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Polymers, Volume 13, Issue 15 (August-1 2021) – 193 articles

Cover Story (view full-size image): The study presented here focuses on the correlation between the microscopic structure and the macroscopic properties of silica-filled SBR rubbers. Specifically, this investigation aims at understanding the reinforcement which results from the substitution of fractal silica filler with anisotropic rod-like Sepiolite or larger spherical nanoparticles. For the first time, this study highlights the direct correlation between the specific orientation of the fillers at the microscopic level and the resulting mechanical properties measured through DMA and tensile tests. In addition, the synergetic effect occurring between two types of hybrid silica-based fillers, fractal/spherical and fractal/anisotropic, is elucidated. View this paper.
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Review
Graphene and Iron Reinforced Polymer Composite Electromagnetic Shielding Applications: A Review
Polymers 2021, 13(15), 2580; https://doi.org/10.3390/polym13152580 - 03 Aug 2021
Cited by 1 | Viewed by 681
Abstract
With advancements in the automated industry, electromagnetic inferences (EMI) have been increasing over time, causing major distress among the end-users and affecting electronic appliances. The issue is not new and major work has been done, but unfortunately, the issue has not been fully [...] Read more.
With advancements in the automated industry, electromagnetic inferences (EMI) have been increasing over time, causing major distress among the end-users and affecting electronic appliances. The issue is not new and major work has been done, but unfortunately, the issue has not been fully eliminated. Therefore, this review intends to evaluate the previous carried-out studies on electromagnetic shielding materials with the combination of [email protected], [email protected], [email protected] and [email protected]@Polymer composites in X-band frequency range and above to deal with EMI. VOSviewer was also used to perform the keyword analysis which shows how the studies are interconnected. Based on the carried-out review it was observed that the most preferable materials to deal with EMI are polymer-based composites which showed remarkable results. It is because the polymers are flexible and provide better bonding with other materials. Polydimethylsiloxane (PDMS), polyaniline (PANI), polymethyl methacrylate (PMMA) and polyvinylidene fluoride (PVDF) are effective in the X-band frequency range, and PDMS, epoxy, PVDF and PANI provide good shielding effectiveness above the X-band frequency range. However, still, many new combinations need to be examined as mostly the shielding effectiveness was achieved within the X-band frequency range where much work is required in the higher frequency range. Full article
(This article belongs to the Section Polymer Applications)
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Article
Tamisolve® NxG as an Alternative Non-Toxic Solvent for the Preparation of Porous Poly (Vinylidene Fluoride) Membranes
Polymers 2021, 13(15), 2579; https://doi.org/10.3390/polym13152579 - 03 Aug 2021
Viewed by 494
Abstract
Tamisolve® NxG, a well-known non-toxic solvent, was used for poly(vinylidene fluoride) (PVDF) membranes preparation via a non-solvent-induced phase separation (NIPS) procedure with water as a coagulation bath. Preliminary investigations, related to the study of the physical/chemical properties of the solvent, the solubility [...] Read more.
Tamisolve® NxG, a well-known non-toxic solvent, was used for poly(vinylidene fluoride) (PVDF) membranes preparation via a non-solvent-induced phase separation (NIPS) procedure with water as a coagulation bath. Preliminary investigations, related to the study of the physical/chemical properties of the solvent, the solubility parameters, the gel transition temperature and the viscosity of the polymer–solvent system, confirmed the power of the solvent to solubilize PVDF polymer for membranes preparation. The role of polyvinylpyrrolidone (PVP) and/or poly(ethylene glycol) (PEG), as pore former agents in the dope solution, was studied along with different polymer concentrations (10 wt%, 15 wt% and 18 wt%). The produced membranes were then characterized in terms of morphology, thickness, porosity, contact angle, atomic force microscopy (AFM) and infrared spectroscopy (ATR-FTIR). Pore size measurements, pore size distribution and water permeability (PWP) tests placed the developed membranes in the ultrafiltration (UF) and microfiltration (MF) range. Finally, PVDF membrane performances were investigated in terms of rejection (%) and permeability recovery ratio (PRR) using methylene blue (MB) in water solution to assess their potential application in separation and purification processes. Full article
(This article belongs to the Special Issue Polymer-Based Membrane Technology and Applications II)
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Article
Plant Byproducts as Part of Edible Coatings: A Case Study with Parsley, Grape and Blueberry Pomace
Polymers 2021, 13(15), 2578; https://doi.org/10.3390/polym13152578 - 03 Aug 2021
Viewed by 414
Abstract
Studies dealing with the development of edible/biodegradable packaging have been gaining popularity since these commodities are marked as being ecofriendly, especially when byproducts are incorporated. Consequently, this study aimed at the development of chitosan-based coatings with plant byproducts. Their sensory properties, colour attributes, [...] Read more.
Studies dealing with the development of edible/biodegradable packaging have been gaining popularity since these commodities are marked as being ecofriendly, especially when byproducts are incorporated. Consequently, this study aimed at the development of chitosan-based coatings with plant byproducts. Their sensory properties, colour attributes, occurrence of cracks in microstructure and biodegradability were analysed. Coatings containing grape and blueberry pomace had statistically significantly (p < 0.05) higher levels of colour intensity. Coating samples were characterised by lower aroma intensity (3.46–4.77), relatively smooth surface (2.40–5.86), and low stickiness (2.11–3.14). In the overall hedonic evaluation, the samples containing parsley pomace in all concentrations and a sample containing 5% grape pomace achieved a statistically significantly (p < 0.05) better evaluation (5.76–5.93). The lowest values of the parameter ΔE2000 were recorded for the sample containing 5% parsley pomace (3.5); the highest was for the sample with 20% blueberry pomace (39.3). An analysis of the coating surface microstructure showed the presence of surface cracks at an 80 K magnification but the protective function of the edible coating was not disrupted by the added plant pomace. The produced samples can be considered to have a high biodegradability rate. The results of our experimentally produced coatings indicate their possible application on a commercial scale. Full article
(This article belongs to the Section Circular and Green Polymer Science)
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Article
Biomimetic Hierarchical Structuring of PLA by Ultra-Short Laser Pulses for Processing of Tissue Engineered Matrices: Study of Cellular and Antibacterial Behavior
Polymers 2021, 13(15), 2577; https://doi.org/10.3390/polym13152577 - 03 Aug 2021
Viewed by 413
Abstract
The influence of ultra-short laser modification on the surface morphology and possible chemical alteration of poly-lactic acid (PLA) matrix in respect to the optimization of cellular and antibacterial behavior were investigated in this study. Scanning electron microscopy (SEM) morphological examination of the processed [...] Read more.
