Search Results (250)

Materials derived from renewable and recycled resources offer a promising route toward more sustainable thermoset composites. In this study, waste poly(ethylene terephthalate) (PET) was depolymerized by glycolysis with propylene glycol to obtain a glycolysate, and subsequently polycondensed with biobased propylene glycol, maleic anhydride, and trimethylolpropane diallyl ether to synthesize biobased UV-curable unsaturated polyester resin (UV-bUPR). The composites were prepared with acryloyl-modified Kraft lignin (K_rL-A) as a reactive bio-filler using a dual-curing approach, in which rapid UV curing was followed by thermal/redox post-curing to improve conversion and network homogeneity. The structure of the synthesized resin and composites was confirmed by FTIR and NMR spectroscopy. Mechanical properties were evaluated by tensile testing and hardness measurements, while morphology and fracture behavior were analyzed by scanning electron microscopy. The unmodified lignin decreased tensile performance due to limited compatibility with the polyester matrix and the formation of interfacial defects and agglomerates. In contrast, K_rL-A exhibited improved dispersion and stronger filler–matrix interactions, resulting in superior mechanical performance. The most pronounced effect of lignin modification was observed at 15 wt.% filler loading, where the tensile strength reached 27.83 MPa, compared with 13.91 MPa for the corresponding unmodified system. The developed composites also showed improved sustainability, assessed through the E-factor, due to the combined use of recycled PET and renewable lignin. Full article

Mesophase pitch (MP) is a high-performance precursor for carbon materials. However, its conventional preparation process is limited by stringent conditions and high costs. In this study, heavy coal tar (HCT) was used as a low-cost carbon source, and polyethylene (PE) was introduced as a modifier to induce MP formation under relatively mild conditions, thereby promoting the thermal polycondensation of HCT. Characterization results show that the addition of different types of PE facilitates the condensation of aromatic molecules and significantly enhances the conversion efficiency of HCT to MP. Among the tested PE types, HDPE exhibits the best performance, with an optimal addition of 6 wt.% at 400 °C, yielding the highest number of uniform mesophase carbon microspheres and the most ordered structure. Based on comprehensive characterization data, an average molecular structure model of the product was constructed, addressing a research gap regarding the role of PE in the thermal polycondensation of HCT. This work provides a new pathway for the energy-efficient preparation and property regulation of MP. Full article

Phenol derivatives display a prominent role in many biologically active molecules. Boron-containing molecules are considered valuable precursors for their synthesis. Therefore, the rise of photochemistry has led many researchers to develop novel, sustainable protocols that exploit the advantages offered by different irradiation sources. For this reason, the application of novel photocatalysts that promote challenging organic transformations is highly valued. Graphitic carbon nitride (g-C₃N₄) is a semiconductor photocatalyst widely used in organic chemistry for promoting complex organic transformations. Herein, we report a green and efficient methodology for the hydroxylation of boronic acids to the corresponding hydroxyl derivatives, using g-C₃N₄ as the photocatalyst. The heterogeneous photocatalyst (g-C₃N₄) was prepared by thermal polycondensation of melamine and characterized by XRD, FESEM/EDS, and UV–Vis diffuse reflectance spectroscopy. Green LED irradiation was employed as the energy source and air as the active oxidant. A variety of substrates were tested, showcasing excellent functional group tolerance in the aerobic photochemical protocol. Mechanistic studies were conducted to investigate the reaction pathway and to identify the oxygen species generated. Full article

