Polymers

36 pages, 5385 KB

Open AccessArticle

An Experimental and Modeling Study on the Interaction of Cements with Varying C₃A Ratios and Different Water-Reducing Admixtures Using the op-ANN and Various Machine Learning Methods

by Veysel Kobya, Hasan Tahsin Öztürk, Kemal Karakuzu, Ali Mardani and Naz Mardani

Polymers 2026, 18(5), 656; https://doi.org/10.3390/polym18050656 (registering DOI) - 7 Mar 2026

Abstract

This study investigates the interaction between polycarboxylate-based water-reducing admixtures (WRAs) and various types of CEM I 42.5R Portland cements, focusing on optimizing input parameters in cementitious systems. Despite the widespread use of WRAs to enhance concrete’s workability, strength, and durability, their compatibility with [...] Read more.

This study investigates the interaction between polycarboxylate-based water-reducing admixtures (WRAs) and various types of CEM I 42.5R Portland cements, focusing on optimizing input parameters in cementitious systems. Despite the widespread use of WRAs to enhance concrete’s workability, strength, and durability, their compatibility with cement remains a critical challenge, often leading to performance issues such as low initial flow, bleeding, and rapid slump loss. This research addresses two significant gaps in the literature: the unexplored use of input parameter reduction in cementitious systems and the application of novel metaheuristic algorithms in optimizing these systems. In this study, 25 WRA were first synthesized to enrich the inputs of machine learning (ML) models. Then, a dataset of 750 entries was generated, and advanced prediction models were developed. To ensure scientific rigor and eliminate data leakage, a triple-split dataset strategy (Training–Validation–Test) and 5-fold cross-validation were implemented. Among the machine learning techniques analyzed, the Optimized Artificial Neural Networks (opANN) architecture decisively demonstrated the highest prediction performance on the isolated test dataset. In the opANN process, 10 different metaheuristics were tested to evaluate their effectiveness in hyperparameter optimization. As a result, the Kepler Optimization (KOA) algorithm was determined as the algorithm with the highest performance in ANN hyperparameter optimization. Furthermore, Shapley Additive Explanations (SHAP) analysis was utilized to bridge the gap between empirical observations and algorithmic predictions, quantitatively corroborating the rheological roles of phosphate and sulfonate groups. The results offer new insights into WRA–cement compatibility and present advanced, interpretable modeling approaches that enhance predictive accuracy, contributing to more reliable and sustainable concrete practices. Full article

(This article belongs to the Special Issue Application of Polymers in Cementitious Materials)

22 pages, 1265 KB

Open AccessArticle

Closed-Loop Chemical Recycling of Polylactide via Glycolysis: From Water-Soluble Oligomers to High-Purity Lactide

by Gadir Aliev, Roman Toms, Matvey Marinichev, Daniil Ismailov, Kirill Kirshanov and Alexander Gervald

Polymers 2026, 18(5), 655; https://doi.org/10.3390/polym18050655 (registering DOI) - 7 Mar 2026

Abstract

Polylactide (PLA) has become widely adopted across biomedical, packaging, and manufacturing sectors due to its biodegradability and renewable sourcing. However, the rapid growth in PLA consumption has created urgent challenges related to waste management and the cleaning of processing equipment. This study investigates [...] Read more.

Polylactide (PLA) has become widely adopted across biomedical, packaging, and manufacturing sectors due to its biodegradability and renewable sourcing. However, the rapid growth in PLA consumption has created urgent challenges related to waste management and the cleaning of processing equipment. This study investigates glycolysis as a promising chemical depolymerization pathway for PLA recycling and in situ reactor cleaning. A systematic analysis of four glycolysis agents (GA) (ethylene glycol, diethylene glycol, propylene glycol, and glycerol) was performed across molar PLA:GA ratios from 1:0.125 to 1:4 at 220 °C, targeting the efficient conversion of high-molecular-weight PLA (Mn ≈ 165 kDa) into low-molecular-weight oligomers. Gel permeation chromatography (GPC) demonstrated that propylene glycol exhibited the highest depolymerization efficiency, yielding oligomers with Mn as low as 200 g·mol⁻¹ even at minimal glycolysis agent ratios, while glycerol produced hydroxyl-rich oligomers optimal for subsequent lactide synthesis. Hydroxyl value (HV) measurements showed excellent agreement with theoretical values (<5% deviation), allowing us to make an assumption about an approximate, close to near-quantitative con-version. Glycolysis products with Mw below 400 g·mol⁻¹ displayed excellent water solubility, making them particularly attractive for reactor cleaning applications. Using glycerol-derived (GL) oligomers (PLA:GL = 1:0.25), purified L-lactide with a melting point of 98.1 °C and high purity (>99%) was obtained through thermocatalytic depolymerization and five recrystallization cycles, as confirmed by ¹H nuclear magnetic resonance (¹H NMR) and differential scanning calorimetry (DSC) analyses. The recovered lactide’s high purity renders it suitable for ring-opening polymerization, enabling closed-loop PLA recycling schemes. Overall, glycolysis emerges as a highly promising chemical recycling route complementary to hydrolysis and pyrolysis: propylene glycol maximizes depolymerization efficiency for cleaning applications, while glycerol optimizes oligomer functionality for lactide recovery and advanced material synthesis. Our results provide practical guidelines for selecting glycolysis agents and conditions for cleaning and recycling applications. Full article

