Perspectives of Epoxy/Graphene Oxide Composite: Significant Features and Technical Applications

In this article, advancement in epoxy/graphene oxide composites is presented. These materials are comprised of graphene oxide (GO) as filler (carbon-based material, thermodynamically stable, two-dimensional, planar and layered structure). Due to improved properties (mechanical response, low density, electrical resistance, and thermal stability), epoxy resins are used in several applications. Graphene oxide proposes unique properties to epoxy composites as high surface area, thermal and electrical conductivity as well as mechanical and barrier properties, relative to neat matrix. The corresponding significance of epoxy/GO-based materials, related challenges, and potential exploitation regarding technical applications (aerospace, gas sensor, electronic devices, etc.) have been overviewed.     

Graphene as initiator/catalyst in polymerization chemistry

One of the most important applications of graphene-based materials is the formation of nanocomposite materials, where graphene in the bulk-polymer matrix transfers its properties onto the polymeric material. Control of the polymer/graphene interface by attached polymeric interlayers is essential to generate nanocomposites, thus avoiding the aggregation of graphene nanoparticles. Among all graphene materials graphene oxide (GO) and reduced graphene oxide (r-GO) can be prepared on large scales useful for mass production graphene/polymer composites. The direct use of graphene materials as both, the polymerization initiator or catalyst and additive not only diminishes the agglomeration of particles in composites but also reduces the process of composite production to one facile step, which in turn avoids further purification regarding to strong acid initiators and metal particles catalysts. Here, literature activities within the past ∼10 years using graphene-based materials either as initiator or catalyst in different polymerization reactions are reviewed.     

Synergetic Effects of Graphene Oxide and Clay on the Microstructure and Properties of HIPS/Graphene Oxide/Clay Nanocomposites

In this paper, double-network structure nanocomposite with improved mechanical and thermal properties were prepared using high-impact polystyrene as a matrix phase, clay and graphene oxide as effective reinforcing fillers through a facile solution intercalation method. The structure and morphology of nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction analysis, and the synergetic effects of clay and graphene oxide on the final properties were investigated using tensile, dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA) analysis. Mechanical analysis showed that the combination of graphene oxide and clay exerted a favorable synergistic effect on the tensile modulus and the yield strength of the ternary composite that are greatly improved as compared with neat high-impact polystyrene, high-impact polystyrene/graphene oxide, and high-impact polystyrene/clay binary composites due to the double-network structure formation between the nanofillers as confirmed by the direct morphological observations using transmission electron microscopy and scanning electron microscopy analysis. The viscoelastic behavior showed that storage modulus of ternary composite significantly improvement over than that of the pure matrix, high-impact polystyrene/graphene oxide and high-impact polystyrene/clay while network structure made. TGA and DMTA measurements also demonstrated that thermal stability of high-impact polystyrene matrix modified by graphene oxide and clay slightly enhanced during the creation of dual network structure of graphene oxide and clay. Our data suggest a potential application for the combination of graphene oxide and clay in graphene-based composite materials.     

Robust and thermo-response graphene–PNIPAm hybrid hydrogels reinforced by hectorite clay

Graphene oxide (GO) based hydrogels were proposed to be used as biomaterials and stimuli-response materials, but their poor mechanical properties restricted their applications. We enhanced GO–poly(N-isopropylacrylamide) (PNIPAm) hydrogels by hybrid with the hectorite clay through in situ polymerization for the first time. This clay was found to stabilize the GO in the aqueous suspension when a reducer was added in a redox initiating pair. These GO–clay–PNIPAm hybrid hydrogels exhibited a high mechanical strength and extensibility with the GO sheets as the cross-linker and with the hectorite clay as both the cross-linker and reinforcing agent. They were thermal-responsive with the volume phase transition at ∼34 °C. Reduction of the GO with l-ascorbic acid under environmental friendly conditions resulted in a high conductivity to the graphene–clay–PNIPAm hydrogels. These graphene–clay–PNIPAm hydrogels still had desirable mechanical properties. This finding has provided an easy method to prepare strong and stimuli-response graphene–polymer hydrogels to meet the demand for the newly developed soft matter.     

