Uniform Dispersion Of Graphene Research Articles

Intercalation structure and toughening mechanism of graphene/urea‐formaldehyde nanocomposites prepared via in situ polymerization

AbstractBased on the industrialized graphene (GN) product, a series of graphene/urea‐formaldehyde nanocomposites were synthesized via in situ polymerization by incorporation of silicon coupling agent with terminal amino groups (SA) as the compatibilizer. The results showed that addition of SA coupling agent led to much more efficient grafting of UF molecules on the GN surface with high layer thickness by formation of hydrogen bonding, and thus complete exfoliation and uniform dispersion of GN were achieved for the composites. Compared with neat UF, the addition of 1.0 wt% GN resulted in a roughly 25% increase in tensile strength and 12% increase in impact strength; meanwhile the impact fracture surfaces of the composite showed obvious ductile fracture characteristics, indicating the reinforcing and toughening effect of GN on the UF matrix. With increasing GN content, the storage modulus, glass transition temperature and crosslinking density of UF increased, while the tan δmax decreased, suggesting that a double crosslinking network structure with GN centered crosslinking point and chemical crosslinking point of UF molecular chains formed, leading to improvement in the stiffness of the composites. The present work showed promising potential for developing high performance UF resin on an industrial scale. © 2017 Society of Chemical Industry

Dispersion of Graphene in Aluminum Powder to Aid Synthesis of Homogenous Nano-Composites

A fairly simple methodology to homogeneously disperse graphene in aluminum powder with potential for further use as composites with superior performances is described. Graphene is indisputably the most superior additive in today’s engineering materials world to perform as reinforcement to different metal matrices to form nano-composites with unusual properties. Challenges arise from the need for uniform dispersion of graphene into metals without which the synthesis of high-performance graphene-reinforced metal matrix composites are not possible. The processing steps involved dispersion of graphene in Ethanol solution via ultrasonication, magnetic stirring, and addition of pure Aluminum powder (99%), followed by controlled grinding/ball milling in methanol or by grinding in pestle and mortar to achieve the desired characteristics. The crystal structure and microstructure of synthesized composite powders were examined via X-ray Diffracatrometry (XRD) and Energy Dispersive X-ray Spectroscopy (EDS) associated with Scanning Electron Microscope (SEM). Results pertaining to homogenous dispersions of graphene with varying concentrations of 0.5, 1 and 1.5% in aluminium powder, with potential to lead towards sintering via powder metallurgy route has been studied and presented in this paper.

Mechanical and dielectric properties of graphene incorporated polypropylene nanocomposites using polypropylene-graft-maleic anhydride as a compatibilizer

To achieve uniform dispersion of graphene in polypropylene, polypropylene-graft-maleic anhydride (PP-g-MA) as compatibilizer was compounded with graphene to obtain masterbatch, and then melt blended with polypropylene using a micro-compounder. Raman study showed the strong interfacial interaction between the surface of functionalized graphene sheets (FGS) and the compatibilizer, while morphologic study indicated the homogeneous dispersion of graphene in polypropylene. Remarkable enhancements in mechanical, thermal and dielectric properties were obtained at low graphene loading. At an effective graphene content of 1.5 wt%, the tensile strength and storage modulus of polypropylene increased by 18% and 33%, respectively. The electrical percolation threshold of the nanocomposites is about 0.55 vol%, which is lower than most of previously reported polypropylene composites prepared by similar melt processing. Near the percolation threshold (0.535 vol% graphene), the dielectric permittivity increased to 15.2 and the loss tangent was kept as low as 0.20 at 103 Hz.

