Graphene Nanoplatelets Loading Research Articles

Microstructural evolution, mechanical profile, and fracture morphology of aluminum matrix composites containing graphene nanoplatelets

Abstract

Electromagnetic interference shielding performance and electromagnetic properties of wood-plastic nanocomposite with graphene nanoplatelets

In this paper, we investigated the electromagnetic interference (EMI) shielding effectiveness of wood-polyvinyl chloride (WP)/graphene nanoplatelets (GNP) nanocomposites (0–9 wt%) which are flexible, lightweight, and resistant, and its EMI shielding performance increases based on the enhancement of graphene amount in nanocomposites. The increase of EMI shielding ability is attributed to the electromagnetic properties of the WP/GNP nanocomposites, such as permeability and permittivity. Scanning electron microscopy pictures show that GNP, even at low proportions, had a good dispersion in WP. This study is achieved by the composites that we produced in laboratory conditions with five different combinations of graphene nanoplatelets, wood, and polyvinyl chloride. According to observation, GNP loading to WP regularly increased its permeability and permittivity so that reaching to good shielding effectiveness. When we look into the contributions of reflection and absorption to the total shielding performance, shielding mostly occurred in reflection mechanism. In addition to that, the WP/GNP-5 nanocomposite with 9 wt% graphene nanoplatelets revealed the highest value of EMI shielding effectiveness (approximately 26 dB) over 8–9 GHz frequency range.

Viscoelastic properties and physical gelation of poly (butylene adipate-co-terephthalate)/graphene nanoplatelet nanocomposites at elevated temperatures

Abstract A series of biodegradable nanocomposites were prepared by dispersing graphene nanoplatelets (GNPs) in poly (butylene adipate-co-terephthalate) (PBAT). Variations of dynamic and steady shear rheology of the nanocomposites with GNP loading and temperature were investigated via oscillatory measurements. Viscoelastic properties of the matrix exhibited significant enhancement with GNP addition. Solid-like flow behaviour was observed for highly filled samples while pure PBAT and nanocomposites with low GNP loadings showed liquid-like behaviour. Interestingly, the liquid-solid transition was found to occur at lower GNP concentrations with increasing temperature; dropping from 11.5 wt% at 160 °C to 7 wt% at 220 °C. Furthermore, in contrast to ideal melts, viscoelastic properties of some of the nanocomposites increased with increasing temperature. These observations suggest that the percolation did not originate only from network formation between the platelets but may be related to a combined GNP-PBAT gelling network, which enhanced with increasing temperature, leading to a more solid-like response at elevated temperatures. Variation of shear viscosity of nanocomposites with temperature also showed that increasing GNP loading reduces the temperature sensitivity of viscosity, leading to an increase in relative viscosity of nanocomposites with increasing temperature.

Determination and Modeling of Mechanical Properties for Graphene Nanoplatelet/Epoxy Composites

Structural components of modern aircraft, such as the fuselage and control surfaces, are commonly constructed using carbon‐filled polymer composites. The addition of graphene nanoplatelets (GNP) to traditional fiber‐reinforced composites often increases the tensile modulus. In this work, composites were fabricated with epoxy (EPON 862 with EPIKURE Curing Agent W) and 1–4 wt% (0.6–2.44 vol%) GNP. The GNP used in this study was Asbury Carbon's TC307. To the authors' knowledge, mechanical data for composites with TC307 have not been published before. Composite specimens were tested for macroscopic tensile modulus and modulus as determined by nanoindentation. The macroscopic tensile modulus increased from 2.72 GPa for neat epoxy to 2.93 GPa for 4 wt% (2.44 vol%) TC307 in epoxy. The modulus as determined by nanoindentation showed a similar trend. For all these composites, the tensile strength ranged from 76 to 81 MPa. A multiscale modeling approach, using molecular dynamics data and micromechanical modeling, was used to verify the experimental data, and both experiments and modeling demonstrated that a three‐dimensional random dispersion of GNP (∼3 to 4 layers) in epoxy was achieved. The constant level of strength with GNP loading is important in applications where GNP is added to the epoxy matrix to increase thermal and electrical conductivity. POLYM. COMPOS., 39:1845–1851, 2018. © 2016 Society of Plastics Engineers

Nucleation and mechanical enhancements in polyethylene-graphene nanoplate composites

