Addition Of Expanded Graphite Research Articles

Preparation and thermal properties of expanded graphite/paraffin/organic montmorillonite composite phase change material

Expanded graphite (EG)/paraffin/organic montmorillonite (OMMT) composite phase change material (PCM) was prepared by using melt intercalation method. The microstructure of EG/paraffin/OMMT is observed by scanning electron microscope (SEM). The thermal properties are investigated by differential scanning calorimetry (DSC). The mass loss of EG/paraffin/OMMT after 50 heating cycles was measured for investigating the influence of EG and OMMT on the thermal properties of paraffin. The results show that EG and OMMT have the ability of adsorption and shape-stability. The melting point EG/paraffin/OMMT is decreased slightly with an addition of paraffin and the latent heat of EG/paraffin/OMMT is determined by the mass ratio of paraffin. The heat transfer efficiency of EG/paraffin/OMMT is strengthened and the heating time is decreased to one-sixth of that of paraffin by addition of EG and OMMT. The thermal stability of EG/paraffin/OMMT is improved by addition of OMMT.

Polyethersulfone-expanded graphite nanocomposites: Charge transport and impedance characteristics

Polyethersulfone (PES)-expanded graphite nanocomposites have been prepared by solution blending route after sonicating expanded graphite in dichloromethane. It has been observed that ultrasonication results in nanosheets formation leading to a low percolation threshold of 3 wt.%. At 5 wt.% filler loading the conductivity is of the order of 10 −2 S/cm. Hopping type of charge transport occurs at 3.2 wt.% expanded graphite in PES below which capacitive effects couple. The effective dielectric constant at low frequency increases with filler concentration. Impedance measurement has been carried out to evaluate interfacial capacitance which, for 3.2 wt.% expanded graphite addition in PES, increases to 110 pF from 32 pF for 1 wt.% expanded graphite in the polymer. DSC analysis shows an increment of 12 °C in the T g of PES with 3 wt.% expanded graphite suggesting interaction between the polymer and filler.

Heat conduction enhanced shape-stabilized paraffin/HDPE composite PCMs by graphite addition: Preparation and thermal properties

Abstract In this study, the thermal conductivity of shape-stabilized paraffin/high density polyethylene (HDPE) composite phase change material (PCM) was improved by addition of graphite powder (GP) and expanded graphite (EG). GP and EG in different mass fractions were added to PCM, and thermal conductivities of paraffin/HDPE/GP and paraffin/HDPE/EG composites were measured by a Hot Disk Thermal Constant Analyzer. An almost linear relationship between mass fractions of GP and EG additives and thermal conductivity of PCMs was found. Furthermore, the physical structures and thermal properties of the composite PCMs were investigated by scanning electron microscope (SEM) and differential scanning calorimetry (DSC), respectively. The experimental results showed that the thermal conductivities of the shape-stabilized paraffin/HDPE composite PCMs could be greatly improved by addition of EG. When the addition of EG was in the ratio of 4.6 wt%, the thermal conductivity of the PCM was up to 1.36 W m−1 K−1, more than 4 times of that without any additives, which was much better than that by addition of GP. The latent heat of the heat conduction enhanced PCMs decreased little due to small amount of EG, and good uniformity structure was confirmed by SEM in this paper.

Effects of expandable graphite and ammonium polyphosphate on the flame‐retardant and mechanical properties of rigid polyurethane foams

AbstractIn this work, the effect of expandable graphite (EG) and ammonium polyphosphate (APP) on the flame retardancy and mechanical properties of the rigid polyurethane foam (RPUF) was studied. The results indicated that both EG and APP could effectively improve the flame retardancy of RPUF, while the retardancy of EG was better than APP. When the flame‐retardant loading was 15 wt %, the limited oxygen index (LOI) values of APP‐ and EG‐filled RPUF were 24.5 and 32 vol %, respectively. According to the LOI test, the optimal ratio of APP to EG in RPUF composites was 1 : 1 by weight, at which the LOI value of 15 wt % (APP + EG)/RPUF was 30.5 vol %. Thermal degradation test of RPUF composites by thermogravimetric analysis indicated that the addition of APP and EG to RPUF could lead to an increase in the amount of high‐temperature residue. Under the same conditions, the residue amount of EG/RPUF was less than that of APP/RPUF at the same temperature. Compression test and dynamic thermal mechanical analysis indicated that both the compressive strength and modulus decreased at a certain extent with the EG‐ or APP‐filled into RPUF, respectively, but with the mixture of EG and APP added into RPUF, the mechanical properties of these materials increased. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Flame retardancy of whisker silicon oxide/rigid polyurethane foam composites with expandable graphite