(This article belongs to the Special Issue Advances in Polymer Recycling and Upcycling: Toward a Circular and Sustainable Future)

31 pages, 7314 KB

Open AccessArticle

Mechanical and Microstructural Response of FDM-Printed PETG and PETG+CF to Variable Infill Architecture and Lubricant Exposure

by Lidija Rihar and Elvis Hozdić

Polymers 2026, 18(5), 654; https://doi.org/10.3390/polym18050654 (registering DOI) - 7 Mar 2026

Abstract

Fused deposition modelling/fused filament fabrication (FDM/FFF) enables rapid manufacturing of functional polymer components; however, the reliability of printed parts remains strongly governed by internal architecture, process-induced porosity, and exposure to service fluids. This study quantifies the combined influence of (i) infill pattern (linear, [...] Read more.

Fused deposition modelling/fused filament fabrication (FDM/FFF) enables rapid manufacturing of functional polymer components; however, the reliability of printed parts remains strongly governed by internal architecture, process-induced porosity, and exposure to service fluids. This study quantifies the combined influence of (i) infill pattern (linear, triangular, hexagonal) at 30% density, (ii) infill density (30%, 60%, 100%) for linear infill, and (iii) short-term lubricant exposure on the tensile and microstructural response of FDM-printed polyethylene terephthalate glycol-modified (PETG) and short-carbon-fibre-reinforced PETG (PETG+CF). Specimens were printed following ISO 527-2 and tensile-tested at 5 mm/min. Microstructural analysis coupled quantitative porosity with mechanical response, Young’s Modulus, and strain-to-break. At 30% density, PETG with hexagonal infill achieved the highest tensile strength (18.54 ± 0.67 MPa), exceeding linear (16.99 ± 0.52 MPa) and triangular (14.15 ± 0.70 MPa) patterns, while triangular and linear patterns exhibited higher Young’s Modulus, indicating topology-driven decoupling of stiffness and strength. Increasing linear infill density raised strength to 31.35 ± 0.33 MPa (PETG) and 38.90 ± 0.28 MPa (PETG+CF) at 100%, consistent with reduced porosity. Seven-day immersion in SAE 15W-40 mineral engine oil reduced PETG strength by ~17% while increasing deformation to failure, whereas PETG+CF showed only minor changes. Overall, the results demonstrate that architecture-aware design, supported by quantitative porosity descriptors, is essential for ensuring the reliable mechanical performance of FDM/FFF-printed PETG-based components exposed to service fluids. Full article

(This article belongs to the Special Issue Research and Characterization of Mechanical, Thermal, and Structural Properties of 3D Printed Polymers)

30 pages, 7099 KB

Open AccessArticle

Hemp Fiber and Expanded Perlite-Incorporated Lightweight Inorganic Polymer Mortars: Mechanical, Thermal Insulation, High-Temperature Resistance, Microstructural Characteristics, and Life Cycle Assessment

by Brial Asif Hayi Paka, Turan Şevki Köker, Ezgi Orklemez, Guy Patrick Bikoula Onono, Ugur Durak, Serhan Ilkentapar, Okan Karahan and Cengiz Duran Atis

Polymers 2026, 18(5), 653; https://doi.org/10.3390/polym18050653 (registering DOI) - 7 Mar 2026

Abstract

In this study, lightweight geopolymer mortars with low environmental impact, high thermal insulation performance, and strong resistance to elevated temperatures were developed. Fly ash, expanded perlite, and bio-based hemp fibers were employed as the binder, aggregate, and reinforcement, respectively. Hemp fibers were prepared [...] Read more.

In this study, lightweight geopolymer mortars with low environmental impact, high thermal insulation performance, and strong resistance to elevated temperatures were developed. Fly ash, expanded perlite, and bio-based hemp fibers were employed as the binder, aggregate, and reinforcement, respectively. Hemp fibers were prepared in lengths of 1, 2, and 3 cm and incorporated into the mixtures at dosages of 0.50%, 0.75%, and 1.00% by weight of binder. Sodium hydroxide was used as the activator, and specimens were heat-cured at 90 °C for 24–48–72 h. The workability, unit weight, UPV, flexural, and compressive strength of the geopolymer mortars were determined. In addition, thermal conductivity, high-temperature resistance, microstructural characteristics, and environmental impacts of selected mixtures were evaluated. The results demonstrated that lightweight geopolymer mortars could be successfully produced using expanded perlite aggregate and that hemp fibers significantly enhanced mechanical performance up to 48% at one day. Moreover, fiber reinforcement improved thermal insulation capability by up to 5.5% and high-temperature resistance. FESEM, EDX, elemental mapping, and XRD analyses supported the mechanical and physical findings through detailed microstructural evidence. Furthermore, LCA results revealed that fiber incorporation improved the environmental performance of geopolymer mortars, resulting in approximately a 21% reduction in global warming potential compared with the reference mixture. Full article

