Graphene Nanoplatelets Composites Research Articles

Core–shell rubbery fillers for massive electrical conductivity enhancement and toughening of polystyrene–graphene nanoplatelet composites

Graphene nanoplatelets (GNPs) are an attractive additive for polymers to provide electrical conductivity to a composite. If the GNP surface and the polymer are incompatible, the interfaces are weak, resulting in a large drop in the flexural strength and toughness of the composite compared to the native polymer. In the present study, we show that adding core–shell rubbery (CSR) nanoparticles, that have a polyisobutadiene (PIB) core and a thin, polystyrene (PS) compatible shell, to a PS–GNP composite enhances the dispersion of the GNP and suppresses their restacking, increasing the electrical conductivity of the composite by several orders of magnitude. In addition, there is complete recovery of the flexural strength and a large increase in toughness compared to PS samples without fillers. The recovery of the mechanical properties is related to a uniform distribution of the CSR and good binding at the interfaces because of the compatibility of the filler surface with the PS matrix, as well as the rubbery nature of the PIB core. This strategy of using a second filler as both a toughening agent as well as a dispersion aid breaks a commonly encountered tradeoff between electrical and mechanical property enhancement by fillers. It can be deployed for applications where both a high electrical conductivity and excellent mechanical properties of polymer composites are desired.

Dry sliding wear behavior of aluminum graphene nanoplatelet (GNP) composites

Abstract Conventional aluminum (Al) and its alloys have been replaced by aluminum matrix composites (AMCs) due to their superior properties in the recent years. There are several attractive candidates as reinforcement for aluminum composites such as Al2O3, B4C and SiC. Nowadays, carbon based materials such as graphite, carbon nanotubes (CNTs) and graphene have attracted much attention owing to their above mentioned mechanical and physical properties. In this study, the wear behavior of Al graphene nanoplatelets (GNPs) composites reinforced with up to 2 wt.-% GNP were investigated. The addition of graphene up to 1 wt.-% decreased coefficient of friction. Experimental data were used to develop linear and nonlinear models. The experimental results are in good agreement with the results of the simulations based on the identified models.

Synthesis and properties of graphene and graphene/carbon nanotube-reinforced soft magnetic FeCo alloy composites by spark plasma sintering

The effect of the addition of graphene nanoplatelets (GNP) and graphene nanoplatelet/carbon nanotube (GNT) mixtures on the mechanical and magnetic properties of spark plasma sintered soft magnetic FeCo alloys was studied. Three different volume fractions (0.5, 1 and 2 vol%) of GNPs and GNTs were investigated. Ball milling was used to disperse the GNPs in monolithic FeCo powder, while magnetic stirring and ultrasonic agitation were used to prepare hybrid GNT prior to ball milling. The highest saturation induction (B sat) of 2.39 T was observed in the 1 vol% GNP composite. An increase in the volume fraction of the ordered nanocrystalline structure was found to reduce the coercivity (H c) of the composites. The addition of CNTs to the GNP composite prevented grain growth, leading to grain refinement. An 18 % increase in hardness was observed in the 1 vol% GNP composite as compared to the as-received FeCo alloy. A reduction in tensile strength was observed in all of the composite materials, except for the 0.5 vol% GNT composite, for which a value of 643 MPa was observed. Raman spectroscopy indicated a reduction in the defect density of the GNPs after adding CNTs.

Thermopower and hall effect in silicon nitride composites containing thermally reduced graphene and pure graphene nanosheets

Composites consisting of dielectric silicon nitride (Si3N4) with diverse percentages of different graphene nanoreinforcements, such as graphene nanoplatelets (GNP) – 17 and 21vol% – and reduced graphene oxide (rGO) sheets − 4 and 7vol% – displayed thermopower effect. Maximum thermopower was observed for the rGO containing composites, which reached a peak Seebeck coefficient (S) of −26μVK−1 at 300K, whereas GNP composites showed top S of +5μVK−1 at the same temperature. Hall effect measurements indicated that current carriers were different in both composites, electrons for the rGO/Si3N4 (n-type conductor) and holes for the GNP/Si3N4 materials (p-type conductor) and also having ∼1.4 times higher carrier concentration the first composites. The enhanced thermopower of the rGO/Si3N4 composites is attributed to the particular defective nature of rGO sheets, which presented edge defects and nanometer scale defect clusters as shown by the high resolution transmission electron microscope images – probably associated to both oxygen atoms remaining after GO reduction during spark plasma sintering and N doping from the Si3N4 matrix.