Abstract Graphene nanoplatelets (GNP) dispersed in high-density polyethylene (HDPE) were found to significantly enhance nucleation of PE crystallization, and thermal/mechanical properties of HDPE-GNP nanocomposites. Excellent dispersion of GNPs was achieved by combining solution blending and twin-screw extrusion homogenization. The dispersion state was confirmed by bimodal AFM and also by the resulting improvements in thermal, mechanical, and transport properties. The crystallization rates were shown to markedly increase at low GNP content (0.1 wt%) and continued to increase with GNP loading up to 15 wt%. The size of secondary structures, or spherulites, decreased with GNP loading. Smaller spherulite sizes and faster kinetics suggested enhanced nucleation with GNP addition. 30–40% reductions in permeability and up to 60% higher Young’s moduli were found in these HDPE-GNP nanocomposites. Restricted polyethylene mobility and enhanced thermal stability with increasing GNP loading were also indicated in these HDPE-GNP nanocomposites.

Polymer bonded explosives (PBXs) with reduced thermal stress and sensitivity by thermal conductivity enhancement with graphene nanoplatelets

The two-dimensional (2D) graphene nanoplatelets (GNPs) were adopted to enhance the thermal conductivity of PBX. The results indicated that, the thermal conductivity of PBX was only slightly improved with very low GNP loading (0.05 wt% and 0.15 wt%). However, a remarkable enhanced effect was observed at a relatively high GNP loading (0.5 wt% and 1 wt%). The thermal conductivity of PBX had a nonlinear dependence on the GNPs loading. The nonlinear dependence of the thermal conductivity on GNPs content was fitted by an analytical model which incorporated all the effects. And the thermal conduction mechanism of GNPs based composite could change from series thermal structure to parallel thermal structure with the GNP loading increasing. Additionally, the calculated thermal shock resistance and thermal stress distribution of PBX was both enhanced with the GNP loading. Finally, the sensitivity of sensitive hexanitrohexaazaisowurtzitane (CL-20) based PBX composition could be improved by GNPs due to enhanced thermal conductivity.

Electrical and electromagnetic interference shielding characteristics of GNP/UHMWPE composites

Conductive polymer composites (CPC) are attractive materials for a wide range of applications because of their weight, corrosion resistivity, design flexibility and low cost. In the present work, the electrical and electromagnetic interference (EMI) shielding characteristics of graphene nanoplatelets (GNP)/ultrahigh molecular weight polyethylene (UHMWPE) composites filled with up to 40 wt% GNP were investigated. In addition, the intrinsic conductivity of the GNP network was estimated based on the statistical power law and the rule of mixtures for randomly oriented filler particles in insulating matrix. Due to the formation of a segregated conductive network at the external surface of UHMWPE powder, an electrical percolation threshold of between 2 and 3 wt% GNP was obtained. At GNP loading of 15 wt%, the composite exhibited an EMI shielding effectiveness of 33 dB, corresponding to 99.95% blocking of the EMI.

Graphene Nanoplatelet–Polystyrene Nanocomposite: Dielectric and Charge Storage Behaviors

Graphene nanoplatelet (GNP)–polystyrene nanocomposites filled with up to 20 wt.% GNPs were prepared by melt mixing. The microstructure, direct-current (dc) electrical percolation behavior, and dielectric characteristics were investigated as functions of frequency. In addition, the effects of dc bias on the complex impedance and charge transport mechanisms were explored. The dc electrical percolation curve showed a gradually transition from the insulating to conducting state. At 15 wt.% GNP loading and frequency greater than 104 Hz, the nanocomposite exhibited dielectric constant and loss factor of 180 and 0.11, respectively, revealing remarkable storage capabilities at high frequencies. For nanocomposites filled with 12 wt.% to 20 wt.% GNPs, the alternating-current conductivity was found to follow the universal dynamic response behavior, implying electron conduction due to tunneling in addition to direct contact between GNPs.

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.

Lightweight graphene nanoplatelet/boron carbide composite with high EMI shielding effectiveness

Lightweight graphene nanoplatelet (GNP)/boron carbide (B4C) composites were prepared and the effect of GNPs loading on the electromagnetic interference (EMI) shielding effectiveness (SE) has been evaluated in the X-band frequency range. Results have shown that the EMI SE of GNP/B4C composite increases with increasing the GNPs loading. An EMI SE as high as 37 ∼ 39 dB has been achieved in composite with 5 vol% GNPs. The high EMI SE is mainly attributed to the high electrical conductivity, high dielectric loss as well as multiple reflections by aligned GNPs inside the composite. The GNP/B4C composite is demonstrated to be promising candidate of high-temperature microwave EMI shielding material.

