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Polymers, Volume 15, Issue 24 (December-2 2023) – 118 articles

Cover Story (view full-size image): New fully biobased thermoset networks were developed by combining a vegetable oil-based epoxy monomer (ELO) with chitosan, derivative from the seafood industry, and natural oxalic or citric acids. By varying the nature of the hardener and the amount of chitosan, as a curing accelerator, the properties of the designed bioresins can be adapted from medical, automotive, or wood protection coatings. View this paper
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14 pages, 5844 KiB  
Article
Manufacture and Combustion Characteristics of Cellulose Flame-Retardant Plate through the Hot-Press Method
Polymers 2023, 15(24), 4736; https://doi.org/10.3390/polym15244736 - 18 Dec 2023
Viewed by 581
Abstract
This study focuses on the increased risk of high heat release and asphyxiation (toxic gas poisoning) in the event of a fire involving polyurethane (PU)- and MDF-based building materials, which are commonly used in buildings. Among them, polyurethane (PU) building materials are very [...] Read more.
This study focuses on the increased risk of high heat release and asphyxiation (toxic gas poisoning) in the event of a fire involving polyurethane (PU)- and MDF-based building materials, which are commonly used in buildings. Among them, polyurethane (PU) building materials are very commonly used in buildings, except in Europe and some other countries, due to their excellent thermal insulation performance. Still, problems of short-term heat release and the spread of toxic gases in the event of a fire continue to occur. To overcome these problems, researchers are actively working on introducing various flame retardants into building materials. Therefore, in this study, we produced a laboratory-sized (500 mm × 500 mm) plate-like flame-retardant board that can be utilized as a building material with a lower heat release rate and a lower toxicity index. The material was made by mixing expanded graphite and ceramic binder as flame retardants in a material that is formulated based on the cellulose of waste paper, replacing the existing building materials with a hot-press method. According to the ISO-5660-1 test on the heat release rate of the plate-like flame-retardant board, the Total Heat Release (THR) value was 2.9 (MJ/m2) for 10 min, showing an effect of reducing the THR value by 36.3 (MJ/m2) compared to the THR value of 39.2 (MJ/m2) of the specimen made using only paper. In addition, the toxicity index of the flame-retardant board was checked through the NES (Naval Engineering Standards)-713 test. As a result, the test specimen showed a toxicity index of 0.7, which is 2.4 lower than the toxicity index of 3.1 of MDF, which is utilized as a conventional building material. Based on the results of this study, the cellulose fire-retardant board showed the effect of reducing the heat release rate and toxicity index of building materials in a building fire, which reduces the risk of rapid heat spread and smoke toxicity. This has the potential to improve the evacuation time (A-SET) of evacuees in fires. It is also important to show that recycling waste paper and utilizing it as the main material for building materials can be an alternative in terms of sustainable development. Full article
(This article belongs to the Special Issue Latest Research and Applications of Cellulose and Nanocellulose)
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13 pages, 2444 KiB  
Article
Mechanistic Insights into Anion-Induced Electrochromism of Ru(II)-Based Metallo-Supramolecular Polymer
Polymers 2023, 15(24), 4735; https://doi.org/10.3390/polym15244735 - 18 Dec 2023
Viewed by 626
Abstract
The metallo-supramolecular polymer (MSP) is considered one of the most promising electrodes for electrochromic devices due to its intrinsically stable redox properties. Nevertheless, despite extensive work focusing on improving the electrochromic and electrochemical properties of MSPs, little experimental evidence exists from in-depth investigations [...] Read more.
The metallo-supramolecular polymer (MSP) is considered one of the most promising electrodes for electrochromic devices due to its intrinsically stable redox properties. Nevertheless, despite extensive work focusing on improving the electrochromic and electrochemical properties of MSPs, little experimental evidence exists from in-depth investigations on the anion-induced electrochromism of MSPs. Herein, Ru-based metallo-supramolecular polymer (polyRu) films with excellent electrochromic performance were fabricated through a novel electrochemical deposition method, and the electrochromic mechanism was further understood. The polyRu films possess fast reaction kinetics with a short switching time of 4.0 s (colored) and 2.8 s (bleached) and highly reversible redox properties due to the resulting impacts on the capacitive behaviors (containing surface, near-surface and intercalation pseudo-capacitance) of the perchlorate ions in the electrochromic process. Moreover, the electrochromic degradation of the polyRu films is considered to stem from the numerous nanopores in the film induced by ClO4 transport and the exchange of counter anions from Cl to ClO4. In addition, a physical model, revealing the transport of conduction ions and the evolution of the structure and properties of the polyRu film during the electrochromic process, is presented. It is observed that the charge balance of Ru3+ and Ru2+, achieved through the adsorption/desorption of ClO4 on the film, provides electrochromic and electrochemical reversibility to the polyRu film under positive/negative bias. Correspondingly, a transformation from polyRu·(Cl)2n to polyRu·(ClO4)x(Cl)2n−x in the polyRu film is induced by a counter anion exchange from Cl to ClO4. Revealing the detailed perchlorate ion transfer kinetics and electrochromic mechanism in this film can offer new insights into the application of metallo-supramolecular polymers in electrochromic devices. Full article
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17 pages, 1012 KiB  
Article
Evaluation of Chemical and Morphological Properties of Spruce Wood Stored in the Natural Environment
Polymers 2023, 15(24), 4734; https://doi.org/10.3390/polym15244734 - 18 Dec 2023
Viewed by 582
Abstract
This paper focuses on the changes in chemical structure and fiber morphological properties of spruce wood during 15 months of its storage in an open forest woodshed. From the chemical composition, the extractives, cellulose, holocellulose, and lignin content were determined. The pH value [...] Read more.
This paper focuses on the changes in chemical structure and fiber morphological properties of spruce wood during 15 months of its storage in an open forest woodshed. From the chemical composition, the extractives, cellulose, holocellulose, and lignin content were determined. The pH value was measured on the wood surface using a contact electrode. Acetic and formic acid, saccharides (glucose, xylose, galactose, arabinose and mannose), and polymerization degree (PD) of cellulose were analyzed using the HPLC method. Fiber length and width were determined using a fiber tester analyzer. After 15 months of storage the content of both cellulose (determined by the Seifert method) and lignin did not change; the quantity of hemicelluloses decreased by 13.2%, due to its easier degradation and less stability compared to cellulose; and the pH value dropped by one degree. HPLC analyses showed a total decrease in the cellulose DP of 9.2% and in saccharides of 40.2%, while the largest decreases were recorded in the quantity of arabinose, by 72%, in the quantity of galactose, by 61%, and in the quantity of xylose, by 43%. Organic acids were not detected due to their high volatility during wood storage. The total decrease in average fiber length was 38.2% and in width was 4.8%. An increase in the proportion of shorter fibers, and a decrease in the proportion of longer fibers, was recorded. It can be concluded that fundamental changes occurred in the wood, which could affect the quality of further products (e.g., chips, pulp, paper, particleboards). Full article
(This article belongs to the Special Issue Biodegradable and Natural Polymers II)
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36 pages, 2112 KiB  
Review
Use of Bio-Epoxies and Their Effect on the Performance of Polymer Composites: A Critical Review
Polymers 2023, 15(24), 4733; https://doi.org/10.3390/polym15244733 - 18 Dec 2023
Cited by 1 | Viewed by 993
Abstract
This study comprehensively examines recent developments in bio-epoxy resins and their applications in composites. Despite the reliability of traditional epoxy systems, the increasing demand for sustainability has driven researchers and industries to explore new bio-based alternatives. Additionally, natural fibers have the potential to [...] Read more.