Mechanical properties of polytetrafluoroethylene composites reinforced with graphene nanoplatelets by solid-state processing

Abstract Polytetrafluoroethylene (PTFE)/graphene nanoplatelet (GnP) composites with varying GnP volume fractions are produced by solid-state milling and hot-pressing. This simple approach is able to be used for any polymer powder without any solvents. High-energy milling is performed to disperse GnPs into the PTFE in the solid-state condition. Morphology of PTFE/GnP powder and the fracture surface of PTFE/GnP composites are observed to investigate the GnP dispersion and the deformation behavior in the composites. The tensile test reveals improved mechanical properties of the PTFE/GnP composites. Yield stress of the PTFE/3 vol.% GnP composite increases by 60%, as compared to the neat PTFE. It is attributed to the interference with the movement of the PTFE chains by the randomly dispersed GnPs. A significant reinforcing effect appears on Young's modulus, which shows an increase of 223% at 3 vol.% GnP loading.

Optimization and Prediction of Mechanical and Thermal Properties of Graphene/LLDPE Nanocomposites by Using Artificial Neural Networks

The focus of this work is to develop the knowledge of prediction of the physical and chemical properties of processed linear low density polyethylene (LLDPE)/graphene nanoplatelets composites. Composites made from LLDPE reinforced with 1, 2, 4, 6, 8, and 10 wt% grade C graphene nanoplatelets (C-GNP) were processed in a twin screw extruder with three different screw speeds and feeder speeds (50, 100, and 150 rpm). These applied conditions are used to optimize the following properties: thermal conductivity, crystallization temperature, degradation temperature, and tensile strength while prediction of these properties was done through artificial neural network (ANN). The three first properties increased with increase in both screw speed and C-GNP content. The tensile strength reached a maximum value at 4 wt% C-GNP and a speed of 150 rpm as this represented the optimum condition for the stress transfer through the amorphous chains of the matrix to the C-GNP. ANN can be confidently used as a tool to predict the above material properties before investing in development programs and actual manufacturing, thus significantly saving money, time, and effort.

Characterization and preparation of conductive exfoliated graphene nanoplatelets kenaf fibre hybrid polypropylene composites

Exfoliated graphene nanoplatelets (GNP) kenaf fiber (KF) hybrid polypropylene (PP) composites materials were prepared by melt extrusion followed by injection molding. PP/KF/MAPP/GNP composites 0–5phr were prepared and characterized using X-ray diffraction (XRD), differential scanning calorimetre (DSC), thermogravimetry analysis (TGA), heat deflection temperature (HDT), thermal mechanical analysis (TMA), Fourier transform infrared (FTIR) spectroscopy analysis, field emission scanning electron microscopy. The morphological studies revealed a homogenous dispersion of GNPs in PP/KF/MAPP/GNP up to 3phr loading after which agglomeration occurred. Flexural strength and modulus were enhanced by 70% and 98% respectively at 3phr GNPs loading which were the highest values obtained. Interestingly, the highest value for the impact strength was also recorded at 3phr loading. Thermal conductivity increased by 88%, CTE decreased by 80%, water absorption and thickness swelling decreased while HDT improved. The thermal stability of the composites were generally improved at all GNP loading with the highest at 3phr. From the overall results, it is obvious that the optimum concentration of GNPs in the PP/KF/MAPP/GNP system in terms of both mechanical and thermal properties was 3phr loading. Although, the mechanical and thermal properties of the composites were improved, the FTIR analysis did not reveal any chemical interaction between GNP and the PP/KF/MAPP system.

Effects of cellulose nanowhiskers on the properties of poly(vinyl alcohol)/graphene nanoplatelets nanocomposites