Morphology, electromagnetic properties and electromagnetic interference shielding performance of poly lactide/graphene nanoplatelet nanocomposites

Biodegradable poly lactide (PLA)/graphene nanoplatelet (GNP) nanocomposites with 0–15wt% (0–9.1vol%) of nanofiller were prepared. Scanning electron micrographs showed good dispersion of GNPs in PLA at low concentrations while above 6wt%, GNPs were found to become physically in contact forming a 3D network within the matrix. X-ray diffraction showed that GNPs had a significant effect on the semi-crystalline structure of PLA which was also confirmed by differential scanning calorimetry measurements. Electromagnetic properties and electromagnetic interference shielding effectiveness of the nanocomposites were determined over C- and X-bands (5.85–12.4GHz). It was observed that GNP embedding in PLA did not alter its magnetic permeability but enhanced its electrical permittivity and conductivity markedly leading to higher shielding effectiveness. The contributions of reflection and absorption to the overall shielding performance of the nanocomposites were determined and reflection was found to be the dominant shielding mechanism. However, the absorption potential of the samples increased by increasing GNP loading with the effective absorbance being more than 80% for a 1.5mm-thick sample containing 15wt% of GNPs compared to less than 0.6% for pristine PLA.

Shape memory nanocomposite of poly(L-lactic acid)/graphene nanoplatelets triggered by infrared light and thermal heating

In this study, the effect of graphene nanoplatelets (GNPs) on the shape memory properties of poly(L-lactic acid) (PLLA) was studied. In addition to thermal activation, the possibility of infrared actuating of thermo-responsive shape mem- ory PLLA/GNPs nanocomposite was investigated. The incorporated GNPs were expected to absorb infrared wave's energy and activate shape memory PLLA/GNPs. Different techniques such as differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), field emission gun scanning electron microscope (FEG-SEM) and dynamic mechanical thermal analysis (DMTA) were used to characterize samples. DSC and WAXD results indicated that GNPs augmented crystallinity due to nucleating effect of graphene particles. GNPs improved both thermal and infrared activating shape memory properties along with faster response. Pure shape memory PLLA was slightly responsive to infrared light and its infrared actuated shape recovery ratio was 86% which increased to more than 95% with loading of GNPs. Drastic improvement in the crystallinity was obtained in nanocomposites with lower GNPs contents (0.5 and 1 wt%) due to finer dispersion of graphene which resulted in more prominent mechanical and shape memory properties enhancement. Infrared activated shape memory PLLA/GNPs nanocomposites can be developed for wireless remote shape control of smart medical and bio-systems.

Enhanced Thermal and Electrical Properties of Polystyrene-Graphene Nanofibers via Electrospinning

Polystyrene- (PS-) graphene nanoplatelets (GNP) (0.1, 1, and 10 wt.%) nanofibers were successfully produced via electrospining of dimethyformamide- (DMF-) stabilized GNP and PS solutions. Morphological analysis of the composite nanofibers confirmed uniform fiber formation and good GNP dispersion/distribution within the PS matrix. The good physical properties of GNP produced by liquid exfoliation were transferred to the PS nanofibers. GNP modified PS nanofibers showed a 6-fold increase in the thermal conductivity and an increase of 7-8 orders of magnitude in electrical conductivity of the nanofibers at 10 wt.% GNP loading.

Novel graphene nanoplatelet reinforced 45S5 bioglass composites fabricated by Spark Plasma Sintering (SPS)

