Effect of Graphene Oxide as a Reinforcement in a Bio-Epoxy Composite

Graphene oxide (GO) has gained interest within the materials research community. The presence of functional groups on GO offers exceptional bonding capabilities and improved performance in lightweight polymer composites. A literature review on the tensile and flexural mechanical properties of synthetic epoxy/GO composites was conducted that showed differences from one study to another, which may be attributed to the oxidation level of the prepared GO. Herein, GO was synthesized from oxidation of graphite flakes using the modified Hummers method, while bio-epoxy/GO composites (0.1, 0.2, 0.3 and 0.6 wt.% GO) were prepared using a solution mixing route. The GO was characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscope (TEM) analysis. The thermal properties of composites were assessed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). FTIR results confirmed oxidation of graphite was successful. SEM showed differences in fractured surfaces, which implies that GO modified the bio-epoxy polymer to some extent. Addition of 0.3 wt.% GO filler was determined to be an optimum amount as it enhanced the tensile strength, tensile modulus, flexural strength and flexural modulus by 23, 35, 17 and 31%, respectively, compared to pure bio-epoxy. Improvements in strength were achieved with considerably lower loadings than traditional fillers. Compared to the bio-epoxy, the 0.6 wt.% GO composite had the highest thermal stability and a slightly higher (positive) glass transition temperature (Tg) was increased by 3.5 °C, relative to the pristine bio-epoxy (0 wt.% GO).

Investigation of Carbon Nanotube Grafted Graphene Oxide Hybrid Aerogel for Polystyrene Composites with Reinforced Mechanical Performance

The rational design of carbon nanomaterials-reinforced polymer matrix composites based on the excellent properties of three-dimensional porous materials still remains a significant challenge. Herein, a novel approach is developed for preparing large-scale 3D carbon nanotubes (CNTs) and graphene oxide (GO) aerogel (GO-CNTA) by direct grafting of CNTs onto GO. Following this, styrene was backfilled into the prepared aerogel and polymerized in situ to form GO–CNTA/polystyrene (PS) nanocomposites. The results of X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy indicate the successful establishment of CNTs and GO-CNT and the excellent mechanical properties of the 3D frameworks using GO-CNT aerogel. The nanocomposite fabricated with around 1.0 wt% GO-CNT aerogel displayed excellent thermal conductivity of 0.127 W/m∙K and its mechanical properties were significantly enhanced compared with pristine PS, with its tensile, flexural, and compressive strengths increased by 9.01%, 46.8%, and 59.8%, respectively. This facile preparation method provides a new route for facilitating their large-scale production.

Performance Evaluation of Red Clay Binder with Epoxy Emulsion for Autonomous Rammed Earth Construction

Existing rammed earth construction methods have disadvantages such as increased initial costs for manufacturing the large formwork and increased labor costs owing to the labor-intensive construction techniques involved. To address the limitations of the existing rammed earth construction methods, an autonomous rammed earth construction method was introduced herein. When constructing an autonomous rammed-earth construction method, an alternative means of assuring the performance at the initial age of the binder in terms of materials is needed. In this study, in order to satisfy the performance of the red clay binder, epoxy emulsion was added to analyze the compressive strength, water loosening, shrinkage, rate of mass change, and microstructure in the range of the initial age. As a result of the analysis, the applicability of the epoxy emulsion was confirmed as a new additive for application to an autonomous rammed-earth construction method.

Thin Nacre-Biomimetic Coating with Super-Anticorrosion Performance

The rigorous organic and inorganic laminated structure of nacre has been developed by millions of years of biological evolution against various external impacts, including mechanical loadings and chemical attacks. Nacre-biomimetic materials have been recognized as an effective strategy to achieve high strength and toughness simultaneously. However, the understanding of nacre-like structure from the perspective of corrosion protection is still very limited. This work investigates the anticorrosion performance of nacre-biomimetic GO/epoxy (NBGE) coatings with alternating layers. Potentiodynamic polarization measurements indicated that the corrosion rate of steel protected by the NBGE coating with 5 layers of GO and 6 layers of epoxy (5NBGE) and a total thickness of 17 μm was 20 times slower than that of steel under the pure epoxy coating twice as thick in 3.5 wt % NaCl solution. Electrochemical impedance spectroscopy measurements revealed the importance and functions of the GO layers in NBGE coatings. The 5NBGE coating exhibited better performance than carbon-based nanoparticle/epoxy mixed coatings. The superior anticorrosion performance of the NB5G6E coating was supported by photographic observations, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and chloride diffusion measurements. The strong cross-linking layer-by-layer structure of NBGE coatings was proved by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analyses. The anticorrosion mechanism of the NBGE coatings was interpreted by the mitigation of chemical reactions occurring at the steel-coating interface due to the restricted intrusion of O₂, H₂O, and Cl^- through the reduced pores and defects by the intercalated GO layers in the coatings.

Effect of Interfacial Polarization and Water Absorption on the Dielectric Properties of Epoxy-Nanocomposites

Five types of nanofillers, namely, silica, surface-silylated silica, alumina, surface-silylated alumina, and boron nitride, were tested in this study. Nanocomposites composed of an epoxy/amine resin and one of the five types of nanoparticles were tested as dielectrics with a focus on (i) the surface functionalization of the nanoparticles and (ii) the water absorption by the materials. The dispersability of the nanoparticles in the resin correlated with the composition (OH content) of their surfaces. The interfacial polarization of the thoroughly dried samples was found to increase at lowered frequencies and increased temperatures. The β relaxation, unlike the interfacial polarization, was not significantly increased at elevated temperatures (below the glass-transition temperature). Upon the absorption of water under ambient conditions, the interfacial polarization increased significantly, and the insulating properties decreased or even deteriorated. This effect was most pronounced in the nanocomposite containing silica, and occurred as well in the nanocomposites containing silylated silica or non-functionalized alumina. The alternating current (AC) breakdown strength of all specimens was in the range of 30 to 35 kV·mm-1. In direct current (DC) breakdown tests, the epoxy resin exhibited the lowest strength of 110 kV·mm-1; the nanocomposite containing surface-silylated alumina had a strength of 170 kV·mm-1. In summary, water absorption had the most relevant impact on the dielectric properties of nanocomposites containing nanoparticles, the surfaces of which interacted with the water molecules. Nanocomposites containing silylated alumina particles or boron nitride showed the best dielectric properties in this study.

The Effect of Graphene on the Protective Properties of Water-Based Epoxy Coatings on Al2024-T3

0.5 and 1% wt. of graphene nanoflakes were added to an anticorrosive additives-free water-based epoxy resin applied to Al2024-T3 samples. Calorimetric (DSC) and adhesion (cross-cut test) tests indicated that the presence of graphene did not affect the polymerization process of the resin or its adhesion to the substrate while it had some effect on its wettability. Electrochemical Impedance Spectroscopy (EIS) results obtained suggested that the addition of a small amount of graphene greatly enhanced the protective properties of the epoxy coating, retarding electrolytes absorption and reducing the total amount of adsorbed water. The latter occurrence suggests that the graphene effect on coating performances is related to both extended diffusion pathway length and graphene/matrix interaction due to the unique properties of graphene.