(This article belongs to the Special Issue High-Performance Polymer Materials and Fiber-Reinforced Composites for Engineering Applications)

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14 pages, 1716 KB

Open AccessArticle

Anisotropic Extrudate Swell from a Slit Die: A Velocity-Centre Hypothesis and Numerical Verification

by Guangdong Zhang, Xinyu Hao and Linzhen Zhou

Polymers 2026, 18(5), 652; https://doi.org/10.3390/polym18050652 (registering DOI) - 7 Mar 2026

Abstract

While anisotropic extrudate swell in polymer processing is fundamentally driven by physical viscoelastic recovery, this paper proposes a theoretical framework to explicitly isolate and map the purely geometric and kinematic components of this phenomenon. Serving as a mathematical proof-of-concept, a multi-velocity-centre hypothesis is [...] Read more.

While anisotropic extrudate swell in polymer processing is fundamentally driven by physical viscoelastic recovery, this paper proposes a theoretical framework to explicitly isolate and map the purely geometric and kinematic components of this phenomenon. Serving as a mathematical proof-of-concept, a multi-velocity-centre hypothesis is proposed. By introducing a semi-empirical, lumped material-flow calibration parameter, the macroscopic diameter swell ratio is mathematically extended to the discrete local flow field of a rectangular slit die. To evaluate its validity, the analytical framework is subjected to a numerical test for kinematic consistency utilizing isothermal, inelastic power-law fluid CFD simulations, thereby separating geometric mapping from complex viscoelastic stress relaxation. Results indicate that analytical predictions show good agreement with CFD data (error < 5%) strictly within the core zone of high-aspect-ratio dies. However, due to the infinite-slit assumption, 3D flow kinematics near die edges induce velocity decay, leading to local deviations that require future empirical corrections. Although comprehensive physical extrusion experiments and non-isothermal viscoelastic coupling are required for industrial deployment, this semi-empirical kinematic mapping provides a foundational mathematical basis that could potentially inform future inverse die-profile design and shape distortion compensation. Full article

(This article belongs to the Section Polymer Processing and Engineering)

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17 pages, 17291 KB

Open AccessArticle

Tensile Behavior of Carbon Fibers Impregnated with Thermoplastics Using Coextrusion Technique

by Victor V. Tcherdyntsev, Andrey A. Stepashkin and Alnis A. Veveris

Polymers 2026, 18(5), 651; https://doi.org/10.3390/polym18050651 - 6 Mar 2026

Abstract

To increase printing speed and quality, a route consisting of using two sequential coextruders to form impregnated fiber immediately before feeding it to the printer. Such an approach, aimed at allowing the use of the most common industrial 12K carbon fibers for additive [...] Read more.

To increase printing speed and quality, a route consisting of using two sequential coextruders to form impregnated fiber immediately before feeding it to the printer. Such an approach, aimed at allowing the use of the most common industrial 12K carbon fibers for additive manufacturing, prevents damage to composite fibers during transportation, storage, and loading. An elaborate system was used to prepare carbon fibers impregnated with polypropylene, ethylene vinyl acetate, and their blends. The used scheme allows the production of composite fibers containing from 60 to 80 wt. % of carbon fibers. It was found that the elastic modulus of the composite fibers is close to those for raw carbon fibers and does not depend on the used polymer. It shows that the used carbon fiber path in the polymer melt and two sequential calibrating nozzles result in a high degree of orientation of the elementary filaments in the fiber at impregnation and maintain the elastic properties of the carbon fiber in the resulting composite. The tensile strength of the composite fibers depends on the polymer content in the composite fiber; the highest tensile strength was observed for fibers impregnated with ethylene vinyl acetate when increasing the coextrusion temperature up to 220 °C, which results in a composite fiber with a polymer content of 30 wt. %. A decrease in the polymer content in composite fibers results in a decrease in strength. Full article

(This article belongs to the Special Issue Fiber-Reinforced Polymer Composites: Progress and Prospects)

20 pages, 4099 KB

Open AccessReview

Alkali-Activated Polymers for Grouting: A Review of Mechanisms, Performance, and Engineering Applications

by Beining Liu and Mengtang Xu

Polymers 2026, 18(5), 650; https://doi.org/10.3390/polym18050650 - 6 Mar 2026

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Polymer Fluids in Geology and Geotechnical Engineering)

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36 pages, 3118 KB

Open AccessReview

Quaternized Chitosan Crosslinked Networks for pH-Responsive Macromolecule Delivery: A Review

by Tongtong Wang and Hui Sun

Polymers 2026, 18(5), 649; https://doi.org/10.3390/polym18050649 - 6 Mar 2026

Abstract

Chitosan, a biocompatible and biodegradable polysaccharide, exhibits notable antibacterial properties. However, its practical applications are often constrained by inherent limitations such as poor solubility (restricted to acidic media) and suboptimal mechanical strength. By constructing dynamic covalent networks with QCS and green crosslinkers (e.g., [...] Read more.