The influence of ultra-short laser modification on the surface morphology and possible chemical alteration of poly-lactic acid (PLA) matrix in respect to the optimization of cellular and antibacterial behavior were investigated in this study. Scanning electron microscopy (SEM) morphological examination of the processed PLA surface showed the formation of diverse hierarchical surface microstructures, generated by irradiation with a range of laser fluences (F) and scanning velocities (V) values. By controlling the laser parameters, diverse surface roughness can be achieved, thus influencing cellular dynamics. This surface feedback can be applied to finely tune and control diverse biomaterial surface properties like wettability, reflectivity, and biomimetics. The triggering of thermal effects, leading to the ejection of material with subsequent solidification and formation of raised rims and 3D-like hollow structures along the processed zones, demonstrated a direct correlation to the wettability of the PLA. A transition from superhydrophobic (θ > 150°) to super hydrophilic (θ < 20°) surfaces can be achieved by the creation of grooves with V = 0.6 mm/s, F = 1.7 J/cm2. The achieved hierarchical architecture affected morphology and thickness of the processed samples which were linked to the nature of ultra-short laser-material interaction effects, namely the precipitation of temperature distribution during material processing can be strongly minimized with ultrashort pulses leading to non-thermal and spatially localized effects that can facilitate volume ablation without collateral thermal damage The obtained modification zones were analyzed employing Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Energy dispersive X-ray analysis (EDX), and optical profilometer. The modification of the PLA surface resulted in an increased roughness value for treatment with lower velocities (V = 0.6 mm/s). Thus, the substrate gains a 3D-like architecture and forms a natural matrix by microprocessing with V = 0.6 mm/s, F = 1.7 J/cm2, and V = 3.8 mm/s, F = 0.8 J/cm2. The tests performed with Mesenchymal stem cells (MSCs) demonstrated that the ultra-short laser surface modification altered the cell orientation and promoted cell growth. The topographical design was tested also for the effectiveness of bacterial attachment concerning chosen parameters for the creation of an array with defined geometrical patterns. Full article
(This article belongs to the Special Issue Advances in Bio-Based and Biodegradable Polymeric Composites)
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Article
Fabrication of Bio-Nanocomposite Based on HNT-Methionine for Controlled Release of Phenytoin
Polymers 2021, 13(15), 2576; https://doi.org/10.3390/polym13152576 - 03 Aug 2021
Viewed by 397
Abstract
In this study, a novel promising approach for the fabrication of Halloysite nanotube (HNT) nanocomposites, based on the amino acid named Methionine (Met), was investigated. For this purpose, Met layered on the outer silane functionalized surface of HNT for controlled release of Phenytoin [...] Read more.
In this study, a novel promising approach for the fabrication of Halloysite nanotube (HNT) nanocomposites, based on the amino acid named Methionine (Met), was investigated. For this purpose, Met layered on the outer silane functionalized surface of HNT for controlled release of Phenytoin sodium (PHT). The resulting nanocomposite (MNT-g-Met) was characterized by FTIR, XRD, Zeta potential, TGA, TEM and FE-SEM. The FT-IR results showed APTES and Met peaks, which proved the modification of the HNTs. The zeta-potential results showed the interaction between APTES (+53.30) and Met (+38.80) on the HNTs (−30.92). The FE-SEM micrographs have displayed the grafting of Met on the modified HNTs due to the nanotube conversion to a rough and indistinguishable form. The amount of encapsulation efficiency (EE) and loading efficiency (LE) of MNT-g-Met was 74.48% and 37.24%, while pure HNT was 57.5%, and 28.75%, respectively. In-vitro studies showed that HNT had a burst release (70% in 6 h) in phosphate buffer while MNT-g-Met has more controlled release profile (30.05 in 6 h) and it was found to be fitted with the Korsmeyer-Peppas model. Due to the loading efficiency and controlled release profile, the nanocomposite promote a good potential for drug delivery of PHT. Full article
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Article
Enhancement of Antioxidant and Hydrophobic Properties of Alginate via Aromatic Derivatization: Preparation, Characterization, and Evaluation
Polymers 2021, 13(15), 2575; https://doi.org/10.3390/polym13152575 - 02 Aug 2021
Cited by 1 | Viewed by 430
Abstract
The preparation of bioactive polymeric molecules requires the attention of scientists as it has a potential function in biomedical applications. In the current study, functional substitution of alginate with a benzoyl group was prepared via coupling its hydroxyl group with benzoyl chloride. Fourier [...] Read more.
The preparation of bioactive polymeric molecules requires the attention of scientists as it has a potential function in biomedical applications. In the current study, functional substitution of alginate with a benzoyl group was prepared via coupling its hydroxyl group with benzoyl chloride. Fourier transform infrared spectroscopy indicated the characteristic peaks of aromatic C=C in alginate derivative at 1431 cm−1. HNMR analysis demonstrated the aromatic protons at 7.5 ppm assigned to benzoyl groups attached to alginate hydroxyl groups. Wetting analysis showed a decrease in hydrophilicity in the new alginate derivative. Differential scanning calorimetry and thermal gravimetric analysis showed that the designed aromatic alginate derivative demonstrated higher thermo-stability than alginates. The aromatic alginate derivative displayed high anti-inflammatory properties compared to alginate. Finally, the in vitro antioxidant evaluation of the aromatic alginate derivative showed a significant increase in free radical scavenging activity compared to neat alginate against DPPH (2,2-diphenyll-picrylhydrazyl) and ABTS free radicals. The obtained results proposed that the new alginate derivative could be employed for gene and drug delivery applications. Full article
(This article belongs to the Section Polymer Applications)
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Article
Enhancement of Light Amplification of CsPbBr3 Perovskite Quantum Dot Films via Surface Encapsulation by PMMA Polymer
Polymers 2021, 13(15), 2574; https://doi.org/10.3390/polym13152574 - 02 Aug 2021
Viewed by 468
Abstract
Photonic devices based on perovskite materials are considered promising alternatives for a wide range of these devices in the future because of their broad bandgaps and ability to contribute to light amplification. The current study investigates the possibility of improving the light amplification [...] Read more.
