Polymers

25 pages, 1716 KB

Open AccessReview

Sustainable Valorisation of End-of-Life Tyres Through Pyrolysis-Derived Recovered Carbon Black in Polymer Composites

by Dharanija Banala, Ylias Sabri, Namita Roy Choudhury and Rajarathinam Parthasarathy

Polymers 2025, 17(20), 2771; https://doi.org/10.3390/polym17202771 (registering DOI) - 16 Oct 2025

More than one billion end-of-life tyres (EOLTs) are produced worldwide every year, and this is continuously increasing and has become an issue in sustainable development. This review discusses recent developments in the management of EOLTs and focuses on pyrolysis, which produces valuable tyre-derived [...] Read more.

More than one billion end-of-life tyres (EOLTs) are produced worldwide every year, and this is continuously increasing and has become an issue in sustainable development. This review discusses recent developments in the management of EOLTs and focuses on pyrolysis, which produces valuable tyre-derived products (TDPs) like steel, gas, oil, and char. This review focuses on recovered carbon black (rCB), a refined char with great potential as a sustainable alternative to commercial carbon black (CB). The review introduces a novel classification system for CB, virgin carbon black (vCB), recovered carbon black (rCB), and sustainable carbon black (sCB) to guide the transition toward environmentally friendly materials. It also examines how rCB enhances polymer properties for addressing price volatility and reducing carbon footprint. Additionally, a SWOT analysis evaluates the strengths (cost-effectiveness, reduced environmental impact), weaknesses (quality consistency), opportunities (emerging markets, circular economy integration), and threats (competition from virgin materials) of using rCB as a polymer reinforcement. By positioning rCB as a key material, this review outlines pathways for addressing the EOLT crisis and advancing a circular economy. Full article

(This article belongs to the Special Issue Polymer Recycling and Upcycling: Toward a Circular Materials Economy)

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18 pages, 3499 KB

Open AccessArticle

Minute Rebond: A Simple Method for Making Lab-Scale Rebonded Foam and Its Application as a Novel Soilless Growing Media

by Michael S. Harris, Harry Charles Wright, Tom Lilly, Nathan Seithel, Chris Hayes, Julie Walker, Jacob Nickles, Duncan Drummond Cameron and Anthony John Ryan

Polymers 2025, 17(20), 2770; https://doi.org/10.3390/polym17202770 (registering DOI) - 16 Oct 2025

Abstract

Polyurethane foams (PUFs) utilised in the comfort industry generate substantial trim waste volumes requiring end-of-life management. Rebonding, one form of mechanical recycling, is a technique involving the mechanical breakdown and subsequent adhesion of PUF using polyurethane prepolymers yielding a recycled material. However, the [...] Read more.

Polyurethane foams (PUFs) utilised in the comfort industry generate substantial trim waste volumes requiring end-of-life management. Rebonding, one form of mechanical recycling, is a technique involving the mechanical breakdown and subsequent adhesion of PUF using polyurethane prepolymers yielding a recycled material. However, the limited investigation into the properties of rebond PUF constrains its potential for novel alternative uses, such as soilless plant-growing media. A laboratory-scale rebond production method has been developed, and a series of rebond PUFs produced to evaluate the influence of crumb size, density, prepolymer chemistry, and prepolymer loading on the properties of the rebond PUFs and their suitability as growing media. The results indicated that higher quality rebonds were obtained with larger crumb sizes (mixed or >7 mm), moderate amounts of prepolymer (4.5 to 7.5% by mass), and higher densities. Increasing density directly influenced plant growth-related properties, including reducing airflow, increasing water uptake through wicking, and increasing water retention through drainage alongside larger crumb sizes [>7 mm]. To demonstrate the method’s utility for rapid screening, a plant growth trial was conducted using density as the key variable. Eruca sativa plants grown in low-density rebonds exhibited comparable growth (leaf length, leaf width, and shoot fresh weight) to mineral wool, whereas medium- and high-density rebonds showed reduced growth. This study validates a lab-scale technique that enables the rapid optimisation of rebond PUFs for novel applications like soilless growing media. Full article

(This article belongs to the Section Circular and Green Sustainable Polymer Science)

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11 pages, 2044 KB

Open AccessArticle

Effect of Debinding Process on Aluminum Nitride Ceramics Fabrication via Digital Light Processing 3D Printing

by Ning Kuang, Wenjie Zhao and Junfei Wu

Polymers 2025, 17(20), 2769; https://doi.org/10.3390/polym17202769 (registering DOI) - 16 Oct 2025

Abstract

Aluminum nitride (AlN) ceramics exhibit exceptional properties, making them attractive for a wide range of applications. To address the growing need for customized and geometrically intricate AlN components, digital light processing (DLP) has garnered significant interest as a highly promising additive manufacturing technology. [...] Read more.

