Synergistic Function between Phosphorus-Containing Flame Retardant and Multi-Walled Carbon Nanotubes towards Fire Safe Polystyrene Composites with Enhanced Electromagnetic Interference Shielding

As a universal polymer material, polystyrene (PS) is widely applied in electrical devices and construction. Thus, it is necessary to improve the flame retardancy and electromagnetic shielding properties of PS material. In this work, PS/silicon-wrapped ammonium polyphosphate/Inorganic acid-treated multi-walled carbon nanotubes composites (PS/SiAPP/aMWCNT, abbreviated as PAC) were prepared via methods of filtration-induced assembly and hot-pressing. Morphology and structure characterization demonstrated that SiAPP and aMWCNT had good dispersion in PS and excellent compatibility with the PS matrix. Thermogravimetric analysis revealed that the addition of aMWCNT to PS improved its thermal stability and carbon-forming characteristics. The peak heat release rate, the peak carbon monoxide production rate, and the peak smoke production rate of the PAC10 composite decreased by 53.7%, 41.9%, and 45.5%, respectively, while its electromagnetic shielding effectiveness reached 12 dB. These enhancements were attributed to the reason that SiAPP and aMWCNT synergistically catalyzed the char generation and SiAPP produced free radical scavengers and numbers of incombustible gases, which could decrease the oxygen concentration and retard the combustion reaction. Therefore, the assembled PS/SiAPP/aMWCNT system provides a new pathway to improve the flame retardant and electromagnetic shielding properties of PS.

Can the Thermophoretic Mobility of Uncharged Colloids Be Predicted?

The thermophoretic motion of nonionic colloids in an inhomogeneous temperature field is due to the solvent-colloid dispersion interactions. The latter form an attractive near-particle "gravity" field that leads to sinking of the colder solvent layers toward a colloid. The spatial extension of this microconvective motion is comparable to the size of the colloids, which prove to be small enough to observe their own regular thermophoretic drift to the cold. The Boussinesq equations of convection are augmented by the boundary conditions at the characteristic molecular distance dividing the immovable and motile solvent layers. For organic liquids, this distance proves to be a property of pure solvent. The thermophoretic mobilities are found for colloids with and without surfacted layers. They are determined by the bulk properties of substances and the Hamaker constant of the solvent-solute interactions. The mobilities weakly (logarithmically) depend on the size of colloids and tend to a universal value in the limiting case of strongly asymmetrical mixtures. This is the first report that shows a prediction of the thermophoretic velocities of uncharged colloids. The relation between the thermophoretic mobility of colloids and the Hamaker constant of the solute-solvent interactions enables an experimental determination of the latter quantity from thermophoresis data.

Constructing segregated polystyrene composites for excellent fire resistance and electromagnetic wave shielding

Electroconductive polystyrene (PS) composites with ideal flame-retardant properties are considered as potential electromagnetic interference (EMI) shielding materials. In this work, PS/silicon wrapped ammonium polyphosphate/multi-wall carbon nanotubes (PS/SiAPP/MWCNT) composites with segregated structure were synthesized via the methods of balling mill and hot-pressing. The obtained results revealed that the SiAPP and MWCNT were successfully introduced onto PS spheres and showed uniform distribution on the PS surface. The thermogravimetric analysis showed that PS/SiAPP/MWCNT containing 7 wt% MWCNT exhibited excellent thermal stability. Furthermore, the results of cone calorimeter test indicated that the heat release rate and total heat release of the PS/SiAPP/MWCNT containing a loading of 7 wt% MWCNT were reduced by 60.5% and 33.9%, respectively. In addition, the EMI shielding performance could reach 11 dB. Above results implied that the synergistic effect between the MWCNT and SiAPP effectively enhanced the flame retardant performance of the PS by promoting the generation of dense and continuous char layer to protect the PS from burning. The multiple reflection and adsorption are responsible for improved EMI shielding effectiveness. Therefore, segregated PS/SiAPP/MWCNT hybrid is an up-and-coming candidate for satisfactory EMI shielding materials with exceptional fire retardancy for electronic devices.