Photonic devices based on perovskite materials are considered promising alternatives for a wide range of these devices in the future because of their broad bandgaps and ability to contribute to light amplification. The current study investigates the possibility of improving the light amplification characteristics of CsPbBr3 perovskite quantum dot (PQD) films using the surface encapsulation technique. To further amplify emission within a perovskite layer, CsPbBr3 PQD films were sandwiched between two transparent layers of poly(methyl methacrylate) (PMMA) to create a highly flexible PMMA/PQD/PMMA waveguide film configuration. The prepared perovskite film, primed with a polymer layer coating, shows a marked improvement in both emission efficiency and amplified spontaneous emission (ASE)/laser threshold compared with bare perovskite films on glass substrates. Additionally, significantly improved photoluminescence (PL) and long decay lifetime were observed. Consequently, under pulse pumping in a picosecond duration, ASE with a reduction in ASE threshold of ~1.2 and 1.4 times the optical pumping threshold was observed for PQDs of films whose upper face was encapsulated and embedded within a cavity comprising two PMMA reflectors, respectively. Moreover, the exposure stability under laser pumping was greatly improved after adding the polymer coating to the top face of the perovskite film. Finally, this process improved the emission and PL in addition to enhancements in exposure stability. These results were ascribed in part to the passivation of defects in the perovskite top surface, accounting for the higher PL intensity, the slower PL relaxation, and for about 14 % of the ASE threshold decrease. Full article
(This article belongs to the Special Issue Polymer Films for Photovoltaic Applications)
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Article
Preparation of Bis[(3-ethyl-3-methoxyoxetane)propyl]diphenylsilane and Investigation of Its Cationic UV-Curing Material Properties
Polymers 2021, 13(15), 2573; https://doi.org/10.3390/polym13152573 - 02 Aug 2021
Viewed by 406
Abstract
Precusor EHO(3-ethyl-3-hydroxymethyloxetane) was synthesized with diethyl carbonate and trihydroxypropane as the main raw materials. Intermediate AllyEHO(3-ethyl-3-allylmethoxyoxetane) was synthesized with 3-ethyl-3-hydroxymethyloxetane and allyl bromide as the main raw materials. Prepolymer bis[(3-ethyl-3-methoxyoxetane)propyl]diphenylsilane was synthesized with 3-ethyl-3-methoxyoxetane)propyl and diphenylsilane. Photoinitiator triarylsulfonium hexafluoroantimonate of 3% was added [...] Read more.
Precusor EHO(3-ethyl-3-hydroxymethyloxetane) was synthesized with diethyl carbonate and trihydroxypropane as the main raw materials. Intermediate AllyEHO(3-ethyl-3-allylmethoxyoxetane) was synthesized with 3-ethyl-3-hydroxymethyloxetane and allyl bromide as the main raw materials. Prepolymer bis[(3-ethyl-3-methoxyoxetane)propyl]diphenylsilane was synthesized with 3-ethyl-3-methoxyoxetane)propyl and diphenylsilane. Photoinitiator triarylsulfonium hexafluoroantimonate of 3% was added to the prepolymer, and a novel kind of the photosensitive resin was prepared. They were analyzed and characterized with FTIR and 1H-NMR. Photo-DSC examination revealed that the bis[(3-ethyl-3-methoxyoxetane)propyl]diphenylsilane has great photosensitivity. The thermal properties and mechanical properties of the photosensitive resin were examined by TGA and a microcomputer-controlled universal material testing machine, with thermal stabilities of up to 446 °C. The tensile strength was 75.5 MPa and the bending strength was 49.5 MPa. The light transmittance remained above 98%. Full article
(This article belongs to the Special Issue Photoactive Polymeric Materials)
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Article
Application of Micromechanical Modelling for the Evaluation of Elastic Moduli of Hybrid Woven Jute–Ramie Reinforced Unsaturated Polyester Composites
Polymers 2021, 13(15), 2572; https://doi.org/10.3390/polym13152572 - 01 Aug 2021
Cited by 1 | Viewed by 718
Abstract
Woven laminated composite has gained researchers’ and industry’s interest over time due to its impressive mechanical performance compared to unidirectional composites. Nevertheless, the mechanical properties of the woven laminated composite are hard to predict. There are many micromechanical models based on unidirectional composite [...] Read more.
Woven laminated composite has gained researchers’ and industry’s interest over time due to its impressive mechanical performance compared to unidirectional composites. Nevertheless, the mechanical properties of the woven laminated composite are hard to predict. There are many micromechanical models based on unidirectional composite but limited to the woven laminated composite. The current research work was conducted to evaluate elastic moduli of hybrid jute–ramie woven reinforced unsaturated polyester composites using micromechanical effectiveness unidirectional models, such as ROM, IROM, Halpin–Tsai, and Hirsch, which are based on stiffness. The hybrid jute–ramie laminated composite was fabricated with different layering sizes, and the stacking sequence was completed via hand lay-up with the compression machine. Tensile modulus values for hybrid composites are between those for single jute and single ramie. Obtained p-values less than 0.05 prove the relationship between layering size and tensile modulus. This study showed that several micromechanical models, such as Halpin–Tsai’s predicted value of homogenized mechanical properties, were in good agreement with the experimental result. In the case of the hybrid composite, the micromechanical model deviates from the experimental result. Several modifications are required to improve the current existing model. A correlation function was calculated based on the differences between the elastic modulus values determined experimentally and those derived from each micromechanical model calculation. Full article
(This article belongs to the Special Issue Mechanical and Adhesive Properties of Polymeric Materials)
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Article
Effect of Rot-, Fire-, and Water-Retardant Treatments on Jute Fiber and Their Associated Thermoplastic Composites: A Study by FTIR
Polymers 2021, 13(15), 2571; https://doi.org/10.3390/polym13152571 - 01 Aug 2021
Viewed by 517
Abstract
Natural renewable materials can play a big role in reducing the consumption of synthetic materials for environmental sustainability. Natural fiber-reinforced composites have attracted significant research and commercial importance due to their versatile characteristics and multi-dimensional applications. As the natural materials are easily rotten, [...] Read more.
Natural renewable materials can play a big role in reducing the consumption of synthetic materials for environmental sustainability. Natural fiber-reinforced composites have attracted significant research and commercial importance due to their versatile characteristics and multi-dimensional applications. As the natural materials are easily rotten, flammable, and moisture absorbent, they require additional chemical modification for use in sustainable product development. In the present research, jute fibers were treated with rot-, fire-, and water-retardant chemicals and their corresponding polymer composites were fabricated using a compression molding technique. To identify the effects of the chemical treatments on the jute fiber and their polymeric composites, a Fourier transformed infrared radiation (FTIR) study was conducted and the results were analyzed. The presence of various chemicals in the post-treated fibers and the associated composites were identified through the FTIR analysis. The varying weight percentage of the chemicals used for treating the fibers affected the physio-mechanical properties of the fiber as well as their composites. From the FTIR analysis, it was concluded that crystallinity increased with the chemical concentration of the treatment which could be contributed to the improvement in their mechanical performance. This study provides valuable information for both academia and industry on the effect of various chemical treatments of the jute fiber for improved product development. Full article
(This article belongs to the Special Issue Mechanical Properties of Polymer Composites)
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Article
Densely Packed Tethered Polymer Nanoislands: A Simulation Study
Polymers 2021, 13(15), 2570; https://doi.org/10.3390/polym13152570 - 01 Aug 2021
Viewed by 416
Abstract
COordinated Responsive Arrays of Surface-Linked polymer islands (CORALS) allow for the creation of molecular surfaces with novel and switchable properties. Critical components of CORALs are the uniformly distributed islands of densely grafted polymer chains (nanoislands) separated by regions of bare surface. The grafting [...] Read more.