Aluminum nitride (AlN) ceramics exhibit exceptional properties, making them attractive for a wide range of applications. To address the growing need for customized and geometrically intricate AlN components, digital light processing (DLP) has garnered significant interest as a highly promising additive manufacturing technology. In this study, the effects of the sintering process on DLP 3D printing of AlN ceramics were investigated. An optimized slurry formulation with a solid loading of 52 vol% was developed, exhibiting excellent rheological properties. By applying a controlled sintering heating rate of 0.5 °C/min, dense AlN ceramic components were successfully fabricated, achieving a bending strength of 212.6 MPa. This provides a novel approach for optimizing the DLP additive manufacturing process of AlN ceramics. Full article

(This article belongs to the Special Issue Polymeric Materials and Their Application in 3D Printing, 2nd Edition)

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13 pages, 3509 KB

Open AccessArticle

Sol–Gel Synthesis and Multi-Technique Characterization of Graphene-Modified Ca_2.95Eu_0.05Co₄O_x Nanomaterials

by Serhat Koçyiğit

Polymers 2025, 17(20), 2767; https://doi.org/10.3390/polym17202767 - 16 Oct 2025

Abstract

This study employs a multi-technique approach to elucidate how graphene incorporation affects phase formation, microstructure, and thermal behavior in PVA-assisted sol–gel synthesized Ca_2.95Eu_0.05Co₄O_x nanomaterials. XRD confirms the preservation of the primary phases (hexagonal CaCO₃ and [...] Read more.

This study employs a multi-technique approach to elucidate how graphene incorporation affects phase formation, microstructure, and thermal behavior in PVA-assisted sol–gel synthesized Ca_2.95Eu_0.05Co₄O_x nanomaterials. XRD confirms the preservation of the primary phases (hexagonal CaCO₃ and cubic CoO) alongside a distinct graphene (002) reflection; a systematic low-angle shift of the calcite (104) peak evidences partial relaxation of residual lattice strain with increasing graphene content, while Scherrer analysis indicates tunable crystallite size. Raman spectroscopy corroborates graphene incorporation through pronounced D (~1300 cm⁻¹) and G (~1580 cm⁻¹) bands and supports the XRD-identified phase coexistence via cobalt-oxide and calcite vibrations in the 200–700 cm⁻¹ region, also indicating increased defect/disorder with graphene loading. SEM shows grain refinement, denser/bridged lamellar textures, and reduced porosity at low–moderate graphene contents (1–3 wt.%), contrasted by agglomeration-driven heterogeneity at higher loadings (5–7 wt.%). EDX reveals increasing carbon with Ca/Co redistribution at accessible surfaces, and TG–DSC corroborates the removal of oxygen-containing groups and oxidative combustion of graphene at mid temperatures. Collectively, Raman–XRD-consistent evidence demonstrates that graphene provides a tunable handle over lattice strain, crystallite size, and grain-boundary architecture, establishing a processing–composition basis for optimizing functional (e.g., electrical/thermoelectric) performance. Full article

(This article belongs to the Special Issue Polymers in Inorganic Chemistry: Synthesis and Applications)

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18 pages, 4082 KB

Open AccessArticle

Design Analysis of Migration Nozzles Using CFD

by Makhsuda Juraeva and Dong-Jin Kang

Polymers 2025, 17(20), 2766; https://doi.org/10.3390/polym17202766 - 15 Oct 2025

Abstract

This paper presents a design analysis approach for migration nozzles used in the spinning process of synthetic fibers. A migration nozzle system consists of a yarn channel, air orifices, and a yarn loading slit. The entire system was analyzed in detail using computational [...] Read more.

This paper presents a design analysis approach for migration nozzles used in the spinning process of synthetic fibers. A migration nozzle system consists of a yarn channel, air orifices, and a yarn loading slit. The entire system was analyzed in detail using computational fluid dynamics (CFD). The design parameters considered include the cross-sectional shape of the yarn channel, as well as the diameter and number of air orifices. Two different cross-sectional shapes, square and circle, were examined. The diameter of the air orifice varied from 0.6 mm to 2.0 mm, and both single and double orifice configurations were studied. A square cross-section resulted in the formation of a secondary vortex above the main vortex, making the circular cross-section preferable. The diameter of the air orifice significantly affects the vortex flow within the yarn channel. Vortex flow characteristics were quantified in two ways: the vorticity averaged across the cross-section in the direction of the yarn channel and the vorticity at the centerline. The highest vorticity at the centerline was observed at a diameter of 1.3 mm for single air orifice and 0.9 mm for double air orifices. These CFD results were validated through comparison with corresponding experimental data. A statistical analysis confirms that the centerline vorticity, particularly in the area of the air orifice, is a key and reliable parameter for evaluating the design of migration nozzles. Full article

(This article belongs to the Special Issue Advanced Study on Polymer-Based Textiles)

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16 pages, 14613 KB

Open AccessArticle

Research on Bio-Inspired Decussated Bamboo-Fiber-Reinforced Epoxy Composites: The Effect of Vertical Fiber Proportion on Tribological Performances

by Heng Xiao, Hao Yi, Zijie Zhou, Ningfeng Wu, Shengwei Liang, Lei Ma and Wen Zhong

Polymers 2025, 17(20), 2765; https://doi.org/10.3390/polym17202765 - 15 Oct 2025

Abstract

Bamboo fiber is a prime green fiber due to its renewability, biodegradability, and high specific strength. Bamboo-fiber-reinforced epoxy (BFRE) composites have seen extensive use and shown great promise for natural biofiber-reinforced friction materials. Inspired by the decussated fiber alignment of bovine enamel, this [...] Read more.

