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Polymers, Volume 13, Issue 21 (November-1 2021) – 251 articles

Cover Story (view full-size image): An important challenge in many mature reservoirs is controlling preferential fluid flows. We proposed the concept of adding both reinforcable and self-healable properties to swellable materials and systematically investigated a novel poly(acrylamide-co-vinyl acetate)/alginate-based interpenetrated gel system (Alg-IPNG). The alginate polymer can take advantage of environmental Ca(Ⅱ) ions in the formation water to reinforce its strength by forming Ca–alginate bonds. Chromium acetate was pre-incorporated into the gel system to provide the delayed crosslinking feature of the swelled gels. View this paper
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Review
Four-Dimensional Printing for Hydrogel: Theoretical Concept, 4D Materials, Shape-Morphing Way, and Future Perspectives
Polymers 2021, 13(21), 3858; https://doi.org/10.3390/polym13213858 - 08 Nov 2021
Viewed by 396
Abstract
The limitations and challenges possessed in static 3D materials necessitated a new era of 4D shape-morphing constructs for wide applications in diverse fields of science. Shape-morphing behavior of 3D constructs over time is 4D design. Four-dimensional printing technology overcomes the static nature of [...] Read more.
The limitations and challenges possessed in static 3D materials necessitated a new era of 4D shape-morphing constructs for wide applications in diverse fields of science. Shape-morphing behavior of 3D constructs over time is 4D design. Four-dimensional printing technology overcomes the static nature of 3D, improves substantial mechanical strength, and instills versatility and clinical and nonclinical functionality under set environmental conditions (physiological and artificial). Four-dimensional printing of hydrogel-forming materials possesses remarkable properties compared to other printing techniques and has emerged as the most established technique for drug delivery, disease diagnosis, tissue engineering, and biomedical application using shape-morphing materials (natural, synthetic, semisynthetic, and functionalized) in response to single or multiple stimuli. In this article, we addressed a fundamental concept of 4D-printing evolution, 4D printing of hydrogel, shape-morphing way, classification, and future challenges. Moreover, the study compiled a comparative analysis of 4D techniques, 4D products, and mechanical perspectives for their functionality and shape-morphing dynamics. Eventually, despite several advantages of 4D technology over 3D technique in hydrogel fabrication, there are still various challenges to address with using current advanced and sophisticated technology for rapid, safe, biocompatible, and clinical transformation from small-scale laboratory (lab-to-bed translation) to commercial scale. Full article
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Article
Functionalization of Graphene Oxide with Polysilicone: Synthesis, Characterization, and Its Flame Retardancy in Epoxy Resin
Polymers 2021, 13(21), 3857; https://doi.org/10.3390/polym13213857 - 08 Nov 2021
Cited by 1 | Viewed by 309
Abstract
A novel polysilicone flame retardant (PMDA) has been synthesized and covalently grafted onto the surfaces of graphene oxide (GO) to obtain GO-PMDA. The chemical structure and morphology of GO-PMDA was characterized and confirmed by the Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectrometer [...] Read more.
A novel polysilicone flame retardant (PMDA) has been synthesized and covalently grafted onto the surfaces of graphene oxide (GO) to obtain GO-PMDA. The chemical structure and morphology of GO-PMDA was characterized and confirmed by the Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectrometer (XPS), atomic force microscope (AFM), and thermogravimetric analysis (TGA). The results of dynamic mechanical analysis (DMA) indicated that the grafting of PMDA improved the dispersion and solubility of GO sheets in the epoxy resin (EP) matrix. The TGA and cone calorimeter measurements showed that compared with the GO, GO-PMDA could significantly improve the thermal stability and flame retardancy of EP. In comparison to pure EP, the peak heat release rate (pHRR) and total heat release (THR) of EP/GO-PMDA were reduced by 30.5% and 10.0% respectively. This greatly enhanced the flame retardancy of EP which was mainly attributed to the synergistic effect of GO-PMDA. Polysilicone can create a stable silica layer on the char surface of EP, which reinforces the barrier effect of graphene. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers)
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Article
Improved Sheet Resistance of Nanofiber-Based Transparent Conducting Electrodes Using Silver Nanowires
Polymers 2021, 13(21), 3856; https://doi.org/10.3390/polym13213856 - 08 Nov 2021
Viewed by 294
Abstract
There is an increased need for research on flexible transparent electrodes (FTEs) because they are critical to next-generation electronic devices, such as wearable computers. In this study, highly conductive transparent conducting electrodes, based on polyvinylidene fluoride (PVDF) nanofiber webs treated with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) [...] Read more.
There is an increased need for research on flexible transparent electrodes (FTEs) because they are critical to next-generation electronic devices, such as wearable computers. In this study, highly conductive transparent conducting electrodes, based on polyvinylidene fluoride (PVDF) nanofiber webs treated with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and silver nanowires (AgNWs), were successfully fabricated. Transparent conducting electrodes (TCEs) were obtained by a brush-painting process using different weight ratios of a AgNWs to PEDOT:PSS solution, and the surface, electrical, optical, and chemical properties, as well as the tensile strength of the samples, were determined. It was found that the electrical conductivity of the samples improved as the AgNW content increased, but the light transmittance decreased. In this work, there was a slight decrease in the optical properties and a considerable increase in the electrical properties due to the hybridization of AgNWs and PEDOT:PSS, compared to using only PEDOT:PSS. When considering both transparency and electrical conductivity, which are essential parameters of TCEs, sample PA2, which was treated by mixing AgNWs and PEDOT:PSS/dimethyl sulfoxide (DMSO) in a ratio of 1:5 (16.67 wt% of AgNWs), was found to be the best sample, with a sheet resistance of 905 Ω/cm2 and light transmittance of 79%. Full article
(This article belongs to the Section Polymer Applications)
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Article
Effect of Thermal Pretreatments on Phosphorylation of Corypha umbraculifera L. Stem Pith Starch: A Comparative Study Using Dry-Heat, Heat-Moisture and Autoclave Treatments
Polymers 2021, 13(21), 3855; https://doi.org/10.3390/polym13213855 - 08 Nov 2021
Viewed by 291
Abstract
Talipot starch, a non-conventional starch source with a high yield (76%) from the stem pith of talipot palm (Corypha umbraculifera L.) was subjected to three different thermal treatments (dry-heat, heat-moisture and autoclave treatments) prior to phosphorylation. Upon dual modification of starch with [...] Read more.
