Search Results (980)

Fiber-reinforced resin matrix composites are generally composed of fibers and matrix with significantly different properties, which are non-uniform and anisotropic in nature. Macro-failure criteria generally view composite plies as a uniform whole and do not accurately reflect fiber- and matrix-scale failures. In this study, the interface phase effect between fiber and matrix has been introduced into the frame of trans-scale analysis to better model the failure process, and the equivalent mechanical property characterization model of the interface phase has also been established. Combined with the macro–micro-strain transfer method, the trans-scale correlation of the mechanical response of the composite laminates between the macro scale and the fiber, matrix and interface micro scale has been achieved. Based on the micro-scale failure criterion and the stiffness reduction strategy, the trans-scale failure analysis method of composite materials incorporating the interface phase effect has been developed, which can simultaneously predict the failure modes of the matrix, fiber and interface phase. A numerical implementation of the developed trans-scale failure analysis method considering interface phase was carried out using the Python and Abaqus 2020 joint simulation technique. Case studies were carried out for three material systems, and the prediction data of the developed trans-scale failure analysis methodology incorporating interface phase effects for composite materials, the prediction data of the Linde failure criterion and the experimental data were compared. The comparison with experimental data confirms that this method has good prediction accuracy, and compared with the Linde and Hashin failure methods, only it can predict the failure mode of the fiber–matrix interface. The case analysis shows that its prediction accuracy has been improved by about 2–3%. Full article

Background: The implant–abutment joint is important for the long-term marginal tissue integrity in terms of biomimetic design that replicates the natural dentition under mastication forces. This study aimed to evaluate conical implant–abutment joints coupled at different tightening torque values through a mechanical fatigue test. Methods: Eighty conic implants (Ø: 3.8 mm L: 10 mm) with a 6° cone morse joint were embedded in resin blocks with an inclination of 30° ± 2°. The samples were divided into 8 groups (4 Test and 4 Control). The implant–abutment joints were coupled with different tightening torques: 25 Ncm (Group I), 30 Ncm (Group II), 35 Ncm (Group III) and 40 Ncm (Group IV). An in vitro cyclic loading test (1 × 10⁴ loads) was performed for 4 Test groups, while 4 Control groups did not receive any forces. All the samples were assessed with Scanning Electron Microscopy to compare the microfractures and microgaps on flexion and extension points. Results: Microscopy observation results showed significant differences among torque groups. We found that 30 Ncm had the best stability with less microgap. Conclusions: Tightening torque plays an important role in the distortion of the cone morse joint under mechanical forces. However, further studies should be conducted to validate the results using different implant–abutment joints for comparison. Full article

The dimensional accuracy of the intaglio surface of complete dentures fabricated using liquid crystal display (LCD) three-dimensional (3D) printing might be influenced by the build angle and post-processing storage conditions. This study evaluated the effect of build angle and natural light exposure duration on the intaglio surface trueness of maxillary complete denture bases. Standardized denture base designs (2 mm uniform thickness) were fabricated using an LCD 3D printer (Lilivis Print; Huvitz, Seoul, Republic of Korea) at build angles of 0°, 45°, and 90° (n = 7 per group). All specimens were printed using the same photopolymer resin (Tera Harz Denture; Graphy, Seoul, Republic of Korea) and identical printing parameters, followed by ultrasonic cleaning and ultraviolet post-curing. Specimens were stored under controlled light-emitting diode lighting and exposed to natural light (400–800 lux) for 0, 14, or 30 days. The intaglio surfaces were scanned and superimposed on the original design data, following the International Organization for Standardization 12836. Quantitative assessment included root mean square deviation, mean deviation, and tolerance percentage. Statistical analyses were performed using one-way analysis of variance and paired t-tests (α = 0.05). Build angle and light exposure duration significantly affected surface trueness (p < 0.05). The 90° build angle group exhibited the highest accuracy and dimensional stability, while the 0° group showed the greatest deviations (p < 0.05). These findings underscore the importance of optimizing build orientation and storage conditions in denture 3D printing. Full article

