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Polymers, Volume 15, Issue 23 (December-1 2023) – 149 articles

Cover Story (view full-size image): Changing Hg radiators to LEDs poses a significant challenge for painting coatings in the furniture industry. The primary goal of the study was to ascertain how the quality of the coating on honeycomb boards was affected by the LED+Hg lamp modules, the grinding procedure, and the quantity and thickness of varnish layers. The nanoindentation method was used to evaluate the hardness and elastic modulus of the coating. Surface roughness was assessed using a digital microscope, and resistance to cold liquids was measured with a colorimeter. The coatings were also tested for abrasion, scratch, and impact resistance. View this paper
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20 pages, 10452 KiB  
Article
Hydrodeoxygenation of Lignin-Based Compounds over Ruthenium Catalysts Based on Sulfonated Porous Aromatic Frameworks
Polymers 2023, 15(23), 4618; https://doi.org/10.3390/polym15234618 - 04 Dec 2023
Viewed by 712
Abstract
Bifunctional catalysts are a major type of heterogeneous catalytic systems that have been widely investigated for biomass upgrading. In this work, Ru-catalysts based on sulfonated porous aromatic frameworks (PAFs) were used in the hydrodeoxygenation (HDO) of lignin-derived compounds: guaiacol, veratrole, and catechol. The [...] Read more.
Bifunctional catalysts are a major type of heterogeneous catalytic systems that have been widely investigated for biomass upgrading. In this work, Ru-catalysts based on sulfonated porous aromatic frameworks (PAFs) were used in the hydrodeoxygenation (HDO) of lignin-derived compounds: guaiacol, veratrole, and catechol. The relationship between the activity of metal nanoparticles and the content of acid sites in synthesized catalysts was studied. Herein, their synergy was demonstrated in the Ru-PAF-30-SO3H/5-COD catalyst. The results revealed that this catalytic system promoted partial hydrogenation of lignin-based compounds to ketones without any further transformations. The design of the Ru-PAF-30-SO3H/5-COD catalytic system opens a promising route to the selective conversion of lignin model compounds to cyclohexanone. Full article
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13 pages, 2132 KiB  
Review
Exploring the Role of Green Microbes in Sustainable Bioproduction of Biodegradable Polymers
Polymers 2023, 15(23), 4617; https://doi.org/10.3390/polym15234617 - 04 Dec 2023
Viewed by 869
Abstract
Research efforts have shifted to creating biodegradable polymers to offset the harmful environmental impacts associated with the accumulation of non-degradable synthetic polymers in the environment. This review presents a comprehensive examination of the role of green microbes in fostering sustainable bioproduction of these [...] Read more.
Research efforts have shifted to creating biodegradable polymers to offset the harmful environmental impacts associated with the accumulation of non-degradable synthetic polymers in the environment. This review presents a comprehensive examination of the role of green microbes in fostering sustainable bioproduction of these environment-friendly polymers. Green microbes, primarily algae and cyanobacteria, have emerged as promising bio-factories due to their ability to capture carbon dioxide and utilize solar energy efficiently. It further discusses the metabolic pathways harnessed for the synthesis of biopolymers such as polyhydroxyalkanoates (PHAs) and the potential for genetic engineering to augment their production yields. Additionally, the techno-economic feasibility of using green microbes, challenges associated with the up-scaling of biopolymer production, and potential solutions are elaborated upon. With the twin goals of environmental protection and economic viability, green microbes pave the way for a sustainable polymer industry. Full article
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13 pages, 6887 KiB  
Article
The Enhancement of the Thermal Conductivity of Epoxy Resin Reinforced by Bromo-Oxybismuth
Polymers 2023, 15(23), 4616; https://doi.org/10.3390/polym15234616 - 04 Dec 2023
Cited by 1 | Viewed by 645
Abstract
With the gradual miniaturization of electronic devices, the thermal conductivity of electronic components is increasingly required. Epoxy (EP) resins are easy to process, exhibit excellent electrical insulation properties, and are light in weight and low in cost, making them the preferred material for [...] Read more.
With the gradual miniaturization of electronic devices, the thermal conductivity of electronic components is increasingly required. Epoxy (EP) resins are easy to process, exhibit excellent electrical insulation properties, and are light in weight and low in cost, making them the preferred material for thermal management applications. In order to endow EPs with better dielectric and thermal conductivity properties, bromo-oxygen-bismuth (BiOBr) prepared using the hydrothermal method was used as a filler to obtain BiOBr/EP composites, and the effect of BiOBr addition on the properties of the BiOBr/EP composites was also studied. The results showed that the addition of a small amount of BiOBr could greatly optimize the dielectric properties and thermal conductivity of EP resin, and when the content of BiOBr was 0.75 wt% and 1.00 wt%, the dielectric properties and thermal conductivity of the composite could reach the optimum, respectively. The high dielectric constant and excellent thermal conductivity of BiOBr/EP composites are mainly due to the good layered structure of BiOBr, which can provide good interfacial polarization and thermal conductivity. Full article
(This article belongs to the Special Issue Functional Polymer Composites for Advanced Applications)
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11 pages, 2417 KiB  
Article
Hybrid Polymer–Surfactant Wormlike Micelles for Concurrent Use for Oil Recovery and Drag Reduction
Polymers 2023, 15(23), 4615; https://doi.org/10.3390/polym15234615 - 04 Dec 2023
Viewed by 735
Abstract
We report on the effect of a hydrocarbon (n-dodecane) on the rheological properties and shapes of the hybrid wormlike micelles (WLMs) of a surfactant potassium oleate with an embedded polymer poly(4-vinylpyridine). With and without hydrocarbon solutions, the hybrid micelles exhibit the same values [...] Read more.
We report on the effect of a hydrocarbon (n-dodecane) on the rheological properties and shapes of the hybrid wormlike micelles (WLMs) of a surfactant potassium oleate with an embedded polymer poly(4-vinylpyridine). With and without hydrocarbon solutions, the hybrid micelles exhibit the same values of viscosity at shear rates typical for hydraulic fracturing (HF) tests, as solutions of polymer-free WLMs. Therefore, similar to WLMs of surfactants, they could be applied as thickeners in HF fluids without breakers. At the same time, in the presence of n-dodecane, the hybrid micelles have much higher drag-reducing efficiency compared to microemulsions formed in polymer-free systems since they form “beads-on-string” structures according to results obtained using cryo-transmission electron microscopy (cryo-TEM), dynamic-light scattering (DLS), and small-angle X-ray scattering (SAXS). Consequently, they could also act as drag-reducing agents in the pipeline transport of recovered oil. Such a unique multi-functional additive to a fracturing fluid, which permits its concurrent use in oil production and oil transportation, has not been proposed before. Full article
(This article belongs to the Special Issue Polymer Colloids: Preparation and Application)
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18 pages, 6035 KiB  
Article
Assessment of Hydrothermal Treatment Effects on Coir Fibers for Incorporation into Polyurethane Matrix Biocomposites Derived from Castor Oil
Polymers 2023, 15(23), 4614; https://doi.org/10.3390/polym15234614 - 04 Dec 2023
Viewed by 743
Abstract
The incorporation of natural lignocellulosic fibers as reinforcements in polymer composites has witnessed significant growth due to their biodegradability, cost-effectiveness, and mechanical properties. This study aims to evaluate castor-oil-based polyurethane (COPU), incorporating different contents of coconut coir fibers, 5, 10, and 15 wt%. [...] Read more.
