Search Results (24)

Developing high-performance bio-based epoxy resins as sustainable alternatives to petroleum-derived bisphenol A (BPA) epoxies for recyclable carbon fiber-reinforced polymers (CFRPs) is pivotal in materials research. Herein, the bio-based bisphenol monomer BDEF was synthesized from the lignin derivative 4-propylguaiacol. The derived epoxy monomer BDEF-EP was cured with adipic acid to form a bio-based vitrimer. Stress relaxation synergistically accelerates through intrinsic dynamic carboxylic acid ester exchange and enhanced chain mobility from the flexible propyl structure. At 220 °C, this vitrimer shows rapid stress relaxation (τ* < 30 s) and repairs ~90% of surface scratches in 30 min. It exhibits tensile and flexural strengths of 69 MPa and 105 MPa, respectively. BDEF-EP’s low viscosity reduces diluent needs in composite fabrication, lowering costs and improving efficiency. The resulting bio-based CFRP achieves tensile and flexural strengths of 543 MPa and 414 MPa, respectively, which are comparable to commercially available petroleum-derived CFRP. In addition, CFRP containing dynamic crosslinked networks demonstrates degradable recyclability in ethylene glycol solvent, preserving the surface morphology and chemical structure of recovered carbon fibers. The results demonstrate that this bio-based epoxy vitrimer has promising potential for developing sustainable, degradable, and recyclable CFRP composites. Full article

Lightweight concrete (LWC) has emerged as a transformative material in sustainable and high-performance construction, driven by innovations in engineered lightweight aggregates, supplementary cementitious materials (SCMs), fiber reinforcements, and geopolymer binders. These advancements have enabled LWC to achieve compressive strengths surpassing 100 MPa while reducing density by up to 30% compared to conventional concrete. Fiber incorporation enhances flexural strength and fracture toughness by 20–40%, concurrently mitigating brittleness and improving ductility. The synergistic interaction between SCMs and lightweight aggregates optimizes matrix densification and interfacial transition zones, curtailing shrinkage and bolstering durability against chemical and environmental aggressors. Integration of recycled and bio-based aggregates substantially diminishes the embodied carbon footprint by approximately 40%—aligning LWC with circular economy principles. Nanomaterials such as nano-silica and carbon nanotubes augment early-age strength development by 25% and refine microstructural integrity. Thermal performance is markedly enhanced through advanced lightweight fillers, including expanded polystyrene and aerogels, achieving up to a 50% reduction in thermal conductivity, thereby facilitating energy-efficient building envelopes. Although challenges persist in cost and workability, the convergence of hybrid fiber systems, optimized mix designs, and sophisticated multi-scale modeling is expanding the applicability of LWC across demanding structural, marine, and prefabricated contexts. In essence, LWC’s holistic development embodies a paradigm shift toward resilient, low-carbon infrastructure, cementing its role as a pivotal material in the evolution of next-generation sustainable construction. Full article

Three-dimensional (3D) printing represents a pivotal technological advancement in dental prosthetics, fundamentally transforming the fabrication of provisional crowns and bridges through innovative vat photopolymerization methodologies, specifically stereolithography (SLA) and digital light processing (DLP). This comprehensive scholarly review critically examines the technological landscape of 3D-printed resin-based dental provisional crowns and bridges, systematically analyzing their material performance, clinical applications, and prospective developmental trajectories. Empirical investigations demonstrate that these advanced restorations exhibit remarkable mechanical characteristics, including flexural strength ranging from 60 to 90 MPa and fracture resistance of 1000–1200 N, consistently matching or surpassing traditional manufacturing techniques. The digital workflow introduces substantial procedural innovations, dramatically reducing fabrication time while simultaneously achieving superior marginal adaptation and internal architectural precision. Despite these significant technological advancements, critical challenges persist, encompassing material durability limitations, interlayer bonding strength inconsistencies, and the current paucity of longitudinal clinical evidence. Contemporary research initiatives are strategically focused on optimizing resin formulations through strategic filler incorporation, enhancing post-processing protocols, and addressing fundamental limitations in color stability and water sorption characteristics. Ultimately, this scholarly review aims to provide comprehensive insights that will inform evidence-based clinical practices and delineate future research trajectories in the dynamically evolving domain of digital dentistry, with the paramount objective of advancing patient outcomes through technological innovation and precision-driven methodological approaches. Full article