AbstractRigid polyurethane foam (RPUF) composites filled with various expandable graphite (EG) or/and whisker silicon (WSi) loadings were prepared with the same density (0.08 g/cm3). When the WSi content reached 10 wt %, the composite had the best mechanical properties, the values of compressive strength and modulus reached 0.74 and 21.0 MPa, respectively. Compared with only EG filled RPUF, the addition of 10 wt % WSi to EG/RPUF would also bring out improvement on their flame retardant and mechanical properties. Maintaining EG 20 wt %, the compressive strength increased from 0.17 (EG/RPUF) to 0.39 MPa (WSi/EG/RPUF), the compressive modulus increased from 9.32 (EG/RPUF) to 10.11 MPa (WSi/EG/RPUF), and the limiting oxygen index value increased from 28 vol % (EG/RPUF) to 32.5 vol % (WSi/EG/RPUF). The thermogravimetric analysis showed that the addition of EG and WSi particles improved the thermal stability of the composites. The dynamical mechanical analysis (DMA) showed that EG and WSi particles led to up‐shift of the glass transition temperature. Moreover, 10 wt % EG and 10 wt % WSi filled RPUF had the highest storage modulus, as the EG and WSi exhibited a desirable synergetic effect on flame retardant properties and dynamic mechanical properties of RPUF composites. The morphologies of the composites were analyzed with scanning electron microscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Properties of new nanocomposite triblock copolymer gels based on expandable graphite

AbstractIn this work, we investigated the effect of expandable graphite (EG) on the property of triblock copolymer prepared from a poly(styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene) (SEBS) imbibed with an EB‐compatible hydrocarbon oil. The rheological properties showed that at a temperature between 30 and 40°C below the gel point, the triblock copolymer gels had a dynamic storage modulus (G′) greater than loss modulus (G‵), thereby indicating that at ambient temperature, a physical network is still present in spite of the addition of nanoparticles. Dynamic rheological measurements of the resultant nanocomposite triblock copolymer gels confirmed that the addition of EG affects the linear viscoelastic properties and maximum operating temperature of the parent triblock copolymer gels. The mechanical properties showed only marginal increase, which can be attributed to the poor dispersion that leads to agglomeration of particle into micrometer size stacks, and thus the particles behave only as inorganic fillers. The morphology and X‐ray diffraction revealed that the EG used to generate nanocomposite triblock copolymer gels is dispersed generally within the swollen copolymer and/or solvent. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Flame retardancy of hollow glass microsphere/rigid polyurethane foams in the presence of expandable graphite

AbstractRigid polyurethane foams (RPUF) filled with various loadings of expandable graphite (EG) or/and hollow glass microspheres (HGM) were prepared by cast molding. The flame retardant properties of these composites were investigated by limiting oxygen index (LOI), horizontal and vertical burning tests. The composite with 10 wt % HGM and 20 wt % EG had the best flame retardant properties, and its LOI value reached 30 vol %. The addition of an appropriate loading of HGM improved the compressive strength and modulus of RPUF and EG/RPUF. When the HGM content arrived at 10 wt %, the compressive strength and modulus of the composites reached the maximum value. The dynamical mechanical analysis (DMA) showed that the addition of EG and HGM made the glass transition temperature shift to a higher temperature, and 10 wt % EG and 10 wt % HGM filled RPUF had the highest storage modulus. The scanning electronic microscope (SEM) observation indicates that the additives led to the decrease in the cell size. In addition, the flame retardant mechanism, the thermal properties, the burned surfaces and the interface surfaces were elucidated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Ethylene vinyl acetate/expanded graphite nanocomposites by solution intercalation: preparation, characterization and properties

Nanodimensional reinforcing agents are introduced to polymer matrices to improve properties at very low loading. Natural graphite (NG) as such is not reinforcing in nature. But when modified to expanded graphite (EG) by high temperature heat treatment, this may be used as reinforcing nanofiller. In the present study, ethylene vinyl acetate (EVA) was reinforced with EG by solution intercalation, and the composite properties were compared with those of the virgin polymer and NG filled composite. The tensile strength exhibited an improvement of 35% with 4 wt% EG addition, while the modulus at 100% elongation was increased by 150% with respect to the control EVA. Another interesting feature was that unlike the conventional fillers, addition of EG did not reduce the elongation at break, due to the lubricating action of graphite. However, at a high loading of 8 wt%, the tensile strength showed a lower value, due to the agglomeration of graphite platelets. The storage modulus also showed increment with the addition of graphite without much change in the glass transition temperature. In addition to these, the EVA-EG nanocomposites exhibited high thermal conductivity and thermal degradation stability as compared to the virgin polymer. About 4 wt% of EG shifted the temperature of maximum rate of degradation by 14 °C towards higher temperature. These results were well supported by the swelling and morphological studies. The NG filled composite exhibited inferior properties to EVA-EG nanocomposites.