Synergistic effect of graphene oxide and sodium carboxymethylcellulose on the properties of poly(vinyl alcohol) hydrogels

Hydrogels are a promising candidate for applications in biomedicine and bioengineering, but their mechanical properties often restrict their applications. To improve the mechanical performance of poly(vinyl alcohol) (PVA) hydrogels, we introduced sodium carboxymethylcellulose (CMC), and graphene oxide (GO) into them. We prepared a series of composite hydrogels composed of PVA, CMC, and GO with epichlorohydrin as a chemical crosslinker. We used Fourier transform infrared spectroscopy and X-ray diffraction to characterize the chemical structures of GO and the hydrogel. The dynamic mechanical analysis results show the synergistic enhancement effects of CMC and GO on the PVA hydrogel. The swelling process of the hydrogels also fit well with the second-order kinetic equation. Scanning electron microscopy results suggest that the neat mesh structure facilitated superior mechanical properties in the hydrogels. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47644.     

Advanced graphene ceramics and their future in bone regenerative engineering

The outstanding properties of graphene materials rely on an exceptional two-dimensional honeycombed lattice. The lattice allows for electrical, thermal, and mechanical reinforcement effects when applied to the ceramic matrix. The biocompatibility of the material allows for providing multifunctional bioceramics applications. However, the potential of graphene lies in its ability to be homogenously distributed as part of a ceramic matrix. Therefore, appropriate processing techniques are important for attaining desired graphene ceramic properties applicable for regenerative biomedical purposes. This article provides an inclusive review of the current knowledge of advanced graphene-based ceramics for bone regenerative engineering. In this review, the opportunities and challenges in utilizing graphene materials in combination with ceramics suitable for applications in load-bearing bone defects are discussed.     

The effect of concentration of graphene nanoplatelets on mechanical and electrical properties of reduced graphene oxide papers

Macroscopic, freestanding graphene-based paper-like materials are of interest for use as mechanically strong, stiff, and flexible and electrically conductive materials. Chemically reduced graphene oxide paper shows promise for such applications. In this work, we studied the mechanical and electrical properties of a set of paper materials prepared by filtration of homogeneous colloidal suspensions of hydrazine-reduced graphene oxide with different concentrations. Young’s modulus, fracture strength, and fracture strain of each type of sample was determined by tensile tests. The paper sample prepared from the colloidal suspension with the lowest concentration of reduced graphene oxide platelets had the highest modulus and fracture strength and showed the smoothest surface morphology. The electrical conductivity measured by the four-probe measurement method increased as the concentration was increased.     

Reduced graphene oxide and ZnO decorated graphene for biomedical applications

The ability of graphene-based materials to enhance the conventional antibiotic resistance is well known and researchers have been interested in improving their antibacterial activity. The reduction of graphene oxide by eco-friendly reducing agents is of great interest on the basis of environmental and human health aspects. Herein we report the synthesis of two forms of graphene derivatives namely, reduced graphene oxide (RGO) through reduction using potato starch and zinc oxide decorated RGO (ZnO-RGO). In the case of ZnO-RGO, the reduction of graphene oxide and the conversion of ZnO to nano ZnO occur simultaneously. The characterization of all the graphene based materials and nanocomposites developed were carried out using FT-IR, XRD, Raman spectra and TEM techniques. The antibacterial activity of these modified materials against E. coli was also studied by well diffusion method. Our results show that ZnO-RGO is more efficient than RGO in their antibacterial properties which we attribute to the synergistic effect of ZnO and RGO towards the bacteria in the nanocomposite. Further we find that the antibacterial effect of ZnO-RGO towards E. coli is due to the disruption of the bacterial cell which could be confirmed by AFM images. Considering the fact that graphene-based materials are less toxic towards mammalian cells, both RGO and ZnO-RGO we have developed can find applications in the field of medicine and life sciences.     

Carbon nanofibers replacing graphene oxide in ceramic composites as a reinforcing-phase: Is it feasible?

