An Overview on Carbon Fiber-Reinforced Epoxy Composites: Effect of Graphene Oxide Incorporation on Composites Performance

Multiscale Carbon Fibre-Carbon Nanotube Composites of Poly(Vinyl Chloride)-An Evaluation of Their Properties and Structure

To date, there has been limited information in the literature on the application of carbon fibre-carbon nanotube systems for the modification of poly(vinyl chloride) (PVC) matrixes by micro- and nanometric fillers and an evaluation of the properties of the unique materials produced. This paper presents the results of newly designed unique multiscale composites. The advantages of the simultaneous use of carbon fibres (CFs) and carbon nanotubes (CNTs) in PVC modification are discussed. To increase the dispersibility of the nanofiller, CFs together with nanotubes were subjected to a sonication process. The resulting material was introduced into PVC blends, which were processed by extrusion. The ratio of components in the hybrid filler with CF_CNT was 20:1, and its proportion in the PVC matrix was 1, 5, and 10 wt.%, respectively. Comparatively, PVC composites modified only with carbon fibres were obtained. The structure, thermal, electrical, and mechanical properties and swelling resistance of the composites were studied. The study showed a favourable homogeneous dispersion of nanotubes in the PVC matrix. This enabled effective modification of the structure at the nanometric level and the formation of an interpenetrating network of well-dispersed hybrid filler, as evidenced by a decrease in volume resistivity and improvement in swelling resistance, as well as an increase in glass transition temperature in the case of PVC/CF_CNT composites.

Surface Degradation of DGEBA Epoxy Resins Cured with Structurally Different Amine Hardeners: Effects of UV Radiation

In this study, the effects of three diamine curing agents (aromatic, cycloaliphatic, aliphatic) on the photochemical behavior of bisphenol A diglycidyl ether networks were comparatively examined. In order to monitor structural changes and study the curing agents' action mode, the cured epoxy resins were characterized before and after photoirradiation by means of Fourier-transform infrared spectroscopy, contact angle, differential scanning calorimetry, scanning electron microscopy, and energy-dispersive X-ray analysis, mass loss, and color modification measurements. Water absorption tests were also conducted. The cured epoxy resins are to be used in different multicomponent polymer materials for outdoor protection. The presence of the cycloaliphatic hardener led to reduced water absorption, and after UV irradiation, an increase in the glass transition temperature and lowest mass loss of the corresponding cured epoxy resin compared to the ones cured with aromatic and aliphatic hardener.

Enhancing the Interfacial Shear Strength and Tensile Strength of Carbon Fibers through Chemical Grafting of Chitosan and Carbon Nanotubes

Multi-scale "rigid-soft" material coating has been an effective strategy for enhancing the interfacial shear strength (IFSS) of carbon fibers (CFs), which is one of the key themes in composite research. In this study, a soft material, chitosan (CS), and a rigid material, carbon nanotubes (CNTs), were sequentially grafted onto the CFs surface by a two-step amination reaction. The construction of the "rigid-soft" structure significantly increased the roughness and activity of the CFs surface, which improved the mechanical interlocking and chemical bonding between the CFs and resin. The interfacial shear strength (IFSS) of the CS- and CNT-modified CFs composites increased by 186.9% to 123.65 MPa compared to the desized fibers. In addition, the tensile strength of the modified CFs was also enhanced by 26.79% after coating with CS and CNTs. This strategy of establishing a "rigid-soft" gradient modulus interfacial layer with simple and non-destructive operation provides a valuable reference for obtaining high-performance CFs composites.

Molecular Understanding of Adhesion of Epoxy Resin to Graphene and Graphene Oxide Surfaces in Terms of Orbital Interactions

The adhesion mechanism of epoxy resin (ER) cured material consisting of diglycidyl ether of bisphenol A (DGEBA) and 4,4'-diaminodiphenyl sulfone (DDS) to pristine graphene and graphene oxide (GO) surfaces is investigated on the basis of first-principles density functional theory (DFT) with dispersion correction. Graphene is often used as a reinforcing filler incorporated into ER polymer matrices. The adhesion strength is significantly improved by using GO obtained by the oxidation of graphene. The interfacial interactions at the ER/graphene and ER/GO interfaces were analyzed to clarify the origin of this adhesion. The contribution of dispersion interaction to the adhesive stress at the two interfaces is almost identical. In contrast, the DFT energy contribution is found to be more significant at the ER/GO interface. Crystal orbital Hamiltonian population (COHP) analysis suggests the existence of hydrogen bonding (H-bonding) between the hydroxyl, epoxide, amine, and sulfonyl groups of the ER cured with DDS and the hydroxyl groups of the GO surface, in addition to the OH-π interaction between the benzene rings of ER and the hydroxyl groups of the GO surface. The H-bond has a large orbital interaction energy, which is found to contribute significantly to the adhesive strength at the ER/GO interface. The overall interaction at the ER/graphene is much weaker due to antibonding type interactions just below the Fermi level. This finding indicates that only dispersion interaction is significant when ER is adsorbed on the graphene surface.