The Role of Reduced Graphene Oxide in the Suspension Polymerization of Styrene and Its Effect on the Morphology and Thermal Properties of the Polystyrene/rGO Nanocomposites

Reduced graphene oxide (rGO) was used to obtain Polystyrene (PS)/rGO nanocomposites via in-situ suspension polymerization. The main goal of the article was to determine how rGO influences the morphology and thermal properties of PS beads. The obtained samples were studied by means of a scanning electron microscope (SEM), and calorimetric and thermogravimetric analysis (DCS, TGA). It was proven that the addition of rGO, due to the presence of polar functional groups, causes significant changes in bead sizes and size distribution, and in their morphology (on the surface and in cross-section). The increasing amount of rGO in the polymer matrix increased the size of beads from 0.36 to 3.17 mm for pure PS and PS with 0.2 wt% rGO content, respectively. PS/rGO nanocomposites are characterized by distinctly improved thermostability, which is primarily expressed in the increase in their decomposition temperature. For a sample containing 0.3 wt% rGO, the difference is more than 12 °C in comparison to pure PS beads.

Mendes J, de O. Souto Silva KK, Zille A. Dog Wool Microparticles/Polyurethane Composite for Thermal Insulation

A polyurethane (PU)-based eco-composite foam was prepared using dog wool fibers as a filler. Fibers were acquired from pet shops and alkaline treated prior to use. The influence of their incorporation on the PU foams’ morphological, thermal, and mechanical properties was investigated. The random and disorganized presence of the microfibers along the foam influence their mechanical performance. Tensile and compression strengths were improved with the increased amount of dog wool microparticles on the eco-composites. The same occurred with the foams’ hydration capacity. The thermal capacity was also slightly enhanced with the incorporation of the fillers. The fillers also increased the thermal stability of the foams, reducing their dilatation with heating. The best structural stability was obtained using up to 120 °C with a maximum of 15% of filler. In the end, the dog wool waste was rationally valorized as a filler in PU foams, demonstrating its potential for insulation applications, with a low cost and minimal environmental impact.

Emerging challenges in the thermal management of cellulose nanofibril-based supercapacitors, lithium-ion batteries and solar cells: A review

In recent years, extensive efforts have been devoted to electronic miniaturization and integration. Accordingly, heating up of electronics has become a critical problem that needs to be urgently solved by efficient and reliable thermal management. Electronic device substrates made of cellulose nanofibrils (CNFs) exhibit outstanding flexibility, mechanical properties, and optical properties. Combining CNFs with high-thermal-conductivly fillers is an effective thermal management technique. This paper focuses on the thermal management of electronic devices and highlights the potential of CNF-based materials for efficient thermal management of energy storage electronic such as supercapacitors, lithium-ion batteries and solar cells. A high-thermal-conductivity composite material for electronic devices can be obtained by combining CNFs as the framework material with carbon nanotubes, graphene, and inorganic nitrides. Moreover, The research progress in the application of CNFs-based materials for supercapacitors, lithium-ion batteries and solar cells is highlighted, and the emerging challenges of different CNFs-based energy storage devices are discussed.

Highly Thermally Conductive Polymer Composite Originated from Assembly of Boron Nitride at an Oil-Water Interface

Thermally conductive polymer packaging material is of great significance for the thermal management of electronics. Inorganic thermally conductive fillers have been demonstrated as a convenient approach to achieve this goal by sacrificing the lightweight and processability of the polymer. To address this problem, an effective 3D boron nitride (BN) network was constructed as a heat conduction pathway in a polystyrene (PS) matrix based on an oil-water interface assembly in this work. Styrene oil droplets were stabilized by BN sheets in the water phase to form Pickering emulsions, and then in situ polymerization was trigged to synthesize PS microspheres with ultrathin BN layer-covered surfaces (PS@BN microspheres). Composite substrates were fabricated through hot-compressing the PS@BN microspheres to form BN networks based on the original microsphere template. Benefited from the network structure, the maximum thermal conductivity of the composite substrate reached 0.94 W/mK at 33.3 wt % BN, which is 626% folds of that of pure PS. It was also demonstrated that the storage modulus and thermal stability of the composite substrate were dramatically improved by the BN network. The reported composite substrate and its fabrication strategy are promising in the development of thermal management of electronics.

