Surfactant-assisted fabrication of graphene frameworks endowing epoxy composites with superior thermal conductivity

With the rapid growth in electronic device performance,there has been an increasing demand for thermally conductive polymer composites to handle the thermal management issue,thus contributing to the great importance to develop the graphene framework,which is evaluated as the most promising reinforcements for enhancing the thermal conductivity of polymer.Vacuum filtration is a common method to fabricate graphene framework,whereas,it is available to prepare a framework with centimeter-scale thickness by filtrating the graphene-water dispersion,due to the fact of sample cracking caused by the mismatch of surface tension between graphene and water.In this work,a surfactantassisted strategy was proposed by adjusting the surface tension of the water close to that of graphene first,then performing a conventional filtration process,to fabricate graphene framework.As a result,a thick graphene framework(thickness:3 cm)was successfully prepared,and after embedding into epoxy,the framework endows the composite(13.6 wt%)with a high in-plane thermal conductivities of12.4 W/mK,which is equivalent to≈64 times higher than that of neat epoxy.Our method is simple and compatible with the conventional filtration process,suggesting great potential for the mass-production of graphene framework to meet the practical application requirements.     

碲化镉纳米晶与聚合物复合研究进展

综述了近年来半导体纳米晶CdTe/聚合物复合材料在电致发光器件和复合发光材料方面的研究和应用进展情况,详细介绍了CdTe与水溶性高分子,非水溶性高分子以及生物大分子的复合情况,并展望了其发展前景。     

A state-of-the-art review on particulate wood polymer composites: Processing,properties and applications

In the present decade, the demands for recyclable, environmentally friendly and low-cost with good strength composites materials have been significantly increased. In this context, the particulate wood polymer composites have attracted the researchers owing to their eco-friendliness, low-cost as they are prepared using waste wood particles, and good mechanical and physical properties. These composites were prepared by filling the waste wood particles into the polymers using different fabrication methods such as extrusion, hand layup, compression moulding, injection moulding and additive manufacturing (3D printing). A good number of research works have been reported on the testing and characterization of wood composites for the various applications so far. This fact motivated to prepare a state-of-the-art review on the recent developments in processing, characterization, and applications of wood composites. This paper presents a discussion on the chemical structure and properties of different types of wood species. The mechanical, thermal and water absorption behaviour of thermosets, thermoplastics and biopolymers based wood composites have also been discussed. Further, characterization of the nano biocomposites prepared using nanocellulose/nanoparticles of wood are also presented. The outcomes of the present review provide a good understanding of wood composites that will encourage the researchers for further research works & developments of novel wood composites for the advanced applications.     

Date palm fibre filled recycled ternary polymer blend composites with enhanced flame retardancy

Flammability of recycled polypropylene (PP)/low density polyethylene (LDPE)/high density polyethylene (HDPE) ternary blends containing date palm fibres is investigated in this study. Melt blending is used for the composite preparation and the palm fibres induce good mechanical strength to the blend composites. The effect of flame retardant magnesium hydroxide, is studied through the limiting oxygen index analysis and cone calorimeter studies. Morphology of the palm fibres in presence of fire retardant reveals interesting facts of base hydrolysis. Since the polymers used are recycled ones and the fibres are obtained from the date palm leaves, the whole composite manufactured stands as low cost, less energy consuming and environmental friendly. Though the flame retardant reduced the mechanical properties, the palm fibres strengthened the whole composite thus helping to achieve the flame retardancy and mechanical properties simultaneously. Flame retardancy is correlated with the thermal degradation and thermal conductivity of the blend fibre composites as well.     

Polyacrylonitrile-based gel polymer electrolyte filled with Prussian blue forhigh-performance lithium polymer batteries

Lithium polymer batteries(LPBs) rely on a high ion transport to gain improved cell performance.Thermostable and porous gel polymer electrolytes(GPEs) have attracted much attention due to their excellent properties in electrolyte wettability and ionic conductivity.In this work,iron-nickel-cobalt trimetal Prussian blue analogue(PBA) nanocubes are filled into the electro spun polyacrylonitrile(PAN)-based membranes to generate GPE composites with morphological superiority consisting of fine fibers and interconnected pores.The thus obtained PBA@PAN fibrous membrane showcases good thermal stability,high porosity and electrolyte uptake,as well as a peak io nic conductivity of 2.7 mS/cm with the addition of 10% PBA,Consequently,the assembled lithium iron phosphate(LiFePO_4) battery using PBA@PAN-10 as the GPE delivers a high capacity of 152.2 mAh/g at 0.2 C and an ultralow capacity decay of0.09% per cycle in a long-te rm cycle life of 350 cycles at 1 C,endorsing its promising applications in LPBs.     

