Polymer Graphite Composites Research Articles

Thermally expanded graphite polyetherimide composite with superior electrical and thermal conductivity

Thermally expanded graphite (EG) polymer composite has high potential for application in the modern thermo-electronic industry due to cost-effectiveness and excellent electrical and thermal properties. In this study, we report electrical and thermal conductivity enhancement of expanded graphite/polyetherimide (EG/PEI) composite fabricated by a simple solution mixing technique. Expanded graphite has the potential to enable larger enhancement in properties relative to graphene nanoplatelets, through the creation of continuous graphitic networks in the composite. Solution casting technique enables preservation of worm structure of expanded graphite in the composite thus enabling the development of continuous graphitic networks throughout the composite, leading to superior property enhancement. Measurements reveal ∼19 orders of magnitude increase in electrical conductivity of composite (yielding values up to 969 Sm-1) through the inclusion of 10 wt% of EG filler, relative to pure polyetherimide (electrical conductivity ∼ 1.2 × 10−17 Sm−1). Theoretical prediction using an effective medium approach reveals the impact of continuous graphitic network on the electrical conductivity of the composites. We also find that composite with 10 wt% EG filler composition exhibits a thermal conductivity (k) value of 7.3 Wm−1K−1, representing a significant enhancement of ∼3070% compared to pure PEI (k ∼ 0.23 Wm−1K−1). Field Emmission Environment Scanning Electron Microscopy (FE-ESEM) reveals the preserved interconnected structure of EG within the composite allowing the development of a conductive interpenetrating network of polymer and filler. Raman spectroscopy, X-ray diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) analysis are further used to characterize the fillers and EG/PEI nanocomposites. Our work identifies the solution casting method as a promising approach for developing high-performance EG/PEI composites in this work.

Influence of Technological Conditions in the Formation of Electrically Conductive Thermoplastic Polymer-Graphite Composites

Influence of Technological Conditions in the Formation of Electrically Conductive Thermoplastic Polymer-Graphite Composites

Electrical conductivity of polyethylene/epoxy/graphite/carbon black composites: synergy of blend immiscibility and hybrid filler

ABSTRACT Polyethylene (PE)/epoxy (EP) blends filled with graphite/carbon black (G/CB) hybrid filler were prepared and characterized in terms of electrical conductivity. As the total filler content increased, electrical conductivity of the PE/EP/G/CB composites increased while conductivity anisotropy decreased. Also, PE/EP/G/CB composites exhibited higher electrical conductivities than the filled individual polymers and PE/EP/G composites at the same filler contents. More continuous conductive networks caused by the synergistic effect of immiscible blend matrix and G/CB hybrid filler led to significant improvement in the overall electrical conductivities of the PE/EP/G/CB composites. This work provides a good insight for further explorations into conducting polymer-graphite composites.

Combination of magnetically actuated flexible graphite–polymer composite cathode and boron-doped diamond anode for electrochemical water softening or wastewater treatment

An electrochemical reactor based on a moving graphite–polymer composite (GPC) cathode and boron-doped diamond anode is developed and used for the electrochemical water softening and treatment of artificial vacuum toilet wastewater. The magnetically actuated cathode is designed for the in situ removal of insoluble compounds, which usually precipitate on the cathode during electrochemical water treatment processes. To obtain a suitable GPC cathode, the chemical stability and conductivity of various composites and their flexion and magnetic actuator characteristics are investigated. The most suitable GPC cathode is a 0.5 mm thick polypropylene-based composite, which presents chemical stability, the lowest resistivity of all analyzed samples (5.06 ± 1.80 mΩ cm), and enables flexions up to 2.4 mm. The water softening performance of the reactor featuring this electrode was evaluated using two configurations. Water hardness was decreased up to 72% and more than 90% in mixed and separated electrolyte modes, respectively. Further investigations demonstrate that this reactor can also be used for wastewater treatment. Artificial toilet wastewater was successfully discolored for reuse as toilet flushing water. Lastly, a treatment test over 120 h demonstrates that the magnetically actuated flexible GPC cathode removes in situ deposits on its surface and requires low maintenance. The performance of the new electrode configuration is similar to that of the state-of-the-art polarity reversal system and does not shorten the electrode service life.