Surface modification of GO by PDA for dielectric material with well-suppressed dielectric loss

To suppress the high dielectric loss of graphene oxide (GO)/poly(vinylidene fluoride) (PVDF) while maintaining high dielectric constant (high- k) near the percolation threshold, in this study, GO nanosheets coated with polydopamine (PDA) were integrated into PVDF to investigate the effects of the PDA shell and its concentrations on the dielectric properties of the nanocomposites. The results indicate that the dissipation factor and conductivity of the GO@PDA/PVDF are significantly suppressed to very low values compared with the pristine GO/PVDF composites, attributable to the PDA interlayer between the GO nanosheets which prevents them from direct contact with each other and remarkably reduces the leakage loss. Furthermore, activation energies of the GO/PVDF and GO@PDA/PVDF composites were calculated as 1.247 and 0.884 eV, respectively, indicating that the presence of PDA interlayer reduces the relaxation activation energy and makes the relaxation occur at low temperature for the GO@PDA/PVDF. The prepared GO@PDA/PVDF nanocomposites with high- k but low loss have potential applications in microelectronic engineering.

High-performance polymer composites with enhanced mechanical and thermal properties from cyanate ester/benzoxazine resin and short Kevlar/glass hybrid fibers

The investigation and design of new polymeric materials with an astonishing combination of properties are nowadays of great importance to facilitate the manufacturing process of high-quality products intended to be utilized in different applications and technical fields. For this intent, novel high-performance blend composites composed of the cyanate ester/benzoxazine resin blend reinforced by different proportions of silane-surface modified Kevlar and glass fibers were successfully fabricated by a compression molding technique and characterized by different experimental tests. The mechanical test results revealed that the bending and impact strength properties were considerably improved when increasing the amount of the hybrid fibers. The studied materials also presented excellent thermal stabilities as compared to the unfilled blend’s properties. With respect to the properties of the reinforcing systems, these improvements seen in either the mechanical or thermal properties could be due to the good dispersion as well as excellent adhesion of the reinforcing fibers inside the resin matrix, which were further evidenced by the Fourier transform infrared spectroscopy and scanning electron microscopy results. Consequently, the improved mechanical and thermal properties promote the use of the fabricated hybrid composites in domestic and industrial applications requiring functional materials with advanced properties for aerospace and military applications.

Investigation of the thermal ageing process and mechanism of benzoxazine/bismaleimide/cyanate ester copolymer

Fibre-reinforced polymer (FRP) composites with thermosetting resin matrices are widely used in civil engineering (e.g. pultruded FRP plates and bars), and their thermal ageing behaviour is a concern when they are subjected to elevated temperatures (e.g. FRP chimney). In the present article, the effects of thermal ageing at 200°C and 250°C in air for up to 1000 h on mechanical properties and mechanism of the benzoxazine (Boz), bisphenol A dicyanate cyanate ester (BADCy), and 4,4′-bismaleimidodiphenyl methane (BMI) have been investigated. The effect of time in thermal ageing on structural and mechanical properties of the Boz/BMI/BADCy resin was deeply studied. The moisture absorption increases linearly with the square root of ageing time and it follows Fick’s second law. There are two main categories of reactions in thermal ageing: the first one is the post-curing process, which leads to a larger crosslinking density and a reduced interior stress; while the other is the formation of microcracks and thermal oxidation at the surface of the Boz/BMI/BADCy resin. The combination of the above factors leads to an increase–decrease variation in the mechanical properties. This work is believed to benefit the wide and safe application of a certain Boz/BMI/BADCy resin system in engineering application.

Development of AlN/Epoxy Composites with Enhanced Thermal Conductivity

AlN/epoxy composites with high thermal conductivity were successfully prepared by infiltrating epoxy into AlN porous ceramics which were fabricated by gelcasting of foaming method. The microstructure, mechanical, and thermal properties of the resulting composites were investigated. The compressive strengths of the AlN/epoxy composites were enhanced compared with the pure epoxy. The AlN/epoxy composites demonstrate much higher thermal conductivity, up to 19.0 W/(m·K), compared with those by the traditional particles filling method, because of continuous thermal channels formed by the walls and struts of AlN porous ceramics. This study demonstrates a potential route to manufacture epoxy-based composites with extremely high thermal conductivity.