Amount Of Expanded Graphite Research Articles

Efficient flame retardancy of polypropylene by cobalt ions doped phytate melamine synergized with expandable graphite

Maintaining a delicate balance between flame retardancy and amount of expandable graphite (EG) in flame retardant polypropylene (PP) is still a formidable challenge, primarily due to the lower flame-retardant efficiency of EG. In order to address this concern, a novel cobalt-doped nanosheet flame retardant (PAMA-Co) was fabricated by a hydrothermal method utilizing phytic acid (PA) and melamine (MA), exhibiting a promising potential in constructing synergistic EG flame retardant PP. Significantly, the incorporation of only 7 wt% PAMA-Co/23 wt% EG system raises the limiting oxygen index (LOI) of PP to 27.3% and UL-94 V0 level, which indicates the excellent synergistic flame-retardant efficiency of PAMA-Co. Furthermore, both the peak heat release rate (PHRR) and the peak smoke production rate (PSPR) of PP composites with 7 wt% PAMA-Co/23 wt% EG are substantially reduced, exhibiting an 81.6% lower PHRR and 87.8% PSPR compared to pure PP. The excellent flame-retardant efficiency is attributed to the following mechanisms: Gas-phase dilution, catalytic cross-linking charring effect, and the suppression of the EG “popcorn effect” of PAMA-Co. In summary, this work not only advances an understanding of flame-retardant mechanisms but also offers a practical, green strategy for enhancing the safety and utility of PP in various applications.

Spatial confinement: An effective strategy to improve H2O and SO2 resistance of the expandable graphite-modified TiO2-supported Pt nanocatalysts for CO oxidation

The expandable graphite (EG) modified TiO2 nanocomposites were prepared by the high shear method using the TiO2 nanoparticles (NPs) and EG as precursors, in which the amount of EG doped in TiO2 was 10 wt.%. Followed by the impregnation method, adjusting the pH of the solution to 10, and using the electrostatic adsorption to achieve spatial confinement, the Pt elements were mainly distributed on the exposed TiO2, thus generating the Pt/10EG-TiO2–10 catalyst. The best CO oxidation activity with the excellent resistance to H2O and SO2 was obtained over the Pt/10EG-TiO2–10 catalyst: CO conversion after 36 hr of the reaction was ca. 85% under the harsh condition of 10 vol.% H2O and 100 ppm SO2 at a high gaseous hourly space velocity (GHSV) of 400,000 hr−1. Physicochemical properties of the catalysts were characterized by various techniques. The results showed that the electrostatic adsorption, which riveted the Pt elements mainly on the exposed TiO2 of the support surface, reduced the dispersion of Pt NPs on EG and achieved the effective dispersion of Pt NPs, hence significantly improving CO oxidation activity over the Pt/10EG-TiO2–10 catalyst. The 10 wt.% EG doped in TiO2 caused the TiO2 support to form a more hydrophobic surface, which reduced the adsorption of H2O and SO2 on the catalyst, greatly inhibited deposition of the TiOSO4 and formation of the PtSO4 species as well as suppressed the oxidation of SO2, thus resulting in an improvement in the resistance to H2O and SO2 of the Pt/10EG-TiO2–10 catalyst.

Suppression effect of expandable graphite on fire hazard of dust layers

Expandable graphite (EG) has potential to inhibit the fire hazard of dust layers. This suppression effect was systematically studied by comparing with that of traditional inertants such as CaCO3 and NaHCO3. The thermal expansion of EG can generate compact char layers with low thermal conductivity, which effectively inhibited the heat transfer between the heat source and the surrounding dusts. Oxygen diffusion was also hindered between the dust layer and the environment. Therefore, a small amount of EG could achieve a suppression effect for layer fires equivalent to a large amount of traditional inertants. A small amount of traditional inertants promoted the combustion of the non-metal dust layer, a phenomenon that did not occur while using EG. In addition, EG also acted as an effective flame retardant on the flame spread of the non-metallic dust layer under inclined conditions. Most important, EG had a suppression effect on down-flowing moving pool fires of non-metallic dust layers and the violent combustion of metal dust layers. This shows great potential not available in traditional inertants. EG could be considered as a novel and well-integrated dust layer fire inhibitor in process industries handing combustible dusts.

