Expanded Graphite Loading Research Articles

Optimization of mechanical and electromagnetic interference shielding properties of expanded graphite/polyurethane composite foams

AbstractThe expanded graphite (EG) was used as a filler in EG/polyurethane (PU) composite foams for electromagnetic interference shielding (EMI). The EG/PU composite foams were characterized by Fourier transform infrared spectroscopy (FTIR) and SEM. The shielding effectiveness (SE) of the EG/PU composite form containing 5 wt% EG was −24 dB at 5 wt% in the 8–12 GHz range. The optimal EG loading was 3 wt% and the corresponding EG/PU composite foam had a total SE of −18.9 dB and fairly good mechanical characteristics (compressive strength: 13.43 MPa and compressive modulus: 4.95 MPa). These attributes position the EG/PU composite foam as a promising candidate for diverse EMI SE applications.Highlights Synthesis by thermal exfoliation and characterization by x‐ray diffraction, Raman and SEM of EG. Preparation of EG/PU foams for enhanced EMI SE. Optimization of the EG loading with regard to SE and mechanical properties of the EG/PU foams.

Synergistic phase change and heat conduction of low melting-point alloy microparticle additives in expanded graphite shape-stabilized organic phase change materials

Organic phase change materials (PCMs) have great potential for efficient thermal energy storage and passive thermal management applications due to their non-corrosiveness, high heat storage capacity and stable operating temperature. However, low thermal conductivity and easy leakage seriously restrict the actual application. Meanwhile, heat transfer enhancers typically have a serious negative effect on the heat storage capacity of the PCMs. In this paper, a novel strategy for preparing high performance shape-stable composite phase change materials (CPCMs) is reported, utilizing paraffin wax (PW) as the energy storage material and expanded graphite (EG) as heat transfer enhancers and supporting material, especially in which low melting-point alloy (LMA) micro particles having same phase change temperature as PW are employed with two purposes: one is to provide extra latent heat, and another is to construct a hybrid three-dimensional thermal conduction network in microscale to achieve synergistic thermal conduction with EG. The resulting CPCMs exhibit excellent characteristics in energy storage capacity, thermal conductivity, and thermal cycling stability. The thermal conductivity of ternary CPCM can reach 5.842 W m−1 K−1 when the LMA and EG loading are 4.55 wt% and 9 wt%, which is about 16.4 times higher than that of pure PW, with no obvious volumetric latent heat reduction. This work provides a novel and promising approach for the preparation of CPCMs with high and fast storage properties.

Reactive processing-microstructure-mechanical performance correlations in biodegradable poly(lactic acid)/expanded graphite nanocomposites.

Reactive extrusion is a promising method to prepare biodegradable nanocomposites with enhanced modulus, strength and toughness. In this study, biodegradable extended nanocomposites based on poly(lactic acid) (PLA)/expanded graphite (EG) were prepared by melt-compounding using a co-rotating twin-screw extruder. Effects of EG loading, aspect ratio, delamination and dispersion state on the mechanical and thermo-mechanical properties of PLA/EG nanocomposites were investigated. Adding the largest EG (EGL) nanoplatelets, having the average particle size of 48.2 μm and aspect ratio of 19.5, to the PLA matrix enhanced the Young modulus, tensile strength, ultimate strain and tensile toughness of the extended PLA sample with benzoyl peroxide (BP) between 40-100%. The observed enhancements originated from restricted PLA molecular motions, assisted PLA crystallization and intensified BP activity in extending the PLA chains. In contrast, EG nanofiller (EGS), with the lowest aspect ratio and size, lowered the PLA relaxation time and accelerated the PLA crystallization. This type of EG showed the weakest reinforcing effect on PLA. For the EG type (EGM) with an intermediate size and aspect ratio, it was observed that the presence of the nanoparticles had a negligible effect on the PLA molecular dynamic and reduced the PLA crystallization rate. The highest impact strength was observed for the PLA/EGM nanocomposite at 1 phr loading.