Population growth and rapid urbanization have significantly increased construction activities and the demand for building materials. It is estimated that approximately 39% of global CO₂ emissions are associated with the construction sector, with nearly 8% directly attributed to Portland cement production. In addition to greenhouse gas emissions, the cement industry is responsible for substantial environmental impacts, including natural resource depletion, soil degradation, and air and water pollution. In this context, the development of alternative and more sustainable binder systems has become a global research priority. Geopolymers have emerged as promising materials produced through either alkaline or acid activation routes, offering advantages such as a reduced carbon footprint, high durability, and rapid strength development. Among these systems, acid-activated materials, particularly phosphate-based geopolymers, differ fundamentally from conventional alkali-activated binders in terms of reaction chemistry and binding phases. The formation of aluminum phosphate (AlPO₄) networks plays a key role in governing the mechanical performance and microstructural stability of these materials. This mini-review provides a critical overview of the fundamental principles of acid activation applied to alternative cementitious materials, with emphasis on dissolution mechanisms, polycondensation reactions, and the nature of binding phases in phosphate-based systems. Unlike previous reviews, this study integrates recent findings on reaction mechanisms with a comparative analysis between acid and alkaline activation routes, highlighting underexplored aspects of precursor reactivity and binder formation. The main types of acids used as activators, the influence of precursor chemical composition, and the conceptual differences between acid and alkaline activation are discussed. In addition, recent advances, current challenges, and future perspectives of acid activation are addressed, highlighting its potential as a viable low-carbon binder route for sustainable construction materials, with strong prospects for partially replacing Portland cement, particularly in high-performance applications requiring enhanced chemical resistance and thermal stability. Full article

Ultra-low-formaldehyde medium-density fiberboard (MDF) is commonly produced using low-molar-ratio urea-formaldehyde (UF) resins; however, the reduced formaldehyde-to-urea ratio also lowers resin reactivity and can complicate curing. The aim of this research work was to investigate and evaluate the performance of ammonium bisulfite and urea–metabisulfite as formaldehyde scavengers for a low-molar-ratio UF resin (F/U = 1.06) at 1, 3, and 5 wt% (based on dry UF resin solids) used for MDF panel manufacturing. The modified adhesive systems were first screened by simultaneous thermal analysis in air to determine changes in the curing profile, and laboratory panels were then produced and evaluated for formaldehyde content by the perforator method (EN ISO 12460-5:2015) and for the main physical and mechanical properties. Ammonium bisulfite shifted the main curing peak to higher temperatures, indicating stronger retardation of the principal polycondensation stage, whereas urea–metabisulfite generated a broader, multi-peak curing profile. Despite these differences, both additives reduced the perforator values substantially. The control MDF already met the E0 level (3.84 mg/100 g oven-dry board), while 3 wt% ammonium bisulfite and 5 wt% urea–metabisulfite reached the super E0 levels (<1.5 mg/100 g; 1.36 and 1.26 mg/100 g, respectively). To note, scavenger addition up to 5 wt% (based on dry UF resin solids) did not significantly affect density, water absorption/thickness swelling, or bending and internal bond properties. The results demonstrate that sulfite-based scavengers can be incorporated into low-molar-ratio UF adhesives to obtain ultra-low-formaldehyde MDF while maintaining the main panel properties. Full article

Polyethylene terephthalate (PET) plays a pivotal role in the chemical fiber industry, constituting over 50% of fiber consumption. However, the reduction of the recycled fiber-derived viscosity of the PET significantly impacts its spinning performance and restricts its closed-loop recycling to high-value regenerated fibers. To address these limitations, this study explored the viscosity improvement of black and white waste fiber-derived polyester particles through a two-step process involving micro-glycolysis and self-polycondensation. Initially, a continuous micro-glycolysis of fiber-derived PET was carried out in a twin-screw extruder with ethylene glycol (EG), which effectively cleaves the ester bonds in the PET chains, generating oligomers with reactive hydroxyl end groups. Subsequently, these oligomers were repolymerized without purification, and a higher molecular weight regenerated PET with enhanced intrinsic viscosity was obtained with antimony ethylene glycolate (Sb-EG) as a catalyst. The results revealed that the intrinsic viscosity decreased exponentially with increasing EG dosage during glycolysis, reaching approximately 50% of the initial value at 0.2–2 phr EG dosages. Optimal viscosity enhancement was achieved at a polycondensation time of 1–3 h, resulting in improved thermal stability and reduced crystallization temperatures. Importantly, regenerated PET samples with EG dosages of ≤2 phr demonstrated intrinsic viscosities of about 0.70 dL/g, meeting the standard for spin-grade polyester fiber, which is used to produce regenerated polyester fibers. This recycling process is low cost, environmentally friendly, and easy to scale-up, contributing significantly to the development of industrial recycling of waste polyester fabrics. Full article