Talipot starch, a non-conventional starch source with a high yield (76%) from the stem pith of talipot palm (Corypha umbraculifera L.) was subjected to three different thermal treatments (dry-heat, heat-moisture and autoclave treatments) prior to phosphorylation. Upon dual modification of starch with thermal treatments and phosphorylation, the phosphorous content and degree of crosslinking significantly increased (p ≤ 0.05) and was confirmed by the increased peak intensity of P=O and P–O–C stretching vibrations compared to phosphorylated talipot starch in the FT-IR spectrum. The highest degree of crosslinking (0.00418) was observed in the autoclave pretreated phosphorylated talipot starch sample. Thermal pretreatment remarkably changed the granule morphology by creating fissures and grooves. The amylose content and relative crystallinity of all phosphorylated talipot starches significantly decreased (p ≤ 0.05) due to crosslinking by the formation of phosphodiester bonds, reducing the swelling power of dual-modified starches. Among all modified starches, dry-heat pretreated phosphorylated starch gel showed an improved light transmittance value of 28.4%, indicating reduced retrogradation tendency. Pasting and rheological properties represented that the thermal pretreated phosphorylated starch formed stronger gels that improved thermal and shear resistance. Autoclave treatment before phosphorylation of talipot starch showed the highest resistant starch content of 48.08%. Full article
(This article belongs to the Special Issue Processing and Applications of Biopolymers)
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Article
Operational Stability, Regenerability, and Thermodynamics Studies on Biogenic Silica/Magnetite/Graphene Oxide Nanocomposite-Activated Candida rugosa Lipase
Polymers 2021, 13(21), 3854; https://doi.org/10.3390/polym13213854 - 08 Nov 2021
Viewed by 441
Abstract
Inorganic biopolymer-based nanocomposites are useful for stabilizing lipases for enhanced catalytic performance and easy separation. Herein, we report the operational stability, regenerability, and thermodynamics studies of the ternary biogenic silica/magnetite/graphene oxide nanocomposite (SiO2/Fe3O4/GO) as a support for [...] Read more.
Inorganic biopolymer-based nanocomposites are useful for stabilizing lipases for enhanced catalytic performance and easy separation. Herein, we report the operational stability, regenerability, and thermodynamics studies of the ternary biogenic silica/magnetite/graphene oxide nanocomposite (SiO2/Fe3O4/GO) as a support for Candida rugosa lipase (CRL). The X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field-electron scanning electron microscopy (FESEM), vibrating sample magnetometry (VSM), and nitrogen adsorption/desorption data on the support and biocatalyst corroborated their successful fabrication. XPS revealed the Fe3O4 adopted Fe2+ and Fe3+ oxidation states, while XRD data of GO yielded a peak at 2θ = 11.67°, with the SiO2/Fe3O4/GO revealing a high surface area (≈261 m2/g). The fourier transform infrared (FTIR) spectra affirmed the successful fabricated supports and catalyst. The half-life and thermodynamic parameters of the superparamagnetic immobilized CRL (CRL/SiO2/Fe3O4/GO) improved over the free CRL. The microwave-regenerated CRL/SiO2/Fe3O4/GO (≈82%) exhibited higher catalytic activity than ultrasonic-regenerated (≈71%) ones. Lower activation (Ea) and higher deactivation energies (Ed) were also noted for the CRL/SiO2/Fe3O4/GO (13.87 kJ/mol, 32.32 kJ/mol) than free CRL (15.26 kJ/mol, 27.60 kJ/mol). A peak at 4.28 min in the gas chromatograph-flame ionization detection (GC-FID) chromatogram of the purified ethyl valerate supported the unique six types of 14 hydrogen atoms of the ester (CAS: 539-82-2) in the proton nuclear magnetic resonance (1H-NMR) data. The results collectively demonstrated the suitability of SiO2/Fe3O4/GO in stabilizing CRL for improved operational stability and thermodynamics and permitted biocatalyst regenerability. Full article
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Article
Dry Fibre Placement: The Influence of Process Parameters on Mechanical Laminate Properties and Infusion Behaviour
Polymers 2021, 13(21), 3853; https://doi.org/10.3390/polym13213853 - 08 Nov 2021
Viewed by 284
Abstract
Within the dry fibre placement (DFP) process, spread and pre-bindered carbon fibre rovings are automatically processed into dry textile preforms using 2-D and 3-D laying systems. The aim was to automate existing hand lay-up processes, reducing the complexity, increasing robustness, and facilitating the [...] Read more.
Within the dry fibre placement (DFP) process, spread and pre-bindered carbon fibre rovings are automatically processed into dry textile preforms using 2-D and 3-D laying systems. The aim was to automate existing hand lay-up processes, reducing the complexity, increasing robustness, and facilitating the handling of the DFP technology. Process reliability, low waste rates, and flexible production are demonstrated. In this publication, the influences of the process parameters, 2 mm wide gaps and the percentage of 90° plies in the laminate, are investigated with regard to the mechanical properties, the permeability, and the infusion times in the preform z-direction (thickness). The effects on stiffness and strength are compared for several use cases. An approach to determine the infusion times as a function of the laminate thickness, the ply structure, and 2 mm wide gaps is demonstrated and analysed using vacuum-assisted process (VAP) infusion tests. The investigations are performed with carbon fibre tows (24 k), a reactive epoxy-based binder system, and a thermoset infusion resin system. Full article
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Article
Mechanical, Fracture, and Microstructural Assessment of Carbon-Fiber-Reinforced Geopolymer Composites Containing Na2O
Polymers 2021, 13(21), 3852; https://doi.org/10.3390/polym13213852 - 08 Nov 2021
Viewed by 293
Abstract
For a sustainable environment, geopolymer (GPO) paste can be used in the construction industry instead of Portland cement. Nowadays, sustainable construction and high-efficacy composites are demanding. Therefore, in the present investigation, the mechanical and microstructural efficacy of carbon-fiber-reinforced fly ash-based GPO with different [...] Read more.
For a sustainable environment, geopolymer (GPO) paste can be used in the construction industry instead of Portland cement. Nowadays, sustainable construction and high-efficacy composites are demanding. Therefore, in the present investigation, the mechanical and microstructural efficacy of carbon-fiber-reinforced fly ash-based GPO with different percentages of nano-sodium dioxide (NS) were studied. The investigated percentages of NS were 0%, 1%, 2%, 3%, and 4%. For all the samples, the carbon fiber content was kept the same at 0.5% by weight. Different percentages of NS for all five fabricated GPO composite pastes were assessed with scanning electron microscopy (SEM). Various mechanical parameters of GPO—the compressive strength, toughness modulus, hardness, toughness indices, impact strength, fracture toughness, flexural strength, and elastic modulus—were evaluated. The results revealed that the use of 3% NS was the most effective for ameliorating the mechanical, microstructural, and fracture behavior of GPO. The use of 3% NS in carbon-fiber-reinforced GPO paste showed the maximum improvements of 22%, 46%, 30%, 40%, 14%, 38.4%, 50.2%, 31%, and 64% for the compressive strength, flexural strength, elastic modulus, toughness modulus, hardness, compressive stiffness, bending stiffness, fracture toughness, and impact strength, respectively. The SEM study showed that the inclusion of NS improved the microstructure and delivered a denser GPO paste by improving the interfacial zones and quickening the polymerization reaction. Full article
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Article
Poly(L-lactic acid) Reinforced with Hydroxyapatite and Tungsten Disulfide Nanotubes
Polymers 2021, 13(21), 3851; https://doi.org/10.3390/polym13213851 - 08 Nov 2021
Viewed by 319
Abstract
Poly(L-lactic acid) (PLLA) is a biocompatible, biodegradable, and semi-crystalline polymer with numerous applications including food packaging, medical implants, stents, tissue engineering scaffolds, etc. Hydroxyapatite (HA) is the major component of natural bone. Conceptually, combining PLLA and HA could produce a bioceramic suitable for [...] Read more.