Electrical profile of ultra violet (UV) curable renewable polymer graphite (PG) composites

<span>The electrical profiles of the renewable polymer graphite (PG) composites upon ultra violet (UV) curing were investigated. Renewable PG films were prepared by mixing with varying weight percent of graphite (with an increment of 5 wt. % of prepared graphite) up to 30 wt.% and crosslinker. Then, the composites solution was slip casted and cured upon stimulated UV irradiation (UV accelerated weathering tester) at different time exposure (up to 1000 hours) was applied. Small changes on the functional groups of the composites were observed due to UV exposure time by Fourier Transform Infrared Spectroscopy (FTIR). Suggesting that chemical crosslink and chain scissions occurred within renewable polymer graphite composites. Further electrical profile through two point probe and four point probe method recorded visibly fluctuating values for both resistivity and conductivity within its composites range. Proposed here that the removal of organic contaminants and weak materials form both renewable polymer and graphite particles through the UV curing may have an effect on the formation of conductive network stability. </span>

Modeling the dielectric breakdown strength and energy storage density of graphite-polymer composites with dielectric damage process

Recent experimental data has demonstrated significant influences of graphite volume concentration on the dielectric breakdown and energy storage behavior of graphite-polymer composites, but no existing homogenization theory has been established to illustrate such dependence in the context of alternating current (AC) loading. In this paper we develop a novel homogenization scheme to connect the microstructural parameters of constituent phases and the AC frequency to the dielectric breakdown strength and energy storage density of the overall composite. The major microstructural features covered are the graphite volume concentration, imperfect bonding effect, graphite aspect ratio, percolation threshold, filler-dependent electron tunneling, Maxwell-Wagner-Sillars polarization, and frequency-dependent electron hopping and dielectric relaxation. A thermodynamic framework is developed to describe the evolution of a dielectric damage parameter with respect to the electric field. We highlight the developed theory with validation through the experimental data of graphite/PVDF composite over a wide range of graphite volume concentration and AC frequency. The results indicate that the dielectric breakdown strength of the graphite-polymer composite decreases with respect to the graphite volume concentration, while the energy storage density increases with it.

Heating Characteristics of Films Prepared with Polymer-Graphite Composites

Heating films were prepared by using poly(methyl methacrylate) and polybutadiene composites containing graphite. The heating film was prepared by casting the as-made polymer composite on the PET film. Copper electrodes were attached to both ends of the as-prepared film, and the heating characteristics of the film were analyzed while applying the DC voltage. The electrical conductivity and the heating temperature of the heating films depended on the size, the structure, the content, and the dispersion characteristics of the graphite in the composite. The electrical resistance of the heating film was controlled to adjust the heating temperature of the film. The relationship between the physical/chemical structure and the heating characteristics of the composite film was studied by measuring the heating temperature as functions of film thickness and resistance by using an infrared thermal imaging camera. The lower the film resistance, the higher the heating temperature of the film. The surface temperature was uniform throughout the film.

Enhancement of Graphite Functionality in Renewable Polymer Composite Properties

The preparation and characterization of composite thin films of renewable polymer graphite (PG) is disclosed. Thin films ~ 0.1 mm thick are prepared using a simple solution mixing with mass proportion of 2/1 (renewable monomer/ Methylene Diphenyl Diisocyanate, MDI), upon differ graphite content (PG0, PG5, PG10, PG15, PG20, PG25 andPG30) and drop casting at room temperature. The morphology-structure relations of renewable PG composites with respect to electrical conductivity were diagnosed using Optical microscope (OM), Fourier transform infra-red spectroscopy (FTIR) and Thermogravimetric analysis (TGA). The homogeneous random dispersion and strong interface between the graphite in the classical insulating renewable polymer matrix were observed. Thus resulting of enhancements in thermal stability with slight shift of decomposition temperature and better mechanical properties through the modulus and tensile strength increment up to ~440% and ~100% respectively. The result shows that it can simultaneously leads to renewable PG conductivity (σ) where the percolation threshold occurs at higher graphite content (PG20, PG25 andPG30) of 103 - 104 S/m. Thus, this non-petroleum based renewable polymer graphite composites have remarkably more to offer as conducting polymer composites material in multidisciplinary applications.