This study comprehensively examines recent developments in bio-epoxy resins and their applications in composites. Despite the reliability of traditional epoxy systems, the increasing demand for sustainability has driven researchers and industries to explore new bio-based alternatives. Additionally, natural fibers have the potential to serve as environmentally friendly substitutes for synthetic ones, contributing to the production of lightweight and biodegradable composites. Enhancing the mechanical properties of these bio-composites also involves improving the compatibility between the matrix and fibers. The use of bio-epoxy resins facilitates better adhesion of natural composite constituents, addressing sustainability and environmental concerns. The principles and methods proposed for both available commercial and especially non-commercial bio-epoxy solutions are investigated, with a focus on promising renewable sources like wood, food waste, and vegetable oils. Bio-epoxy systems with a minimum bio-content of 20% are analyzed from a thermomechanical perspective. This review also discusses the effect of incorporating synthetic and natural fibers into bio-epoxy resins both on their own and in hybrid form. A comparative analysis is conducted against traditional epoxy-based references, with the aim of emphasizing viable alternatives. The focus is on addressing their benefits and challenges in applications fields such as aviation and the automotive industry. Full article
(This article belongs to the Collection Progress in Polymer Composites and Nanocomposites)
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14 pages, 5169 KiB  
Article
Evaluation of the Mechanical and Tribological Behavior of Polyether Ether Ketone Fiber-Reinforced Resin-Based Friction Materials Fabricated by Wet Granulation
Polymers 2023, 15(24), 4732; https://doi.org/10.3390/polym15244732 - 18 Dec 2023
Viewed by 590
Abstract
Resin-based friction materials (RBFMs) strengthened by polyether ether ketone (PEEK) fiber were designed and prepared in this study. Specimens incorporating PEEK fiber of 2–8 wt.% were fabricated based on wet granulation, and then the effects of the PEEK fiber content on the mechanical [...] Read more.
Resin-based friction materials (RBFMs) strengthened by polyether ether ketone (PEEK) fiber were designed and prepared in this study. Specimens incorporating PEEK fiber of 2–8 wt.% were fabricated based on wet granulation, and then the effects of the PEEK fiber content on the mechanical and tribological properties of RBFMs were systematically investigated. The results showed that PEEK fiber can sense the braking temperature and then effectively regulate the comprehensive properties of RBFMs. The specimen incorporating 6 wt.% PEEK fiber obtained the optimal comprehensive performance with a stable friction coefficient (COF), excellent fade resistance and recovery properties, and better wear resistance. The worn surface was inspected using a scanning electron microscope. After the friction–wear test, the specimen with 6 wt.% PEEK fiber presented a number of primary and secondary plateaus and a reduced number of pits with wear debris on the worn surface. The study indicated that PEEK fiber could not only enhance the mechanical and tribological properties of RBFMs at low temperatures because of their high strength and self-lubrication but also adhere to wear debris to reduce abrasive wear at high temperatures; furthermore, the adhered wear debris could form a secondary plateau under normal pressure, which could alleviate abrasion. Full article
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16 pages, 4243 KiB  
Article
Synthesis and Properties of Modified Biodegradable Polymers Based on Caprolactone
Polymers 2023, 15(24), 4731; https://doi.org/10.3390/polym15244731 - 17 Dec 2023
Viewed by 748
Abstract
In this paper, the synthesis and characterization of two polycaprolactone-polydimethylsiloxane (PDMS-CL) copolymers with biodegradable properties are reported. A comparative study was carried out using an aminopropyl-terminated polydimethylsiloxane macro-initiator (APDMS) with two different molecular weights. The copolymers (PDMS-CL-1 and PDMS-CL-2) were obtained by ring-opening [...] Read more.
In this paper, the synthesis and characterization of two polycaprolactone-polydimethylsiloxane (PDMS-CL) copolymers with biodegradable properties are reported. A comparative study was carried out using an aminopropyl-terminated polydimethylsiloxane macro-initiator (APDMS) with two different molecular weights. The copolymers (PDMS-CL-1 and PDMS-CL-2) were obtained by ring-opening polymerization of ɛ-caprolactone using APDMS as initiators and stannous 2-ethylhexanoate as a catalyst. The copolymer’s structures were confirmed by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (1H-NMR) spectra, and energy dispersion spectroscopy (EDX). Surface morphology was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The hydrophobic properties of the copolymers were demonstrated by the water contact angle and water vapor sorption capacity. Additionally, biological tests were conducted on San Marzano type tomato plants (Lypercosium esculentum) to assess the synthesized copolymers’ susceptibility to the environment in terms of biological stability and metabolic activity. The biodegradation of PDMS-CL-1 and PDMS-CL-2 copolymers does not have a dangerous effect on the metabolic activity of plants, which makes it a convenient product in interaction with the environment. Full article
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14 pages, 3400 KiB  
Article
Exploitation of a New Nucleating Agent by Molecular Structure Modification of Aryl Phosphate and Its Effect on Application Properties of the Polypropylene
Polymers 2023, 15(24), 4730; https://doi.org/10.3390/polym15244730 - 17 Dec 2023
Viewed by 930
Abstract
In this work, a novel α-nucleating agent (NA) for polypropylene (PP) termed APAl-3C-12Li was prepared and evaluated compared with the commercially available type NA-21. For the synthesis of the organophosphate-type NA (APAl-3C), the -OH group of the acid part of NA-21 was substituted [...] Read more.