Low-density polycarbonate composites with robust hollow glass microspheres by tailorable processing variables

Polycarbonate (PC) composites with low weight have been required for mobile applications. Herein, the incorporation of 15 phr (parts per hundred of resin) soda-lime borosilicate hollow glass microspheres (HGMs) into a PC matrix reduced the specific gravity by 15.2%. The microsphere preservation rate was systematically examined depending on HGM compressive strength, and processing conditions for extrusion (side-feeding vs. main-feeding vs. screw configuration) and injection molding (mild condition for edge gate vs. extreme condition for pinpoint gate). Various transition temperatures such as glass transition temperatures and heat distortion temperature were investigated as a function of HGM. The coefficient of thermal expansion of the 15 phr HGM-embedded PC composites was reduced by 51.9%. The rheological behavior of the composites was also probed. The toughness was reduced due to the ductile-to-brittle transition of PC caused by the incorporation of fillers despite the enhanced modulus. The incorporation of the robust hollow glass microspheres into a PC composite via a delicately designed screw configuration and suitable processing conditions can be used for low-density composites such as mobile applications.     

高分子导热复合材料结构设计及性能研究进展

近年来,电子设备的需求逐渐向集成化、微型化发展,随之带来了愈发严重的发热问题已经成为了阻碍电子设备发展的重要因素之一。作为电子设备重要组成材料之一的高分子材料对优良导热性能的要求也越来越高,导热高分子复合材料的研究已经成为当前功能复合材料的重要发展方向。本文综述了高分子导热复合材料的发展趋势,介绍了当前选用填料法来制备单一填料、混杂填料高分子导热复合材料以及双逾渗结构、隔离结构等复杂多相结构的高分子导热复合材料的研究进展。重点介绍了通过多种导热填料的组合利用来制备高性能导热高分子复合材料。最后,对填料法高导热高分子复合材料的发展方向做出了简要展望。     

Heat transfer studies in natural carbonates from San Juan (Argentina)

A method based on the analysis of the temperature profiles is proposed to identify changes in the physical structure and/or in the chemical composition of a solid when a constant heat flow passes through it. This analysis is applied to natural carbonates which are important from an industrial point of view. The thermal conductivity of the calcined and non-calcined naturals carbonates is determined in order to relate variations in the temperature profiles with changes in the structure of the solids under study. A mathematical model, which predicts temperature profiles in spherical samples for heat transport processes similar to those studied, is proposed. This model is able to predict temperature profiles in heat transport processes, with or without chemical reaction, and with the chemical reaction fitting the progressive conversion model or the unreacted core one.     

Polymer microcantilever biochemical sensors with integrated polymer composites for electrical detection

Micro fabricated sensors based on nanomechanical motion with piezoresistive electrical readout have become a promising biochemical sensing tool. The conventional microcantilever materials are mostly silicon-based. The sensitivity of the sensor depends on Young's modulus of the structural material, thickness of the cantilever as well as on the gauge factor of the piezoresistor. UV patternable polymers such as SU-8 have a very low Young's modulus compared to the silicon-based materials. Polymer cantilevers with a piezoresistive material having a large gauge factor and a lower Young's modulus are therefore highly suited for sensing applications. In this work, a spin coatable and photopatternable mixture of carbon black (CB) and SU-8, with proper dispersion characteristics, has been demonstrated as a piezoresistive thin film for polymer microcantilevers. Results on percolation experiments of SU-8/CB composite and fabrication of piezoresistive SU-8 microcantilevers using this composite are presented. With our controlled dispersion experiments, we could get a uniform piezoresistive thin film of thickness less than 1.2 μm and resistivity of 2.7 Ω cm using 10 wt% of CB in SU-8. The overall thickness of the SU-8/composite/SU-8 is approximately 3 μm. We further present results on the electromechanical characterization and biofunctionalization of the cantilever structures for biochemical sensing applications. These cantilevers show a deflection sensitivity of 0.55 ppm/nm. Since the surface stress sensitivity is 4.1 × 10⁻³ [N/m]⁻¹, these cantilevers can well be used for detection of protein markers for pathological applications.     

Novel filled polymer composites prepared from in situ polymerization via a colloidal approach: I. Kaolin/Nylon-6 in situ composites

A mineral-filled in situ composite was prepared by a colloidal approach by first suspending kaolin filler particles in aqueous caprolactam, and then polymerizing caprolactam in situ at high pressure and temperature. The purpose of this colloidal in situ polymerization is to improve particle dispersion and to enhance interaction of the filler to the polymer matrix. X-ray diffraction studies of the in situ kaolin/Nylon-6 composites revealed that the x-ray peak corresponding to the α-crystal form of Nylon-6 diminished with increasing kaolin loading, while the γ-crystal structure became more pronounced. The degree of crystallinity of Nylon-6 remained fairly unchanged with the kaolin loading level in the in situ composites. Calorimetric and dynamic mechanical studies exhibited that the glass transition temperature of the resulting composite increased significantly with increase in kaolin concentration, suggesting strong filler-matrix interaction at the kaolin/Nylon-6 interface. Scanning electron microscopic (SEM) results showed uniform filler dispersion in the in situ composites relative to the conventional melt-mixed composites. Modulus and tensile strength of these in situ composites were found to be distinctively higher than that of the conventional melt-mixed kaolin/Nylon-6 composites. However, as typical for composite materials, drawability and fracture toughness decreased with increasing kaolin loading. © 1996 John Wiley & Sons, Inc.     