The incorporation of natural lignocellulosic fibers as reinforcements in polymer composites has witnessed significant growth due to their biodegradability, cost-effectiveness, and mechanical properties. This study aims to evaluate castor-oil-based polyurethane (COPU), incorporating different contents of coconut coir fibers, 5, 10, and 15 wt%. The investigation includes analysis of the physical, mechanical, and microstructural properties of these composites. Additionally, this study evaluates the influence of hydrothermal treatment on the fibers, conducted at 120 °C and 98 kPa for 30 min, on the biocomposites’ properties. Both coir fibers (CFs) and hydrothermal-treated coir fibers (HTCFs) were subjected to comprehensive characterization, including lignocellulosic composition analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The biocomposites were subjected to water absorption analysis, bending tests, XRD, SEM, FTIR, and TGA. The results indicate that the 30 min hydrothermal treatment reduces the extractive content, enhancing the interfacial adhesion between the fiber and the matrix, as evidenced by SEM. Notably, the composite containing 5 wt% CF exhibits a reduced water absorption, approaching the level observed in pure COPU. The inclusion of 15 wt% HTCF results in a remarkable improvement in the composite’s flexural strength (100%), elastic modulus (98%), and toughness (280%) compared to neat COPU. TGA highlights that incorporating CFs into the COPU matrix enhances the material’s thermal stability, allowing it to withstand temperatures of up to 500 °C. These findings underscore the potential of CFs as a ductile, lightweight, and cost-effective reinforcement in COPU matrix biocomposites, particularly for engineering applications. Full article
(This article belongs to the Section Polymer Composites and Nanocomposites)
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19 pages, 13536 KiB  
Article
A Comparative Study on Crystallisation for Virgin and Recycled Polyethylene Terephthalate (PET): Multiscale Effects on Physico-Mechanical Properties
Polymers 2023, 15(23), 4613; https://doi.org/10.3390/polym15234613 - 04 Dec 2023
Viewed by 770
Abstract
Poly(Ethylene Terephthalate) (PET) is one of the most used polymers for packaging applications. Modifications induced by service conditions and the means to make this matter circular have to be understood to really close the loop (from bottle to bottle for example). Physico-chemical properties, [...] Read more.
Poly(Ethylene Terephthalate) (PET) is one of the most used polymers for packaging applications. Modifications induced by service conditions and the means to make this matter circular have to be understood to really close the loop (from bottle to bottle for example). Physico-chemical properties, crystalline organisation, and mechanical behaviour of virgin PET (vPET) are compared with those of recycled PET (rPET). Using different combined experimental methods (Calorimetry, Small Angle X-ray Scattering [SAXS], Atomic Force Microscopy [AFM], Dynamic Mechanical Analysis [DMA], and uniaxial tensile test), it has been proven that even if there is no change in the crystallinity of PET, the crystallisation process shows some differences (size and number of spherulites). The potential impact of these differences on local mechanical characterisation is explored and tends to demonstrate the development of a homogeneous microstructure, leading to well-controlled and relevant local mechanical property characterisation. The main contribution of the present study is a better understanding of crystallisation of PET and recycled PET during forming processes such as thermoforming or Injection Stretch Blow Moulding (ISBM), during which elongation at the point of breaking can depend on the microstructure conditioned by the crystallisation process. Full article
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13 pages, 9905 KiB  
Article
Synthesis and Application of Hybrid Aluminum Dialkylphosphinates as Highly Efficient Flame Retardants for Polyamides
Polymers 2023, 15(23), 4612; https://doi.org/10.3390/polym15234612 - 04 Dec 2023
Viewed by 668
Abstract
Hybrid aluminum dialkylphosphinates were synthesized from mixed diethyl-, ethylisobutyl-, and diisobutylphosphinates and Al3+ in water. The XRD, DSC, and TGA results of these Al phosphinates established that phosphinate ligands are randomly distributed in the species. The thermal and thermoxidative stabilities of the [...] Read more.
Hybrid aluminum dialkylphosphinates were synthesized from mixed diethyl-, ethylisobutyl-, and diisobutylphosphinates and Al3+ in water. The XRD, DSC, and TGA results of these Al phosphinates established that phosphinate ligands are randomly distributed in the species. The thermal and thermoxidative stabilities of the hybrid phosphinates were easily adjustable by varying the ratio of phosphinate ligands, a desirable feature for efficient flame retardants. The hybrid aluminum dialkylphosphinates with a relatively low ratio of diethylphosphinate demonstrated higher efficiency than Al diethylphosphinate and Al diisobutylphosphinate in flame-retarding polyamide 66. Detailed investigations on the thermal and thermoxidative stabilities of Al dialkylphosphinates and the morphologies of char obtained in UL-94 tests revealed that timely vaporization of degradation products of hybrid dialkylphosphinates at a temperature which closely matches the degradation temperature of polyamides and their ability to promote char formation of polyamides are two key factors which contribute to the excellent performance of hybrid aluminum dialkylphosphinates. Full article
(This article belongs to the Special Issue Recent Advances in Flame Retardant Polymers)
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19 pages, 4712 KiB  
Article
Poly(Vinyl Alcohol)/Bovine Serum Albumin Hybrid Hydrogels with Tunable Mechanical Properties
Polymers 2023, 15(23), 4611; https://doi.org/10.3390/polym15234611 - 04 Dec 2023
Viewed by 846
Abstract
In this study, a new strategy was adopted for obtaining polymer/protein hybrid hydrogels with shape stability and tunable mechanical or rheological characteristics by using non-toxic procedures. A chemical network was created using a poly(vinyl alcohol)(PVA)/bovine serum albumin (BSA) mixture in aqueous solution in [...] Read more.
In this study, a new strategy was adopted for obtaining polymer/protein hybrid hydrogels with shape stability and tunable mechanical or rheological characteristics by using non-toxic procedures. A chemical network was created using a poly(vinyl alcohol)(PVA)/bovine serum albumin (BSA) mixture in aqueous solution in the presence of genipin and reduced glutathione (GSH). Then, a second physical network was formed through PVA after applying freezing/thawing cycles. In addition, the protein macromolecules formed intermolecular disulfide bridges in the presence of GSH. In these conditions, multiple crosslinked networks were obtained, determining the strengthening and stiffening into relatively tough porous hydrogels with tunable viscoelasticity and a self-healing ability. A SEM analysis evidenced the formation of networks with interconnected pores of sizes between 20 μm and 50 μm. The mechanical or rheological investigations showed that the hydrogels’ strength and response in different conditions of deformation were influenced by the composition and crosslinking procedure. Thus, the dynamics of the hybrid hydrogels can be adjusted to mimic the viscoelastic properties of the native tissues. The dynamic water vapor-sorption ability, swelling behavior in an aqueous environment, and bioadhesive properties were also investigated and are discussed in this paper. The hybrid hydrogels with tunable viscoelasticity can be designed on request, and they are promising candidates for tissue engineering, bioinks, and wound dressing applications. Full article
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27 pages, 5651 KiB  
Article
Assessment of the Influence of Protective Polymer Coating on Panda Fiber Performance Based on the Results of Multivariant Numerical Simulation
Polymers 2023, 15(23), 4610; https://doi.org/10.3390/polym15234610 - 03 Dec 2023
Viewed by 726
Abstract
This article considers the deformation behavior of Panda optical fiber using different models of material behavior for the tasks of predicting residual stresses after drawing when cooling from 2000 °C to room temperature (23 °C) and indenting the fiber into an aluminum half-space [...] Read more.
