Search Results (165)

FDM-printed polylactic acid (PLA) composites containing 5 and 10 wt% obsidian powder sourced from the Kars region of Eastern Anatolia (Turkey) were produced via twin-screw masterbatch extrusion and subsequent single-screw filament dilution. Mechanical (tensile, three-point flexure, notched Charpy impact, Shore D), physical (density), thermal (simultaneous TGA/DSC) and microstructural (macroscopic fractography and SEM at 100×–1000×) characterizations were performed on FDM-printed specimens. Young’s modulus rose monotonically by +9.0% at 5 wt% and +18.2% at 10 wt%, while ultimate tensile strength decreased by 12.4% and 17.3%, respectively. The flexural modulus increased by +15.2% at 5 wt% and plateaued at 10 wt% (+16.7%), whereas the flexural strength decreased by only 3.5% at 10 wt%, indicating that flexure-mode loading is markedly more tolerant of obsidian filler than axial tension. Shore D hardness rose by +2.11 points from 0 to 5 wt% with saturation thereafter. TGA showed a dual thermal effect: T₅ and T₁₀ dropped by 5–6 °C from 5 to 10 wt%, while the main decomposition rate decreased by ~46% and the decomposition interval widened from 9.7 to 23.5 °C, indicating a barrier/heat-shielding effect of dispersed silicate particles. SEM revealed a continuous ductile → transitional → brittle progression with increasing obsidian content; extended interfacial debonding lines at 10 wt% identified weak unmodified filler/matrix coupling as the principal performance-ceiling factor. Density measurements indicated a ~3–6% residual void fraction consistent with the inter-bead voids observed by SEM. To the authors’ knowledge, this is the first systematic study of obsidian as a reinforcing filler in PLA; the 5 wt% composition is identified as a strong candidate for esthetic, flexure-dominant, and low-load structural applications. Full article

The rapid development of additive manufacturing has enabled the production of personalized biomedical devices, including custom orthoses that must retain their structural integrity under demanding physiological conditions. This study evaluates the performance of 3D-printed polymers—blue and white polylactic acid (PLA), Standard Blue Resin, and an ecological soy-based resin—after exposure to simplified, controlled saline environments related to sweat contact and hygiene-associated conditions. Moisture absorption and Shore A hardness were analyzed as response variables to assess material stability under different experimental conditions. A surface methodology based on a Box–Behnken design was used to quantify the effects of specimen thickness (x₁), NaCl concentration (x₂), and immersion time (x₃) on the selected dependent variables. The results indicate that Standard Blue Resin showed the greatest surface hardness stability, whereas the bio-based materials (PLA and ecological resin) were more susceptible to moisture absorption, particularly in thinner polymeric sheets. The fitted quadratic models provide a predictive framework for optimizing material selection and geometric design in biomimetic wearable devices, supporting the development of orthoses with improved durability, hygiene, and long-term functional performance. Full article

Flexible thermoplastic polyurethane (TPU) materials fabricated using fused deposition modeling (FDM) are increasingly used in engineering and biomedical applications where exposure to moisture is unavoidable. However, the relationship between material hardness, water absorption, diffusion behaviour, and dimensional stability remains insufficiently understood and investigated. In this study, the hygroscopic behaviour of eight commercially available TPU filaments (60A–98A Shore hardness) was systematically investigated. Specimens were produced using an FDM 3D printer under controlled processing conditions and immersed in physiological solution (0.9% NaCl) for up to 96 h. Water absorption, dimensional changes, and diffusion characteristics were analyzed. Diffusion coefficients were determined using the Fickian diffusion model based on the initial stage of water uptake. The results suggest a transition in behaviour between lower- and higher-hardness materials. Softer TPU materials (60A–85A) exhibited higher water absorption (up to ~1.80%) and an apparent linear trend between hardness and absorption within the investigated material group (R² = 0.999). In contrast, higher-hardness materials (89A–98A) showed lower absorption (~1.18–1.42%) and a weaker apparent relationship with hardness (R² = 0.4214). Diffusion coefficients ranged from 1.40 × 10⁻¹³ to 3.40 × 10⁻¹² m² s⁻¹, with no monotonic dependence on hardness. Additionally, no clear correlation between diffusion kinetics and equilibrium absorption or volumetric expansion was observed. These findings indicate that hygroscopic behaviour of FDM-printed TPU materials cannot be reliably predicted based solely on hardness, and that diffusion, absorption, and swelling may be influenced by different mechanisms. The identified transition from hardness-dependent to behaviour potentially influenced by material structure provides new insight for the design and selection of flexible polymer components in moisture-exposed environments, particularly in biomedical applications. Full article