Thermal conductivity and latent heat thermal energy storage characteristics of paraffin/expanded graphite composite as phase change material

Abstract This study aimed determination of proper amount of paraffin ( n -docosane) absorbed into expanded graphite (EG) to obtain form-stable composite as phase change material (PCM), examination of the influence of EG addition on the thermal conductivity using transient hot-wire method and investigation of latent heat thermal energy storage (LHTES) characteristics of paraffin such as melting time, melting temperature and latent heat capacity using differential scanning calorimetry (DSC) technique. The paraffin/EG composites with the mass fraction of 2%, 4%, 7%, and 10% EG were prepared by absorbing liquid paraffin into the EG. The composite PCM with mass fraction of 10% EG was considered as form-stable allowing no leakage of melted paraffin during the solid–liquid phase change due to capillary and surface tension forces of EG. Thermal conductivity of the pure paraffin and the composite PCMs including 2, 4, 7 and 10 wt% EG were measured as 0.22, 0.40, 0.52, 0.68 and 0.82 W/m K, respectively. Melting time test showed that the increasing thermal conductivity of paraffin noticeably decreased its melting time. Furthermore, DSC analysis indicated that changes in the melting temperatures of the composite PCMs were not considerable, and their latent heat capacities were approximately equivalent to the values calculated based on the mass ratios of the paraffin in the composites. It was concluded that the composite PCM with the mass fraction of 10% EG was the most promising one for LHTES applications due to its form-stable property, direct usability without a need of extra storage container, high thermal conductivity, good melting temperature and satisfying latent heat storage capacity.

Expandable Graphite For Halogen-Free Flame-Retardant of High-Density Rigid Polyurethane Foams

ABSTRACT We obtained the high-density rigid polyurethane foam (RPUF) filled with expandable graphite (EG) by airtight cast molding, and its fire performance was evaluated. The results show that the LOI values increase linearly with EG content, especially the LOI value of the 20 wt% EG-filled RPUF composites increases rapidly to 39.5% from 22.5% of pure RPUF. When the pure RPUF was burned, no clear transition process between burning spots and virgin material is observed. But when the EG/RPUF composite was burned, EG produced high-volume expanded graphite and covered the surfaces of the materials, which can prevent combustible gases from feeding the flame, and it also separates oxygen from the burning material efficiently. The thermal degradation of foam was investigated using thermogravimetric analysis (TGA). The result shows that the thermo-oxidative degradation of pure RPUF takes place in the range of 220–350°C and 450–650°C, respectively. The thermal stability of RPUF composites increased slightly when it contained 20 wt% EG. The mechanical and electrical properties of EG/RPUF were also discussed. Generally, addition of EG resulted in a slight decrease in the mechanical properties and no influence on the electrical conductivity.

Electrical and mechanical properties of expanded graphite‐reinforced high‐density polyethylene

AbstractHigh‐density polyethylene (HDPE) was reinforced with expanded and untreated graphite in a melt‐compounding process. Viscosity increased upon addition of graphite phase, with the expanded graphite (EG) showing more dramatic rise than the untreated graphite (UG) in viscosity. The increase in viscosity was attributed to the increased surface‐to‐volume ratio for the EG filler after acid treatment. Electrical conductivity also increased from that pertaining to an insulator to one characteristic of a semiconductor. The EG system showed a lower percolation threshold for transition in conductivity compared to that in the UG system. DSC results indicated that the fillers acted as a nucleating agent in inducing the crystallization of HDPE in the composites. However, the overall degree of crystallinity and melting temperature of HDPE decreased with the addition of EG and UG. Mechanical properties improved as a function of filler content but the overall enhancement was not impressive. It was conjectured that the filler–matrix interface was not optimized in the melt‐mixing process. However, the role of EG as a reinforcement phase for both electrical and mechanical properties was unambiguously established. The EG composites demonstrated potentially useful attributes for antistatic, barrier, mechanical, electrical, and cost‐effective applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:2781–2788, 2004

Intumescent char structures and flame‐retardant mechanism of expandable graphite‐based halogen‐free flame‐retardant linear low density polyethylene blends

