Infusion Simulation of Graphene-Enhanced Resin in LCM for Thermal and Chemo-Rheological Analysis

The present numerical study proposes a framework to determine the heat flow parameters-specific heat and thermal conductivity-of resin-graphene nanoplatelets (GNPs) (modified) as well as non-modified resin (with no GNPs). This is performed by evaluating the exothermic reaction which occurs during both the filling and post-filling stages of Liquid Composite Moulding (LCM). The proposed model uses ANSYS Fluent to solve the Stokes-Brinkman (momentum and mass), energy, and chemical species conservation equations to a describe nano-filled resin infusion, chemo-rheological changes, and heat release/transfer simultaneously on a Representative Volume Element (RVE). The transient Volume-of-Fluid (VOF) method is employed to track free-surface propagation (resin-air interface) throughout the computational domain. A User-Defined Function (UDF) is developed together with a User-Defined Scaler (UDS) to incorporate the heat generation (polymerisation), which is added as an extra source term into the energy equation. A separate UDF is used to capture intra-tow (microscopic) flow by adding a source term into the momentum equation. The numerical findings indicate that the incorporation of GNPs can accelerate the curing of the resin system due to the high thermal conductivity of the nanofiller. Furthermore, the model proves its capability in predicting the specific heat and thermal conductivity of the modified and non-modified resin systems utilising the computed heat of reaction data. The analysis shows an increase of ∼15% in the specific heat and thermal conductivity due to different mould temperatures applied (110-170 °C). This, furthermore, stresses the fact that the addition of GNPs (0.2 wt.%) improves the resin-specific heat by 3.68% and thermal conductivity by 58% in comparison to the non-modified thermoset resin. The numerical findings show a satisfactory agreement with and in the range of experimental data available in the literature.

Model Approach to Thermal Conductivity in Hybrid Graphene-Polymer Nanocomposites

The thermal conductivity of epoxy nanocomposites filled with self-assembled hybrid nanoparticles composed of multilayered graphene nanoplatelets and anatase nanoparticles was described using an analytical model based on the effective medium approximation with a reasonable amount of input data. The proposed effective thickness approach allowed for the simplification of the thermal conductivity simulations in hybrid graphene@anatase TiO2 nanosheets by including the phenomenological thermal boundary resistance. The sensitivity of the modeled thermal conductivity to the geometrical and material parameters of filling particles and the host polymer matrix, filler's mass concentration, self-assembling degree, and Kapitza thermal boundary resistances at emerging interfaces was numerically evaluated. A fair agreement of the calculated and measured room-temperature thermal conductivity was obtained.

Polymerization Kinetics of Acrylic Photopolymer Loaded with Graphene-Based Nanomaterials for Additive Manufacturing

Graphene-based nanomaterials (GBN) can provide attractive properties to photocurable resins used in 3D printing technologies such as improved mechanical properties, electrical and thermal conductivity, and biological capabilities. However, the presence of GBN can affect the printing process (e.g., polymerization, dimensional stability, or accuracy), as well as compromising the quality of structures. In this study an acrylic photocurable resin was reinforced with GBN, using methyl methacrylate (MMA) to favor homogenous dispersion of the nanomaterials. The objective was to investigate the influence that the incorporation of GBN and MMA has on polymerization kinetics by Differential Scanning Calorimetry using Model Free Kinetics, ultra-violet (UV) and thermal triggered polymerization. It was found that MMA catalyzed polymerization reaction by increasing the chain's mobility. In the case of GBNs, graphene demonstrated to inhibit both, thermally and UV triggered polymerization, whilst graphene oxide showed a double effect: it chemically inhibited the polymerization reaction during the initialization stage, but during the propagation stage it promoted the reaction. This study demonstrated that MMA can be used to achieve photocurable nanocomposites with homogenously dispersed GBN, and that the presence of GBN significantly modified the polymerization mechanism while an adaptation of the printing parameters is necessary in order to allow the printability of these nanocomposites.

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).

The correlated effects of polyetheramine-functionalized graphene oxide loading on the curing reaction and the mechanical properties of epoxy composites

In this study, the effects of polyetheramine (D230) functionalized graphene oxide loading on the curing reaction, thermal and mechanical properties of epoxy composites were studied and the correlation between structure and property of epoxy composite was established. In the functionalization of graphene oxide (GO), the effect of the mass ratio of D230 to GO on chemical properties of the functionalized GO was investigated. Results showed that D230 were successfully covalently grafted onto surface of two-dimensional functionalized GO sheet. The functionalized GO sheets prepared under optimal condition of D230/GO ratio of 1:1 dispersed evenly in epoxy composites, indicating the possibility of the epoxy composite fabrication by the solvent-free technique. The analysis of qualitative Cure Index suggested that epoxy composites were subjected to excellent curing. The quantitative evaluation of curing kinetics demonstrated that the functionalized GO exhibited a chemical facilitation on the curing reaction. However, the functionalized GO simultaneously physically restricted the curing reactivity, especially at high loading. These contributed to the improved interfacial properties and high toughness of the epoxy composites. Compared to neat epoxy, the epoxy composites showed effective tensile strength improvement of ∼10.0% (77.0 MPa), tensile modulus enhancement of ∼7.7% (3.34 GPa), flexural modulus increment of ∼12.1% (3.43 GPa), and flexural strength increment of ∼10.6% (124.3 MPa). This study demonstrated an effective and environment-friendly strategy to design GO reinforced epoxy composites with favorable dispersion and interfacial bonding, and it further clarified the relationship between the crosslinking network/interfacial structure and the mechanical properties of epoxy composites.