This article considers the deformation behavior of Panda optical fiber using different models of material behavior for the tasks of predicting residual stresses after drawing when cooling from 2000 °C to room temperature (23 °C) and indenting the fiber into an aluminum half-space at different parameters. These studies were conducted for single- and double-layer protective coatings (PCs), at different values of external load and thickness of single-layer PC. This paper determined the fields of residual stresses in the fiber formed during the drawing process. They are taken into account in modeling the fiber performance in the further process of this research. This article investigated two variants of PC behavior. The influence of behavior models and the number of covering layers on the deformation of the “fiber-half-space” system was analyzed. This paper establishes qualitative and quantitative regularities of the influence of the external load magnitude and relaxation properties of PCs on the deformation and optical characteristics of Panda optical fiber. Full article
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27 pages, 33153 KiB  
Article
Machine Learning Models in Drilling of Different Types of Glass-Fiber-Reinforced Polymer Composites
Polymers 2023, 15(23), 4609; https://doi.org/10.3390/polym15234609 - 03 Dec 2023
Viewed by 698
Abstract
The aim of the research presented in this paper was to simulate the relationship between selected technological drilling parameters (cutting speed, vc, and feed per tooth, fz) and cutting forces and the delamination in machining of a new glass-fiber-reinforced [...] Read more.
The aim of the research presented in this paper was to simulate the relationship between selected technological drilling parameters (cutting speed, vc, and feed per tooth, fz) and cutting forces and the delamination in machining of a new glass-fiber-reinforced polymer (GFRP) composite. Four different types of new materials were manufactured with the use of a specially designed pressing device and differed in the fiber type (plain and twill woven materials) and weight fraction (wf) ratio, but they had the same number of layers and the same stacking sequence. A vertical machining center Avia VMC800HS was used for drilling holes with a two-edge carbide diamond coated drill. Measurements of the cutting force Fz in the drilling process conducted with variable technological parameters were carried out on a special test stand, 9257B, from Kistler. The new ink penetration method, involving covering the drilled hole surface with a colored liquid that spreads over the inner surface of the hole showing damage, was used to determine the delamination area. The cause-and-effect relationship between the drilling parameters was simulated with the use of five machine learning (ML) regression models (Linear Regression; Decision Tree Regressor; Decision Tree Regressor with Ada Boost; XGBRF Regressor; Gradient Boosting Regressor). Gradient Boosting Regressor results showed that the feed per tooth had the greatest impact on delamination—the higher the feed was, the greater the delamination became. Push-out delamination factors had higher values for materials that were made of plain woven fibers. The lowest amplitude of the cutting force component Fz was obtained for the lowest tested feed per tooth of 0.04 mm for all tested materials, with the lowest values obtained for the materials with twill fibers. Full article
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18 pages, 6499 KiB  
Article
Does a Compatibilizer Enhance the Properties of Carbon Fiber-Reinforced Composites?
Polymers 2023, 15(23), 4608; https://doi.org/10.3390/polym15234608 - 03 Dec 2023
Viewed by 669
Abstract
We have evaluated the effectiveness of compatibilizers in blends and composites produced using a solvent manufacturing process. The compatibilizers were two different types of polyethylene (linear low-density and high-density) grafted with maleic anhydride (MAH) and a highly functionalized, epoxy-based compatibilizer with the tradename [...] Read more.
We have evaluated the effectiveness of compatibilizers in blends and composites produced using a solvent manufacturing process. The compatibilizers were two different types of polyethylene (linear low-density and high-density) grafted with maleic anhydride (MAH) and a highly functionalized, epoxy-based compatibilizer with the tradename Joncryl. The selected material combinations were an ultra-high-molecular-weight polyethylene (UHMWPE) with MAH-based materials as compatibilizers and a polyphenylene sulfide plus polytetrafluoroethylene (PPS-PTFE) polymer blend with an epoxy-based compatibilizer. The findings revealed that while the compatibilizers consistently enhanced the properties, such as the impact strength and hardness of PPS-based compositions, their utility is constrained to less complex compositions, such as fibrous-reinforced PPS or PPS-PTFE polymer blends. For fibrous-reinforced PPS-PTFE composites, the improvement in performance does not justify the presence of compatibilizers. In contrast, for UHMWPE compositions, compatibilizers demonstrated negligible or even detrimental effects, particularly in reinforced UHMWPE. Overall, the epoxy-based compatibilizer Joncryl stands out as the only effective option for enhancing mechanical performance. Thermal and chemical characterization indicated that the compatibilizers function as chain extenders and enhance the fiber–matrix interface in PPS-based compositions, while they remain inactive in UHMWPE-based compositions. Ultimately, the incompatibility of the compatibilizers with certain aspects of the manufacturing method and the inconsistent integration with the polymer are the main reasons for their ineffectiveness in UHMWPE compositions. Full article
(This article belongs to the Special Issue Fiber-Reinforced Polymer Composites)
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14 pages, 3393 KiB  
Article
Programming and Reprogramming the Viscoelasticity and Magnetic Response of Magnetoactive Thermoplastic Elastomers
Polymers 2023, 15(23), 4607; https://doi.org/10.3390/polym15234607 - 03 Dec 2023
Viewed by 608
Abstract
We present a novel type of magnetorheological material that allows one to restructure the magnetic particles inside the finished composite, tuning in situ the viscoelasticity and magnetic response of the material in a wide range using temperature and an applied magnetic field. The [...] Read more.
