Influence of Oxidation Level of Graphene Oxide on the Mechanical Performance and Photo-Oxidation Resistance of a Polyamide 6

Packaging Materials Based on Styrene-Isoprene-Styrene Triblock Copolymer Modified with Graphene

This study presents the improved stabilization effects of graphene on a polymer substrate, namely a styrene-isoprene-styrene triblock copolymer (SIS) which creates opportunities for long-term applications and radiation processing. The added graphene has a remarkable activity on the protection of polymer against their oxidation due to the penetration of free macroradical fragments into the free interlayer space. The chemiluminescence procedure used for the evaluation of the progress of oxidation reveals the delaying effect of oxidative degradation by the doubling extension of oxidation induction time, when the material formulation containing graphene is oxidized at 130 °C. The pristine polymer that is thermally aged requires an activation energy of 142 kJ mol^-1, while the modified material needs 148, 158 and 169 kJ mol^-1, for the oxidative degradation in the presence of 1, 2 and, respectively, 3 wt% of graphene. The contribution of graphene content (1 wt%) on the stability improvement of SIS is demonstrated by the increase of onset oxidation temperature from 190 °C for neat polymer to 196 °C in the presence of graphene and to 205 °C for the polymer stabilized with graphene and rosemary extract. The addition of graphene into the polymer formulations is a successful method for enlarging durability instead of the modification of receipt with synthesis antioxidants. The presumable applications of these studied materials cover the areas of medical wear, food packaging, commodities, sealing gaskets and others that may also be included through the products for nuclear power plants.

Hierarchically Structured Hybrid Membranes for Continuous Wastewater Treatment via the Integration of Adsorption and Membrane Ultrafiltration Mechanisms

Growing environmental concerns are stimulating researchers to develop more and more efficient materials for environmental remediation. Among them, polymer-based hierarchical structures, attained by properly combining certain starting components and processing techniques, represent an emerging trend in materials science and technology. In this work, graphene oxide (GO) and/or carbon nanotubes (CNTs) were integrated at different loading levels into poly (vinyl fluoride-co-hexafluoropropylene) (PVDF-co-HFP) and then electrospun to construct mats capable of treating water that is contaminated by methylene blue (MB). The materials, fully characterized from a morphological, physicochemical, and mechanical point of view, were proved to serve as membranes for vacuum-assisted dead-end membrane processes, relying on the synergy of two mechanisms, namely, pore sieving and adsorption. In particular, the nanocomposites containing 2 wt % of GO and CNTs gave the best performance, showing high flux (800 L × m^-2 h^-1) and excellent rejection (99%) and flux recovery ratios (93.3%), along with antifouling properties (irreversible and reversible fouling below 6% and 25%, respectively), and reusability. These outstanding outcomes were ascribed to the particular microstructure employed, which endowed polymeric membranes with high roughness, wettability, and mechanical robustness, these capabilities being imparted by the peculiar self-assembled network of GO and CNTs.

Effects of Moisture and Synthesis-Derived Contaminants on the Mechanical Properties of Graphene Oxide: A Molecular Dynamics Investigation

This paper reports on the effects of the chemical composition of graphene oxide (GO) sheets on the mechanical properties of bulk GO. Three key factors were analyzed: (i) the oxygenated functional groups' concentration, (ii) the content of intersheet water (moisture), and (iii) the presence of residual contaminants observed from the synthesis of GO. Molecular dynamics simulations using the reactive force field ReaxFF were conducted to model tensile strength, indentation, and shear stress tests. The structural integrity of the carbon basal plane was the primary variable that determined mechanical behavior of GO slabs. Hydrogen-bond networks played an essential role in the tensile fracture mechanism, delaying the onset of fracture whenever strong hydrogen bonds existed in the intersheet space. The presence of interlayer sulfate ion contaminants negatively impacted the tensile strength, stiffness, and toughness of GO. Moreover, it was observed that intersheet sulfate ions improved the resistance to fracture of GO at low sulfur concentrations, while lower fracture strains were observed beyond a critical concentration. Alike the tensile stress findings, the indentation properties were determined by the integrity of the carbon basal plane. Our findings agree with experimental mechanical property measurements and reveal the importance of considering synthesis-derived contaminants in molecular models of GO.

Functional groups in graphene oxide

Graphene oxide consists of diverse surface chemistry which allows tethering GO with additional functionalities and tuning its intrinsic properties. This review summarizes recently advanced methods to covalently modify GO for specific applications.

An Overview of Functionalized Graphene Nanomaterials for Advanced Applications

Interest in the development of graphene-based materials for advanced applications is growing, because of the unique features of such nanomaterials and, above all, of their outstanding versatility, which enables several functionalization pathways that lead to materials with extremely tunable properties and architectures. This review is focused on the careful examination of relationships between synthetic approaches currently used to derivatize graphene, main properties achieved, and target applications proposed. Use of functionalized graphene nanomaterials in six engineering areas (materials with enhanced mechanical and thermal performance, energy, sensors, biomedical, water treatment, and catalysis) was critically reviewed, pointing out the latest advances and potential challenges associated with the application of such materials, with a major focus on the effect that the physicochemical features imparted by functionalization routes exert on the achievement of ultimate properties capable of satisfying or even improving the current demand in each field. Finally, current limitations in terms of basic scientific knowledge and nanotechnology were highlighted, along with the potential future directions towards the full exploitation of such fascinating nanomaterials.

