Polymer/boron nitride nanosheet composite with high thermal conductivity and sufficient dielectric strength

An efficient method was reported to fabricate boron nitride (BN) nanosheets using a sonication–centrifugation technique in DMF solvent. Then non‐covalent functionalization and covalent functionalization of BN nanosheets were performed by octadecylamine (ODA) and hyperbranched aromatic polyamide (HBP), respectively. Then, three different types of epoxy composites were fabricated by incorporation of BN nanosheets, BN‐ODA, and BN‐HBP. Among all three epoxy composites, the thermal conductivity and dielectric strength of epoxy composites using BN‐HBP nanosheets display the highest value, efficiently enhancing to 9.81 W/m K at 50 vol% and 34.8 kV/mm at 2.7 vol% (increase by 4057% and 9.4% compared with the neat epoxy), respectively. The significantly improved thermal conductivity and dielectric strength are attributed to the large surface area, which increases the contact area between nanosheets and nanosheets, as well as enhancement of the interfacial interaction between nanosheets and epoxy matrix. Copyright © 2015 John Wiley & Sons, Ltd.     

Silane surface modification of boron nitride for high thermal conductivity with polyphenylene sulfide via melt mixing method

Polyphenylene sulfide (PPS) is a promising engineering polymer, which is used for various industrial applications. In this study, we developed a highly thermally conductive PPS composite containing boron nitride (BN) as a thermally conductive ceramic filler. (3‐Aminopropyl) triethoxysilane was doped onto the surface of hydroxyl‐functionalized BN using a simple sol–gel process. The modified BN particles were embedded in a PPS matrix via a melt mixing process using a twin extruder to form BN‐Si composites. The maximum thermal conductivity 3.09 W/m·K was exhibited by the surface‐modified BN‐Si containing 60 wt%. This value was 116% higher than the thermal conductivities of the pristine BN and PPS matrix, respectively. The surface‐treated composites also showed an improved storage modulus because of an improvement in the interfacial adhesion and interaction between the BN filler and the PPS matrix. Copyright © 2017 John Wiley & Sons, Ltd.     

Very high thermal conductivity obtained by boron nitride-filled polybenzoxazine

A thermal conductivity of 32.5 W/mK is achieved for a boron nitride-filled polybenzoxazine at its maximum filler loading of 78.5% by volume (88% by weight). The extraordinarily high conductivity value results from outstanding properties of the polybenzoxazine matrix and the boron nitride filler. The bisphenol-A–methylamine-based polybenzoxazine possesses very low A-stage viscosity which aids in filler wetting and mixing. The filler particles with an average size of ca. 225 μm are large aggregates of boron nitride flake-like crystals. It has bimodal particle size distribution which assists in increasing the particle packing density. This filler–matrix system provides a highly thermally conductive composite due to the capability of forming conductive networks with low thermal resistance along the conductive paths. The SEM picture of the composite fracture surface reveals good interfacial adhesion between the boron nitride filler and polybenzoxazine matrix. Water absorption of the filled systems at 24 h is <0.1% and decreases with increasing filler content.     

导热增强聚乙二醇相变复合材料的制备及其性能

本文以聚乙二醇(PEG)为相变材料,通过添加不同的无机填料,采用熔融共混浇筑方式制备了导热增强型相变复合材料。 通过扫描电子显微镜(SEM)、热常数分析仪、差示扫描量热仪(DSC)、红外热成像和热重分析仪研究了所制备复合材料的微观结构、导热性能与相变过程。 研究结果表明,相比于碳酸钙和氧化铝,在相同添加含量下,氮化硼(BN)可有效提高PEG的导热系数,当BN质量分数为40%时,导热系数可达到3.40 W/(m·K);当填料添加量相同时,片状BN和不规则纳米碳酸钙(CaCO₃)比球形氧化铝(Al₂O₃)对PEG具有更加优良的定型效果,在相变过程中,能够更加有效阻隔PEG的流动,保持复合材料的形状稳定性。     

Achieving a high thermal conductivity for segregated BN/PLA composites via hydrogen bonding regulation through cellulose network

