Synergetic effect of hybrid boron nitride and multi-walled carbon nanotubes on the thermal conductivity of epoxy composites

This study investigates the synergistic effect of combining multi-walled carbon nanotubes (MWCNTs) and boron nitride (BN) flakes on thermally conductive epoxy composite. The surface of the two fillers was functionalized to form covalent bonds between the epoxy and filler, thereby reducing thermal interfacial resistance. The hybrid filler provided significant enhancement of thermal conductivity, adding 30 vol% modified BN and 1 vol% functionalized MWCNTs achieving a 743% increase in thermal conductivity (1.913 W mK⁻¹, compared to 0.2267 W mK⁻¹ of neat epoxy).     

BN表面改性对BN/环氧树脂复合材料导热性能的影响

采用十八烷基三甲基溴化铵（OTAB）阳离子表面活性剂对BN微米片进行有机化改性,研究了BN表面改性对BN/环氧树脂复合材料导热性能的影响。当OTAB浓度为0.6 g · L^-1时,BN表面的OTAB吸附量接近饱和。BN表面改性提高了环氧树脂对BN的浸润性,降低了BN的导热系数。SEM观察及黏度测试结果表明：BN表面改性改善了BN/环氧树脂复合材料的界面性能及体系相容性。由于界面热阻的降低,改性BN/环氧树脂复合材料的导热系数高于未改性BN/环氧树脂复合材料,当BN填充量为30%（填料与树脂基体的质量比）时,改性BN/环氧树脂复合材料的导热系数为1.03 W （m · K）^-1,是未改性BN/环氧树脂导热系数（0.48 W （m · K）^-1）的2.15倍。     

高导热型铝基覆铜板研究

为研究一种高导热铝基覆铜板,以合成的双马改性环氧树脂为基体,最佳质量配比的氮化铝、氮化硅、氮化硼等混合粒子为导热填料制备了绝缘导热胶粘剂,并以此导热胶成功制备了高导热铝基覆铜板.分析了树脂配方设计,探讨了填料含量对绝缘层导热、耐高温、电绝缘及粘接强度的影响.研究表明,研制的基板热导率达1.38 W/(m.K),热阻0.65℃/W,体、表电阻率分别为3.2×1014Ω.cm及4.6×1013Ω,可长期在160℃下使用,剥离强度13 N/cm,与低导热基板相比具有良好的传热能力.     

Moisture absorption by cyanate ester modified epoxy resin matrices. Part III. Effect of blend composition

The moisture absorption of thermally cured cyanate ester modified epoxy resin matrices has been studied under constant hygrothermal conditions and with a series of thermal spikes. Various resin blends of differing composition were studied, so that the effect of resin structure on moisture absorption could be assessed. It was found that intermittently applied thermal spikes can enhance the moisture absorption by cyanate esters and their blends with epoxy resin. The equilibrium moisture concentration was found to increase with the fraction of cyanate ester in the blend. The results of the desorption study on both control and spiked specimens showed that some of the water molecules remain entrained in the resin, probably as a result of hydrolysis of the polymer matrix. Up to a thermal spiking temperature of 160 °C, the crosslink density remained constant but at higher temperatures tended to decrease, as observed by examination of the modulus above the glass transition temperature.     

A detailed thermal analysis of nanocomposites filled with SiO2, AlN or boehmite at varied contents and a review of selected rules of mixture

In order to investigate and compare the thermal and mechanical properties of nanocomposites filled with various nanoparticles multiple experiments have been carried out. The aim of this study was to enhance the thermal and mechanical properties of epoxy resin for fiber reinforces structures by the addition of nanoparticles. These altered properties were analyzed and reconciled with each other as well as compared to data developed from different rules of mixture. A hot curing epoxy system based on bisphenol-A (DGEBA) has been filled with different contents of silicon dioxide (SiO₂), aluminum nitride (AlN) and boehmite nanoparticles to examine the effects in the material’s thermal and mechanical behavior with variable filler materials and contents compared to the unfilled epoxy. The glass transition temperature fluctuates very little with varied filler content. The coefficient of thermal expansion can be reduced with increasing filler content. This improvement recurs also in thermal conductivity and during dynamic mechanical analysis. Several rules of mixture have been applied to be verified on the basis of varied materials and filler contents. The results did not always match the experiments. The deviations are ascribed to the influence of interphases that build up in the vicinity of the nanoparticles during the process of curing.     