Under dual challenges of global infrastructure expansion and industrial solid waste management, alkali-activated polymers (AAP), as industrial solid-waste-based low-carbon cementitious materials, exhibit immense potential in grouting engineering applications. This review synthesizes current research progress through three critical dimensions: reaction mechanisms, performance characteristics, and grouting applications (grouting for reinforcement and water-blocking). The reaction mechanism universally comprises three stages: dissolution, depolymerization, and polycondensation. Key performance determinants include precursor composition (e.g., slag, fly ash, metakaolin) and alkaline activator properties (type, modulus, concentration). The multifunctional advantages of AAP are fundamentally governed by their microstructural evolution. Specifically, the rapid formation of highly cross-linked C-(A)-S-H and N-A-S-H gels directly contributes to rapid setting and high early strength development, with high-calcium precursors such as slag exhibiting faster strength gain than low-calcium systems, such as fly ash and metakaolin. Furthermore, the absence of vulnerable calcium hydroxide phases, combined with a densified, low-porosity aluminosilicate network, provides superior thermal stability, corrosion resistance, frost durability, and low permeability. Nevertheless, pronounced autogenous shrinkage and drying shrinkage, driven by mesopore moisture loss and the highly viscoelastic solid skeleton, remain primary constraints for field implementation. In grouting reinforcement, AAP can effectively enhance the strength and structural integrity of weak soils, such as soft clay, loess, and sulfate-rich saline soils. For grouting water-blocking, particularly in sodium-silicate-based binary systems, AAP achieves rapid gelation, superior washout resistance, and high anti-seepage pressure, proving optimal for groundwater inflow control. Future research must prioritize (i) standardized mix design protocols for performance consistency, (ii) advanced shrinkage mitigation strategies, (iii) systematic durability assessment under coupled environmental stressors (e.g., wet–dry cycling, chemical attack, thermal fatigue), and (iv) cross-disciplinary collaboration for industrial-scale validation. Full article

Polyamide 6 (PA6) is limited in its application in precision and high-temperature fields due to its high moisture absorption, low heat resistance, and poor barrier properties. To overcome these intrinsic deficiencies, a rigid 9-(carboxyphenyl)carbazole-based diacid monomer (CzIPA) was incorporated into the PA6 backbone via one-step melt polycondensation. Structural analyses confirmed successful copolymer formation and effective modulation of hydrogen-bonding interactions and chain rigidity. The introduction of the bulky carbazole units markedly enhanced the thermal and physical properties of PA6. The glass transition temperature increased by up to 35.5 °C, while the maximum decomposition temperature rose by 23.8 °C, reflecting the reduced chain mobility and strengthened thermal resistance. The decreased amide-group density led to a 15% reduction in water absorption, improving dimensional stability. The Young’s modulus, flexural strength, and flexural modulus of the prepared copolymers were significantly improved compared to PA6, while the toughness was slightly reduced. Furthermore, oxygen and water-vapor permeabilities were simultaneously reduced by 30–35%, attributed to restricted diffusion pathways in the modified microstructure. Despite the increased rigidity, the copolymers maintained good melt processability with clear shear-thinning behavior. This study demonstrates CzIPA copolymerization as an efficient structural design strategy for producing high-performance PA6 materials with enhanced thermal stability, lower hygroscopicity, and superior barrier properties. Full article