A new electrospun graphene-silk fibroin composite scaffolds for guiding Schwann cells

Graphene (Gr) has been made of various forms used for repairing peripheral nerve injury with favorable electroactivity, however, graphene-based scaffolds in peripheral nerve regeneration are still rarely reported due to the difficulty of realizing uniform dispersion of graphene and electroactive materials at nanoscale as well as lacking biocompatibility. In this paper, graphene-silk fibroin (SF) composite nanofiber membranes with different mass ratios were prepared via electrospinning. Microscopic observation revealed that electrospun Gr/SF membranes had a nanofibrous structure. Electrochemical analysis provided electroactivity characterization of the Gr/SF membranes. The physiochemical results showed that the physiochemical properties of electrospun Gr/SF membranes could be changed by varying Gr concentration. Swelling ratio and contact angle measurements confirmed that electrospun Gr/SF membranes possessed large absorption capacity and hydrophilic surface, and the mechanical property was improved with increasing Gr concentration. Additionally, in-vitro cytotoxicity with L929 revealed that all the electrospun Gr/SF membranes are biocompatible. Moreover, the morphology and quantity showed that the membranes supported the survival and growth of the cultured Schwann cells. Collectively, all of the results suggest that the electrospun Gr/SF membranes combine the excellent electrically conductivity and mechanical strength of the graphene with biocompatibility property of silk to mimic the natural neural cell micro-environment for nerve development.

Fabricating graphene-titanium composites by laser sintering PVA bonding graphene titanium coating: Microstructure and mechanical properties

Abstract Graphene reinforced titanium (Ti-Gr) nanocomposite was prepared by laser sintering of the mixture of PVA bonding graphene sheets and titanium powders. During laser sintering process, the survival and uniform dispersion of graphene have been demonstrated, which embedded in Ti matrix, and formed Ti-Gr nanocomposites. Microstructures and components of the nanocomposites were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and Raman spectroscopy. The survival of graphene sheets in nanocomposite is due to rapid heating/cooling in laser sintering process. Hardness measurements showed that the laser sintered Ti-Gr nanocomposites achieved more than 2-fold Vickers Hardness value of barely sintered Ti.

A strategy to synthesize graphene-incorporated lignin polymer composite materials with uniform graphene dispersion and covalently bonded interface engineering

Graphene-incorporated polymer composites have been demonstrated to have excellent mechanical and electrical properties. In the field of graphene-incorporated composite material synthesis, there are two main obstacles: Non-uniform dispersion of graphene filler in the matrix and weak interface bonding between the graphene filler and polymer matrix. To overcome these problems, we develop an in-situ polymerization strategy to synthesize uniformly dispersed and covalently bonded graphene/lignin composites. Graphene oxide (GO) was chemically modified by 4,4'-methylene diphenyl diisocyanate (MDI) to introduce isocyanate groups and form the urethane bonds with lignin macromonomers. Subsequential polycondensation reactions of lignin groups with caprolactone and sebacoyl chloride bring about a covalent network of modified GO and lignin-based polymers. The flexible and robust lignin polycaprolactone polycondensate/modified GO (Lig-GOm) composite membranes are achieved after vacuum filtration, which have tunable hydrophilicity and electrical resistance according to the contents of GOm. This research transforms lignin from an abundant biomass into film-state composite materials, paving a new way for the utilization of biomass wastes.

Mechanical reinforcement of graphene/poly(vinyl chloride) composites prepared by combining the in-situ suspension polymerization and melt-mixing methods

Abstract In order to obtain uniform dispersion of graphene and significant mechanical reinforcement of graphene filled poly(vinyl chloride) (PVC) composites, we used in-situ suspension polymerization to obtain graphene/PVC compounded resins with uniform dispersion of graphene, and subsequently prepared graphene/PVC composites using conventional melt-mixing technique. The microstructure, graphene dispersion, mechanical and thermal properties of the nanocomposites were investigated in detail. We found that the combination of in-situ polymerization and melt-mixing was effective in obtaining graphene/PVC composites with uniform graphene dispersion and significant mechanical reinforcement. The tensile strength, impact toughness, and thermal stability of the nanocomposites were greatly improved even at an extremely low graphene loading (0.3 wt%), which is mainly attributed to the uniform dispersion of graphene and strong graphene-PVC interactions. By virtue of their excellent mechanical properties and easy production, the graphene/PVC composites have great potential to be used as high-performance composites in many fields.

