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.     

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.     

Surface modification of boron nitride by bio‐inspired polydopamine and different chain length polyethylenimine co‐depositing

We established a novel, easy, and versatile method of obtaining diverse and controllable interphases between epoxy resin and fillers. The method involved the co‐deposition of polydopamine (PDA) and polyethyleneimine (PEI) with different molecular lengths on boron nitride (BN) surface. The obtained PDA/PEI‐modified BN composites showed significantly improved mechanical properties, including tensile strength, toughness, and elongation at break. For example, the tensile strength, fracture toughness, and elongation at break of EP composite increased by 51%, 132%, and 170% compared with EP when the PEI molecular weight was 10 000, respectively. These results suggested that the interphases between BN and EP matrix can be adjusted by changing the molecular lengths of grafted modifiers, thereby offering a new method for the reasonable designing and exploitation of the BN‐based composite materials.     

Enhanced thermal conductivity and mechanical properties of polymeric composites through formation of covalent bonds between boron nitride and rubber chains

Hexagonal boron nitride (BN) platelets, also known as white graphite, are often used to improve the thermal conductivities of polymeric matrices. Due to the poor interfacial compatibility between BN platelets and polymeric matrices, in this study, polyrhodanine (PRd) was used to modify BN platelets and prepared functionalized BN-PRd platelets, thereby enhancing the interfacial interaction between the thermal conductive filler and polymeric matrix. Then, BN-PRd platelets were dispersed into the nitrile butadiene rubber (NBR) matrix to yield high thermally conductive composites. The presence of N? C═S groups in PRd allowed the combination of PRd and NBR chains containing stable covalent bonds via vulcanization reaction. The thermal conductivity of the as-prepared 30 vol% BN-PRd/NBR composite reached 0.40 W/mK, representing an increment of 135% over pure NBR (0.17 W/mK). In addition, the largest tensile strength of NBR composite containing 30 vol% BN-PRd platelets was 880% times of pure NBR. The 30 vol% BN-PRd/NBR composite also displayed a relatively high dielectric constant (9.35 at 100 Hz) and a low dielectric loss tangent value (0.07 at 100 Hz), indicating their usefulness as dielectric flexible materials of microelectronics. In sum, the simplicity and good efficiency of formation of covalent bonds between boron nitride and rubber chains look very promising for large-scale industrial production of high thermally conductive composites.     

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.     

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.     

The surface modification of boron nitride particles

Journal of Thermal Analysis and Calorimetry - The use of coupling agents to enhance the thermal conductivity of composites of epoxy and boron nitride (BN) has been investigated. Two types of BN...     

Synergistic effect of hybrid graphene and boron nitride on the cure kinetics and thermal conductivity of epoxy adhesives

In the present study, the synergistic effect of hybrid boron nitride (BN) with graphene on the thermal conductivity of epoxy adhesives has been reported. Graphene was prepared by chemical reduction of graphite oxide (GO) in a mixture of concentrated H₂SO₄/H₃PO₄ acid. The particle size distribution of GO was found to be ~10 μm and a low contact angle of 54° with water indicated a hydrophilic surface. The structure of prepared graphene was characterized by Fourier transform infrared (FTIR), X‐ray diffraction (XRD), Raman spectroscopy and atomic force microscopy (AFM). The thermal conductivity of adhesives was measured using guarded hot plate technique. Test results indicated an improvement in the thermal conductivity up to 1.65 W/mK, which was about ninefold increase over pristine epoxy. Mechanical properties of different epoxy formulations were also measured employing lap shear test. The surface characterization of different epoxy adhesive systems was characterized through XRD, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies. Fourier transform infrared also served to determine the nature of interactions between filler particles and epoxy resin. Non‐isothermal differential scanning calorimetric (DSC) technique was used to investigate the effects of graphene and BN particles on the cure kinetics and cross‐linking reaction of epoxy cured with amine curing agent. The Kissinger equation, the model‐free isoconversional Flynn–Wall–Ozawa method and the Ozawa model were used to analyze the kinetic parameter. Copyright © 2017 John Wiley & Sons, Ltd.     

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.     