Bamboo fiber is a prime green fiber due to its renewability, biodegradability, and high specific strength. Bamboo-fiber-reinforced epoxy (BFRE) composites have seen extensive use and shown great promise for natural biofiber-reinforced friction materials. Inspired by the decussated fiber alignment of bovine enamel, this study investigated how fiber orientation influences the tribological properties of BFRE composites. Specifically, the proportion of fibers oriented vertically to the surface was varied at seven levels: 0%, 25%, 33%, 50%, 67%, 75%, and 100%. The tribological performance was assessed through wear reciprocating testing and microscopic morphological characterization techniques. Results indicate that the bio-inspired fiber decussation can reduce the wear loss of the BFRE composites. Among all bio-inspired BFRE composites, BFRE composites with 67% vertical fibers achieve the best wear resistance. The vertical fibers in the BFRE composites can withstand pressure to provide a “compression–rebound” effect, while the parallel fibers can resist shear stress. The decussated structure inhibits crack initiation and propagation during wear and promotes transfer film formation, reducing wear loss. The findings expand understanding of the correlation between the bovine-tooth-like decussated structure and its tribological mechanisms, thereby offering essential guidance for the biomimetic design of high-performance BFRE composites for friction material application. Full article

(This article belongs to the Section Polymer Fibers)

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20 pages, 2361 KB

Open AccessArticle

Additive Manufacturing in Dentistry: A Comparative Study of Polymeric Surgical Guide Fabrication

by Joshua García Montagut, Ana González, Rubén Paz, Luis Suárez, Pablo Bordón, Zaida Ortega, Iulian Antoniac, Ilaria Cacciotti, Adriana Ileana and Mario Monzón

Polymers 2025, 17(20), 2764; https://doi.org/10.3390/polym17202764 (registering DOI) - 15 Oct 2025

Abstract

Additive manufacturing (AM), or 3D printing, has revolutionized surgical guide fabrication in dentistry by enabling the creation of complex, customized parts. This study aims to evaluate and compare three predominant AM technologies for polymers—Material Extrusion (MEX), Vat Photopolymerization (VPP), and Powder Bed Fusion [...] Read more.

Additive manufacturing (AM), or 3D printing, has revolutionized surgical guide fabrication in dentistry by enabling the creation of complex, customized parts. This study aims to evaluate and compare three predominant AM technologies for polymers—Material Extrusion (MEX), Vat Photopolymerization (VPP), and Powder Bed Fusion (PBF)—for producing surgical guides, focusing on desktop-level equipment. The analysis centers on key criteria: dimensional accuracy, manufacturing time, process complexity, and cost, both for single-set and multiple-set productions. The results reveal that while VPP and MEX technologies offer sufficient dimensional accuracy for clinical use, PBF technology falls short in this regard. In terms of cost and time, VPP proves to be the most efficient technology for manufacturing multiple sets of guides, a common scenario in dental clinics. However, MEX technology demonstrates its competitiveness, particularly in single-set, on-demand fabrication due to its fast-processing time and the potential for lower material costs with proper material selection. The study concludes that while VPP has been the traditional choice, advancements have made MEX a viable and practical option for a rapid and easy integration into smaller dental clinics. Full article

(This article belongs to the Special Issue Additive Manufacturing for Plastics: Latest Advances and Future Challenges)

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19 pages, 6627 KB

Open AccessArticle

Functional Data Analysis for the Structural, Chemical, Thermal, and Mechanical Properties of PA12 Additively Manufactured via SLS

by Alejandro García Rodríguez, Yamid Gonzalo Reyes, Edgar Espejo Mora, Carlos Alberto Narváez Tovar and Marco Antonio Velasco Peña

Polymers 2025, 17(20), 2763; https://doi.org/10.3390/polym17202763 - 15 Oct 2025

Abstract

Additive manufacturing via selective laser sintering (SLS) enables the rapid production of geometrically complex polyamide 12 (PA12) components. However, conventional pointwise analysis techniques often overlook the full depth of continuous experimental datasets, thus limiting the interpretation of structure–function relationships that are essential to [...] Read more.

