# Preparation and Properties of Epoxy Composites with Multi-Scale BN Sheets
## 1 Introduction  
As the electronics industry has grown towards miniaturization, multifunction, and high energy density, the generation of waste heat has become an inevitable risk leading lower performance and shortened product lifetimes [1; 2]. To ensure the normal operation of the electronic equipment, the heat dissipation problem facing more and more challenges [3; 4; 5]. Due to the excellent insulation, corrosion resistance, low raw material cost and good process of Epoxy resin (EP), which always used in electronic devices as an ideal thermal interface material. In recent years, many scholars pay attention to the heat dissipation performance of epoxy resin [6; 7]. However, epoxy resin has low thermal conductivity (about 0.2 Wm\({}^{-1}\cdot\)K\({}^{-1}\)) [8; 9]. The intrinsic modification of epoxy has little effect on improving the thermal conductivity [10; 11]. Most researchers use the addition of inorganic particles to improve the thermal conductivity of epoxy composite [12; 13; 14]. Boron nitride (BN) is an essential inorganic filler for the preparation of high thermal conductivity and insulation polymers with its unique layered structure, high surface thermal conductivity, and other comprehensive properties [15; 16]. [PERSON] [17] noticed that a polyethylene glycol (PEG) is introduced through a mild Diels-Alder reaction to improve its dispersibility and compatibility with epoxy resin matrix. The thermal conductivity of epoxy composites with different filler content show that the \(h\)-BN covalently modified by PEG with the content of 50 wt% can increase the thermal conductivity to 1.14 W/(m\(\cdot\)K). [PERSON] [18] reported that the dopamine with catechol groups and coupling agent to modify boron nitride (the dopamine-modified BN (DBN) and k-DBN (DBN modifiedby coupling agent KH-560). The results showed that surface modification improved the dispersibility of BN in the Epoxy resin matrix and compatibility with the resin. Among BN/EP, DBN/EP, k-DBN/EP composites, k-DBN/EP composites had the highest thermal conductivity at the same number of additions. When the k-DBN/EP content was 30 wt%, the thermal conductivity of the composite was 0.892 W/(m\(\cdot\)K), which was an increase of 25.5% compared with the BN/EP composite. Through these studies found that high thermal conductivity of epoxy composite with high content of BN, it will bring problems such as reduced insulation performance. The second filler to build a thermally conductive bridge inside the material to reduce the amount of filler used to solve this problem [19; 20; 21]. [PERSON] [22] prepared epoxy-matrix composites using the micro- and nano-sized boron nitride (BN) as filler for thermal management in electrical applications. The thermal conductivity of the Epoxy resin shows up to a fourfold increase for the composite containing 20 wt% of BN. The addition of BN results in an increase of the breakdown strength of the host matrix (about 10%) accompanied by improved robustness (less scattering of the measured values), both very important factors for any electrical application. [PERSON] [23] used 33.3% volume fraction of micron BN and graphene microplates (SNPs) hybrid co-filled polylactic acid (PLA). When, BN particles form effective connection points between SNPs and matrix. The formation of heat conduction network strengthens the phonon transfer effect at the interface. With the increase of GNPs/BN ratio, the thermal conductivity of PLA increases and the mixing changes. The thermal conductivity of PLA changed with the highest relative proportion of hybrid particles. It was 2.28-2.77 W/(m\(\cdot\)K), more than 12 times that of pure PLA. [PERSON] [24] found that the mixed mass ratio of BN, AlN and Al\({}_{2}\)O\({}_{3}\) was 20/5/5, the thermal conductivity of PE with mixed filling reaches the maximum (1.12 W/(m\(\cdot\)K)), which is higher than the same content particle filled polystyrene (PS).