Modified boron nitride as an efficient synergist to flame retardant natural rubber: preparation and properties

A new flame retardant system with organic modified boron nitride (m‐BN) and intumescent flame retardant (IFR) was used in this paper, and the synergistic flame retardancy of m‐BN and IFR on natural rubber (NR) was studied. NR/IFR/m‐BN composites were characterized by X‐ray photoelectron spectroscopy(XPS), Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis, UL‐94, limiting oxygen index (LOI), tensile testing, cone calorimeter testing, and thermal conductivity testing. When 4 wt% m‐BN was added, the flame retardancy and mechanical properties of the composites were improved. The LOI value of NR/IFR/4 phr m‐BN reached 26.8%, and suppressed fire spread in a UL‐94 test. Compared with pure NR, the peak heat release rate (pHRR) was reduced by 52.2%, the total heat release (THR) was reduced by 27.6%, and CO yields were reduced by 51.4%. As a key aspect of fire safety, the ignition time is effectively delayed to 23 seconds due to the increased thermal conductivity of NR/IFR/m‐BN. Since the synergistic effect of m‐BN effectively improves the flame retardancy of NR, it provides a feasible method for improving the fire safety of polymers.     

Room temperature processable heat‐resistant epoxy‐oxazolidone‐based syntactic foams

Syntactic foams based on oxazolidone‐modified epoxy resin using glass microballoons as reinforcing filler with varying densities were processed. The influence of various grades of microballoons and their concentration on the mechanical, thermal, thermomechanical, and flammability characteristics were investigated. The effect of temperature on the compressive strength with density was monitored in detail. By incorporating the microballoons, T_g of the syntactic foam increased from 90 °C to 115 °C. Thermal conductivity was found to decrease from (0.064 to 0.056 W/(m·K)) in conjunction with decreasing resin to filler ratio. In the case of composites filled with K25 alone, the creation of large voids due to less effective packing between the microballoons led to lower thermal conductivity. The specific heat of the different composites was in the range of 0.32 to 0.44 cal/g/°C, and the coefficient of thermal expansion was in the range of 13.2 to 17.4 × 10⁻⁶/°C with limiting oxygen index of 28% to 33%.     

An overview of boron nitride based polymer nanocomposites

Recently, boron nitride (BN) based materials have received significant attention in both academic and industrial sectors due to its interesting properties like large energy band gap, good resistance to oxidation, excellent thermal conductivity, thermal stability, chemical inertness, significant mechanical property and widespread applications. This review article deals with the preparation and properties of boron nitride and its nanocomposites with various polymers. Diverse polymers have been explored for the preparation of boron nitride filled polymer nanocomposites by adopting different mixing methods. Properties of the resulting polymer nanocomposites mainly depend up on filler size and dispersion, mixing conditions and type of interaction between polymer matrix and the filler. Herein, the structure, preparation and properties of various boron nitride based polymer nanocomposites are reviewed in detail along with a brief overview of different classes of BN nanomaterials.     

Phosphorus‐free boron nitride/cerium oxide hybrid: A synergistic flame retardant and smoke suppressant for thermally resistant cyanate ester resin

Establishing a phosphorus‐free strategy to fabricate high‐performance thermosetting resins owning outstanding thermal resistance, good flame retardancy, and smoke suppression is important for sustainable development. Herein, a unique phosphorus‐free hybrid (BN@CeO₂) was synthesized through chemically grafting cerium oxide (CeO₂) on surface of exfoliated boron nitride (BN) nanosheet with the aids of γ‐aminopropyltriethoxysilane and polydopamine coating, which was then embedded into bisphenol A cyanate ester (BCy) resin to fabricate new BN@CeO₂/BCy composites with high thermal resistance. Compared with BCy resin, the BN@CeO₂/BCy composite with 4 wt% BN@CeO₂ not only has delayed initial ignition time by 23 seconds but also severally shows 58.1%, 23.1%, and 44.4% lower smoke produce rate, total heat release, and peak heat release rate. The study on mechanism behind outstanding flame retardancy reveals that the improved heat resistance and flame retardancy of BN@CeO₂/BCy composite are attributed to multiply effects induced by BN@CeO₂ and its interaction with BCy resin; specifically, these effects come from BN (physical barrier) and CeO₂ (free radical trapping effect and catalytic char layer formation) as well as those from the synergistic effect of BN and CeO₂. These excellent comprehensive properties of BN@CeO₂/BCy composites demonstrate that BN@CeO₂ is an environment‐friendly and synergistic modifier for developing heat‐resisting thermosetting resins with outstanding flame retardancy and smoke suppression.     

Cleaning of pyrolytic hexagonal boron nitride surfaces

Hexagonal boron nitride (h‐BN) has recently garnered significant interest as a substrate and dielectric for two‐dimensional materials and devices based on graphene or transition metal dichalcogenides such as molybdenum disulfide (MoS₂). As substrate surface impurities and defects can negatively impact the structure and properties of two‐dimensional materials, h‐BN surface preparation and cleaning are a critical consideration. In this regard, we have utilized X‐ray photoelectron spectroscopy to investigate the influence of several ex situ wet chemical and in situ thermal desorption cleaning procedures on pyrolytic h‐BN surfaces. Of the various wet chemistries investigated, a 10 : 1 buffered HF solution was found to produce surfaces with the lowest amount of oxygen and carbon contamination. Ultraviolet/ozone oxidation was found to be the most effective ex situ treatment for reducing carbon contamination. Annealing at 1050 °C in vacuum or 10^?5 Torr NH₃ was found to further reduce oxygen and carbon contamination to the XPS detection limits. Copyright © 2015 John Wiley & Sons, Ltd.     