Additive manufacturing via selective laser sintering (SLS) enables the rapid production of geometrically complex polyamide 12 (PA12) components. However, conventional pointwise analysis techniques often overlook the full depth of continuous experimental datasets, thus limiting the interpretation of structure–function relationships that are essential to high-performance design. This study employs functional data analysis (FDA) to elucidate the microstructural, chemical, thermal, and mechanical behaviours of SLS-fabricated PA12, focusing on the effects of build orientation (horizontal, transverse, vertical) and wall thickness (2.0–3.0 mm). The samples were produced via a commercial SLS platform and characterised via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and tensile testing. The FDA was applied to raw, normalised, and first derivative datasets via Python’s Scikit-FDA package, increasing the sensitivity to latent material variations. The findings demonstrate that the build orientation has a marked influence on the crystallinity and mechanical performance: horizontal builds yield narrower gamma-phase XRD peaks, greater structural order, and enhanced tensile properties, whereas vertical builds exhibit broader peak dispersion and greater thermal sensitivity. The wall thickness effects were minor, with only isolated flux-related anomalies. The FTIR spectra confirmed the consistent chemical stability across all the conditions. The FDA successfully identified subtle transitions and anisotropies that eluded traditional methods, underscoring its methodological strength for advanced polymer characterisation. These insights offer practical guidance for refining SLS process parameters and improving predictive design strategies in polymer-based additive manufacturing. Full article

(This article belongs to the Special Issue 3D Printing Polymers: Advancements in Materials and Applications, 2nd Edition)

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15 pages, 2955 KB

Open AccessArticle

Dual-Responsive Hybrid Microgels Enabling Phase Inversion in Pickering Emulsions

by Minyue Shen, Lin Qi, Li Zhang, Panfei Ma, Wei Liu, To Ngai and Hang Jiang

Polymers 2025, 17(20), 2762; https://doi.org/10.3390/polym17202762 - 15 Oct 2025

Abstract

Pickering emulsions have emerged as promising multiphase systems owing to their high stability and diverse applications in materials and chemical engineering. However, achieving precise and stimuli-responsive regulation of emulsion type, particularly reversible phase inversion between oil-in-water and water-in-oil states under fixed formulation without [...] Read more.

Pickering emulsions have emerged as promising multiphase systems owing to their high stability and diverse applications in materials and chemical engineering. However, achieving precise and stimuli-responsive regulation of emulsion type, particularly reversible phase inversion between oil-in-water and water-in-oil states under fixed formulation without additional stabilizers, remains a considerable challenge. In this work, we developed a sol–gel strategy, i.e., in situ hydrolysis and condensation of silane precursors to form a silica shell directly on responsive microgels, to produce H-SiO₂@P(NIPAM-co-MAA) hybrid microgels. The resulting hybrid particles simultaneously retained pH and temperature responsiveness, enabling the transfer of these properties from the polymeric network to the emulsion interface. When employed as stabilizers, the hybrid microgels allowed the controlled formation of Pickering emulsions that remained stable for one week under testing conditions. More importantly, they facilitated in situ reversible phase inversion under external stimuli. Overall, this work establishes a sol–gel approach to fabricate organic–inorganic hybrid microgels with well-defined dispersion and uniform silica deposition, while preserving dual responsiveness and enabling controlled phase inversion of Pickering emulsions. Full article

(This article belongs to the Section Polymer Chemistry)

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29 pages, 6756 KB

Open AccessArticle

Aldehyde–Aminotriazole Condensation Products as Novel Corrosion Inhibitors for Mild Steel in Hydrochloric Acid

by Daniil R. Bazanov, Yaroslav G. Avdeev, Tatyana A. Nenasheva, Andrey Yu. Luchkin, Dmitrii M. Mazur, Yury B. Makarychev, Tatiana E. Andreeva, Andrey I. Marshakov and Yurii I. Kuznetsov

Polymers 2025, 17(20), 2761; https://doi.org/10.3390/polym17202761 (registering DOI) - 15 Oct 2025

Abstract

The significance of this study arises from the urgent need to develop new corrosion inhibitors for the oil and gas industry. These inhibitors should be synthesized from readily available raw materials and be capable of providing effective protection for steel structures against corrosion [...] Read more.

The significance of this study arises from the urgent need to develop new corrosion inhibitors for the oil and gas industry. These inhibitors should be synthesized from readily available raw materials and be capable of providing effective protection for steel structures against corrosion when exposed to technological hydrochloric acid solutions over a wide temperature range (20–100 °C). The search for such environmentally acceptable and cost-efficient inhibitors is crucial for improving the durability and operational safety of oilfield equipment under aggressive acidic conditions. A new high-temperature corrosion inhibitor for steel in hydrochloric acid solutions has therefore been developed. The inhibitor, designated CATA, is the product of chemical condensation between cinnamaldehyde and 3-amino-1,2,4-triazole. Its protective action is based on the formation of an organic layer up to 12 nm thick, strongly bound to the steel surface. The results suggest with high probability that this protective film consists of polymeric products formed through chemical transformation of CATA on the corroding metal surface. It was shown that the addition of CATA significantly suppresses the electrode processes of steel, affecting both cathodic and anodic partial reactions as well as the kinetics of hydrogen permeation. Adsorption of CATA on steel is satisfactorily described by the Temkin isotherm. The free energy of adsorption (−ΔG_ads) was determined to be 54 kJ mol⁻¹, which is characteristic of chemisorption. This unique inhibition mechanism enables effective corrosion protection of steel in HCl solutions over a wide temperature range (20–100 °C). Under the most aggressive experimental conditions (2 M HCl, 100 °C), the addition of 10 mM CATA achieved an inhibition efficiency of 99.6%, with a corrosion rate of 3.3 g m⁻² h⁻¹, which represents an outstanding result. Furthermore, for spring steels, even in hot HCl solutions (20–60 °C), CATA strongly suppresses hydrogen uptake and allows complete preservation of their ductility. Full article