Exploring biomass based carbon black as filler in epoxy composites: Flexural and thermal properties

Carbon blacks (CB), derived from bamboo stem (BS-CB), coconut shells (CNS-CB) and oil palm empty fiber bunch (EFB-CB), were obtained by pyrolysis of fibers at 700 °C, characterized and used as filler in epoxy composites. The results obtained showed that the prepared carbon black possessed well-developed porosities and are predominantly made up of micropores. The BS-CB, CNS-CB and EFB-CB filled composites were prepared and characterized using scanning electron microscope (SEM) and thermogravimetric analyzer (TGA). The SEM showed that the fractured surface of the composite indicates its high resistance to fracture. The CBs–epoxy composites exhibited better flexural properties than the neat epoxy, which was attributed to better adhesion between the CBs and the epoxy resin. TGA showed that there was improvement in thermal stability of the carbon black filled composites compared to the neat epoxy resin.     

The effect of interfacial state on the thermal conductivity of functionalized Al2O3 filled glass fibers reinforced polymer composites

Rapidly increasing packaging density of electronic devices puts forward higher requirements for thermal conductivity of glass fibers reinforced polymer (GFRP) composites, which are commonly used as substrates in printed circuit board. Interface between fillers and polymer matrix has long been playing an important role in affecting thermal conductivity. In this paper, the effect of interfacial state on the thermal conductivity of functionalized Al₂O₃ filled GFRP composites was evaluated. The results indicated that amino groups-Al₂O₃ was demonstrated to be effective filler to fabricate thermally conductive GFPR composite (1.07 W/m K), compared with epoxy group and graphene oxide functionalized Al₂O₃. It was determined that the strong adhesion at the interface and homogeneous dispersion of filler particles were the key factors. Moreover, the effect of interfacial state on dielectric and thermomechanical properties of GFRP composites was also discussed. This research provides an efficient way to develop high-performance GFRP composites with high thermal conductivity for integrated circuit packaging applications.     

Effects of carbon nanotubes and carbon fiber reinforcements on thermal conductivity and ablation properties of carbon/phenolic composites

The ablation properties and thermal conductivity of carbon nanotube (CNT) and carbon fiber (CF)/phenolic composites were evaluated for different filler types and structures. It was found that the mechanical and thermal properties of phenolic-polymer matrix composites were improved significantly by the addition of carbon materials as reinforcement. The concentrations of CF and CNT reinforcing materials used in this study were 30 vol% and 0.5 wt%, respectively. The thermal conductivity and thermal diffusion of the different composites were observed during ablation testing, using an oxygen–kerosene (1:1) flame torch. The thermal conductivity of CF mat/phenolic composites was higher than that of random CF/phenolic composites. Both CF mat and CNT/phenolic composites exhibited much better thermal conductivity and ablation properties than did neat phenolic resin. The more conductive carbon materials significantly enhanced the heat conduction and dissipation from the flame location, thereby minimizing local thermal damage.     

Enhancement of tensile and thermal properties of epoxy nanocomposites through chemical hybridization of carbon nanotubes and alumina

This paper presents the properties of epoxy nanocomposites, prepared using a synthesized hybrid carbon nanotube–alumina (CNT–Al₂O₃) filler, via chemical vapour deposition and a physically mixed CNT–Al₂O₃ filler, at various filler loadings (i.e., 1–5%). The tensile and thermal properties of both nanocomposites were investigated at different weight percentages of filler loading. The CNT–Al₂O₃ hybrid epoxy composites showed higher tensile and thermal properties than the CNT–Al₂O₃ physically mixed epoxy composites. This increase was associated with the homogenous dispersion of CNT–Al₂O₃ particle filler; as observed under a field emission scanning electron microscope. It was demonstrated that the CNT–Al₂O₃ hybrid epoxy composites are capable of increasing tensile strength by up to 30%, giving a tensile modulus of 39%, thermal conductivity of 20%, and a glass transition temperature value of 25%, when compared to a neat epoxy composite.     