Poly(L-lactic acid) (PLLA) is a biocompatible, biodegradable, and semi-crystalline polymer with numerous applications including food packaging, medical implants, stents, tissue engineering scaffolds, etc. Hydroxyapatite (HA) is the major component of natural bone. Conceptually, combining PLLA and HA could produce a bioceramic suitable for implants and bone repair. However, this nanocomposite suffers from poor mechanical behavior under tensile strain. In this study, films of PLLA and HA were prepared with small amounts of nontoxic WS2 nanotubes (INT-WS2). The structural aspects of the films were investigated via electron microscopy, X-ray diffraction, Raman microscopy, and infrared absorption spectroscopy. The mechanical properties were evaluated via tensile measurements, micro-hardness tests, and nanoindentation. The thermal properties were investigated via differential scanning calorimetry. The composite films exhibited improved mechanical and thermal properties compared to the films prepared from the PLLA and HA alone, which is advantageous for medical applications. Full article
(This article belongs to the Special Issue Advances in Biocompatible and Biodegradable Polymers)
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Article
Fe, N-Doped Metal Organic Framework Prepared by the Calcination of Iron Chelated Polyimines as the Cathode-Catalyst of Proton Exchange Membrane Fuel Cells
Polymers 2021, 13(21), 3850; https://doi.org/10.3390/polym13213850 - 08 Nov 2021
Viewed by 301
Abstract
Aromatic polyimine (PIM) was prepared through condensation polymerization between p-phenylene diamine and terephthalaldehyde via Schiff reactions. PIM can be physically crosslinked with ferrous ions into gel. The gel-composites, calcined at two consecutive stages, with temperatures ranging from 600 to 1000 °C, became Fe- [...] Read more.
Aromatic polyimine (PIM) was prepared through condensation polymerization between p-phenylene diamine and terephthalaldehyde via Schiff reactions. PIM can be physically crosslinked with ferrous ions into gel. The gel-composites, calcined at two consecutive stages, with temperatures ranging from 600 to 1000 °C, became Fe- and N-doped carbonaceous organic frameworks (FeNC), which demonstrated both graphene- and carbon nanotube-like morphologies and behaved as an electron-conducting medium. After the two-stage calcination, one at 1000 °C in N2 and the other at 900 °C in a mixture of N2 and NH3, an FeNC composite (FeNC-1000A900) was obtained, which demonstrated a significant O2 reduction peak in its current–voltage curve in the O2 atmosphere, and thus, qualified as a catalyst for the oxygen reduction reaction. It also produced a higher reduction current than that of commercial Pt/C in a linear scanning voltage test, and the calculated e-transferred number reached 3.85. The max. power density reached 400 mW·cm−2 for the single cell using FeNC-1000A900 as the cathode catalyst, which was superior to other FeNC catalysts that were calcined at lower temperatures. The FeNC demonstrated only 10% loss of the reduction current at 1600 rpm after 1000 redox cycles, as compared to be 25% loss for the commercial Pt/C catalyst in the durability test. Full article
(This article belongs to the Special Issue Advanced Polymer Nanocomposites II)
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Article
Optimization of the Warpage of Fused Deposition Modeling Parts Using Finite Element Method
Polymers 2021, 13(21), 3849; https://doi.org/10.3390/polym13213849 - 08 Nov 2021
Viewed by 464
Abstract
Fused deposition modeling (FDM) is one of the most affordable and widespread additive manufacturing (AM) technologies. Despite its simplistic implementation, the physics behind this FDM process is very complex and involves rapid heating and cooling of the polymer feedstock. As a result, highly [...] Read more.
Fused deposition modeling (FDM) is one of the most affordable and widespread additive manufacturing (AM) technologies. Despite its simplistic implementation, the physics behind this FDM process is very complex and involves rapid heating and cooling of the polymer feedstock. As a result, highly non-uniform internal stresses develop within the part, which can cause warpage deformation. The severity of the warpage is highly dependent on the process parameters involved, and therefore, currently extensive experimental studies are ongoing to assess their influence on the final accuracy of the part. In this study, a thermomechanical Finite Element model of the 3D printing process was developed using ANSYS. This model was compared against experimental results and several other analytical models available in the literature. The developed Finite Element Analysis (FEA) model demonstrated a good qualitative and quantitative correlation with the experimental results. An L9 orthogonal array, from Taguchi Design of Experiments, was used for the optimization of the warpage based on experimental results and numerical simulations. The optimum process parameters were identified for each objective and parts were printed using these process parameters. Both parts showed an approximately equal warpage value of 320 μm, which was the lowest among all 10 runs of the L9 array. Additionally, this model is extended to predict the warpage of FDM printed multi-material parts. The relative percentage error between the numerical and experimental warpage results for alternating and sandwich specimens are found to be 1.4% and 9.5%, respectively. Full article
(This article belongs to the Special Issue Advanced Polymer Simulation and Processing)
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Article
Interfacial Behavior of Solid- and Liquid-like Polyelectrolyte Complexes as a Function of Charge Stoichiometry
Polymers 2021, 13(21), 3848; https://doi.org/10.3390/polym13213848 - 07 Nov 2021
Viewed by 404
Abstract
We systematically investigate in this work the surface activity of polyelectrolyte complex (PECs) suspensions as a function of the molar charge ratio Z (= [-]/[+]) from two model systems: the weakly and strongly interacting poly (diallyldimethylammonium chloride)/poly (acrylic acid sodium salt) (PDADMAC/PANa) and [...] Read more.
We systematically investigate in this work the surface activity of polyelectrolyte complex (PECs) suspensions as a function of the molar charge ratio Z (= [-]/[+]) from two model systems: the weakly and strongly interacting poly (diallyldimethylammonium chloride)/poly (acrylic acid sodium salt) (PDADMAC/PANa) and poly (diallyldimethylammonium chloride)/poly (sodium 4- styrenesulfonate) (PDADMAC/PSSNa) pairs, respectively. For both systems, the PEC surface tension decreases as the system approaches charge stoichiometry (Z = 1) whenever the complexation occurs in the presence of excess PDADMAC (Z < 1) or excess polyanion (Z > 1) consistent with an increased level of charge neutralization of PEs forming increasingly hydrophobic and neutral surface-active species. The behavior at stoichiometry (Z = 1) is also particularly informative about the physical nature of the complexes. The PDADMAC/PANa system undergoes a liquid–liquid phase transition through the formation of coacervate microdroplets in equilibrium with macroions remaining in solution. In the PDADMAC/PSSNa system, the surface tension of the supernatant was close to that of pure water, suggesting that the PSSNa-based complexes have completely sedimented, consistent with a complete liquid–solid phase separation of an out-of-equilibrium system. Besides, the high sensitivity of surface tension measurements, which can detect the presence of trace amounts of aggregates and other precursors in the supernatant, allows for very accurate determination of the exact charge stoichiometry of the complexes. Finally, the very low water/water interfacial tension that develops between the dilute phase and the denser coacervate phase in the PDADAMAC/PANa system was measured using the generalized Young–Laplace method to complete the full characterization of both systems. The overall study showed that simple surface tension measurements can be a very sensitive tool to characterize, discriminate, and better understand the formation mechanism of the different structures encountered during the formation of PECs. Full article
(This article belongs to the Special Issue Advances in Polyelectrolyte Complexes)
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Article
Lignin Biopolymer for the Synthesis of Iron Nanoparticles and the Composite Applied for the Removal of Methylene Blue
Polymers 2021, 13(21), 3847; https://doi.org/10.3390/polym13213847 - 07 Nov 2021
Viewed by 403
Abstract
In the current study, lignin, an abundant natural polymer, was dissolved in ethylene glycol and acidic H2O to form nanoscale lignin. Then, zero-valent iron (ZVI) nanoparticles were synthesized in nanoscale lignin, producing a nZVI/n-lignin composite, via the borohydride reduction method. The [...] Read more.