We present a novel type of magnetorheological material that allows one to restructure the magnetic particles inside the finished composite, tuning in situ the viscoelasticity and magnetic response of the material in a wide range using temperature and an applied magnetic field. The polymer medium is an A-g-B bottlebrush graft copolymer with side chains of two types: polydimethylsiloxane and polystyrene. At room temperature, the brush-like architecture provides the tissue mimetic softness and strain stiffening of the elastomeric matrix, which is formed through the aggregation of polystyrene side chains into aggregates that play the role of physical cross-links. The aggregates partially dissociate and the matrix softens at elevated temperatures, allowing for the effective rearrangement of magnetic particles by applying a magnetic field in the desired direction. Magnetoactive thermoplastic elastomers (MATEs) based on A-g-B bottlebrush graft copolymers with different amounts of aggregating side chains filled with different amounts of carbonyl iron microparticles were prepared. The in situ restructuring of magnetic particles in MATEs was shown to significantly alter their viscoelasticity and magnetic response. In particular, the induced anisotropy led to an order-of-magnitude enhancement of the magnetorheological properties of the composites. Full article
(This article belongs to the Special Issue Magnetic Polymer Composites: Design and Application II)
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16 pages, 6198 KiB  
Article
Preparation and Performance Evaluation of Amphiphilic Polymers for Enhanced Heavy Oil Recovery
Polymers 2023, 15(23), 4606; https://doi.org/10.3390/polym15234606 - 02 Dec 2023
Viewed by 855
Abstract
The continuous growth in global energy and chemical raw material demand has drawn significant attention to the development of heavy oil resources. A primary challenge in heavy oil extraction lies in reducing crude oil viscosity. Alkali–surfactant–polymer (ASP) flooding technology has emerged as an [...] Read more.
The continuous growth in global energy and chemical raw material demand has drawn significant attention to the development of heavy oil resources. A primary challenge in heavy oil extraction lies in reducing crude oil viscosity. Alkali–surfactant–polymer (ASP) flooding technology has emerged as an effective method for enhancing heavy oil recovery. However, the chromatographic separation of chemical agents presents a formidable obstacle in heavy oil extraction. To address this challenge, we utilized a free radical polymerization method, employing acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, lauryl acrylate, and benzyl acrylate as raw materials. This approach led to the synthesis of a multifunctional amphiphilic polymer known as PAALB, which we applied to the extraction of heavy oil. The structure of PAALB was meticulously characterized using techniques such as infrared spectroscopy and Nuclear Magnetic Resonance Spectroscopy. To assess the effectiveness of PAALB in reducing heavy oil viscosity and enhancing oil recovery, we conducted a series of tests, including contact angle measurements, interfacial tension assessments, self-emulsification experiments, critical association concentration tests, and sand-packed tube flooding experiments. The research findings indicate that PAALB can reduce oil–water displacement, reduce heavy oil viscosity, and improve swept volume upon injection into the formation. A solution of 5000 mg/L PAALB reduced the contact angle of water droplets on the core surface from 106.55° to 34.95°, shifting the core surface from oil-wet to water-wet, thereby enabling oil–water displacement. Moreover, A solution of 10,000 mg/L PAALB reduced the oil–water interfacial tension to 3.32 × 10−4 mN/m, reaching an ultra-low interfacial tension level, thereby inducing spontaneous emulsification of heavy oil within the formation. Under the condition of an oil–water ratio of 7:3, a solution of 10,000 mg/L PAALB can reduce the viscosity of heavy oil from 14,315 mPa·s to 201 mPa·s via the glass bottle inversion method, with a viscosity reduction rate of 98.60%. In sand-packed tube flooding experiments, under the injection volume of 1.5 PV, PAALB increased the recovery rate by 25.63% compared to traditional hydrolyzed polyacrylamide (HPAM) polymer. The insights derived from this research on amphiphilic polymers hold significant reference value for the development and optimization of chemical flooding strategies aimed at enhancing heavy oil recovery. Full article
(This article belongs to the Special Issue New Studies of Polymer Surfaces and Interfaces)
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35 pages, 8312 KiB  
Article
How to Make the Stress Relaxation Experiment for Polymers More Informative
Polymers 2023, 15(23), 4605; https://doi.org/10.3390/polym15234605 - 02 Dec 2023
Viewed by 824
Abstract
Different viscoelastic models and characteristics are commonly used to describe, analyze, compare and improve the mechanical properties of polymers. A time-dependent linear relaxation modulus next to frequency-domain storage and loss moduli are the basic rheological material functions of polymers. The exponential Maxwell model [...] Read more.
Different viscoelastic models and characteristics are commonly used to describe, analyze, compare and improve the mechanical properties of polymers. A time-dependent linear relaxation modulus next to frequency-domain storage and loss moduli are the basic rheological material functions of polymers. The exponential Maxwell model and the exponential stretched Kohlrausch–Williams–Watts model are, probably, the most known linear rheological models of polymers. There are different identification methods for such models, some of which are dedicated to specific models, while others are general in nature. However, the identification result, i.e., the best model, always depends on the specific experimental data on the basis of which it was determined. When the rheological stress relaxation test is performed, the data are composed of the sampling instants used in the test and on the measurements of the relaxation modulus of the real material. To build a relaxation modulus model that does not depend on sampling instants is a fundamental concern. The problem of weighted least-squares approximation of the real relaxation modulus is discussed when only the noise-corrupted time-measurements of the relaxation modulus are accessible for identification. A wide class of models, that are continuous, differentiable and Lipschitz with respect to parameters, is considered for the relaxation modulus approximation. The main results concern the models that are selected asymptotically as the number of measurements tends to infinity. It is shown that even when the true relaxation modulus description is completely unknown, the approximate optimal model parameters can be derived from the measurement data that are obtained for sampling instants that are selected randomly due to the appropriate randomization introduced whenever certain conditions regarding the adopted class of models are satisfied. It is shown that the most commonly used stress relaxation models, the Maxwell and Kohlrausch–Williams–Watts models, satisfy these conditions. Since the practical problems of the identification of relaxation modulus models are usually ill posed, Tikhonov regularization is applied to guarantee the stability of the regularized solutions. The approximate optimal model is a strongly consistent estimate of the regularized model that is optimal in the sense of the deterministic integral weighted square error. An identification algorithm leading to the best regularized model is presented. The stochastic-type convergence analysis is conducted for noise-corrupted relaxation modulus measurements, and the exponential convergence rate is proved. Numerical studies for different models of the relaxation modulus used in the polymer rheology are presented for the material described by a bimodal Gauss-like relaxation spectrum. Numerical studies have shown that if appropriate randomization is introduced in the selection of sampling instants, then optimal regularized models of the relaxation modulus being asymptotically independent of these time instants can be recovered from the stress relaxation experiment data. The robustness of the identification algorithm to measurement noises was demonstrated both by analytical and numerical analyses. Full article
(This article belongs to the Special Issue Time-Dependent Mechanical Behavior of Polymers and Polymer Composites)
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12 pages, 3732 KiB  
Article
Rheological Properties and Kinetics of Gelation of Binary Polymers between Xanthan Gum and Locust Bean Gum
Polymers 2023, 15(23), 4604; https://doi.org/10.3390/polym15234604 - 02 Dec 2023
Viewed by 637
Abstract
The synergistic interaction and gelling kinetics between xanthan gum (XG) and locust bean gum (LBG) at different mass ratios (XG/LBG 9:1, 7:3, 5:5, 3:7, 1:9) were investigated using a rheometer. The results showed that the mixtures of XG and LBG induced gel formation, [...] Read more.
