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Recently, the growth of the recyclability of carbon fiber reinforced polymer (CFRP) composites has been driven by environmental and circular economic aspects. The main aim of this research work is to investigate the strength retention of a bio-based vitrimer composite reinforced with carbon fibers, which offers both recyclability and material reusability. The composite formulation consisted of an epoxy resin composed of diglycidyl ether of bioshpenol A (DGEBA) combined with tricarboxylic acid (citric acid, CA) and cardanol, which was then reinforced with carbon fibers to enhance its performance. Differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were performed to analyze the chemical composition and curing behavior of the vitrimer. Mechanical testing under tensile loading at room temperature was carried out on epoxy, vitrimer, and associated carbon fiber reinforced composite materials. The results demonstrated that the DGEBA/CA/cardanol vitrimer exhibited thermomechanical properties comparable to those of an epoxy cured with petroleum-based curing agents. It was observed that the maximum tensile strength of vitrimer is about 50 MPa, which is very close to the range of epoxy resins cured with petroleum-based curing agents. Notably, the ability of the vitrimer composite to be effectively dissolved in a dimethylformamide (DMF) solvent is a significant advantage, as it enables the recovery of the fibers. The recovered carbon fiber retained comparable tensile strength to that of the fresh carbon composites. More than 95% strength was retained after the first recovery, which confirms the use of fibers for primary and secondary applications. These research results open up new avenues for efficient recycling and contribute to the overall sustainability of the composite material at an economic level. [ABSTRACT FROM AUTHOR]

The objective of this study is to assess, characterize, and forecast the aging effects on the mechanical properties of a vegetable‐based polyurethane foam (PUF) derived from castor oil under elevated relative humidity conditions and at two distinct load orientations (aligned with the expansion direction and perpendicular to it). Ten specimens were subjected to temperatures of 60, 75, and 90°C, along with a relative humidity of 90%, for a duration of up to 60 days. Compression tests, following ASTM D1621‐16 standards and supplemented by 3D digital image correlation, revealed nearly isotropic behavior with marginally lower compression strength in the expansion direction. On the other hand, the strength of the foams at 90°C was higher in that direction. This led to a smaller activation energy (Ea) in this property, which ended up showing a shorter lifespan prediction considering the strength retention in this direction. The stiffness values were proportionally more similar in both directions than the strength ones and this was observed in the Ea for those curves. In contrast to several other foams and polyurethanes, the one examined in this study exhibited consistently higher Ea values for its mechanical properties, particularly in the transverse direction to expansion, surpassing 94 kJ/mol. This indicates a robust diffusion and chemical stability, suggesting its potential for prolonged utilization compared to conventional oil‐based foams. A prediction was made that this foam would lose 50% of its stiffness and strength in around 9.8 and 9.5 years at 20°C, respectively, considering the directions more sensitive to the aging process. This research offers valuable insights for predicting lifespan based on operating temperatures and property retention needs, contributing to the advancement of sustainable materials in structural applications. Highlights: Fifty specimens investigated for each of two directions.Evaluation of vegetable‐based PUF aging process unveils density changes.Unique behavior noted: different Ea values for each direction.High Ea values indicate enhanced mechanical stability over oil‐based foams.Lifespan prediction enhances material application prospects. [ABSTRACT FROM AUTHOR]

This overview aims at gathering the various existing works on interphases within epoxy/metal bonded assemblies. Indeed, this particular area plays an important role on the adhesion but also on the behavior in wet environment. Polymeric materials being hydrophilic, water diffusion occurs when they are in a humid environment. The water molecules then have an important impact on the mechanical and physical properties. The effect of water on the interfacial properties of adhesive joints is large discussed in literature. In this article, a complete interphase formation model is be proposed. This two-scenario model explain all the experimental results observed in the literature on the interfaces of a bonded joint. Moreover, hypotheses is made on the water diffusion mechanisms and the diffusive properties of the interface. This is allow explaining the change of the fracture surface observed during the wet aging of a bonded joint. A large number of studies have observed the transition from cohesive to adhesive failure. [ABSTRACT FROM AUTHOR]

Concrete is a major construction material that produces high levels of carbon dioxide in its manufacturing process. Hence the construction sector is responsible for relevant environmental impacts. This justifies the need to find materials as green and ecological alternatives to common Portland cement. Geopolymers represent the most promising alternative due to its proven durability, mechanical and thermal properties. This study investigates the effects of solid-to-liquid and alkali activator ratios on the synthesis of slag-based pure geopolymer and their relation to the geopolymerization process. Two activating solutions were used: a) a mixture of sodium hydroxide, sodium silicate, and water; and b) a mixture of potassium hydroxide solution, potassium silicate, and water. As precursor material, ground blast furnace slag was used. Precursors and activators were mixed with solid-to-liquid ratios in range of 1.5 to 2.2. In the first stage of the study, the mechanical properties were evaluated for each activating solution. In the following stage, different formulations, with variations in the water percentage and solid-to-liquid ratio were tested for mechanical properties and SEM observations. Test results indicate that the resulting geopolymer has the potential for high compressive strength and is directly affected by the composition of the activating solution. It can also be observed that compressive strength was affected by solid-to-liquid ratio and % of water added to the mixture, and strength increased with ageing day.