Normally, the effective dispersion of thermal conductive fillers is a prerequisite for ensuring thermally conductive networks formed in polymer composites. In this work, a facile method was provided by using cellulose to alter the distribution state of boron nitride (BN) for the preparation of high thermally conductive polylactic acid (PLA). After powder mixing and hot‐pressing process, the Cellulose@BN was located at the boundaries of PLA granules to form consecutive thermally conductive networks with more compact structure. Morphology observation and FTIR spectra confirmed that BN edges absorbed on the cellulose surface under the intermolecular hydrogen bond interaction between PLA and BN. At the BN content of 25 wt%, contrasted with traditional BN/PLA segregated polymer composites (SPCs), thermal conductivity coefficient of Cellulose@BN/PLA SPCs improved by 53.5% from 0.71 to 1.09 Wm^?1 K^?1. This enhancement could be attributed to the reason that the cellulose regulated stripe aggregation allowed the BN connect with each other more compact, thus a thermal conduction networks with reduced phonon scattering were formed.     

Thermal conductivity epoxy resin composites filled with boron nitride

Boron nitride (BN) micro particles modified by silane coupling agent, γ‐aminopropyl triethoxy silane (KH550), are employed to prepare BN/epoxy resin (EP) thermal conductivity composites. The thermal conductivity coefficient of the composites with 60% mass fraction of modified BN is 1.052 W/mK, five times higher than that of native EP (0.202 W/mK). The mechanical properties of the composites are optimal with 10 wt% BN. The thermal decomposition temperature, dielectric constant, and dielectric loss increase with the addition of BN. For a given BN loading, the surface modification of BN by KH550 exhibits a positive effect on the thermal conductivity and mechanical properties of the BN/EP composites. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface modification of boron nitride via poly (dopamine) coating and preparation of acrylonitrile‐butadiene‐styrene copolymer/boron nitride composites with enhanced thermal conductivity

A biology‐inspired approach was utilized to functionalize hexagonal boron nitride (h‐BN), to enhance the interfacial interactions in acrylonitrile‐butadiene‐styrene copolymer/boron nitride (ABS/BN) composites. The poly (dopamine), poly (DOPA) layer, was formed on the surface of BN platelets via spontaneously oxidative self‐polymerization of DOPA in aqueous solution. The modified BN (named as mBN) coated with poly (DOPA) was mixed with ABS resin by melting. The strong interfacial interactions via π‐π stacking plus Van der Waals, both derived from by poly (DOPA), significantly promoted not only the homogeneous dispersion of h‐BN in the matrix, but also the effective interfacial stress transfer, leading to improve the impact strength of ABS/mBN even at slight mBN loadings. A high thermal conductivity of 0.501 W/(m·K) was obtained at 20 wt% mBN content, reaching 2.63 times of the value for pure ABS (0.176 W/(m·K)). Meanwhile, the ABS/mBN composites also exhibited an excellent electrical insulation property, which can be expected to be applied in the fields of thermal management and electrical enclosure.     

Study on insulating thermal conductive BN/HDPE composites

Thermal conductivity of boron nitride (BN) reinforced high density polyethylene (HDPE) composites was investigated under a special dispersion state of BN particles in HDPE, i.e., BN particles surrounding HDPE matrix particles. The results indicated that the special dispersion of BN in matrix gives the composites high thermal conductivity at low filler content; moreover, the smaller BN particles can more easily form conductive chains of filler compared to the larger filler particles. Examining the dependence of electrical insulation and mechanical properties of the composites on BN content demonstrated that the reinforced composites containing 30% by volume of filler has good electrical insulation and mechanical properties.     

Facile fabrication of organically modified boron nitride nanosheets and its effect on the thermal stability,flame retardant,and mechanical properties of thermoplastic polyurethane

Although hexagonal boron nitride (h‐BN) has presented a potential prospect in polymer composite fields, undesirable interfacial interaction with polymer matrix that generates serious aggregation of nanomaterials has suppressed its enhancement effect. Moreover, the chemically inert surface of h‐BN also makes the commonly used approach that improves the interfacial interaction between nanofillers and polymeric matrix invalid. Herein, the functionalized modification of chemically inert h‐BN was successfully fabricated by the adsorption of cetyl‐trimethylammonium bromide, with electrostatic interactions. The obtained h‐BN (cetyl‐trimethylammonium bromide‐BN) was well characterized by systematic tests and then added into thermoplastic polyurethane (TPU) matrix. The inclusion of functionalized h‐BN can dramatically improve thermal stability, flame retardant, and mechanical properties of TPU composites. With the incorporation of as low as 4.0 wt% nanofillers, maximal value of heat release rate and total heat release of TPU were reduced by 57.5% and 17.8%, compared with those of pure TPU, respectively. Moreover, tensile strength of TPU composite with a loading of 2.0 wt% was increased by 79.3% in comparison with that of neat TPU. The facile functionalized approach of chemically inert h‐BN paves the way for promising applications of h‐BN in the development of flame retardant polymer materials.     