Our investigation into Hibiscus rosa-sinensis fibers (HRFs) for composite applications involved a multi-step process, primarily fiber extraction through water retting and subsequent surface modification by using sodium hydroxide (NaOH) and trimethoxy methyl silane (TMMS). Through the compression molding technique, untreated HRF-reinforced poly-lactic acid (PLA) composites (UHRFCs), NaOH-treated HRF-reinforced PLA composites (NHRFCs), and TMMS-treated HRF-reinforced PLA composites (THRFCs) were fabricated. The experiments were conducted, and the findings revealed a substantial increase in properties of both NHRFCs and THRFCs compared to UHRFCs. Notably, these enhancements encompassed tensile strength (13.66% and 19.39%), tensile modulus (13.41% and 20.70%), flexural strength (15.98% and 23.17%), flexural modulus (17.13% and 26.58%), impact strength (15.62% and 33.07%), Shore-D hardness (4.19% and 5.00%), storage modulus (9.88% and 13.07%), loss modulus (7.52% and 17.36%), dielectric constant at 6.5 Hz (13.22% and 23.96%), and significant improvements in the acoustic resonance frequency at 1897 Hz (79.50% and 81%). Peak thermal degradation temperatures of these composites are 420.62 ± 3.43 °C, 439.51 ± 3.54 °C, and 469.07 ± 3.11 °C, respectively, and biodegradability results showing accelerated degradation within 30 days. These findings highlight the substantial effectiveness of treatments in enhancing diverse properties, underscoring the potential applicability of these composites in various industrial sectors requiring superior performance and sustainable materials. Full article

The aim of this study was to evaluate setting time, hardness, solubility, bioactivity and interaction with dentin of four calcium silicate-based sealers (CSBS). Three single-phase CSBS (AH Plus Bioceramic/AHB, CeraSeal/CSL, TotalFill BC/TFL), one powder/liquid CSBS (BioRoot RCS/BRT) and an epoxy control (AH Plus Jet/AHP) were investigated. Setting time was evaluated on glass (G1) and dentin (G2) surfaces, by adding 1%wt purified water to single-phase products. For hardness measurements, the Shore-D hardness test was used. Solubility was assessed according to the ISO 6876:2012 standard. For bioactivity screening, 1-week set specimens were immersed in SBF or water (30 days/37 °C) and examined by ATR–FTIR spectroscopy. Interaction with dentin was tested by ATR–FTIR before and after contact with the sealers. For setting time in G1, all CSBS failed to comply with the ISO standard, while in G2, most materials were set in the range of 6–8 h, except for CSL. The ranking of significant differences in hardness was AHP, BRT > CSL, AHB, TFL. Regarding solubility, AHB, BRT and AHP were found to comply with the ISO standard, whereas CSL and TFL failed. For bioactivity, characteristic peaks of calcium phosphates were found in all CSBS, with TFL being the most bioactive. A chemical interaction between CSBS and dentin was registered, with a strong reduction in collagen peaks and an increase in carbonates. The CSBS tested exhibited great variance in their behaviour regarding the properties assessed, although a strong deproteinating effect was registered on dentin for all. Full article

Purpose: Pure three-dimensional (3D)-printed resin for denture base shows strength in comparison with the conventional heat-cured materials. The purpose of this study was to assess how physical and mechanical properties of 3D-printed denture base resins are affected by the addition of cerium zirconium oxide nanofibers (CeZrO₄ NFs), which have a unique combination of thermophysical and mechanical properties. Materials and Methods: The specimens were digitally created utilizing Microsoft Corporation’s 3D builder software through computer-aided design. To meet the test criteria for transverse strength, impact strength, hardness, radiopacity, and degree of conversion (DC), specimens were designed and printed with specific dimensions according to the relevant standards. The 3D-printed denture base resin was mixed with CeZrO₄ NFs (diameter: 300–800 nm, length: 2–10 µm) at weight percentages of 0.5, 1.0%, 1.5%, 2%, and 2.5%. The data were analyzed using Tukey’s post hoc test (α = 0.05) and ANOVA. Field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX) were used to evaluate surface morphologies of the composites and nanofibers, and the dispersion of the NFs within the resin matrix respectively. Results: The results demonstrated that compared with those of the control group, the average transverse strength, impact strength, and hardness values of the CeZrO₄ NF reinforcement groups significantly increased up to a nanofiller concentration of 1.5 wt.%., whereas those of the other reinforcement groups significantly decreased. For example, the impact strength significantly increased from 5.84 kJ/m² (0 wt.%) to the maximum value 8.76 kJ/m² at 1.0 wt.% CeZrO₄ NF. On the other hand, the Shore D hardness increased from 80.84 for the control group to the maximum value 83.27 at 1.5 wt.% CeZrO₄ NF. The radiopacity increased as the NF concentration increased. Although Fourier transform infrared (FTIR) spectroscopy analysis did not show any noticeable change in the chemical structure of the resin after incorporating the NFs, there was a notable improvement in the DC of the nanocomposites with NF concentrations of 0.5, 1.0 and 1.5 wt.%. Energy dispersive X-ray spectroscopy (EDX) and field emission scanning electron microscopy (FESEM) showed evidence of uniform distribution of the CeZrO₄ NFs in the 3D-printed specimens. Conclusions: The properties of the denture bases fabricated from 3D-printed resin were enhanced by the addition of 0.5%, 1 wt.% and 1.5 wt.% CeZrO₄-milled NFs, though the latter two concentrations produced the most significant results. Full article