This study investigates how natural fillers of different origins and morphologies influence the structural, thermal, rheological, and mechanical properties of thermoplastic elastomers (TPEs). Two series of materials were prepared: one based on a biobased matrix, poly(butylene 2,5-furandicarboxylate)-block-poly(tetramethylene oxide) (PBF-PTMO), and one based on a petroleum-derived matrix, poly(butylene terephthalate)-block-poly(tetramethylene oxide) (PBT-PTMO). Both series incorporated a range of natural modifiers, i.e., lignocellulosic fibers and ground fractions of Arundo donax L., cyanobacterial biomass (Spirulina platensis), and silica-rich mineral dust originating from volcanic stone quarries. The materials were obtained via melt blending, while the reference matrices (neat block copolymers) were synthesized through melt polycondensation. The chemical structure and limiting viscosity number (LVN) of the neat matrices were confirmed, while differential scanning calorimetry (DSC) provided insight into their morphology and phase composition. Scanning electron microscopy (SEM) was employed to evaluate the morphology and distribution of the modifiers within the polymer matrices. To assess how the fillers influenced processing windows and performance, thermogravimetric analysis (TGA), oscillatory rheological measurements, and tensile testing were performed. The results provide insight into structure–property relationships governing natural filler–TPE interactions and support the development of more sustainable elastomeric composites with tailored performance. Full article

Two-dimensional graphitic carbon nitride 2D g-C₃N₄ has the potential for gas sensing as a metal-free semiconductor with a layered structure, high surface area, and tunability of electronic properties. In this context, 2D g-C₃N₄ nanosheets were prepared by the thermal polycondensation of urea followed by ultrasonic exfoliation. X-ray diffraction revealed diffraction peaks corresponding to the (110) and (002) crystallographic planes of g-C₃N₄. Scanning electron microscopy showed a nanosheet structure with a 10-nm crystallite size, while energy-dispersive X-ray spectroscopy demonstrated a uniform distribution of carbon and nitrogen. Ultraviolet–visible absorption spectroscopy revealed a band gap of 2.8 eV. Gas sensing measurements exhibited an increase in response to isopropanol and ethanol as the operating temperature and gas concentration increased. Impedance spectroscopy provided additional insight into the sensing mechanism. Observed depressed semicircles in Nyquist plots were fitted with a charge transfer resistance R_ct in parallel with a constant phase element model. The charge transfer resistance R_ct fell systematically with isopropanol exposure, confirming the crucial role of adsorption-induced electron transfer in the gas sensing response. Full article

Deoxynivalenol (DEOX), a dangerous mycotoxin, causes serious health problems for humans and animals. Hence, the on-site monitoring of DEOX has begun to be important in the health and food sectors in recent years. In the present study, a molecularly imprinted surface plasmon resonance (SPR) sensor based on sulfur-doped boron graphitic carbon nitride (S-B-g-C₃N₄) was developed and applied for detecting DEOX in drinking water and orange juice samples, achieving high recovery. After the S-B-g-C₃N₄ nanocomposite was synthesized via thermal polycondensation and microwave treatment with a highly environmentally friendly approach, a SPR chip was modified with the S-B-g-C₃N₄ nanocomposite considering the high affinity between gold and sulfur. Then, the molecularly imprinted SPR sensor based on the S-B-g-C₃N₄ nanocomposite was prepared in the presence of methacryloylamidoglutamic acid (MAGA) as the monomer and N,N′-azobisisobutyronitrile (AIBN) as the initiator. The DEOX-imprinted SPR sensor based on the S-B-g-C₃N₄ nanocomposite showed linearity from 1.0 to 10.0 ng L⁻¹, with a limit of quantification (LOQ) of 1.0 ng L⁻¹ and a limit of detection (LOD) of 0.30 ng L⁻¹. Finally, the selectivity, repeatability, and reproducibility of the DEOX-imprinted SPR sensor based on the S-B-g-C₃N₄ nanocomposite were investigated. Full article

Owing to their outstanding thermal and mechanical properties, polyimides (PIs), polyamides (PAs), and poly(amide-imides) (PAIs) are essential for developing and manufacturing modern high-tech products, including electroactive ones. Despite their large-scale production for diverse applications, the synthesis of these polymers traditionally relies on highly toxic solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone (NMP), and m-cresol. This work investigates the possibility of replacing these hazardous solvents with a more sustainable and “green” alternative, N-butyl-2-pyrrolidone (NBP). We have thoroughly studied and analyzed the synthesis of various PIs, PAs, and PAIs via one- and two-step polycondensation of tetracarboxylic acid dianhydrides with diamines, low-temperature polycondensation of terephthaloyl chloride with diamines, and low-temperature polycondensation of tetracarboxylic acid dianhydrides and terephthaloyl chloride with diamines, respectively. Our results demonstrate that substituting NBP for NMP presents distinct characteristics and outcomes for each process. By optimizing the reaction conditions, we were able to obtain high-molecular-weight products (M_n = 37–346 kDa; M_w = 133–537 kDa) for all polymer classes studied. Thus, this work establishes NBP as a suitable and promising solvent for synthesizing PIs, PAs, and PAIs with diverse chemical structures and tunable molecular weight characteristics. Full article