Chitosan, a biocompatible and biodegradable polysaccharide, exhibits notable antibacterial properties. However, its practical applications are often constrained by inherent limitations such as poor solubility (restricted to acidic media) and suboptimal mechanical strength. By constructing dynamic covalent networks with QCS and green crosslinkers (e.g., genipin, dialdehyde cellulose), materials acquire excellent pH-responsive intelligence. This review elaborates on the molecular design, crosslinking strategies, and applications in intelligent packaging and targeted therapy. The synergistic Schiff-base/hydrogen-bonding mechanism enables dual (pH/enzyme) responsive release. We clarify the relationship between quaternization degree and cytotoxicity as a key challenge for clinical translation and analyze how green crosslinkers are molecular bridges to tailor network properties. The ‘perception-response’ integrated design principle of QCS demonstrates significant potential for intelligent packaging and antibacterial−anticancer synergistic therapy, while addressing key biosafety considerations. Full article

(This article belongs to the Section Polymer Applications)

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14 pages, 2645 KB

Open AccessArticle

Tailoring Flame Retardance and Thermal Conductivity of Epoxy/Benzoxazine Mixtures via Aluminum Trihydrate and Ceramic Hybridization

by Kyung-Soo Sung, Hye-Won Cho, Kyu-Hwan Kwon and Namil Kim

Polymers 2026, 18(5), 648; https://doi.org/10.3390/polym18050648 - 6 Mar 2026

Abstract

A composite meeting the UL94 V-0 rating was produced by adding 30 wt% epoxy silane-modified aluminum trihydrate (EPATH) to a 60/40 epoxy/benzoxazine matrix. Various bimodal and trimodal composites containing 20–40 wt% of three types of ceramic fillers, i.e., aluminum oxide (Al₂O [...] Read more.

A composite meeting the UL94 V-0 rating was produced by adding 30 wt% epoxy silane-modified aluminum trihydrate (EPATH) to a 60/40 epoxy/benzoxazine matrix. Various bimodal and trimodal composites containing 20–40 wt% of three types of ceramic fillers, i.e., aluminum oxide (Al₂O₃), boron nitride (BN), and magnesium oxide (MgO), were prepared to simultaneously achieve flame-retardant and thermal conductive properties. The bimodal composites with 40 wt% of Al₂O₃ and MgO exhibited thermal conductivities of 1.22 W/m∙K and 1.29 W/m∙K, respectively, which were superior to that of the composite containing the same amount of ATH (1.0 W/m∙K). In contrast, both the coefficient of thermal expansion (CTE) and shear strength decreased with increasing ceramic filler content. For agglomerated BN, the filler loading was constrained above 30 wt% because its high specific volume caused a significant rise in the viscosity. In the trimodal composites with a total filler content of 40 wt% of Al₂O₃ and BN, a BN fraction of 7.5 wt% yielded the highest thermal conductivity of 1.64 W/m∙K and the lowest water absorption of 0.69%. When the trimodal composites were exposed to −55 °C and 150 °C for 1000 h, they exhibited a reduction in shear strength of less than 30% compared to their initial values. Full article

(This article belongs to the Special Issue Advanced Research on the Thermal Properties and Flame Retardancy of Polymer Composites, 2nd Edition)

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15 pages, 1882 KB

Open AccessArticle

Aging-Feature-Extraction Method Based on the Short-Axis Diameter Ratio of Serviced Rubber Strips

by Yujia Chen, Bo Xu, Yun Tan, Jia He, Youchun Pi, Hu Li, Chunyu Meng, Yiyi Liang, Mengyue Bai and Yuansi Wei

Polymers 2026, 18(5), 647; https://doi.org/10.3390/polym18050647 - 6 Mar 2026

Abstract

In this paper, aiming at the aging problem of rubber sealing strips in key parts of hydropower units under long-term load, this study proposes a quantitative aging-feature-extraction technique centered on the ratio of the short-axis length to the original diameter (b/ [...] Read more.