The synergistic interaction and gelling kinetics between xanthan gum (XG) and locust bean gum (LBG) at different mass ratios (XG/LBG 9:1, 7:3, 5:5, 3:7, 1:9) were investigated using a rheometer. The results showed that the mixtures of XG and LBG induced gel formation, and the strongest gel structure was found for the mixture of XG/LBG 3:7 according to the yield stress, storage modulus (G′), and power law parameters. Temperature ramp studies indicated that heating destroyed the gels at 55~60 °C, while cooling induced the sol–gel transition at around 52 °C for all mixtures. Structure developing rate (SDR) curves showed that XG/LBG 3:7 exhibited the highest SDR during the cooling ramp among all the samples. Non-isothermal kinetic analysis demonstrated that the gelation process of XG/LBG mixtures during cooling included two steps: a high-temperature region (55~39 °C) needing higher activation energy (Ea, 111.97 to 199.20 kJ/mol for different mixtures) and a low-temperature region (39~20 °C) needing lower Ea (74.33 to 85.31 kJ/mol), which indicated higher energy barriers to overcome at the initial stage of gel formation. The lowest Ea of 74.33 kJ/mol was found for XG/LBG 3:7 in the low-temperature region. Scanning electron microscopy (SEM) showed that the gel of XG/LBG 3:7 presented the densest entanglements. These results indicated the strongest synergism interaction occurred in XG/LBG 3:7 to form gel network structures. This study will help promote the application of XG-LBG blends to design novel food structures. Full article
(This article belongs to the Special Issue Advances in Natural Polysaccharides: Function and Application)
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11 pages, 2409 KiB  
Article
The Synergistic Effect of GH13 and GH57 GBEs of Petrotoga mobilis Results in α-Glucan Molecules with a Higher Branch Density
Polymers 2023, 15(23), 4603; https://doi.org/10.3390/polym15234603 - 02 Dec 2023
Viewed by 602
Abstract
Glycogen is a biopolymer consisting of glycosyl units, with a linear backbone connected by α-1,4-linkages and branches attached via α-1,6-linkages. In microorganisms, glycogen synthesis involves multiple enzymes, with glycogen branching enzymes (GBEs) being vital for creating α-1,6-linkages. GBEs exist in two families: glycoside [...] Read more.
Glycogen is a biopolymer consisting of glycosyl units, with a linear backbone connected by α-1,4-linkages and branches attached via α-1,6-linkages. In microorganisms, glycogen synthesis involves multiple enzymes, with glycogen branching enzymes (GBEs) being vital for creating α-1,6-linkages. GBEs exist in two families: glycoside hydrolase (GH) 13 and GH57. Some organisms possess either a single GH13 or GH57 GBE, while others, such as Petrotoga mobilis, have both types of GBEs. In this study, the simultaneous use of a GH13 and GH57 GBE each from Petrotoga mobilis for α-glucan modification was investigated using a linear maltodextrin substrate with a degree of polymerization of 18 (DP18). The products from modifications by one or both GBEs in various combinations were analyzed and demonstrated a synergistic effect when both enzymes were combined, leading to a higher branch density in the glycogen structure. In this cooperative process, PmGBE13 was responsible for creating longer branches, whereas PmGBE57 hydrolyzed these branches, resulting in shorter lengths. The combined action of the two enzymes significantly increased the number of branched chains compared to when they acted individually. The results of this study therefore give insight into the role of PmGBE13 and PmGBE57 in glycogen synthesis, and show the potential use of both enzymes in a two-step modification to create an α-glucan structure with short branches at a high branch density. Full article
(This article belongs to the Special Issue Study of Starch in Food Chemistry)
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15 pages, 3651 KiB  
Article
Effect of Powder Bed Fusion Laser Sintering on Dimensional Accuracy and Tensile Properties of Reused Polyamide 11
Polymers 2023, 15(23), 4602; https://doi.org/10.3390/polym15234602 - 02 Dec 2023
Viewed by 674
Abstract
Polyamide 11 (PA11) is a plant-based nylon made from castor beans. Powder bed fusion laser sintering (PBF-LS) is an additive manufacturing process used for PA11 which allows for the reuse of the unsintered powder. The unsintered powder is mixed with virgin powders at [...] Read more.
Polyamide 11 (PA11) is a plant-based nylon made from castor beans. Powder bed fusion laser sintering (PBF-LS) is an additive manufacturing process used for PA11 which allows for the reuse of the unsintered powder. The unsintered powder is mixed with virgin powders at different refresh rates, a process which has been studied extensively for most semi-crystalline polyamides. However, there is lack of information on the effect of using 100% reused PA11 powder and the effect of the number of times it is reused on its own, during powder bed fusion laser sintering. This paper investigates the effect of reusing PA11 powder in PBF-LS and the effect of the number of times it is reused on the dimensional accuracy, density and thermal and tensile properties. From the 100% virgin powder to the third reuse of the powder, there is a decrease in powder wastage, crystallinity and tensile strength. These are associated with the polymerisation and cross-linking process of polymer chains, upon exposure to high temperatures. This results in a higher molecular weight and, hence, a higher density. From the fourth reuse to the tenth reuse, the opposite is observed, which is associated with an increase in high-viscosity unmolten particles, resulting in defects in the PBF-LS parts. Full article
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17 pages, 3703 KiB  
Article
Structure, Thermal, and Mechanical Behavior of the Polysulfone Solution Impregnated Unidirectional Carbon Fiber Yarns
Polymers 2023, 15(23), 4601; https://doi.org/10.3390/polym15234601 - 02 Dec 2023
Viewed by 681
Abstract
The paper is devoted to the study of thermal and mechanical behavior and structural features of the polysulfone solution impregnated unidirectional carbon fiber yarns depending on fabrication conditions and appearance for optimum production method of the composites. The effect of producing conditions, such [...] Read more.
The paper is devoted to the study of thermal and mechanical behavior and structural features of the polysulfone solution impregnated unidirectional carbon fiber yarns depending on fabrication conditions and appearance for optimum production method of the composites. The effect of producing conditions, such as polysulfone solution concentration, drying and post-heating temperatures, and the residual solvent content on the structure, mechanical, and thermal properties of the carbon fiber-reinforced composites was studied. The polysulfone solution impregnated carbon fiber yarns show relatively high mechanical properties, realizing up to 80% of the carbon fibers’ tensile strength, which can be attributed to good wettability and uniform polymer matrix distribution throughout the entire volume of the composites. It was found that the composites impregnated with 40 wt.% of the polysulfone solution showed lower porosity and higher mechanical properties. The results of a dynamic mechanical analysis indicate that residual solvent has a significant effect on the composites’ thermal behavior. The composites heated to 350 °C for a 30 min showed higher thermal stability compared to ones dried at 110 °C due to removal of residual solvent during heating. The impregnated carbon fiber yarns can be used for the further producing bulk unidirectional composites by compression molding and the proposed method can be easily transformed to continuous filament production, for example for further use in 3-D printing technology. Full article
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14 pages, 5101 KiB  
Article
Effects of ZIF-L Morphology on PI@PDA@PEI/ZIF-L Composite Membrane’s Adsorption and Separation Properties for Heavy Metal Ions
Polymers 2023, 15(23), 4600; https://doi.org/10.3390/polym15234600 - 01 Dec 2023
Viewed by 604
Abstract
Composite polymolecular separation membranes were prepared by combining multi-branched ZIF-L with high-porosity electrospinning nanofibers PI. Meanwhile, PDA and PEI were introduced into the membrane in order to improve its adhesion. The new membrane is called the “PI@PDA@PEI/ZIF-L-4” composite membrane. Compared with the PI@PDA@PEI/ZIF-8 [...] Read more.