Phosphorylated cellulose is proposed as a bio-resin for the removal of heavy metals, as a substitute for synthetic polymer-based materials. Phosphorylation is carried out using kraft pulp fibers as the cellulose source, with phosphate esters and urea as reactants to prevent significant fiber degradation. Herein, phosphorylated fibers, with three types of counterions (sodium, ammonium, or hydrogen), are used in adsorption trials involving four individual metals: nickel, copper, cadmium, and lead. The Langmuir isotherm model is applied to determine the maximum adsorption capacities at four different temperatures (10, 20, 30, and 50 °C), enabling the calculation of the Gibbs free energy (ΔG), entropy (ΔS), and enthalpy (ΔH) of adsorption. The results show that the adsorption capacity of phosphorylated fibers is equal or even higher than that of commercially available resins (1.7–2.9 vs. 2.4–2.6 mmol/g). However, the nature of the phosphate counterion plays an important role in the adsorption capacity, with the alkaline form showing a superior ion exchange capacity than the hybrid form and acid form (2.7–2.9 vs. 2.3–2.7 vs. 1.7–2.5 mmol/g). The thermodynamic analysis indicates the spontaneous (ΔG = (-)16–(-)30 kJ/mol) and endothermic nature of the adsorption process with positive changes in enthalpy (0.45–15.47 kJ/mol) and entropy (0.07–0.14 kJ/mol·K). These results confirm the high potential of phosphorylated lignocellulosic fibers for ion exchange applications, such as the removal of heavy metals from process or wastewaters. Full article

Polyoxometalates (POMs) surrounded by organic cations and related systems composed of POMs immobilized on functionalized Merrifield resin (MR) were synthesized, characterized and tested as catalysts for the oxidation of two natural terpenes, β-myrcene and β-caryophyllene, using H₂O₂ and TBHP as green oxidants. The ionic immobilization enabled easy catalyst recovery and reuse. The results showed high conversion and selectivity, with some catalysts maintaining their efficiency for at least three runs without leaching. The catalytic performances of both homogeneous and heterogeneous systems, along with the necessary characterizations, are discussed. Full article

There has been a growing interest in polymer-based materials in recent years, and current research is focused on reducing fossil-derived epoxy compounds. This review examines the potential of epoxidised vegetable oils (EVOs) as sustainable alternatives to these systems. Epoxidation processes have been systematically analysed and their influence on chemical, thermal, and mechanical properties has been assessed. Results indicate that basic, low-toxicity epoxidation methods resulted in resins with comparable performance to those obtained through more complex common/commercial procedures. In total, 5–7% oxirane oxygen content (OOC) was found to be optimal to achieve a balanced crosslink density, thus enhancing tensile strength. Furthermore, mechanical properties have been insufficiently studied, as less than half of the studies were conducted at least tensile or flexural strength. Reinforcement strategies were also explored, with nano-reinforcing carbon nanotubes (CBNTs) showing the best mechanical and thermal results. Natural fibres reported better mechanical performance when mixed with EVOs than conventional systems. On the other hand, one of the main constraints observed is the lack of consistency in reporting key chemical and mechanical parameters across studies. Environmental properties and end-of-life use are significant challenges to be addressed in future studies, as there remains a significant gap in understanding the end-of-life of these materials. Future research should focus on the exploration of eco-friendly epoxidation reagents and standardise protocols to compare and measure oil properties before and after being epoxidised. Full article

Biodiesel, a renewable and environmentally friendly alternative to fossil fuels, has attracted significant attention due to its potential to reduce greenhouse gas emissions. However, high production costs and complex processing remain challenges. Heterogeneous catalysts have shown promise in overcoming these barriers by offering benefits, such as easy separation, reusability, low-cost raw materials, and the ability to reduce reaction times and energy consumption. This review evaluates key classes of heterogeneous catalysts, such as metal oxides, ion exchange resins, and zeolites, and their performance in transesterification and esterification processes. It highlights the importance of catalyst preparation methods, textural properties, including surface area, pore volume, and pore size, activation techniques, and critical operational parameters, like the methanol-to-oil ratio, temperature, time, catalyst loading, and reusability. The analysis reveals that catalysts supported on high surface area materials often achieve higher biodiesel yields, while metal oxides derived from natural sources provide cost-effective and sustainable options. Challenges, such as catalyst deactivation, sensitivity to feedstock composition, and variability in performance, are discussed. Overall, the findings underscore the potential of heterogeneous catalysts to enhance biodiesel production efficiency, although further optimization and standardized evaluation protocols are necessary for their broader industrial application. Full article

Epoxy adhesives derived from bisphenol A diglycidyl ether (BADGE) are widely utilized in segmental construction—particularly in precast concrete structures—and in building structural strengthening, owing to their outstanding adhesion properties and long-term durability. These materials constitute a significant class of polymeric adhesives in structural engineering applications. However, BADGE-based epoxy adhesives are susceptible to aging under service conditions, primarily due to environmental stressors such as thermal cycling, oxygen exposure, moisture ingress, ultraviolet radiation, and interaction with corrosive media. These aging processes lead to irreversible physicochemical changes, manifested as degradation of microstructure, mechanical properties, and dynamic mechanical properties to varying degrees, with performance deterioration becoming increasingly significant over time. Notably, for the mechanical properties of concern, the decline can exceed 40% in accelerated aging tests. A comprehensive understanding of the aging behavior of BADGE-based epoxy resin under realistic environmental conditions is essential for predicting long-term performance and ensuring structural safety. This paper provides a critical review of existing studies on the aging behavior of BADGE-based epoxy resins. This paper summarizes the findings of various aging tests involving different influencing factors, identifies the main degradation mechanisms, and evaluates current methods for predicting long-term durability (such as the Arrhenius method, Eyring model, etc.). Furthermore, this review provides recommendations for future research, including investigating multifactorial aging, conducting natural exposure tests, and establishing correlations between laboratory-based accelerated aging and field-exposed conditions. These recommendations aim to advance the understanding of long-term aging mechanisms and enhance the reliability of BADGE-based epoxy resins in structural applications. Full article