This study investigates the combined effects of thermal and moisture aging on PVC-insulated low voltage (LV) photovoltaic (PV) cables using an accelerated-aging design to represent realistic PV operating conditions commonly encountered in hot and humid climates. Thermal aging was carried out at 90 °C for five aging cycles, with each thermal cycle followed by controlled moisture injection to simulate moisture stress. The degradation behavior was evaluated using broadband dielectric spectroscopy, FTIR analysis, and Shore D hardness measurements. Changes in dielectric dissipation factor (tanδ) and real permittivity (${\epsilon }^{\prime }$) were analyzed over a wide frequency range, with 100 kHz selected for its high sensitivity to aging-induced oxidation-related dipolar and interfacial polarization mechanisms. Degradation indices (DI) and degradation rates (DR) were derived from tanδ and correlated with mechanical and chemical changes. The results showed a 5% and 7% increase in tanδ at 100 kHz and in hardness, respectively, with decreases of 68% and 75% in the carbonyl and hydroxyl indices, respectively. Three distinct aging stages were identified: early thermo-oxidation with limited functional impact; mid-stage dehydrochlorination and moisture interaction; and late-stage chain scission, plasticizer loss, and insulation stiffening. The findings demonstrate the importance of climate-specific aging assessment and confirm the effectiveness of integrated electrical, mechanical, and chemical diagnostics for PV cable condition monitoring. Full article

Material-extrusion (MEX) printing with automated filament switching enables single-build multi-material laminates, but interfaces between dissimilar polymers may govern failure. Here, monolithic PETG, monolithic PC–ABS, and an alternating PETG/PC–ABS laminate (COMP) with 0.2 mm laminae (4 mm total) were fabricated and benchmarked. Tensile behavior was measured using ISO 527-2 Type 1B specimens at 5 and 50 mm/min, complemented by three-point bending in horizontal/vertical orientations, unnotched Charpy impact (ISO 179), Shore D hardness (ISO 868), and SEM fractography. COMP delivered the highest horizontal flexural strength (159.82 ± 25.42 MPa), exceeding both single-material baselines, indicating improved bending load capacity in the preferred orientation. In Charpy impact, COMP absorbed more energy than PETG in the horizontal condition (0.86 ± 0.14 J vs. 0.57 ± 0.06 J) but remained below PC–ABS. In tension, COMP strength decreased by ~21–23% relative to PETG and by ~5–6% relative to PC–ABS at both speeds, consistent with interface-controlled damage. SEM revealed void-assisted crack initiation and interfacial debonding aligned with raster paths, highlighting interfacial strengthening and porosity reduction as key routes to improve tensile performance while retaining favorable flexural and impact response. Full article

This study investigates the effect of goat horn powder (GHP) reinforcement on the hardness, microstructure, and mechanical properties of wood-like polyurethane composites. GHP, a keratin-based animal waste, was incorporated into the polyurethane matrix at weight fractions of 5, 10, 15, 20, and 25 wt.%. The mechanical behavior was evaluated through tensile, three-point bending, Charpy impact, and Shore D hardness tests, complemented by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses. Results indicate that GHP significantly enhances impact resistance, with 10 wt.% loading achieving a 140% improvement in impact energy compared to the neat matrix. Tensile stress improved by 12.89% at 5 wt.% loading. However, reinforcement levels exceeding 10–15 wt.% led to a decline in tensile and flexural performance due to particle agglomeration and weak interfacial adhesion. Shore D hardness increased systematically with higher GHP content across all ratios. The study demonstrates that GHP is a functional, sustainable reinforcing element that improves toughness and hardness while supporting environmental waste management. Full article