COordinated Responsive Arrays of Surface-Linked polymer islands (CORALS) allow for the creation of molecular surfaces with novel and switchable properties. Critical components of CORALs are the uniformly distributed islands of densely grafted polymer chains (nanoislands) separated by regions of bare surface. The grafting footprint and separation distances of nanoislands are comparable to that of the constituent polymer chains themselves. Herein, we characterize the structural features of the nanoislands and semiflexible polymers within to better understand this critical constituent of CORALs. We observe different characteristics of grafted semiflexible polymers depending on the polymer island’s size and distance from the center of the island. Specifically, the characteristics of the chains at the island periphery are similar to isolated tethered polymer chains (full flexible chains), while chains in the center of the island experience the neighbor effect such as chains in the classic polymer brush. Chains close to the edge of the islands exhibit unique structural features between these two regimes. These results can be used in the rational design of CORALs with specific interfacial characteristics and predictable responses to external stimuli. It is hoped that this the discussion of the different morphologies of the polymers as a function of distance from the edge of the polymer will find applications in a wide variety of systems. Full article
(This article belongs to the Special Issue Semiflexible Polymers II)
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Article
Kinetics and Mechanism of Synthesis of Carboxyl-Containing N-Vinyl-2-Pyrrolidone Telehelics for Pharmacological Use
Polymers 2021, 13(15), 2569; https://doi.org/10.3390/polym13152569 - 01 Aug 2021
Viewed by 435
Abstract
It was found that sulfanylethanoic and 3-sulfanylpropanoic acids are effective regulators of molecular weight with chain transfer constants of 0.441 and 0.317, respectively, and show an unexpected acceleration effect on the radical polymerization of N-vinyl-2-pyrrolidone, initiated by 2,2’-azobisisobutyronitrile. It was determined for the [...] Read more.
It was found that sulfanylethanoic and 3-sulfanylpropanoic acids are effective regulators of molecular weight with chain transfer constants of 0.441 and 0.317, respectively, and show an unexpected acceleration effect on the radical polymerization of N-vinyl-2-pyrrolidone, initiated by 2,2’-azobisisobutyronitrile. It was determined for the first time that the thiolate anions of mercapto acids form a high-temperature redox initiating system with 2,2’-azobisisobutyronitrile during the radical polymerization of N-vinyl-2-pyrrolidone in 1,4-dioxane. Considering the peculiarities of initiation, a kinetic model of the polymerization of N-vinyl-2-pyrrolidone is proposed, and it is shown that the theoretical orders of the reaction rate, with respect to the monomer, initiator, and chain transfer agent, are 1, 0.75, 0.25, and are close to their experimentally determined values. Carboxyl-containing techelics of N-vinyl-2-pyrrolidone were synthesized so that it can slow down the release of the anticancer drug, doxorubicin, from aqueous solutions, which can find its application in the pharmacological field. Full article
(This article belongs to the Special Issue Polymer Reaction Modeling and Kinetics)
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Review
Graphitic Carbon Nitride as a New Sustainable Photocatalyst for Textile Functionalization
Polymers 2021, 13(15), 2568; https://doi.org/10.3390/polym13152568 - 31 Jul 2021
Viewed by 527
Abstract
As a promising organic semiconducting material, polymeric graphitic carbon nitride (g-C3N4) has attracted much attention due to its excellent optical and photoelectrochemical properties, thermal stability, chemical inertness, nontoxicity, abundance, and low cost. Its advantageous visible light-induced photocatalytic activity has [...] Read more.
As a promising organic semiconducting material, polymeric graphitic carbon nitride (g-C3N4) has attracted much attention due to its excellent optical and photoelectrochemical properties, thermal stability, chemical inertness, nontoxicity, abundance, and low cost. Its advantageous visible light-induced photocatalytic activity has already been beneficially used in the fields of environmental remediation, biological applications, healthcare, energy conversion and storage, and fuel production. Despite the recognized potential of g-C3N4, there is still a knowledge gap in the application of g-C3N4 in the field of textiles, with no published reviews on the g-C3N4-functionalization of textile materials. Therefore, this review article aims to provide a critical overview of recent advances in the surface and bulk modification of textile fibres by g-C3N4 and its composites to tailor photocatalytic self-cleaning, antibacterial, and flame retardant properties as well as to create a textile catalytic platform for water disinfection, the removal of various organic pollutants from water, and selective organic transformations. This paper highlights the possibilities of producing g-C3N4-functionalized textile substrates and suggests some future prospects for this research area. Full article
(This article belongs to the Section Polymer Chemistry)
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Article
Influence of Graphene Nanoplatelet Lateral Size on the Electrical Conductivity and Electromagnetic Interference Shielding Performance of Polyester Nanocomposites
Polymers 2021, 13(15), 2567; https://doi.org/10.3390/polym13152567 - 31 Jul 2021
Viewed by 459
Abstract
Polyester nanocomposites reinforced with graphene nanoplatelets (GnPs) with two different lateral sizes are prepared by high shear mixing, followed by compression molding. The effects of the size and concentration of GnP, as well as of the processing method, on the electrical conductivity and [...] Read more.
Polyester nanocomposites reinforced with graphene nanoplatelets (GnPs) with two different lateral sizes are prepared by high shear mixing, followed by compression molding. The effects of the size and concentration of GnP, as well as of the processing method, on the electrical conductivity and electromagnetic interference (EMI) shielding behavior of these nanocomposites are experimentally investigated. The in-plane electrical conductivity of the nanocomposites with larger-size GnPs is approximately one order of magnitude higher than the cross-plane volume conductivity. According to the SEM images, the compression-induced alignments of GnPs is found to be responsible for this anisotropic behavior. The orientation of the small size GnPs in the composite is not influenced by the compression process as strongly, and consequently, the electrical conductivity of these nanocomposites exhibits only a slight anisotropy. The maximum EMI shielding effectiveness (SE) of 27 dB (reduction of 99.8% of the incident radiation) is achieved at 25 wt.% of the smaller-size GnP loading. Experimental results show that the EMI shielding mechanism of these composites has a strong dependency on the lateral dimension of GnPs. The non-aligned smaller-size GnPs are leveraged to obtain a relatively high absorption coefficient (≈40%). This absorption coefficient is superior to the existing single-filler bulk polymer composite with a similar thickness. Full article
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Article
Preparation of Poly(ethylene glycol)@Polyurea Microcapsules Using Oil/Oil Emulsions and Their Application as Microreactors
Polymers 2021, 13(15), 2566; https://doi.org/10.3390/polym13152566 - 31 Jul 2021
Viewed by 467
Abstract
The development process of catalytic core/shell microreactors, possessing a poly(ethylene glycol) (PEG) core and a polyurea (PU) shell, by implementing an emulsion-templated non-aqueous encapsulation method, is presented. The microreactors’ fabrication process begins with an emulsification process utilizing an oil-in-oil (o/o) emulsion of PEG-in-heptane, [...] Read more.