Synergetic effect of thermal conductivity and flame retardancy of cyanate ester composites containing DOPO and BN with great dielectric properties

DOPO and boron nitride (BN) fillers with different particle sizes and several loadings were employed to improve the properties of cyanate ester (CE) resin. The effects of BN content and particle size on the thermal conductivity of the BN‐DOPO/CE ternary composites were discussed. The influence of enhancing the thermal conductivity of the ternary composites on their flame retardancy was studied. The consequences showed that increasing the thermal conductivity of BN‐DOPO/CE composites had an active impact on their flame retardancy. Approving flame retardancy of the ternary composites was certified by the high limiting oxygen index (LOI), UL‐94 rating of V‐0, and low heat release rate (HRR) and total heat release (THR). For instance, in contrast with pure CE matrix, peak of HRR (pk‐HRR), average of HRR (av‐HRR), THR, and average of effective heat of combustion (av‐EHC) of CEP/BN_{0.5 μm}/10 composite were decreased by 51.7%, 33.8%, 18.7%, and 18.9%, respectively. Thermal gravimetry analysis (TGA) showed that the addition of BN fillers improves the thermal stability of the composites. Moreover, the ternary composites possess good dielectric properties. Their dielectric constants (ε) are less than 3, and dielectric loss tangent (tgδ) values are lower than neat CE resin.     

Enhancement of the thermal and mechanical properties of a surface‐modified boron nitride–polyurethane composite

Thermoplastic polyurethane (PU) elastomer, prepared from poly(tetramethylene glycol) and methyl diphenyl diisocyanate, was blended with boron nitride (BN) to fabricate a thermally conductive interface material. BN treated by a silane coupling agent (BN―NH₂) and PU‐grafted BN were prepared to fabricate a composite that has better thermal conductivity and mechanical strength. The surface‐modified filler showed enhanced dispersibility and affinity because of the surface treatment with functional groups that affected the surface free energy, along with the structural similarity of the doped crystallized diisocyanate molecule with the matrix. The thermal conductivity increased from 0.349 to 0.467 W mk^?1 on 20 wt% PU‐grafted BN loading that is a 1.34‐fold higher value than in the case of pristine BN loading at the same weight fraction. Moreover, the number of BN particles acting as defects, thereby reducing the mechanical strength, is decreased because of strong adhesion. We can conclude that these composite materials may be promising materials for a significant performance improvement in terms of both the thermal and mechanical properties of PU‐based polymers. Copyright © 2014 John Wiley & Sons, Ltd.     

聚乙二醇/氮化硼复合材料相变导热性能及其结晶行为

本文采用熔融共混浇筑的方法制备了聚乙二醇/氮化硼(PEG/BN)相变复合材料,并研究了不同尺度片状BN对相变复合材料导热性能和结晶行为的影响。 通过扫描电子显微镜(SEM)、热常数分析仪、红外热成像分析仪和差示扫描量热仪(DSC)研究了相变复合材料的微观形貌、导热系数和相变过程,并利用莫志深法对DSC结果进行了非等温结晶动力学分析。 结果表明,较大片状直径(50 μm)的BN可以更有效地提高聚乙二醇的导热系数,当BN填料质量分数为40%时,相变复合材料的导热系数可达到5.04 W/(m·K)。 在快速降温条件下,片径为50 μm的BN填料可以缩短PEG的半结晶时间,提高结晶速率,使相变复合材料具有较大的相变焓。     

Performance improvement of EPDM and EPDM/Silicone rubber composites using modified fumed silica,titanium dioxide and graphene additives

In this work, a polymeric composite was prepared from ethylene propylene diene monomer (EPDM) and silicone rubber (S) with additives of modified fumed silica (MFS), titanium dioxide (TiO₂) and graphene. The dielectric and thermal performances of the EPDM-based composites were studied. An increase in the dielectric constant and AC dielectric breakdown strength was observed for the EPDM rubber composites containing MFS, TiO_2, and graphene additives. In addition, the incorporation of the additives resulted7in a significant increase in the thermal stability (~30–50 °C) and thermal conductivity (~7–35%) of the composites. The combination of these various improvements gives suitable performance advantage to the polymeric composite for use in insulating applications.     