Thermal performance evaluation of isopropyl stearate-expanded graphite based shape stabilized phase change material composite targeting cold chain application

The prime regard of this this study is to provide major insights on energy storage system using phase change materials (PCM) within cold-cool temperature ranges (2–15 °C). Isopropyl stearate (IPS) had been employed as PCM, and expanded graphite (EG) was considered to act as a supporting matrix. Five composites with fixed loading of IPS in a varying amount of EG were prepared in the ratios as 10:1, 10:1.25, 10:1.5, 10:1,75, 10:2. After taking leakage of IPS from EG into account, IPS/EG-based phase change material composite with a mass ratio of 10:1.25 was chosen for thermal buffering performance analysis. Energy storage and thermophysical properties of IPS/EG composites were investigated via FESEM, FTIR, TGA, and DSC. Field emission scanning electron microscope (FESEM) micrographs proved that PCM was uniformly distributed in the porous network structure of EG. All composites exhibited their melting point between 8.5 °C and 9.5 °C. Fourier transforms infrared spectroscopy (FT-IR) confirmed that no chemical interactions had occurred between IPS and EG, and IPS was well contained in the pores of EG. From differential scanning calorimetry (DSC) measurements, a phase change enthalpy of 172.25 ± 2.05 J g−1 and stable performance during 250 thermal cycles with IPS/EG (10:1.25) were recorded. From thermo gravimetric analysis (TGA), the decomposition temperature of all composites was found to be at 188 °C, which is considerably higher than the working temperature range. The thermal buffering performance of PCM-composite was verified by incorporating them in a vaccine carrier box. The box was then exposed to three different temperatures, i.e., 30 ± 1, 40 ± 1, 50 ± 1 °C as well as areal-time application by exposing the box to direct sunlight. After analyzing the composites’ performance, thus prepared IPS/EG composite has a substantial potential to be applied as a temperature controlling system for products that need to be stored below 15 °C during their transportation.

Stearic acid/expanded graphite composite phase change material with high thermal conductivity for thermal energy storage

In this study, expanded graphite (EG) was added to melted stearic acid (SA) by the melt blending method to prepare SA/EG composite phase change material (PCM) with different ratios. EG with ultra-high porosity and large specific surface area can effectively adsorb melted SA through capillary force and van der Waals force. The results showed that when the loading amount of EG was 12 wt.%, almost no liquid leakage occurred and the composite showed excellent stability. In addition, the three-dimensional network structure of EG interconnection provides an efficient heat transfer path and reduces the thermal resistance of the interface. Therefore, the thermal conductivity of the composite was as high as 6.54 W m−1 K−1, which was 19.179 times higher than that of pure SA. Furthermore, the melting enthalpy and melting temperature of the composite were 163.35 J g−1 and 67.08 °C, respectively. X-ray diffraction and Fourier transform infrared spectroscopy shown that physical interaction instead of chemical reaction happened between EG and SA. When the mass fraction of EG is 12 wt.%, the composite PCM shows a relatively more balanced and uniform thermal image compared with SA, and the heat storage rate of the composite PCM was about 2.3 times of SA, and the heat release rate was 3.1 times of SA. In addition, the composite PCM showed excellent thermal stability, chemical stability, and cyclic stability, indicating that the working performance of the composite PCM was relatively stable within the temperature range of 100 °C.

Effects of Various Types of Expandable Graphite and Blackcurrant Pomace on the Properties of Viscoelastic Polyurethane Foams.

