Search Results (304)

Although induced Joule heating in carbon/epoxy laminates has been studied, how it can affect their anisotropic electrical conduction has not been well established. The objectives of this work were to ascertain the electrical current–temperature relationship, the effect of induced temperatures on specimen sizes, clamping torques, and electrical conductivity of, and the Lorenz proportionality constants between, thermal and electrical conductivities, all verified with analytical corroborations. A 2-probe method was used in electrical conduction measurements with machined specimens in various dimensions. The specific contributions of elevated temperatures to the electrical conduction through specimen size and clamping torque were ascertained. The thermal conductivities of laminate samples were measured using differential scanning calorimetry. From test results, a parabolic relationship between induced temperature and electrical current was found in both in-plane and through-the-thickness directions. The temperatures in the small specimens rose parabolically. Increasing clamping torques led to linear reductions in temperatures. Over the range of temperatures, the effect of induced temperatures on the electrical conductivity was very small, because the rising of temperatures did not alter the electrical conduction mechanisms. The proportionality constants between thermal and electrical conductivities were established for the first time. This means that just one kind of these measurements needs to be conducted for the same laminates. Full article

This study investigates the residual stresses developed during the curing process of polymer fiber-reinforced composites and their influence on fracture behavior, particularly the initiation and propagation of interlaminar cracks. The main objective is to quantify how different curing histories, including incomplete cure, alter the spatial distribution of residual stresses and, in turn, affect the mode-I fracture response of carbon-fiber/epoxy laminates. A transient thermal–structural finite element framework incorporating an autocatalytic cure kinetics model was used to simulate the curing process and predict residual stress development in a unidirectional carbon-fiber/epoxy laminate with an edge crack, considering thermal, chemical, and geometric effects. The cure model was calibrated using isothermal differential scanning calorimetry data to determine the degree of cure under different thermal conditions. The key novelty of this work is the integration of a validated cure-kinetics-based curing simulation with fracture analysis, enabling direct correlation of thermal history and degree of cure with spatially varying residual stresses at the crack front and their effect on fracture toughness. Numerical load–displacement predictions were compared with double cantilever beam experimental results and showed good agreement for the curing profiles examined. The results demonstrate that residual stresses generated by different cure cycles, including hold conditions and incomplete curing, significantly influence fracture toughness. In particular, the incomplete-cure profile produced an approximately 40% reduction in toughness compared with profiles that achieved complete cure, highlighting the importance of cure history in determining final structural performance. Full article

Degradable polymers, such as poly(L-lactide) (PLLA), are widely investigated for biomedical applications, including drug delivery systems and temporary implants. Their functionality can be expanded by incorporating degradable metal microparticles that may influence degradation behaviour and enable additional surface modification strategies. In this study, the feasibility of composites consisting of PLLA and biodegradable iron microparticles was investigated. Composites were fabricated by solvent casting, providing a gentle alternative to thermal processing methods, which often compromise polymer integrity. Composites were evaluated by thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy (SEM), tensile testing, dynamic mechanical analysis, and X-ray photoelectron spectroscopy (XPS). Incorporation of iron altered thermal behaviour and crystallinity of PLLA, indicating interactions between polymer matrix and dispersed metal phase that may affect degradation kinetics and material stability. While iron addition reduced Young’s modulus, tensile strength, and elongation at break, composites maintained sufficient structural integrity for potential biomedical applications. XPS and SEM confirmed the embedding of particles within the polymer matrix, enabling potential post-processing approaches. In vitro direct contact and eluate tests demonstrated good cell viability, whereas exposure to free iron particles resulted in dose- and time-dependent cytotoxic effects. Overall, the results demonstrate the feasibility of solvent-cast PLLA–iron composites for resorbable biomedical applications. Full article

The commercialization of poly(butylene succinate-co-adipate) (PBSA), a biodegradable and potentially fully biobased random copolyester, is still ongoing. Due to its high relevance as mono material or as blend component in flexible film applications, a sound understanding of compounding, further processing and film properties is necessary. In this work, PBSA, poly (lactic acid) (PLA) and blends at three different compositions thereof were processed into flat films and blown films, respectively. Investigating the films with X-ray diffraction (XRD), multivariate confocal Raman microscopy (CRM) and scanning electron microscopy (SEM) revealed the semicrystalline order as well as the blend morphology. While PBSA is semicrystalline, PLA remains amorphous after the processing step. As imaged by CRM, flat films exhibit lamellar-like domains formed during uniaxial stretching and rapid cooling, whereas blown films show no pronounced preferential orientation. Tensile tests in both the machine and transverse directions demonstrate the versatility of PBSA and its blends in spanning a wide range of mechanical strength and flexibility, covering and partly exceeding the stiffness and strength ranges typically reported for commodity polyolefins while exhibiting reduced ductility. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) provide further insights into the thermal properties of the pure and blend materials. Full article