The development process of catalytic core/shell microreactors, possessing a poly(ethylene glycol) (PEG) core and a polyurea (PU) shell, by implementing an emulsion-templated non-aqueous encapsulation method, is presented. The microreactors’ fabrication process begins with an emulsification process utilizing an oil-in-oil (o/o) emulsion of PEG-in-heptane, stabilized by a polymeric surfactant. Next, a reaction between a poly(ethylene imine) (PEI) and a toluene-2,4-diisocyanate (TDI) takes place at the boundary of the emulsion droplets, resulting in the creation of a PU shell through an interfacial polymerization (IFP) process. The microreactors were loaded with palladium nanoparticles (NPs) and were utilized for the hydrogenation of alkenes and alkynes. Importantly, it was found that PEG has a positive effect on the catalytic performance of the developed microreactors. Interestingly, besides being an efficient green reaction medium, PEG plays two crucial roles: first, it reduces the palladium ions to palladium NPs; thus, it avoids the unnecessary use of additional reducing agents. Second, it stabilizes the palladium NPs and prevents their aggregation, allowing the formation of highly reactive palladium NPs. Strikingly, in one sense, the suggested system affords highly reactive semi-homogeneous catalysis, whereas in another sense, it enables the facile, rapid, and inexpensive recovery of the catalytic microreactor by simple centrifugation. The durable microreactors exhibit excellent activity and were recycled nine times without any loss in their reactivity. Full article
(This article belongs to the Section Polymer Applications)
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Article
Phase and Structure Behavior vs. Electromechanical Performance of Electrostrictive P(VDF-HFP)/ZnO Composite Nanofibers
Polymers 2021, 13(15), 2565; https://doi.org/10.3390/polym13152565 - 31 Jul 2021
Viewed by 515
Abstract
In this work, we improved the electromechanical properties, electrostrictive behavior and energy-harvesting performance of poly(vinylidenefluoridene-hexafluoropropylene) P(VDF-HFP)/zinc oxide (ZnO) composite nanofibers. The main factor in increasing their electromechanical performance and harvesting power based on electrostrictive behavior is an improved coefficient with a modified crystallinity [...] Read more.
In this work, we improved the electromechanical properties, electrostrictive behavior and energy-harvesting performance of poly(vinylidenefluoridene-hexafluoropropylene) P(VDF-HFP)/zinc oxide (ZnO) composite nanofibers. The main factor in increasing their electromechanical performance and harvesting power based on electrostrictive behavior is an improved coefficient with a modified crystallinity phase and tuning the polarizability of material. These blends were fabricated by using a simple electrospinning method with varied ZnO contents (0, 5, 10, 15 and 20 wt%). The effects of the ZnO nanoparticle size and content on the phase transformation, dielectric permittivity, strain response and vibration energy harvesting were investigated. The characteristics of these structures were evaluated utilizing SEM, EDX, XRD, FT-IR and DMA. The electrical properties of the fabrication samples were examined by LCR meter as a function of the concentration of the ZnO and frequency. The strain response from the electric field was observed by the photonic displacement apparatus and lock-in amplifier along the thickness direction at a low frequency of 1 Hz. Moreover, the energy conversion behavior was determined by an energy-harvesting setup measuring the current induced in the composite nanofibers. The results showed that the ZnO nanoparticles’ component effectively achieves a strain response and the energy-harvesting capabilities of these P(VDF-HFP)/ZnO composites nanofibers. The electrostriction coefficient tended to increase with a higher ZnO content and an increasing dielectric constant. The generated current increased with the ZnO content when the external electric field was applied at a vibration of 20 Hz. Consequently, the ZnO nanoparticles dispersed into electrostrictive P(VDF-HFP) nanofibers, which offer a large power density and excellent efficiency of energy harvesting. Full article
(This article belongs to the Special Issue Structure-Property Relationships in Polymer Fibers)
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Article
Role of Chemically Functionalization of Bamboo Fibers on Polyethylene-Based Composite Performance: A Solution for Recycling
Polymers 2021, 13(15), 2564; https://doi.org/10.3390/polym13152564 - 31 Jul 2021
Viewed by 429
Abstract
Low-density polyethylene is the most common polymer for manufacturing containers, bottles, tubes, plastic bags, computer components and so on. There is an urgent need to find solutions for its recycling and reintegration in high volume production components such as non-structural auto applications. The [...] Read more.
Low-density polyethylene is the most common polymer for manufacturing containers, bottles, tubes, plastic bags, computer components and so on. There is an urgent need to find solutions for its recycling and reintegration in high volume production components such as non-structural auto applications. The reinforcement of recycled low-density polyethylene with natural fibers represents a solution for the re-use of the recycled low-density polyethylene. However, there is a lack of understanding of how the natural fibers influence the behavior of the bare low-density polyethylene, and furthermore, how the interface between the fibers and the matrix can be controlled in composite to obtain the designed toughness, strength, stiffness and damping. In this sense, the study presents an in-depth analysis of the behavior of three coupling agents used in the chemically functionalized bamboo fibers interface for reinforcing low-density polyethylene composites. Through mechanical tests, the mechanical properties are determined and compared and finally, a correlation between the viscous behavior of the resulted composites and the toughening mechanism is proposed. The conclusion of the study enables a flexible design of polymer composite components fabricated of recycled and non-recycled low-density polyethylene and natural fibers. Full article
(This article belongs to the Special Issue Polymer Composites for Structural Applications)
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Review
Main Morphological Characteristics of Tubular Polymeric Scaffolds to Promote Peripheral Nerve Regeneration—A Scoping Review
Polymers 2021, 13(15), 2563; https://doi.org/10.3390/polym13152563 - 31 Jul 2021
Viewed by 447
Abstract
The “nerve guide conduits” (NGC) used in nerve regeneration must mimic the natural environment for proper cell behavior. Objective: To describe the main morphological characteristics of polymeric NGC to promote nerve regeneration. Methods: A scoping review was performed following the Preferred Reporting Items [...] Read more.
