Photopolymers are one of the fastest growing 3D printing material classes, despite the lack of diversity in performance or composition. A simple addition of graphite nanopowder is explored for ...tailoring aliphatic polycarbonate performance and enhancing advanced material properties, targeting the mechanical performance of the norbornene‐containing poly(norbornene trimethyl carbonate) using poly(trimethyl propane allyl ether carbonate) for thermoset formation using thiol‐ene photochemistry. A 30 wt% graphite‐composite photopolymer ink displays shear thinning behavior suitable for pneumatic direct ink write (DIW) printing, along with enhanced elastic modulus (15–542 MPa) and an increase in ultimate strength (2–22 MPa for the composite ink) without significant variation in the glass transition temperature. The composites are further demonstrated as 4D materials including shape memory, conductivity, and recyclability, with this work serving as a guide for designing DIW inks from photopolymer resins.
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.
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•Dielectric breakdown strength and energy storage density are predicted by homogenization scheme and validated by experiments.•Energy storage properties of composite are connected to microstructural features of constituent phases and interface effects.•Thermodynamic evolution equations with dissipation potential and driving force are derived for dielectric damage process.
The bipolar plate is one of the most significant components of a polymer electrolyte membrane (PEM) fuel cell, and contributes substantially to the cost structure and the weight of the stacks. A ...number of graphite polymer composites with different fabrication techniques have been reported in the literature. Graphite composites show excellent electromechanical properties and chemical stability in acidic environments. Compression and injection molding are the most common manufacturing methods being used for mass production. In this study, a competitive bipolar plate design and fabrication technique is adopted in order to develop a low-cost and light-weight expanded graphite (EG) polymer composite bipolar plate for an air-breathing PEM fuel cell. Cutting molds are designed to cut fuel flow channels on thin expanded graphite (EG) sheets (0.6 mm thickness). Three separate sheets, with the flow channel textures removed, are glued to each other by a commercial conductive epoxy to build a single bipolar plate. The final product has a density of 1.79 g/cm3. A bipolar plate with a 20 cm2 active area weighs only 11.38 g. The manufacturing cost is estimated to be 7.77 $/kWe, and a total manufacturing time of 2 minutes/plate is achieved with lab-scale fabrication. A flexural strength value of 29 MPa is obtained with the three-point bending method. A total resistance of 22.3 milliohms.cm2 is measured for the three-layer bipolar plate. We presume that the suggested design and fabrication process can be a competitive alternate for the small-scale, as well as mass production of bipolar plates.
The electrochemical behavior of Prussian blue films galvanostatically electrodeposited on graphite+epoxy-resin composite electrodes was studied. The composite electrodes were prepared with different ...graphite proportions and their effect on electrochemical reduction of the Prussian blue was analyzed by means of the uncompensated resistance approximation and the electrical percolation theory. The results suggest that the electrode with 60% graphite reaches the second percolation threshold and its internal structure changes from a compact to a porous one. Mechanical tensile tests were performed in order to confirm the critical behavior of this material at the percolation thresholds. The percolation threshold measured agrees with those calculated theoretically.
The surface of indium tin oxide (ITO) and graphite+polymer composite electrodes can be modified by Nafion
® films containing a little amount of dispersed electroactive substances, such as ...phthalocyanines. This procedure allows the recovery of electroanalytical information on the electroactive deposited substance. The preparation methods for these types of modified electrodes are discussed from the voltammetric results obtained in this work. The Nafion
® net acts as a permeable membrane to the hydrogen ions. Furthermore, the presence of methylviologen within the Nafion
® film makes the electron transport throughout this membrane easy.
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.
The impedance spectra of graphite + polyethylene and graphite + epoxy composite electrodes were recorded for different concentrations of aqueous KCl. The spectrum of the graphite + polyethylene ...composite could be explained using percolation theory because of the weak interaction between the graphite particles and the polymer. However, the chemical interactions taking place in the graphite + epoxy system prevented it being considered as a conducting-insulating percolation problem.
A facile method with the advantage of using only one single solvent throughout the whole processing was introduced to prepare graphite nanoplatelet (GNP) filled thermoplastic polyurethane (TPU) ...nanocomposites. Morphological studies showed that the employed method could provide the uniform dispersion of GNPs in the TPU matrix. Storage modulus of the nanocomposites was increased with increasing GNP content, and the improvement was more obvious at temperatures below the glass transition temperature (
T
g) of TPU. For the nanocomposite that contains 3.9
vol% (the maximum loading employed in this study) of GNP, it still showed a long elongation at break of over 600%. Thermogravimetric analysis (TGA) showed that the incorporation of GNPs could improve the thermal stability of the nanocomposites. In addition, cone calorimetry results showed that the GNPs could act as intumescent flame retardant and significantly reduced the heat release rate (HRR), thus improved the flame retardancy of the TPU matrix.
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