This study investigates the utilization of Abies alba exudate resin for the development of hybrid resins intended as matrices for composite materials. The novelty of this work lies in demonstrating that physically hybridized, bio-derived resin systems based on Abies alba exudate can exhibit distinct mechanical and dynamic behaviors solely by adjusting the solvent-assisted formulation route, without intentional chemical modification and without spectroscopic evidence of co-network formation within the limits of ATR-FTIR analysis, although limited interfacial interactions cannot be excluded. Two formulation routes were explored: (i) dilution of Abies alba exudate in turpentine derived from pine buds, (ii) dilution in ethanol (96%). The diluted resins were subsequently blended with a commercial epoxy system, which was cured with its amine hardener to form solid matrices in which the Abies alba component was physically incorporated. The resulting hybrid resins were characterized by multiple testing methods and further applied in the fabrication of cotton fiber-reinforced composites. The turpentine-based hybrid resin (HR1) showed a rigid mechanical response, with tensile strengths of approximately 13.2–13.5 MPa, compressive strengths of about 30 MPa, Shore D hardness values of 56–58.5, and a low damping ratio (≈0.026). In contrast, the ethanol-based hybrid resin (HR2) exhibited a highly deformable mechanical response, characterized by low tensile strength (≈0.5 MPa), very high elastic recovery, low hardness (<10 Shore D), and a significantly higher damping ratio (≈0.139). To demonstrate their applicability in composite manufacturing, the HR1 matrix was reinforced with cotton fabric, leading to a substantial improvement in tensile strength (25–26 MPa) and flexural strength (35–36 MPa), together with an increased natural frequency. Water absorption tests revealed limited moisture uptake for the neat hybrid resins (≤0.04 g), while the cotton-reinforced composite exhibited higher but largely reversible water absorption (≈21.5%), associated with the hydrophilic nature of the reinforcement. Full article

Additive manufacturing technologies such as Multi-Jet Fusion (MJF) enable the production of polymer parts with relatively isotropic mechanical properties; however, their surface condition often limits direct functional application. This study investigates the feasibility of selected surface treatments applied to PA12GB (glass bead-filled PA12) parts manufactured by MJF, with the aim of improving abrasion resistance and temperature-related performance through the modification of surface properties. Five surface treatments were evaluated: base coating (BC), acrylic coating (AC), chemical vapor smoothing (PostPro3D), glasscoat (epoxy-based SiO₂ system), and a ceramic-filled 2K epoxy coating. Untreated samples served as a reference. Surface layer thickness, roughness (ISO 21920-2:2021), coefficient of friction (ASTM G99-23), and Shore D hardness (ASTM D2240-15R21) were measured. The results showed significant differences among treatments. Glasscoat and ceramic coatings formed the thickest and hardest layers (≈265 μm and ≈409 μm; Shore D ≈ 84) but exhibited substantially increased friction coefficients. Vapor smoothing and BC produced thinner layers with properties comparable to untreated samples. Acrylic coating reduced surface roughness while moderately increasing hardness. The findings demonstrate that surface treatments substantially alter the tribological and mechanical surface behavior of MJF-printed PA12GB parts. The suitability of a given treatment strongly depends on the intended functional requirements, particularly with respect to friction and surface hardness. Full article

Developing polymer composites with improved mechanical and thermal properties requires strategies to overcome the problem of agglomeration and weak interfacial interactions of carbon nanofillers. This paper presents an effective strategy for the covalent functionalization of graphene oxide (GO) with melamine to create high-performance epoxy nanocomposites. The functionalization results in the formation of nitrogen-containing heterocyclic structures on the GO surface, as confirmed by FTIR and Raman spectroscopy. The addition of the obtained modified filler (mel-GO) into the epoxy matrix provides a synergistic effect: the melamine amino groups catalytically accelerate curing, reducing the gelation time from 146 to 48 min and increasing the maximum self-heating temperature from 94 to 122 °C, thus indicating enhanced interfacial interaction. This interaction results in a remarkable overall improvement in mechanical properties: tensile and flexural strengths increase by more than 20%, and elastic moduli by 31% and 58%, respectively, compared to the composite containing unmodified GO. At the same time, impact strength (from 14 to 23 kJ/m²) and hardness (up to 87 Shore D) increase. A key achievement is a dramatic increase in thermal and thermal-oxidative stability: the onset temperature of decomposition (T₅%) increases by 27 °C, the half-decomposition temperature (T₅₀%) by 45 °C, and the thermal stability index (THRI) increases from 119.3 to 128.9 °C. A more than twofold increase in coke residue yield (to 9.29%) and an increase in the Vicat softening point to 175 °C confirm the formation of an effective thermally stabilizing barrier layer due to the combined action of nitrogen-containing groups and dispersed graphene flakes. The proposed approach to functionalizing graphene oxide with melamine opens the way for the creation of next-generation epoxy composites with a record-breaking combination of strength, impact toughness, and thermal stability for applications in aerospace, electronics, and composite structures operating under extreme conditions. Full article