In the current study, lignin, an abundant natural polymer, was dissolved in ethylene glycol and acidic H2O to form nanoscale lignin. Then, zero-valent iron (ZVI) nanoparticles were synthesized in nanoscale lignin, producing a nZVI/n-lignin composite, via the borohydride reduction method. The use of nZVI/n-lignin for environmental remediation was tested by the removal of methylene blue in aqueous solutions at room temperature. The nZVI/n-lignin composite achieved a higher methylene blue removal ratio than that achieved by traditional nZVIs. Moreover, its excellent dispersibility in water and stability against oxidation in the air were observed. The functions of the nanoscale lignin in the composite material are (1) prevention of further growth and aggregation of the nZVI nanoparticles, (2) protection of nZVI from serious oxidation by H2O/O2, and (3) allowing better dispersibility of nZVI in aqueous solutions. These three functions are important for the field applications of nZVI/n-lignin, namely, to travel long distances before making contact with environmental pollutants. The present method for producing nZVI/n-lignin is straightforward, and the combination of nZVI and lignin is an efficient and environmentally friendly material for environmental applications. Full article
(This article belongs to the Special Issue Functional Natural-Based Polymers)
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Article
Numerical Simulation and Experimental Validation of Hybrid Injection Molded Short and Continuous Fiber-Reinforced Thermoplastic Composites
Polymers 2021, 13(21), 3846; https://doi.org/10.3390/polym13213846 - 07 Nov 2021
Viewed by 396
Abstract
In-situ thermoforming and overmolding of continuous fiber-reinforced thermoplastic composites by hybrid injection molding enables the mass production of thermoplastic lightweight structures with a complex geometry. In this study, the anisotropic mechanical behavior of such hybrid injection molded short and continuous fiber-reinforced thermoplastics and [...] Read more.
In-situ thermoforming and overmolding of continuous fiber-reinforced thermoplastic composites by hybrid injection molding enables the mass production of thermoplastic lightweight structures with a complex geometry. In this study, the anisotropic mechanical behavior of such hybrid injection molded short and continuous fiber-reinforced thermoplastics and the numerical simulation of the resulting mechanical properties under flexural loading were investigated. For this, the influence of the volume flow rate between 25 and 100 cm3/s during injection molding of a PP/GF30 short fiber-reinforced overmolding material was studied and showed a strong effect on the fiber orientation but not on the fiber length, as investigated by computer tomography and fiber length analysis. Thus, the resulting anisotropies of the stiffness and strength as well as the strain hardening investigated by tensile testing were considered when the mechanical behavior of a hybrid test structure of short and continuous fiber-reinforced thermoplastic composites was predicted by numerical simulations. For this, a PP/GF60 and PP/GF30 hybrid injection molded test structure was investigated by a numerical workflow with implemented injection molding simulation data. In result, the prediction of the mechanical behavior of the hybrid test structure under flexural loading by numerical simulation was significantly improved, leading to a reduction of the deviation of the numerically predicted and experimentally measured flexural strength from 21% to 9% in comparison to the isotropic material model without the implementation of the injection molding data. Full article
(This article belongs to the Special Issue Advanced Polymer Simulation and Processing)
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Article
Recycling of Plastics from Cable Waste from Automotive Industry in Poland as an Approach to the Circular Economy
Polymers 2021, 13(21), 3845; https://doi.org/10.3390/polym13213845 - 07 Nov 2021
Viewed by 547
Abstract
This paper presents the contemporary problems of polymer waste recycling, mainly recycling cables from end-of-life vehicles. The authors developed a new material based on mixed polymer waste (ASR) modified with a ductile polymer, mainly recycled low-density polyethylene (rLDPE), to produce moisture-resistant boards with [...] Read more.
This paper presents the contemporary problems of polymer waste recycling, mainly recycling cables from end-of-life vehicles. The authors developed a new material based on mixed polymer waste (ASR) modified with a ductile polymer, mainly recycled low-density polyethylene (rLDPE), to produce moisture-resistant boards with beneficial mechanical properties. The ASR-based compositions without and with homogenization process—including physical, chemical, and shear-assisted compatibilization—were successfully applied and verified by evaluating final recycled product properties. The results showed that recycled polyethylene (rLDPE) was effective as a modifier increasing tensile modulus and flexural strength compare to an ASR mixture. It was found that the adding 5 wt % of polyethylene-grafted maleic anhydride (PE-g-MAH) as a compatibilizer to the ASR mixture significantly increases the homogenization of the components in the ASR matrix. The optimal solution for management cable waste is the manufacture of ASR composites with homogenization using an internal mixer the adding 20 wt % of rLDPE and 5 wt % of PE-g-MAH to the mixed plastics cable waste. The results obtained demonstrate that the hot-pressing with the pre-blending with rLDPE and compatibilizer of the ASR based waste provides a high gain in mechanical and usage properties, enabling the circular economy of plastics from automotive cables. Full article
(This article belongs to the Special Issue Advances in Plastic Materials Recycling and Reuse)
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Article
Effects of Water and Alkaline Solution on Durability of Carbon-Glass Hybrid Fiber Reinforced Polymer Bars
Polymers 2021, 13(21), 3844; https://doi.org/10.3390/polym13213844 - 07 Nov 2021
Viewed by 349
Abstract
The glass fiber reacts with the hydroxyl owing to the concrete pore solution. A thin coat of carbon fiber wraps around the internal GFRP bars to improve the durability of internal GFRP bars in harsh environments. This paper investigates the effect of a [...] Read more.
