Low Graphene Loading Research Articles

Tailoring Assembly of Reduced Graphene Oxide Nanosheets to Control Gas Barrier Properties of Natural Rubber Nanocomposites

Self-assembling of reduced graphene oxide platelets, as a tailored interconnected network within a natural rubber matrix, is proposed as a mean for obtaining nanocomposites with improved gas barrier, as compared to neat natural rubber. Interestingly, this nanocomposite structure results to be much more effective than homogeneous dispersion of graphene platelike particles, even at low graphene loadings. Such behavior is interpreted on the grounds of a theoretical model describing permeability of heterogeneous systems specifically accounting for self-segregated graphene morphology.

Ultralow Percolation Threshold in Aerogel and Cryogel Templated Composites

We demonstrate a novel concept for preparing percolating composites with ultralow filler content by utilizing nanofiller-loaded aerogel and cryogels as a conductive template. This concept is investigated for several porous systems, including resorcinol-formaldehyde (RF), silica, and polyacrylamide (PAM) gels, and both graphene and carbon nanotubes are utilized as nanofiller. In each case, a stable, aqueous nanofiller dispersion is mixed with a sol-gel precursor and polymerized to form a hydrogel, which can then be converted to an aerogel by critical point drying or cryogel by freeze-drying. Epoxy resin is infused into the pores of the gels by capillary action without disrupting the monolithic structure. We show that conductive graphene/epoxy composites are formed with a very low graphene loading; a percolation threshold as low as 0.012 vol % is obtained for graphene-RF cryogel/epoxy composite. This is the lowest reported threshold of any graphene-based nanocomposites. Similar values are achieved in other aerogel and nanofiller systems, which demonstrates the versatility of this method.

Graphene for tough and electroconductive alumina ceramics

A simple, fast and upscalable method is described to produce graphene/alumina (G/Al2O3) composites by spark plasma sintering (SPS) with a significant improvement on both mechanical and electrical properties of monolithic Al2O3. Graphene oxide (GO) was mixed with Al2O3 using a colloidal method obtaining an excellent dispersion of GO in the alumina matrix. The material was consolidated by SPS that allowed, in one-step, the in situ reduction of the GO during the sintering process. A detailed Raman analysis was found to be very useful to study the orientation of the graphene in the composite and to evaluate and optimise its thermal reduction. Graphene platelets acted as elastic bridges avoiding crack propagation and providing this material with a crack bridging reinforcement mechanism. A very low graphene loading (0.22 wt%) led to a 50% improvement on the mechanical properties of the alumina and to an increase of the electrical conductivity up to eight orders of magnitude.

Vulcanization kinetics of graphene/natural rubber nanocomposites

In the present work, the influence of graphene (GE) on the vulcanization kinetics of natural rubber (NR) with sulfur curing system was investigated in detail for the first time. It is found that on adding graphene the induction period of the vulcanization process is remarkably depressed, whereas the vulcanization rate is enhanced at low graphene loading and then suppressed. As a result, the optimum cure time decreases dramatically at first and subsequently shows a slight increase with increasing graphene loading. At the same time, the crosslinking density of NR increases monotonically, because graphene takes part in the vulcanization process. The exothermal peak of the vulcanization reactions is split into two peaks on adding ≥0.5 phr graphene. It is interpreted in terms of two reaction stages, i.e., chemical reaction controlling stage and diffusion controlling stage. The activation energy of the former stage decreases with increasing graphene loading, while that of the latter stage is higher than the former one and increases with graphene loading. A possible mechanism was proposed to interpret the accelerating effect of graphene and the enhanced crosslinking density of NR.

Preparation and characterisation of graphene composite hydrogels

Stable dispersions containing graphene and gellan gum are used to form composite films. Incorporation of graphene into the gellan gum matrix results in mechanical reinforcement and electrical conductivity at low and high graphene loading fractions, respectively. Graphene-containing gellan gum hydrogel films are prepared by immersion of composite films in Ca2+ cross-linking solutions. The resulting hydrogels are electrically conducting and exhibit reinforcement compared to the corresponding gellan gum hydrogels.

