Graphite Nanoplatelet Composites Research Articles

Electrical Conductivity of PA6/Graphite and Graphite Nanoplatelets Composites using Two Processing Streams

The percolation threshold (PT) of any polymer/particulate carbon composite depends on the processing, the dispersed state of the filler, the matrix used and the morphology attained. Sonication technique was used to make PA6/G and PA6/GNP composites employing in situ polymerisation, after which their electrical conductivity behaviours were investigated. While overhead stirring and horn sonication were used to distribute and disperse the carbon fillers, the composites were made in 2 streams 40/10 and 20/20. The 40/10 stream implies that while dispersing the carbon fillers in PA6 monomer, 40% amplitude of sonication was applied for 10 minutes whereas the 20/20 stream implies 20% amplitude of sonication for 20 minutes. In both streams, the dispersing strain imparted on the monomer/carbon mixture was 400 in magnitude. Purely ohmic electrical conductivity behaviour was attained at 9.75 G wt. % for IG 40/10 system. For composites in the IG 20/20 system, same was attained at 10.00 G wt. %. Electrical conductivity sufficient for electrostatic discharge applications was achieved above 15 G wt. % in the IG 40/10 system. Using the power law percolation theory, percolation threshold was attained at 9.7 G wt. % loading in IG 40/10 system, while same was attained at 7.6 G wt. % loading in IG 20/20 system. For the GNP based systems, percolation threshold occurred at 5.2 GNP wt. % in the INP 40/10 system whereas same occurred at 7.4 GNP wt. % in the IG 20/20 system.

Modelling of mechanical properties of Pa6 based reinforced graphite and graphite nano platelets composites using different aspect ratio

PurposeThis study aims to fabricate and study the effect of five cumulative graphite (G) and graphite nanoplatelets (GNP) filler loading composites by polymerising PA6 precursor; monomer epsilon caprolactam with the two carbons in situ while taking cognisance of the mixing effects (simultaneous stirring and sonication at varying amplitudes and duration). Different aspect ratios will be used to model the two streams of polymerisations.Design/methodology/approachHigh viscosity extrusion grade PA6 and synthetic G of less than 2 µm particle size were used as fillers. GNP and G are dried for 6 h in vacuum oven at 90°C. Prior to in situ polymerisation, probe sonication was applied to disperse fillers in molten ɛ-caprolactam, the PA6 monomer. Five carbon loadings were made, that is 5–25 Wt.% for G and 0.5–2.5 Wt.% for GNP composites. Two different sonification regimes were applied 20% sonication amplitude for 20 min (20/20) and 40% sonication amplitude for 10 min (40/10).FindingsBetter tensile properties were achieved using the 20/20 processing streams for both G and GNP. The G- and the GNP-based composites systems of the 20/20 processing stream had tensile modulus and yield strength retained or improved above the unfilled PA6 value. The highest modulus obtained in the 20/20 streams are 1,878 and 1,201 MPa, respectively, for GNP and G at the highest loading levels, while the 40/10 processing streams had 963 and 1,247 MPa, respectively, for the GNP and G.Originality/valueTo the best of the authors’ knowledge, nobody has ever used sonification amplitude to compare mechanical properties.

Enhanced electrical conductivity and structural, mechanical characterization of standalone poly(vinyl alcohol)‐graphite nanoplatelets composite films

AbstractPolymer based nanocomposites are gaining attention in various fields of science and technology due to its tunable properties. In this work, we report for the first time, the preparation and study on electrical and mechanical properties of standalone poly(vinyl alcohol) (PVA) based graphite nanoplatelet (GnP) composite films using modified film casting technique. Our modified tape casting method can produce films with uniform thickness, and uniform dispersion of filler deprived of pinholes. This technique is scalable for the mass production of polymer composite films for device application. We have obtained a significant enhancement in the electrical conductivity of 9 orders of magnitude and a maximum value of 0.143 S/m using PVA–GnP composites. To the best of our knowledge, this increase is the highest among the reported values for PVA–GnP composite films. However, a reduction in crystallinity and tensile strength can be seen with the addition of GnP fillers. The maximum tensile strength obtained for PVA–GnP composite films was 15 MPa and is adequate for use in electronic applications and devices. The effect of filler addition in PVA is discussed in detail.