(This article belongs to the Special Issue Polymer-Based Coatings for Corrosion Protection)

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66 pages, 8494 KB

Open AccessReview

Hydrogels from Renewable Resources: Advances in 3D Networks Based on Cellulose and Hemicellulose

by Diana Elena Ciolacu

Polymers 2025, 17(20), 2760; https://doi.org/10.3390/polym17202760 - 15 Oct 2025

Abstract

In recent years, natural polymers have gained significant attention due to their abundance, biodegradability and versatility, offering a promising alternative to conventional synthetic polymers. Among natural polymers, cellulose and hemicellulose hold a special place, being the most abundant plant polysaccharides in nature, which [...] Read more.

In recent years, natural polymers have gained significant attention due to their abundance, biodegradability and versatility, offering a promising alternative to conventional synthetic polymers. Among natural polymers, cellulose and hemicellulose hold a special place, being the most abundant plant polysaccharides in nature, which serve as key structural materials in the synthesis of hydrogels. Cellulose has attracted significant attention in the development of hydrogels due to the fact that it confers desirable mechanical properties, high water absorption and biocompatibility. Hemicellulose, although with a more amorphous structure than cellulose, contains various functional groups that facilitate its chemical modification. With an environmentally friendly nature and low cost, these polysaccharides have gained major interest and are highly appreciated by both the academic and industrial communities. This review comprehensively presents recent advances in the design and development of hydrogels made from renewable biopolymers—cellulose and hemicellulose—providing an in-depth exploration of the information recorded over the past five years. The latest strategies for the synthesis of hydrogels, their formation mechanisms and their most important properties are analyzed and summarized in detail from the perspective of physical and chemical crosslinking. A comparative analysis is performed between these hydrogels, highlighting not only the advantages and disadvantages of each type of hydrogel but also the main challenges associated with the balance between mechanical strength, swelling capacity, biodegradability and cost-effectiveness. Finally, the advanced biomedical applications of these hydrogels in areas such as drug delivery, wound dressings and tissue engineering are presented in detail. Full article

(This article belongs to the Special Issue Advances in Cellulose-Based Polymers and Composites, 2nd Edition)

19 pages, 5246 KB

Open AccessArticle

Effects of the Mixing Method of Expanded Graphite on Thermal, Electrical, and Water Transport Properties of Thermosetting Nanocomposites

by Raffaele Longo, Elisa Calabrese, Francesca Aliberti, Luigi Vertuccio, Giorgia De Piano, Roberto Pantani, Marialuigia Raimondo and Liberata Guadagno

Polymers 2025, 17(20), 2759; https://doi.org/10.3390/polym17202759 - 15 Oct 2025

Abstract

The present research aims to investigate the impact of various mixing techniques (centrifugal planetary mixing, ultrasonication, and high-temperature magnetic stirring) on the properties of nanocomposite epoxy resins using expanded graphite particles. Differential scanning calorimetry reveals that the curing behavior and glass transition temperature [...] Read more.

The present research aims to investigate the impact of various mixing techniques (centrifugal planetary mixing, ultrasonication, and high-temperature magnetic stirring) on the properties of nanocomposite epoxy resins using expanded graphite particles. Differential scanning calorimetry reveals that the curing behavior and glass transition temperature are influenced by the selected method, indicating that a suitable choice allows increasing curing degree (C.D.) and glass transition temperature up to 10% and 12%, respectively. Morphological analysis performed via Scanning Electron Microscopy and Tunneling Atomic Force Microscopy offers detailed insights into the dispersion characteristics of fillers within polymer matrices, which sensitively affect the properties of the materials. The electrical conductivity values vary by more than five orders of magnitude among the various mixing methods. Centrifugal mixing leads to a decrease in the equilibrium concentration of water (C_eq) by up to 23% compared to that of the unfilled matrix, thanks to the chemical interactions that occur between the graphitic particles and the epoxy matrix (detectable via Fourier Transform Infrared Spectroscopy). Such a reduction is strongly desired in strategic fields such as the transport sector. The analysis of the obtained results suggests choosing the dispersion method of the filler in the matrix by considering the required performance for the specific planned application. Full article

(This article belongs to the Special Issue Synthesis, Design, Preparation and Processing of Functional Polymer Composites)

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22 pages, 2340 KB

Open AccessArticle

Glass Transition and Crystallization of Chitosan Investigated by Broadband Dielectric Spectroscopy

by Massimiliano Labardi, Margherita Montorsi, Sofia Papa, Laura M. Ferrari, Francesco Greco, Giovanni Scarioni and Simone Capaccioli

Polymers 2025, 17(20), 2758; https://doi.org/10.3390/polym17202758 - 15 Oct 2025

Abstract

Chitosan films obtained by solution casting were investigated by broadband dielectric spectroscopy (BDS) to explore both their glass transition and the effects of thermal annealing on molecular dynamics, deriving from residual water content as well as from cold crystallization. Glass transition at low [...] Read more.