Event Abstract Back to Event Novel graphene nanoplatelet reinforced 45S5 bioglass composites fabricated by Spark Plasma Sintering (SPS) Zhong Li1*, Nay Win Khun1, Xiu-Zhi Tang1 and Khiam Aik Khor1 1 Nanyang Technological University, School of Mechanical & Aerospace Engineering, Singapore Introduction: The insufficient fracture toughness of 45S5 Bioglass® (45S5) constraints its extensive application as major load-bearing orthopedic implants[1],[2]. Satisfactory wear resistance is crucial for the in vivo fixation, integration and lifetime of 45S5-based prosthesis, but the tribological properties of bulk 45S5 are rarely reported[3],[4]. This study attempts to fabricate graphene nanoplatelet (GNP) toughened 45S5 composites by Spark Plasma Sintering (SPS) and investigate the effect of GNP addition on the composite’s wear properties. Materials and Methods: 45S5 powder was supplied by XL Sci-Tech Inc., US. Graphene oxide (GO) was synthesized using a modified Hummers method[5]. A colloidal process was utilized to obtain the GO/45S5 composite powders. The composites were sintered at 550°C for 3 min by an SPS system (Dr. Sinter 1050, SCM, Japan). In situ reduction of GO and enhancement of 45S5 matrix were simultaneously realized in this process. Sintered pellets with 0, 0.1, 0.5, and 1 wt.% GO added in the raw powder are denoted as BG0, BG0.1, BG0.5 and BG1, respectively. Samples were extensively characterized by SEM, TEM, Raman Spectroscopy, XRD, XPS, Nanoindentation, and Vickers indentation fracture toughness test[6]. Tribological properties were investigated by a ball-on-disk micro-tribological test (CSM High Temperature Tribometer, Switzerland) and surface profilometry. Results and Discussion: While the pristine 45S5 powder was amorphous, the sintered pellets were crystalline (Fig. 1a). Raman spectra shown in Fig. 1b prove that GNP survived the SPS process. The significantly decreased defect index ID/IG (intensity ratio of the D band and G band, values given in brackets) of sintered composites ("S" – sintered pellet, "P" – powder, and "W" – wear track) can be attributed to the restoration of sp2 bonds in the graphitic lattice[7]. Composite pellets showed lower Young’s modulus (E) and hardness (H) than BG0 (Fig 2a), possibly caused by more residual pores introduced by GNP addition. BG0.5 possessed the highest E and H among the three composites. All composite pellets showed higher fracture toughness (KIC) than BG0 (Fig. 2b). BG0.5 had the highest KIC of 1.22 MPa∙m1/2, corresponding to an exciting improvement of 130.2 % compared with BG0. Different toughening mechanisms, including crack deflection, crack bridging and sheet pull-out, can be clearly seen in Fig. 2c-f. BG0.5 showed the best wear resistance with the shallowest wear track (Fig. 3). Compared with BG0, its friction coefficient and specific wear rate were decreased by 21.3 % and 62.0 %, respectively, because of its improved KIC and the lubrication effect of GNP[8]. Wear resistance decreased from BG0.5 to BG1, possibly due to excessive GNP loading. The obviously increased ID/IG values after wear tests probably stem from new structural defects introduced by tearing off of graphene layers during repeated sliding. Conclusions: Novel GNP/45S5 nanocomposites were successfully fabricated through in situ GO reduction in SPS. The addition of 0.5 wt.% GO was proved to be the optimum which could improve KIC by 130.2 % and decrease friction coefficient and specific wear rate by 21.3 % and 62.0 %, respectively. The encouraging and exciting enhancement in both fracture toughness and wear resistance achieved in our study has opened new doors for broader application of 45S5 in bone tissue engineering. Z. Li thanks NTU for the University Research Scholarship

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.

Investigation the effect of Graphene on The Morphology, Mechanical and Thermal properties of PLA/PMMA Blends

In this work, Poly Lactic Acid/Poly methyl Methacrylate (PLA/PMMA) blends in various compositions prepared and morphology and properties of these blends was investigated. Moreover, the effect of adding different amounts of Graphene Nanoplatelets (GNP) on the morphology of the blends (by SEM), the interaction of nanopalates with polymer phases (by FTIR) and its effect on the mechanical properties and thermal stability of the samples were examined. The results of the study showed that in different amounts of graphene, these plates were preferentially located in the polymer phases dissimilarly and thus, caused the change of the blend morphology. In addition, measuring the mechanical properties by tensile test and results of thermal analysis by TGA indicated the improvement of thermal stability, modulus and mechanical strength and reduction of the elongation at break of graphene containing blends with increasing the loading of GNP. The changing behavior of the mechanical and thermal properties was proportional to the Graphene localization in blend phases.

