Junwei Gu

High thermal conductivity graphite nanoplatelet/UHMWPE nanocomposites

High thermal conductivity graphite nanoplatelet/ultra-high molecular weight polyethylene (GNPs/UHMWPE) nanocomposites are fabricated via mechanical ball milling followed by a hot-pressing method. The GNPs are located at the interface of the UHMWPE matrix. The thermal conductivity coefficient of the GNPs/UHMWPE nanocomposite is greatly improved to 4.624 W m−1 K−1 with 21.4 vol% GNPs, 9 times higher than that of the original UHMWPE matrix. The significantly high improvement of the thermal conductivity is ascribed to the formation of multidimensional thermally conductive GNPs–GNPs networks, and the GNPs have a strong ability to form continuous thermally conductive networks. The method of cooling-pressing on the machine is more beneficial for the improvement of the thermal conductivity, by increasing the crystallinity of the UHMWPE matrix. Furthermore, the thermal stabilities of the GNPs/UHMWPE nanocomposites are increased with increasing addition of GNPs.

Ideal dielectric thermally conductive bismaleimide nanocomposites filled with polyhedral oligomeric silsesquioxane functionalized nanosized boron nitride

Silane coupling reagent γ-glycidoxy propyl trimethoxy silane/polyhedral oligomeric silsesquioxane (KH-560/POSS) functionalized nanosized boron nitride (POSS-g-nBN) fillers were performed to fabricate thermally conductive bismaleimide/diallylbisphenol A (BMI/DABA) nanocomposites combining excellent dielectric properties and outstanding thermal stability. POSS molecules have been grafted on the surface of the nBN fillers. The POSS-g-nBN/BMI/DABA nanocomposite with 15.4 vol% POSS-g-nBN is an excellent dielectric composite material with high thermal conductivity and outstanding thermal stability; the corresponding dielectric constant e is 3.42, the dielectric loss factor tanδ is 0.0085, the thermally conductive coefficient λ is 0.607 W m−1 K−1 (increased by 266% compared to that of pure BMI/DABA), and the 5 wt% thermal weight loss temperature (T5) reaches up to 428 °C, which holds potential for use in the integration and the miniaturization of microelectronic devices.

Thermal conductivities, mechanical and thermal properties of graphite nanoplatelets/polyphenylene sulfide composites

Functionalized pristine graphite nanoplatelets (fGNPs) by methanesulfonic acid/isopropyltrioleictitanate (MSA/NDZ-105) are used to fabricate fGNPs/polyphenylene sulfide (fGNPs/PPS) composites by mechanical ball milling followed by a compression molding method. The thermal conductive coefficient of the fGNPs/PPS composite with 40 wt% fGNPs is greatly improved to 4.414 W m−1 K−1, 19 times higher than that of the original PPS. For a given GNP loading, the surface functionalization of GNPs by MSA/NDZ-105 results in the fGNPs/PPS composites improving thermal conductivities by minimizing the interfacial thermal resistance. The thermal stabilities of the fGNPs/PPS composites are increased with the increasing addition of fGNPs.

Ultralow dielectric, fluoride-containing cyanate ester resins with improved mechanical properties and high thermal and dimensional stabilities

In this contribution, we present a new strategy for the fabrication of modified cyanate ester resins combined with ultralow dielectric properties, improved mechanical properties and high thermal and dimensional stabilities. The fluoride-containing compound 2-((3-(trifluoromethyl)phenoxy)methyl)oxirane (TFMPMO), synthesized from m-(trifluoromethyl)phenol (TFMP) and epichlorohydrin (ECH), was used to modify bisphenol A dicyanate ester (BADCy) resins via copolymerization reaction. The BADCy resin modified with 15 wt% TFMPMO presented ultralow dielectric constant (e, 2.75) and dielectric loss tangent values (tan δ, 6.7 × 10−3), high mechanical properties (impact strength of 15.4 kJ m−2 and flexural strength of 141.0 MPa), and superior thermal and dimensional stability (THeat-resistance index of 206 °C and coefficient of thermal expansion of 6.4 × 10−5), and it possesses great potential application in radomes and antenna systems of aircraft.

Flame-Retardant, Thermal, Mechanical and Dielectric Properties of Structural Non-Halogenated Epoxy Resin Composites

First, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and epoxy resin (E-51) were employed to synthesize a structural non-halogenated epoxy resin (ED). And a novelphenolic aldehyde curing agent, 2,4,6-tri (phenol-methylene-amide)-triazine (MFP) was also synthesized for preparing high-performance MFP/ED composites. Results showed that, the flame-retardant and thermal stabilities of the composites were improved with the increasing phosphorus content. When the content of phosphorus was 3wt%, the initial decomposing temperature of the composite was over 325°C, and the charring rate was 30.3% at 650°C, could meet the requirements of UL 94-V0 rating. However, all the flexural and impact, dielectric constant and loss and the glass transition temperature (Tg) of the composites were decreased with the increasing phosphorus content.