The “nerve guide conduits” (NGC) used in nerve regeneration must mimic the natural environment for proper cell behavior. Objective: To describe the main morphological characteristics of polymeric NGC to promote nerve regeneration. Methods: A scoping review was performed following the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) criteria in the PubMed, Web of Science, Science Direct, and Scientific Electronic Library Online (SciELO) databases. Primary studies that considered/evaluated morphological characteristics of NGC to promote nerve regeneration were included. Result: A total of 704 studies were found, of which 52 were selected. The NGC main morphological characteristics found in the literature were: (I) NGC diameter affects the mechanical properties of the scaffold. (II) Wall thickness of NGC determines the exchange of nutrients, molecules, and neurotrophins between the internal and external environment; and influences the mechanical properties and biodegradation, similarly to NGC (III) porosity, (IV) pore size, and (V) pore distribution. The (VI) alignment of the NGC fibers influences the phenotype of cells involved in nerve regeneration. In addition, the (VII) thickness of the polymeric fiber influences neurite extension and orientation. Conclusions: An NGC should have its diameter adjusted to the nerve with wall thickness, porosity, pore size, and distribution of pores, to favor vascularization, permeability, and exchange of nutrients, and retention of neurotrophic factors, also favoring its mechanical properties and biodegradability. Full article
(This article belongs to the Special Issue Biopolymer-Based Scaffolds for Regenerative Medicine Applications)
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Article
Novel Aminosilane (APTES)-Grafted [email protected] Oxide (PANI-GO) Nanocomposite for Electrochemical Sensor
Polymers 2021, 13(15), 2562; https://doi.org/10.3390/polym13152562 - 31 Jul 2021
Viewed by 482
Abstract
Lead is a potentially toxic element (PTE) that has several adverse medical effects in humans. Its presence in the environment became prominent due to anthropogenic activities. The current study explores the use of newly developed composite materials (organic–inorganic hybrid) based on PANI-GO-APTES for [...] Read more.
Lead is a potentially toxic element (PTE) that has several adverse medical effects in humans. Its presence in the environment became prominent due to anthropogenic activities. The current study explores the use of newly developed composite materials (organic–inorganic hybrid) based on PANI-GO-APTES for electrochemical detection of Pb2+ in aqueous solution. The composite material (PANI-GO-APTES) was synthesized by chemical method and was characterized with SEM, XPS, XEDS, XRD, TGA, FTIR, EIS and CV. The result of characterization indicates the successful synthesis of the intended material. The PANI-GO-APTES was successfully applied for electrochemical detection of Pb2+ using cyclic voltammetry and linear sweep voltammetry method. The limit of detection of Pb2+ was 0.0053 µM in the linear range of 0.01 µM to 0.4 µM. The current response produced during the electrochemical reduction of Pb2+ catalyzed by PANI-GO-APTES was also very repeatable, reproducible and rapid. The application of PANI-GO-APTES-modified GCE in real sample analysis was also established. Therefore, PANI-GO-APTES is presented as a potential Pb2+ sensor for environmental and human health safety. Full article
(This article belongs to the Special Issue Polymer-Based Sensor)
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Review
Biodegradable Packaging Materials from Animal Processing Co-Products and Wastes: An Overview
Polymers 2021, 13(15), 2561; https://doi.org/10.3390/polym13152561 - 31 Jul 2021
Cited by 1 | Viewed by 635
Abstract
Biodegradable polymers are non-toxic, environmentally friendly biopolymers with considerable mechanical and barrier properties that can be degraded in industrial or home composting conditions. These biopolymers can be generated from sustainable natural sources or from the agricultural and animal processing co-products and wastes. Animals [...] Read more.
Biodegradable polymers are non-toxic, environmentally friendly biopolymers with considerable mechanical and barrier properties that can be degraded in industrial or home composting conditions. These biopolymers can be generated from sustainable natural sources or from the agricultural and animal processing co-products and wastes. Animals processing co-products are low value, underutilized, non-meat components that are generally generated from meat processing or slaughterhouse such as hide, blood, some offal etc. These are often converted into low-value products such as animal feed or in some cases disposed of as waste. Collagen, gelatin, keratin, myofibrillar proteins, and chitosan are the major value-added biopolymers obtained from the processing of animal’s products. While these have many applications in food and pharmaceutical industries, a significant amount is underutilized and therefore hold potential for use in the generation of bioplastics. This review summarizes the research progress on the utilization of meat processing co-products to fabricate biodegradable polymers with the main focus on food industry applications. In addition, the factors affecting the application of biodegradable polymers in the packaging sector, their current industrial status, and regulations are also discussed. Full article
(This article belongs to the Special Issue Biopolymers for Food Packaging Films and Coatings)
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Article
Multi-Objective Optimization of Resistance Welding Process of GF/PP Composites
Polymers 2021, 13(15), 2560; https://doi.org/10.3390/polym13152560 - 31 Jul 2021
Viewed by 366
Abstract
Thermoplastic composites (TPCs) are promising materials for aerospace, transportation, shipbuilding, and civil use owing to their lightweight, rapid prototyping, reprocessing, and environmental recycling advantages. The connection assemblies of TPCs components are crucial to their application; compared with traditional mechanical joints and adhesive connections, [...] Read more.
Thermoplastic composites (TPCs) are promising materials for aerospace, transportation, shipbuilding, and civil use owing to their lightweight, rapid prototyping, reprocessing, and environmental recycling advantages. The connection assemblies of TPCs components are crucial to their application; compared with traditional mechanical joints and adhesive connections, fusion connections are more promising, particularly resistance welding. This study aims to investigate the effects of process control parameters, including welding current, time, and pressure, for optimization of resistance welding based on glass fiber-reinforced polypropylene (GF/PP) TPCs and a stainless-steel mesh heating element. A self-designed resistance-welding equipment suitable for the resistance welding process of GF/PP TPCs was manufactured. GF/PP laminates are fabricated using a hot press, and their mechanical properties were evaluated. The resistance distribution of the heating elements was assessed to conform with a normal distribution. Tensile shear experiments were designed and conducted using the Taguchi method to evaluate and predict process factor effects on the lap shear strength (LSS) of GF/PP based on signal-to-noise ratio (S/N) and analysis of variance. The results show that current is the main factor affecting resistance welding quality. The optimal process parameters are a current of 12.5 A, pressure of 2.5 MPa, and time of 540 s. The experimental LSS under the optimized parameters is 12.186 MPa, which has a 6.76% error compared with the result predicted based on the S/N. Full article
(This article belongs to the Special Issue Fiber-Reinforced Polymers (FRPs))
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Article
Carbon Capture Utilization for Biopolymer Foam Manufacture: Thermal, Mechanical and Acoustic Performance of PCL/PHBV CO2 Foams
Polymers 2021, 13(15), 2559; https://doi.org/10.3390/polym13152559 - 31 Jul 2021
Viewed by 482
Abstract
Biopolymer foams manufactured using CO2 enables a novel intersection for economic, environmental, and ecological impact but limited CO2 solubility remains a challenge. PHBV has low solubility in CO2 while PCL has high CO2 solubility. In this paper, PCL is [...] Read more.