Mullite–corundum ceramics are pivotal in heat transfer pipelines and thermal energy storage systems due to their excellent mechanical properties, thermal stability, and chemical resistance. Establishing relationships and mechanisms through traditional experiments is time-consuming and labor-intensive. In this study, gradient boosting regression (GBR), random forest (RF), and artificial neural network (ANN) models were developed to predict essential properties such as apparent porosity, bulk density, water absorption, and flexural strength of mullite–corundum ceramics. The GBR model (R² 0.91–0.95) outperformed the RF and ANN models (R² 0.83–0.89 and 0.88–0.91, respectively) in accuracy. Feature importance and partial dependence analyses revealed that sintering temperature and K₂O (~0.25%) positively affected bulk density while negatively influencing apparent porosity and water absorption. Additionally, sintering temperature, additives, and Fe₂O₃ (optimal content ~5% and 1%, respectively) were positively related to flexural strength. This approach provided new insight into the relationships between feedstock compositions and sintering process parameters and ceramic properties, and it explored the possible mechanisms involved. Full article

The bending stiffness of beams represents a pivotal parameter influencing both the dimensions of the elements during their design and their subsequent utilisation. It is evident that excessive deflections can cause discomfort to users and contribute to further structural degradation. The objective of this study was to enhance the bending stiffness of timber beams by bonding a composite sheet to their external surfaces. A carbon sheet exhibiting an ultra-high modulus of elasticity and low elongation at rupture was employed. Two variables of analysis can be distinguished including whether the reinforcement was applied or not and the number of reinforcement layers. The beams, with nominal dimensions of 80 × 80 × 1600 mm, were subjected to a four-point bending test in order to ascertain their mechanical properties. In total, 15 beams were tested (5 unreinforced and 10 reinforced). The reinforcement had no appreciable impact on the increase in flexural load capacity, with the maximum average increase recorded at 9%. Nevertheless, an increase in stiffness of 34% was observed. Additionally, significant increases were observed in ductility up to 248%. However, the ductile behaviour of the beam occurred after the rupture of the reinforcement. In all instances, the failure was attributed to the fracturing of the wooden components or the UHM CFRP (ultra-high-modulus-carbon-fibre-reinforced polymer) sheet. The numerical analysis proved to be a valuable tool for predicting the stiffness of the wood–composite system, with a relatively low error margin of a few percentage points. The modified approach, based on the equivalent cross-section method, permits the determination of a bilinear load deflection relationship for reinforced beams. The aforementioned curve is indicative of the actual behaviour. Given the propensity for the sudden rupture of reinforcement, the described method of reinforcement is recommended for beams subjected to lower levels of stress. Full article

The production of multipurpose sustainable fillers is a matter of great interest, and biochar can play a pivotal role. Biochar is a biomass-derived carbon source that can act as a versatile platform for the engineering of fillers as neat or functionalized materials. In this work, we investigate the utilization of 800 °C annealed Miscanthus-derived biochar as a filler for the production of epoxy composites with promising mechanical and electrical properties. We also used it in the production of an iron-rich hybrid filler in order to fine-tune the surface and bulk properties. Our main findings reveal that hybrid composites containing 20 wt.% biochar exhibit a 27% increase in Young’s modulus (YM), reaching 1.4 ± 0.1 GPa, while the ultimate tensile strength (UTS) peaks at 30.3 ± 1.8 Mpa with 10 wt.% filler, a 27% improvement over pure epoxy. However, higher filler loadings (20 wt.%) result in decreased UTS and maximum elongation. The optimal toughness of 0.58 ± 0.14 MJ/m³ is observed at 5 wt.% filler content. For organic composites, YM sees a notable increase of 90%, reaching 2.1 ± 0.1 Gpa at 20 wt.%, and UTS improves by 32% with the same filler content. Flexural tests indicate an enhanced elastic modulus but reduced maximum elongation as filler content rises. Electromagnetic evaluations show that hybrid fillers maintain a primarily dielectric behavior with a negligible impact on permittivity, while biochar–epoxy composites exhibit increased conductivity at higher filler loadings, suitable for high-frequency applications. In light of these results, biochar-based fillers demonstrate significant potential for enhancing the mechanical and electrical properties of epoxy composites. Full article