Spherical filler-promoting thermally conductive pathway in graphite-containing polymer composites for high heat radiation

Graphite is an efficient and affordable filler for polymer composites, allowing the control of thermal conductivity. In comparison to other thermally conductive fillers, graphite is lightweight and flexible but affords anisotropic thermal conductivity. Herein, the control of thermal conductivity of graphite-containing polymer composite sheet using spherical polymer particles as additional fillers is described. The thermal conductivity in the through-plane direction (λ_t) of the composite sheet is enhanced by varying the composition ratio of the two fillers (flaky graphite and spherical particles), and optimizing the forming temperature and pressure. Graphite-containing (25 wt%) polymer composite sheet formed by compression at 150 °C and 10 MPa exhibits λ _t value of 0.66 W/m K. Upon mixing of polystyrene microspheres, λ _t is successfully increased. The maximum value of thermal conductivity for a composite sheet with 35 wt% of graphite and 50 wt% of spherical particles is 7.51 W/m K, at 180 °C and 10 MPa. The graphite-containing polymer matrix forms a sequentially connected network-like structure in the composite sheet. Excess polymer microspheres lead to the formation of void structures inside the composite sheet, reducing the thermal conductivity. Thermo-camera observations proved that the composite sheets with higher λ _t value showed comparably high heat radiations. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 607–615     

Novel filled polymer composites prepared from in situ polymerization via a colloidal approach: II. Blends of kaolin/Nylon-6 in situ composites with conventional Nylon-6 and -66

A novel in situ composite comprised of kaolin clay fillers and polyamide 6 (Nylon-6) was synthesized via a colloidal approach by suspending kaolin particles in aqueous caprolactam and then polymerizing the caprolactam under elevated temperature and pressure. This in situ polymerization technique enables the deposition of nylon molecules directly onto the filler surface. It offers a much larger contact surface area for the nylon molecules to interact with the filler particles and enhances filler/matrix interaction through polymer miscibility. The kaolin particles were shown to be uniformly dispersed in Nylon-6 matrix without appreciable agglomeration. In the highly clay-loaded composites such as the 50/50 kaolin/Nylon-6 in situ composite, the deposited nylon molecules probably form a coated layer on the filler particles. This kind of nylon coated fillers may be applied as a reinforcing entity to commercial Nylon-6 or −;66 by improving particle dispersion and melt processability. The 50/50 kaolin/Nylon-6 in situ composites have been used as a masterbatch for blending with commercial Nylon-6 and Nylon-66 to take advantage of their good properties and to reduce cost. Rheology and mechanical properties of the masterbatch/nylon composites have been investigated in comparison with those of the conventional melt-mixed composites. The improvement of rheological and mechanical properties of the in situ composites has been discussed in relation to the composite structure. © 1996 John Wiley & Sons, Inc.     

Poly(lactic acid)-based polymer composites with high electric and thermal conductivity and their characterization

Electrically and thermally conductive polymer composites on the basis of biodegradable poly(lactic acid) (PLA) were developed and studied in this work. Pristine single-walled carbon nanotubes (CNTs) and powder of natural graphite (G) were used as fillers in polymer composites. PLA-based composites were prepared by melt-compounding method. The volume resistivity of PLA/CNT composites can be changed by more than ten orders of magnitude compared to that for neat PLA. The thermal conductivity of PLA/G composites can be changed from 0.193 W⋅m⁻¹⋅K⁻¹ (neat PLA) up to 2.73 W⋅m⁻¹⋅K⁻¹. Loading small quantity of CNTs into PLA/G composites increases the thermal conductivity not less than by 40% of magnitude. Besides, all developed PLA-based composites are suitable for processing by injection molding, extrusion or additive manufacturing technology (3D printing).     

The role of graphene interactions and geometry on thermal and electrical properties of epoxy nanocomposites: A theoretical to experimental approach

The influence of dispersion procedure and nanofiller geometry on thermal and electrical properties of graphene nanoplatelet (GNP) based composites has been investigated. A theoretical model, based on the contacts between adjacent nanoparticles, has been proposed aiming to connect thermal and electrical properties. It has been observed that GNP overlapping (type I) induces a decrease on thermal conductivity. Its effect on electrical conductivity is more complex and depends on the areas of overlap and in-plane contacts (type II). A higher type I area in comparison to type II implies an increase of electrical conductivity with overlapping whereas the opposite effect is found when type II area is higher than type I. The predicted results of the theoretical model fitted experimental measurements at different GNP contents and three roll milling processing conditions, giving a better overview of the influence of GNP geometry and interactions on electrical and thermal properties of nanocomposites.     