Preparation of polyester resin/graphene oxide nanocomposite with improved mechanical strength

AbstractGraphene oxide (GO) has attracted huge scientific interest due to its unique physical and chemical properties as well as its wide‐scale applicability including facile synthesis and high yield. Here, we report preparation of nanocomposites based on GO and unsaturated polyester resin (PE). The synthesized samples were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and tensile strength measurements. A good dispersion of the GO sheets within the resin matrix was observed from the morphological analysis. A significant enhancement in mechanical properties of the PE/GO composites is obtained at low graphene loading. Around 76% improvement of tensile strength and 41% increase of Young's modulus of the composites are achieved at 3 wt % loading of GO. Thermal analysis of the composite showed a noticeable improvement in thermal stability in comparison to neat PE. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Fabrication and characterization of polyamide 6-functionalized graphene nanocomposite fiber

Graphene oxide was prepared by the Hummers’ method and then functionalized with 4-substituted benzoic acid via “direct Friedel–Crafts” acylation in a mild reaction medium of polyphosphoric acid/phosphorous pentoxide (P2O5). Raman spectroscopy, differential scanning calorimetry, thermo-gravimetric analysis, and transmission electron microscopy were used to characterize the resultant structure. The results show that 4-substituted benzoic acid functionalized graphene (FG) sheets were achieved without pretreatment of oxidation. Polycaprolactam (PA6)-FG composites were prepared by in situ polymerization of e-caprolactam in the presence of FG. Nanocomposite fiber with 0.01–0.5 wt% content of FG was prepared with a piston spinning machine and hot-roller drawing machine. A significant enhancement of mechanical properties of the PA6-FG composites’ fiber is obtained at low graphene loading; that is, a 29 % improvement of tensile strength and a three times increase of Young’s modulus are achieved at a graphene loading of only 0.1 wt%. The “graft-from” methodologies pave the way to prepare graphene-based nanocomposites of condensation polymers with promising performance and functionality.

Poly(urethane‐co‐vinyl imidazole)/graphene nanocomposites

AbstractPoly(urethane‐co‐vinyl imidazole) (PUVI)/graphene nanocomposites were facilely prepared by a kind of noncovalent way. Herein, the 1‐vinylimidazole acted as dispersion agent as well as monomer, graphene was uniformly dispersed in the copolymer matrix without obviously agglomeration. A significant enhancement of mechanical and thermal properties of the PUVI/graphene nanocomposites were obtained at low graphene loading; specifically, a 147% improvement of tensile strength, a nearly 10 times increase of elastic modulus and a 12°C enhancement of thermal decomposition temperature were achieved at a graphene loading of 1.5 wt%. Moreover, the volume resistivity of the PUVI/graphene nanocomposites decreased by an order of magnitude after adding 0.5 wt% graphene, demonstrating an obvious change in the electrical property of the nanocomposites prepared. POLYM. COMPOS. 2012. © 2012 Society of Plastics Engineers

Improved properties of chemically modified graphene/poly(methyl methacrylate) nanocomposites via a facile in-situ bulk polymerization

The nanosheet of graphene was chemically modified by long alkyl chain for enhanced compatibility with poly- mer matrix and graphene/poly(methyl methacrylate) (PMMA) nanocomposites with homogeneous dispersion of the nanosheets and enhanced nanofiller-matrix interfacial interaction were fabricated via a facile in-situ bulk polymerization. The nanocomposites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy and thermogravimetry. The results showed that the graphene nanosheets were fully exfoliated in PMMA matrix and the thermal and mechanical properties of the nanocomposites were significantly improved at low graphene loadings. Large shifts of 15°C in the glass transition temperature and 27°C improvement of onset thermal degradation temperature were achieved with graphene loading as low as 0.07 wt%. A 67% increase in tensile strength was also observed by the addi- tion of only 0.5 wt% graphene. The method used in this study provided a novel route to other graphene-based polymers.

Unique photocatalytic oxidation reactivity and selectivity of TiO2–graphene nanocomposites

Mesoporous TiO(2)-graphene nanocomposites are fabricated in high yield via two successive steps: (1) hydrothermal hydrolysis of Ti(SO(4))(2) in an acidic suspension of graphene oxide to gain TiO(2)-graphene oxide nanocomposites; (2) UV-assisted photocatalytic reduction of graphene oxide to get the TiO(2)-graphene nanocomposites. The anatase TiO(2) nanocrystals with a crystallite size of 10-20 nm are densely packed and supported on meshy graphene sheets with close interfacial contacts, which is confirmed by transmission electron microscopy (TEM) together with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Although a low graphene loading (0-2 wt%) slightly influences the textural properties (including the crystallite size, specific surface areas, and pore volume etc.), the incorporation of graphene in TiO(2)-graphene nanocomposites greatly increases the adsorption capacity towards azo dyes such as MO and MB, which is possibly associated with their unique surface properties. Significantly, the incorporated graphene exerts combined effects on the adsorption and charge transfer dynamics in TiO(2)-graphene nanocomposites, which together endow them with good photocatalytic reactivity and tunable photocatalytic selectivity in decomposing MO and MB in aqueous solution.