Cellulose nanowhisker (CNW) is a kind of ideal reinforcing filler due to its biodegradability and renewability together with superior mechanical properties. CNW hybridization with graphene nanoplatelet (GN) incorporated into poly(vinyl alcohol) (PVA) films were produced by ultrasonication mixing prior to solution casting. CNW showed positive effects on the PVA/GN composite films, which improved the dispersion of GN and refined GN by replacing partial GN with CNW in PVA/GN composite films. The addition of CNW effectively prevented the aggregation of GN in PVA matrices during the evaporation of water. Lateral size of GN is reduced by replacement of 0.1 and 0.4 wt% GN with an equivalent amount of CNW. The grain size of PVA decreased from 3.2 nm for PVA‐0.5%GN to 2.8–3.1 nm for PVA/CNW/GN composite films. Young's modulus, tensile strength, and elongation at break of PVA/GN composite films increased by 12%, 13%, and 150% when 0.1 wt% GN was replaced by CNW, respectively. The glass transition temperature moved from 30.6°C for pure PVA to 40.4°C for PVA/CNW/GN composite and the storage modulus of composite increased by 93%. With only 0.1%CNW addition, the swelling ratio of PVA‐0.5%GN composites decreased by 15% and the conductivity of PVA‐0.5%GN composites increase by 156%. The PVA‐based composite with improved water resistance and electrical conductivity are potential for functional applications in the industrial field. POLYM. COMPOS., 38:E98–E107, 2017. © 2015 Society of Plastics Engineers

Tribological performance under dry sliding conditions of graphene/silicon carbide composites

The role played by graphene in the friction and wear behaviour of graphene/silicon carbide (SiC) composites, tested under dry sliding conditions and using silicon nitride balls as counterbodies, is investigated as a function of the graphene nanoplatelets (GNPs) content and the graphene source. GNPs composites show an enhanced wear resistance as compared to monolithic SiC, with maximum improvements of ∼70% for the material containing up to 20vol.% of GNPs; whereas the friction performance depends on the sliding distance and GNPs content. The analysis of the wear debris by micro-Raman spectroscopy evidenced that the tribological behaviour of the GNPs/SiC materials is linked to the formation of an adhered lubricating and protecting tribofilm. Multilayered graphene fillers participate more actively in the protecting tribofilm than other graphene sources such as reduced graphene oxide or in-situ grown graphene flakes.

Investigation on microstructural, mechanical and electrochemical properties of aluminum composites reinforced with graphene nanoplatelets

In present study, the microstructure, mechanical and electrochemical properties of aluminum–graphene nanoplatelets (GNPs) composites were investigated before and after extrusion. The contents of graphene nanoplatelets (GNPs) were varied from 0.25 to 1.0wt.% in aluminum matrix. The composites were fabricated thorough powder metallurgy method, and the experimental results revealed that Al-0.25%GNPs composite showed better mechanical properties compared with pure Al, Al-0.50%GNPs and Al-0.1.0%GNPs composites. Before extrusion, the Al-0.25%GNPs composite showed ~13.5% improvement in ultimate tensile strength (UTS) and ~50% enhancement in failure strain over monolithic matrix. On the other hand, Al-0.50%GNPs and Al-0.1.0%GNPs composites showed the tensile strength lower than monolithic matrix. No significant change was observed in 0.2% yield strength (YS) of the composites. However, the extruded materials showed different trends. The 0.2%YS of composites increased with increase in GNPs filler weight fractions. Surprisingly, UTS of composites with 0.25 and 0.50% GNPs was lower than monolithic matrix. The failure strain of the baseline matrix was enhanced by ~46% with 0.25% graphene nanoplatelets. The superior mechanical properties (in terms of failure strain) of the Al-0.25%GNPs composite maybe attributed to 2-D structure, high surface area and curled nature of graphene. In addition, the corrosion resistance of pure Al and its composites reinforced with 0.5 and 1.0wt% GNPs was also investigated. It was found that the corrosion rate increased considerably by the presence of GNPs.

Dielectric relaxation behaviour of ethylene-vinyl acetate–exfoliated graphene nanoplatelets (xGnP) composites

The dielectric relaxation behaviour of the composites prepared by solution casting of exfoliated graphene nanoplatelets (xGnP) and ethylene vinyl acetate (EVA) were investigated. The percolation threshold was achieved at 17 phr (parts per hundred rubber) of xGnP loading. Filler contributions to the electrical property were observed by the increase in ac conductivity and permittivity in the composites. The effect of filler loading on the complex and real parts of the impedance were investigated. The effect of temperature on dielectric loss tangent, ac conductivity and Nyquist plot of xGnP reinforced EVA also been studied. A careful comparison of the experimental complex impedance plots and model fitted plots were studied which satisfied the accuracy of the data obtained experimentally.