In recent years, the interest of graphene and graphene-oxide has increased extraordinarily due to the outstanding properties concurring in this material. In ceramic science, the possibility of combining excellent electrical conductivities together with an enhancement of mechanical properties has motivated the research in fabrication of graphene oxide-reinforced ceramic composites despite the intrinsic difficulties for sintering. In this work a comparison is made between graphene oxide-reinforced alumina composites and carbon nanofiber-reinforced alumina ones. It will be concluded that the improvement of mechanical properties is scarce, if any. Since carbon nanofibers have also a good electrical conductivity their importance for future applications as a replacement of more sophisticated but expensive graphene-based ceramic composites will be stressed.     

Graphene-based polymer nanocomposites

Graphene-based materials are single- or few-layer platelets that can be produced in bulk quantities by chemical methods. Herein, we present a survey of the literature on polymer nanocomposites with graphene-based fillers including recent work using graphite nanoplatelet fillers. A variety of routes used to produce graphene-based materials are reviewed, along with methods for dispersing these materials in various polymer matrices. We also review the rheological, electrical, mechanical, thermal, and barrier properties of these composites, and how each of these composite properties is dependent upon the intrinsic properties of graphene-based materials and their state of dispersion in the matrix. An overview of potential applications for these composites and current challenges in the field are provided for perspective and to potentially guide future progress on the development of these promising materials.     

Poly(2‐hydroxyethyl acrylate) hydrogels reinforced with graphene oxide: Remarkable improvement of water diffusion and mechanical properties

A series of hybrid hydrogels of poly(2‐hydroxyethyl acrylate), PHEA, and graphene oxide, G? O, with G? O content up to 2 wt % has been prepared by in situ polymerization. Because PHEA has been used as biomaterial in various applications, has a side chain with the hydroxyl functional group and its mechanical properties are poor, it is a good candidate for reinforcement with G? O. Fourier transform (infrared) spectroscopy, atomic force microscopy, differential scanning calorimetry, the thermal, mechanical, and water sorption properties of neat PHEA and PHEA/G? O composites have been studied in order to elucidate the dispersion and interaction between both components. An increase in the water diffusion coefficient and dramatic changes in its mechanical properties are the most remarkable results. Thus, at a nanofiller load of 2 wt %, the novel materials present an increased diffusion coefficient higher than 380% and the elastic modulus is enhanced by more than 650% in dry state and by more than 100% in swollen state, both compared to neat PHEA. These results have been attributed to the excellent interaction between the matrix, PHEA, and the reinforcement, G? O, and could open the door to new applications in the field of biomaterials with higher structural requisites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46158.     

Graphene-Based Polymer Composites and Their Applications

Recently, graphene has attracted both academic and industrial interest because it can produce a dramatic improvement in properties at low filler content. The utilization of graphene-based materials in the fabrication of nanocomposities with different polymer matrixes has been explored. This review article presents and discusses the development of graphene-based polymer composites and their applications in different fields such as electronics devices, energy storage, sensors, ESD and EMI shielding and biomedical applications.     

Enhanced mechanical and thermal properties of polyurethane/functionalised graphene oxide composites by in situ polymerisation

ABSTRACT

Isocyanate-functionalised graphene (iGO) was prepared and incorporated into a thermoplastic polyurethane via an in situ polymerisation. Firstly, graphene oxide was successfully modified using a mixture of isocyanate- and diisocyanate-containing compounds, leading to the formation of good dispersions of resulting functional graphene oxide in organic solvents, such as N,N-dimethylacetamide and N,N-dimethylformamide. The addition of iGO into polyurethane matrix improved both mechanical and thermal properties in the polyurethane/iGO composites relative to neat polyurethane. An addition of only 0.03?wt-% of functionalised graphene into the polyurethane increased Young’s modulus by 1.4 times and tensile strength by two times. Meanwhile, the elongation at break was similar to that of the neat polymer. In addition, dynamic mechanical analysis also confirmed the improvement in storage modulus of the polymer composites especially at high-temperature range. We believe that the developed modification approach for graphene oxide and polyurethane/graphene composites presented herein could be useful in polymer/graphene composite development.     