We investigated the effect of the type and amount of expandable graphite (EG) and blackcurrant pomace (BCP) on the flammability, thermal stability, mechanical properties, physical, and chemical structure of viscoelastic polyurethane foams (VEF). For this purpose, the polyurethane foams containing EG, BCP, and EG with BCP were obtained. The content of EG varied in the range of 3–15 per hundred polyols (php), while the BCP content was 30 php. Based on the obtained results, it was found that the additional introduction of BCPs into EG-containing composites allows for an additive effect in improving the functional properties of viscoelastic polyurethane foams. As a result, the composite containing 30 php of BCP and 15 php of EG with the largest particle size and expanded volume shows the largest change in the studied parameters (hardness (H) = 2.65 kPa (+16.2%), limiting oxygen index (LOI) = 26% (+44.4%), and peak heat release rate (pHRR) = 15.5 kW/m2 (−87.4%)). In addition, this composite was characterized by the highest char yield (m600 = 17.9% (+44.1%)). In turn, the change in mechanical properties is related to a change in the physical and chemical structure of the foams as indicated by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analysis.

Synergistic Action of Polyethylene Glycol/Expanded Graphite/Cellulose Nanofibers With Superior Infrared Stealth Performance

A series of high comprehensive performance composite phase-change materials (PCMs) were designed and prepared by a physical blending and evaporation method. Cellulose nanofibers (CNF) were introduced as supporting materials to keep the shape of polyethylene glycol (PEG) stable during the phase-change process, and expanded graphite (EG) was used to synergize with the PEG to enhance the infrared thermal stealth performance. The comprehensive performance and structure–property relationships of the composite PCMs were investigated by means of various characterization techniques. The CNF30/PEG69/EG1 composite exhibited the best comprehensive performance: a high PEG melting enthalpy of 144.3 J/g due to a high crystallinity of the PEG, good thermal stability, a shape stabilization effect and superior IR attenuation performance. The EG was proved to be an effective supporting material which contributed to the enhancement of the crystallinity of PEG, and played an important role as a nucleating agent in the crystallization process of the PEG. The synergistic effect of PEG and the small amount of EG gave the composites excellent infrared stealth performance.

Intumescent polypropylene: Interactions between physical and chemical expansion

SummaryTo decrease the reaction to fire of a highly flammable plastic, polypropylene (PP), the concept of intumescence was applied. Two intumescent systems were designed on the basis of different mechanisms: physical expansion with expandable graphite (EG) and chemical expansion with modified ammonium polyphosphate (AP). Fire behavior of PP containing EG, AP, or an AP/EG mixture with a total loading of 10 wt% was evaluated by cone calorimetry at 35 kW·m−2. Thermocouples allowed measuring the temperature at the backside or inside samples over time and evaluating the thermal barrier of these intumescent materials. Two grades of AP (difference in composition) and several grades of EG (difference in expansion characteristics) were compared. Mixing AP and EG does not create a synergistic effect in studied conditions. Contrarily, the incorporation of small amount of EG in PP‐AP modifies heat transfer in the coating, creating a strong anisotropy. Graphite worms are trapped vertically into the expanded AP, which increases the transverse heat conductivity (lower efficiency of the thermal barrier) and decreases the fire performance. This phenomenon disappears in thicker specimens. While a higher expansion volume of graphite worms improves fire performances of PP with only small amount of EG (1 wt%), this effect is not noticeable with AP/EG mixtures.

Thermal performance enhancement of a phase change material with expanded graphite via ultrasonication

It is desirable to improve the performance of phase change materials (PCM)-based thermal energy storage (TES) systems because it increases energy efficiency while decreasing primary energy consumption for low environmental loading. Given that PCM suffers from low thermal conductivity (e.g., due to high latent heat capacity and low phase separation), we investigated several efficient options to improve the thermal conductivity of organic PCM (n-octadecane) based on the addition of (0.1wt%) expanded graphite (EG). The suspension prepared via ultrasonication led to an improvement of 40% in thermal conductivity corresponding to 0.28W/m when compared to that of n-octadecane corresponding to 0.20W/mK. Additionally, the ultrasonication effectively dispersed EG in the PCM for an extended duration relative to the stirring method. A PCM-EG reaction was not evident under ultrasonication conditions. Thus, the thermal conductivity of the PCM exhibited maximum improvement when the two conditions involving extremely low amount of EG and its stable dispersion under sonication condition were maintained. The study demonstrated that a significant improvement in thermal conductivity is obtained with a very low amount of EG and that dispersion stability is obtained even with short ultrasonication times.