Biopolymer foams manufactured using CO2 enables a novel intersection for economic, environmental, and ecological impact but limited CO2 solubility remains a challenge. PHBV has low solubility in CO2 while PCL has high CO2 solubility. In this paper, PCL is used to blend into PBHV. Both unfoamed and foamed blends are examined. Foaming the binary blends at two depressurization stages with subcritical CO2 as the blowing agent, produced open-cell and closed-cell foams with varying cellular architecture at different PHBV concentrations. Differential Scanning Calorimetry results showed that PHBV had some solubility in PCL and foams developed a PCL rich, PHBV rich and mixed phase. Scanning Electron Microscopy and pcynometry established cell size and density which reflected benefits of PCL presence. Acoustic performance showed limited benefits from foaming but mechanical performance of foams showed a significant impact from PHBV presence in PCL. Thermal performance reflected that foams were affected by the blend thermal conductivity, but the impact was significantly higher in the foams than in the unfoamed blends. The results provide a pathway to multifunctional performance in foams of high performance biopolymers such as PBHV through harnessing the CO2 miscibility of PCL. Full article
(This article belongs to the Special Issue Advanced Cellular Polymers)
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Review
Understanding Wood Surface Chemistry and Approaches to Modification: A Review
Polymers 2021, 13(15), 2558; https://doi.org/10.3390/polym13152558 - 31 Jul 2021
Viewed by 361
Abstract
Wood was designed, after millions of years of evolution, to perform in a wet environment. Nature is programmed to recycle it, in a timely way, back to the basic building blocks of carbon dioxide and water. All recycling chemistries start with an invasion [...] Read more.
Wood was designed, after millions of years of evolution, to perform in a wet environment. Nature is programmed to recycle it, in a timely way, back to the basic building blocks of carbon dioxide and water. All recycling chemistries start with an invasion of the wood surface. The surface of wood is porous, hygroscopic, viscoelastic, and anisotropic that is better defined in interface/interphase zones. This surface is dynamic and in constant change with changing humidity, temperature, oxygen levels, ultraviolet energy, microorganisms and stress. This chapter is a review of the chemical properties of a wood surface and performance issues associated with it. Full article
(This article belongs to the Special Issue Durability and Modification of Wood Surfaces)
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Article
Effect of Crystallinity on the Properties of Polycaprolactone Nanoparticles Containing the Dual FLAP/mPEGS-1 Inhibitor BRP-187
Polymers 2021, 13(15), 2557; https://doi.org/10.3390/polym13152557 - 31 Jul 2021
Viewed by 415
Abstract
Seven polycaprolactones (PCL) with constant hydrophobicity but a varying degree of crystallinity prepared from the constitutional isomers ε-caprolactone (εCL) and δ-caprolactone (δCL) were utilized to formulate nanoparticles (NPs). The aim was to investigate the effect of the crystallinity of the bulk polymers on [...] Read more.
Seven polycaprolactones (PCL) with constant hydrophobicity but a varying degree of crystallinity prepared from the constitutional isomers ε-caprolactone (εCL) and δ-caprolactone (δCL) were utilized to formulate nanoparticles (NPs). The aim was to investigate the effect of the crystallinity of the bulk polymers on the enzymatic degradation of the particles. Furthermore, their efficiency to encapsulate the hydrophobic anti-inflammatory drug BRP-187 and the final in vitro performance of the resulting NPs were evaluated. Initially, high-throughput nanoprecipitation was employed for the εCL and δCL homopolymers to screen and establish important formulation parameters (organic solvent, polymer and surfactant concentration). Next, BRP-187-loaded PCL nanoparticles were prepared by batch nanoprecipitation and characterized using dynamic light scattering, scanning electron microscopy and UV-Vis spectroscopy to determine and to compare particle size, polydispersity, zeta potential, drug loading as well as the apparent enzymatic degradation as a function of the copolymer composition. Ultimately, NPs were examined for their potency in vitro in human polymorphonuclear leukocytes to inhibit the BRP-187 target 5-lipoxygenase-activating protein (FLAP). It was evident by Tukey’s multi-comparison test that the degree of crystallinity of copolymers directly influenced their apparent enzymatic degradation and consequently their efficiency to inhibit the drug target. Full article
(This article belongs to the Special Issue Advances in Biocompatible and Biodegradable Polymers)
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Article
Chemically Functionalized Cellulose Nanocrystals as Reactive Filler in Bio-Based Polyurethane Foams
Polymers 2021, 13(15), 2556; https://doi.org/10.3390/polym13152556 - 31 Jul 2021
Viewed by 376
Abstract
Cellulose Nanocrystals, CNC, opportunely functionalized are proposed as reactive fillers in bio-based flexible polyurethane foams to improve, mainly, their mechanical properties. To overcome the cellulose hydrophilicity, CNC was functionalized on its surface by linking covalently a suitable bio-based polyol to obtain a grafted-CNC. [...] Read more.
Cellulose Nanocrystals, CNC, opportunely functionalized are proposed as reactive fillers in bio-based flexible polyurethane foams to improve, mainly, their mechanical properties. To overcome the cellulose hydrophilicity, CNC was functionalized on its surface by linking covalently a suitable bio-based polyol to obtain a grafted-CNC. The polyols grafted with CNC will react with the isocyanate in the preparation of the polyurethane foams. An attractive way to introduce functionalities on cellulose surfaces in aqueous media is silane chemistry by using functional trialkoxy silanes, X-Si (OR)3. Here, we report the synthesis of CNC-grafted-biopolyol to be used as a successful reactive filler in bio-based polyurethane foams, PUFs. The alkyl silanes were used as efficient coupling agents for the grafting of CNC and bio-polyols. Four strategies to obtain CNC-grafted-polyol were fine-tuned to use CNC as an active filler in PUFs. The effective grafting of the bio polyol on CNC was evaluated by FTIR analysis, and the amount of grafted polyol by thermogravimetric analysis. Finally, the morphological, thermal and mechanical properties and hydrophobicity of filled PUFs were thoughtfully assessed as well as the structure of the foams and, in particular, of the edges and walls of the cell foams by means of the Gibson–Ashby model. Improved thermal stability and mechanical properties of PU foams containing CNC-functionalized-polyol are observed. The morphology of the PU foams is also influenced by the functionalization of the CNC. Full article
(This article belongs to the Special Issue Bio-Based Materials and Natural Fillers)
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Article
Dielectric, Thermal and Water Absorption Properties of Some EPDM/Flax Fiber Composites
Polymers 2021, 13(15), 2555; https://doi.org/10.3390/polym13152555 - 31 Jul 2021
Viewed by 416
Abstract
This paper deals with the dielectric and sorption properties of some flax fiber-reinforced ethylene-propylene-diene monomer (EPDM) composites containing different fiber loadings as well as their behavior after exposure to different doses of electron beam irradiation. Three relaxation processes were evinced, a weak relaxation [...] Read more.