Synergistic thermal conductivity enhancement of PC/ABS composites containing alumina/magnesia/graphene nanoplatelets

Graphene nanoplatelets (GNPs) have attracted considerable attention in the field of thermal management materials due to their unique structure and exceptional thermal conductive properties. In this work, we demonstrate a significant synergistic effect of GNPs, alumina (Al2O3), and magnesia (MgO) in improving the thermal conductivity of polycarbonate/acrylonitrile‐butadiene‐styrene polymer alloy (PC/ABS) composites. The thermal conductivity of the composites prepared through partial replacement of Al2O3 and MgO with GNPs could increase dramatically compared with that without GNPs. The maximum thermal conductivity of the composite is 3.11 W mK−1 at total mass fraction of 70% with 0.5 wt% GNPs loading. It increases 60% compared with that without GNPs (1.95 W mK−1). The synergistic effect results from the compact packing structure formed by Al2O3/MgO and the bridging of GNPs with Al2O3/MgO, thus promoting the formation of effective thermal conduction pathways within PC/ABS matrix. More importantly, together with the intrinsically high thermal conductivity of GNPs, boosted and effective pathways for phonon transport can be created, thus decrease the thermal resistance at the interface between fillers and PC/ABS matrix and increase the thermal conductivity of composites. POLYM. COMPOS., 38:2221–2227, 2017. © 2015 Society of Plastics Engineers

Effect of plate-like particles on properties of poly(lactic acid)/poly(butylene adipate-co-terephthalate) blend: A comparative study between modified montmorillonite and graphene nanoplatelets

Abstract Surface-modified montmorillonite (mMMT) and graphene nanoplatelets (GNPs), both possessing plate-like structure, were adopted as property enhancers for a blend based on poly(lactic acid) and poly(butylene adipate- co -terephthalate). Unlike mMMT, GNPs contributed to higher stretchability of the solvent-cast films compared to that of the polymer-clay composite films. Fine dispersion of GNPs throughout the polymer host promoted several improved properties of the blend. Compared to the mMMT at identical filler amount, GNPs enhanced thermal stability and water vapor barrier property while decreased light transmittance in controllable fashion by simply tuning the GNP loading content (0.1–1 phr). In contrast, the clay did not show any obvious trend of property enhancement. Thus, GNPs functioned as promising property improver for this selected blend. Finally, the polymer-graphene composite could find further application in conductive coating of metal electrodes. This paper shows the simple preparation of polymer composite films by using fillers without any complicated functionalization. The findings will also benefit further facile processing of engineering composites.

Enhancing the thermal, electrical, and mechanical properties of silicone rubber by addition of graphene nanoplatelets

Graphene nanoplatelets (GNPs)/silicone rubber composites were prepared with the assistance of the Flacktek SpeedMixer. A scanning electron microscope (SEM), transmission electron microscopy (TEM), Raman spectra, Fourier-transform infrared spectra (FTIR), and X-ray photoelectron spectra (XPS) were carried out to characterize the structure of graphene nanoplatelets. An electronic universal testing machine, laser thermal conductivity analysis (LFA), thermogravimetric analysis (TGA), and a scanning electron microscope (SEM) reveal the effects of GNP loading content on the thermal conductivity, electrical, and mechanical properties of the composites. The results show that the GNPs present a homogeneous dispersion in silicone rubber and the thermal conductivity of composites exhibits improving from 0.16 to 0.26W/(m·K) (an increase of 53.1%) and the tensile strength varies from 0.240 to 0.608MPa (an increase of 153%) with the addition of a low content (0–8%) of GNPs. In addition, the thermal stability of silicone rubber composites is significantly enhanced.

Morphology, thermal, and electrical properties of polypropylene hybrid composites co‐filled with multi‐walled carbon nanotubes and graphene nanoplatelets

ABSTRACTIn this study, nanocomposites of polypropylene (PP) with various loadings of multi‐wall carbon nanotubes (MWCNT) and graphene nanoplatelets (GnP) were formed by masterbatch dilution/mixing approach from individual masterbatches PP‐MWCNT and PP‐GnP. Melt mixing on a twin‐screw extruder at two different processing temperatures was followed by characterization of morphology by transmitted‐light microscopy including the statistical analysis of agglomeration behavior. The influence of processing temperature and weight fractions of both nanofillers on the dispersion quality is reported. Thermal properties of the nanocomposites investigated by DSC and TGA show sensitivity to the nanofillers weight fraction ratio and to processing conditions. Electrical conductivity is observed to increase up to an order of magnitude with the concentration of each nanofiller increasing from 0.5 wt % to 1.0 wt %. This is related with a decrease of electrical conductivity observed for unequal concentration of both nanofillers. This particular behavior shows the increase of electrical properties for higher MWCNT loadings and the increase of thermo‐mechanical properties for higher GnP loadings. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42793.