Effect of graphene addition on flexural properties of al 6061 nanocomposites

Aluminium and its composites established themselves for various industrial applications due to its potential properties like low density and good structural rigidity. In the recent years, Graphene is being one of the allotropes of carbon; although with the limited studies shows it can be considered as nanofiller and perfect reinforcement for conventional structural materials. The current research work is carried out to prepare and perform characterization of Al 6061 matrix nanocomposites reinforced by Graphene with different filling content (0.2, 0.4, 0.6, 0.8 weight%). The uniform dispersion of Graphene in the matrix is done by ultrasonic liquid processer followed by ball milling and the mixtures were consolidated by powder metallurgy (PM) approach. The SEM and EDX analysis were done on prepared nanocomposites. The mechanical properties like microhardness, density and flexural strengths are investigated as a function of Graphene weight fraction. A three point flexural test is performed on the composites in a uniaxial loading system. A maximum enhancement in strength and relevant strengthening mechanism involved in the Al6061 – Graphene composites in comparison with monolithic Al 6061 alloy are discussed.

Processing and Characterization of Al 6061 – Graphene Nanocomposites

As one of the most important engineering materials, Aluminum alloys and its composites have been widely used in Aerospace and automobile industriesdue to its potential properties like low density and good structural rigidity. However, the important criteria in enhancing the mechanical properties without compromising the ductility is always challenging in Aluminum and its alloys based composites. In the recent years, enormous research has been carried on ceramic based and Carbon based reinforcement materials used in Aluminum metal matrix composites. But Graphene, being one of the allotropes of carbon; although with the limited studies, shows it can be considered as nanofiller and perfect reinforcement for conventional structural materials. The current research work is carried out to process, synthesize and perform the characterization of Al 6061 matrix nanocomposites. Graphene with different filling content (0.25, 0.5, 0.75, 1.0 weight%) is used use as reinforcement in the Aluminum matrix. The uniform dispersion of Graphene in the matrix is carried out by ultrasonic liquid processing method and the mixtures were consolidated by powder metallurgy (PM) approach followed by SEM and XRD analysis. Thus prepared compacts are sintered at various temperature and mechanical properties like microhardness, density are investigated as a function of sintering temperature and Graphene weight fraction. Diametrical expansions and relevant strengthening mechanism involved in the Al6061 – Graphene composites in comparison with monolithic Al 6061 alloy are discussed.

Multifunctional properties of 3D printed poly(lactic acid)/graphene nanocomposites by fused deposition modeling

ABSTRACTIn this work, three-dimensional (3D) printing system based on fused deposition modeling (FDM) is used for the fabrication of conductive polymer nanocomposites. This technology consists in the additive multilayer deposition of polymeric nanocomposite based on poly(lactic acid) (PLA) and graphene by means of a in house made low-cost commercial bench-top 3D printer. Further, 3D printed PLA/graphene nanocomposites containing 10 wt% graphene in PLA matrix were characterized for their mechanical, electrical and electromagnetic induction shielding properties of the nanocomposite. Furthermore X-ray computed micro-tomography analyses showed that printed samples have good dimensional accuracy and are significantly closer to the predefined design and the results of scanning electron microscopy (SEM) printed samples showed a uniform dispersion of graphene in PLA matrix The proposed material has uniquely advantageous when implemented in 3D printed structures, because incorporation of multifunctional graphene has been shown to substantially improve the properties of the resulting nanocomposite.

Bioinspired Interface Engineering in Elastomer/Graphene Composites by Constructing Sacrificial Metal-Ligand Bonds.

