Study On Preparation Of Boron Nitride-based Composites And Its Thermal Conductivity

With the development of miniaturization,multifunction and high power of modern electronic devices and integrated circuits,efficient heat dissipation has become a new demand in the fields of quantum communication,electronic information and energy storage technology.At present,it is widely considered as an effective strategy to add inorganic high thermal conductive fillers to polymer substrate to prepare new thermal conductive composites.Among them,because of its excellent thermal conductivity,stable structure,good mechanical properties,very low coefficient of thermal expansion and strong oxidation resistance,hexagonal boron nitride has attracted extensive attention of researchers.However,the mechanical properties and thermal stability of the composites will inevitably decrease due to the addition of fillers.Therefore,how to build efficient and orderly heat conduction network in polymer substrate and how to improve the interface contact between inorganic fillers and polymer substrate have become current problems.This paper studies the thermal conductivity of composite from the perspective of constructing three-dimensional heat conduction network skeleton,improving the intrinsic thermal conductivity of polymer and adding two component composite filler.The specific research contents are as follows:（1）The modified polyurethane foam was used as a three-dimensional network skeleton.The three-dimensional heat conduction network was constructed by electrostatic adsorption combined with hydroxylated boron nitride nanosheets（BNNS-OH）.The PVA was coated on the surface by microwave assisted synthesis,which could be used as a hydrogen bond and a hydrogen bond donor.The results show that the thermal conductivity of the composite is 4.68 W·m^-1·K^-1 when the loading amount of BNNS-OH is 10 wt%.In addition,the composite still has excellent mechanical properties and thermal stability.（2）Rod-like nanocellulose was prepared to use microcrystalline cellulose as raw material by three different methods.The intrinsic thermal conductivity of cellulose was increased from 0.36 W·m^-1·K^-1 to 1.06 W·m^-1·K^-1,which provided a direction for the study of improving the intrinsic thermal conductivity of polymer.Then,we prepared the super flexible composite film by hydrogen bonding of BNNS-OH and nanocellulose.The results show that the thermal conductivity of the film is 2.86 W·m^-1·K^-1 when the loading amount of BNNS-OH is 10 wt%.（3）The structure of dendritic heat conduction network was constructed by BNNS-OH and hydroxylated carbon nanotubes（CNT-OH）.The results show that the thermal conductivity of the composite film is 3.86 W·m^-1·K^-1 when the equivalent amount of BNNS-OH and CNT-OH is 4 wt%and the total loading is 8 wt%.The thermal conductivity of the composite film is 5.16 W·m^-1·K^-1 when the ratio of the two fillers is 1:3 and the total loading is 10 wt%,which provides a new idea for the study of adding multi-component fillers to improve the thermal conductivity of the polymer.In order to further verify the practical application value of the composites prepared in this paper,we put the composites on the LED lamp for heat dissipation experiment,observe the heat dissipation on the surface of the LED lamp with the infrared thermal imager,and simulate the heat dissipation diagram with the finite element analysis.The results also show that the composites we prepared in this paper have a certain potential value.