In this paper, aiming at the aging problem of rubber sealing strips in key parts of hydropower units under long-term load, this study proposes a quantitative aging-feature-extraction technique centered on the ratio of the short-axis length to the original diameter (b/D) of serviced rubber strips. Through a systematic approach combining theoretical analysis, numerical simulation, and measured data calculations, the research first derives from energy principles that the elastic modulus (E) and yield stress (σ_s) are key physical parameters characterizing rubber aging, reflecting the material’s energy storage capacity and irreversible deformation threshold, respectively. Based on this, a radial compression simulation model of rubber strips is established, focusing on the cross-sectional deformation laws under 25% and 30% compression ratios in serviced conditions. It is found that the short-axis diameter ratio b/D exhibits a significant linear relationship with the dimensionless yield stress (σ_s/E), and a quadratic relationship with the dimensionless unit-length reaction force (F/ED). Using measured data, fluororubber (FKM) and nitrile rubber (NBR) specimens after 17 years of service are selected for radial compression experiments to extract the elastic modulus. The calculated results are compared with elasticity modulus estimates based on hardness empirical formulas (Gent’s and Qi’s formulas), showing consistency, particularly with Qi’s formula for NBR. This method enables rapid and accurate assessment of rubber aging, demonstrating the effectiveness and practicality of using b/D as a feature parameter. The study provides a quantitative and convenient tool for condition monitoring and life prediction of industrial equipment seals, especially suitable for the operation and maintenance of rubber components in complex environments such as hydropower units. Full article

(This article belongs to the Special Issue Aging Behavior and Durability of Polymer Materials, 2nd Edition)

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19 pages, 4904 KB

Open AccessArticle

Research on the Influence of Different Wax-Based Warm Mix Additives on Rheological and Aging Behaviors of High-Viscosity Modified Asphalt

by Jingqing Huang, Bei Chen, Yingchun Cai, Jinchao Yue, Bishuai Hong and Guoqi Tang

Polymers 2026, 18(5), 646; https://doi.org/10.3390/polym18050646 - 6 Mar 2026

Abstract

This study introduces five types of wax materials to replace traditional Sasobit warm mix agents (WMAs), aiming to reduce the aging performance of high-viscosity modified asphalt (HMA) under high temperatures and optimize wax-based WMAs for a better warm mix effect and more stable [...] Read more.

This study introduces five types of wax materials to replace traditional Sasobit warm mix agents (WMAs), aiming to reduce the aging performance of high-viscosity modified asphalt (HMA) under high temperatures and optimize wax-based WMAs for a better warm mix effect and more stable performance of HMA. In this study, styrene–butadiene–styrene (SBS) modifier was first used to prepare HMA, and then wax materials were added to prepare HMA. Thin-Film Oven Tests (TFOTs) and Pressure Aging Vessel (PAV) aging tests were conducted, followed by dynamic shear rheology (DSR) tests, to study the high-temperature rheological properties of each warm mix HMA. Fourier-transform infrared spectroscopy (FTIR) tests and fluorescence microscopy were used to observe the microstructures of the asphalt. The results show that all six wax materials exhibited good warm mix effects, among which refined Fischer–Tropsch Wax 1 (RFW1) outperforms conventional Sasobit WMA in terms of warm mix effect, high-temperature rheological properties, and anti-aging performance, indicating its potential to replace Sasobit in engineering applications. Full article

(This article belongs to the Section Polymer Analysis and Characterization)

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15 pages, 6259 KB

Open AccessArticle

Development of Bio-Based Thermosetting Resins from Maltodextrin–Itaconate Systems Toward Styrene-Free Unsaturated Polyesters

by Naoki Wada, Ryota Saito and Kenji Takahashi

Polymers 2026, 18(5), 645; https://doi.org/10.3390/polym18050645 - 6 Mar 2026

Abstract

The transition to sustainable thermosetting resins is frequently hindered by the trade-off between high bio-based content and processability. This study reports a novel strategy in developing a highly bio-based, styrene-free unsaturated polyester resin (UPR) by leveraging maltodextrin-derived mixed esters dissolved in dimethyl itaconate [...] Read more.

The transition to sustainable thermosetting resins is frequently hindered by the trade-off between high bio-based content and processability. This study reports a novel strategy in developing a highly bio-based, styrene-free unsaturated polyester resin (UPR) by leveraging maltodextrin-derived mixed esters dissolved in dimethyl itaconate (DMI). Unlike conventional polysaccharide-based systems that suffer from extreme viscosity, our functionalized prepolymer–DMI system achieves a low-viscosity curing solution without requiring petroleum-derived diluents such as styrene. Fourier-transform infrared spectroscopy confirmed the formation of a robust crosslinked network via the complete consumption of C=C bonds. Consequently, the cured resin exhibits exceptional thermal and mechanical performance, outperforming many existing bio-based analogs: a glass transition temperature (T_g) reaching 141 °C, a decomposition onset near 250 °C, and superior dimensional stability with a linear thermal expansion coefficient as low as 77 ppm/°C. Demonstrating a fully renewable, easy-to-process formulation with a flexural strength of 44 MPa, this work provides a design template for the next generation of high-performance, eco-friendly industrial thermosets. Full article

(This article belongs to the Special Issue Development of Bio-Based Materials: Synthesis, Characterization, and Applications, 3rd Edition)

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17 pages, 2026 KB

Open AccessArticle

Numerical Investigation of MWCNT Effects on Elastic Properties of PA6/POM Blends

by Katarina Pisačić, Srečko Glodež and Aleš Belšak

Polymers 2026, 18(5), 644; https://doi.org/10.3390/polym18050644 - 6 Mar 2026

Abstract

To ensure the viability of polymer materials, given the properties and limitations of polymers, hybrid materials have been developed that blend the features of all included components. Researchers have not explored the impacts of the length aspect ratio of nanofillers on the mechanical [...] Read more.