The resistance of pathogenic bacteria to antimicrobial agents is currently one of the most significant health challenges. Polymers and nano-polymer composites with antimicrobial properties are widely used, particularly in hospitals, biocompatible implants, and the medical device industry. Syzygium aromaticum (clove) contains several bioactive compounds, including potent antioxidants and antimicrobials, which confer antioxidant, antibacterial, and antiseptic properties. For this purpose, polyvinyl alcohol (PVA) films were produced at three different concentrations using a direct integration method and doped with clove essential oil. The spectral, structural, and thermal properties of the produced films were analyzed, and their antibacterial activity against Klebsiella pneumoniae was tested. Fourier Transform Infrared Spectroscopy (FTIR) results confirm that the structural integrity of the PVA matrix is preserved and that the essential oil is physically trapped within the polymer network. Overall, the Differential Scanning Calorimetry (DSC) results confirm that Syzygium aromaticum essential oil (SAEO) acts as an effective plasticizer in PVA films, significantly modifying the glass transition behavior and enhancing polymer chain mobility in a concentration-dependent manner. The Dynamic Mechanical Analysis (DMA) results, supported by DSC analysis, clearly demonstrate that SAEO acts as an effective plasticizing agent in PVA films by increasing molecular mobility, lowering the glass transition temperature (Tg), and promoting thermally induced deformation. The concentration-dependent increase in the diameter of the inhibition zone of essential-oil-added films showed that their antibacterial efficacy increased as the S. aromaticum essential oil content increased (0.5%, 0.75%, and 1.0%). Additionally, molecular docking was performed to examine interactions between selected virulence proteins of K. pneumoniae and the main components of clove essential oil. As a result, S. aromaticum essential oil conferred antibacterial properties to the polyvinyl alcohol films without significantly altering their transparency and thermal properties. Full article

Background: Pantoprazole is a widely used proton pump inhibitor that is highly unstable under acidic conditions. This limits the performance of conventional formulations and typically requires enteric-coated dosage forms or alternative modified-release approaches. This study reports the development of polymeric matrix mini-tablets designed to protect pantoprazole during gastric exposure and to enable pH-dependent release under intestinal conditions. The formulations combine Eudragit^® S 100, a pH-dependent polymer, with HPMC, a hydrophilic matrix former that modulates drug release through hydration and swelling. Methods: Matrix mini-tablets were prepared by blending pantoprazole with selected excipients at optimised proportions and compressing the blends by direct compression using an eccentric tablet press. Powder blends and mini-tablets were characterised according to pharmacopoeial specifications. Analytical techniques—including High-Performance Liquid Chromatography (HPLC), Differential Scanning Calorimetry (DSC), Fourier-Transform Infrared Absorption Spectroscopy (FT-IR), Powder X-Ray Diffraction (PXRD), and Scanning Electron Microscopy (SEM)—were employed to evaluate drug content uniformity, thermal behaviour, and potential drug–excipient interactions. In vitro dissolution studies were performed under sequential pH conditions, and the release kinetics were analysed using mathematical models. Results: Dissolution testing identified formulations F2 and F6 as providing the most suitable gastro-resistant performance in the acidic stage, together with sustained release up to 24 h. Kinetic modelling supported formulation-dependent release mechanisms, and multivariate analysis (PCA) highlighted relationships between physico-mechanical attributes and drug-release behaviour. Conclusions: The proposed matrix system shows potential as a robust, coating-free platform for the modified delivery of acid-labile drugs using direct compression, simplifying manufacturing. These findings support the rational design of oral modified-release formulations based on polymeric matrices. Full article