Background/objectives: Propolis, known for its medicinal properties, faces challenges in pharmaceutical applications due to its low aqueous solubility, attributed to its resinous and hydrophobic nature. This limits oral administration, reducing its bioavailability and pharmacological activities. To overcome these barriers, cyclodextrins (CDs), cyclic oligosaccharides, are widely studied as carrier systems that enhance the solubility and bioavailability of propolis and other nonpolar compounds. This study aimed to review patents that developed innovative therapeutic approaches to improve the physicochemical and biological properties of propolis through complexation with CDs. Methods: Active and application patents registered over the last 17 years were searched across multiple databases, resulting in the selection of eight inventions for detailed analysis. Results: These patents highlight therapeutic applications of propolis–CD systems for conditions such as diabetes and skin and gastrointestinal cancers, as well as antimicrobial, immunostimulant, and antioxidant effects. Additionally, novel extraction processes free of organic solvents, including nanometric-scale powder extracts, are described. Conclusions: Findings from scientific articles support the patent data, demonstrating that CD complexation significantly enhances the solubility and therapeutic efficacy of propolis. Thus, these patents present an innovative and promising strategy for developing propolis-based pharmaceutical products. Full article

This work presents the development of two vanillin-based vitrimer epoxy flax fibre-reinforced composites, with both the VER1-1-FFRC (a vitrimer-to-epoxy ratio of 1:1) and VER1-2-FFRC (a vitrimer-to-epoxy ratio of 1:2), via a vacuum-assisted resin infusion. The thermal and mechanical properties of the resulting vitrimer epoxy flax composites were characterised using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and mechanical four-point bending tests, alongside studies of solvent resistance and chemical recyclability. Both the VER1-1-FFRC (degradation temperature T_deg of 377.0 °C) and VER1-2-FFRC (T_deg of 395.9 °C) exhibited relatively high thermal stability, which is comparable to the reference ER-FFRC (T_deg of 396.7 °C). The VER1-1-FFRC, VER1-2-FFRC, and ER-FFRC demonstrated glass transition temperatures T_g of 54.1 °C, 68.8 °C, and 83.4 °C, respectively. The low T_g of the vitrimer composite is due to the low crosslink density in the vitrimer epoxy resin. Particularly, the crosslinked density of the VER1-1-FFRC was measured to be 319.5 mol·m⁻³, which is lower than that obtained from the VER1-2-FFRC (434.7 mol·m⁻³) and ER-FFRC (442.9 mol·m⁻³). Furthermore, the mechanical properties of these composites are also affected by the low crosslink density. Indeed, the flexural strength of the VER1-1-FFRC was found to be 76.7 MPa, which was significantly lower than the VER1-2-FFRC (116.2 MPa) and the ER-FFRC (138.3 MPa). Despite their lower thermal and mechanical performance, these vitrimer composites offer promising recyclability and contribute to advancing sustainable composite materials. Full article

The increasing demand for sustainable materials has intensified the interest in natural fiber-reinforced composites (NFRCs) as environmentally friendly alternatives to synthetic composites. However, NFRCs often face limitations in thermal stability, restricting their use in high-temperature environments. To address this, the present study explores the hybridization of cellulosic flax fibers with protein-based wool fibers to improve thermal stability without compromising mechanical integrity. Wool–flax hybrid composites were fabricated using a bio-based epoxy resin through a resin infusion technique with different fiber proportions. The flexural properties of these composites were evaluated under varying temperature conditions to assess the influence of fiber composition and thermal conditions. This study specifically examined the impact of wool fiber content on the flexural performance of the composites under thermal conditions, including behavior near and above the matrix’s glass transition temperature. The results showed that the flexural properties of the hybrid biocomposites were significantly affected by temperature. Compared with specimens tested at room temperature, the flexural modulus of all variants decreased by 85–94%, while the flexural strength declined by 79–85% at 120 °C, depending on the variant. The composite variant with a higher wool content (variant 3W) exhibited enhanced flexural performance, demonstrating an average of 15% greater flexural strength than other variants at 60 °C and 5% higher at 120 °C. These findings suggest that incorporating wool fibers into flax-based composites can effectively improve thermal stability while maintaining flexural properties, supporting the development of sustainable biocomposites for structural applications. Full article