This article focuses on the development of a 3D-printed 2-degree-of-freedom (DOF) joint for the payloads’ orientation on small satellites. This system is a compliant mechanism, meaning that this monolithic system composed of cross-axis flexural pivots (CAFPs) produces complex movements through the elastic deformation of its structure. Using fused filament fabrication (FFF), a demonstrator made of Polyetherketoneketone (PEKK) is printed to determine its potential compatibility with space conditions. Focusing on a segment of the joint, the CAFP, this study aims for an enhancement of its mechanical behavior through the study of its printing direction and the creation of an accurate finite element model of this compliant mechanism. First, material characterization of 3D-printed PEKK is achieved through differential scanning calorimetry tests of the filament and flexural and tensile tests of specimens printed in different printing directions. Then, these data are used to perform a finite element analysis of different CAFP designs and compare their mechanical response of their 3D-printed twin using digital image correlation software. Finally, the CAFP structures were observed by X-ray tomography. The results show that printing direction greatly influences both flexural and tensile strength. Voids induced by the FFF process could impact the mechanical behavior of 3D-printed parts as the simple CAFP design has a better test/model correlation than complex ones. This could influence its resistance to space environment. Full article

The flywheel is a widespread mechanical component used for the storage of kinetic energy and angular momentum. It typically consists of cylindrical inertia rotating about its axis on rolling bearings, which involves undesired friction, lubrication, and wear. This paper presents an alternative mechanism that is functionally equivalent to a classical flywheel while relying exclusively on limited-stroke flexure joints. This novel one-degree-of-freedom zero-force mechanism has no wear and requires no lubrication: it is thus compatible with extreme environments, such as vacuum, cryogenics, or ionizing radiation. The mechanism is composed of two coupled pivoting rigid bodies whose individual angular momenta vary during motion but whose sum is constant at all times when the pivoting rate is constant. The quantitative comparison of the flexure-based flywheel to classical ones based on a hollow cylinder as inertia shows that the former typically stores 6 times less angular momentum and kinetic energy for the same mass while typically occupying 10 times more volume. The freedom of design of the shape of the rigid bodies offers the possibility of modifying the ratio of the stored kinetic energy versus angular momentum, which is not possible with classical flywheels. For example, a flexure-based flywheel with rigid pivoting bodies in the shape of thin discs stores 100 times more kinetic energy than a classical flywheel with the same angular momentum. A proof-of-concept prototype was successfully built and characterized in terms of reaction moment generation, which validates the presented analytical model. Full article

The escalating global demand for polymer products and the consequent disposal challenge necessitate technological and sustainable solutions. Recent advances in the development of materials used in 3D printing equipment are described in this review, with a focus on new biocomposite materials. The investigation delves into biocomposites comprising PLA and its blends with other polymers, reinforced by plant fibers, with a particular focus on research conducted over the last five years. The information related to the raw materials’ physical, chemical, and processing properties necessary for creating biocomposite filament and printed parts were summarized. The best results in terms of tensile and flexural strength were presented and discussed, signposting future research avenues and desirable objectives. The findings elucidate that the inclusion of plant fibers led to a reduction in mechanical strength relative to pure PLA; however, when smaller particle sizes of plant fibers were added in volumes below 10%, it resulted in improved performance. Moreover, physical and/or chemical pretreatment of fibers, along with the isolation of cellulose fibrils, emerged as pivotal strategies for bolstering mechanical strengths. Noteworthy are the promising prospects presented by the incorporation of additives, while the refinement of printing parameters is key to improving the tensile and flexural strength of printed components. Full article