In this work, a novel α-nucleating agent (NA) for polypropylene (PP) termed APAl-3C-12Li was prepared and evaluated compared with the commercially available type NA-21. For the synthesis of the organophosphate-type NA (APAl-3C), the -OH group of the acid part of NA-21 was substituted by the isopropoxy group. The structure of APAl-3C was analyzed by spectroscopy and element analysis, the results of which were consistent with the theoretical molecular formula. APAl-3C’s thermal stability was studied by differential scanning calorimetry (DSC) and thermogravimetry (TG), which showed only weak mass loss below 230 °C, meaning that it would not decompose during the processing of PP. The APAl-3C-12Li was used as a novel nucleating agent, studying its effects on crystallization, microstructure, mechanical and optical properties. Tests were performed in a PP random copolymer at different contents, in comparison to the commercial NA-21. The composite with 0.5 wt% APAl-3C-12Li has a similar crystallization temperature of 118.8 °C as with the addition of 0.5 wt% NA-21. An advantage is that the composite with the APAl-3C-12Li has a lower haze value of 9.3% than the counterpart with NA-21. This is due to the weaker polarity of APAl-3C-12Li after the introduction of methyl and better uniform dispersion in the PP matrix, resulting in stronger improvement of optical and mechanical properties. Full article
(This article belongs to the Special Issue Recent Development of Polymer Additives)
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15 pages, 5037 KiB  
Article
Parallel Catalyst Synthesis Protocol for Accelerating Heterogeneous Olefin Polymerization Research
Polymers 2023, 15(24), 4729; https://doi.org/10.3390/polym15244729 - 17 Dec 2023
Viewed by 571
Abstract
The data scientific approach has become an indispensable tool for capturing structure–performance relationships in complex systems, where the quantity and quality of data play a crucial role. In heterogeneous olefin polymerization research, the exhaustive and multi-step nature of Ziegler-Natta catalyst synthesis has long [...] Read more.
The data scientific approach has become an indispensable tool for capturing structure–performance relationships in complex systems, where the quantity and quality of data play a crucial role. In heterogeneous olefin polymerization research, the exhaustive and multi-step nature of Ziegler-Natta catalyst synthesis has long posed a bottleneck in synthetic throughput and data generation. In this contribution, a custom-designed 12-parallel reactor system and a catalyst synthesis protocol were developed to achieve the parallel synthesis of a magnesium ethoxide-based Ziegler-Natta catalyst. The established system, featuring a miniature reaction vessel with magnetically suspended stirring, allows for over a tenfold reduction in synthetic scale while ensuring the consistency and reliability of the synthesis. We demonstrate that the established protocol is highly efficient for the generation of a catalyst library with diverse compositions and physical features, holding promise as a foundation for the data-driven establishment of the structure–performance relationship in heterogeneous olefin polymerization catalysis. Full article
(This article belongs to the Special Issue Catalytic Olefin Polymerization and Polyolefin Materials)
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16 pages, 10468 KiB  
Article
Manufacturing Process, Tensile-Compressive, and Impact Properties of Tungsten (W)-Particle-Reinforced SLA Methacrylate
Polymers 2023, 15(24), 4728; https://doi.org/10.3390/polym15244728 - 17 Dec 2023
Viewed by 641
Abstract
The interest in research and development for additive manufacturing (AM) processes has grown significantly over the last years and attracts both industry and academia alike. Among the available AM technologies, stereolithography (SLA) is one of the most discussed, researched, and employed. On the [...] Read more.
The interest in research and development for additive manufacturing (AM) processes has grown significantly over the last years and attracts both industry and academia alike. Among the available AM technologies, stereolithography (SLA) is one of the most discussed, researched, and employed. On the other hand, being based on thermoset resins, all the limitations of this typology of materials still apply, limiting the range of applications of this highly versatile process. To overcome these limitations, especially brittleness, this research analyzes the effects of Tungsten (W) micro-size (average size 1 μm) particles reinforcement on a methacrylate base material. First, the manufacturing process for creating the W-reinforced methacrylate material is presented and investigated to define the effect of pre- and post-processing operations on the quality of the pre-cured solution considering 4% and 10% wt. W particles concentrations. Afterward, tensile, compressive, and impact specimens were manufactured with both concentrations and compared with the experimental results from clear (unfilled) resin-based specimens used as the benchmark. The addition of tungsten particles showed a strong improvement in the impact strength of the methacrylate base material, quantified in 28% for the 4% and 55% for the 10% wt., respectively, although at the expense of a slight reduction in elastic and yield properties on average −12%. Furthermore, using Scanning Electron Microscope (SEM) analyses, the particle–matrix interaction was investigated, showing the interaction between the polymer matrix and the reinforcement and the mechanism by which the impact resistance is enhanced. Full article
(This article belongs to the Special Issue Advances in Polymeric Additive Manufacturing)
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15 pages, 7742 KiB  
Article
Simulation of a Composite with a Polyhydroxybutyrate (PHB) Matrix Reinforced with Cylindrical Inclusions: Prediction of Mechanical Properties
Polymers 2023, 15(24), 4727; https://doi.org/10.3390/polym15244727 - 17 Dec 2023
Viewed by 1129
Abstract
Biocomposite development, as a sustainable alternative to fossil-derived materials with diverse industrial applications, requires expediting the design process and reducing production costs. Simulation methods offer a solution to these challenges. The main aspects to consider in simulating composite materials successfully include accurately representing [...] Read more.
Biocomposite development, as a sustainable alternative to fossil-derived materials with diverse industrial applications, requires expediting the design process and reducing production costs. Simulation methods offer a solution to these challenges. The main aspects to consider in simulating composite materials successfully include accurately representing microstructure geometry, carefully selecting mesh elements, establishing appropriate boundary conditions representing system forces, utilizing an efficient numerical method to accelerate simulations, and incorporating statistical tools like experimental designs and re-regression models. This study proposes a comprehensive methodology encompassing these aspects. We present the simulation using a numerical homogenization technique based on FEM to analyze the mechanical behavior of a composite material of a polyhydroxybutyrate (PHB) biodegradable matrix reinforced with cylindrical inclusions of flax and kenab. Here, the representative volume element (RVE) considered the geometry, and the numerical homogenization method (NHM) calculated the macro-mechanical behavior of composites. The results were validated using the asymptotic homogenization method (AHM) and experimental data, with error estimations of 0.0019% and 7%, respectively. This model is valuable for predicting longitudinal and transverse elastic moduli, shear modulus, and Poisson’s coefficient, emphasizing its significance in composite materials research. Full article
(This article belongs to the Special Issue Computational Modeling and Simulation of Polymer Composites)
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25 pages, 14466 KiB  
Article
Non-Covalent Functionalization of Graphene Oxide with POSS to Improve the Mechanical Properties of Epoxy Composites
Polymers 2023, 15(24), 4726; https://doi.org/10.3390/polym15244726 - 16 Dec 2023
Viewed by 702
Abstract
Phenyl polyhedral oligomeric silsesquioxane (POSS) is modified onto the GO surface by using the strong π–π coupling between a large number of benzene rings at the end of the phenyl POSS structure and the graphite structure in the GO sheet, realizing the non-covalent [...] Read more.