As a large class of natural organic compounds, vegetable oil is generally composed of 95% fatty acid triglycerides and very few complex non-triglycerides. It has many advantages, such as sufficient yield, low price, distinct structural characteristics, and biodegradability. UV curing technology is known as a new method for the green industry in the 21st century due to its high efficiency, economy, energy conservation, high adaptability, and environmental friendliness. Therefore, UV-curable resins based on UV-curing technology has attracted widespread attention, converting epoxy soybean oil, castor oil, tung oil and other vegetable oils into high-performance plant oil-based UV-curable resins with higher molecular weight, multi-rigid ring and high reactivity, and the curing performance has been greatly improved, and the technology has been widely used in the field of polymer materials such as coatings, inks and adhesives. In this article, the recent research progress on this topic was summarized, and emphasis was put on the research on the resins from soybean oil and castor oil. Full article

The dependence of conventional epoxy resins on fossil fuels and the environmental and health hazards associated with bisphenol A (BPA) demand the creation of sustainable alternatives. Because lignin is a natural resource and has an aromatic ring skeleton structure, it could be used as an alternative to fossil fuels. This study effectively resolved this challenge by utilizing a sustainable one-step epoxidation process to transform lignin into a bio-based epoxy resin. The results verified the successful synthesis of epoxidized bamboo lignin through systematic characterization employing Fourier transform infrared spectroscopy, hydrogen spectroscopy/two-dimensional heteronuclear single-quantum coherent nuclear magnetic resonance, quantitative phosphorus spectroscopy, and gel permeation chromatography. Lignin-based epoxy resins had an epoxy equivalent value of 350–400 g/mol and a weight-average molecular weight of 4853 g/mol. Studies on the curing kinetics revealed that polyetheramine (PEA-230) demonstrated the lowest apparent activation energy (46.2 kJ/mol), signifying its enhanced curing efficiency and potential for energy conservation. Mechanical testing indicated that the PEA-230 cured network demonstrated the maximum tensile strength (>25 MPa), whereas high-molecular-weight polyetheramine (PEA-2000) imparted enhanced elongation to the material. Lignin-based epoxy resins demonstrated superior heat stability. This study demonstrates the conversion of bamboo lignin into bio-based epoxy resins using a simple, environmentally friendly synthesis process, demonstrating the potential to reduce fossil resource use, efficiently use waste, develop sustainable thermosetting materials, and promote a circular bioeconomy. Full article

We report the fabrication of lightweight porous carbon structures via UV-assisted photopolymerization molding using a commercial photocurable resin modified with natural tannin and sodium carboxymethyl cellulose (NaCMC) as sustainable additives. A systematic analysis was conducted by applying a Design of Experiments (DOE) approach and regression modeling to evaluate the effects of varying blend compositions on carbon yield and mechanical strength. The results indicate that increasing the tannin content led to a maximum carbon yield of 13.43%, with an average porosity of approximately 80% and a compressive strength around 1 kPa. NaCMC was found to effectively control the resin viscosity within printable limits of 0.2537 Pa·s, although NaCMC indirectly improved carbonization efficiency through normalized yield analysis. This work highlights the synergistic role of bio-based polymers in tuning porous carbon properties. The findings provide a data-driven framework for designing sustainable polymer-derived carbon materials, bridging additive manufacturing with green chemistry. Full article

Sustainability and the circular economy are increasingly recognized as global priorities, particularly in industrial waste management. This study explores the development of a sustainable composite material using wood waste and natural fibers, contributing to circular economy practices. Sandwich panels were manufactured with a green epoxy resin matrix, incorporating wood waste in the core and flax fibers in the outer layers. Mechanical tests on the sandwich panel revealed a facing bending stress of 92.79 MPa and a core shear stress of 2.43 MPa. The panel demonstrated good compressive performance, with an edgewise compressive strength of 61.39 MPa and a flatwise compressive strength of 96.66 MPa. The material’s viscoelastic behavior was also characterized. In stress relaxation tests (from an initial 21 MPa), the panel’s stress decreased by 20.2% after three hours. The experimental relaxation data were successfully fitted by the Kohlrausch–Williams–Watts (KWW) model for both short- and long-term predictions. In creep tests, the panel showed a 21.30% increase in displacement after three hours under a 21 MPa load. For creep behavior, the KWW model was preferable for short-term predictions, while the Findley model provided a better fit for long-term predictions. Full article