It remains a huge challenge to create advanced elastomers combining high strength and great toughness. Despite enhanced strength and stiffness, elastomeric nanocomposites suffer notably reduced extensibility and toughness. Here, inspired by the concept of sacrificial bonding associated with many natural materials, a novel interface strategy is proposed to fabricate elastomer/graphene nanocomposites by constructing a strong yet sacrificial interface. This interface is composed of pyridine-Zn(2+) -catechol coordination motifs, which is strong enough to ensure uniform graphene dispersion and efficient stress transfer from matrix to fillers. Moreover, they are sacrificial under external stress, which dissipates much energy and facilitates chain orientation. As a result, the strength, modulus, and toughness of the elastomeric composites are simultaneously strikingly enhanced relative to elastomeric bulk. This work suggests a promising methodology of designing advanced elastomers with exceptional mechanical properties by engineering sacrificial bonds into the interface.

Effect of exfoliated graphite nanoplatelets on thermal and heat deflection properties of kenaf polypropylene hybrid nanocomposites

Abstract Exfoliated graphite nanoplatelet (GNP) polypropylene (PP)/kenaf fiber (KF) hybrid nanocomposites (PP/KF/MAPP/GNP collectively presented as PKMG) were developed through melt extrusion using a co-rotating screw speed extruder. The loadings of GNPs in nanocomposites were varied from 1–5 phr and characterized for thermal conductivity, stability and behavior, morphology, and heat deflection temperature (HDT). Results revealed increasing effective thermal conductivity with increasing inclusion of GNP. This behavior was attributed to the formation of thermally conductive, interconnected, sheets of GNP which enhanced heat dissipation. Thermal stability analysis revealed high thermal residue content at 3 phr loading attributed to uniform dispersion of GNP sheets in polymer matrix and the formation of enhanced oxygen-barrier due to effective char formation. Results also revealed enhanced HDT (0.46 MPa/1.8 MPa) with increasing incorporation of GNP ascribed to high modulus and thermal stability of GNP sheets. This implies capability of material to sustain loading at high temperatures without losing its rigidity. Thermal behavior revealed increased crystallization temperature and reduced degree of crystallization with slight increase in melting temperature in the range of 2–5°C. Morphological analysis using transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) revealed exfoliated and uniform dispersion of graphene in matrix polymer at 3 phr loading.

Synthesis and Microwave Absorption Properties of Polyaniline-Graphene Nanocomposites

To develop novel microwave absorbing materials, polyaniline (PANI) composites filled with graphene was prepared, and the morphology, crystallographic structures and microwave parameters of the composites were investigated by SEM, XRD, FTIR and HP8722ES network analyzer. The uniform dispersion of graphene significantly enhanced the formation of conductive pathways in the PANI arrays and the interfacial affinity between PANI and graphene increases the number of conductive pathways of electron transfer. The composites show great microwave absorbing properties of −17dB. This study reveals that the PANI-Graphene composite is promising for applications as microwave absorbing material.

Effect of graphene loading on thermomechanical properties of poly(vinyl alcohol)/starch blend

ABSTRACTPolymer nanocomposites based on poly(vinyl alcohol) (PVA)/starch blend and graphene were prepared by solution mixing and casting. Glycerol was used as a plasticizer and added in the starch dispersion. The uniform dispersion of graphene in water was achieved by using an Ultrasonicator Probe. The composites were characterized by FTIR, tensile properties, X‐ray diffraction (XRD), thermal analysis, and FE‐SEM studies. FTIR studies indicated probable hydrogen bonding interaction between the oxygen containing groups on graphene surface and the –OH groups in PVA and starch. Mechanical properties results showed that the optimum loading of graphene was 0.5 wt % in the blend. XRD studies indicated uniform dispersion of graphene in PVA/starch matrix upto 0.5 wt % loadings and further increase caused agglomeration. Thermal studies showed that the thermal stability of PVA increased and the crystallinity decreased in the presence of starch and graphene. FE‐SEM studies showed that incorporation of graphene increased the ductility of the composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41827.