Chitosan films obtained by solution casting were investigated by broadband dielectric spectroscopy (BDS) to explore both their glass transition and the effects of thermal annealing on molecular dynamics, deriving from residual water content as well as from cold crystallization. Glass transition at low temperatures could be evidenced in as-produced as well as thermally annealed films, where non-Arrhenian dielectric relaxation processes, consistent with a structural (α) relaxation, could be detected. The process detected at low temperatures could reflect the dynamics of residual water slaved by the polymer matrix. Secondary (β) relaxations, along with a slow process ascribed to interfacial polarization at the amorphous/crystalline interfaces, were concurrently detected. In most cases, a further Arrhenian process at intermediate temperatures (α_c) was present, also indicative of crystallization. Notably, the α processes, due to the primary relaxation of the polymer matrix plasticized by water, could be discriminated from other processes, present in the same frequency range, thanks to improvements in the dielectric fitting strategy. All relaxation processes showed the expected dependence on T_a. The more accurate exploration of the glass transition for chitosan helps to better rationalize its crystallization behavior, in view of an optimized application of this biopolymer. Full article

(This article belongs to the Special Issue From Biomass Fractionation to Final Biobased Polymer Nanocomposites in European Sustainable Biobased Nanomaterials Community (BIOMAC))

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18 pages, 2243 KB

Open AccessArticle

Development and Properties of Disposable Plates Made of Cellulosic Pulp from Mango Agro-Industrial Waste

by Maribel García-Mahecha, Herlinda Soto-Valdez, María Guadalupe Lomelí-Ramírez, Hilda Palacios-Juárez, José Anzaldo-Hernández, Tomás Jesús Madera-Santana, Citlali Colín-Chávez, Elizabeth Peralta, Rafael Auras and Elizabeth Carvajal-Millan

Polymers 2025, 17(20), 2757; https://doi.org/10.3390/polym17202757 - 15 Oct 2025

Abstract

Recent studies have shown that using conventional plastics to produce disposable tableware significantly impacts the environment. Alternatively, using cellulosic pulp from harnessing agro-industrial wastes, such as mango, provides a unique opportunity to create eco-friendly and biodegradable disposable tableware, a high-volume single-use item. Cellulosic [...] Read more.

Recent studies have shown that using conventional plastics to produce disposable tableware significantly impacts the environment. Alternatively, using cellulosic pulp from harnessing agro-industrial wastes, such as mango, provides a unique opportunity to create eco-friendly and biodegradable disposable tableware, a high-volume single-use item. Cellulosic pulp from the tegument of mango (cultivar Tommy Atkins) was successfully obtained by a semichemical pulping process to manufacture biodegradable plates. Refining times of 0, 5, 10, and 15 min were tested, and it was observed that a refining time of 10 min yielded a notably stronger material of 2.15 km in breaking length. Moreover, when the mango fibers were blended with pine fibers in a 70:30 (mango/pine) ratio, the material’s porosity significantly improved from 0 to 0.60 s/100 cc air. Alkyl ketene dimer at 1.5% was incorporated to impart water-resistant properties, changing the contact angle drop test from 0 to >120°. The biodegradation test indicated that the samples achieved a significant biodegradation level of 62.14 and 67.65 after 182 days of testing. The results demonstrated that the tegument from mango agro-industrial waste has the potential to be a source of cellulosic pulp to produce biodegradable and disposable tableware, contributing to the decrease in the use of conventional plastics. Full article

(This article belongs to the Special Issue Biopolymers for Food Packaging and Agricultural Applications)

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24 pages, 3341 KB

Open AccessArticle

Experimental Study on the Evolution of Mechanical Properties and Their Mechanisms in a HTPB Propellant Under Fatigue Loading

by Feiyang Feng, Xiong Chen, Jinsheng Xu, Yi Zeng, Wei Huang and Junchao Dong

Polymers 2025, 17(20), 2756; https://doi.org/10.3390/polym17202756 - 15 Oct 2025

Abstract

In this study, we explored the evolution of mechanical properties in hydroxyl-terminated polybutadiene (HTPB) propellants under fatigue loading by performing fatigue tests with varying maximum stresses and cycle numbers, followed by uniaxial tensile tests on post-fatigue specimens. Residual elongation was used as a [...] Read more.

