Electrochemical behavior of multifunctional graphene–polyimide nanocomposite film in two different electrolyte solutions

The effect of solvent on specific capacitance, bulk resistance, and charge/discharge capacity of graphene/polyimide composite films is studied by electrochemical methods. Composite films are synthesized by in situ condensation polymerization of poly (amic acid) in the presence of 50 wt % partly exfoliated graphene sheets followed by thermal curing at 250°C. Raman spectrum of the exfoliated graphene sheets show an increase in the ratio of I_D to I_G peak intensities from 0.167 to 0.222, suggesting increased defects in graphene basal planes. Electrochemical measurements carried out by using 0.4M potassium hexafluorophosphate (KPF₆) dissolved in propylene carbonate and N‐methylpyrrolidone at 25°C show that the composite system exhibits both pseudocapacitance and supercapacitance behaviors, with an average capacitance of 40 and 36.5 F g^?1, respectively. Bulk resistance of the composite obtained by using KPF₆–propylene carbonate electrolyte solution is 300% lower than that obtained in KPF₆–N‐methylpyrrolidone solution, with a fairly stable specific capacity of 85 μAhr g^?1, with 80% retention observed after 30 charge–discharge cycles. Fourier transform infrared spectroscopy measurements show shifts in the cyclic imide carbonyl peak from 1778 to 1774 cm^?1, which suggests that some form of interaction exists between the graphene and polyimide. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42673.     

Microstructure and properties of carbon fiber sized with pickering emulsion based on graphene oxide sheets and its composite with epoxy resin

The Graphene oxide (GO) sheets were used for preparing the epoxy resin Pickering emulsion. The particle size and the zeta potential of the Pickering emulsion were measured to evaluate its stability. The stable emulsion could be served as the film former of sizing agent for carbon fiber (CF). The effect of the Pickering emulsion stabilized by GO sheets on the properties of CF and the interfacial adhesion property of CF reinforced composite were investigated. Scanning electron microscopy (SEM) images showed that there existed a layer of sizing agent film with GO sheets evenly on the CF surface. Abrasion resistance and stiffness values of CF were tested and the results indicated that the sized CF conformed to the requirement of CF handleability. The interlaminar shear strength (ILSS) test indicated that the interfacial adhesion of the composite could be greatly improved. The fracture surfaces of CF composites were examined by SEM after ILSS tests. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42285.     

The Improvement in Mechanical and Barrier Properties of Poly(Vinyl Alcohol)/Graphene Oxide Packaging Films

In this study, poly(vinyl alcohol) (PVA)‐graphite oxide and PVA‐graphene oxide (XGO) films were prepared by simple and environmentally friendly method. Fourier transform infrared spectroscopy, X‐ray diffraction and scanning electron microscope revealed the strong hydrogen‐bonding interactions between XGO and PVA matrix and the layered structure of tensile fracture surfaces of exfoliated PVA‐XGO films. These resulted in a remarkable improvement on mechanical and barrier properties of XGO/PVA nanocomposite films. The addition of 0.3 and 2.0 wt.% XGO showed an increase in tensile strength (49%) and failure stain (13–22%), in comparison with the neat PVA films. The dramatic improvement of 144% in elastic modulus was observed in PVA/2.0 wt.% XGO. Both O₂ and water vapour permeability coefficients of PVA film decreased by about 76% and 21% at an XGO loading of 2.0 wt.%, respectively. Preliminary test was performed to determine the use of nanocomposite films to extend the shelf life of bananas. It was found that bananas packaged in nanocomposite films were ripened slower than those unpackaged or packaged in PVA films. These results demonstrate that such films could dramatically promote the application of PVA‐based films in the packaging industry. Copyright © 2015 John Wiley & Sons, Ltd.