The glass fiber reacts with the hydroxyl owing to the concrete pore solution. A thin coat of carbon fiber wraps around the internal GFRP bars to improve the durability of internal GFRP bars in harsh environments. This paper investigates the effect of a thin carbon fiber coat on the durability of the carbon–glass hybrid fiber reinforced polymer bars (HFRP bars) in water, and compares the performance of FRP bars in alkaline solution. To this end, the water absorption behavior, interlaminar shear strength of both the GFRP bars and the HFRP bars was characterized in water and alkaline solution. The results indicate that the diffusivity coefficient of the carbon fiber coat is higher than that of internal GFRP in water. Compared to the GFRP bars in water, the HFRP bars have a higher diffusivity coefficient and saturation water absorption. It caused that the interlaminar shear strength of the HFRP bars aged in water at a temperature of 60 °C for 140 days decreases more markedly than that of the GFRP bars aged under similar conditions. Finally, it was proved that the thin carbon fiber coat does not slow the deterioration of the GFRP bars in water, while the carbon fiber coat significantly improves the retention of the interlaminar shear strength of the HFRP bars in the alkaline solution owing to the prevention of internal glass fiber reactivated by alkali ions. Full article
(This article belongs to the Section Polymer Processing and Engineering)
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Article
N,N′-Bis(3-methylphenyl)-N,N′-dyphenylbenzidine Based Distributed Feedback Lasers with Holographically Fabricated Polymeric Resonators
Polymers 2021, 13(21), 3843; https://doi.org/10.3390/polym13213843 - 06 Nov 2021
Viewed by 303
Abstract
The molecule N,N′-bis(3-methylphenyl)-N,N′-dyphenylbenzidine (TPD) has been widely used in optoelectronic applications, mainly for its hole-transporting properties, but also for its capability to emit blue light and amplified spontaneous emission, which is important for the development of organic lasers. Here, we [...] Read more.
The molecule N,N′-bis(3-methylphenyl)-N,N′-dyphenylbenzidine (TPD) has been widely used in optoelectronic applications, mainly for its hole-transporting properties, but also for its capability to emit blue light and amplified spontaneous emission, which is important for the development of organic lasers. Here, we report deep-blue-emitting distributed feedback (DFB) lasers based on TPD dispersed in polystyrene (PS), as active media, and dichromated gelatin layers with holographically engraved relief gratings, as laser resonators. The effect of the device architecture (with the resonator located below or on top of the active layer) is investigated with a dye (TPD) that can be doped into PS at higher rates (up to 60 wt%), than with previously used dyes (<5 wt%). This has enabled changing the index contrast between film and resonator, which has an important effect on the laser performance. With regards to thresholds, both architectures behave similarly for TPD concentrations above 20 wt%, while for lower concentrations, top-layer resonator devices show lower values (around half). Remarkably, the operational durability of top-layer resonator devices is larger (in a factor of around 2), independently of the TPD concentration. This is a consequence of the protection offered by the resonator against dye photo-oxidation when the device is illuminated with pulsed UV light. Full article
(This article belongs to the Special Issue Photopolymer Materials for Optical Applications)
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Effect of Fibre Surface Treatment and Nanofiller Addition on the Mechanical Properties of Flax/PLA Fibre Reinforced Epoxy Hybrid Nanocomposite
Polymers 2021, 13(21), 3842; https://doi.org/10.3390/polym13213842 - 06 Nov 2021
Viewed by 346
Abstract
Natural fibre-based materials are gaining popularity in the composites industry, particularly for automotive structural and semi-structural applications, considering the growing interest and awareness towards sustainable product design. Surface treatment and nanofiller addition have become one of the most important aspects of improving natural [...] Read more.
Natural fibre-based materials are gaining popularity in the composites industry, particularly for automotive structural and semi-structural applications, considering the growing interest and awareness towards sustainable product design. Surface treatment and nanofiller addition have become one of the most important aspects of improving natural fibre reinforced polymer composite performance. The novelty of this work is to examine the combined effect of fibre surface treatment with Alumina (Al2O3) and Magnesia (MgO) nanofillers on the mechanical (tensile, flexural, and impact) behaviour of biotex flax/PLA fibre reinforced epoxy hybrid nanocomposites. Al2O3 and MgO with a particle size of 50 nm were added in various weight proportions to the epoxy and flax/PLA fibre, and the composite laminates were formed using the vacuum bagging technique. The surface treatment of one set of fibres with a 5% NaOH solution was investigated for its effect on mechanical performance. The results indicate that the surface-treated reinforcement showed superior tensile, flexural, and impact properties compared to the untreated reinforcement. The addition of 3 wt. % nanofiller resulted in the best mechanical properties. SEM morphological images demonstrate various defects, including interfacial behaviour, fibre breakage, fibre pullout, voids, cracks, and agglomeration. Full article
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Article
Passive Fire Protection of Taeda pine Wood by Using Starch-Based Surface Coatings
Polymers 2021, 13(21), 3841; https://doi.org/10.3390/polym13213841 - 06 Nov 2021
Viewed by 336
Abstract
The present paper reports the preliminary results relating to the development, subsequent application, and testing of environmentally benign starch-based formulations for passive fire protection of wood substrates. This study evaluated the effectiveness of starch colloid coatings applied onto the wood surface with a [...] Read more.
The present paper reports the preliminary results relating to the development, subsequent application, and testing of environmentally benign starch-based formulations for passive fire protection of wood substrates. This study evaluated the effectiveness of starch colloid coatings applied onto the wood surface with a view to improving its performance when exposed to the external heat flux (35 kW/m2) during cone calorimetric tests. The formulations were prepared from aqueous colloid solutions of either starch alone, or in combination with inorganic salts, such as: sodium carbonate, Na2CO3, potassium carbonate, K2CO3, and diammonium hydrogen phosphate, (NH4)2HPO4. The fire performance of Taeda pine wood samples, where their top surfaces were treated with these formulations, was compared with the control sample. The thermal and combustion characteristics of the tested samples were determined with the aid of thermo-gravimetric analysis (TGA), bomb and cone calorimetric techniques, and a steady state tube furnace coupled to an FT-IR spectrometer. A significant boost of fire protection was observed when starch formulations with added inorganic salts were applied onto the wood surfaces, compared with the control sample. For example, the presence of K2CO3 in starch colloid solutions resulted in a notable delay of the ignition and exhibited a reduction in the heat release parameters in comparison with the untreated wood substrate. Full article
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Article
Prediction of Strength Properties of Filling Packets in Selected Cooling Towers
Polymers 2021, 13(21), 3840; https://doi.org/10.3390/polym13213840 - 06 Nov 2021
Viewed by 264
Abstract
The operating conditions of thermoplastic polymer materials determine the changes in their functional properties. Accelerated aging tests do not give a full picture of the changes taking place in the polymer material, hence the conclusions drawn on the basis of exposure of these [...] Read more.