Improving Bond Performance and Reducing Cross-Linker Dosage of Soy Protein Adhesive via Hyper-Branched and Organic-Inorganic Hybrid Structures

Eco-friendly soybean protein adhesives could be an ideal substitute for replacing traditional formaldehyde-based adhesives in wood industry. However, a large number of cross-linking agents are required in soy protein adhesive formulations to obtain sufficiently performing properties. Inspired by the high performance of nacre and branched structures, a hyper-branched amine (HBPA) was synthesized and grafted to graphene oxide (GO), generating a hyper-branched amine-functionalized GO (FGO). A novel soy protein-based adhesive was developed by mixing FGO with soy protein (SPI) and a low dose polyamidoamine-epichlorohydrin (PAE). Results showed that the addition of only 0.4 wt% FGO and 0.75 wt% PAE to the SPI adhesive formulation enhanced the wet shear strength of plywood to 1.18 MPa, which was 181% higher than that of the adhesive without enhancement. The enhanced performance is attributed to the denser cross-linking structure and improved toughness of the adhesive layer. Using FGO in the adhesive formulation also greatly reduced the concentration of the additive cross-linker by up to 78.6% when compared with values reported in the literature. Thus, using a hyper-branched functionalized nano-material to form an organic-inorganic hybrid structure is an effective and efficient strategy to reinforce the composites and polymers. It significantly reduces the chemical additive levels, and is a practical way to develop a sustainable product.

Self-healable fiber-reinforced vitrimer composites: overview and future prospects

To achieve sustainable development goals, approaches towards the preparation of recyclable and healable polymeric materials is highly attractive. Self-healing polymers and thermosets based on bond-exchangeable dynamic covalent bonds, so called "vitrimers" could be a great effort in this direction. In order to match the industrial importance, enhancement of mechanical strength without sacrificing the bond exchange capability is a challenging issue, however, such concerns can be overcome through the developments of fiber-reinforced vitrimer composites. This article covers the outstanding features of fiber-reinforced vitrimer composites, including their reprocessing, recycling and self-healing properties, together with practical applications and future perspectives of this unique class of materials.

Bio-Vitrimers for Sustainable Circular Bio-Economy

The aim to achieve sustainable development goals (SDG) and cut CO₂-emission is forcing researchers to develop bio-based materials over conventional polymers. Since most of the established bio-based polymeric materials demonstrate prominent sustainability, however, performance, cost, and durability limit their utilization in real-time applications. Additionally, a sustainable circular bioeconomy (CE) ensures SDGs deliver material production, where it ceases the linear approach from production to waste. Simultaneously, sustainable circular bio-economy promoted materials should exhibit the prominent properties to involve and substitute conventional materials. These interceptions can be resolved through state-of-the-art bio-vitrimeric materials that display durability/mechanical properties such as thermosets and processability/malleability such as thermoplastics. This article emphasizes the current need for vitrimers based on bio-derived chemicals; as well as to summarize the developed bio-based vitrimers (including reprocessing, recycling and self-healing properties) and their requirements for a sustainable circular economy in future prospects.

Novel Composites of Poly(vinyl chloride) with Carbon Fibre/Carbon Nanotube Hybrid Filler

This article presents the results of studies of poly(vinyl chloride) (PVC) composites modified with a hybrid carbon filler of carbon fibres (CFs) and multiwalled carbon nanotubes (MWCNTs). The hybrid filler was produced by a solvent method, using poly(vinyl acetate) (PVAc) as an adhesive. The proportion of components in the hybrid filler with CF-CNT-PVAc was 50:2.5:1, respectively. The obtained hybrid filler was evaluated by SEM, TG, and Raman spectroscopy. The PVC composites were produced by extrusion with proportions of the hybrid filler as 1 wt%, 5 wt%, or 10 wt%. Thermal stability by the TG method, mechanical properties, and the glass transition temperature (T_g) by the DMA and DSC methods were determined. The composite structure was evaluated by SEM and Raman spectroscopy. The effect of the hybrid filler on electrical properties was investigated by studying the cross and surface resistivity. It was concluded that, aside from a substantial increase in the elastic modulus, no substantial improvement in the PVC/CF/CNT composites' mechanical properties was observed; however, slight increases in thermal stability and Tg were noted. The addition of the hybrid filler contributed to a substantial change in the composites' electrical properties. SEM observations demonstrated improved CNT dispersibility in the matrix, however, without a completely homogeneous coverage of CF by CNT.

Methods for Enhancing the Electrical Properties of Epoxy Matrix Composites

This paper presents ways to modify epoxy resin matrix composites to increase their electrical conductivity. Good electrical properties are particularly important for materials used in the construction of vehicles (cars, trains, airplanes) and other objects exposed to lightning (e.g., wind turbines). When the hull plating is made of an electrical conductor (e.g., metal alloys) it acts as a Faraday cage and upon lightning discharge the electrical charge does not cause damage to the structure. Epoxy-resin-based composites have recently been frequently used to reduce the weight of structures, but due to the insulating properties of the resin, various modifications must be applied to improve the conductivity of the composite. The methods to improve the conductivity have been categorized into three groups: modification of the matrix with conductive fillers, modification of the composite reinforcement, and addition of layers with increased electrical conductivity to the composite.