Polyester/cotton blended fabrics—valued for comfort and durability—face significant fire hazards due to a synergistic “scaffold effect” during combustion. Conventional treatments with high temperature or some acidic phosphorus flame retardants during preparation often compromise the mechanical strength. Inspired by mussel adhesion chemistry, a mechanically enhanced polyester/cotton fabric was developed by using a novel bio-inspired phosphorus/nitrogen (P/N) synergistic coating. A uniform polydopamine-polyethylenimine (PDA-PEI) layer is rapidly deposited via co-deposition, suppressing dopamine self-polymerization. Subsequent covalent bonding with 2,2-dimethyl-1,3-propanediyl bis (phosphoryl chloride) (DPPC) establishes a robust P/N network. The fabricated PDA-PEI/DPPC coating reduces peak heat release rate (pHRR) and total heat release (THR) by 57.7% and 32.6%, respectively, in cone calorimetry, achieving self-extinguishment and a high limiting oxygen index (LOI) of 24.6%. Remarkably, the coating simultaneously increases the weft-direction breaking strength by 55% and elongation at break by 27.2%; these changes overcome the typical mechanical degradation associated with acidic phosphorus flame retardants. A comprehensive analysis reveals a synergistic mechanism: phosphoric acids catalyze cellulose dehydration and char layer formation in the condensed phase (90% stable C–C bonds), while radical scavengers (PO·, HPO·, and PDA) and non-flammable gases suppressed gas-phase combustion. This work presents a facile and effective strategy for fabricating high-performance and mechanically robust flame retardant polyester/cotton textiles, demonstrating the significant potential for improving fire safety in practical applications. Full article

We report the first examples of bent-shaped LC dimers based on a seven-membered bridged stilbene. We synthesized nonylene- and ether-linked cyano-terminated dimers (sC9-tCN and sOC7O-tCN, respectively) and a homologous series of nonylene-linked alkyl-terminated dimers (sC9-tCn) with alkyl carbon atoms n = 1–6. Polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction measurement were employed to investigate the phase-transition behavior and LC phase structures. sC9-tCN and sOC7O-tCN only exhibited a nematic (N) phase, whereas sC9-tCn (n = 1–5) formed both the N_TB and N phases. sC9-tC5 additionally formed an unidentified X phase from the N_TB phase and sC9-tC6 exhibited a smectic A phase from the N phase. The weak dispersion force and intermolecular affinity provided by the terminal alkyl chains are likely to be preferable to the large dipole–dipole interactions by the cyano termini for the N_TB phase formation of the present dimers. The isotropic points of sC9-tCn showed an odd–even oscillation with n, whereas the N–N_TB phase transition temperatures were comparable. Remarkably, the N_TB stripe textures of sC9-tCn appeared perpendicular to the rubbing direction, and the N–N_TB phase transitions exhibited their second-order nature. This study revealed the unique N_TB phase properties of the 7-membered bridged stilbene-based LC dimers. Full article

The paper continues the authors’ efforts to characterize and control the shape memory effect (SME) occurring in 3D printed specimens of recycled polyethylene terephthalate (rPET) and polyethylene terephthalate glycol (rPETG). Lamellar and “dog-bone” configuration specimens were 3D printed in the form of stratified composites with five different rPET/rPETG ratios, 100:0, 60:40, 50:50, 40:60, and 0:100, and two different angles between the specimen’s axis and the deposition direction, 0° and 45°. The lamellar specimens were used for: (i) free-recovery SME-investigating experiments, which monitored the variation of the displacement, of the free end of specimens which were bent at room temperature (RT), vs. temperature, during heating, (ii) differential scanning calorimetry (DSC), which emphasized heat flow variation vs. temperature, during glass transition and (iii) dynamic mechanical analysis (DMA), which recorded storage modulus vs. temperature in the glass transition interval. Dog-bone specimens were subjected to tensile failure and loading-unloading tests, performed at RT. The broken gauges were metallized with an Au layer and analyzed by scanning electron microscopy (SEM). The results showed that the specimens printed with 0° raster developed larger free-recovery SME strokes, the largest one corresponding to the specimen with rPET/rPETG = 40:60, which experienced the highest storage modulus increase, 872 MPa, and maximum value, 1818 MPa, during heating. The straight lamellar composite specimens experienced a supplementary shape recovery when bent at RT and heated, in such a way that their upper surface became concave, at the end of heating. Most of the specimens 3D printed at 0° raster developed stress failure plateaus, which were associated with the formation of delamination areas on SEM fractographs, while the specimens printed with 45° raster angle experienced necking failures, associated with the formation of crazing areas. The results suggested that 3D printed stratified rPET-rPETG composites, with dedicated spatial configurations, have the potential to serve as executive elements of light actuators for low-temperature operation. Full article