The operating conditions of thermoplastic polymer materials determine the changes in their functional properties. Accelerated aging tests do not give a full picture of the changes taking place in the polymer material, hence the conclusions drawn on the basis of exposure of these materials to damaging effects in real operating conditions are particularly important. The aim of the study was to determine the degree of degradation of polypropylene films used in the drainage blocks of cooling towers in a selected power plant in the Silesian voivodship, which allowed forecasting the operating time over a period of 10 years. A number of 600 mm high drip blocks were tested, on which 300 mm high blocks were mounted. The tests were carried out on films subjected to the aging process in the conditions of continuous operation of a cooling tower (almost 100% humidity). The water flow is accompanied by heat exchange, the side effect of which is deposits formation on the surface of the drip blocks, negatively affecting the operation of the cooling tower. The degree of degradation resulting from operational aging was assessed on the basis of the strength properties determined in the static tensile test, thermogravimetric analysis and FTIR spectra. Changes in properties during operation were determined on the basis of the obtained results of the strength tests, which were compared with the tensile strength and elongation at break of reference samples (not subjected to aging in the operating conditions of cooling tower drip blocks). The obtained results were related to the properties of the reference samples not subjected to the degradation process. Based on the collected data, the tensile strength and deformation at fracture after a 10-year service life were predicted. Full article
(This article belongs to the Special Issue Fatigue and Aging Degradation of Polymeric Materials)
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Article
Assessment of the Antigenotoxic Effects of Alginate and ZnO/Alginate–Nanocomposites Extracted from Brown Alga Fucus vesiculosus in Mice
Polymers 2021, 13(21), 3839; https://doi.org/10.3390/polym13213839 - 06 Nov 2021
Viewed by 268
Abstract
Mitomycin C (MMC) is an alkylating chemotherapy drug that could induce DNA damage and genetic alteration. It has been used as a model mutagen for in vivo and in vitro studies. The current study aimed to evaluate the protective role of Zinc oxide [...] Read more.
Mitomycin C (MMC) is an alkylating chemotherapy drug that could induce DNA damage and genetic alteration. It has been used as a model mutagen for in vivo and in vitro studies. The current study aimed to evaluate the protective role of Zinc oxide alginate–nanocomposites (ZnO-Alg/NCMs) against MMC–induced genotoxicity in mice. Animals were treated as follows: the control group, the groups treated with Algin (400 mg/kg b.w), the groups treated with ZnO-Alg/NCMs (400 mg/kg b.w), the group treated with MMC, and the groups treated with MMC plus Algin or ZnO-Alg/NCMs. Pre-treatment with Algin and ZnO-Alg/NCMs was repeated for one or seven days. Zinc oxide alginate-nanocomposites (ZnO-Alg/NCMs) were synthesized with the aim of incorporating the intrinsic properties of their constituents as an antigenotoxic substance. In this study, alginate was extracted from the brown marine alga Fucus vesiculosus, Zinc oxide nanoparticles were synthesized by using water extract of the same alga, and loaded in alginate to synthesize ZnO-Alg/NCMs. ZnO-NPs and ZnO-Alg/NCMs were characterized by TEM, SEM, EDX, and Zeta potential. The obtained results confirmed that by TEM and SEM, ZnO-NPs are rod shaped which modified, when loaded in alginate matrix, into spherical shape. The physical stability of ZnO-Alg/NCMs was reported to be higher than ZnO-NPs due to the presence of more negative charges on ZnO-Alg/NCMs. The EDX analysis indicated that the amount of zinc was higher in ZnO-NPs than ZnO-Alg/NCMs. The in vivo results showed that treatment with MMC induced genotoxic disturbances. The combined treatment with Algin and ZnO-Alg/NCMs succeeded in inducing significant protection against MMC. It could be concluded that ZnO-Algin/NCMs is a promising candidate to protect against MMC–induced genotoxicity. Full article
(This article belongs to the Topic Sustainable Polymer Technologies)
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Article
Printable Resin Modified by Grafted Silver Nanoparticles for Preparation of Antifouling Microstructures with Antibacterial Effect
Polymers 2021, 13(21), 3838; https://doi.org/10.3390/polym13213838 - 06 Nov 2021
Viewed by 311
Abstract
The usage of three-dimensional (3D) printed materials in many bioapplications has been one of the fastest-growing sectors in the nanobiomaterial industry in the last couple of years. In this work, we present a chemical approach for grafting silver nanoparticles (AgNPs) into a resin [...] Read more.
The usage of three-dimensional (3D) printed materials in many bioapplications has been one of the fastest-growing sectors in the nanobiomaterial industry in the last couple of years. In this work, we present a chemical approach for grafting silver nanoparticles (AgNPs) into a resin matrix, which is convenient for 3D printing. In this way, the samples can be prepared and are able to release silver ions (Ag+) with excellent antibacterial effect against bacterial strains of E. coli and S. epidermidis. By the proposed process, the AgNPs are perfectly mixed and involved in the polymerization process and their distribution in the matrix is homogenous. It was also demonstrated that this approach does not affect the printing resolution and the resin is therefore suitable for the construction of microstructures enabling controlled silver ion release and antifouling properties. At the same time the physical properties of the material, such as viscosity and elasticity modulus are preserved. The described approach can be used for the fabrication of facile, low-cost 3D printed resin with antifouling-antibacterial properties with the possibility to control the release of Ag+ through microstructuring. Full article
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Article
Preclinical Evaluation of Polymeric Nanocomposite Containing Pregabalin for Sustained Release as Potential Therapy for Neuropathic Pain
Polymers 2021, 13(21), 3837; https://doi.org/10.3390/polym13213837 - 06 Nov 2021
Viewed by 461
Abstract
This study offers a novel oral pregabalin (PG)-loaded drug delivery system based on chitosan and hypromellose phthalate-based polymeric nanocomposite in order to treat neuropathic pain (PG-PN). PG-PN has a particle size of 432 ± 20 nm, a polydispersity index of 0.238 ± 0.001, [...] Read more.
This study offers a novel oral pregabalin (PG)-loaded drug delivery system based on chitosan and hypromellose phthalate-based polymeric nanocomposite in order to treat neuropathic pain (PG-PN). PG-PN has a particle size of 432 ± 20 nm, a polydispersity index of 0.238 ± 0.001, a zeta potential of +19.0 ± 0.9 mV, a pH of 5.7 ± 0.06, and a spherical shape. Thermal and infrared spectroscopy confirmed nanocomposite generation. PG-PN pharmacokinetics was studied after a single oral dose in male Wistar rats. PG-PN showed greater distribution and clearance than free PG. The antinociceptive effect of PG-PN in neuropathic pain rats was tested by using the chronic constriction injury model. The parameter investigated was the mechanical nociceptive threshold measured by the von Frey filaments test; PG-PN showed a longer antinociceptive effect than free PG. The rota-rod and barbiturate sleep induction procedures were used to determine adverse effects; the criteria included motor deficit and sedative effects. PG-PN and free PG had plenty of motors. PG-PN exhibited a less sedative effect than free PG. By prolonging the antinociceptive effect and decreasing the unfavorable effects, polymeric nanocomposites with pregabalin have shown promise in treating neuropathic pain. Full article
(This article belongs to the Special Issue Drug-Loaded Colloidal Systems in Nanomedicine II)
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Article
SEBS as an Effective Nucleating Agent for Polystyrene Foams
Polymers 2021, 13(21), 3836; https://doi.org/10.3390/polym13213836 - 06 Nov 2021
Viewed by 331
Abstract
Different percentages of an elastomeric phase of styrene-ethylene-butylene-styrene (SEBS) were added to a polystyrene (PS) matrix to evaluate its nucleating effect in PS foams. It has been demonstrated that a minimum quantity of SEBS produces a high nucleation effect on the cellular materials [...] Read more.