Preparation of Conductive Polymer Graphite (PG) Composites

The preparation of conductive polymer graphite (PG) composites thin film is described. The thickness of the PG composites due to slip casting method was set approximately ~0.1 mm. The optical microscope (OM) and fourier transform infra-red spectroscopy (FTIR) has been operated to distinguish the structure–property relationships scheme of PG composites. It shows that the graphite is homogenously dispersed in polymer matrix composites. The electrical characteristics of the PG composite were measured at room temperature and the electrical conductivity (σ) was discovered with respect of its resistivity (Ω). By achieving conductivity of 103 S/m, it is proven that at certain graphite weight loading (PG20, PG25 and PG30) attributes to electron pathway in PG composites.

Expanded Graphite–Epoxy–Flexible Silica Composite Bipolar Plates for PEM Fuel Cells

AbstractSilica impregnated expanded graphite–epoxy composites are developed as bipolar plates for proton exchange membrane (PEM) fuel cells. These composite plates were prepared by solution impregnation, followed by compression molding and curing. Mechanical properties, electrical conductivities, corrosion resistance, and contact angles were determined as a function of impregnated content. The plates show high flexural strength with 5% methyltrimethoxysilane (MTMS) addition (20 MPa) and in‐plane conductivity of 131 S cm−1 that meet the DOE target (>100 S cm−1). Corrosion current values as low as 1.09 μA cm−2 were obtained. The contact angle was found to be 80°. Power density of 1 W cm−2 was achieved with custom made expanded graphite–polymer composite plates. High efficiency values were obtained at low current regions.

Evaluation of a simple finite element method for the calculation of effective electrical conductivity of compression moulded polymer–graphite composites

Finite element (FE) techniques can be used for the calculation of the effective properties of random heterogeneous materials, the required input simply consisting of phase properties and representative three-dimensional models of material microstructure. This approach has been widely exploited in recent years, although limited by the considerable amount of computational power required to obtain statistically accurate results. By using simple microstructural models of compression moulded polymer–graphite composites and a FE code modified for execution on graphical processing units, we show that reliable predictions of electrical properties for these materials can now be obtained in a reasonable computational time and with acceptable accuracy and precision. By using an approach based on design of experiments, we also perform a set of simulations aimed at determining the microstructural details which are most significant for the effective properties of these materials.

Effect of methanol absorption on properties of polymer composite bipolar plates for direct methanol fuel cells

The effect of the methanol absorption on thermal, mechanical and electrical properties of highly-filled graphite polymer composite plates destined for direct methanol fuel cells was investigated. Poly (vinylidene fluoride) (PVDF), Poly (phenylene sulphide) (PPS) and Poly (propylene Glycol) (PPG) compounds were considered in this study. It was shown that the absorbed amount of methanol for PVDF compound increased linearly with the square root of time as in Fickian diffusion. The methanol uptake in the saturation stage reached the value 2% after 1500 h methanol exposure. A significant change of the thermal conductivity as well as the flexural strength was reported for PVDF compound after methanol exposure, while the electrical conductivity was not altered. Additionally PPS compound exhibited a long term resistance to methanol exposure and met to a great extent the requirements defined by the US Department of Energy on the thermal and electrical conductivity. The PPS compound is a potential candidate to be used for applications as bipolar plates in direct methanol fuel cells.

CNTs nanostructuring effect on the properties of graphite composite bipolar plate

Intent of present investigation is to improve the properties of graphite–polymer composite bipolar plate by nanostructuring. This involves the incorporation of different vol.% of multiwall carbon nanotubes (MWNTs) in graphite–polymer composite bipolar plate. It has been found that by inclusion of 1 vol.% of MWNTs in graphite composite plate, the electrical and thermal conductivity of nanocomposite increased by 100%. The thermal conductivity of nanocomposite plate increases from 1 W/m K to 13 W/m K in through-plane and in-plane from 25 W/m K to 50 W/m K at 1 vol.% of MWNTs. This significant enhancement is due to the orientation of MWNTs in all the directions of composite, positive synergistic effect of MWNTs and heat transfer along the axis directions. However, bending strength of nanocomposite increases by 25% and maximum augmentation is in case of 1 vol.% of MWNTs. The improvement in conductivity of nanocomposite plate is due to an increase in the electron transfer ability within the composite plate which influences the I– V performance of ultimate fuel cell. These observations confirm that the optimal content of MWNTs is 1 vol.%, in graphite–polymer composite.