Impact of expandable graphite on flame retardancy and mechanical properties of rigid polyurethane foam

Flame retardant (FR) and mechanical performance properties of two different rigid polyurethane foams (RPUFs) containing expandable graphite (EG) as FR additive were studied. The impact of EG on the foam properties were evaluated. Cellular structures were less homogeneous in foams containing EG. Thermal conductivities of RPUF increased slightly with EG addition. FR properties of the foams were evaluated by limiting oxygen index (LOI) test, vertical burning test (UL94), and cone calorimeter test. The addition of EG improved the FR performance and increased the density of the foams. For example, LOI value was increased from 18.4 to 25.2 in EG10PU1, whereas for EG10PU2, LOI increased from 19.2 to 29.8. In UL94 test, EG10PU1 reached V‐1 rating, while EG8PU2 passed V‐0 rating. Results from cone calorimeter test showed that the EG in the RPUF effectively reduced heat release rate, total heat released, total smoke production, and mass loss rate with increase in EG. This improvement was more efficient for the higher density foam. In addition, low loading of EG in PU1 increased the compression performance but decreased as the amount of EG was further increased. POLYM. COMPOS., 40:E1705–E1715, 2019. © 2018 Society of Plastics Engineers

Investigation on the thermophysical properties and transient heat transfer characteristics of composite phase change materials

In this paper, the thermophysical properties and transient heat transfer characteristics of composite phase change materials (CPCMs) were investigated numerically and experimentally in details. Two kinds of microencapsulated phase change materials (MEPCMs) paraffin with melting temperatures of 28 and 37 °C, respectively, were employed in this paper. The CPCMs were fabricated by intercalating expanded graphite (EG) with average diameter of 45 m into MEPCMs. The addition amount of EG were 10%, 30%, and 50% in weight. The thermophysical properties, including density, thermal conductivity and specific heat, of the CPCMs were measured and the latent heat and specific heat were calculated from data with differential scanning calorimetry (DSC). In the experiment, the square enclosure has a cross-section dimension of 100 by 100 mm and it was 15 mm in thickness. The top side wall of the enclosure was heated with isothermal cooling on the bottom side wall while the remaining side walls were thermally insulated. The numerical model which is designed to meet the conditions of the experimental parameters was employed to examine the transient heat transfer characteristics for the CPCMs in the enclosure. Results show that MEPCMs with increasing EG would increase the thermal conductivity and the heat transfer rate. However, the specific heat of CPCMs would decrease. The numerical predictions agree well with the experimental data. In addition, the results disclose that the CPCMs could enhance the rate of heat transfer and energy storage, but minor loss in total energy storage.

Enhancement of physical and reaction to fire properties of crude glycerol polyurethane foams filled with expanded graphite

The reation to fire of polyurethane foams (PUFs) has been a subject of increasing relevance, so in this study the reaction to fire performance of PUFs derived from crude glycerol (CG) has been improved using expanded graphite (EG). The influence of different loadings of EG on the physical–mechanical properties of composite foams has been assessed and the results obtained show that it has significant positive impact. Moreover, the reaction to fire of the PUF and EG/PUF composites has been investigated and the results obtained showed that the fire behavior of composite foams containing as little as 5 wt% of EG are significantly improved. Indeed a dramatic reduction of the rate of heat release, mass loss rate, effective heat of combustion and specific extinction area, has been observed even for a relative low amount of EG. Likewise, the use of Infrared Thermography as a function of time has proven that, when EG is used, the combustion stops suddenly and the temperature drops sharply compared with the behavior of the unfilled PUF sample, which suggests that EG acts like a flame extinguisher. The results obtained have proven the suitability of CG for the production of PUFs and that the addition of EG considerably improves the reaction to fire of composite foams.