Composite polymolecular separation membranes were prepared by combining multi-branched ZIF-L with high-porosity electrospinning nanofibers PI. Meanwhile, PDA and PEI were introduced into the membrane in order to improve its adhesion. The new membrane is called the “PI@PDA@PEI/ZIF-L-4” composite membrane. Compared with the PI@PDA@PEI/ZIF-8 composite membrane, the new membrane’s filtration rates for heavy metal ions such as Cd2+, Cr3+, and Pb2+ were increased by 7.0%, 6.6%, and 9.3%, respectively. Furthermore, the new membrane has a permeability of up to 1140.0 L·m−2·h−1·bar−1, and displayed a very stable performance after four repeated uses. The separation mechanism of the PI@PDA@PEI/ZIF-L composite membrane was analyzed further in order to provide a basis to support the production of separation membranes with a high barrier rate and high flux. Full article
(This article belongs to the Special Issue New Polymeric Materials for Extreme Environments)
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19 pages, 10845 KiB  
Article
Enhanced Dynamic Impact Resistance of 3D-Printed Continuous Optical Fiber-Reinforced Helicoidal Polylactic Acid Composites
Polymers 2023, 15(23), 4599; https://doi.org/10.3390/polym15234599 - 01 Dec 2023
Viewed by 758
Abstract
Characterized by light weight and high strength, composites are widely used as protective materials in dynamic impact loading under extreme conditions, such as high strain rates. Therefore, based on the excellent tensile properties of continuous fiber and the good flexibility and toughness of [...] Read more.
Characterized by light weight and high strength, composites are widely used as protective materials in dynamic impact loading under extreme conditions, such as high strain rates. Therefore, based on the excellent tensile properties of continuous fiber and the good flexibility and toughness of the bionic spiral structure, this study uses a multi-material 3D printer to incorporate continuous fiber, and then modifies the G-CODE file to control the printing path to achieve the production of a continuous fiber-reinforced Polylactic Acid composite helicoidal (spiral angle 60°) structure (COF-HP). Dynamic behavior under high-strain-rate impact experiments have been conducted using the Split Hopkinson Pressure Bar (SHPB). Stress–strain curves, impact energy curves and high-speed camera photographs with different strain rates at 680 s1 and 890 s1 have been analyzed to explore the dynamic process and illustrate the damage evolution. In addition, some detailed simulation models considering the incorporation of continuous optical fiber (COF) and different strain rates have been established and verified for deeper investigations. The results show that the COF does enhance the impact resistance of the laminates. When the porosity is reduced, the maximum stress of the continuous fiber-reinforced composite material is 4~7% higher than that of the pure PLA material. Our findings here expand the application of COF and provide a new method for designing protective materials, which have broad application prospects in the aerospace and automotive industries. Full article
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19 pages, 5941 KiB  
Article
Self-Rotation of Electrothermally Responsive Liquid Crystal Elastomer-Based Turntable in Steady-State Circuits
Polymers 2023, 15(23), 4598; https://doi.org/10.3390/polym15234598 - 01 Dec 2023
Viewed by 618
Abstract
Self-excited motions, characterized by their ability to harness energy from a consistent environment and self-regulate, exhibit significant potential in micro-devices, autonomous robotics, sensor technology, and energy generation. This study introduces an innovative turntable system based on an electrothermally responsive liquid crystal elastomer (LCE). [...] Read more.
Self-excited motions, characterized by their ability to harness energy from a consistent environment and self-regulate, exhibit significant potential in micro-devices, autonomous robotics, sensor technology, and energy generation. This study introduces an innovative turntable system based on an electrothermally responsive liquid crystal elastomer (LCE). This system facilitates self-rotation within a steady-state circuit. Employing an electrothermal LCE model, we have modeled and numerically analyzed the nonlinear dynamics of an LCE-rope within steady-state circuits, utilizing the four-order Runge–Kutta method for calculations. The numerical results reveal the emergence of two distinct motion patterns in the turntable system under steady-state conditions: a self-rotation pattern and a static pattern. The self-rotation is initiated when the system’s absorbed energy surpasses the energy lost due to damping effects. Furthermore, this paper delves into the critical conditions necessary for initiating self-rotation and examines the influence of various key dimensionless parameters on the system’s rotation amplitude and frequency. These parameters include gravitational acceleration, the initial position of the mass ball, elastic stiffness of the LCE and spring, limiting temperature, heating zone angle, thermal shrinkage coefficient, and damping factor. Our computational findings establish that these parameters exert a modulatory impact on the rotation amplitude and period. This research enhances the understanding of self-excited motions and offers promising avenues for applications in energy harvesting, monitoring, soft robotics, medical devices, and micro- and nano-devices. Full article
(This article belongs to the Special Issue Polymeric Materials in Energy Conversion and Storage)
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22 pages, 5186 KiB  
Article
Integrated Hemicellulose Extraction and Papermaking Fiber Production from Agro-Waste Biomass
Polymers 2023, 15(23), 4597; https://doi.org/10.3390/polym15234597 - 01 Dec 2023
Viewed by 632
Abstract
The present study deals with the valorization of corn stalks in an integrated processing strategy targeting two products: extracted hemicelluloses (HC) and papermaking fibers. Preliminary trials were conducted to assess the individual or the combined effects of biomass treatment on the quality of [...] Read more.
The present study deals with the valorization of corn stalks in an integrated processing strategy targeting two products: extracted hemicelluloses (HC) and papermaking fibers. Preliminary trials were conducted to assess the individual or the combined effects of biomass treatment on the quality of the obtained hemicelluloses and papermaking fibers. Depending on the hot alkaline extraction (HAE) conditions, the extracted HC had a xylan content between 44–63%. The xylan removal yield ranged between 19–35%. The recovery of HC from the extraction liquor and final black liquor was significantly affected by process conditions. The experimental approach continued with the study of HAE conditions on the obtained paper’s mechanical properties. The optimization approach considered conserving paper strength properties while achieving an equilibrium with the highest possible HC extraction yield. The optimal values are sodium hydroxide concentration (1%), process time (33 min), and temperature (100 °C). The xylan content in the separated HC sample was ~55%. An extended extraction of HC from the resulting pulp under hot alkaline conditions with 5% NaOH was performed to prove the HC influence on paper strength. The xylan content in HC samples was 65%. The consequence of xylan content reduction in pulp leads to 30–50% mechanical strength loss. Full article
(This article belongs to the Special Issue Advances in Natural Polymers: Extraction Methods and Applications)
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15 pages, 1937 KiB  
Review
Recent Progress in the Field of Intrinsic Self-Healing Elastomers
Polymers 2023, 15(23), 4596; https://doi.org/10.3390/polym15234596 - 01 Dec 2023
Viewed by 747
Abstract
Self-healing elastomers refer to a class of synthetic polymers that possess the unique ability to autonomously repair from internal and external damages. In recent years, significant progress has been made in the field of self-healing elastomers. In particular, intrinsic self-healing elastomers have garnered [...] Read more.