In-situ shear exfoliation and thermal conductivity of SBS/Graphite nanoplatelet nanocomposites

Rapid developments of miniaturization and integration of modern electronic devices have been accompanied by increasing power density, which bring about urgent demands for polymer-based thermal interface materials (TIMs) with efficient thermal conductive properties. However, poor dispersibility of thermal conductive nano-fillers severely limits further improvement in the thermal conductivity of TIMs. Herein, poly(styrene-b-butadiene-b-styrene) (SBS)/graphite nanoplatelet (GNP) nanocomposites with well-dispersed GNPs were fabricated by in-situ shear exfoliation of graphite in SBS solution, followed by a co-precipitation process. The SBS macro-molecules were immobilized on the surfaces of exfoliated GNPs through π-π interaction, which not only prevented the exfoliated GNPs from restacking in the suspension, but also improved their dispersibility in SBS matrix. Thus, GNPs were uniformly dispersed in SBS/GNP nanocomposites and possessed strong interfacial adhesion with SBS, which formed efficient thermal conductive filler networks with reduced interfacial thermal resistance. Hence, at 14.7 vol% filler, SBS/GNP nanocomposites displayed an excellent thermal conductivity of 1.55 W m−1 K−1, which is 204% higher than SBS/commercial GNP (c-GNP) composites (0.51 W m−1 K−1) prepared by simply adding c-GNPs in SBS matrix. Moreover, SBS/GNP nanocomposites displayed enhanced tensile moduli and higher glass transition temperatures. Therefore, this work has provided a facile and promising route to manufacture high-performance TIMs in large scale.

Influence of different carbon materials on electrical properties of epoxy-based composite for bipolar plate applications

During the last years, polymer composite bipolar plates have been developed from appropriate carbon materials and polymers. Considering these materials, several factors influence the effective electrical properties of bipolar plates for polymer electrolyte fuel cell (PEFC) applications. This research focuses on the development of a composite of graphite/epoxy resin/aliphatic amine, which be technically feasible as a material for use in PEFC and meet international commercial standards. A synergic mixture of Expanded Graphite (EG) as a primary filler and different secondary fillers was analyzed. The effect of Carbon Black (CB) and Graphite Nanoplatelets (GNP) as secondary fillers in proportions of 0, 0.5, 1, 2, and 3 wt% on EG with particle size greater than 300 µm and content of 40 wt% are analyzed. The methodology in this composite processing did not include any solvent and relatively low temperature processing is performed. The processing conditions were studied to understand the impact on the electrical properties of the composite. The best results were obtained with carbon black at 1%, obtaining an in-plane electrical conductivity at about 50 S/cm. The appropriate dispersion of the CB through the Epoxy/EG matrix creates bridges connecting plates that improve the flow of electrons compared to GNP composites.

Microstructure Characterization and Properties of Ti Carbohydride/Cu–Ti/GNP Nanocomposites Prepared by Wet Ball Milling and Subsequent Magnetic Pulsed Compaction

Wide application of hard composite materials in modern technologies stimulates a search for new compositions and more efficient and cheaper ways of their obtaining. A novel Ti carbohydride/CuTi/CuTi2/GNP (few-layer graphene or graphite nanoplatelets) composites were produced via magnetic pulsed compaction of Ti, Cu and graphite powders mechanically milled in liquid organic medium for 4 h. Phase composition and microstructure were examined by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. Density, microhardness, ultimate compression strength, abrasive wear resistance and sliding wear resistance of the composites were studied. The composites consisted of hexagonal and cubic titanium carbohydrides, CuTi2 and CuTi intermetallics, ~ 5 wt% of GNP and amorphous carbon. The presence of GNP and amorphous carbon resulted in higher wear resistance under conditions of dry friction against steel (1 wt%C, 1.5 wt%Cr) but lower composite density, microhardness, ultimate compression strength and abrasion wear resistance as compared with the GNP-free composites.

Mechanical enhancement of graphite nanoplatelet composites: Effect of matrix material on the atmospheric plasma-treated GnP reinforcement

Graphite nanoplatelets (GnPs) are currently employed to manufacture a new class of carbon nanomaterial composites with unique electrical and thermal as well as mechanical properties. However, due to their unreactive graphitic structure, surface activation of GnPs is critical to promote bonding to the matrix material. In a previous study, the effect of atmospheric plasma treatment (APT) on the mechanical performance of GnP epoxy composites was evaluated where the GnP surface activation resulted in a significant increase in composite strength. The current investigation evaluates the effect of GnP plasma activation when using a polycyanurate (PCN) resin as the matrix material. GnPs (5, 25 microns in particle size) were surface treated as a function of plasma exposure durations and then used to manufacture composites. Flexural strengths of these plasma-treated PCN composites increased by 25%, for both the 0.5 wt.% loaded M25 and M5 composite systems. The higher loaded systems (1.0 wt.%) exhibited smaller increases in strength (11%) with APT, due to increased particle-to-particle interactions. The glass transition temperature (Tg) of surface-treated GnP PCN composites exhibited little variation with APT, which was in sharp contrast to APT-treated GnP epoxy composites that exhibited Tg increase up to 20℃. This suggests that the oxygen functional groups formed on the surface of GnPs are less chemically reactive toward the PCN than epoxy resins, translating to relatively limited composite strength improvements when utilizing oxygen APT-treated GnPs in PCN matrices.