Boron Nitride Nanosheets (BNNSs) Chemically Modified by “Grafting‐From” Polymerization of Poly(caprolactone) for Thermally Conductive Polymer Composites

To meet the growing demand for rapid heat dissipation in electronic devices to ensure their reliable performance with a high level of safety, many polymer composites with thermally conductive but electrically insulating 2D boron nitride nanosheets (BNNSs) are being developed. Here we present an efficient way to enhance the thermal conductivity (TC) of a polymer composite by means of “grafting‐from” polymerization of a poly(caprolactone) (PCL) onto BNNSs. The BNNSs, which were exfoliated from bulk BN by means of ultra‐sonication, were prepared by means of radical oxidation. These oxidized BNNSs (oxi‐BNNSs) were employed as initiators for subsequent ring‐opening polymerization of PCL, which successfully resulted in PCL chemically grafted onto BNNSs (PCL‐g‐BNNSs). The excellent dispersion of PCL‐g‐BNNSs in common solvents allowed us to readily fabricate a polymer composite that contained PCL‐g‐BNNSs embedded in a PCL matrix, and the composite showed TC values that were five and nine times greater in the out‐of‐plane and in‐plane mode, respectively, than those of pristine PCL.     

Effect of 2-D BN on enhanced corona-resistant characteristic of PI/AlN+BN composite investigated by quasi-in-situ technology

Incorporating two-dimensional (2-D) boron nitride (BN) into polyimide/aluminum nitride (PI/AlN) renders a simple strategy in producing new ternary composite films with longer corona aging life and higher breakdown strength compared with PI/AlN. During corona aging process, the effects of 2-D BN on adjusting the microstructure evolution of ternary composites were investigated using quasi-in-situ technology systematically as follow: (SEM), (AFM), (FTIR), (XRD) and (SAXS) at different corona time. Quasi-in-situ characterization results show that the corona aging modes of the two composite films are quite different, the introduction of BN nanosheets could protect the C–N–C and C–O–C bonds from breaking as well as accelerate the fillers expose via autoxidation reaction. In addition, BN nanosheets could induce the distance between PI molecular chains to shorten during the corona process, resulting in more dense structures coordinating with AlN and PI. Different corona aging mechanism compared with that of the PI/AlN composite films was proposed. This work demonstrated the effect of 2-D BN nanosheets in the PI/AlN+BN ternary composites, which can be used to expand their application in insulating polymer based composites.     

Barium Titanate-reinforced Acrylonitrile-Butadiene Rubber: Synergy Effect of Carbon-based Secondary Filler

Acrylonitrile rubber(NBR) composites filled with barium titanate(BT) were prepared using an internal mixer and a two-roll mill. Also, a secondary filler, namely carbon nanotubes(CNT), was added in order to find a potential synergistic blend ratio of BT and CNT. The cure characteristics, tensile and dielectric properties(dielectric constant and dielectric loss) of the composites were determined. It was found that NBR/BT composites with CNT secondary filler, at a proper BT:CNT ratio, exhibited shorter scorch time(t_(s1)) and cure time(t_(c90)) together with superior tensile properties and reinforcement efficiency, relative to the one with only the primary filler. In addition, the NBR/BT-CNT composite with 80 phr BT and 1-2 phr CNT had dielectric constant of 100-500, dielectric loss of 12-100 and electrical conductivity below 10~(-4) S/m together with high thermal stability. Thus, with a proper BT:CNT mix and filler loading, we can produce mechanically superior rubber composites that are easy to process and low-cost, for flexible dielectric materials application.     