Self-healing elastomers refer to a class of synthetic polymers that possess the unique ability to autonomously repair from internal and external damages. In recent years, significant progress has been made in the field of self-healing elastomers. In particular, intrinsic self-healing elastomers have garnered a great deal of attention. This mini-review outlines recent advancements in the mechanisms, preparation methods, and properties of various intrinsic self-healing elastomers based on non-covalent bond systems, reversible covalent bond systems, and multiple dynamic bond composite systems. We hope that this review will prove valuable to researchers in order to facilitate the development of novel strategies and technologies for preparing high-performance self-healing elastomers for advanced applications. Full article
(This article belongs to the Special Issue Advances in Interfacial Compatibility of Polymer Materials)
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18 pages, 8427 KiB  
Article
Chitosan–Polyvinyl Alcohol Nanocomposites for Regenerative Therapy
Polymers 2023, 15(23), 4595; https://doi.org/10.3390/polym15234595 - 01 Dec 2023
Viewed by 748
Abstract
Tissue accidents provide numerous pathways for pathogens to invade and flourish, causing additional harm to the host tissue while impeding its natural healing and regeneration. Essential oils (EOs) exhibit rapid and effective antimicrobial properties without promoting bacterial resistance. Clove oils (CEO) demonstrate robust [...] Read more.
Tissue accidents provide numerous pathways for pathogens to invade and flourish, causing additional harm to the host tissue while impeding its natural healing and regeneration. Essential oils (EOs) exhibit rapid and effective antimicrobial properties without promoting bacterial resistance. Clove oils (CEO) demonstrate robust antimicrobial activity against different pathogens. Chitosan (CS) is a natural, partially deacetylated polyamine widely recognized for its vast antimicrobial capacity. In this study, we present the synthesis of four membrane formulations utilizing CS, polyvinyl alcohol (PVA), and glycerol (Gly) incorporated with CEO and nanobioglass (n-BGs) for applications in subdermal tissue regeneration. Our analysis of the membranes’ thermal stability and chemical composition provided strong evidence for successfully blending polymers with the entrapment of the essential oil. The incorporation of the CEO in the composite was evidenced by the increase in the intensity of the band of C-O-C in the FTIR; furthermore, the increase in diffraction peaks, as well as the broadening, provide evidence that the introduction of CEO perturbed the crystal structure. The morphological examination conducted using scanning electron microscopy (SEM) revealed that the incorporation of CEO resulted in smooth surfaces, in contrast to the porous morphologies observed with the n-BGs. A histological examination of the implanted membranes demonstrated their biocompatibility and biodegradability, particularly after a 60-day implantation period. The degradation process of more extensive membranes involved connective tissue composed of type III collagen fibers, blood vessels, and inflammatory cells, which supported the reabsorption of the composite membranes, evidencing the material’s biocompatibility. Full article
(This article belongs to the Section Biomacromolecules, Biobased and Biodegradable Polymers)
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16 pages, 1807 KiB  
Article
Facile Coaxial Electrospinning Synthesis of Polyacrylonitrile/Cellulose Acetate Nanofiber Membrane for Oil–Water Separations
Polymers 2023, 15(23), 4594; https://doi.org/10.3390/polym15234594 - 30 Nov 2023
Viewed by 777
Abstract
Oil-contaminated water and industrial oily wastewater discharges have adversely affected aquatic ecosystems and human safety. Membrane separation technology offers a promising solution for effective oil–water separation. Thus, a membrane with high surface area, hydrophilic–oleophobic properties, and stability is a promising candidate. Electrospinning, a [...] Read more.
Oil-contaminated water and industrial oily wastewater discharges have adversely affected aquatic ecosystems and human safety. Membrane separation technology offers a promising solution for effective oil–water separation. Thus, a membrane with high surface area, hydrophilic–oleophobic properties, and stability is a promising candidate. Electrospinning, a straightforward and efficient process, produces highly porous polymer-based membranes with a vast surface area and stability. The main objective of this study is to produce hydrophilic–oleophobic polyacrylonitrile (PAN) and cellulose acetate (CA) nanofibers using core–shell electrospinning. Incorporating CA into the shell of the nanofibers enhances the wettability. The core PAN polymer improves the electrospinning process and contributes to the hydrophilicity–oleophobicity of the produced nanofibers. The PAN/CA nanofibers were characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, X-ray diffraction, and surface-wetting behavior. The resulting PAN/cellulose nanofibers exhibited significantly improved surface-wetting properties, demonstrating super-hydrophilicity and underwater superoleophobicity, making them a promising choice for oil–water separation. Various oils, including gasoline, diesel, toluene, xylene, and benzene, were employed in the preparation of oil–water mixture solutions. The utilization of PAN/CA nanofibers as a substrate proved to be highly efficient, confirming exceptional separation efficiency, remarkable stability, and prolonged durability. The current work introduces an innovative single-step fabrication method of composite nanofibers, specially designed for efficient oil–water separation. This technology exhibits significant promise for deployment in challenging situations, offering excellent reusability and a remarkable separation efficiency of nearly 99.9%. Full article
(This article belongs to the Special Issue Polymeric Membranes: Fabrication, Characterization, and Applications)
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15 pages, 2833 KiB  
Review
Polyelectrolytes: From Seminal Works to the Influence of the Charge Sequence
Polymers 2023, 15(23), 4593; https://doi.org/10.3390/polym15234593 - 30 Nov 2023
Viewed by 645
Abstract
We propose a selected tour of the physics of polyelectrolytes (PE) following the line initiated by de Gennes and coworkers in their seminal 1976 paper. The early works which used uniform charge distributions along the PE backbone achieved tremendous progress and set most [...] Read more.
We propose a selected tour of the physics of polyelectrolytes (PE) following the line initiated by de Gennes and coworkers in their seminal 1976 paper. The early works which used uniform charge distributions along the PE backbone achieved tremendous progress and set most milestones in the field. Recently, the focus has shifted to the role of the charge sequence. Revisited topics include PE complexation and polyampholytes (PA). We develop the example of a random PE in poor solvent forming pearl-necklace structures. It is shown that the pearls typically adopt very asymmetric mass and charge distributions. Individual sequences do not necessarily reflect the ensemble statistics and a rich variety of behaviors emerges (specially for PA). Pearl necklaces are dynamic structures and switch between various types of pearl-necklace structures, as described for both PE and PA. Full article
(This article belongs to the Special Issue Advances in Polyelectrolytes and Polyelectrolyte Complexes)
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11 pages, 7155 KiB  
Article
Curing Behavior of Sucrose with p-Toluenesulfonic Acid
Polymers 2023, 15(23), 4592; https://doi.org/10.3390/polym15234592 - 30 Nov 2023
Viewed by 761
Abstract
With respect to the fossil resources shortage, the development of bio-based wood adhesives is an important research topic in wood science. There has been research on using sucrose for bio-based adhesives. However, a high acid catalyst content and a high hot-pressing temperature are [...] Read more.