This paper deals with the dielectric and sorption properties of some flax fiber-reinforced ethylene-propylene-diene monomer (EPDM) composites containing different fiber loadings as well as their behavior after exposure to different doses of electron beam irradiation. Three relaxation processes were evinced, a weak relaxation β at sub-Tg temperatures and two α-type relaxations above the Tg. The EPDM/flax composites exhibited higher values of dielectric constant, dielectric loss and conductivity as compared to a pristine EPDM sample. Using thermogravimetric analysis (TG) coupled with Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS) (TG/FTIR/MS system), the degradation products can be identified. The water uptake increased as the flax fiber level increased in composites. The water uptake tests of irradiated composites showed that the highest water content was obtained for a flax fiber level of 20 phr. Full article
(This article belongs to the Special Issue Polymer-Based Dielectric Materials)
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Article
The Adaptive Power of Ammophila arenaria: Biomimetic Study, Systematic Observation, Parametric Design and Experimental Tests with Bimetal
Polymers 2021, 13(15), 2554; https://doi.org/10.3390/polym13152554 - 31 Jul 2021
Viewed by 445
Abstract
The aim of our study was to apply a biomimetic approach, inspired by the Ammophila arenaria. This organism possesses a reversible leaf opening and closing mechanism that responds to water and salt stress (hydronastic movement). We adopted a problem-based biomimetic methodology in [...] Read more.
The aim of our study was to apply a biomimetic approach, inspired by the Ammophila arenaria. This organism possesses a reversible leaf opening and closing mechanism that responds to water and salt stress (hydronastic movement). We adopted a problem-based biomimetic methodology in three stages: (i) two observation studies; (ii) how to abstract and develop a parametric model to simulate the leaf movement; and (iii) experiments with bimetal, a smart material that curls up when heated. We added creases to the bimetal active layer in analogy to the position of bulliform cells. These cells determine the leaf-closing pattern. The experiments demonstrated that creases influence and can change the direction of the bimetal natural movement. Thus, it is possible to replicate the Ammophila arenaria leaf-rolling mechanism in response to temperature variation and solar radiation in the bimetal. In future works, we will be able to propose responsive facade solutions based on these results. Full article
(This article belongs to the Special Issue Natural Fibers: High Performance Sustainable Materials)
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Article
Halogen-Free Flame Retardant Polypropylene Fibers with Modified Intumescent Flame Retardant: Preparation, Characterization, Properties and Mode of Action
Polymers 2021, 13(15), 2553; https://doi.org/10.3390/polym13152553 - 31 Jul 2021
Viewed by 396
Abstract
A novel intumescent flame retardant (IFR) agent designated as Dohor-6000A has been used to prepare halogen-free flame retardant polypropylene (PP) fibers via melting spinning. Before being blended with PP resin, a surface modification of Dohor-6000A was carried out to improve its compatibility with [...] Read more.
A novel intumescent flame retardant (IFR) agent designated as Dohor-6000A has been used to prepare halogen-free flame retardant polypropylene (PP) fibers via melting spinning. Before being blended with PP resin, a surface modification of Dohor-6000A was carried out to improve its compatibility with the PP matrix. The rheological behavior of flame retardant Dohor-6000A/PP resin, the structure, morphology, mechanical properties, flammability of the Dohor-6000A/PP fibers were studied in detail, as well as the action mode of flame retardant. X-ray diffraction (XRD) showed that the addition of Dohor-6000A did not damage the crystal as well as the orientation structure of PP matrix, which was helpful to the maintenance of mechanical properties. The presence of the IFR significantly improved the flame retardant performance and thermal stability of PP fibers. When the content of Dohor-6000A reached 25%, the fibers displayed a limiting oxygen index (LOI) value of 29.1% and good melt-drop resistance. Moreover, the peak heat release rate (PHRR) and total heat release (THR) from microscale combustion colorimetry (MCC) tests were decreased by 26.0% and 16.0% in comparison with the same conditions for pure PP fibers. In the condensed phase, the IFR promoted a carbonization process and promoted the formation of a glassy or stable foam protective layer on the surface of the polymer matrix. In addition, the IFR decomposed endothermically to release of non-combustible gases such as NH3 and CO2 which dilutes the combustible gases in the combustion zone. Full article
(This article belongs to the Special Issue Advances in Flame Retardant Polymeric Materials II)
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Article
Clinical Efficacy of Polycaprolactone β-Calcium Triphosphate Composite for Osteoconduction in Rabbit Bone Defect Model
Polymers 2021, 13(15), 2552; https://doi.org/10.3390/polym13152552 - 31 Jul 2021
Viewed by 382
Abstract
The combination of β-tricalcium phosphate (β-TCP) with polycaprolactone (PCL) has been considered a promising strategy for designing scaffolds for bone grafting. This study incorporated PCL with commercially available β-TCP (OsteoceraTM) to fabricate an injectable bone substitute and evaluate the effect of [...] Read more.
The combination of β-tricalcium phosphate (β-TCP) with polycaprolactone (PCL) has been considered a promising strategy for designing scaffolds for bone grafting. This study incorporated PCL with commercially available β-TCP (OsteoceraTM) to fabricate an injectable bone substitute and evaluate the effect of PCL on compressive strength and setting time of the hydraulic cement. The mechanical testing was compliant with the ASTM D695 and ASTM C191-13 standards. Results showed that PCL-TCP composite presented a well-defined architecture with uniform pore distribution and a significant increase in compressive strength compared with β-TCP alone. Eighteen rabbits, each with two surgically created bone defects, were treated using the PCL-TCP composites. The composite materials were resorbed and replaced by newly formed bone tissue. Both PCL-TCP and β-TCP demonstrated equivalent clinical effects on osteoconduction property in terms of the percentage of newly formed bone area measured by histomorphometric analysis. PCL-TCP was proven to be as effective as the commercially available β-TCP scaffold (OsteoceraTM). Full article
(This article belongs to the Special Issue Advanced Polymer Nanocomposites II)
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Article
Influence of Polyethylene Terephthalate Powder on Hydration of Portland Cement
Polymers 2021, 13(15), 2551; https://doi.org/10.3390/polym13152551 - 31 Jul 2021
Viewed by 408
Abstract
The management of plastic waste is a massive challenge and the recycling of plastics for newer applications is a potential solution. This study investigates the feasibility of using polyethylene terephthalate (PET) powder in cementitious composites. The changes in the strength and microstructure of [...] Read more.
The management of plastic waste is a massive challenge and the recycling of plastics for newer applications is a potential solution. This study investigates the feasibility of using polyethylene terephthalate (PET) powder in cementitious composites. The changes in the strength and microstructure of Portland cement incorporating PET powder with different replacement ratios were systematically analyzed through the measurements of compressive strength, isothermal calorimetry, X-ray diffraction, thermogravimetric analysis, and Raman spectroscopy. In addition, the possible chemical changes of cement paste samples were studied upon exposure to different conditions, including deionized water, seawater, and simulated pore solution. Based on the test results and analysis, no apparent chemical changes were observed in the cement paste samples, regardless of the exposure conditions. In contrast, the PET powder incorporated into concrete exhibited remarkable changes, which may have occurred during the mixing process. The results also suggested that the maximum replacement ratio of PET powder should be less than 10% of the binder (by mass) to minimize its influence on cement hydration, due to the interaction between water and PET. The PET-containing samples showed the presence of calcium aluminate hydrates which were absent in the neat paste sample. Full article
(This article belongs to the Special Issue Polymer Concrete and Composites)
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