Graphene Oxides Derivatives Prepared by an Electrochemical Approach: Correlation between Structure and Properties

Graphene oxide (GO) can be defined as a single monolayer of graphite with oxygen-containing functionalities such as epoxides, alcohols, and carboxylic acids. It is an interesting alternative to graphene for many applications due to its exceptional properties and feasibility of functionalization. In this study, electrochemically exfoliated graphene oxides (EGOs) with different amounts of surface groups, hence level of oxidation, were prepared by an electrochemical two-stage approach using graphite as raw material. A complete characterization of the EGOs was carried out in order to correlate their surface topography, interlayer spacing, defect content, and specific surface area (SSA) with their electrical, thermal, and mechanical properties. It has been found that the SSA has a direct relationship with the d-spacing. The EGOs electrical resistance decreases with increasing SSA while rises with increasing the D/G band intensity ratio in the Raman spectra, hence the defect content. Their thermal stability under both nitrogen and dry air atmospheres depends on both their oxidation level and defect content. Their macroscopic mechanical properties, namely the Young’s modulus and tensile strength, are influenced by the defect content, while no correlation was found with their SSA or interlayer spacing. Young moduli values as high as 54 GPa have been measured, which corroborates that the developed method preserves the integrity of the graphene flakes. Understanding the structure-property relationships in these materials is useful for the design of modified GOs with controllable morphologies and properties for a wide range of applications in electrical/electronic devices.

The Effects of Nanoclay on the Mechanical Properties, Carvacrol Release and Degradation of a PLA/PBAT Blend

The formulation of polymeric films endowed with the abilities of controlled release of antimicrobials and biodegradability is the latest trend of food packaging. Biodegradable polymer (Bio-Flex^®)-based nanocomposites containing carvacrol as an antimicrobial agent, and a nanoclay as a filler, were processed into blown films. The presence of such hybrid loading, while not affecting the overall filmability of the neat matrix, led to enhanced mechanical properties, with relative increments up to +70% and +200% in terms of elastic modulus and elongation at break. FTIR/ATR analysis and release tests pointed out that the presence of nanoclay allowed higher carvacrol loading efficiency, reasonably hindering its volatilization during processing. Furthermore, it also mitigated the burst delivery, thereby enabling a more controlled release of the antimicrobial agent. The results of mass loss tests indicated that all the formulations showed a rather fast degradation with mass losses ranging from 37.5% to 57.5% after 876 h. The presence of clay and carvacrol accelerated the mass loss rate of Bio-Flex^®, especially when added simultaneously, thus indicating an increased biodegradability. Such ternary systems could be, therefore, particularly suitable as green materials for food packaging applications, and for antimicrobial wrapping applications.

Tailorable Synthesis of Highly Oxidized Graphene Oxides via an Environmentally-Friendly Electrochemical Process

Graphene oxide (GO) is an attractive alternative to graphene for many applications due to its captivating optical, chemical, and electrical characteristics. In this work, GO powders with a different amount of surface groups were synthesized from graphite via an electrochemical two-stage process. Many synthesis conditions were tried to maximize the oxidation level, and comprehensive characterization of the resulting samples was carried out via elemental analysis, microscopies (TEM, SEM, AFM), X-ray diffraction, FT-IR and Raman spectroscopies as well as electrical resistance measurements. SEM and TEM images corroborate that the electrochemical process used herein preserves the integrity of the graphene flakes, enabling to obtain large, uniform and well exfoliated GO sheets. The GOs display a wide range of C/O ratios, determined by the voltage and time of each stage as well as the electrolyte concentration, and an unprecedented minimum C/O value was obtained for the optimal conditions. FT-IR evidences strong intermolecular interactions between neighbouring oxygenated groups. The intensity ratio of D/G bands in the Raman spectra is high for samples prepared using concentrated H2SO4 as an electrolyte, indicative of many defects. Furthermore, these GOs exhibit smaller interlayer spacing than that expected according to their oxygen content, which suggests predominant oxidation on the flake edges. Results point out that the electrical resistance is conditioned mostly by the interlayer distance and not simply by the C/O ratio. The tuning of the oxidation level is useful for the design of GOs with tailorable structural, electrical, optical, mechanical, and thermal properties.

Composite Films of Polydimethylsiloxane and Micro-Graphite with Tunable Optical Transmittance

In this paper we introduce a polydimethylsiloxane (PDMS) composite fabricated using a simple production process and demonstrate the optical transmittance properties of this composite in the 300–1000 nm wavelength region. We control the material’s transmittance by varying the microcrystalline graphite powder concentration or the composite film’s thickness. In addition, we tailor the specimens into various trapezoidal shapes and load these specimens by mechanically stretching them in the direction perpendicular to both their base lines and their top lines. The advantage of this method is that a wide range of transmittance properties can be obtained for a given specimen. Furthermore, samples with different trapezoidal shapes have different transmittance tuning capabilities.