Construction of highly efficient heat conduction channels within expanded graphite/paraffin phase change composites and their thermophysical properties

Paraffin waxes (PW) are organic phase change materials (PCMs) that can be potentially applied for the storage/release of low-temperature latent heat and thermal management. However, they have serious liquid leakage and poor thermal conductivity, which greatly restrict their practical application. Although numerous studies have been conducted to address these problems, it is challenging to achieve phase change composites (PCCs) that are characterized by high thermal conductivity and excellent phase change behavior. Herein, we put forward a novel strategy for preparing expanded graphite (EG)/PW binary PCCs with EG loading varying in the range of 10–40 wt%. The method is developed by constructing graphite sheets with high orientation inside the PCCs following compression induction. The highly oriented graphite sheets provide channels for highly efficient heat transfer, which significantly improves the thermal conductivity of the resulting EG/PW PCCs. The in-plane thermal conductivities of the EG/PW PCCs are in the range of 10.7–49.7 W m−1 K−1 under 10–40 wt% EG loading conditions, much larger than those of the previously reported EG/PW PCCs with the same EG content. The EG/PW composites also exhibit excellent compatibility, uniformity, thermostability, reliability, and phase change behaviors. These remarkable properties make the EG/PW composites promising for application in thermal management and heat storage. This work provides an efficient and generic strategy for designing and constructing high-efficiency heat transfer channels within the PCCs using sheet-shaped fillers with high thermal conductivity.

Thermally conductive and form-stable phase change composite for building thermal management

Phase change materials (PCMs) have aroused tremendous interest in building thermal management (BTM) owing to their operational simplicity and comparable energy storage density. However, the application of PCM-based BTM is generally hindered by the bottlenecks of low thermal conductivity and liquid leakage. To solve this problem, a novel thermally conductive and form-stable phase change composite (PCC) is prepared by employing n-Octadecane (ODE) as PCM, olefin block copolymer (OBC) as supporting material, and expanded graphite (EG) as thermally conductive additives. The characterization results show that the as-synthesized PCCs exhibit good physicochemical compatibility. The introduction of EG enables PCC an enhanced and antistrophic thermal conductivity. The radial thermal conductivities of PCCs reach up to 3.8–20.6 W/m∙K with EG loading of 5–25 wt%. The thermogravimetric analyzer (TGA) and leakage-proof analysis indicate that the resultant PCCs have a good thermal stability and the combination of OBC and EG greatly alleviated the leakage problem. In addition, BTM test shows that the indoor temperature of the PCM room is more stable and the maximum temperature differences between PCM room and reference room are 2.5 °C and 3.6 °C during the heating and cooling processes. These results indicate that the as-synthesized ODE-OBC/EG composites have significant potential for BTM application.

High‐performance and cost‐effective melt blended poly(ether ether ketone)/expanded graphite composites for mass production of antistatic materials

AbstractIn this study unfunctionalized expanded graphite (EG) was incorporated into poly(ether ether ketone) (PEEK) using twin‐screw extrusion and injection moulding to manufacture cost‐effective PEEK/EG composites for mass production of high‐performance antistatic materials. Direct current electrical conductivity, morphology, rheological and thermal properties of the composites were investigated. At an EG loading of 5 vol%, the electrical conductivity exhibited an abrupt increase to 1.45 × 10−5 S m−1 which was in the required range of electrical conductivity of antistatic materials. The frequency dependence of the storage modulus of the melt containing 2 vol% EG decreased significantly at low frequencies. Viscosity did not increase much with the addition of EG in comparison with other nanofillers such as carbon nanotubes. The crystallinity of PEEK increased to 41.11% from 35.87% upon addition of 3 vol% EG. EG improved the thermal stability of PEEK by an increase in the initiation temperature of its decomposition steps. © 2021 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Thermally Conductive Polyethylene/Expanded Graphite Composites as Heat Transfer Surface: Mechanical, Thermo-Physical and Surface Behavior.

Composites of high-density polyethylene (HDPE) and expanded graphite (EG) are prepared for heat exchangers in multi-effect distillation (MED) desalination. At 50 wt.% EG loading, the thermal conductivity of HDPE was increased by 372%. Moreover, the surface wettability of the HDPE/EG composite was enhanced by corona and RF plasma treatment as demonstrated by the increase in surface free energy from 28.5 mJ/m2 for untreated HDPE/EG to 55.5 and 54.5 mJ/m2 for HDPE/EG treated by corona and RF plasma, respectively. This enhanced surface wettability was retained over a long time with only a 9% and 18% decrease in RF and corona plasma-treated samples’ surface energy after two months. The viscoelastic moduli and the complex viscosity profiles indicated that EG content dictates the optimum processing technique. At loading below 30 wt.%, the extrusion process is preferred, while above 30 wt.% loading, injection molding is preferred. The plasma treatment also improved the HDPE/EG composite overall heat transfer coefficient with an overall heat transfer coefficient of the composite reaching about 98% that of stainless steel. Moreover, the plasma-treated composite exhibited superior resistance to crystallization fouling in both CaSO4 solution and artificial seawater compared to untreated composites and stainless-steel surfaces.