Largely improved thermal conductivity of HDPE/expanded graphite/carbon nanotubes ternary composites via filler network-network synergy

Utilizing the synergistic effect of various fillers is an efficient strategy to enhance the thermal conductivity of polymer composites, in which the key is to modulate their dispersion and network formation in polymer matrix. In this work, expanded graphite (EG) was individually added into high density polyethylene (HDPE) to fabricate first the binary composites through melt blending. The electrical conductivity of the prepared composites was measured to determine the percolation threshold for HDPE/EG composites. Then HDPE/EG composites with three compositions, representing below percolation, just percolation and above percolation, respectively, were chosen as matrix and melt mixed with carbon nanotubes (CNTs) to make HDPE/EG/CNTs ternary composites. It was found that adding CNTs results in a linear increase of thermal conductivity for HDPE/EG composites with composition below percolation, along the line by adding the same amount of EG. While a jump of thermal conductivity was observed by adding CNTs for HDPE/EG composites with composition just and above percolation. The electrical conductivity and rheology property were measured and SEM experiment was carried out to explore the filler dispersion and their network formation in HDPE matrix. All the results suggested a possible location CNTs in EG filler network for HDPE/EG composites with composition just and above percolation. Thus the formation of CNTs network within EG network is attributed to the main reason for the largely enhanced thermal property. This work endows a new enlightenment to fabricate the composites with a great thermal conductivity.

A study on mechanical, thermal and flame retardant properties of epoxy/expandable graphite composites

PurposeThe purpose of this paper is to investigate the effect of expandable graphite (EG) plates’ incorporation on the mechanical, thermal and fire-retardant properties of an epoxy–aliphatic amine system. In addition, the optimum amount of EG in epoxy/EG composites is determined to achieve the best thermal and mechanical properties at the same time.Design/methodology/approachThe epoxy/EG composites were prepared by using (1-4) phr of EG. The morphological structure of epoxy/EG composites was studied by using scanning electron microscopy. The thermal, flame-retardant and mechanical properties of epoxy/EG composites were evaluated by using thermogravimetric analysis (TGA), oxygen index test and dynamic mechanical analysis and tensile and impact test, respectively.FindingsTGA results showed that the incorporation of EG to the epoxy resin increased the initial decomposition temperature and residue weight of the composites. It was found that, with increasing EG concentration up to 4 phr, the oxygen index, glass transition temperature and Young’s modulus of epoxy/EG composites increased up to 60 per cent, 4.1°C and 50 per cent, respectively. On the other hand, the sample with 2 phr EG provided the maximum values of tensile strength, storage modulus, cross-linking density, ultimate tensile strain and impact strength.Practical implicationsPrepared epoxy/EG composites can be used as halogen-free flame-retardant composites. The proposed process for the preparation of the composites is simple and can easily be implicated in the industry.Originality/valueTo the best of the authors’ knowledge, there is no other publication that considers mechanical, thermal and fire-retardant properties of epoxy/EG composites in one paper. In this work, the optimum concentration of EG in epoxy/EG composites was determined, considering all these properties.

Effect of expandable graphite on flame retardant, thermal and mechanical properties of thermoplastic polyurethane composites filled with huntite&hydromagnesite mineral

The effect of expandable graphite (EG) was studied on the flame retardant, thermal and mechanical properties of thermoplastic polyurethane (TPU) containing huntite&hydromagnesite (HH). According to the flammability tests results, the synergistic interaction was observed between HH and EG. The maximum limiting oxygen index (LOI) value was observed at a ratio of 1:1 (HH:EG) and the highest vertical burning test (UL-94) rating of V0 was observed at a ratios of 4:1, 3:2 and 1:1. The synergistic interaction between EG and HH was also deduced at low percentage of EG (10%) by the help of the mass loss calorimeter test results. Mechanical test observations revealed that the inclusion of HH reduced the tensile strength and elongation at break values and increased the elastic modulus and glass transition temperature of pristine TPU. The addition of EG was further improved the elastic modulus of composites as the loaded amount of EG increased.