This research primarily delves into a comprehensive investigation concerning the synergistic effects of fly ash (FA) with yellow pigment (YP) and red pigment (RP) in the workability, physical characteristics, and mechanical properties of colored mortars, both pre-and post-exposure to high temperatures. Within the experimental design, FA was employed as a 20% substitute for cement, while YP and RP were systematically incorporated into the cement mixtures at varying concentrations (1%, 3%, and 5% by weight). The specimens underwent controlled exposure to high temperatures, ranging from 300 °C to 800 °C. This study’s outcomes unveiled that while the introduction of FA positively influenced mortar workability, including YP and RP adversely impacted spreading diameters (SD), resulting in a discernible reduction in overall workability. Despite these effects, FA emerged as a pivotal factor to enhancing the residual compressive strength (RCS) and residual flexural strength (RFS) of the colored mortars. For instance, after 90 days at 800 °C, the control concrete (R0) exhibited a notable 66.13% decrease in RCS, and the sample solely incorporating FA (R1) demonstrated a reduced reduction of 55.39%. Similarly, mortars with YP additives (R2–R4) and RP additives (R5–R7) showcased RCS reductions within the range of 53.32% to 55.12% and 54.51% to 56.04%, respectively. Full article

The incorporation of thermoplastics with pigments imparts diverse aesthetic qualities and properties to colored thermoplastic products. The selection of pigment type and content, along with specific processing conditions, plays a pivotal role in influencing color properties and overall product performance. This study focuses on optimizing these parameters to ensure the desired color quality and product functionality. Two types of polypropylene copolymer (PPCP) with different melt flow rates (MFRs) and acrylonitrile butadiene styrene (ABS) were compounded with ultramarine blue pigment masterbatch (MB) in concentrations ranging from 1 to 5 wt.% using a twin-screw extruder. The compounding process was conducted at a constant screw speed of 200 rpm and a die temperature of 210 °C. The effects of screw speed and die temperature were investigated at a constant MB of 3 wt.%. Colored samples were fabricated by injection molding. Microscopic analysis revealed a well-dispersed pigment within the PPCP matrix when using the MB. Rheological properties, assessed through the power law index, confirmed effective pigment dispersion, facilitated by shear thinning behavior and controlled shear rate via the manipulation of screw speed and die temperature. The effects of masterbatch contents and processing conditions on color spaces were evaluated using CIELAB and CIELCH, with one-way ANOVA employed to identify statistical significance. Higher opacity in high-MFR PPCP and ABS resulted in increased lightness and color strength, surpassing low-MFR PPCP by 15–40% at equivalent MB contents. Masterbatch content emerged as a significant factor influencing the color spaces of all colored thermoplastics. Further analysis, including Fisher pairwise comparisons of one-way ANOVA, revealed that screw speed influenced the redness and hue of low-MFR PPCP, whereas die temperature affected the lightness and hue of high-MFR PPCP and ABS. Interestingly, the blueness and chroma of colored thermoplastics were minimally affected by both screw speed and die temperature. Notably, regardless of processing conditions, the flexural properties of colored thermoplastics remained comparable to the neat polymer when incorporated with ultramarine blue pigment masterbatch. Full article

Natural and synthetic fibers offer a multitude of advantages within the automotive sector, primarily due to their lightweight properties, including appealing characteristics such as adequate mechanical strength, low density, improved acoustic–thermal insulation, cost-effectiveness, and ready availability. In this study, we aimed to strengthen epoxy-based composites with natural and synthetic fibers using bamboo and glass, respectively. Additionally, the reinforcement processing of this hybrid composite material was optimized using a Taguchi L9 (nine experimental runs) orthogonal array design with linear modeling through the Design of Experiment (DoE) principles. The fibers were alkali-treated with sodium hydroxide (NaOH), and the composites were manufactured through the hand lay-up process at ambient temperature and characterized comprehensively using ASTM standard methods. The experimental results of the bamboo–glass fiber composite materials presented a significantly high tensile strength of 232.1 MPa and an optimum flexural strength of 536.33 MPa. Based on the overall Taguchi and linear modeling analysis, the NaOH treatment, fiber content, and epoxy resin concentration were optimized. These findings reveal that the ideal combination consists of 20% fiber content, 8% NaOH treatment, and 65% epoxy resin concentration. The statistical method Analysis of Variance (ANOVA) was employed to confirm the significance of these factors. The integration of the amount (%) of bamboo fiber used played a pivotal role in influencing the mechanical properties of this hybrid composite. Overall, this study demonstrates that the reinforcement of natural fiber with polymeric material composites on epoxy enhanced the composite characteristics and quality. Therefore, this bamboo–glass–epoxy-based composite can be recommended for lightweight structural applications, especially in the automotive sector, in the future. Full article