Effects of aluminium nitride inclusions on thermal and electrical properties of epoxy and polypropylene: An experimental investigation

Thermal and dielectric properties of polymers reinforced with micro-sized aluminium nitride (AlN) particles have been studied. A set of epoxy–AlN composites, with filler content ranging from 0 to 25 vol% is prepared by hand lay-up technique. With similar filler loading, polypropylene -AlN composites are fabricated by compression molding technique. Density (ρ_c), effective thermal conductivity (k_eff), glass transition temperature (T_g), coefficient of thermal expansion (CTE) and dielectric constant (ε_c) of these composites are measured experimentally. The various experimental data were interpreted using appropriate theoretical models. Incorporation of AlN in both the resin increases the k_eff and T_g whereas CTE of composite decreases favourably. The dielectric constant of the composite also found to get modified with filler content. With improved thermal and modified dielectric characteristics, these AlN filled polymer composites can possibly be used for microelectronics applications.     

Thermal conductivity of epoxy composites with a binary-particle system of aluminum oxide and aluminum nitride fillers

Aluminum oxide and aluminum nitride with different sizes were used alone or in combination to prepare thermally conductive polymer composites. The composites were categorized into two systems, one including composites filled with large-sized aluminum nitride and small-sized aluminum oxide particles, and the other including composites filled with large-sized aluminum oxide and small-sized aluminum nitride. The use of these hybrid fillers was found to be effective for increasing the thermal conductivity of the composite, which was probably due to the enhanced connectivity offered by the structuring filler. At a total filler content of 58.4 vol.%, the maximum values of both thermal conductivities in the two systems were 3.402 W/mK and 2.842 W/mK, respectively, when the volume ratio of large particles to small particles was 7:3. This result was represented when the composite was filled with the maximum packing density and the minimum surface area at the same volume content. As such, the proposed thermal model predicted thermal conductivity in good agreement with experimental values.     

熔盐法合成高导热磷化硼及其热管理性能研究

随着电力电子器件封装密度提高, 开发导热性能优异的热界面材料受到了广泛关注。绝大多数传统导热填料的热导率较低, 因此合成新型高导热填料是提高热界面材料导热性能的重要途径。本研究通过简单的熔盐法合成了高导热的磷化硼(BP)颗粒, 与氮化硼(h-BN)混合并通过搅拌和浇注的方法填充到环氧树脂(EP)基体中制备得到树脂基复合材料(BP-BN/EP)。实验结果表明：采用三盐法(NaCl : KCl : LiCl)合成的BP产率最高达到74%, 相对于单盐法(41%)和双盐法(39%)分别提高了33%和35%。对于BP-BN/EP复合材料, 复合材料的微结构显示BP和BN颗粒均匀分布在环氧树脂基体。当混合填料体积分数为30%时, 该复合材料的热导率达到1.81 W•m^-1•K^-1, 是纯树脂热导率(0.21 W•m^-1•K^-1)的8.6倍, 这与BP颗粒作为桥梁连接相邻BN颗粒形成导热网络有关。除此以外, 相较于不含BP的复合材料(SBN-BN/EP), BP-BN/EP复合材料展现出更加优异的热导率、热稳定性和较好的热力学性能。因此, 熔盐法合成的BP在热管理领域具有较大的应用前景。     

Thermal conductivity of boron nitride reinforced polyethylene composites

The thermal conductivity of boron nitride (BN) particulates reinforced high density polyethylene (HDPE) composites was investigated under a special dispersion state of BN particles in HDPE, i.e., BN particles surrounding HDPE particles. The effects of BN content, particle size of HDPE and temperature on the thermal conductivity of the composites were discussed. The results indicate that the special dispersion of BN in matrix provides the composites with high thermal conductivity; moreover, the thermal conductivity of composites is higher for the larger size HDPE than for the smaller size one. The thermal conductivity increases with increasing filler content, and significantly deviates the predictions from the theoretic models. It is found also that the combined use of BN particles and alumina short fiber obtains higher thermal conductivity of composites compared to the BN particles used alone.     