With respect to the fossil resources shortage, the development of bio-based wood adhesives is an important research topic in wood science. There has been research on using sucrose for bio-based adhesives. However, a high acid catalyst content and a high hot-pressing temperature are required when manufacturing particleboards. In this study, to explore the possibility of p-toluenesulfonic acid (PTSA) as a promising acid catalyst for sucrose-based adhesives, the curing behavior of sucrose with PTSA (Suc-PTSA) was clarified. The thermal analysis results showed that the thermal properties of sucrose decreased significantly with the addition of PTSA. Based on the results of the insoluble matter rate, the optimal mixture ratio and heating conditions were determined to be 95:5 and 180 °C for 10 min, respectively. According to the results of FT−IR, the heat-treated Suc-PTSA contained furan compounds. In the context of the dynamic viscoelasticity, the onset temperature at which the storage modulus (E′) begins to rise was significantly lower than those of the other sucrose-based adhesives. PTSA has the potential to cure sucrose more efficiently and at lower temperatures than previous sucrose-based adhesives, making it a promising acid catalyst for sucrose. Full article
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11 pages, 2194 KiB  
Article
Recycled PET Composites Reinforced with Stainless Steel Lattice Structures Made by AM
Polymers 2023, 15(23), 4591; https://doi.org/10.3390/polym15234591 - 30 Nov 2023
Viewed by 505
Abstract
Polyethylene terephthalate (PET) recycling is one of the most important environmental issues, assuring a cleaner environment and reducing the carbon footprint of technological products, taking into account the quantities used year by year. The recycling possibilities depend on the quality of the collected [...] Read more.
Polyethylene terephthalate (PET) recycling is one of the most important environmental issues, assuring a cleaner environment and reducing the carbon footprint of technological products, taking into account the quantities used year by year. The recycling possibilities depend on the quality of the collected material and on the targeted product. Current research aims to increase recycling quantities by putting together recycled PET in an innovative way as a filler for the additive manufactured metallic lattice structure. Starting from the structures mentioned above, a new range of composite materials was created: IPC (interpenetrating phase composites), materials with a complex architecture in which a solid phase, the reinforcement, is uniquely combined with the other phase, heated to the temperature of melting. The lattice structure was modeled by the intersection of two rings using Solid Works, which generates the lattice structure, which was further produced by an additive manufacturing technique from 316L stainless steel. The compressive strength shows low values for recycled PET, of about 26 MPa, while the stainless-steel lattice structure has about 47 MPa. Recycled PET molding into the lattice structure increases its compressive strength at 53 MPa. The Young’s moduli are influenced by the recycled PET reinforcement by an increase from about 1400 MPa for the bare lattice structure to about 1750 MPa for the reinforced structure. This sustains the idea that recycled PET improves the composite elastic behavior due to its superior Young’s modulus of about 1570 MPa, acting synergically with the stainless-steel lattice structure. The morphology was investigated with SEM microscopy, revealing the binding ability of recycled PET to the 316L surface, assuring a coherent composite. The failure was also investigated using SEM microscopy, revealing that the microstructural unevenness may act as a local tensor, which promotes the interfacial failure within local de-laminations that weakens the composite, which finally breaks. Full article
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15 pages, 4091 KiB  
Article
Synthesis of Thermo-Responsive Monofunctionalized Diblock Copolymer Worms
Polymers 2023, 15(23), 4590; https://doi.org/10.3390/polym15234590 - 30 Nov 2023
Viewed by 596
Abstract
Poly(glycerol monomethacrylate)-block-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) with worm-like morphology is a typical example of reversible addition–fragmentation chain transfer (RAFT) dispersion polymerized thermo-responsive copolymer via polymerization-induced self-assembly (PISA) in aqueous solution. Chain transfer agents (CTAs) are the key component in controlling RAFT, the structures [...] Read more.
Poly(glycerol monomethacrylate)-block-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) with worm-like morphology is a typical example of reversible addition–fragmentation chain transfer (RAFT) dispersion polymerized thermo-responsive copolymer via polymerization-induced self-assembly (PISA) in aqueous solution. Chain transfer agents (CTAs) are the key component in controlling RAFT, the structures of which determine the end functional groups of the polymer chain. It is therefore of interest to monofunctionalize the polymers via CTA moiety, for bioactive functionality conjugation and in the meantime maintain the precisely controlled morphology of the copolymers and the related property. In this work, a newly designed CTA 5-(2-(tert-butoxycarbonylamino) ethylamino)-2-cyano-5-oxopentan-2-yl benzodithioate (t-Boc CPDB) was synthesized and used for the RAFT polymerization of PGMA45-PHPMA120. Subsequently, PGMA45-PHPMA120 copolymers with primary amine, maleimide, and reduced L-glutathione (a tripeptide) monofunctionalized terminals were synthesized via deprotection and conjugation reactions. These monofunctionalized copolymers maintain worm-like morphology and thermo-responsive property in aqueous solution (10% w/v), as confirmed by the transmission electron microscopy (TEM) images, and the observation of the phase transition behavior in between 4 °C and room temperature (~20 °C), respectively. Summarily, a range of thermo-responsive monofunctionalized PGMA45-PHPMA120 diblock copolymer worms were successfully synthesized, which are expected to offer potential biomedical applications, such as in polymer therapeutics, drug delivery, and diagnostics. Full article
(This article belongs to the Special Issue Protein-Based Biopolymer)
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19 pages, 5065 KiB  
Article
Study on Self-Humidification in PEMFC with Crossed Flow Channels and an Ultra-Thin Membrane
Polymers 2023, 15(23), 4589; https://doi.org/10.3390/polym15234589 - 30 Nov 2023
Viewed by 585
Abstract
In this study, a 3D model of a proton exchange membrane fuel cell (PEMFC) with crossed channels and an ultra-thin membrane is developed to investigate the feasibility of self-humidification; experiments utilizing a PEMFC stack with identical configurations are conducted to validate the simulation [...] Read more.
In this study, a 3D model of a proton exchange membrane fuel cell (PEMFC) with crossed channels and an ultra-thin membrane is developed to investigate the feasibility of self-humidification; experiments utilizing a PEMFC stack with identical configurations are conducted to validate the simulation results and further investigate the effects of various operating conditions (OCs) on self-humidification. The results indicate that the crossed flow channel leads to enhanced uniformity of water distribution, resulting in improved cell performance under low/no humidification conditions. External humidifiers for the anode can be removed since the performance difference is negligible (≤3%) between RHa = 0% and 100%. Self-humidification can be achieved in the stack at 90 °C or below with an appropriate back pressure among 100–200 kPa. As the current density increases, there is a gradual convergence and crossing of the voltage at low RH with that at high RH, and the crossover points are observed at 60–80 °C with suitable pressure when successful self-humidification is achieved. Below the current density of the point, the stack’s performance is inferior at lower RH due to membrane unsaturation, and conversely, the performance is inferior at higher RH due to flooding; this current density decreases with higher pressure and lower temperature. Full article
(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)
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