Different percentages of an elastomeric phase of styrene-ethylene-butylene-styrene (SEBS) were added to a polystyrene (PS) matrix to evaluate its nucleating effect in PS foams. It has been demonstrated that a minimum quantity of SEBS produces a high nucleation effect on the cellular materials that are produced. In particular, the results show that by adding 2% of SEBS, it is possible to reduce the cell size by 10 times while maintaining the density and open cell content of the foamed materials. The influence of this polymeric phase on the glass transition temperature (Tg) and the shear and extensional rheological properties has been studied to understand the foaming behavior. The results indicate a slight increase in the Tg and a decrease of the shear viscosity, extensional viscosity, and strain hardening coefficient as the percentage of SEBS increases. Consequently, an increase in the density and a deterioration of the cellular structure is detected for SEBS amounts higher than 3%. Full article
(This article belongs to the Section Polymer Processing and Engineering)
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Article
Polyvinyl Alcohol Polymer Functionalized Graphene Oxide Decorated with Gadolinium Oxide for Sequestration of Radionuclides from Aqueous Medium: Characterization, Mechanism, and Environmental Feasibility Studies
Polymers 2021, 13(21), 3835; https://doi.org/10.3390/polym13213835 - 06 Nov 2021
Viewed by 385
Abstract
Uranium (U(VI)) and thorium (Th(IV)) ions produced by the nuclear and mining industries cause water pollution, thereby harming the environment and human health. In this study, gadolinium oxide-decorated polyvinyl alcohol-graphene oxide composite (PGO–Gd) was developed using a simple hydrothermal process to treat U(VI) [...] Read more.
Uranium (U(VI)) and thorium (Th(IV)) ions produced by the nuclear and mining industries cause water pollution, thereby harming the environment and human health. In this study, gadolinium oxide-decorated polyvinyl alcohol-graphene oxide composite (PGO–Gd) was developed using a simple hydrothermal process to treat U(VI) and Th(IV) ions in water. The developed material was structurally characterized by highly advanced spectroscopy and microscopy techniques. The effects of pH, equilibration time and temperature on both radionuclides (U(VI) and Th(IV)) adsorption by PGO–Gd were examined. The PGO–Gd composite adsorbed both metal ions satisfactorily, with adsorption capacities of 427.50 and 455.0 mg g−1 at pH 4.0, respectively. The adsorption properties of both metal ions were found to be compatible with the Langmuir and pseudo–second-order kinetic models. Additionally, based on the thermodynamic characteristics, the adsorption was endothermic and spontaneous. Furthermore, the environmental viability of PGO–Gd and its application was demonstrated by studying its reusability in treating spiked surface water. PGO–Gd shows promise as an adsorbent in effectively removing both radionuclides from aqueous solutions. Full article
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Review
Possibility Routes for Textile Recycling Technology
Polymers 2021, 13(21), 3834; https://doi.org/10.3390/polym13213834 - 06 Nov 2021
Viewed by 810
Abstract
The fashion industry contributes to a significant environmental issue due to the increasing production and needs of the industry. The proactive efforts toward developing a more sustainable process via textile recycling has become the preferable solution. This urgent and important need to develop [...] Read more.
The fashion industry contributes to a significant environmental issue due to the increasing production and needs of the industry. The proactive efforts toward developing a more sustainable process via textile recycling has become the preferable solution. This urgent and important need to develop cheap and efficient recycling methods for textile waste has led to the research community’s development of various recycling methods. The textile waste recycling process can be categorized into chemical and mechanical recycling methods. This paper provides an overview of the state of the art regarding different types of textile recycling technologies along with their current challenges and limitations. The critical parameters determining recycling performance are summarized and discussed and focus on the current challenges in mechanical and chemical recycling (pyrolysis, enzymatic hydrolysis, hydrothermal, ammonolysis, and glycolysis). Textile waste has been demonstrated to be re-spun into yarn (re-woven or knitted) by spinning carded yarn and mixed shoddy through mechanical recycling. On the other hand, it is difficult to recycle some textiles by means of enzymatic hydrolysis; high product yield has been shown under mild temperatures. Furthermore, the emergence of existing technology such as the internet of things (IoT) being implemented to enable efficient textile waste sorting and identification is also discussed. Moreover, we provide an outlook as to upcoming technological developments that will contribute to facilitating the circular economy, allowing for a more sustainable textile recycling process. Full article
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Article
Development of Natural Polysaccharide–Based Nanoparticles of Berberine to Enhance Oral Bioavailability: Formulation, Optimization, Ex Vivo, and In Vivo Assessment
Polymers 2021, 13(21), 3833; https://doi.org/10.3390/polym13213833 - 05 Nov 2021
Viewed by 438
Abstract
The phytogenous alkaloid berberine (BBR) has become a potential drug for the treatment of diabetes, hyperlipidemia, and cancer. However, its therapeutic potential is limited because ofpoor intestinal absorption due to its efflux by the P-gp expressed in the intestinal lumen. Therefore, we [...] Read more.
The phytogenous alkaloid berberine (BBR) has become a potential drug for the treatment of diabetes, hyperlipidemia, and cancer. However, its therapeutic potential is limited because ofpoor intestinal absorption due to its efflux by the P-gp expressed in the intestinal lumen. Therefore, we aimed to design and fabricate a nanoparticulate system for delivery of BBR employing naturally derived biodegradable and biocompatible polymers, mainly chitosan and alginate, to enhance the oral bioavailability of BBR. A chitosan-alginate nanoparticle system loaded with BBR (BNPs) was formulated by ionic gelation method and was optimized by employing a three-factor, three-level Box-Behnken statistical design. BNPs were characterized for various physicochemical properties, ex vivo, and in vivo evaluations. The optimized BNPs were found to be 202.2 ± 4.9 nm in size, with 0.236 ± 0.02 of polydispersity index, zeta potential −14.8 ± 1.1 mV, and entrapment efficiency of 85.69 ± 2.6%. BNPs showed amorphous nature with no prominent peak in differential scanning calorimetry (DSC) investigation. Similarly, fourier-transform infrared spectroscopy (FTIR) studies did not reveal any interaction between BBR and excipients used. The drug release followed Higuchi kinetics, since these plots demonstrated the highest linearity (R2 = 0.9636), and the mechanism of release was determined to be anomalous or non-Fickian in nature. An ex-vivo gut permeation study showed that BNPs were better internalized into the cells and more highly permeated through the intestine. Furthermore, in vivo pharmacokinetic analysis in female Wistar rats showed a 4.10−fold increase in the oral bioavailability of BBR from BNPs as compared to BBR suspension. With these findings, we have gained new insight into the effective delivery of poorly soluble and permeable drugs via a chitosan-alginate nanoparticle system to improve the therapeutic performance of an oral nanomedicine. Full article
(This article belongs to the Special Issue Natural Polymers in Drug Controlled Release Systems)
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Article
Influence of Ionomer Content in the Catalytic Layer of MEAs Based on Aquivion® Ionomer
Polymers 2021, 13(21), 3832; https://doi.org/10.3390/polym13213832 - 05 Nov 2021
Viewed by 267
Abstract
Perfluorinated sulfonic acid (PFSA) polymers such as Nafion® are widely used for both electrolyte membranes and ionomers in the catalytic layer of membrane-electrode assemblies (MEAs) because of their high protonic conductivity, σH, as well as chemical and thermal stability. The [...] Read more.