Synergistic effect of boron nitride flakes and tetrapod-shaped ZnO whiskers on the thermal conductivity of electrically insulating phenol formaldehyde composites

Tetrapod-shaped zinc oxide (T-ZnO) whiskers and boron nitride (BN) flakes were employed to improve the thermal conductivity of phenolic formaldehyde resin (PF). A striking synergistic effect on thermal conductivity of PF was achieved. The in-plane thermal conductivity of the PF composite is as high as 1.96 W m⁻¹ K⁻¹ with 30 wt.% BN and 30 wt.% T-ZnO, which is 6.8 times higher than that of neat PF, while its electrical insulation is maintained. With 30 wt.% BN and 30 wt.% T-ZnO, the flexural strength of the composite is 312.9% higher than that of neat PF, and 56.2% higher that of the PF composite with 60 wt.% BN. The elongation at break is also improved by 51.8% in comparison with that of the composite with 60 wt.% BN. Such a synergistic effect results from the bridging of T-ZnO whiskers between BN flakes facilitating the formation of effective thermal conductance network within PF matrix.     

Characterization of epoxy functionalized graphite nanoparticles and the physical properties of epoxy matrix nanocomposites

This work presents a novel approach to the functionalization of graphite nanoparticles. The technique provides a mechanism for covalent bonding between the filler and matrix, with minimal disruption to the sp² hybridization of the pristine graphene sheet. Functionalization proceeded by covalently bonding an epoxy monomer to the surface of expanded graphite, via a coupling agent, such that the epoxy concentration was measured as approximately 4 wt.%. The impact of dispersing this material into an epoxy resin was evaluated with respect to the mechanical properties and electrical conductivity of the graphite–epoxy nanocomposite. At a loading as low as 0.5 wt.%, the electrical conductivity was increased by five orders of magnitude relative to the base resin. The material yield strength was increased by 30% and Young’s modulus by 50%. These results were realized without compromise to the resin toughness.     

氮化物对增强线性酚醛树脂导热性能的对比研究

目的对比探讨氮化物陶瓷颗粒AlN和BN对热塑性酚醛树脂复合材料导热率的影响,制备高导热复合材料,并将其应用于电子塑封领域。方法首先,采用硅烷偶联剂对AlN和BN进行表面改性,以增强其在有机聚合物中的分散性。然后通过在线性酚醛树脂中添加不同粒径的陶瓷颗粒,对比粒径及填料含量对线性酚醛树脂复合材料导热率的影响,从声子角度分析,获取适合作为提高复合材料导热性能的填料。结果经过硅烷偶联剂表面改性后,陶瓷颗粒AlN、BN与水的接触角变大,与树脂的接触角变小,能够更好地分散在线性酚醛树脂中。在线性酚醛树脂中添加不同粒径、不同含量的AlN和BN,发现在不同含量范围内,填料粒径对复合材料导热率的影响不同。根据声子传递热量理论分析,BN较AlN在与C形成的界面上更容易传输热量,从而实现了较高的导热率。结论氮化物陶瓷颗粒能够很好地增强复合材料的导热率,尤其是BN,其态密度和C的态密度重叠率极高,更适合在BN与C的界面快速传递热量。     

Magnetic-aligned,magnetite-filled epoxy composites with enhanced thermal conductivity