In this study, we explored the evolution of mechanical properties in hydroxyl-terminated polybutadiene (HTPB) propellants under fatigue loading by performing fatigue tests with varying maximum stresses and cycle numbers, followed by uniaxial tensile tests on post-fatigue specimens. Residual elongation was used as a key parameter to characterize mechanical behavior, while scanning electron microscopy (SEM) provided insights into the mesostructural morphological changes that occur under different loading conditions, revealing the mechanisms responsible for variations in mechanical properties. The results show that, as the number of loading cycles increases, residual elongation decreases, with three distinct phases of decline—slow change, gradual decline, and rapid deterioration—depending on the stress levels. SEM analysis identified damage mechanisms such as “dewetting” and particle fragmentation at the mesostructural level, which compromise the material’s structural integrity, leading to reduced residual elongation. A novel aspect of this study is the application of Williams–Landel–Ferry (WLF) theory to construct a master curve describing residual elongation decay. This approach enabled the development of a generalized model to predict the material’s degradation under fatigue loading, with experimental validation of the fitted evolution model, offering a new and effective method for assessing the long-term performance of HTPB propellants. Full article

(This article belongs to the Special Issue Dynamic Behavior of Polymer Composite Materials and Structures, 2nd Edition)

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22 pages, 333 KB

Open AccessReview

Bio-Based Coatings on Cellulosic Materials Resistant to Humidity and Fats

by Bastián Rozas, Julio E. Bruna, Abel Guarda, María José Galotto, Cristopher Reyes, Ximena Valenzuela, Francisco Rodríguez-Mercado and Alejandra Torres

Polymers 2025, 17(20), 2755; https://doi.org/10.3390/polym17202755 - 15 Oct 2025

Abstract

Cellulose stands out as a promising alternative to conventional polymers in food packaging due to its abundance, renewability, biodegradability and structural robustness. Despite these advantages, its natural low resistance to water and fats limits its direct application, necessitating the use of protective coatings [...] Read more.

Cellulose stands out as a promising alternative to conventional polymers in food packaging due to its abundance, renewability, biodegradability and structural robustness. Despite these advantages, its natural low resistance to water and fats limits its direct application, necessitating the use of protective coatings to enhance its functionality. In this context, the use of biopolymeric coatings such as poly(lactic acid) (PLA), starch, lignin, chitin and chitosan has emerged as a sustainable solution, providing effective barriers against moisture and oils. These coatings not only improve the functional performance of cellulosic substrates but also reduce reliance on fossil-based plastics, fostering compostable systems and supporting a circular economy. This review analyzes recent developments in biopolymer-coated cellulosic packaging materials, focusing on their resistance to water and fats. The aim is to assess their potential for sustainable food packaging applications. The findings highlight how these innovations contribute to global sustainability goals, such as reducing plastic waste, lowering carbon emissions, and decreasing dependence on non-renewable resources. Full article

(This article belongs to the Special Issue Polymer-Based Coatings: Principles, Development and Applications)

21 pages, 3991 KB

Open AccessArticle

Development and Characterization of Biodegradable Films on Native and Esterified Peruvian Purple Yam (Dioscorea trifida) Starches and Tara Gum

by Paola Cornejo, Naomi Chalco, Sebastian Gutiérrez, Katherine Junco, Ronal Lopinta, Fiorela Peña-Carrasco, Carmen Velezmoro-Sánchez and Patricia Martínez-Tapia

Polymers 2025, 17(20), 2754; https://doi.org/10.3390/polym17202754 - 15 Oct 2025

Abstract

The aim was to evaluate if purple yam starch esterification with octenyl succinic anhydride (PYS-OSA) enhances the properties of purple yam starch (PYS)-based films in a blend with tara gum (TG). PYS was isolated from purple yam tubers (PYTs) with distilled water; then, [...] Read more.

The aim was to evaluate if purple yam starch esterification with octenyl succinic anhydride (PYS-OSA) enhances the properties of purple yam starch (PYS)-based films in a blend with tara gum (TG). PYS was isolated from purple yam tubers (PYTs) with distilled water; then, starch was dual-modified by ultrasound (as a pretreatment) and esterification (PYS-OSA). The films PYS:TG and PYS-OSA:TG were characterized through physicochemical and mechanical characterization. The thermal properties (T_o, T_c, T_p, and ΔH) of PYS-OSA decreased in the range of 3.4–7.6% compared to PYS. Fourier transform infrared spectroscopy (FTIR) confirmed esterification, revealing two new absorption bands at 1563.0 and 1726.5 cm⁻¹, and the degree of substitution (DS) was 0.023. The moisture content and solubility in water were 50.7 and 40.5% greater, respectively, for PYS-OSA:TG films compared to PYS:TG ones, but both films exhibited similar optical properties. The tensile strengths of PYS-OSA:TG films were higher than those of PYS:TG ones; however, the elongation at break was lower. PYS:TG and PYS-OSA:TG films were disintegrated by more than 70% after 13 days of being buried in soil. This work contributes to a better understanding of the starch isolated from purple yam tuber, with potential relevance for sustainable packaging applications. Full article

(This article belongs to the Special Issue Biodegradable Polymers: Innovations in Processing, Diverse Applications, and Sustainable Solutions)

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16 pages, 4007 KB

Open AccessArticle

Investigation of Mechanical, Thermal and Microstructural Properties of Waste Micro-Nano Nichrome (NiCr 80/20) Powder-Reinforced Composites with Polyamide 66 (PA66) Matrix

by Mehmet Ceviz

Polymers 2025, 17(20), 2753; https://doi.org/10.3390/polym17202753 - 15 Oct 2025

Abstract

This study investigates the mechanical, thermal, electrical, and microstructural properties of polyamide 66 (PA66) composites reinforced with waste-derived micro–nano NiCr (80/20) powders. Composites containing 2, 5, and 8 wt% NiCr were prepared using thermokinetic mixing and compression molding, followed by characterization via tensile [...] Read more.