Perfluorinated sulfonic acid (PFSA) polymers such as Nafion® are widely used for both electrolyte membranes and ionomers in the catalytic layer of membrane-electrode assemblies (MEAs) because of their high protonic conductivity, σH, as well as chemical and thermal stability. The use of PFSA polymers with shorter side chains and lower equivalent weight (EW) than Nafion®, such as Aquivion® PFSA ionomers, is a valid approach to improve fuel cell performance and stability under drastic operative conditions such as those related to automotive applications. In this context, it is necessary to optimize the composition of the catalytic ink, according to the different ionomer characteristics. In this work, the influence of the ionomer amount in the catalytic layer was studied, considering the dispersing agent used to prepare the electrode (water or ethanol). Electrochemical studies were carried out in a single cell in the presence of H2-air, at intermediate temperatures (80–95 °C), low pressure, and reduced humidity ((50% RH). %). The best fuel cell performance was found for 26 wt.% Aquivion® at the electrodes using ethanol for the ink preparation, associated to a maximum catalyst utilization. Full article
(This article belongs to the Section Polymer Membranes and Films)
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Communication
Functional or Nonfunctional Cusps Preservation for Molars Restored with Indirect Composite or Glass-Ceramic Onlays: 3D FEA Study
Polymers 2021, 13(21), 3831; https://doi.org/10.3390/polym13213831 - 05 Nov 2021
Viewed by 420
Abstract
Evidence regarding the effect of the onlay preparation design for different CAD/CAM restorative materials considering the preservation of cusps is lacking. Molars were 3D-modeled in four preparation designs for onlay restoration: traditional design with functional cusp coverage (TFC), non-retentive design with functional cusp [...] Read more.
Evidence regarding the effect of the onlay preparation design for different CAD/CAM restorative materials considering the preservation of cusps is lacking. Molars were 3D-modeled in four preparation designs for onlay restoration: traditional design with functional cusp coverage (TFC), non-retentive design with functional cusp coverage (NFC), traditional design with non-functional cusp coverage (TNFC) and non-retentive design with non-functional cusp coverage (NNFC). The restorations were simulated with two CAD/CAM restorative materials: LD—lithium disilicate (IPS e.max CAD) and RC—resin composite (GrandioBloc). A 100 N axial load was applied to the occlusal surface, simulating the centric contact point. Von Mises (VM) and maximum principal (Pmax) stress were evaluated for restorations, cement layer and dental substrate. The non-retentive preparation design reduced the stress concentration in the tooth structure in comparison to the conventional retentive design. For LD onlays, the stress distribution on the restoration intaglio surface showed that the preparation design, as well as the prepared cusp, influenced the stress magnitude. The non-retentive preparation design provided better load distribution in both restorative materials and more advantageous for molar structure. The resin composite restoration on thenon-functional cusp is recommended when the functional cusp is preserved in order to associate conservative dentistry and low-stress magnitude. Full article
(This article belongs to the Special Issue Bioactive Polymer Composites and Their Clinical Applications)
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Article
Stress–Strain Behaviour of Reparable Composite Panel with Step-Variable Thickness
Polymers 2021, 13(21), 3830; https://doi.org/10.3390/polym13213830 - 05 Nov 2021
Viewed by 254
Abstract
There is an urgent problem of finding an economically viable method of maintenance and restoration of the bearing capacity of structures of various applications. Repair of structures with patches made of polymeric composite materials is one of the most promising repair technologies. However, [...] Read more.
There is an urgent problem of finding an economically viable method of maintenance and restoration of the bearing capacity of structures of various applications. Repair of structures with patches made of polymeric composite materials is one of the most promising repair technologies. However, an improper choice of parameters of the composite patch leads to unjustified increase in the structure mass and the cost of its further operation. These situations result from the lack of reliable methods for developing the repair process, which take into account the influence of the patch geometry and conditions for performance of repair works on the bearing capacity of the repaired structure. The mathematical model of the reparable composite shell–type panel taking into account inhomogeneity of transverse shear deformations at stepped variation of its thickness has been developed. In contrast to the classical theory of layered shells, the model allows simplifying a three-dimensional problem by setting of the displacement field on the layers’ interfaces and their linear interpolation over thickness of the panel, as well as considering the transverse shear deformations resulting from the strength, temperature, or shrinkage loading. According to results, the maximum rise in stresses in the case of a notched panel occurs in the weakened layer, and it is from this layer the failure of the structure will start. In the event of the patch, the panel surface opposite the reinforcement is the most loaded (i.e., susceptible to failure) surface. To confirm the reliability of the developed model, we compared the analytical calculations with the results of experimental and numerical studies of the deformed state of a panel of step–variable thickness by the method of holographic interferometry and modelling by the finite element method. Displacement fields available from experiments correspond to the predicted theoretical results. The resulting maximum error does not exceed 7%. The data obtained during numerical modelling allowed us to conclude that the accuracy of theoretical calculations is sufficient for engineering practice. Results of the work can be used to solve the practical problems such as determination of stress–strain behaviour of a damaged structure or structure after repair, specification of the permissible delamination dimensions, and defining of parameters of the bonded repair process. Full article
(This article belongs to the Section Polymer Processing and Engineering)
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Article
Inhomogeneities in PNIPAM Aqueous Solutions: The Inside View by Spin Probe EPR Spectroscopy
Polymers 2021, 13(21), 3829; https://doi.org/10.3390/polym13213829 - 05 Nov 2021
Viewed by 226
Abstract
Coil to globule transition in poly(N-isopropylacrylamide) aqueous solutions was studied using spin probe continuous-wave electronic paramagnetic resonance (CW EPR) spectroscopy with an amphiphilic TEMPO radical as a guest molecule. Using Cu(II) ions as the “quencher” for fast-moving radicals in the liquid phase allowed [...] Read more.
Coil to globule transition in poly(N-isopropylacrylamide) aqueous solutions was studied using spin probe continuous-wave electronic paramagnetic resonance (CW EPR) spectroscopy with an amphiphilic TEMPO radical as a guest molecule. Using Cu(II) ions as the “quencher” for fast-moving radicals in the liquid phase allowed obtaining the individual spectra of TEMPO radicals in polymer globule and observing inhomogeneities in solutions before globule collapsing. EPR spectra simulations confirm the formation of molten globules at the first step with further collapsing and water molecules coming out of the globule, making it denser. Full article
(This article belongs to the Special Issue Advances in Thermoresponsive Polymers)
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