Theoretical Analysis of Conductivity for Composite Bipolar Plate

Conductive composite bipolar plate is made of composite materials filled with high content conductive filler. The conductivity of this bipolar plate is influenced by many factors. It is difficult to use a formula to accurately calculate its conductivity, and current models have certain defaults. In this paper, in view of the contact resistance, a model is estab- lished and the conductivity formula has been educed. The conductivity formula reveals some factors that influence the conductivity, especially the particle size and pressure. Several ways to improve the conductivity of the composite material are discussed. Conductive composite bipolar plate is the mainstream development direction of bipolar plate. The composite mate- rials consisting of conductive graphite filler and resins adhe- sives can be produced into bipolar plates with flow field through compression moulding or injection moulding tech- nology, which is high production efficiency and easy to be mass produced, and it is a significant decline in costs. Poly- mer composite bipolar plate has the same performance of corrosion resistance as graphite bipolar. Graphite polymer composite bipolar plates are made of composite materials filled with high content conductive filler. The high conductivity of bipolar plate demands for high content of graphite. But the mechanical performance will decrease if the content of graphite is much too high. So, the key problem of how to meet the requirement of conduc- tivity of a composite bipolar plate with the addition of a small amount of conductive fillers is needed to be resolved. Theoretical analysis is necessary on the basis of the conduc- tive mechanisms of the composite materials. There are many kinds of theories about the electric conductivity mechanism which is the result of the combination of those theories in general view. However, most of the theories are suit for composite materials filled with low content conductive filler. For those filled with high content, we argues that the mutual contact of the filler particles is the main contribution to the conductivity of composite materials, while the effect of the tunnel current on the conductivity is so little that it can be negligible.

Carbon-polymer biocomposites for amperometric sensing

New electrochemical sensing biocomposite materials are reported. These materials are based on polymer technology and are prepared mixing graphite powder, a non-conducting polymer resin and a lyophilized enzyme. The resulting biosensing material is inexpensive, robust, polishable and easy to machine. A survey of potentially suitable polymeric matrices was carried out. Epoxy, silicone, methacrylate and polyester polymers have been used to prepare rigid conducting composite materials of the graphite-polymer type. For each material, an optimal graphite content was determined. Amperometric transducers built with these materials were characterized electrochemically using cyclic voltammetry and linear-sweep voltammetry. Their linear response to hydrogen peroxide was evaluated. The applicability of these conducting polymer-graphite composites has been extended to the construction of conventional glucose biosensors. In these devices the conducting composite is bulk-modified with the addition of glucose oxidase. The amperometric detection of hydrogen peroxide serves as the analytical signal. Following the same construction method, it is also possible to obtain other biosensing systems. New biocomposites have been prepared, using a different enzyme in each case, i.e. acetylcholinesterase and peroxidase.

Studies of semiconducting organic polymer-graphite composites from d.c. to microwave frequencies

Our samples are mixtures consisting of particles of graphite dispersed within a matrix of a doped substituted polyacetylene. The electrical impedance spectra are discussed in terms of inhomogeneity and intrinsic contributions. The frequency dependence of the a.c. conductivity and permittivity has been measured at frequencies between 10 kHz and 12 GHz. The a.c. conductivity is given by the power-law relation σ( ω) ∝ ω n with 0 < n < 0.4 at frequencies below 30 MHz, 0.5 < n < 1 at frequencies between 30 MHz and 2 GHz and 1 < n < 2 at frequencies between 2 GHz and 8 GHz. A saturation occurs at approximately 8 GHz. Various theoretical approaches are presented in order to support such behaviour.

Corrosion of Graphite Composites in Phosphoric Acid Fuel Cells

Polymers, polymer-graphite composites and different carbon materials are being considered for many of the fuel cell stack components. Exposure to concentrated phosphoric acid in the fuel cell environment and to high anodic potential results in corrosion. Relative corrosion rates of these materials, failure modes, plausible mechanisms of corrosion and methods for improvement of these materials are investigated.