Thermal performance of galactitol/mannitol eutectic mixture/expanded graphite composite as phase change material for thermal energy harvesting

The eutectic mixture of galactitol and mannitol with the melting point of 157.6 °C and high latent heat of fusion (ΔHm=271.07 kJ/kg) is regarded as an ideal phase change material used in medium temperatures. However, the shortcomings of low thermal conductivity and severe supercooling restrict its application for thermal energy storage. To address these challenges, expanded graphite (EG) was introduced to obtain eutectic mixture/EG composites by vacuum impregnation method. SEM images showed that the pores of EG were filled by sugar alcohols and no chemical reaction happened during this process as confirmed by FTIR spectroscopy and XRD. The thermophysical properties of phase change material (PCM) composites were measured. The result revealed that the supercooling degree (Tsc) of PCM composites decreased more than 26.2% compared to that of the eutectic mixture. Although the ΔHm of PCM composites decreased with an increase in content of EG, most of them are higher than 200 kJ/kg. Unlikely the ΔHm of PCM composites, the latent heat of crystallization (ΔHc) first rose by 15.3% and then dropped slightly. Their thermal conductivities were greatly improved by EG, especially with a 14 wt.% EG loading producing a more than 30-fold increase. Also, the PCM composite with 14 wt.% EG loading shows great form stability and thermal reliability after 20 charging-discharging cycles. These results prove that galactitol/mannitol eutectic mixture/EG composite has a promising prospect in potential for thermal energy harvesting and thermal management systems application.

In situ intercalation polymerization approach to polyamide-6/graphite nanoflakes for enhanced thermal conductivity

Abstract Traditional polymer composites generally present limited thermal conductivity (TC) even highly loaded with highly thermally conductive fillers due to the lack of large interfacial thermal resistance between the fillers and the surrounding polymers. In this work, polyamide-6/graphite nanoflakes (PA6/GnF) composites with high TC can be obtained through a one-step in situ intercalation polymerization. The caprolactam onium ion (CL ⊕ ) catalysted by 6-aminocaproic acid can effectively intercalate into the interlayer of expanded graphite (EG) and lead to the separation of EG into GnF after in situ polymerization. Thereafter the homogeneous dispersions of GnF with ordered arrangement and strong interfacial interactions between PA6 and GnF can be formed within the PA6/GnF composites, which can favor the formation of the consecutive thermal conductive pathways or networks at a relatively low EG loading. The obtained composites, at only EG loading of 12 wt%, exhibit a high TC (2.49 W/mK), corresponding to an enhancement of 678% compared to that of neat PA6. This strategy offers new insights into the fabrication of graphene based composites, and provides a straightforward and highly industrializable process for fabrication of high-performance GnF-based thermally conductive composites.

Thermal optimization of composite phase change material/expanded graphite for Li-ion battery thermal management

Paraffin (RT44HC)/expanded graphite (EG) composite phase change material (CPCM) with enhanced thermal conductivity improves the thermal management of Li-ion batteries. The thermal management of these batteries may be further improved via optimizing the CPCM composition. In this study, the thermal management performance of CPCM, with different mass fractions of EG, is investigated for Li-ion batteries. CPCM samples were prepared by absorbing RT44HC into porous EG. The properties of composites, such as thermal conductivity and liquid phase change material (PCM) leakage, were measured. Our results show that: (1) EG incorporation dramatically enhances the thermal conductivity of CPCM and leads to a significant decrease in the temperature rise of Li-ion batteries; and (2) CPCM, with EG mass fractions varying from 9% to 20%, shows outstanding thermal management performance. Liquid PCM leakage, which decreases with an increase in EG loading, occurs during phase transition. We propose, taking into account liquid PCM leakage during phase transition, that CPCM with 16–20wt.% EG can be viewed as the most promising alternative for Li-ion battery thermal management.

