Design,Fabrication,and Property Study Of High Thermal Conductive Rubber Functional Materials Based On Novel Carbon Materials

Thermally conductive rubber nanocomposites play an irreplaceable role in many fields due to their unique high elasticity and flexibility.Under static conditions,thermally conductive rubber composites can be used as highly efficient thermal management materials to assist in heat dissipation,which is essential to ensure the safe operation of equipment for the microelectronics industry,automotive power systems,photovoltaic systems,communications,and other fields.As the performance of microelectronic equipment continues to improve,the thermal conductivity of rubber composites also increases.For rubber composites serving under dynamic operating conditions,such as tires and drive belts,a large amount of heat is generated during their operation.The accumulation of this heat may adversely affect the performance and service life of the material.Therefore,improving the thermal conductivity of rubber composites under dynamic conditions is essential to ensure the safety of products such as tires and to extend their service life.By enhancing the thermal conductivity of these materials,heat can be effectively managed,and the risk of overheating can be reduced,thereby improving the overall performance and reliability of the product.In this thesis,systematic research has been carried out on the enhancement of the thermal conductivity of rubber composites in service under dynamic and static operating conditions.The main innovative research results are summarised as follows:（1）Preparation and structural properties of carbon nanotube whisker-loaded nano-alumina hybrid filler/micron alumina/silicone rubber composites:nano-alumina（n-Al₂O₃）with particle size of about 12 nm and whisker-loaded carbon nanotubes（CNW）with diameter of about 75 nm are used to prepare nano-alumina hetero-fillers（CNW@n-Al₂O₃）hybrid fillers by electrostatic self-assembly process,and then combined with 5μm alumina（n-Al₂O₃）and 5μm alumina（CNW@n-Al₂O₃）to produce nano-alumina hetero-fillers.Then,the silicone rubber composites with micro-nano multilevel network structure were prepared by mechanical blending with micron alumina（m-Al₂O₃）and silicone rubber（PDMS）with a particle size of 5μm.The experimental results show that CNW@n-Al₂O₃ nanohybrids can make full use of the high thermal conductivity of CNW while shielding its electrical conductivity.The thermal conductivity of the m-Al₂O₃/PDMS composites filled with 2 phr of CNW@n-Al₂O₃ and 200phr of m-Al₂O₃/PDMS was significantly improved to 1.137 W/（m K）,with the volume resistance as high as 1.323×10⁹Ω·cm.The electrical and thermal conductivity mechanisms of the micro-and nano-multilevel network-structured composites were explained by constructing a microstructural model.The ability of CNW@n-Al₂O₃ to build a thermally conductive pathway was calculated using the HS boundary model and combined with the Foygel model calculations to show that nano hybridization of CNW reduces the thermal resistance of interfacial contact between fillers.Finally,the prepared composites were practically applied to electronic chips for heat dissipation,showing the potential as excellent thermal interface materials（TIM）.（2）Preparation and structural properties of three-dimensional graphene/boron nitride aerogel and its high thermal conductivity silicone rubber composites:Inspired by the structure of the swallow’s nest,the three-dimensional（3D）filler skeleton rGO/BN was prepared by employing reduced graphene oxide（rGO）and boron nitride（BN）.rGO/BN was then transformed into T-rGO/BN by a high-temperature heat treatment at 1000℃,which further reduces the surface defects and improves the lattice structure of rGO.Surface defects decrease,and the lattice structure is improved,enhancing thermal conductivity.The 3D T-rGO/BN/PDMS composites prepared based on this possess high flexibility and exhibit significantly enhanced thermal conductivity（up to 1.41 W/（m·K））at a low filler content（14.3 vol%）.Foygel and Agari models were used for fitting analysis and combined with finite element simulations to explore the simulation of the formation mechanism of the composites with excellent thermal conductivity at low filler.The results confirm that the 3D packing network has higher heat transfer efficiency,and rGO can act as a"thermal bridge"between neighboring BNs,thus reducing the contact thermal resistance.Meanwhile,the 3D skeleton design can effectively promote the dispersion of thermally conductive fillers and the formation of thermally conductive pathways,which significantly improves the thermal conductivity of the composites.（3）Preparation and properties of whiskered carbon nanotube/natural rubber thermally conductive composites:CNW with a diameter of about 75 nm was selected as the reinforcing filler and mechanically blended with natural rubber（NR）.Through the in-depth study of the effects of different CNW additions on the thermal conductivity,heat generation behavior,and dynamic and static mechanical properties of CNW/NR composites,it was found that the CNW/NR composites prepared with the CNW additions of 20 phr had good dynamic and static mechanical properties,and also balanced the contradictory aspects of compression fatigue heat generation and thermal conductivity.In addition,the most suitable modifier,TESPT,was screened out by examining the effects of different silane coupling agents on the properties of CNW/NR composites.In order to further improve the mechanical properties of CNW/NR composites,the addition of arrayed carbon nanotubes（CNBs）and the treatment of CNW by plasma ball milling were explored.The results show that the addition of a small amount of CNB can improve the mechanical properties of CNW/NR composite properties and drastically increase the compression fatigue temperature of the composites.By treating the CNW plasma ball mill,the shape coefficient can be effectively changed,the dispersion can be improved,and the internal friction can be reduced so as to improve its dynamic mechanical properties further.Compared with the comprehensive thermal conductivity of the existing thermally conductive rubber composites,it is found that the thermal conductivities of the composites produced with the addition of 20 phr and 30phr of CNW are 0.62 W/（m·K）and 0.99 W/（m·K）,respectively.The loss factor tanδdoes not exceed 0.1 at 60°C.The thermal conductivities of the composites are also improved by increasing the CNW fraction,which is the most important factor in the thermal conductivity of the composite.