Rapid construction with an energy-efficient approach is a major challenge in the present construction industry. Cement, a carbon-intensive material, is mainly used in the construction industry and hence increases the sector’s carbon footprint on the environment. The current review focuses on the study of 3D concrete printing (3DCP), in which cement is partially replaced with industrial byproducts such as ground granulated blast furnace slag (GGBS), fly ash, and silica fume. Walling material is primarily targeted in 3DCP. There is a need to include energy efficiency to achieve a thermally comfortable environment. The life cycle assessment (LCA) of concrete is studied to discover the potential conflicts affecting the environment. The sand-to-binder ratio is pivotal in determining the performance of concrete. The content of the supplements is decided based on this factor. The rheological, physical, and mechanical properties of 3DCP are studied further and analysed. GGBS demonstrates better performance in the compressive and flexure strength of concrete. The usage of fly ash and silica fume has reduced the thermal conductivity of the material, whereas GGBS has increased it. An LCA study shows that 3DCP can be made sustainable with the use of these supplementary cementitious materials. Full article

Three-dimensional (3D) printing is proving to be a pivotal technology for developing personalized dosage forms with bench to bedside feasibility. Fused deposition modelling (FDM) 3D printing has emerged as the most used technique wherein molten drug-loaded polymer filaments are deposited layer-by-layer to fabricate a predefined shape and internal geometry. However, for precise FDM 3D printing, it is imperative for the filaments to have peculiar mechanical/physicochemical properties, which the majority of the FDA/GRAS approved polymers lack. In the current study, a novel water-soluble polymer, Poly(2-ethyl-tetra-oxazoline) [PETOx] has been investigated as an extrudable and printable polymer with two different types of drug molecule—dextromethorphan hydrobromide (DXM) and hydrochlorothiazide (HCTZ). Hot-stage microscopy experiments of drug:polymer (1:1 w/w) and filaments were carried out at 25–275 °C. HCTZ-loaded filament showed higher toughness of 17 ± 3.25 × 10⁶ J/m³ compared with DXM and drug-free filament. Moisture sorption and flexural analysis was performed to understand the correlation of mechanical properties and storage humidity to printability. Varying the number of outer perimeters of each layer (shell number) was observed to affect the drug release pattern from the printlets. The DXM one-shell printlet showed >80%, whereas the DXM five-shell printlet showed >60% of the drug release within 60 min. PETOx could prove to be a high-performance and versatile 3D printable polymer. Full article

This work describes the advances on a micro-newton torsional thrust balance for ionic liquid electrospray thruster (ILET) being developed in the National University of Defense Technology. The torsional thrust balance adopts an asymmetric pendulum arm about a flexural pivot, and an electrostatic comb device is used for calibration, which makes the balance compact and allows the measurement of the micro-newton level thrust with high accuracy. To minimize the influence of gravity on the measurement results, a two-dimensional adjustable counterweight mechanism is adapted to balance the entire arm and make its mass center close to the pivot axis. Mechanical oscillations are passively damped with an eddy current damper. A series of experimental studies are carried out in a vacuum chamber; the results provide validation that the balance has good linearity in the range of 2–30 μN, with the resolution better than 0.21 μN and the settling time to a step force is less than 7 s, which can meet the thrust measurement requirements of the ILET operating in the mode of alternating work voltage polarity. In addition, we find that the electrostatic force generated by the power supply wire has a non-negligible influence on thrust measurement results, which needs to be considered in the actual thrust measurement. Full article