A modern approach to the solution and analysis of the Simha-Somcynsky model for the description of pressure-volume-temperature properties of polymer fluids

We revisit the Simha-Somcynsky model of polymer fluids with the purpose of developing novel theoretical and computational approaches to simplify and speed up its solution as well as the fitting of experimental data, and decrease its level of mathematical complexity. We report a novel method that allows us to solve one of the two equations of the model exactly, thus putting the level of mathematical difficulty on a par with the one of other models for polymer fluids. Moreover, we describe a computational algorithm capable of fitting all five parameters of the model in an unbiased way. The results obtained reproduce literature results and fit experimental pressure-volume-temperature and solubility parameter data for three polymers very accurately. Moreover, the new techniques allow for the investigation of the model at very low temperatures. Unexpectedly, the model predicts behaviors that could be interpreted as a glass transition, as routinely observed in dilatometry and differential scanning calorimetry, and a glass phase. We compared the predicted and experimental T g’s for cis poly(1,4-butadiene) and found an excellent quantitative agreement.     

Thermal decomposition kinetics of natural fibers: Activation energy with dynamic thermogravimetric analysis

Dynamic TG analysis under nitrogen was used to investigate the thermal decomposition processes of 10 types of natural fibers commonly used in the polymer composite industry. These fibers included wood, bamboo, agricultural residue, and bast fibers. Various degradation models including the Kissinger, Friedman, Flynn-Wall-Ozawa, and modified Coats-Redfern methods were used to determine the apparent activation energy of these fibers. For most natural fibers approximately 60% of the thermal decomposition occurred within a temperature range between 215 and 310 °C. The result also showed that an apparent activation energy of 160-170 kJ/mol was obtained for most of the selected fibers throughout the polymer processing temperature range. These activation energy values allow developing a simplified approach to understand the thermal decomposition behavior of natural fibers as a function of polymer composite processing.     

Effects of ceramic filler in poly(vinyl chloride)/poly(ethyl methacrylate) based polymer blend electrolytes

Effects of nano-ceramic filler titanium oxide (TiO₂) have been investigated on the ionic conductance of polymeric complexes consisting of poly(vinyl chloride) (PVC)/poly(ethyl methacrylate) (PEMA), and lithium perchlorate (LiClO₄). The composite polymer blend electrolytes were prepared by solvent casting technique. The TiO₂ nanofillers were homogeneously dispersed in the polymer electrolyte matrix and exhibited excellent interconnection with PVC/PEMA/PC/LiClO₄ polymer electrolyte. The addition of TiO₂ nanofillers improved the ionic conductivity of the polymer electrolyte to some extent when the content of TiO₂ is 15 wt%. The addition of TiO₂ also enhanced the thermal stability of the electrolyte. The changes in the structural and complex formation properties of the materials are studied by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques. The scanning electronmicroscope image of nano-composite polymer electrolyte membrane confirms that the TiO₂ nanoparticles were distributed uniformly in the polymer matrix.     

Nonsteady-state processes of water transfer in solid-polymer membrane: a mathematical model

The regularities of electroosmotic and diffusion water transport are shown in the case of hydrogen ionization in the porous anode layer applied on the proton-exchange membrane surface. The possibility of critical phenomena due to drying of a membrane region adjacent to the anode is shown.     

A convection–diffusion porous media model for moisture transport in polymer composites: Model development and validation

Moisture may cause many detrimental effects to polymers and their composites, thus inhibiting the applications of polymeric materials in hot and humid environments. In this article, a convection–diffusion porous media model is derived to better characterize rapid moisture transport in polymer composites at high temperatures. The model considers both continuum diffusion in solid and high‐pressure convection taking place in the pore network. Coupling of convection and diffusion is achieved by combining the law of conservation of mass, Darcy's law, the liquid–vapor chemical equilibrium, and the ideal gas law. The presented model is validated by conducting experimental tests on an epoxy compound. It is found that the proposed convection–diffusion model is more effective than diffusion‐only and convection‐only models for interpreting rapid desorption tests at high temperatures. A numerical study is also performed to predict maximum vapor pressure during a rapid heating process. Vapor pressure is found to be as high as 6.5 MPa at a heating rate of 10 K/s. It is concluded that the convection–diffusion model is able to capture both vapor dynamics and diffusion mechanism in porous polymeric materials, and can be potentially used to further investigate polymer‐moisture interactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1440–1449