Phenyl polyhedral oligomeric silsesquioxane (POSS) is modified onto the GO surface by using the strong π–π coupling between a large number of benzene rings at the end of the phenyl POSS structure and the graphite structure in the GO sheet, realizing the non-covalent functionalization of GO (POSS-GO). The POSS-GO-reinforced EP (POSS-GO/EP) composite material is prepared using the casting molding process. The surface morphology of GO before and after modification and its peel dispersion in EP are examined. Furthermore, the mechanical properties, cross-sectional morphology, and reinforcement mechanism of POSS-GO/EP are thoroughly examined. The results show that the cage-like skeleton structure of POSS is embedded between the GO layers, increasing the spacing between the GO layers and leading to a steric hindrance effect, which effectively prevents their stacking and aggregation and improves the dispersion performance of GO. In particular, the 0.4 phr POSS-GO/EP sample shows the best mechanical properties. This is because, on the one hand, POSS-GO is uniformly dispersed in the EP matrix, which can more efficiently induce crack deflection and bifurcation and can also cause certain plastic deformations in the EP matrix. On the other hand, the POSS-GO/EP fracture cross-section with a stepped morphology of interlaced “canine teeth” shape is rougher and more uneven, leading to more complex crack propagation paths and greater energy consumption. Moreover, the mechanical meshing effect between the rough POSS-GO surface and the EP matrix is stronger, which is conducive to the transfer of interfacial stress and the strengthening and toughening effects of POSS-GO. Full article
(This article belongs to the Special Issue Molecular Simulation of Polymers)
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13 pages, 4741 KiB  
Article
Dielectric and Viscoelastic Behavior of Polyvinyl Butyral Films
Polymers 2023, 15(24), 4725; https://doi.org/10.3390/polym15244725 - 16 Dec 2023
Viewed by 586
Abstract
Dielectric and thermal properties of polyvinyl butyral (PVB) were studied in this work, using dynamic electrical analysis (DEA) at frequencies from 100 Hz to 1 MHz and temperatures from 293 K to 473 K. Two electrical relaxation processes were investigated: glass transition and [...] Read more.
Dielectric and thermal properties of polyvinyl butyral (PVB) were studied in this work, using dynamic electrical analysis (DEA) at frequencies from 100 Hz to 1 MHz and temperatures from 293 K to 473 K. Two electrical relaxation processes were investigated: glass transition and interfacial polarization. Above the glass transition temperature (~343 K), interfacial polarization dominates conductive behavior in polyvinyl butyral. The framework of the complex electric modulus was used to obtain information about interfacial polarization. The viscoelastic behavior was analyzed through dynamic mechanical analysis (DMA), where only the mechanical manifestation of the glass transition is observed. The experimental results from dielectric measurements were analyzed with fractional calculus, using a fractional Debye model with one cap-resistor. We were successful in applying the complex electric modulus because we had a good correlation between data and theoretical predictions. The fractional order derivative is an indicator of the energy dissipated in terms of molecular mobility, and the calculated values close to 1 suggest a conductive behavior at temperatures above the glass transition temperature of PVB. Full article
(This article belongs to the Special Issue State-of-the-Art Polymer Science and Technology in Mexico)
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14 pages, 4801 KiB  
Article
Prediction of Aging Performance of Particle-Filled Polymer Composites Based on RVE Model
Polymers 2023, 15(24), 4724; https://doi.org/10.3390/polym15244724 - 16 Dec 2023
Viewed by 558
Abstract
In this study, the aging performance of particle-filled polymer composites (PFPCs) under thermo-oxidative conditions was investigated on multiple scales. High-temperature-accelerated tests were conducted to analyze the effects of aging time and temperature. A representative volume element (RVE) model was established for the PFPCs [...] Read more.
In this study, the aging performance of particle-filled polymer composites (PFPCs) under thermo-oxidative conditions was investigated on multiple scales. High-temperature-accelerated tests were conducted to analyze the effects of aging time and temperature. A representative volume element (RVE) model was established for the PFPCs using a random particle-filling algorithm. A predictive model for the crosslink density was conducted based on the closed-loop chain reaction of polymer oxidation. According to the theory of polymer physics, the relation between the crosslink density and matrix modulus was determined. The particle/matrix interface in the RVE model was represented by the cohesive zone model (CZM). The parameters of the CZM were determined by the inversion techniques. Then, a comprehensive multiscale RVE model was constructed, which was applied to predict the modulus and dewetting strain of the aged PFPCs. The predicted results show good agreement with the test results, which verifies the reliability of our model. Full article
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11 pages, 2678 KiB  
Article
Form-Stable Composite Phase Change Materials Based on Porous Copper–Graphene Heterostructures for Solar Thermal Energy Conversion and Storage
Polymers 2023, 15(24), 4723; https://doi.org/10.3390/polym15244723 - 16 Dec 2023
Viewed by 660
Abstract
Solar–thermal energy conversion and storage technology has attracted great interest in the past few decades. Phase change materials (PCMs), by storing and releasing solar energy, are able to effectively address the imbalance between energy supply and demand, but they still have the disadvantage [...] Read more.
Solar–thermal energy conversion and storage technology has attracted great interest in the past few decades. Phase change materials (PCMs), by storing and releasing solar energy, are able to effectively address the imbalance between energy supply and demand, but they still have the disadvantage of low thermal conductivity and leakage problems. In this work, new form-stable solar thermal storage materials by impregnating paraffin PCMs within porous copper–graphene (G–Cu) heterostructures were designed, which integrated high thermal conductivity, high solar energy absorption, and anti-leakage properties. In this new structure, graphene can directly absorb and store solar energy in the paraffin PCMs by means of phase change heat transfer. The porous structure provided good heat conduction, and the large surface area increased the loading capacity of solar thermal storage materials. The small pores and superhydrophobic surfaces of the modified porous G–Cu heterostructures effectively hindered the leakage issues during the phase change process. The experimental results exhibited that the thermal conductivity of the prepared form-stable PCM composites was up to 2.99 W/(m·K), and no leakage took place in the solar–thermal charging process. At last, we demonstrated that the PCM composites as an energy source were easily integrated with a thermoelectric chip to generate electric energy by absorbing and converting solar energy. Full article
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16 pages, 3647 KiB  
Article
Depolymerization of Pine Wood Organosolv Lignin in Ethanol Medium over NiCu/SiO2 and NiCuMo/SiO2 Catalysts: Impact of Temperature and Catalyst Composition
Polymers 2023, 15(24), 4722; https://doi.org/10.3390/polym15244722 - 15 Dec 2023
Viewed by 659
Abstract
The process of thermocatalytic conversion of pine ethanol lignin in supercritical ethanol was studied over NiCu/SiO2 and NiCuMo/SiO2 catalysts bearing 8.8 and 11.7 wt.% of Mo. The structure and composition of ethanol lignin and the products of its thermocatalytic conversion were [...] Read more.