Nitrogen-doped graphene oxide as a catalyst for the oxidation of Rhodamine B by hydrogen peroxide: application to a sensitive fluorometric assay for hydrogen peroxide

The authors report that nitrogen-doped graphene oxide (NGO) catalyzes the oxidative decomposition of the fluorophore Rhodamine B (RhB) by hydrogen peroxide. The catalytic decomposition of hydrogen peroxide yields free hydroxyl radicals that destroy RhB so that the intensity of the yellow fluorescence is reduced. Nitrogen doping enhances the electronic and optical properties and surface chemical reactivities of GO such as widening of bandgap, increase in conductivity, enhanced quenching and adsorbing capabilities etc. The catalytic properties of NGO are attributed to its large specific surface and high electron affinity of nitrogen atoms. The chemical and structural properties of GO and NGO were characterized by XRD, FTIR, SEM, UV-visible and Raman spectroscopies. The method was optimized by varying the concentration of RhB, nitrogen dopant and hydrogen peroxide. The fluorescent probe, best operated at excitation/emission wavelengths of 554/577 nm, allows hydrogen peroxide to be determined in concentrations as low as 94 pM with a linear range spanning from 1 nM to 1 μM. Graphical abstract Schematic illustration of a fluorescence quenching method for the determination of H₂O₂. Upon addition of H₂O₂, nitrogen-doped graphene oxide (NGO) catalyzes the oxidation of Rhodamine B dye due to hydroxyl radical generation, which leads to a sensitive quenchometric methd for H₂ O₂.

Evaluation on Curing Properties and Kinetics of Isophthalonitrile Oxide

N,N-dihydroxybenzene-1,3-dicarboximidoyl dichloride was synthesized from benzene-1,3-dicarboxaldehyde and characterized by fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H and 13C NMR). The elastomer was prepared through the 1,3-dipolar cycloaddition of reaction between liquid polybutadiene (LPB) and isophthalonitrile oxide in this work. The tensile strength of different elastomer was enhanced from 0.14 MPa to 0.33 MPa as the elongation at break decreased from 145% to 73%, and the modulus increased from 0.09 kPa to 0.47 kPa. The parameters of kinetic indicated that the curing reaction was fi rst order reaction and the apparent activation energy of each curing system was less than 10.10 kJ/mol when the content of N,N-dihydroxybenzene-1,3- dicarboximidoyl dichloride was increased from 7% to 12%. These results suggested that nitrile oxides achieved curing of polymer binders at room temperature and this work had defi nite guiding signifi cance for the application of nitrile oxides in polymer binders.

Effects of Graphene Oxide and Chemically-Reduced Graphene Oxide on the Dynamic Mechanical Properties of Epoxy Amine Composites

Composites based on epoxy/graphene oxide (GO) and epoxy/reduced graphene oxide (rGO) were investigated for thermal-mechanical performance focusing on the effects of the chemical groups present on nanoadditive-enhanced surfaces. GO and rGO obtained in the present study have been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD) demonstrating that materials with different oxidation degrees have been obtained. Thereafter, GO/epoxy and rGO/epoxy nanocomposites were successfully prepared and thoroughly characterized by dynamic mechanical thermal analysis (DMTA) and transmission electron microscopy (TEM). A significant increase in the glass transition temperature was found in comparison with the neat epoxy. The presence of functional groups on the graphene surface leads to chemical interactions between these functional groups on GO and rGO surfaces with the epoxy, contributing to the possible formation of covalent bonds between GO and rGO with the matrix. The presence of oxidation groups on GO also contributes to an improved exfoliation, intercalation, and distribution of the GO sheets in the composites with respect to the rGO based composites.

Imidazolium Ionic Liquid Modified Graphene Oxide: As a Reinforcing Filler and Catalyst in Epoxy Resin

Surface modification of graphene oxide (GO) is one of the most important issues to produce high performance GO/epoxy composites. In this paper, the imidazole ionic liquid (IMD-Si) was introduced onto the surface of GO sheets by a cheap and simple method, to prepare a reinforcing filler, as well as a catalyst in epoxy resin. The interlayer spacing of GO sheets was obviously increased by the intercalation of IMD-Si, which strongly facilitated the dispersibility of graphene oxide in organic solvents and epoxy matrix. The addition of 0.4 wt % imidazolium ionic liquid modified graphene oxide (IMD-Si@GO), yielded a 12% increase in flexural strength (141.3 MPa), a 26% increase in flexural modulus (4.69 GPa), and a 52% increase in impact strength (18.7 kJ/m²), compared to the neat epoxy. Additionally the IMD-Si@GO sheets could catalyze the curing reaction of epoxy resin-anhydride system significantly. Moreover, the improved thermal conductivities and thermal stabilities of epoxy composites filled with IMD-Si@GO were also demonstrated.