Thermal Measurements on Polymeric Epoxy-Expandable Graphite Material

Combustion measurements, such as heat release rate, critical flux, time-to-ignition, ignition temperature, thermal inertia, and kinematics—activation energy as well as preexponential factor—on epoxy polymer (Prime™20LV) with expandable graphite (EG) inorganic filler of different weight percentage composites, are conducted using the Dual Cone Calorimeter, the thermogravimetric analysis (TGA), and Linseis (Germany) THB100 Transient Hot Bridge thermal conductivity analyser. The results indicate that increasing the amount of EG in polymer composite leads to reduction in the critical flux, the time-to-ignition, the ignition temperature, the thermal inertia, the average thermal conductivity, and the activation energy (from 159.1 ± 2.3 to 145.9 ± 3.1 kJ/mol for neat epoxy to 3 wt.% EG-epoxy) of the composite samples. There is, however, an increase in the heat of gasification with increasing EG content.

Study on Properties of Expandable Graphite in Waterborne Fire Retardant Coating

Influence of addition amount and granularity of expandable graphite on the facing waterborne silicone-acrylic emulsion fire retardant coating was investigated. The results show that the waterborne silicone-acrylic emulsion fire retardant coating adding expandable graphite can improve its flame retardant time. The coating gets the best flame retardant effect when the addition amount of expandable graphite is 4%(by mass). The smaller granularity of expandable graphite can be more effective for improving the fire retardant performance.

Thermal and mechanical behaviour of flexible polyurethane foams modified with graphite and phosphorous fillers

Flexible polyurethane foams (FPF) are polymer materials that have high flammability. Fyrol PNX (FPNX) and expandable graphite (EG), have been used to modify the properties of these materials. The aim of this study was to assess the possibility of improving the thermal stability and flame retardancy of FPF by the addition of FPNX and EG fillers. The prepared foams were characterised by their apparent density, hardness, flexibility, irreversible strain and linear flammability, as well as thermogravimetric analysis (TGA), dynamic mechanical analysis, Fourier transform infrared spectroscopy (FT-IR) and pyrolysis combustion flow calorimetry (PCFC) measurements. The apparent density, hardness, flexibility and irreversible strain results showed that the addition of graphite and phosphorous fillers to the FPF makes slight changes to the mechanical properties, which remain within the acceptable norms. It was also observed that reducing the amount of Fyrol PNX and replacing it with the same amount of EG allowed similar values of linear flammability to be obtained with a simultaneous increase in thermal stability, as shown in the TGA study and the PCFC test. Moreover, it was found that the modification of flexible polyurethane foam by the addition of a mixture of FPNX and EG fillers allows the best properties of this type of materials to be obtained. This result indicates that this type of modification could be an effective way to improve the thermal stability of FPF.

Mechanical and tribological properties of acrylonitrile–butadiene rubber filled with graphite and carbon black

In this work, acrylonitrile–butadiene rubber (NBR)/expanded graphite (EG)/carbon black (CB) micro- and nanocomposites were prepared by two different methods, and the resulting mechanical and tribological properties were compared with those of NBR/CB composites. Meanwhile, the effects of graphite dispersion and loading content, as well as the applied load and sliding velocity on the tribological behavior of the above composites under dry friction condition were also evaluated. The worn surfaces were analyzed by scanning electron microscopy (SEM) to disclose wear mechanism. As expected, the better the dispersion of graphite, the more remarkable enhancement on tensile and dynamic mechanical properties, and the greater reduction in the coefficient of friction (COF) and specific wear rate (Ws). It was found that a small amount of EG could effectively decrease COF and Ws of NBR/CB composites because of the formation of graphite lubricant films. The COF and Ws of NBR/CB/EG composites show a decreasing trend with a rise in applied load and sliding velocity. NBR/CB/EG nanocomposite always shows a stable wearing process with relatively low COF and Ws. It is thought that well-dispersed graphite nano-sheets were beneficial to the formation of a fine and durable lubricant film.

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

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.