The process of thermocatalytic conversion of pine ethanol lignin in supercritical ethanol was studied over NiCu/SiO2 and NiCuMo/SiO2 catalysts bearing 8.8 and 11.7 wt.% of Mo. The structure and composition of ethanol lignin and the products of its thermocatalytic conversion were characterized via 2D-HSQC NMR spectroscopy, GC-MC. The main aromatic monomers among the liquid products of ethanol lignin conversion were alkyl derivatives of guaiacol (propyl guaiacol, ethyl guaiacol and methyl guaiacol). The total of the monomers yield in this case was 12.1 wt.%. The temperature elevation up to 350 °C led to a slight decrease in the yield (to 11.8 wt.%) and a change in the composition of monomeric compounds. Alkyl derivatives of pyrocatechol, phenol and benzene were observed to form due to deoxygenation processes. The ratio of the yields of these compounds depended on the catalyst, namely, on the content of Mo in the catalyst composition. Thus, the distribution of monomeric compounds used in various industries can be controlled by varying the catalyst composition and the process conditions. Full article
(This article belongs to the Special Issue Natural Polymer Materials: Cellulose, Lignin and Chitosan)
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13 pages, 2942 KiB  
Article
Effect of Bletilla Striata Polysaccharide on the Pasting, Rheological and Adhesive Properties of Wheat Starch
Polymers 2023, 15(24), 4721; https://doi.org/10.3390/polym15244721 - 15 Dec 2023
Viewed by 555
Abstract
A combination of starch and hydrocolloids is a facile method for physically modifying native starch. Bletilla striata polysaccharide (BSP) is a glucomannan with various applications in the food and cosmetic industries as a thickening agent. This study focused on investigating the impact of [...] Read more.
A combination of starch and hydrocolloids is a facile method for physically modifying native starch. Bletilla striata polysaccharide (BSP) is a glucomannan with various applications in the food and cosmetic industries as a thickening agent. This study focused on investigating the impact of BSP on the pasting, rheological and adhesive properties of wheat starch (WS). Results from a Rapid Visco-Analyzer (RVA) revealed that the addition of BSP (below 0.2%) resulted in increases in peak viscosity, breakdown and setback values. However, for the addition of BSP at a higher concentration (0.3%), the opposite trend was observed. Rheological measurements indicated that the presence of BSP increased the viscoelastic properties of WS–BSP gels. TGA results demonstrated that the presence of BSP promoted the thermal stability of starch. FTIR results indicated the short-range order structure decreased at low addition concentrations of BSP (0.05% and 0.1%) and increased with higher BSP addition concentrations (0.2% and 0.3%). SEM observation showed that the BSP improved the hydrophilic property of starch gels and decreased the size of pores in the starch gels. Further, the mechanical properties of paper samples unveiled that the present of BSP in starch gels obviously increased its bonding strength as an adhesive. Full article
(This article belongs to the Section Biomacromolecules, Biobased and Biodegradable Polymers)
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11 pages, 3884 KiB  
Article
Generation of PVP Membranes Using Extracts/Phenolic Fraction of Dysphania ambrosioides, Opuntia ficus-indica, and Tradescantia pallida
Polymers 2023, 15(24), 4720; https://doi.org/10.3390/polym15244720 - 15 Dec 2023
Viewed by 577
Abstract
In the present work, electrospun membranes of polyvinylpyrrolidone (PVP) nanofibers were manufactured using extracts and phenolic fractions of Dysphania ambrosioides (epazote), Opuntia ficus-indica (nopal), and Tradescantia pallida (chicken grass). The characterization of the membranes was carried out by scanning electron microscopy and Fourier [...] Read more.
In the present work, electrospun membranes of polyvinylpyrrolidone (PVP) nanofibers were manufactured using extracts and phenolic fractions of Dysphania ambrosioides (epazote), Opuntia ficus-indica (nopal), and Tradescantia pallida (chicken grass). The characterization of the membranes was carried out by scanning electron microscopy and Fourier transform infrared spectroscopy. The membranes synthesized through the use of the extracts generally showed a slight decrease in the diameter of the fibers but an increase in the size of the pores due to the presence of nanoparticles (rosaries) on the surface of the fibers, while the membranes synthesized using the phenolic fraction demonstrated an inversely proportional relationship between the compounds of this family with the diameter of the fibers and the size of the pore, allowing to elucidate part of the polymerization mechanisms of PVP nanofibers, in addition to proposing a reaction mechanism in the interaction between PVP and phenolic compounds for surface functionalization. Likewise, we demonstrate that the generation of reaction seeds through functionalization allows the addition of other compounds to the fibers in the membranes synthesized using the complete extract. Full article
(This article belongs to the Special Issue High Performance Polymer Membranes II)
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11 pages, 6623 KiB  
Article
The 3D Printing of Novel Honeycomb–Hollow Pyramid Sandwich Structures for Microwave and Mechanical Energy Absorption
Polymers 2023, 15(24), 4719; https://doi.org/10.3390/polym15244719 - 15 Dec 2023
Viewed by 618
Abstract
Honeycomb sandwich (HS) structures are important lightweight and load-bearing materials used in the aerospace industry. In this study, novel honeycomb–hollow pyramid sandwich (HPS) structures were manufactured with the help of fused deposition modeling techniques using PLA and PLA/CNT filaments. The microwave and mechanical [...] Read more.
Honeycomb sandwich (HS) structures are important lightweight and load-bearing materials used in the aerospace industry. In this study, novel honeycomb–hollow pyramid sandwich (HPS) structures were manufactured with the help of fused deposition modeling techniques using PLA and PLA/CNT filaments. The microwave and mechanical energy absorption properties of the HPS structures with different geometry parameters were studied. Compared with the HS structure, the HPS structure enhanced both microwave absorption and mechanical properties. The HPS structures possessed both broadband and wide-angle microwave absorption characteristics. Their reflection loss at 8–18 GHz for incident angles of up to 45° was less than −10 dB. As the thickness of the hollow pyramid increased from 1.00 mm to 5.00 mm, the compressive strength of the HPS structure increased from 4.8 MPa to 12.5 MPa, while mechanical energy absorption per volume increased from 2639 KJ/m3 to 5598 KJ/m3. The microwave absorption and compressive behaviors of the HPS structures were studied. Full article
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27 pages, 4607 KiB  
Article
Influence of Compounding Parameters on Color Space and Properties of Thermoplastics with Ultramarine Blue Pigment
Polymers 2023, 15(24), 4718; https://doi.org/10.3390/polym15244718 - 15 Dec 2023
Viewed by 688
Abstract
The incorporation of thermoplastics with pigments imparts diverse aesthetic qualities and properties to colored thermoplastic products. The selection of pigment type and content, along with specific processing conditions, plays a pivotal role in influencing color properties and overall product performance. This study focuses [...] Read more.