Advances in Biologically Applicable Graphene-Based 2D Nanomaterials

Climate change and increasing contamination of the environment, due to anthropogenic activities, are accompanied with a growing negative impact on human life. Nowadays, humanity is threatened by the increasing incidence of difficult-to-treat cancer and various infectious diseases caused by resistant pathogens, but, on the other hand, ensuring sufficient safe food for balanced human nutrition is threatened by a growing infestation of agriculturally important plants, by various pathogens or by the deteriorating condition of agricultural land. One way to deal with all these undesirable facts is to try to develop technologies and sophisticated materials that could help overcome these negative effects/gloomy prospects. One possibility is to try to use nanotechnology and, within this broad field, to focus also on the study of two-dimensional carbon-based nanomaterials, which have excellent prospects to be used in various economic sectors. In this brief up-to-date overview, attention is paid to recent applications of graphene-based nanomaterials, i.e., graphene, graphene quantum dots, graphene oxide, graphene oxide quantum dots, and reduced graphene oxide. These materials and their various modifications and combinations with other compounds are discussed, regarding their biomedical and agro-ecological applications, i.e., as materials investigated for their antineoplastic and anti-invasive effects, for their effects against various plant pathogens, and as carriers of bioactive agents (drugs, pesticides, fertilizers) as well as materials suitable to be used in theranostics. The negative effects of graphene-based nanomaterials on living organisms, including their mode of action, are analyzed as well.     

The role of microwave absorption on formation of graphene from graphite oxide

By means of manipulating the oxygen content in graphite oxides (GO) and/or graphene-based materials, we demonstrate that the microwave absorption capacity of carbon materials is highly dependent on their chemical composition and structure. The increase of oxygen in GO remarkably decreases its microwave absorption capacity due to the size decrease of the π–π conjugated structure in these materials, and vice versa. It was revealed that graphene is an excellent microwave absorbent while GO with poor microwave absorption capacity, the unoxidized graphitic region “impurities” in GO act as the microwave absorbents to initiate the microwave-induced deoxygenation. The addition of a small amount graphene to GO leads to avalanche-like deoxygenation reaction of GO under microwave irradiation (MWI) and graphene formation, which was used for electrode materials in supercapacitors. The interaction between microwaves and graphene or graphene-based materials may be used for the fabrication of a variety of graphene-based nanocomposites with exceptional properties and a wealth of practical applications.     

Identifying efficient natural bioreductants for the preparation of graphene and graphene-metal nanoparticle hybrids with enhanced catalytic activity from graphite oxide

The implementation of green approaches towards the preparation of graphene and graphene-based materials with enhanced functionality from graphite oxide has been relatively little explored. Particularly, the use of bioreductants and the testing of their relative efficacies is an incipient area of research. Here, a pool of 20 environmentally friendly, natural antioxidants have been tested for their ability to reduce graphene oxide. These antioxidants were mostly vitamins, amino acids and organic acids. By establishing a protocol to systematically compare and optimize their performance, several new efficient bioreductants of graphene oxide have been identified, namely, pyridoxine and pyridoxamine (vitamin B₆), riboflavin (vitamin B₂), as well as the amino acids arginine, histidine and tryptophan. These biomolecules were used to prepare reduced graphene oxide–silver nanoparticle hybrids that displayed colloidal stability in water in the absence of additional dispersants. Particularly, hybrids prepared with pyridoxamine exhibited a combination of long-term colloidal stability and exceptionally high catalytic activity among silver nanoparticle-based catalysts in the reduction of p-nitrophenol with NaBH₄. Thus, in addition to expanding substantially the number of green reductants available for graphene oxide reduction, the present results underline the idea that proper selection of bioreductant can be relevant to achieve graphene-based materials with improved performance.     

Photopolymerized hydrogel composites from poly(ethylene glycol) and hydroxyapatite for controlled protein delivery in vitro

The incorporation of hard particles into soft hydrogels can improve the mechanical properties and provide necessary bioactivity to the hydrogels for desired biomedical applications. Hydrogel composites containing hydroxyapatite (HA) are promising materials for orthopedic applications. In this study, injectable poly(ethylene glycol) (PEG) hydrogel precursor solutions containing HA particles and model protein bovine serum albumin (BSA) were synthesized in situ by photopolymerization. In vitro BSA release properties from the hydrogel composites containing various amounts of HA were investigated and discussed. Fourier transform infrared spectroscopy and scanning electron microscopy were employed to investigate the interaction between HA and the hydrogel network and the morphology of the hydrogel composites. It is found that PEG hydrogel composites containing HA sustained the release of BSA for at least 5 days and the presence of HA slowed down BSA release. Photopolymerized hydrogel composites containing HA may find potential use as a drug delivery matrix for orthopedic tissue engineering. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Biomimetic strain hardening in interpenetrating polymer network hydrogels