Effect of surfactant and electron treatment on the electrical and thermal conductivity as well as thermal and mechanical properties of ethylene vinyl acetate/expanded graphite composites

ABSTRACTThis study presents an investigation of the electrical and thermal conductivities of composites based on an ethylene vinyl acetate (EVA) copolymer matrix and nanostructured expanded graphite (EG). To improve the EG dispersion in EVA, EG sheets were modified by treating them with the anionic surfactant sodium dodecyl sulphate (SDS) in water. The modified SDS‐EG platelets, after being filtered and dried, were melt‐mixed with EVA to prepare the composites. Finally, both EVA/EG and EVA/SDS‐EG composites were subjected to 50 kGy electron beam (EB) irradiation. SEM images confirm that the irradiated EVA/EG samples had improved interfacial adhesion, while the irradiated EVA/SDS‐EG samples showed even better interfacial adhesion. The gel contents of the irradiated samples without and with SDS treatment increased with increase in EG loading. The EVA/EG composites exhibited a sharp transition from an insulator to a conductor at an electrical percolation threshold of 8 wt %, but with SDS‐EG the electrical conductivity was extremely low, showing no percolation up to 10 wt % of filler. The EB irradiation had no influence on electrical conductivity. The thermal conductivity linearly increased with EG content, and this increase was more pronounced in the case of SDS‐EG, but decreased after EB irradiation. The thermal properties were little influenced by EB irradiation, while better polymer–filler interaction and better filler dispersion as a result of SDS treatment, and the EB irradiation initiated formation of a cross‐linked network, had a positive effect on the tensile properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42396.

Thermal conductivities and characteristics of ternary eutectic chloride/expanded graphite thermal energy storage composites

Abstract Ternary eutectic chloride (NaCl–CaCl 2 –MgCl 2 )/expanded graphite (EG) composites were prepared for thermal energy storage applications at a solar thermal power plant. Heat capacity and latent heat thermal energy storage (LHTES) characteristics of the composites including the melting temperature and latent heat capacity were investigated using a differential scanning calorimetry (DSC) technique, and the effects of EG additives in the composite on thermal conductivities were evaluated using a hot disk analyzer. The ternary eutectic chloride/EG composites with expanded volumes ranging from 150 to 250 g/L and the EG mass fractions ranging from 0 to 5 wt% were prepared by absorbing liquid chlorides into the EG at high temperature. Experimental results indicated that the specific heat capacity of solid composites decreased with EG mass fraction and temperature. In the liquid state, the effect of the EG loading on the specific heat was not uniform. Specific heat capacity reached maximum at 1 wt% of EG loading and the specific heat capacities of all samples rose with temperature. The melting temperatures of the composites were the same as the pure ternary eutectic chloride, but the phase change latent heat decreased with the mass percentages of EG in the composites. The thermal conductivities of the composites were 1.35–1.78 times higher than that of the pure ternary eutectic chloride.

Tetradecanol/expanded graphite composite form-stable phase change material for thermal energy storage

Natural flake graphite was chemically intercalated to prepare expandable graphite. The expandable graphite was then expanded by means of microwave irradiation to obtain expanded graphite (EG). Tetradecanol (TD)/EG composite form-stable phase change materials (PCMs) were prepared by mixing TD with EG through an autoclave method. The highest loading of TD in the composite form-stable PCMs with good form-stability was 93wt%. The composite form-stable PCMs exhibited excellent thermal energy storage capacity. The melting enthalpy (ΔHm) and crystallization enthalpy (ΔHc) of the composite form-stable PCM containing 93wt% TD were 202.6 and 201.2J/g, respectively. However, the solid–solid phase transition of TD in the composite form-stable PCMs was hindered as TD was strongly absorbed by EG. As a result, the ΔHm and ΔHc of the composite form-stable PCMs were slightly lower than the theoretical value. The thermal conductivity of the composite form-stable PCMs was greatly enhanced by EG and was increased with the increasing of EG loading. The thermal conductivity of the composite form-stable PCM containing 7wt% EG attained 2.76W/mK. Besides, effects of the prepared EG on properties of the composite form-stable PCMs were compared with those of EG derived from commercially obtained expandable graphite.