The incorporation of thermoplastics with pigments imparts diverse aesthetic qualities and properties to colored thermoplastic products. The selection of pigment type and content, along with specific processing conditions, plays a pivotal role in influencing color properties and overall product performance. This study focuses on optimizing these parameters to ensure the desired color quality and product functionality. Two types of polypropylene copolymer (PPCP) with different melt flow rates (MFRs) and acrylonitrile butadiene styrene (ABS) were compounded with ultramarine blue pigment masterbatch (MB) in concentrations ranging from 1 to 5 wt.% using a twin-screw extruder. The compounding process was conducted at a constant screw speed of 200 rpm and a die temperature of 210 °C. The effects of screw speed and die temperature were investigated at a constant MB of 3 wt.%. Colored samples were fabricated by injection molding. Microscopic analysis revealed a well-dispersed pigment within the PPCP matrix when using the MB. Rheological properties, assessed through the power law index, confirmed effective pigment dispersion, facilitated by shear thinning behavior and controlled shear rate via the manipulation of screw speed and die temperature. The effects of masterbatch contents and processing conditions on color spaces were evaluated using CIELAB and CIELCH, with one-way ANOVA employed to identify statistical significance. Higher opacity in high-MFR PPCP and ABS resulted in increased lightness and color strength, surpassing low-MFR PPCP by 15–40% at equivalent MB contents. Masterbatch content emerged as a significant factor influencing the color spaces of all colored thermoplastics. Further analysis, including Fisher pairwise comparisons of one-way ANOVA, revealed that screw speed influenced the redness and hue of low-MFR PPCP, whereas die temperature affected the lightness and hue of high-MFR PPCP and ABS. Interestingly, the blueness and chroma of colored thermoplastics were minimally affected by both screw speed and die temperature. Notably, regardless of processing conditions, the flexural properties of colored thermoplastics remained comparable to the neat polymer when incorporated with ultramarine blue pigment masterbatch. Full article
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20 pages, 9703 KiB  
Article
High-Density Polyethylene/Carbon Black Composites in Material Extrusion Additive Manufacturing: Conductivity, Thermal, Rheological, and Mechanical Responses
Polymers 2023, 15(24), 4717; https://doi.org/10.3390/polym15244717 - 15 Dec 2023
Viewed by 1255
Abstract
High-density polyethylene polymer (HDPE) and carbon black (CB) were utilized to create HDPE/CB composites with different filler concentrations (0.0, 2.0, 4.0, 6.0, 8.0, 10.0, 16.0, 20.0, and 24.0 wt.%). The composites were extruded into filaments, which were then utilized to fabricate 3D-printed specimens [...] Read more.
High-density polyethylene polymer (HDPE) and carbon black (CB) were utilized to create HDPE/CB composites with different filler concentrations (0.0, 2.0, 4.0, 6.0, 8.0, 10.0, 16.0, 20.0, and 24.0 wt.%). The composites were extruded into filaments, which were then utilized to fabricate 3D-printed specimens with the material extrusion (MEX) method, suitable for a variety of standard mechanical tests. The electrical conductivity was investigated. Furthermore, thermogravimetric analysis and differential scanning calorimetry were carried out for all the HDPE/CB composites and pure HDPE. Scanning electron microscopy in different magnifications was performed on the specimens’ fracture and side surfaces to investigate the morphological characteristics. Rheological tests and Raman spectroscopy were also performed. Eleven different tests in total were performed to fully characterize the composites and reveal connections between their various properties. HDPE/CB 20.0 wt.% showed the greatest reinforcement results in relation to pure HDPE. Such composites are novel in the MEX 3D printing method. The addition of the CB filler greatly enhanced the performance of the popular HDPE polymer, expanding its applications. Full article
(This article belongs to the Special Issue Polymeric Materials in 3D Printing)
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13 pages, 6427 KiB  
Article
Anionic Anchoring Enhanced Quasi Solid Composite Polymer Electrolytes for High Performance Lithium Metal Battery
Polymers 2023, 15(24), 4716; https://doi.org/10.3390/polym15244716 - 15 Dec 2023
Cited by 1 | Viewed by 662
Abstract
Herein, ZIF-8 inorganic particles with different sized reinforced poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) solid composite polymer electrolytes (PVDF-HFP/10%ZIF-8) were prepared via a facile blade-coating approach, and free-standing quasi solid-state composite electrolytes (PVDF-HFP/10%ZIF-8(0.6)/Plasticizer, abbreviated as PH/10%ZIF-8(0.6)/P), were further obtained through the introduction of plasticizer. Optimized [...] Read more.
Herein, ZIF-8 inorganic particles with different sized reinforced poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) solid composite polymer electrolytes (PVDF-HFP/10%ZIF-8) were prepared via a facile blade-coating approach, and free-standing quasi solid-state composite electrolytes (PVDF-HFP/10%ZIF-8(0.6)/Plasticizer, abbreviated as PH/10%ZIF-8(0.6)/P), were further obtained through the introduction of plasticizer. Optimized PH/10%ZIF-8(0.6)/P exhibited a high ionic conductivity of 2.8 × 10−4 S cm−1 at 30 °C, and superior Li+ transfer number of 0.89 with an ultrathin thickness (26 µm). Therefore, PH/10%ZIF-8(0.6)/P could effectively inhibit the growth of lithium dendrites, and the assembled Li/LiFePO4 cell delivered good cycling stability with a capacity retention rate of 89.1% after 100 cycles at 0.5 C. Full article
(This article belongs to the Special Issue Polymer Electrolyte: Recent Progress and Applications)
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22 pages, 8253 KiB  
Article
Development of an Electroactive and Thermo-Reversible Diels–Alder Epoxy Nanocomposite Doped with Carbon Nanotubes
Polymers 2023, 15(24), 4715; https://doi.org/10.3390/polym15244715 - 15 Dec 2023
Cited by 1 | Viewed by 686
Abstract
The manufacturing of Diels–Alder (D-A) crosslinked epoxy nanocomposites is an emerging field with several challenges to overcome: the synthesis is complex due to side reactions, the mechanical properties are hindered by the brittleness of these bonds, and the content of carbon nanotubes (CNT) [...] Read more.
