadecyl isocyanate-functionalized fBNNSs were homogeneously mixed in solvent and added into PMIA matrix to fabricate D@BTW-fBNNSs/PMIA composite.The dielectric properties and breakdown strengths of D@BTW-fBNNSs/PMIA composites were researched.The results showed that D@BTW nanowires were tightly adhered to fBNNSs particles;With increasing content of D@BTW-fBNNSs fillers,the dielectric constants of D@BTW-fBNNSs/PMIA composites obviously increased,indicating D@BTW nanowires were conductive to improve dielectric constants of D@BTW-fBNNSs/PMIA composites.For example,the dielectric constant of PMIA composite containing 15 wt%D@BTW-fBNNSs particles was increased to 4.9 at 1 KHz,which is75%higher than that of pure PMIA.In addition,due to the extremely high breakdown strength of fBNNSs,the negative effect of D@BTW on the breakdown strength of the PMIA matrix was offset.With increasing content of hybrid fillers,the breakdown strength of D@BTW-fBNNSs/PMIA composite was not significantly reduced.Furthermore,due to the highly thermal conductivity of fBNNSs particles,the thermal conductivity of D@BTW-fBNNSs/PMIA composite was significantly enhanced.When the content of D@BTW-fBNNSs was 15 wt%,the thermal conductivity of corresponding composite was increased to 0.57 W/?m·K?,t which was 1.5 times than that of pure PMIA.The improved thermal conductivity could effectively dissipate the waste heat generated by dielectric loss and control temperature during operation.These consequences indicate that D@BTW-fBNNSs/PMIA composite can be used as high-performance dielectric material in the field of energy storage.