Jatropha curcas oil based alkyd/epoxy resin/expanded graphite (EG) reinforced bio-composite: Evaluation of the thermal, mechanical and flame retardancy properties

Bio-composites were prepared from blends of Jatropha curcas oil based alkyd and epoxy resin with different weight percentage of expanded graphite (EG). The effect of EG loading on the thermal, mechanical, flame retardancy and water absorption properties of the bio-composites were studied. Significant improvement in thermal and mechanical properties was observed with 5wt% EG loading. The prepared bio-composites were characterized by fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, X-ray diffractometry and tensile strength measurement. Morphological study showed the homogeneous dispersion of the EG sheets in the resin matrix. Limiting oxygen index (LOI) of the bio-composites showed a noticeable improvement in flame retardancy in comparison to neat blend of alkyd and epoxy resin. In vitro degradation of the bio-composites showed low degradation in phosphate buffer solution (pH 7.4).

Effect of expanded graphite on thermal, mechanical and dielectric properties of ethylene–propylene–diene terpolymer/hexa fluoropropylene–vinylidinefluoride dipolymer rubber blends

Expanded graphite (EG) filled with compatibilized and uncompatibilized EPDM/FKM (50/50, w/w) blends were prepared by two-roll mill mixing. Maleic anhydride grafted EPDM (MA-g-EPDM) is used as a compatibilizer. The cure characteristics, filler dispersion, mechanical properties and DC electrical conductivity of the composites were evaluated. The thermal stability of the EG loaded EPDM/FKM blends was studied using thermogravimetric analysis (TGA). The activation energy of the composites was evaluated by the Coats–Redfern method. The microwave properties like dielectric permittivity, dielectric loss, conductivity, dielectric heating coefficient and absorption coefficient were evaluated. At higher EG loading, the optimum cure time (T90) decreases due to the increased thermal transition of the blends in presence of EG. The tensile properties of all the composites, especially those with compatibilizer, increased with aging. The AC and DC conductivities increase with increase in EG loading, due to the formation of enhanced conductive networks by EG platelets. The flammability and thermal characteristics are improved by the addition of EG. The morphology of the composites was investigated using scanning electron microscopy (SEM).

Synthesis and characterization of conducting gas barrier polyacrylonitrile/graphite nanocomposites

AbstractGraphite platelets were expanded by functionalization with inorganic acids followed by strong thermal treatment. The expanded graphite (EG) was exfoliated on the polyacrylonitrile (PAN) matrix through in situ emulsion sonication technique with different proportions of EG. The Ultraviolet‐visible (UV) spectroscopy revealed the interaction between EG and PAN matrix. In Fourier Transform Infrared spectroscopy (FTIR), the chemical interaction between EG and the cyanide group of PAN was evidenced to the formation of PAN/EG composites. The X‐ray diffraction pattern of raw graphite (RG), expanded graphite (EG), polyacrylonitrile (PAN), and PAN/EG nanocomposites were evidenced the dispersion of EG with the PAN matrix. The morphology of EG, PAN, and PAN/EG composites were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The tensile strength of PAN/EG nanocomposite was measured and found to be increased with increase in EG concentrations. The conductivity and impedance of composites were measured as function of EG concentration. It was found that, conductivity of composites gradually increased with the increase in EG loading. Oxygen permeability of PAN/EG was reduced substantially with rise of EG proportion. To investigate the flame retardancy behavior of PAN/EG nanocomposites, the limiting oxygen indexes were calculated. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Mechanical and functional properties of composites based on graphite and carboxylated acrylonitrile butadiene rubber

AbstractIn this study, carboxylated acrylonitrile butadiene rubber (xNBR)/expanded graphite (EG) nanocomposites were prepared with a latex compounding technique by ultrasonic stirring. The dispersion of EG in the xNBR matrix was investigated with transmission electron microscopy, scanning electron microscopy, and X‐ray diffraction analysis. EG could be exfoliated into lots of nanosheets dispersing in the xNBR matrix. More EG loading resulted in the presence of a few incompletely exfoliated agglomerates. The mechanical properties (hardness, tensile modulus, and tensile strength) of the xNBR/EG composites were determined. Dynamic mechanical thermal analysis was also performed, and it showed that the nanosheets of EG somewhat immobilized the motion of rubber macromolecular chains and led to the shifting and broadening of the tan δ peak toward higher temperatures. Many other functional properties of EG‐filled xNBR composites were studied, and it was established that the composites had excellent electrical conductivity as well as gas‐barrier and wear properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010