Construction of superhydrophilic/underwater superoleophobic polydopamine‐modified h‐BN/poly(arylene ether nitrile) composite membrane for stable oil‐water emulsions separation

Oil/water emulsion separation in harsh environments remains a big challenge. Herein, a double layered nanofibrous composite membrane was developed by assembly of polydopamine‐modified hexagonal boron nitride (h‐BN‐PDA) onto a poly(arylene ether nitrile) (PEN) nanofibrous mat. Owing to the synergistic effect of a h‐BN‐PDA skin layer and a PEN nanofibrous mat supporting layer, as‐prepared composite membrane exhibited high thermal stability, corrosion resistance, and superhydrophilic/underwater superoleophobic property. Consequently, the PEN composite membrane showed good antifouling performance and a high rejection ratio (>99.0%) for various oil/water emulsions. After 10 cycles, the separation flux of PEN composite membrane still reached 588.1 L/m² h under the operating pressure of 0.04 MPa. Furthermore, the PEN composite membrane could still achieve high separation efficiency and high flux in high‐temperature (65 °C) and strongly corrosive conditions (pH = 1‐13). Therefore, the stable and efficient h‐BN‐PDA/PEN composite membrane showed potential application for treating oily wastewater in harsh environments.     

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.     

Enhanced directional thermal conductivity of polylactic acid/polybutylene adipate terephthalate ternary composite filled with oriented and surface treated boron nitride

A combination of solution casting and melt extrusion technique was used to fabricate Boron nitride (BN)-filled Polylactic acid (PLA)/polybutylene adipate terephthalate (PBAT) blend composites. The BN particles were surface treated with a silane coupling agent and functionalization was confirmed via spectroscopic analysis. Field emission scanning electron microscopy confirmed that the BN surface treatment improved the particle adhesion with the polymer matrices and acted as a compatibilizer for the polymers. Moreover, changes in the particle orientation in the blend composite yielded improved thermal conductivity in different directions. The inclusion of the treated BN particles enhanced the in-plane (~1.1 W m⁻¹K⁻¹) and through-plane (~0.8 W m⁻¹K⁻¹) thermal conductivity of the composites as compared to the neat PLA. In addition, the storage modulus of the composite become more than 3 GPa that is twice that of the PLA/PBAT blend with a reasonable tensile property. In general, compared with the PLA/PBAT blend, the blend composites exhibited superior thermal and mechanical properties.     

Thermal conductivity of nanostructured boron nitride materials

We have measured the thermal conductivity of bulky pellets made of various boron nitride (BN)-based nanomaterials, including spherical nanoparticles, perfectly structured, bamboo-like nanotubes, and collapsed nanotubes. The thermal conductivity strongly depends on the morphology of the BN nanomaterials, especially on the surface structure. Spherical BN particles have the lowest thermal conductivity while the collapsed BN nanotubes possess the best thermoconductive properties. A model was proposed to explain the experimental observations based on the heat percolation passage considerations.     

Poly(dopamine) assisted epoxy functionalization of hexagonal boron nitride for enhancement of epoxy resin anticorrosion performance

Hexagonal boron nitride (h‐BN) is modified by a simple and green method based on self‐oxidation of dopamine and epoxy groups functionalized silane (KH560) grafting. The surface modification and microstructure of h‐BN are characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. The poly(dopamine) and epoxy groups not only increase the compatibility of the h‐BN and enhance its interaction with epoxy matrix but also exhibit a remarkable superiority in enhancing the anticorrosion performance of epoxy coatings. In addition, the anticorrosion mechanisms of h‐BN@PDA‐KH560 are tentatively discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Phase transformation of boron nitride under hypothermal conditions

Phase transformation among different boron nitride (BN) phases in hydrothermal solution was investigated. It was found that hexagonal boron nitride (hBN) firstly formed in the solution at relatively low temperature (i.e., 220 °C). After that, a spot of hBN began to transform into wurtzite boron nitride (wBN) and cubic boron nitride (cBN) at 230 °C. More and more hBN converted into wBN and cBN with the increase in temperature, and this transformation process completed at 300 °C. In this paper, we have explained the mechanism of the above phase transformation by using a reported “puckering mechanism”.