Ammonia sensor based on polypyrrole–graphene nanocomposite decorated with titania nanoparticles

A composite of polypyrrole (PPy) and graphene nanoplatelets (GNs) decorated with titanium dioxide (TiO2) nanoparticles (TiO2@PPy–GN) was synthesized by a sol–gel process combined with in situ chemical polymerization. The microstructure, morphology, and crystallinity of the TiO2@PPy–GN nanocomposite were characterized by Fourier-transform infrared spectrometry, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results indicate that the TiO2 nanoparticles with a diameter of 10–30nm were well dispersed on the PPy–GN composite. The TiO2@PPy–GN nanocomposite exhibited good electrical-resistance response to NH3 at room temperature. Compared to the PPy–GN thin film, the TiO2@PPy–GN thin film showed enhanced NH3-sensing properties in the form of higher sensitivity and much faster response under the same conditions. The selectivity and stability of the NH3 sensor based on theTiO2@PPy–GN nanocomposite were also investigated.

Tribological properties of silica–graphene nano-platelet composites

Graphene nano-platelets (GNP) were synthesised using a liquid phase exfoliation method and then used to produce well dispersed silica–GNP composites. The tribological properties of the silica–GNP composites with different vol% GNP loading were investigated. The wear behaviour at room temperature was studied using a ball on disc technique with alumina and borosilicate (BS) balls as the tribological counterpart. In the case of alumina balls, GNP above a critical concentration decreased the coefficient of friction of the composite by ~20% while increasing the wear resistance of the composite by ~5.5 times. In the case of using BS balls there was an improvement of ~8.5 times in the wear resistance while the coefficient of friction did not change. In both cases a percolating network of GNP above a critical concentration provided a lubricating effect to the silica matrix, resulting in a significant improvement in the tribological properties of the nano-composites. The extent of damage to GNP during tribology testing was quantified using Raman spectroscopy.

Crystallization and melting behavior of poly (ethylene succinate) in presence of graphene nanoplatelets

• Poly (ethylene succinate)/graphene nanocomposites were characterized in this work. • Dynamic and isothermal crystallization rates were enhanced upon graphene addition. • Overall crystallinity and melting remained almost unchanged in presence of graphene. • Graphene changed crystal perfection and its effect was found concentration-dependent. In this study, poly (ethylene succinate)/graphene nanoplatelets composites were prepared via solution casting method in different compositions and analyzed via differential scanning calorimetry. Crystallization and melting characteristics in both dynamic (non-isothermal) and isothermal modes were investigated at various cooling rates and isothermal temperatures. It was confirmed that graphene, while being incompatible with the matrix polymer, could act as nucleating agent so that hot (melt) crystallization rates, intensities, and positions were increased in the dynamic mode. However, the overall crystallinity remained almost unchanged. Cold crystallization was also decreased to lower temperatures on graphene addition; however its enthalpy was also reduced. Similar findings were observed for the isothermal mode, but to a lesser extent. The presence of graphene changed the perfection of crystals as their thermodynamic stability against heating and recrystallization behavior varied.

Processing and bioactivity of 45S5 Bioglass®-graphene nanoplatelets composites

Well dispersed 45S5 Bioglass(®) (BG)-graphene nanoplatelets (GNP) composites were prepared after optimising the processing conditions. Fully dense BG nanocomposites with GNP loading of 1, 3 and 5 vol% were consolidated using Spark plasma sintering (SPS). SPS avoided any structural damage of GNP as confirmed using Raman spectroscopy. GNP increased the viscosity of BG-GNP composites resulting in an increase in the sintering temperature by ~50 °C compared to pure BG. Electrical conductivity of BG-GNP composites increased with increasing concentration of GNP. The highest conductivity of 13 S/m was observed for BG-GNP (5 vol%) composite which is ~9 orders of magnitude higher compared to pure BG. For both BG and BG-GNP composites, in vitro bioactivity testing was done using simulated body fluid for 1 and 3 days. XRD confirmed the formation of hydroxyapatite for BG and BG-GNP composites with cauliflower structures forming on top of the nano-composites surface. GNP increased the electrical conductivity of BG-GNP composites without affecting the bioactivity thus opening the possibility to fabricate bioactive and electrically conductive scaffolds for bone tissue engineering.