High‐performance hexagonal boron nitride/bismaleimide composites with high thermal conductivity,low coefficient of thermal expansion,and low dielectric loss

High‐performance insulating materials have been increasingly demanded by many cutting‐edge fields. A new kind of high‐performance composites with high thermal conductivity, low coefficient of thermal expansion (CTE), and low dielectric loss was successfully developed, consisting of hexagonal boron nitride (hBN) and 2,2′‐diallylbisphenol A (DBA)‐modified 4,4′‐bismaleimidodiphenylmethane (BDM) resin. The effects of hBN and its content on the integrated properties, including curing behavior of uncured system, the CTE, thermal conductivity, dielectric properties, and thermal resistance of cured composites, are systematically investigated and discussed. Results show that there are amino groups on the surface of hBN, which supply desirable interfacial adhesion between hBN and BDM/DBA resin and a good dispersion of hBN in the resin. With the increase of the hBN content, the thermal conductivity increases linearly, whereas the CTE value decreases linearly; in addition, dielectric loss gradually decreases and becomes more stable over the whole frequency from 10 to 10⁹ Hz. In the case of the composite with 35 wt% hBN, its thermal conductivity, CTE in glassy state, and dielectric loss are about 3.3, 0.63, and 0.5 times of the corresponding value of BDM/DBA resin, respectively. These attractive integrated properties suggest that hBN/BDM/DBA composites are high‐performance insulating materials, which show great potential in applications, especially for electronics and aerospace industries. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermodynamic properties of liquid Au-Cu-Sn alloys determined from electromotive force measurements

A thermally conductive linear low-density polyethylene (LLDPE) composite with aluminum nitride (AlN) as filler was prepared in a heat press molding. Differential scanning calorimeter results indicated that the AlN filler decreases the degree of crystallinity of LLDPE, and has no obvious influence on the melting temperature of LLDPE. Experimental results demonstrated that the LLDPE composites display a high thermal conductivity of 1.25 W/m K and improved thermal stability at 70 wt% AlN content as compared to pure LLDPE. The dielectric constant and dissipation factor increased with AlN content, however, they still remained at relatively low levels, i.e., <5 in wider frequency range from 10 to 10⁶ Hz. The surface treatment of AlN particles had a beneficial effect on improving the thermal conductivity and dielectric constant, whereas, the dissipation factor was less affected. Additionally, the obtained AlN/LLDPE composites have possessed rather low dielectric constant and high electrical insulation, which is suitable for substrate and packaging materials.     

Design of thermal hybrid composites based on liquid crystal polymer and hexagonal boron nitride fiber network in polylactide matrix

Development of high thermally conductive and electrically insulative composites is of interest for electronic packaging industry. Advancements in smaller and more compact electronic devices required improvements in packing materials, including their weight, thermal conductivity, and electrical resistivity. In addition, with the increasing environmental awareness, the usage of green (bio‐based) alternatives was equally important. In the present study a hybrid based on fibers of highly concentrated hexagonal boron nitride (hBN) in liquid crystal polymer (LCP) matrix were fabricated. These hybrids were formed by arranging hBN platelets into LCP fiber form to reach high filler concentration and then randomly mix it in polylactide (PLA) matrix. With appropriate filler interaction within the hybrid, thermal conductivity similar to that of pure fiber could be achieved. Filler interaction may be tailored by optimizing the fibers aspect ratio. This study demonstrated the effect of random fillers in fibers shape in increasing the overall thermal conductivity of PLA polymeric hybrid using hBN and LCP fibers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 457–464     

兼具导热和自修复功能的聚合物复合材料

针对聚合物复合材料存在的结构受损导致导热和力学强度降低的问题,提出利用导热填料增强自修复聚合物,实现导热性能和力学强度的快速修复.通过对双(3-氨丙基)封端的聚二甲基硅氧烷(H2N-PDMS-NH2)进行端基改性,得到脲基嘧啶酮(UPy)双封端的聚二甲基硅氧烷(UPy-PDMS-UPy),于60℃下20 h后拉伸强度修复效率可达86.6%.进一步填充羟基化氮化硼(mBN)制备兼具自修复功能的导热复合材料,研究发现mBN的填充导致复合材料强度提高但韧性降低,对导热性能和自修复功能分别起积极和不利影响.当mBN含量为30 wt%时,热导率高达2.579 W·m^?1·K^?1,于60℃下40 h后拉伸强度修复效率达82.0%.红外热像仪显示,损伤处接触10 h后,mBN-30/UPy-PDMS-UPy上表面温度接近初始温度,展现出导热通路的修复特征,实现导热与自修复功能的兼备.