This study investigates the wear behavior and multi-technique characterization of 3D printed thermoplastic polyurethane (TPU) intended for friction layers in transmission belts used in pharmaceutical manipulators. Two flexible TPU grades—TPU 51A and TPU 60A—were printed using fused deposition modeling (FDM) with varying printing temperatures (255–265 °C for 51A; 225–235 °C for 60A) and layer counts (three or four layers). Specimens were evaluated for Shore A hardness, wear resistance (mass loss using a Baroid lubricity tester under dry sliding against carton), tensile properties, crystallinity (XRD), chemical structure (FTIR), thermal stability (TGA), and scanning electron microscopy (SEM). The results show that printing parameters significantly influence the mechanical and tribological behavior of the materials. For TPU 51A, increasing the printing temperature to 265 °C and using four layers led to a substantial reduction in cumulative mass loss, although hardness decreased. In contrast, for TPU 60A, higher printing temperature and layer count increased hardness but also resulted in higher wear. Tensile tests indicated that specimens printed with fewer layers exhibited higher yield strength and strain, indicating improved interlayer bonding. XRD analysis confirmed the predominantly amorphous nature of the printed samples, with a reduction in crystallinity compared to the raw filaments. FTIR spectra showed no significant chemical degradation during printing, while thermogravimetric analysis revealed good thermal stability up to approximately 250–260 °C. The results demonstrate that wear behavior is governed by a combination of hardness, interlayer cohesion, and microstructural organization rather than crystallinity alone. Among the investigated conditions, TPU 51A printed at 265 °C with four layers exhibited the most favorable balance between wear resistance and mechanical properties, highlighting its suitability for friction layer applications. Full article

This study presents the fabrication and optimization of eco-efficient epoxy composites reinforced with ground natural stone fillers, namely pebble, sandstone, and marble, at loadings of up to 15.6 wt.%. Low content of a bio-based modifier, modified castor oil (MCO ≈ 0.5 wt.%), is incorporated to improve filler dispersion, processing behavior, and matrix–filler interfacial compatibility. The composites are designed to enhance mechanical, thermal, and dielectric performance using low-cost, abundant, and environmentally sustainable constituents. An experimental optimization approach is employed to evaluate and optimize bulk density, Shore D hardness, thermal conductivity, dielectric constant, and tensile strength. The results demonstrate that pebble-reinforced composites exhibit the highest tensile strength (≈30 MPa) and surface hardness (≈82 Shore D), which are attributed to the angular morphology and high intrinsic rigidity of pebble particles. Marble-filled systems show superior thermal stability, with residual mass increasing from approximately 2.5 wt.% for neat epoxy to over 11 wt.% at 550 °C, owing to the thermally stable calcium carbonate phase. In contrast, sandstone-reinforced composites exhibit the lowest dielectric constant (≈3.2), indicating enhanced electrical insulation capability. Fourier–transform infrared spectroscopy (FTIR) results confirm that the epoxy network structure is preserved upon filler incorporation, while MCO promotes improved interfacial interactions through physical interactions. Thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) reveal enhanced thermal resistance, reduced microvoid formation, and improved filler–matrix adhesion at optimal filler contents of approximately 3.5 wt.%. Full article

Global outdoor furniture consumes large amounts of virgin wood and polyolefins, while multilayer beverage cartons and rice husks are often landfilled or burnt despite their polymeric and lignocellulosic value. This study aims to evaluate the feasibility of converting both waste streams into pilot-scale, wood-like boards for low-load urban furniture using an industrially relevant extrusion plus compression-moulding route, and to identify a balanced PolyAl–rice husk formulation. Hybrid composites based on recycled Tetra Pak PolyAl and ground rice husk were manufactured as full-thickness boards and characterised in terms of density, tensile and flexural behaviour, Shore D hardness, and moisture uptake. A preliminary UV screening was also performed using short-term narrow-band UVC irradiation at 254 nm, which should not be interpreted as outdoor weathering. Increasing rice husk content enhanced hardness and stiffness but increased water uptake, evidencing the expected stiffness–durability trade-off in lignocellulosic-filled systems. Overall, the intermediate 70PolyAl–30rice husk composition provided the most balanced performance for the targeted low-load applications, supporting an industrial symbiosis pathway that valorises two locally available residues into a potentially scalable product. Full article