The manufacturing of Diels–Alder (D-A) crosslinked epoxy nanocomposites is an emerging field with several challenges to overcome: the synthesis is complex due to side reactions, the mechanical properties are hindered by the brittleness of these bonds, and the content of carbon nanotubes (CNT) added to achieve electroactivity is much higher than the percolation thresholds of other conventional resins. In this work, we develop nanocomposites with different D-A crosslinking ratios (0, 0.6, and 1.0) and CNT contents (0.1, 0.3, 0.5, 0.7, and 0.9 wt.%), achieving a simplified route and avoiding the use of solvents and side reactions by selecting a two-step curing method (100 °C-6 h + 60 °C-12 h) that generates the thermo-reversible resins. These reversible nanocomposites show ohmic behavior and effective Joule heating, reaching the dissociation temperatures of the D-A bonds. The fully reversible nanocomposites (ratio 1.0) present more homogeneous CNT dispersion compared to the partially reversible nanocomposites (ratio 0.6), showing higher electrical conductivity, as well as higher brittleness. For this study, the nanocomposite with a partially reversible matrix (ratio 0.6) doped with 0.7 CNT wt.% was selected to allow us to study its new smart functionalities and performance due to its reversible network by analyzing self-healing and thermoforming. Full article
(This article belongs to the Special Issue Epoxy Thermoset Polymer Composites)
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11 pages, 2070 KiB  
Article
Recyclability of Post-Consumer Polystyrene at Pilot Scale: Comparison of Mechanical and Solvent-Based Recycling Approaches
Polymers 2023, 15(24), 4714; https://doi.org/10.3390/polym15244714 - 15 Dec 2023
Viewed by 885
Abstract
Solvent-based and mechanical recycling technology approaches were compared with respect to each process’s decontamination efficiency. Herein, post-consumer polystyrene (PS) feedstock was recycled by both technologies, yielding recycled PS resins (rPS). The process feedstock was subjected to four recycling cycles in succession to assess [...] Read more.
Solvent-based and mechanical recycling technology approaches were compared with respect to each process’s decontamination efficiency. Herein, post-consumer polystyrene (PS) feedstock was recycled by both technologies, yielding recycled PS resins (rPS). The process feedstock was subjected to four recycling cycles in succession to assess the technology perennity. The physico-chemical and mechanical properties of the rPS were then evaluated to discern the advantages and drawbacks of each recycling approach. The molecular weight of the mechanically recycled resin was found to decrease by 30% over the reprocessing cycles. In contrast, the solvent-base recycling technology yielded a similar molecular weight regarding the feedstock. This consistency in the rPS product is critical for consumer applications. Further qualitative and quantitative analyses on residual organic compounds and inorganic and particulate contaminants were investigated. It was found that the solvent-based technology is very efficient for purifying deeply contaminated feedstock in comparison to mechanical recycling, which is limited to well-cleaned and niche feedstocks. Full article
(This article belongs to the Special Issue Eco-Design of Polymeric Materials)
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24 pages, 9299 KiB  
Article
Electrical, Thermal, and Structural Characterization of Plant-Based 3D Printed Gel Polymer Electrolytes for Future Electrochemical Applications
Polymers 2023, 15(24), 4713; https://doi.org/10.3390/polym15244713 - 15 Dec 2023
Cited by 1 | Viewed by 972
Abstract
In this work, a plant-based resin gel polymer electrolyte (GPE) was prepared by stereolithography (SLA) 3D printing. Lithium perchlorate (LiClO4) with a concentration between 0 wt.% and 25 wt.% was added into the plant-based resin to observe its influence on electrical [...] Read more.
In this work, a plant-based resin gel polymer electrolyte (GPE) was prepared by stereolithography (SLA) 3D printing. Lithium perchlorate (LiClO4) with a concentration between 0 wt.% and 25 wt.% was added into the plant-based resin to observe its influence on electrical and structural characteristics. Fourier transform infrared spectroscopy (FTIR) analysis showed shifts in the carbonyl, ester, and amine groups, proving that complexation between the polymer and LiClO4 had occurred. GPEs with a 20 wt.% LiClO4 (S20) showed the highest room temperature conductivity of 3.05 × 10−3 S cm−1 due to the highest number of free ions as determined from FTIR deconvolution. The mobility of free ions in S20 electrolytes was also the highest due to greater micropore formation, as observed via field emission scanning electron microscopy (FESEM) images. Transference number measurements suggest that ionic mobility plays a pivotal role in influencing the conductivity of S20 electrolytes. Based on this work, it can be concluded that the plant-based resin GPE with LiClO4 is suitable for future electrochemical applications. Full article
(This article belongs to the Special Issue Polymer Electrolyte: Recent Progress and Applications)
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29 pages, 5588 KiB  
Review
Research Advances in Wood Composites in Applications of Industrial Wastewater Purification and Solar-Driven Seawater Desalination
Polymers 2023, 15(24), 4712; https://doi.org/10.3390/polym15244712 - 14 Dec 2023
Viewed by 828
Abstract
In recent years, the ecosystem has been seriously affected by sewage discharge and oil spill accidents. A series of issues (such as the continuous pollution of the ecological environment and the imminent exhaustion of freshwater resources) are becoming more and more unmanageable, resulting [...] Read more.
In recent years, the ecosystem has been seriously affected by sewage discharge and oil spill accidents. A series of issues (such as the continuous pollution of the ecological environment and the imminent exhaustion of freshwater resources) are becoming more and more unmanageable, resulting in a crisis of water quality and quantity. Therefore, studies on industrial wastewater purification and solar-driven seawater desalination based on wood composites have been widely considered as an important development direction. This paper comprehensively analyzes and summarizes the applications of wood composites in the fields of solar-driven seawater desalination and polluted water purification. In particular, the present situation of industrial wastewater containing heavy metal ions, microorganisms, aromatic dyes and oil stains and related problems of solar-driven seawater desalination are comprehensively analyzed and summarized. Generally, functional nanomaterials are loaded into the wood cell wall, from which lignin and hemicellulose are selectively removed. Alternatively, functional groups are modified on the basis of the molecular structure of the wood microchannels. Due to its three-dimensional (3D) pore structure and low thermal conductivity, wood is an ideal substrate material for industrial wastewater purification and solar-driven seawater desalination. Based on the study of objective conditions such as the preparation process, modification method and selection of photothermal conversion materials, the performances of the wood composites in filtration, adsorption and seawater desalination are analyzed in detail. In addition, this work points out the problems and possible solutions in applying wood composites to industrial wastewater purification and solar-driven seawater desalination. Full article
(This article belongs to the Special Issue Recent Developments in Wood Polymer Composites)
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22 pages, 5154 KiB  
Article
Connecting Structural Characteristics and Material Properties in Phase-Separating Polymer Solutions: Phase-Field Modeling and Physics-Informed Neural Networks
Polymers 2023, 15(24), 4711; https://doi.org/10.3390/polym15244711 - 14 Dec 2023
Viewed by 802
Abstract
The formed morphology during phase separation is crucial for determining the properties of the resulting product, e.g., a functional membrane. However, an accurate morphology prediction is challenging due to the inherent complexity of molecular interactions. In this study, the phase separation of a [...] Read more.