MQ copolymers, consisting of monofunctional (M) and tetrafunctional (Q) siloxane units, are versatile materials used as additives, adhesives, and in composite materials. Functional groups, such as vinyl substituents, in M-units allow for the tailoring of properties for specific applications. This study aimed to synthesize vinyl-containing MQ copolymers (M^VinMQ) via a controlled, chlorine-free method to explore the regulation of their composition and properties. The results demonstrated precise control over the copolymer architecture, with hydroxyl content and molecular weight increasing alongside the Q-unit fraction. All obtained copolymers exhibited high thermal stability, with 5% mass loss occurring above 295 °C in air and 365 °C in argon. Fractionation data supported a molecular composite model consisting of an inorganic core and an organic shell. Polycondensation in an active medium is an effective method for the directed synthesis of structurally tunable M^VinMQ copolymers, offering a versatile platform for developing functional hybrid materials, modifiers, and cross-linking agents. Full article

The combination of gold nanoparticles (AuNPs) with hydrogels has drawn significant interest in the design of smart materials as advanced platforms for biomedical applications. These systems endow light-responsiveness enabled by the AuNPs localized surface plasmon resonance (LSPR) phenomenon. In this study, we propose a nanocomposite hydrogel in which gold nanorods (AuNRs) are included in an agarose–carbomer–hyaluronic acid (AC-HA)-based hydrogel matrix to study the correlation between light irradiation, local temperature increase, and drug release for potential light-assisted drug delivery applications. The gel is obtained through a facile microwave-assisted polycondensation reaction, and its properties are investigated as a function of both the hyaluronic acid molecular weight and ratio. Afterwards, AuNRs are incorporated in the AC-HA formulation, before the sol–gel transition, to impart light-responsiveness and optical properties to the otherwise inert polymeric matrix. Particular attention is given to the evaluation of AuNRs/AC-HA light-induced heat generation and drug delivery performances under near-infrared (NIR) laser irradiation in vitro. Spatiotemporal thermal profiles and high-resolution thermal maps are registered using fiber Bragg grating (FBG) sensor arrays, enabling accurate probing of maximum internal temperature variations within the composite matrix. Lastly, using a high-steric-hindrance protein (BSA) as a drug mimetic, we demonstrate that moderate localized heating under short-time repeated NIR exposure enhances the release from the nanocomposite hydrogel. Full article

Fluorine-containing polyarylates (F-PARs) were synthesized via interfacial polycondensation of hexafluorobisphenol A (BPAF), bisphenol A (BPA), and two acyl chloride monomers under four feeding strategies. Sequential feeding affords the highest M_w (2.02 × 10⁵ g/mol) and high alternating sequence content; the one-pot method gives intermediate M_w and a random sequence; and segmented and parallel methods yield lower-M_w polymers and pseudo-block sequences. Time-resolved GPC results reveal that the concentration of -CF₃-activated acyl chloride termini during chain propagation controls the subsequent chain propagation and, thus, the final M_w. Consequently, sequential feeding delivers the highest T_g (215 °C) and stiffness (2.51 GPa) for thermal–mechanical loads; the one-pot protocol maximizes optical clarity (T₄₅₀ = 85%) for transparent films. Systematic variation in the BPAF/BPA ratio via sequential feeding further reveals that higher BPAF content increases M_w, enhances thermal stability, and blue-shifts UV absorption, whereas BPA-rich compositions improve the tensile strength and modulus. These findings provide a quantitative roadmap for the rational design of F-PAR chain architectures, enabling on-demand tuning of thermal, mechanical, and optical properties without additional synthetic complexity. Full article