A high throughput method for preparation of highly conductive functionalized graphene and conductive polymer nanocomposites

Highly conductive graphene sheets were prepared by coating graphene oxide with polydopamine (PDA) followed by reduction with hydrazine. Polyacrylonitrile/graphene nanocomposites prepared via solution blending exhibit high electrical conductivities at very low graphene loadings owing to the good exfoliation and relatively planar conformation of the PDA-coated graphene in the polymer matrix.

Effective Reinforcement of Graphene in Poly (vinyl alcohol) Nanocomposites at Low Loading via Enhanced Interfacial Interaction

The graphene/poly(vinyl alcohol) nancomposites with enhanced filler-matrix interfacial interaction were fabricated via water-blending partially reduced graphene oxide (PRGO) and poly(vinyl alcohol)(PVA). The nanocomposites were characterized by X-ray Diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), Scanning Electron Microscopy(SEM), thermogravimetry(TG). The results showed that the graphene nanosheets were homogeniously dispersed in the PVA matrix and enhanced interfacial adhesion was greatly enhanced due to new covalent linkage and hydrogen-bonding between graphene and PVA backbone. The mechanical and thermal properties of the nanocomposites were significantly improved at low graphene loadings. An 116% increase in tensile strength and a 19°C improvement of onset thermal degradation temperature were achieved by the addition of only 0.8 wt% graphene.

Enhanced interfacial interaction for effective reinforcement of poly(vinyl alcohol) nanocomposites at low loading of graphene

The graphene/poly(vinyl alcohol) (PVA) nancomposites with homogeneous dispersion of the nanosheet and enhanced nanofiller–matrix interfacial interaction were fabricated via water blending partially reduced graphene oxide and PVA. The nanocomposites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetry. The graphene nanosheets were fully exfoliated in the PVA matrix and a new covalent linkage was formed between graphene and PVA matrix. Uncommon to conventional method, the enhanced interfacial adhesion resulted from covalent interaction and hydrogen bondings between graphene and PVA backbone. The mechanical and thermal properties of the nanocomposites were significantly improved at low graphene loadings. An 116% increase in tensile strength and a 19 °C improvement of onset thermal degradation temperature were achieved by the addition of only 0.8 wt% graphene.

Vacuum-assisted synthesis of graphene from thermal exfoliation and reduction of graphite oxide

We report a vacuum-assisted method for thermal exfoliation and in situreduction of graphite oxide in large quantity at a temperature as low as 135 °C. The resulting graphene sheets contain only few-layered sheets with an average thickness of 0.9 nm, and their specific surface area (758 m2 g−1) is comparable to that of conventional graphene generated at 1050 °C at atmospheric pressure (700 m2 g−1). The in situ thermal reduction during the exfoliation process was confirmed by the increased C/O atomic ratio compared to that of graphite oxide. The restoration of the graphitic sp2 network makes it highly efficient in improving the electrical conductivity of polymers at a low graphene loading.

Enhanced Mechanical Properties of Graphene-Based Poly(vinyl alcohol) Composites

Graphene, flat carbon nanosheets, has generated huge activity in many areas of science and engineering due to its unprecedented physical and chemical properties. With the development of wide-scale applicability including facile synthesis and high yield, this exciting material is ready for its practical application in the preparation of polymer nanocomposites. Here we report that nanocomposites based on fully exfoliated graphene nanosheets and poly(vinyl alcohol) (PVA) are prepared via a facial aqueous solution. A significant enhancement of mechanical properties of the graphene/PVA composites is obtained at low graphene loading; that is, a 150% improvement of tensile strength and a nearly 10 times increase of Young’s modulus are achieved at a graphene loading of 1.8 vol %. The comparison between the experimental results and theoretical simulation for Young’s modulus indicates that the graphene nanosheets in polymer matrix are mostly dispersed randomly in the nanocomposite films.