Understanding the effect of silica nanoparticles and exfoliated graphite nanoplatelets on the crystallization behavior of isotactic polypropylene

This study explores how the presence of nanofillers with different structural and chemical characteristics, specifically silica nanoparticles and exfoliated graphite nanoplatelets (GNP), alters the crystallization behavior and polymorphism of a semicrystalline polymer, such as polypropylene (PP). The main focus of this research is to investigate how silica and GNP affect the nucleation and growth of PP crystals during isothermal crystallization. The nonisothermal crystallization behavior, including crystal structures, crystallization temperature, and rate, is also determined. PP composites with nanomaterial content up to 7 wt% were produced by melt mixing and injection molding. Both silica and graphite were found to be effective nucleating agents, significantly increasing the crystallization rate during isothermal crystallization, with greater changes observed in case of GNP composites. The effect of filler type and amount on the PP polymorphism and lamella thickness was studied by X-ray diffraction and modulated differential scanning calorimetry. Both silica and graphite were found to be effective nucleating agents for the less common b-phase of PP crystals even at low nanomaterial concentration. a-2crystal perfection and the recrystallization of the b-form in the a-form and/ or at the transcrystalline regime were found to be responsible for the recrystallization occurring upon melting in nanocomposites at high silica or medium GNP content. POLYM. ENG. SCI., 55:672–680, 2015. V C 2014 Society of Plastics Engineers

Room temperature ionic liquids for epoxy nanocomposite synthesis: Direct dispersion and cure

Abstract Nanocomposites of silica, single-wall carbon nanotubes, and graphite nanoplatelets in an epoxy matrix were prepared using a novel single-step room temperature ionic liquid (RTIL) preparation strategy. Silica nanocomposites showed improved fracture toughness and modulus, carbon nanotube composites showed electrical network percolation at 8.6 × 10 −5 volume fraction, and graphite nanoplatelets composites showed electrical percolation at 1.7 × 10 −2 volume fraction. These results were compared with literature results for nanocomposites made with volatile solvents, demonstrating the viability of the RTIL nanocomposite preparation strategy.

Investigation of the stability of paraffin–exfoliated graphite nanoplatelet composites for latent heat thermal storage systems

Organic materials, such as paraffin wax, are sought as stable and environmentally friendly phase change materials (PCM) for thermal energy storage, but they suffer from low thermal conductivity which limits the rate at which thermal energy flows into and out of the material. A common method to improve the PCM thermal behavior is through loading with high thermal conductivity particulate fillers. However, the stability of these composites in the molten state is a concern as settling of the fillers will change the effective thermal conductivity. In this work, we investigate the stability of wax loaded with exfoliated graphite nanoplatelets either of 1 μm (xGnP-1) or 15 μm (xGnP-15) diameter. The effect of dispersants, oxidation of the wax, viscosity of the wax, mixing time, and hydrocarbon chain length on stability is reported. It was found that the addition of octadecylphosphonic acid (ODPA) is an effective dispersant for xGnP in paraffin and microcrystalline wax. In addition, mixing time, viscosity, and oxidation of the wax influence stability in the molten state. Overall, it was found that a mixing time of 24 hours for xGnP-15 along with ODPA mixed in a high viscosity, oxidized microcrystalline wax results in composite PCM systems with the greatest stability determined at 80 °C in the molten state.

Incorporation of electron tunnelling phenomenon into 3D Monte Carlo simulation of electrical percolation in graphite nanoplatelet composites

The percolation threshold problem in insulating polymers filled with exfoliated conductive graphite nanoplatelets (GNPs) is re-examined in this 3D Monte Carlo simulation study. GNPs are modelled as solid discs wrapped by electrically conductive layers of certain thickness which represent half of the electron tunnelling distance. Two scenarios of ‘impenetrable’ and ‘penetrable’ GNPs are implemented in the simulations. The percolation thresholds for both scenarios are plotted versus the electron tunnelling distance for various GNP thicknesses. The assumption of successful dispersion and exfoliation, and the incorporation of the electron tunnelling phenomenon in the impenetrable simulations suggest that the simulated percolation thresholds are lower bounds for any experimental study. Finally, the simulation results are discussed and compared with other experimental studies.

Electrical conductivity and dielectric response of poly(vinylidene fluoride)–graphite nanoplatelet composites

Poly(vinylidene fluoride)/graphite nanoplatelets (PVDF/GNP) composites were fabricated using solution mixing followed by compression molding. The electric conducting and dielectric behavior of such nanocomposites were determined over a wide frequency range from 10 2 to 10 7. The results showed that the electrical behavior of PVDF/GNP nanocomposites can be well described by the percolation theory. Both conductivity and dielectric constant were found to be greatly enhanced at the percolation threshold. A large dielectric constant of 173 and low loss tangent of 0.65 were observed in the PVDF/2.5 wt% GNP nanocomposite at 1 kHz. Moreover, dynamic mechanical analysis was also used to characterize the relaxations of polymers in PVDF/GNP nanocomposites. Dielectric and mechanical relaxations of PVDF/GNP nanocomposites showed strong dependence with frequency and temperature. The activation energy for glass transition determined from mechanical relaxation is considerably higher than that evaluated from the dielectric analysis. This resulted from different operating mechanisms for dielectric and mechanical relaxation processes.