This paper investigates the influence of magnetic field-assisted filler alignment technology on the morphology and the thermal conductivity of magnetite-filled epoxy composites. A magnetic field was applied during the solidification of the composite in order to change the position of the filler and its distribution in the polymer matrix. It is shown that the applied procedure leads to the filler being oriented along the direction of the magnetic field, and as a result, the thermal conductivity is improved by up to 120 % compared to a composite with randomly oriented filler obtained without the assistance of a magnetic field. This positive effect is caused by the appearance of conductive paths at a much lower content of the filler when the composite solidification is assisted by a magnetic field, relative to an equivalent isotropic sample. These morphological changes were confirmed by microscopic and X-ray microtomography imaging. The temperature dependences of thermal conductivity were also investigated over a broad temperature range for a magnetite-filled epoxy composite sample and compared to the bulk magnetite reference, showing that thermal behaviour of the magnetite-filled composite is stable, which is a promising result when considering the future application of the technology.     

Preparation and properties of hollow glass microsphere-filled epoxy-matrix composites

Hollow glass microsphere (HGM)–filled epoxy composites, with filler content ranging from 0 to 51.3 vol.%, were prepared in order to modify the dielectric properties of the epoxy. The results showed that the dielectric constant (D_k) and dielectric loss (D_f) of the composites decreased simultaneously with increasing HGM content, which was critical for the provision of superior high-frequency device performance. Other properties of the composite, such as the coefficient of thermal expansion (CTE) and the glass transition temperature (T_g), were also improved. The improvement in these properties was related to strong interaction between the HGM and epoxy, which was indicated by the formation of an interphase between the HGM and epoxy-matrix. It was unsatisfactory in this study that the thermal conductivity of the composites also decreased with HGM content. In order to obtain relatively high thermal conductivity and a low dielectric constant simultaneously, this paper suggests further adding other filler.     

Thermal conductivity of polymer composites based on the length of multi-walled carbon nanotubes

The anisotropic development of thermal conductivity in polymer composites was evaluated by measuring the isotropic, in-plane and through-plane thermal conductivities of composites containing length-adjusted short and long multi-walled CNTs (MWCNTs). The thermal conductivities of the composites were relatively low irrespective of the MWCNT length due to their high contact resistance and high interfacial resistance to polymer resins, considering the high thermal conductivity of MWCNTs. The isotropic and in-plane thermal conductivities of long-MWCNT-based composites were higher than those of short-MWCNT-based ones and the trend can accurately be calculated using the modified Mori-Tanaka theory. The in-plane thermal conductivity of composites with 2 wt% long MWCNTs was increased to 1.27 W/m·K. The length of MWCNTs in polymer composites is an important physical factor in determining the anisotropic thermal conductivity and must be considered for theoretical simulations. The thermal conductivity of MWCNT polymer composites can be effectively controlled in the processing direction by adjusting the length of the MWCNT filler.     

Silane modification on mesoporous silica coated carbon nanotubes for improving compatibility and dispersity in epoxy matrices

A simple synthetic method for placing a mesoporous silica coating on multi-wall carbon nanotubes (CNTs@MS) was developed to improve the surface compatibility with regard to a polar epoxy matrix. In addition, the mesoporous silica shell with silanol groups on the CNTs provides a platform to attach silane molecules (e.g. 3-glycidoxypropyltrimethoxysilane, GPTMS) that enable the CNTs@MS to be incorporated into the epoxy matrix at a content of up to 20 wt.%. The viscosities of the CNTs@MS- and GPTMS-modified-CNTs@MS–epoxy composites are much lower than that of the CNTs–epoxy, and then the voids in the GPTMS-modified-CNTs@MS–epoxy composites are most significantly reduced. The effects of the CNTs@MS and GPTMS-modified CNTs@MS on the mechanical and thermal properties of the epoxy composite are investigated. The results show that the GPTMS-modified CNTs@MS improved the filler–epoxy matrix interaction, and has better compatibility in epoxy than the CNTs@MS. As the surface compatibility and interaction strength increase in the epoxy matrix, the enhancement in storage modulus, thermal conductivity and reduction in the coefficient of thermal expansion are in the following order: GPTMS-modified CNTs@MS > CNTs@MS ≫ CNTs.