The valorization of dredged sediments represents a major environmental and logistical challenge, particularly in the context of forthcoming regulations restricting their marine disposal. This study investigates the potential of untreated dredged sediments as sustainable raw materials for geopolymer binder development, with the dual objective of sustainable sediment management and reduction in cement-related environmental impact. Dredged sediments from the Grand Port Maritime de Bordeaux (GPMB) were activated with sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃), both alone and in combination, with supplementary aluminosilicate and calcium-rich co-products, to assess their reactivity and effect on binder performance. A multi-scale experimental approach combining mechanical testing, calorimetry, porosity analysis, Scanning Electron Microscopy and Energy-Dispersive Spectroscopy (SEM–EDS), X-ray diffraction (XRD), Thermogravimetric Analysis (TGA), and solid-state Nuclear Magnetic Resonance (NMR) was employed to challenge the commonly assumed inert behavior of sediments within geopolymer matrices, to elucidate gel formation mechanisms, and to optimize binder formulation. The results show that untreated sediments actively participate in alkali activation, reaching compressive strengths of up to 5.16 MPa at 90 days without thermal pre-treatment. Calcium-poor systems exhibited progressive long-term strength development associated with the formation of homogeneous aluminosilicate gels and refined microporosity, whereas calcium-rich systems showed higher early age strength but more limited long-term performance, linked to heterogeneous gel coexistence and increased total porosity. These findings provide direct evidence of the intrinsic reactivity of untreated dredged sediments and highlight the critical role of gel chemistry and calcium content in controlling long-term performance. The proposed approach offers a viable pathway for low-impact, on-site sediment valorization in civil engineering applications. Full article

To address the thermal management challenges in electronic devices, this study systematically investigates the effects of injection molding and compression molding on the microstructure and thermal conductivity of poly(vinylidene fluoride)/boron nitride nanosheet (PVDF/BNNs) composites. Using 10 μm diameter BNNs as thermal conductive fillers and PVDF as the matrix, the composites were characterized via scanning electron microscopy (SEM), thermal conductivity measurements, rheological analysis, X-ray diffraction (XRD), and mechanical tests. The results demonstrate that the strong shear stress in injection molding induces significant alignment of BNNs along the flow direction, leading to remarkable thermal conductivity anisotropy. At a PVDF/BNNs mass ratio of 90/10, the in-plane thermal conductivity of the injection-molded composite reaches 1.26 W/(m·K), while the through-plane conductivity is only 0.40 W/(m·K). In contrast, compression molding, which involves minimal shear, results in randomly dispersed BNNs and isotropic thermal conductivity, with both in-plane and through-plane values around 0.41 W/(m·K) at the same filler loading. Both processing methods preserve the coexistence of α- and β-crystalline phases in PVDF. However, injection molding enhances matrix crystallinity through stress-induced crystallization, yielding composites with higher density and superior tensile properties. Compression molding, due to slower cooling, leads to incomplete PVDF crystallization, as evidenced by a shoulder peak near 164 °C in differential scanning calorimetry (DSC) curves. This study elucidates the mechanism by which processing methods regulate the structure and properties of PVDF/BNNs composites, offering theoretical and practical guidance for designing high-performance thermally conductive materials. Full article

This article investigates the thermodynamic driving force of the interaction between lysozyme (Lys) and sulfated β-cyclodextrin (β-CDS), with a particular emphasis on the elusive role of hydration during polyelectrolyte–protein binding. Using isothermal titration calorimetry (ITC), the binding affinity was quantified across varying temperatures and salt concentrations, employing a recently developed thermodynamic framework that explicitly separates the contributions from counterion release and hydration effects. The study reveals that while counterion release is minimal in the Lys/β-CDS system, hydration effects become a dominant factor influencing the binding free energy ΔG_b, especially as experimental temperature deviates from the characteristic temperature T₀. It demonstrates that hydration contributions can substantially weaken binding at increased salt concentration c_s. The high characteristic temperature T₀ and the salt-dependent heat capacity change indicate a complex interplay of water structure and ion association—significantly departing from commonly linear interpretations of ΔG_b vs. log c_s based solely on counterion release effects. This work advances the understanding of polyelectrolyte–protein interactions by providing the first direct quantification of the hydration effect in such complexes and may have an impact on the rational design of biomolecular assemblies and therapeutic carriers. Full article