To ensure the viability of polymer materials, given the properties and limitations of polymers, hybrid materials have been developed that blend the features of all included components. Researchers have not explored the impacts of the length aspect ratio of nanofillers on the mechanical properties of hybrids in great detail previously. Multi-walled carbon nanotubes are a valuable option because they exhibit improved mechanical properties. Using numerical simulation, the impacts of nanofiller content and the size aspect ratio on two base materials—polyamide 6, polyoxymethylene—and their blends, were determined as a function of the volume ratio, the MWCNTs aspect ratio and the base material blend composition. Numerical analysis employed the ANSYS Material Designer. Random samples of chopped-fibre representative volume elements were generated, meshed and analysed by finite element analysis to obtain the Young’s modulus and Poisson’s ratio for each sample. The results showed a generally linear dependence. Rises in both aspect ratio and volume fraction of MWCNTs increased the Young’s modulus up to 46% and decreased the Poisson’s ratio up to 1.6%. The findings suggest that although the impact of the aspect ratio is not as large as that of the volume ratio, longer MWCNTs are preferable. Full article

(This article belongs to the Section Polymer Composites and Nanocomposites)

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14 pages, 2990 KB

Open AccessArticle

Improvement of Flame Retardancy on Polyamide 6 Composites via Melamine Polyphosphate-Modified Carbon Nanotubes

by Xuejun Shi, Xiangxiang Du, Xiaodong Zhao, Meiying Wang, Quanshuai Liu, Bo Hong, Yongjun Han, Haoxuan Sun and Wei Yuan

Polymers 2026, 18(5), 643; https://doi.org/10.3390/polym18050643 - 6 Mar 2026

Abstract

Melamine polyphosphate (MPP) is a widely employed additive-type flame retardant for polyamide 6. Generally, a higher loading of MPP leads to improved flame retardancy of polyamide 6 composites. Nevertheless, excessive addition tends to cause problems such as flame-retardant migration, leakage, and exudation. Against [...] Read more.

Melamine polyphosphate (MPP) is a widely employed additive-type flame retardant for polyamide 6. Generally, a higher loading of MPP leads to improved flame retardancy of polyamide 6 composites. Nevertheless, excessive addition tends to cause problems such as flame-retardant migration, leakage, and exudation. Against this background, this work focuses on covalently grafting melamine polyphosphate onto the surface of carbon nanotubes via a facile chemical reaction, with the aim of alleviating the migration and leakage of the flame retardant in the polyamide 6 matrix. Carbon nanotubes (CNTs) were surface modified with a silane coupling agent (KH560) to obtain CNTs bearing epoxy groups (CNT-KH560). Subsequently, a ring-opening addition reaction was conducted between the CNT-KH560 and melamine polyphosphate (MPP) yielding carbon nanotubes with surface-bonded flame-retardant MPP (CNTM). Polyamide 6 composite slices (PA6/CNTM) were prepared via twin-screw extrusion blending and compounding and then by hot-press molding into test specimens. The modified carbon nanotubes were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The results confirmed the successful grafting of MPP onto the carbon nanotube surface, with a grafting degree of 9.1 g/100 g measured. The flame retardancy of the PA6/CNTM composites were evaluated through UL 94 vertical burning and limiting oxygen index (LOI) tests and cone calorimeter. These flame retardancy results indicated that when the content of flame-retardant-modified carbon nanotubes was 10 wt%, the PA6/CNTM10 composites achieved UL 94 V-2 and the limiting oxygen index increased from 24.5% of pure PA6 to 29.1%. The PHRR value of pure PA6 decreased from 750 kW/m² to 614 kW/m². This design of surface-grafted flame retardant provides a new strategy for the preparation and application of high-performance polyamide 6 flame-retardant composites. Full article

(This article belongs to the Special Issue Advances in Flame-Retardant Polymer Composites)

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19 pages, 2065 KB

Open AccessArticle

Effects of Antigen Dosage and Chitosan Micro/Nanoparticle Size on Immune Responses in Mice Immunized with H5N1 Influenza Vaccine

by Anh Dzung Nguyen, Yen Nhi Nguyen, Hong Pham, Tam Duong Le Ha, Hanh Lan Nguyen, Lien Le, Van Bon Nguyen, Dinh Sy Nguyen, Huu Hung Dinh, San-Lang Wang and Van Cao

Polymers 2026, 18(5), 642; https://doi.org/10.3390/polym18050642 - 5 Mar 2026

Abstract

Highly pathogenic avian influenza A/H5N1 remains a persistent threat to public health and poultry production. H5N1 antigens are typically poorly immunogenic and require effective adjuvants for antigen dose-sparing. Here, we evaluated chitosan microparticles (CSMs) and nanoparticles (CSNs) as polymeric nano-adjuvants for an H5N1 [...] Read more.