In this paper, we present the systematic development of mechanically enhanced interpenetrating polymer network (IPN) hydrogels with Young's moduli rivaling those of natural load-bearing tissues. The IPNs were formed by synthesis of a crosslinked poly(acrylic acid) (PAA) network within an end-linked poly(ethylene glycol) (PEG) macromonomer network. The strain-hardening behavior of these PEG/PAA IPNs was studied through uniaxial tensile testing and swelling measurements. The interaction between the independently crosslinked networks within the IPN was varied by (1) changing the molecular weight of the PEG macromonomer, (2) controlling the degree of PAA ionization by changing pH, and (3) increasing the polymer content in the PAA network. Young's moduli and the maximum stress-at-break of the swollen hydrogels were normalized on the basis of their polymer content. Strain hardening in the IPNs exhibited a strong dependence on the molecular weight of the first network macromonomer, the pH of the swelling buffer, as well as the polymer content of the second network. The results indicate that the mechanical enhancement of these IPNs is mediated by the strain-induced intensity of physical entanglements between the two networks. The strain can be applied either by mechanical deformation or by changing the pH to modulate the swelling of the PAA network. At pHs below the pK_a of PAA (4.7), entanglements between PEG and PAA are reinforced by interpolymer hydrogen bonds, yielding IPNs with high fracture strength. At pHs above 4.7, a “pre-stressed” IPN with dramatically enhanced modulus is formed due to ionization-induced swelling of the PAA network within a static PEG network. The modulus enhancement ranged from two-fold to over 10-fold depending on the synthesis conditions used. Variation of the network parameters and swelling conditions enabled “tuning” of the hydrogels' physical properties, yielding materials with water content between 58% and 90% water, tensile strength between 2.0 MPa and 12.0 MPa, and initial Young's modulus between 1.0 MPa and 19.0 MPa. Under physiologic pH and salt concentration, these materials attain “biomimetic” values for initial Young's modulus in addition to high tensile strength and water content. As such, they are promising new candidates for artificial replacement of natural tissues such as the cornea, cartilage, and other load-bearing structures.     

Graphene-based membranes for molecular and ionic separations in aqueous environments

Graphene-based laminar materials open up to new applications for molecular and ionic separations in aqueous environments due to the atomic thickness,mechanical strength, chemical stability and other fantastic properties.Recent advances on controlling the structure and chemical functionality of graphene-based membranes can potentially lead to new classes of tools for desalination, dehydration, toxicant rejection, specific ionic separation and so on. The recent developments of graphene-based membranes prepared by using a concept to form interlayer space between graphene sheets and creating nanoscale or sub-nanoscale pores in a graphene lattice, together with their mass-transfer mechanisms and potential applications in aqueous environments are reviewed. A summary and outlook is further provided on the opportunities and challenges in this arising field. This article is expected to address the intricate details of mass transport through two distinct graphene-based membranes in aqueous environment and to optimize the fabrication of graphene-based membranes as a fascinating separation system for a wide range of applications.     

Polymer and Graphite-Derived Nanofiller Composite: An Overview of Functional Applications

In this article, applications of polymer and graphite-derived nanofiller composite have been presented with special emphasis on epoxy composite. Various types of graphitic nanofillers such as graphite, graphene oxide, graphene, and graphene nanoplatelets are reviewed. Recently, polymer/graphite, polymer/graphene oxide, polymer/graphene, and polymer/graphene nanoplatelet-based materials have gained interest due to high performance. Property enhancement is due to high aspect ratio; high surface area; excellent electrical, thermal, and mechanical properties of nanofillers. The filler dispersion depends upon selection of suitable fabrication technique. We also reported on applications of epoxy/graphite-based filler composites in technical fields such as Li-ion batteries, sensors, and solar cells.