Fire-retardant intumescent coatings offer an effective means of enhancing the fire resistance of combustible substrates such as wood. These coatings have a complex chemical composition and, when exposed to temperatures above 200 °C, undergo an intumescent reaction accompanied by the release of non-flammable gases, forming an expanded, charred layer with low thermal conductivity. This provides thermal insulation and acts as a physical barrier against heat, oxygen, and flammable volatiles. In this study, the applicability of several thermoanalytical techniques for evaluating the performance of three different intumescent coatings applied to spruce wood was investigated. Simultaneous thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) showed that coating No. 3 was the most efficient, initiating substrate protection at the lowest temperature and reducing the combustion enthalpy by approximately 50% compared to uncoated wood. DSC-microscopy visualization enabled direct observation of the intumescent expansion, degradation of the carbonized protective layer, and delayed thermal decomposition of coated wood. Furthermore, a comparison between TGA-MS and TGA-IST16-GC-MS demonstrated the superiority of chromatographic separation for identifying evolved gaseous products. While TGA-MS is effective for detecting small gaseous species (e.g., H₂O, CO₂, formaldehyde), TGA-IST16-GC-MS enables the deconvolution of many degradation products evolving simultaneously, allowing for distinction between flame-retardant-related species, polymer backbone fragments, nitrogen-rich heterocycles, and small oxygenated molecules in the most effective coating. Full article

This paper presents the potential use of sunflower seed hulls (SSH) as a sustainable filler for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) biocomposites. Ground SSH were incorporated into the PHBV matrix at loadings of 15, 30, and 45 wt% via extrusion and injection molding. The Fourier Transform Infrared Spectroscopy (FTIR) analysis indicated the presence of possible interactions between the filler and the matrix. Mechanical testing revealed a significant increase in stiffness, with the tensile modulus increasing from 2.6 GPa for pure PHBV to approximately 4.5 GPa for the composite containing 45 wt% SSH. However, the tensile strength decreased by approximately 10–40%, while elongation at break dropped to 1.0–1.5%, depending on the SSH dosage, respectively. The thermal analysis indicated that high filler contents suppress crystallization during cooling under laboratory conditions in Differential Scanning Calorimetry (DSC) analysis due to the confinement effect. The key practical advantage is the exceptional improvement in dimensional stability with a processing shrinkage reduction of approximately 80% in the thickness direction. Although water absorption increased with filler loading, biocomposites containing 15–30 wt% SSH exhibited the optimal balance of high stiffness, hardness, and dimensional accuracy. These properties make the developed material a promising option for the production of precise technical molded parts. Full article

This work characterizes hybrid hydrogels prepared via the combination of natural and synthetic polymers. By incorporating a biocompatible compound, poly(ethylene glycol) diacrylate (PEGDA, M_n = 400), into alginate and carboxymethyl cellulose (CMC)-based hydrogels, the in situ UV crosslinking of these materials was assessed. A custom direct-write (DW) 3D bioprinter was utilized to prepare hybrid hydrogel constructs and scaffolds. A control sample, which consisted of 4% w/v alginate and 4% w/v CMC, was prepared and evaluated in addition to three PEGDA (4.5, 6.5, and 10% w/v)-containing hybrid hydrogels. Rotational rheology was utilized to evaluate the thixotropic behavior of these materials. Filament fusion tests were employed to generate bilayer constructs of various pore sizes, providing metrics for the printability and diffusion rate of hydrogels post-extrusion. Printability indicates the shape fidelity of pore geometry, whereas diffusion rate represents material spreading after deposition. Curing kinetics of PEGDA-containing hydrogels were evaluated using photo-Differential Scanning Calorimetry (DSC) and photorheology. The Kamal model was fitted to photo-DSC results, enabling an assessment and comparison of the curing kinetics for PEGDA-containing hydrogels. Photorheological results highlight the increase in hydrogel stiffness concomitant with PEGDA content. The range of obtained complex moduli (G*) provides utility for the development of brain, kidney, and heart tissue (620–4600 Pa). The in situ UV irradiation of PEGDA-containing hydrogels improved the shape fidelity of printed bilayers and decreased filament diffusion rates. In situ UV irradiation enabled 10-layer scaffolds with 1 × 1 mm pore sizes to be printed. Ultimately, this study highlights the utility of PEGDA-containing hybrid hydrogels for high-resolution DW 3D bioprinting and potential application toward customizable tissue analogs. Full article