Highly pathogenic avian influenza A/H5N1 remains a persistent threat to public health and poultry production. H5N1 antigens are typically poorly immunogenic and require effective adjuvants for antigen dose-sparing. Here, we evaluated chitosan microparticles (CSMs) and nanoparticles (CSNs) as polymeric nano-adjuvants for an H5N1 influenza vaccine, focusing on the roles of antigen dose and particle size. A purified hemagglutinin antigen was adsorbed onto chitosan particles at doses ranging from 0.15 to 5.0 µg. Both CSNs and CSMs showed consistently high loading efficiency (97–99%). BALB/c mice were immunized intramuscularly in a prime–boost schedule. Chitosan nanoparticles significantly enhanced IgG and hemagglutination inhibition (HI) titers at low antigen doses compared with aluminum hydroxide and antigen-only controls (p < 0.05). Immune responses reached saturation at a 1.5 µg dose of antigen for chitosan nanoparticles and 3.0 µg for chitosan microparticles. IgG subtype analysis suggested a balanced IgG1/IgG2a profile. Collectively, these findings support chitosan-based polymeric nanoparticles as promising adjuvants enabling dose-sparing H5N1 vaccination. Full article

(This article belongs to the Section Biobased and Biodegradable Polymers)

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15 pages, 7693 KB

Open AccessArticle

Effects of Overload Current on the Ignition and Burning Hazards of Polyethylene-Insulated Wires

by Heran Song, Qingwen Lin, Zhurong Dong, Songfeng Liang, Ruichao Wei, Zhanyu Li, Shenshi Huang, Yiting Yan and Yang Li

Polymers 2026, 18(5), 641; https://doi.org/10.3390/polym18050641 - 5 Mar 2026

Abstract

To quantitatively elucidate the effects of overload current on the ignition and burning hazards of polyethylene-insulated wires, 2.5 mm² polyethylene-insulated copper wires used commercially were tested in an electrical fire fault simulation system. Experiments were conducted to study the evolution of overloads, [...] Read more.

To quantitatively elucidate the effects of overload current on the ignition and burning hazards of polyethylene-insulated wires, 2.5 mm² polyethylene-insulated copper wires used commercially were tested in an electrical fire fault simulation system. Experiments were conducted to study the evolution of overloads, ignition, and burning. The entire process, from insulation smoking and ignition to sustained burning and final extinction driven by wire fusing, was recorded using synchronized digital and high-speed imaging. Video-based measurements were used to extract the following: smoking emission duration, ignition time, burning duration, maximum flame height, and segmented flame width. The results show that stable ignition and sustained burning occur when the overload current is greater than or equal to 180 A. As the current increases, ignition occurs earlier, while the smoking stage becomes shorter but exhibits nonmonotonic fluctuations. The burning duration shows a staged response. It first increases, then decreases toward a relatively stable level. This reflects the competition between enhanced Joule heating and accelerated wire melting and fusing. Maximum flame height and segmented flame width vary nonmonotonically with current, and the segmented flame width peaks at 200 A. A multi-indicator fire hazard evaluation framework was established and an entropy-weight TOPSIS method was applied to integrate the quantification and ranking. The overall fire hazard is greatest at 200 A. These findings provide experimental insight into overload-induced ignition and combustion behavior and contribute to a quantitative understanding of fire hazard evolution in overloaded electrical wires. Full article

(This article belongs to the Special Issue Fire Safety in Polymeric Composite Materials: Design, Simulation, and Testing)

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15 pages, 3308 KB

Open AccessArticle

Effects of Poly-γ-Glutamic Acid Molecular Weight on Lettuce Growth, Soil Properties, and Bacterial Community Structure

by Yu Lin, Linye Wang, Lin Shu, Huizhen Chen, Zhiqun Liang and Wei Zeng

Polymers 2026, 18(5), 640; https://doi.org/10.3390/polym18050640 - 5 Mar 2026

Abstract

Poly-γ-glutamic acid (γ-PGA) can regulate soil physicochemical properties and enhance crop yield. However, the effect of γ-PGA molecular weight (Mw) on plant growth remains unclear. In this study, we investigated the effects of γ-PGAs with low (70–100 kDa), high (700–1100 kDa), and ultra-high [...] Read more.