This study investigates the mechanical, thermal, electrical, and microstructural properties of polyamide 66 (PA66) composites reinforced with waste-derived micro–nano NiCr (80/20) powders. Composites containing 2, 5, and 8 wt% NiCr were prepared using thermokinetic mixing and compression molding, followed by characterization via tensile testing, Shore D hardness, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), and thermal/electrical conductivity measurements. Results showed a progressive increase in tensile modulus, tensile strength, hardness, and thermal conductivity with increasing NiCr content, reaching maximum values at 8 wt% filler. However, elongation at break decreased, indicating reduced ductility due to restricted polymer chain mobility. DSC and FTIR analyses revealed that low NiCr loadings promoted nucleation and crystallinity, while higher contents disrupted crystalline domains. Electrical conductivity exhibited a slight upward trend, remaining sub-percolative up to 8 wt% NiCr; conductivity modulation is modest at high filler loadings. SEM–EDS confirmed uniform dispersion at low–moderate contents and agglomeration at higher levels. The use of industrial waste NiCr powder not only enhanced material performance but also contributed to sustainable materials engineering by valorizing by-products from the coatings industry. These findings suggest that NiCr/PA66 composites have potential applications in automotive, electronics, and thermal management systems requiring improved mechanical rigidity and heat dissipation. Full article

(This article belongs to the Special Issue Smart Polymers and Composites in Multifunctional Systems)

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21 pages, 1778 KB

Open AccessArticle

Immune Protective Effect of Chitosan Oligosaccharide on Lipopolysaccharide-Stimulated Coelomocytes of Sea Cucumber Apostichopus japonicus In Vitro

by Rongyue Wang, Xiaoyu Nie, Xiaofan Li, Jinwei Tang, Chong Huang and Juan Liu

Polymers 2025, 17(20), 2752; https://doi.org/10.3390/polym17202752 - 14 Oct 2025

Abstract

In recent years, chitosan oligosaccharide (COS) has demonstrated promising applications in enhancing the immune protective function of sea cucumbers. However, the immune-protective effect of COS on sea cucumber coelomocytes in vitro remains unclear. This study investigated the effect of COS on lipopolysaccharide (LPS)-stimulated [...] Read more.

In recent years, chitosan oligosaccharide (COS) has demonstrated promising applications in enhancing the immune protective function of sea cucumbers. However, the immune-protective effect of COS on sea cucumber coelomocytes in vitro remains unclear. This study investigated the effect of COS on lipopolysaccharide (LPS)-stimulated inflammation in sea cucumber coelomocytes. First, we measured the effects of COS and LPS on the viability of coelomocytes. COS exhibited no toxic effects on sea cucumber coelomocytes. Furthermore, pre-incubating the coelomocytes with COS significantly improved coelomocytes’ viability after LPS stimulation (p < 0.05). Secondly, the phagocytic activity and respiratory burst of the coelomocytes were assessed to evaluate their immune levels. COS alone significantly increased the respiratory burst and phagocytic activity of the coelomocytes (p < 0.05). However, with LPS stimulated, COS significantly increased both the respiratory burst and phagocytic activity of the coelomocytes. The activities of lysozyme (Lyz), total nitric oxide synthase (T-NOSs), and superoxide dismutase (SOD) in sea cucumber coelomocytes were measured to evaluate their response to LPS stimulation. The results indicated that LPS stimulation significantly increases the activities of Lyz, T-NOSs, and SOD in sea cucumber coelomocytes (p < 0.05). Additionally, it was found that COS could inhibit the LPS-mediated expression of Lyz, T-NOSs, and SOD activities in the coelomocytes (p < 0.05). Furthermore, the relative expression of six immune-related genes—Aj-IL-17, Aj-TNF-α, Aj-i-Lys, Aj-NOS, Aj-Rel, Aj-P105—were analyzed in the coelomocytes stimulated by LPS after being cultured with COS. Finally, through transcriptomic technology analysis, it was determined that COS primarily alleviates LPS-induced inflammation via the tumor necrosis factor signaling pathway and the phagosome signaling pathway. The findings demonstrated that COS inhibited the expression of immune genes in sea cucumber coelomocytes in a dose-dependent manner. In summary, pretreatment with chitosan oligosaccharides appears to confer an immune protective role in LPS-stimulated sea cucumber coelomocytes. Full article

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

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