Preparation and characterization of palmitic acid/graphene nanoplatelets composite with remarkable thermal conductivity as a novel shape-stabilized phase change material

This paper mainly concentrates on the shape stability and thermal conductivity of palmitic acid (PA)/graphene nanoplatelets (GNPs) composite phase change material (PCM). The impregnation method was done to prepare shape stabilized PCM with GNPs for three different specific surface areas of 300, 500 and 750 m2/g. The maximum mass percentage of PA absorbed by GNPs was 91.94 wt% without leakage of PA in molten state as proven by dropping point test. Scanning electron microscope (SEM), Transmission electron microscopy (TEM), X-ray diffractometer (XRD) and Fourier transform infrared spectroscope (FT-IR) were applied to determine microstructure and chemical structure of palmitic acid (PA)/GNPs composites, respectively. Differential scanning calorimeter (DSC) test was done to investigate thermal properties which include melting and solidification temperatures and latent heats. The thermogravimetric analyzer (TGA) results show that thermal stability of PA was increased by using GPNs. The thermal reliability and chemical stability of composite PCM were determined by cycling test for 2500 cycles of melting and freezing. The improvement of thermal conductivity was calculated to be 10 times that of the PA. As a result, due to their acceptable thermal properties, good thermal reliability, chemical stability and great thermal conductivities, we can consider the prepared shape-stabilized composites as highly conductive PCMs for thermal energy storage applications.

Graphene NanoPlatelets reinforced tantalum carbide consolidated by spark plasma sintering

Graphene NanoPlatelets (GNP) reinforced tantalum carbide composites are synthesized by spark plasma sintering (SPS) at processing conditions of 1850°C and 80–100MPa. The GNP addition enhances the densification of TaC–GNP composites to 99% theoretical density, while reducing the grain size by over 60% through grain wrapping mechanism. Survival and structure retention of GNP is confirmed through scanning electron microscopy and micro-Raman spectroscopy. Nanoindentation and high load (20–30N) microindentation are utilized to evaluate elastic modulus and hardness. GNP improves fracture toughness of TaC by up to 99% through toughening mechanisms such as GNP bending, sheet sliding, cracking bridging, and crack deflection.

Photocatalytic activity of spark plasma sintered TiO2–graphene nanoplatelet composite

This study reports on the photocatalytic activity of TiO 2 –1 vol.% graphene nanoplatelet (GNP) composite synthesized by spark plasma sintering. Graphene platelets form a strong interface with sub-micron TiO 2 grains providing increased pathways for improved electron transport. The photocatalytic activity of TiO 2 –GNP was measured by methylene blue solution decomposition under UV light exposure. The addition of 1 vol.% GNP to TiO 2 improved its photocatalytic property by 25% by enhancing the electron mobility and reducing the photoexcited electron–hole recombination rate.

Electrical Discharge Machining of Ceramic/Carbon Nanostructure Composites

The miniaturization of mechanical components with complex shapes is a great challenge in emerging applications. Silicon nitride (Si3N4) ceramics are excellent candidates for such applications due to their outstanding mechanical, thermal, and tribological properties. However, they are difficult to machine using normal mechanical machining methods. If the material were electrically conductive, electrical discharge machining (EDM) could be applied to produce precise and complex shapes. In this paper, in order to investigate the effects of electrical conductivity on the EDM characteristics, several carbon nanostructure composite materials are fabricated and EDMed using the assisting electrode method proposed by the current authors. The performance of the process is evaluated as a function of the carbon nanostructure content and type. The former is separately selected to be close to the electrical percolation threshold (0.9 vol.% and 5.3 vol.% for carbon nanotube (CNT) and graphene Nano platelet (GNP) composites, respectively), and well above that limit (5.3 vol.% and 20.6 vol.%), where electrical conductivities on the order of 10 and 100 S·m-1 are attained for CNTs and GNPs-based nanocomposites, respectively. In addition, bare Si3N4 specimens are also tested. Material removal rate, electrode wear ratio, and surface roughness of the machined pieces are analyzed for all testing conditions.

Magnetic Graphene Nanoplatelet Composites toward Arsenic Removal

Magnetic graphene nanoplatelet composites (MGNCs) decorated with core-shell Fe-Fe2O3 nanoparticles (NPs) have been synthesized using a facile one-pot thermal decomposition method. The graphene nanoplatelets (GNPs) decorated with uniformly dispersed NPs are observed to exhibit a strong magnetization and can be magnetically separated from the liquid mixture by a permanent magnet. These MGNCs demonstrate an effective and efficient adsorption of arsenic(III) in the polluted water due to the increased adsorption sites in the presence of magnetic NPs. The adsorption behavior is well fitted with both Langmuir and Freundlich models, which show a significantly higher adsorption capacity (11.34 mg/g) than the other adsorption values reported on the conventional iron oxide based adsorbents (∼1 mg/g). The results show a nearly complete As(III) removal within 1 ppb.