AbstractThe structures of the intumescent charred layers formed from expandable graphite (EG)‐based intumescent halogen‐free flame retardant (HFFR) linear low‐density polyethylene (LLDPE) blends and their flame‐retardant mechanism in the condensed phase have been studied by dynamic Fourier transform infrared (FTIR), X‐ray photoelectron spectroscopy (XPS), laser Raman spectroscopy (LRS), scanning electron microscopy (SEM), differential thermal analysis (DTA) and thermal conductivity (TC) measurements. The dynamic FTIR, XPS and LRS data show that the carbonaceous structures of intumescent charred layers consist of EG and various numbers of condensed benzene rings and/or phosphocarbonaceous complexes attached by the POC and PN bonds or quaternary nitrogen products. The addition of EG can hasten the formation of these phosphocarbonaceous structures. The above results show that the flame‐retardant mechanism in the condensed phase is that the compact char structures, as observed by SEM, slow down heat and mass transfer between the gas and condensed phase and prevent the underlying polymeric substrate from further attack by heat flux in a flame. The DTA and TC data show that carbonaceous charred layers are good heat‐insulating materials, the TC value of which is only about one‐tenth of that of the corresponding blend and that they increase the oxidization temperature and decrease thermal oxidization heat of the LLDPE/EG/HFFR systems.© 2003 Society of Chemical Industry

Flammability characterization and synergistic effects of expandable graphite with magnesium hydroxide in halogen-free flame-retardant EVA blends

The flammability characterization and synergistic effects of different types of expandable graphite (EG) with magnesium hydroxide (MH) in halogen-free flame-retardant (HFFR) ethylene vinyl acetate (EVA) blends have been studied by cone calorimeter test (CCT), thermogravimetric analysis (TGA), limiting oxygen index (LOI), and UL-94 test. The results show that the particle size and expansion ratio of EG have a great effect on the flammability of the HFFR EVA/MH/EG blends. The EG with bigger particle size and higher expansion ratio can apparently increase the LOI value and improve the UL-94 flammability properties of EVA blends. The data obtained from the CCT indicate that the heat release rate (HRR), the effective heat of combustion (EHC), and the mass loss rate (MLR) of EVA/MH/EG blends decrease remarkably with increasing the particle size and expansion ratio of EG. However, the specific extinction area (SEA) data show that the addition of EG can apparently increase the smoke emission of EVA/MH/EG blends. The TGA results show that the thermal stability of EVA/MH/EG blends increase with increasing the EG particle size and expansion ratio.

Synergistic effects of expandable graphite with some halogen-free flame retardants in polyolefin blends

The synergistic effects of expandable graphite (EG) with some halogen-free flame retardant (HFFR) additives in the polyolefin (PO) blends have been studied by cone calorimeter test (CCT), thermal analysis (TGA and DTA), limiting oxygen index (LOI), and mechanical properties measurements etc. The results in this work show that EG combined with some HFFR additives, such as ammonium polyphosphate, zincborate, phosphorus-nitrogen containing compound NP28, and microcapsulated red phosphorus, can apparently increase the LOI values and improve the flammability properties of PO blends. The data obtained from the CCT indicate that the heat release rate (HRR) and effective heat of combustion (EHC) decrease and the residues of carbonaceous chars increase remarkably with addition of EG and/or the other HFFR additives. The TGA and DTA data give the positive evidence that the decreases of HRR and EHC values of the retarded PO materials are due to the increase of oxidative degradation temperature and the decrease of oxidization heat. By optimizing the formulation system and using ethylene vinylacetate copolymer as a compatilizer, the PO/EG/HFFR blends with good flame-retardant and mechanical properties have been obtained in this study.

Thermo-oxidative degradation behaviors of expandable graphite-based intumescent halogen-free flame retardant LLDPE blends

Abstract The thermo-oxidative degradation behaviors of expandable graphite (EG)-based intumescent halogen-free flame retardant LLDPE blends under different thermo-oxidation conditions have been studied by real time Fourier transform infrared (FTIR) spectroscopy or FTIR photoacoustic spectroscopy (FTIR–PAS), X-ray photoelectron spectroscopy (XPS), and wide-angle X-ray diffraction (WAXD). The real time FTIR results show that the pyrolysis of LLDPE at high temperature leads to the breakdown of PE chains and the formation of various kinds of thermal oxidation products. The addition of EG can improve the stability of thermo-oxidative degradation effectively. The FTIR–PAS and XPS data show that the thermo-oxidative degradation of LLDPE decreases remarkably with the increase of EG concentration and/or its synergists and increases dramatically with the increases of pyrolytic temperature and thermal degradation time. The thermo-oxidative degradation products have been identified as various kinds of carbonyl compounds, such as ethers, esters, ketone or carboxyl products. The WAXD measurements demonstrate that the crystalline structures of LLDPE/EG or LLDPE/EG/HFFR blends after the thermo-oxidation degradation have been destroyed partly or totally dependent on the pyrolytic temperature and thermal degradation time. The changes of crystalline structure in the LLDPE/EG/HFFR blends are due to the breakdown of LLDPE chains and a series of reaction products with FR additives.