Poly-γ-glutamic acid (γ-PGA) can regulate soil physicochemical properties and enhance crop yield. However, the effect of γ-PGA molecular weight (Mw) on plant growth remains unclear. In this study, we investigated the effects of γ-PGAs with low (70–100 kDa), high (700–1100 kDa), and ultra-high (>3000 kDa) Mws on lettuce growth and soil properties. The results showed that γ-PGA application reduced the infiltration rate of red soil. In pot experiments, γ-PGAs with different Mws at 0.1% promoted lettuce growth, and blade length and width increased with increasing Mw. However, the excessive application of ultra-high Mw γ-PGA inhibited lettuce growth. Soil chemical properties revealed that γ-PGA treatments significantly increased soil ammonium nitrogen and available potassium content. Furthermore, bacterial community structure analysis indicated that adding γ-PGA reduced bacterial diversity and richness, particularly under low and high Mw γ-PGA treatments, while increasing the relative abundance of beneficial plant-associated bacteria, including Proteobacteria and Acidobacteriota. Overall, ultra-high Mw γ-PGA exhibited the strongest effects on soil water retention and nutrient regulation, whereas low application rate was more favorable for plant growth. These findings can provide insights into the agricultural application of γ-PGA. Full article

(This article belongs to the Section Biobased and Biodegradable Polymers)

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27 pages, 12850 KB

Open AccessArticle

Multi-Objective Optimization of the Dry Towpreg Filament Winding Process for Carbon/Epoxy Type IV Hydrogen Storage Vessels

by Ruiqi Li, Kaidong Zheng, Xiaoyu Yan, Haonan Liu, Yu Zhang, Guangming Huo, Haixiao Hu, Dongfeng Cao, Hao Li, Hongda Chen and Shuxin Li

Polymers 2026, 18(5), 639; https://doi.org/10.3390/polym18050639 - 5 Mar 2026

Abstract

Hydrogen storage vessels are critical components in hydrogen energy systems, and improving their manufacturing efficiency and structural performance is essential for next-generation Type IV vessel designs. Compared with conventional wet filament winding, towpreg dry filament winding offers higher efficiency, reduced environmental impact, and [...] Read more.

Hydrogen storage vessels are critical components in hydrogen energy systems, and improving their manufacturing efficiency and structural performance is essential for next-generation Type IV vessel designs. Compared with conventional wet filament winding, towpreg dry filament winding offers higher efficiency, reduced environmental impact, and better adaptability to complex structures. In this study, key process parameters, including winding tension, heating temperature, and winding speed were systematically optimized using the tensile strength and interlaminar shear strength of NOL ring specimens as evaluation metrics. A response surface methodology (RSM) regression model was established to correlate process variables with mechanical properties, followed by multi-objective optimization using the non-dominated sorting genetic algorithm II (NSGA-II) and final parameter selection through the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method. The results indicate that shear strength is primarily affected by heating temperature, whereas tensile strength is mainly governed by winding tension. The optimal parameter combination (79 N, 360 °C, and 11 m/min) yielded tensile and shear strengths of 2462.2 MPa and 64.4 MPa, respectively, with prediction errors below 0.5%. A 9 L Type IV hydrogen storage vessel manufactured under these conditions showed approximately 15.4% lower mass and about 17% higher gravimetric hydrogen storage efficiency than a comparable wet wound vessel. Full article

(This article belongs to the Topic Advanced Composites Manufacturing and Plastics Processing, 2nd Volume)

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26 pages, 4390 KB

Open AccessArticle

Polyethylene Recovery from Multilayer Plastic Packaging Waste

by Anareth Cavuquila, Luanna Maia, Germano A. Carreira, Inês Portugal, Carlos M. Silva and Ana Barros-Timmons

Polymers 2026, 18(5), 638; https://doi.org/10.3390/polym18050638 - 5 Mar 2026

Abstract

Multilayer plastic packaging waste (MPPW) represents a major challenge for waste management due to its widespread use in single-use applications and its complex, heterogeneous structure. Variations in polymer composition, layer thickness and number of layers significantly hinder conventional recycling processes, leading most MPPW [...] Read more.

Multilayer plastic packaging waste (MPPW) represents a major challenge for waste management due to its widespread use in single-use applications and its complex, heterogeneous structure. Variations in polymer composition, layer thickness and number of layers significantly hinder conventional recycling processes, leading most MPPW to be disposed of through landfilling or incineration. This study presents the development and optimization of a dissolution–precipitation process using toluene to recover polyethylene (PE) from MPPW. The proposed method successfully produced PE with less than 5 wt% polypropylene (PP), meeting common recycling quality requirements. Design of experiments (DoEs) combined with response surface methodology (RSM) was applied to evaluate the influence of key operating parameters, including temperature, dissolution time, solvent to waste ratio and agitation speed, to identify optimal processing conditions. The results demonstrated that temperature had the most significant influence on both dissolution yield and polymer purity. Optimal conditions of 100 °C, 30 min, 400 rpm, and a solvent-to-waste ratio of 15 mL/g resulted in a total recovery yield of 39.1% with a polymer composition of 97.7 wt% PE and 2.3 wt% PP. Owing to the use of established and scalable unit operations, the process shows strong potential for industrial-scale implementation without requiring complex or specialized infrastructure. Full article

(This article belongs to the Special Issue Sustainable Polymers and Polymer Recycling Technologies)

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