A New Electrochemical Approach for the Synthesis of Copper-Graphene Nanocomposite Foils with High Hardness

Graphene has proved its significant role as a reinforcement material in improving the strength of polymers as well as metal matrix composites due to its excellent mechanical properties. In addition, graphene is also shown to block dislocation motion in a nanolayered metal-graphene composites resulting in ultra high strength. In the present paper, we demonstrate the synthesis of very hard Cu-Graphene composite foils by a simple, scalable and economical pulse reverse electrodeposition method with a well designed pulse profile. Optimization of pulse parameters and current density resulted in composite foils with well dispersed graphene, exhibiting a high hardness of ~2.5 GPa and an increased elastic modulus of ~137 GPa while exhibiting an electrical conductivity comparable to that of pure Cu. The pulse parameters are designed in such a way to have finer grain size of Cu matrix as well as uniform dispersion of graphene throughout the matrix, contributing to high hardness and modulus. Annealing of these nanocomposite foils at 300°C, neither causes grain growth of the Cu matrix nor deteriorates the mechanical properties, indicating the role of graphene as an excellent reinforcement material as well as a grain growth inhibitor.

Self-Initiated Free Radical Grafting of Styrene Homo- and Copolymers onto Functionalized Graphene

Herein we report on the solvent-free free radical grafting of styrene homo- and copolymers onto functionalized graphene nanosheets without requiring initiator addition. The key intermediate is an organophilic stearylamine-modified graphite oxide (Stearyl-GO), containing both olefinic unsaturation and stable graphene radicals. According to the online tracking of the C-centered graphene radicals by time-resolved EPR spectroscopy, the graphene radical concentration markedly increases during the early stage of polymerization and is depleted as the viscosity builds up with progressing styrene conversion. “Grafting-to” by addition of polystyrene radicals to graphene and “grafting-from” by graphene-initiated free radical polymerization afford high graft yields, as determined by ultracentrifugal separation of polystyrene-grafted functionalized graphene (PS-g-FG) from the styrene homopolymer byproduct. The addition of TEMPO enables control of the further grafting yields by a controlled radical “grafting-from” polymerization. In sharp contrast to graphene/polystyrene solution blends (PS/Stearyl-GO), morphological and rheological investigations reveal that the in situ formation of PS-g-FG accounts for much more uniform graphene dispersion in polystyrene melts and also in various organic solvents. This is paralleled by enhanced elasticity of the graphene particle network and markedly improved electrical conductivity of the resulting graphene/polystyrene nanocomposites. Owing to the effective polymer radical addition to FG, both Stearyl-GO and PS-g-FG significantly improve the thermal stability of polystyrene, as measured by thermogravimetric analysis of thermal decomposition during prolonged heating at 250 °C. This versatile in situ self-initiated polymerization process enables grafting of styrene copolymers with butyl acrylate and acrylonitrile.

Graphene‐reinforced biodegradable poly(ethylene succinate) nanocomposites prepared by in situ polymerization

ABSTRACTIn this study, poly(ethylene succinate)(PES)/graphene nanocomposites were facilely prepared by in situ melt polycondensation of succinic acid and ethylene glycol in which contained well dispersed graphene oxide (GO). Fourier transform infrared (FTIR), GPC, TGA, and XRD were used to characterize the composites. The FTIR spectra and TGA measurement confirmed that PES chains had been successfully grafted onto GO sheets along with the thermal reduction of GO to graphene during the polymerization. GPC results indicated that increasing amounts of graphene caused a slight decrease in number average molecular weight of PES matrix when polymerization time was kept constant. The content of grafted PES chains on graphene sheets was also determined by TGA and was to be about 60%, which made the graphene sheets homogeneously dispersed in the PES matrix, as demonstrated by SEM and XRD investigations. Furthermore, the incorporation of thermally reduced graphene improved the thermal stability and mechanical properties of the composites significantly. With the addition of 0.5 wt % graphene, onset decomposition temperature of the composite was increased by 12°C, and a 45% improvement in tensile strength and 60% in elongation at break were also achieved. The enhanced performance of the composites is mainly attributed to the uniform dispersion of graphene in the polymer matrix and the improved interfacial interactions between both components. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3212–3220, 2013