Structural Design And Performance Study Of Functionalized Polymer Composites Based On The Construction Of Thermal Conductive Network

The accumulated heat of electronic equipment can seriously affect its operating speed,efficiency,and reliability,so it is necessary to export accumulated heat to the external environment quickly and effectively.In recent years,thermal management materials with excellent thermal conductivity have been studied extensively,among which polymer materials have been focused on due to their corrosion resistance,light weight and easy processing and forming.However,most polymer materials cannot meet the thermal management requirements in practical applications because of their extremely low thermal conductivity,so the development of novel polymer composites with high thermal conductivity is of great significance for the development of electronics industry.Compounding thermally conductive fillers with polymers is the most widely used method to prepare high thermal conductivity polymer composites,and the key is to reduce the interfacial thermal resistance and construct efficient thermal conductive networks in polymer composites.In order to construct an efficient thermal conductive network in polymer matrix,this paper carried out a series of work from surface functionalization modification of fillers,hybridization and compounding of fillers,control of filler orientation and construction of three-dimensional filler networks.In this paper,polydopamine（PDA）was first used to functionalize the surface of inert boron nitride（BN）and carbon nanotubes（CNTs）,and then the prepared PDA modified BN（BN-PDA）and PDA modified CNTs（CNTs-PDA）were used to fill and modify ethylene vinyl acetate（EVA）matrix.The effect of PDA on the internal structure and thermal conductivity of the prepared EVA composites was emphatically studied.The results showed that PDA could improve the interfacial bonding between BN and EVA matrix without destroying the intrinsic structure of BN,and both BN-PDA and CNTs-PDA could be uniformly dispersed in the EVA matrix.The uniformly dispersed CNTs-PDA served as a“bridge”connecting adjacent BN-PDA sheets,thus further promoting the formation of efficient thermal conductive pathways in EVA composites.When 30 vol%BN and 2 vol%CNT were added,the in-plane thermal conductivity of the composite reached 9.61 W·m^-1·K^-1,which was about 3225%higher than that of EVA matrix.The excellent thermal management capability of the prepared EVA composite was further demonstrated by its sensitive response to temperature.The contribution of PDA to the auxiliary enhancement of the thermal conductivity and thermal management capability of the composites was further verified by fitting and calculating the interfacial thermal resistance of the prepared composites.In addition,the composite also has good electrical insulation and thermal stability.In order to reduce the interfacial thermal resistance between filler and filler in polymer composites,this paper further designed an amidation reaction to connect CNTs and BN with covalent bonds,so as to prepare a new carbon nanotubes@boron nitride（CNTs@BN）hybrid material.The structure and morphology of the prepared CNTs@BN hybrid materials were characterized in detail,and their effects on the internal structure as well as the thermal conductivity of EVA composites were investigated.When the mass ratio of BN to CNTs was20:1,the prepared CNTs@BN hybrid material had the best thermal conductivity enhancement effect on EVA matrix.The preparation of CNTs@BN hybrid materials not only effectively improved the interfacial bonding between BN and EVA matrix,but also avoided the agglomeration of CNTs,thus giving full play to the synergistic thermal conductivity effect of BN and CNTs.At the same time,the covalent bond connection between CNTs and BN effectively reduced the interfacial thermal resistance,which further promoted the construction of a continuous and efficient heat conduction network in the EVA matrix.Finally,the in-plane thermal conductivity of the prepared EVA composites reached 7.84 W·m^-1·K^-1,which was2613%higher than that of the pure EVA matrix.In addition,the prepared EVA composite material also exhibited excellent thermal stability and stable electrical insulation performance.Then,this paper used 3D printing technology to control the orientation of the anisotropic thermal conductive fillers in the polymer matrix to prepare polymer composites with high through-plane thermal conductivity.A novel reduced graphene oxide-boron nitride（r GO-BN）hybrid was firstly prepared by designing Michael addition and Schiff base reactions,and the prepared r GO-BN hybrid was applied as thermal conductive filler in fused deposition molding（FDM）3D printing of thermoplastic polyurethane（TPU）composites.The structure and morphology of the r GO-BN hybrids were characterized in detail,and their effects on the internal structure and properties of TPU composites were investigated.It was found that the preparation of r GO-BN hybrids not only effectively improved the interfacial bonding between BN and TPU matrix,but also avoided the agglomeration of r GO,thus enabling BN and r GO to exert excellent synergistic thermal conductivity effects.The orientation and alignment of fillers and voids in the TPU matrix were effectively controlled by flexibly adjusting the arrangement of FDM 3D printing,thus promoting the construction of efficient heat conduction paths.Finally,the through-plane thermal conductivity of the prepared TPU composites reached 2.61 W·m^-1·K^-1,which was 1022%higher than that of pure TPU.In addition,the effects of different molding methods on the internal structure,thermal conductivity,mechanical properties and volume resistivity of TPU composites were compared and studied,and the corresponding mechanisms were analyzed and discussed in depth.Next,this paper further optimized the thermal conductivity enhancement effect of the fillers by constructing segregated filler network in the polymer matrix,and ultimately prepared a multi-functional TPU composite with segregated structure.TPU composite particles（TPU@RGO@Ag）modified by reduced graphene oxide（RGO）and silver（Ag）were firstly prepared,and the structure and morphology of the composite particles were characterized in detail.On this basis,TPU composites with segregated RGO/Ag networks were prepared by hot-pressing the TPU@RGO@Ag composite particles,and the structure-property relationships in the composites were systematically investigated.When 1.0vol%RGO and 2.3 vol%Ag were added,the through-plane thermal conductivity,electrical conductivity and electromagnetic interference shielding effectiveness of the prepared TPU composite reached 1.03 W·m^-1·K^-1,9.85×10⁴ S/m and 86.5 d B,respectively.In addition,the prepared TPU composite material also maintained good mechanical flexibility.Thanks to the construction of continuous and segregated RGO/Ag network,the TPU composite obtained a variety of excellent functions with low filler content.Finally,a high thermal conductivity TPU/EVA composite with three-dimensional filler network was prepared.A novel graphite@carbon nanotubes（Graphite@CNTs）hybrid material was firstly prepared using Graphite and CNTs,and its structure and morphology were characterized in detail.A three-dimensional filler skeleton was prepared using the sacrificial salt template method with EVA as the binder,sodium chloride as the salt template and the Graphite@CNTs hybrid material as the filler.On this basis,a TPU/EVA composite with a three-dimensional filler network was prepared by filling the filler skeleton with TPU.The internal structure and properties of the prepared TPU/EVA composites were systematically investigated,and the structure-property relationships of the materials were analyzed in depth.It was found that the design of Graphite@CNTs hybrid material effectively reduced the interfacial thermal resistance of the composites,which enabled the synergistic thermal conductivity effect between Graphite and CNTs to be fully exploited.The three-dimensional filler network inside the TPU/EVA composite also ensured the regular distribution of fillers,promoted the formation of an efficient thermal conductive network,and enabled the composite to obtain excellent thermal conductivity.Finally,the through-plane thermal conductivity of the prepared TPU/EVA composite reached 2.37 W·m^-1·K^-1,which is882.9%higher than that of the TPU/EVA matrix.In addition,the TPU/EVA composite also achieved excellent conductivity and mechanical properties.