Reinforced Cyanate Ester Resins with Carbon Nanotubes: Surface Modification, Reaction Activity and Mechanical Properties Analyses

The reinforcement and toughness of cyanate ester (CE) resins with multiwalls carbon nanotubes (MW-CNTs) were investigated in this paper. Based on the surface modification of MW-CNTs, the reaction activity of CE resins, desperation of MW-CNTs, mechanical properties and thermal properties of MW-CNTs/CE composites were addressed. TEM and XRD analyses demonstrate that the MW-CNTs with regular arrangement and perfect crystals structures can be achieved after the treatments with pyrolysis and dense HNO3/H2SO4 acids oxidation. The reaction activity of CE systems with MW-CNTs is increased with the incorporation of carbon nanotubes. The mechanical analysis, dynamic mechanical analysis (DMA), and thermal gravimetric analysis (TGA) indicate that the addition of MW-CNTs can enhance both impact strength and flexural strength of cured CE resins without decreasing their thermal stability. The storage module for the MW-CNTs/CE composites is much higher than that of the pure CE sample in a wide temperature range. After aging in boiling distilled water, the water absorption of is less than that of CE resins.

Study on Preparation of SiO2/Epoxy Resin Hybrid Materials by Means of Sol-Gel

Silicon dioxide/epoxy resin hybrid material was prepared by means of Sol-Gel based on epoxy resin, tetraethyl orthosioate (TEOS), [H2N(CH2)3Si(OC2H5)3](KH-550), Methyltetrahydrophthalic anhydride (MeTHPA), dimethyl phthalate (DMP-30) and (HOCH2CH2)N. The contents of TEOS, KH-550 and reacting temperature influencing on the properties of hybrid materials were studied. The behaviors of the hybrid materials were characterized by differential scanning calorimentry (DSC), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier transform-infrared ray (FT-IR) spectroscopy. The results showed that the properties of the material was optimal at approximately 3% TEOS, 2% KH-550, reacting at 60°C, and the mechanical and thermal properties were significantly improved compared with the pure epoxy resin. The dimension of SiO2 particles was about 20 nm, and distributed homogeneously in the system.

Fast and facile fabrication of porous polymer particles via thiol–ene suspension photopolymerization

A fast and facile method of preparing porous polymer particles via thiol–ene suspension photopolymerization was studied. The porous particles were fabricated by adding the porogen to the click chemistry system. In this paper, the photopolymerization of dipentaerythritol hexakis (3-mercaptopropionate), pentaerythritol tetrakis (3-mercaptopropionate), 1,3,5-tri-2-propenyl-1,3,5-triazine- 2,4,6(1H,3H,5H)-trione, sodium dodecyl sulfate, chloroform and different amounts of linear polymer porogen (polymethyl methacrylate, PMMA) was discussed in detail. The two crucial factors, polymerization time and amount of porogen, were investigated. It was demonstrated that the conversion of monomers could reach 80% within 15 s of irradiation, which further verified the high efficiency of click chemistry. By varying the amount of PMMA, we were able to tailor the particle size, pore diameters and morphology of the porous particles. Results of the mercury porosimetry indicated that the median pore diameter of particles was about 12.39 μm and the surface area was 4.393 m2 g−1. Moreover, the Tg of the particles given by DSC was about 45 °C.

Studies on the Preparation of Polystyrene Thermal Conductivity Composites

Various thermally conductive fillers including aluminum oxide(Al2O3), magnesium oxide(MgO), β-silicon carbide particle(β-SiCp) and β-silicon carbide whisker(β-SiCw) were used to prepare polystyrene thermal conductivity composites. Experimental results showed that, for given filler loading, the thermal conductivity of the composites was higher for PS flake than that of PS particle, and the thermal conductivity was optimal by powder blending method. The SiCw filler was more favorable to improve the thermal conductivity of the composites; a much higher thermal conductivity of 1.18 W/mK could be achieved for the composite with 40 vol% SiCw, about six times higher than that of native polystyrene. The experimental thermal conductivity values were in agreement with those predicted by lower bound of Maxwell-Eueken model. For given SiC loading, the thermal conductivity increased with the increasing shape parameter of n. The SiCw was much easier to form the thermal conductivity chains and network than that of SiCp.

Hyperbranched polyborosilazane and boron nitride modified cyanate ester composite with low dielectric loss and desirable thermal conductivity

In this paper, we presented a new strategy for fabrication of polymeric composites combined with low dielectric loss and desirable thermal conductivity. With the incorporation of hyperbranched polyborosilazane (hb-PBSZ) into bisphenol A cyanate ester (BADCy) matrix, the modified hb-PBSZ/BADCy resin with 4 wt% hb-PBSZ possessed a low dielectric constant (å) value of 2.37 and relatively low dielectric loss tangent value of 0.008 at 1MHz. Furthermore, by integrating micrometer boron nitride particles (mBN) into hb-PBSZ/BADCy matrix, the mBN/hb-PBSZ/BADCy composites presented relatively low å of 3.09, desirable thermally conductive coefficient (λ of 0.63 W/(m·K)) and thermal diffusivity (α of 0.42 mm2/s) values. It provides an important perspective for designing dielectric and thermally conductive polymeric composites for electrical packaging and energy storage fields.