The formed morphology during phase separation is crucial for determining the properties of the resulting product, e.g., a functional membrane. However, an accurate morphology prediction is challenging due to the inherent complexity of molecular interactions. In this study, the phase separation of a two-dimensional model polymer solution is investigated. The spinodal decomposition during the formation of polymer-rich domains is described by the Cahn–Hilliard equation incorporating the Flory–Huggins free energy description between the polymer and solvent. We circumvent the heavy burden of precise morphology prediction through two aspects. First, we systematically analyze the degree of impact of the parameters (initial polymer volume fraction, polymer mobility, degree of polymerization, surface tension parameter, and Flory–Huggins interaction parameter) in a phase-separating system on morphological evolution characterized by geometrical fingerprints to determine the most influential factor. The sensitivity analysis provides an estimate for the error tolerance of each parameter in determining the transition time, the spinodal decomposition length, and the domain growth rate. Secondly, we devise a set of physics-informed neural networks (PINN) comprising two coupled feedforward neural networks to represent the phase-field equations and inversely discover the value of the embedded parameter for a given morphological evolution. Among the five parameters considered, the polymer–solvent affinity is key in determining the phase transition time and the growth law of the polymer-rich domains. We demonstrate that the unknown parameter can be accurately determined by renormalizing the PINN-predicted parameter by the change of characteristic domain size in time. Our results suggest that certain degrees of error are tolerable and do not significantly affect the morphology properties during the domain growth. Moreover, reliable inverse prediction of the unknown parameter can be pursued by merely two separate snapshots during morphological evolution. The latter largely reduces the computational load in the standard data-driven predictive methods, and the approach may prove beneficial to the inverse design for specific needs. Full article
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29 pages, 227522 KiB  
Article
Influence of 3D Printing Direction in PLA Acoustic Guitars on Vibration Response
Polymers 2023, 15(24), 4710; https://doi.org/10.3390/polym15244710 - 14 Dec 2023
Viewed by 613
Abstract
The design of musical instruments is a discipline that is still carried out in an artisanal way, with limitations and high costs. With the additive manufacturing technique, it is possible to obtain results for the generation of not only electrical but also acoustic [...] Read more.
The design of musical instruments is a discipline that is still carried out in an artisanal way, with limitations and high costs. With the additive manufacturing technique, it is possible to obtain results for the generation of not only electrical but also acoustic instruments. However, it is necessary to generate a procedure to evaluate the influence of the process on the final result of the acoustics obtained. This study focuses on investigating the relationship between the construction of acoustic guitars and their final sound. The reinforcement structures at the top of the instrument are analysed, as well as how this design affects the vibratory behaviour of the top in the first five vibratory modes. Specifically, this article presents a procedure for the design of customised acoustic guitars using additive manufacturing through parametrisation and a vibrational analysis of the designed tops using finite element (FEA) and experimental physical tests, in order to develop a methodology for the study of stringed instruments. As a result, an 11% increase in the high-frequency response was achieved with a printing direction of +45°, and a reduction in the high-frequency response with ±45°. In addition, at high frequencies, a relative error of 5% was achieved with respect to the simulation. This work fulfils an identified need to study the manufacture of acoustic guitars using polylactic acid (PLA), and to be able to offer the musician a customised instrument. This represents a breakthrough in the use of this manufacturing technology, extending its relationship with product design. Full article
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14 pages, 7872 KiB  
Article
Bio-Based Alkali Lignin Cooperative Systems for Improving the Flame Retardant and Mechanical Properties of Rigid Polyurethane Foam
Polymers 2023, 15(24), 4709; https://doi.org/10.3390/polym15244709 - 14 Dec 2023
Viewed by 597
Abstract
Lignin was utilized as an environmentally friendly synergistic agent to augment the fire resistance and mechanical characteristics of rigid polyurethane foam (PUF)/melamine–formaldehyde resin ammonium polyphosphate (MFAPP). The incorporation of lignin significantly enhanced the charring capability and flame retardancy of PUF/MFAPP. Specifically, PUF/MFAPP12 [...] Read more.
Lignin was utilized as an environmentally friendly synergistic agent to augment the fire resistance and mechanical characteristics of rigid polyurethane foam (PUF)/melamine–formaldehyde resin ammonium polyphosphate (MFAPP). The incorporation of lignin significantly enhanced the charring capability and flame retardancy of PUF/MFAPP. Specifically, PUF/MFAPP12/A-lignin3 exhibited a charring residue of 23.1% at 800 °C, accompanied by an increase in the limiting oxygen index (LOI) to 23.1%, resulting in a UL-94 V-0 rating. The cone calorimeter test (CCT) revealed that the peak heat release rate (PHRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) values of PUF/MFAPP12/A-lignin3 were all lower than for pure PUF. MFAPP and alkali lignin exerted a noticeable influence on the physical and mechanical properties, leading to increases in density (35.4 kg/m3), thermal conductivity (32.68 mW/(m·K)), and compressive strength (160.5 kPa). Observations of the morphology and elemental composition of char residues after combustion indicated the formation of an intact, thick, and continuous char layer enriched with nitrogen and phosphorus elements, which acted as a protective shield for the underlying foam. Full article
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1 pages, 164 KiB  
Retraction
RETRACTED: Liu et al. The Effect of Intrinsic Mechanical Properties on Reducing the Friction-Induced Ripples of Hard-Filler-Modified HDPE. Polymers 2023, 15, 268
Polymers 2023, 15(24), 4708; https://doi.org/10.3390/polym15244708 - 14 Dec 2023
Viewed by 676
Abstract
The Polymers Editorial Office retracts the article “The Effect of Intrinsic Mechanical Properties on Reducing the Friction-Induced Ripples of Hard-Filler-Modified HDPE” [...] Full article
15 pages, 13350 KiB  
Article
Study on Rheological Properties and Pouring Process of Hydroxyl-Terminated Polybutadiene (HTPB) Propellants
Polymers 2023, 15(24), 4707; https://doi.org/10.3390/polym15244707 - 14 Dec 2023
Viewed by 675
Abstract
The process of solid propellant production, which is the most widely used high-energy material, has garnered significant attention from researchers. However, there have been relatively few studies on its processing, due to the unique nature of the casting process. This paper aims to [...] Read more.
The process of solid propellant production, which is the most widely used high-energy material, has garnered significant attention from researchers. However, there have been relatively few studies on its processing, due to the unique nature of the casting process. This paper aims to further analyze the pouring process of the propellant slurry. Initially, we obtained a sample of the propellant slurry and measured its rheological parameters using a rotary rheometer. From the analysis of the experimental results, we derived the viscosity parameters and the yield values of the propellant slurry. Subsequently, we simulated the pouring process, setting the slurry parameters based on the data obtained from the rheological measurement experiment. The simulation results demonstrated that the flower plate significantly impacts upon the cutting and separating effect on the slurry during pouring. Upon leaving the flower plate, the slurry descends onto the core mold platform under the influence of gravity, gradually flowing along the edge of the core mold. Although there may be some small voids in the pouring process, the voids will disappear completely at the end of pouring. A comparison with the actual pouring situation revealed a higher consistency between the simulation results and reality, thus establishing the reliability of the simulation method as a reference for analyzing the pouring process. Full article
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