This work seeks to improve the understanding of the durability of pure slag-based geopolymer composites containing glass fibers. Degradation by attack of saline mist, simulated by the salt-spray essay, was carried out for a period of 30 days. The test simulates the conditions found in the sea and nearby environments. The chamber works at relative humidity ∼97%, by nebulizing sodium chloride solutions with a concentration of 5% at 35 + 2 °C, solution pH between 6.5 and 7.2. After the cycle, the loss of mass and the compressive strength of the specimens were measured. The efflorescence formation in slag-based geopolymers is also assessed in this study to provide a better understanding of the effect of the synthesis parameters. It is noted that physical and chemical properties of geopolymers, and environmental exposure conditions can affect the rate of efflorescence formation. Besides the control set group, two different solutions to prevent efflorescence were tested, MgO and an efflorescence reduction agent from Sika®. The work aims to examine the effect of efflorescence formation on mechanical properties, through flexural and compressive strengths. A compromise between durability and mechanical properties was found for specimens enriched with 2% of efflorescence reduction agent. [ABSTRACT FROM AUTHOR]

The goal of this paper is to evaluate the strain-based partitioning method (SBM), an analytical method based on beam analysis, for the mixed-mode fracture characterization of asymmetric cracks. The fracture energy is calculated at the crack tip of mixed-mode bending (MMB) test with asymmetric geometry and asymmetric material parameters. The fracture energy obtained using SBM is benchmarked against the widely applied Williams' partitioning method (WM) and numerical results from finite element models using the virtual crack closure technique (VCCT). Results show that WM produces inaccurate fracture modes in asymmetric conditions. However, if using SBM, the fracture mode ratio of bi-material cracks was obtained with accuracy. SBM describes a coupling function between mode I and mode II fracture that allows the mode partitioning as long the specimen complies with a simple design criterion based on the longitudinal strain equivalence between arms. Experimental results of composite-to-metal bonded joints validate the results of the parametric study. SBM proves to be an easy and reliable solution for the mixed-mode fracture characterization of bi-material cracks. [ABSTRACT FROM AUTHOR]

Biodegradable, renewable, and environmentally friendly glycerol-based wood adhesives were synthesized through polycondensation reaction between dicarboxylic acids (sebacic and citric acid) and glycerol using different molar ratios, i.e. poly(glycerol sebacate) – PGS, poly(glycerol citrate-co-sebacate) – PGCS, and poly(glycerol citrate) – PGC. Thermal properties of the synthesized polymers were evaluated after cross-linking. Results showed that thermal stability was influenced by polymer molecular structure, being lower for PGC due to the presence of quaternary carbons of citric acid. Differential scanning calorimetry analyses showed an intermediate glass transition for the copolymer in comparison with homopolymers. Tensile shear strength tests showed that the presence of citric acid in the polymer improves adhesion and reduces adhesive flexibility, contrary to what happens to polymers with sebacic acid. This behavior was also proved through morphological analyses of the fracture surface. Adhesives with tailor-made properties were produced from glycerol, opening up new revenues for a by-product of the biodiesel production chain. [ABSTRACT FROM AUTHOR]

In the last years, the use of adhesive bonding is increasing as an alternative to traditional joining techniques due to their advantages such as ease of application, low weight and the good mechanical properties. To ensure good adherence between the substrates, adequate materials and surface treatment are required. The main objective of this work is to evaluate the adherence of epoxy and polyurethane adhesives between a pultruded composite material and a geopolymer. Two different surface treatments were evaluated: unidirectional abrasion (UA) and bidirectional abrasion (BA). Epoxy and polyurethane adhesives were tested. The epoxy and polyurethane adhesives showed, respectively, ductile and fragile behavior. The adherence of the bonded joints was evaluated using pull-off tests. Pultruded samples treated with UA and bonded with the polyurethane adhesive presented higher strength (13MPa). Geopolymer samples bonded with the epoxy adhesive and treated with UA reached a failure tensile of 8MPa. Considering the different testing conditions evaluated in this work, the best combination of an adhesive type and surface treatment produced an increase in the pull-off strength of 220 and 240% in pultruded composite bonded joints and geopolymer bonded joints, respectively. [ABSTRACT FROM AUTHOR]

The aim of this study is to assess the interlaminar adhesion of carbon-epoxy laminates under salt water condition. Carbon-epoxy laminate specimens were immersed in a salt water tank for 60 days. Some specimens were then dried at room temperature for 280 days, until recovering their initial weight. Specimens were tested using the composite peel test, an adaptation of the floating roller peel tests for composite materials. The results showed a degradation of peel strength in some areas due to the ageing process. The drying process did not affect the test results. A scanning electron microscopic analysis carried out on the fracture surface of the specimens revealed a typical mode I failure microstructure. A mixture of matrix failure and fibre/matrix interfacial failure was observed in non-aged specimens. Finally, a chemical characterization of the fracture surfaces with energy-dispersive spectroscopy confirmed the penetration of salt water in regions near the edge of the specimens. A degradation of the fibre/matrix interface adhesion was observed in affected areas. Floating roller peel tests proved to be a fast and effective method to access the interlaminar adhesion performance of composite laminates. [ABSTRACT FROM AUTHOR]