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Polymers, Volume 13, Issue 12 (June-2 2021) – 131 articles

Cover Story (view full-size image): The paper discusses the possibility of using in situ generated nanofibrillar polymer nanocomposites as polymeric materials with triple shape memory, which, unlike conventional polymer blends with triple shape memory, are characterized by fully separated phase transition temperatures and strongest bonding between the polymer blends’ phase interfaces, which are critical to the shape fixing and recovery. The in situ generated nanofibrillar composites showed drastically higher values of strain recovery ratios, strain fixity ratios, faster recovery rate and better mechanical properties compared to the blend. View this paper
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11 pages, 2149 KiB  
Article
Differentiation of Polyamide 6, 6.6, and 12 Contaminations in Polyolefin-Recyclates Using HPLC Coupled to Drift-Tube Ion-Mobility Quadrupole Time-of-Flight Mass Spectrometry
by Andrea Schweighuber, Jörg Fischer and Wolfgang Buchberger
Polymers 2021, 13(12), 2032; https://doi.org/10.3390/polym13122032 - 21 Jun 2021
Cited by 5 | Viewed by 2195
Abstract
Recycling is a current hot topic with a focus especially on plastics. The quality of such plastic recyclates is of utmost importance for further processing because impurities lead to a reduction thereof. Contaminations originating from other polymers are highly problematic due to their [...] Read more.
Recycling is a current hot topic with a focus especially on plastics. The quality of such plastic recyclates is of utmost importance for further processing because impurities lead to a reduction thereof. Contaminations originating from other polymers are highly problematic due to their immiscibility with the recyclate, leading to possible product failures. Therefore, methods for the determination of polymer impurities in recyclates should be investigated. In this paper, an approach for the identification of three different polyamide grades (polyamide 6, 6.6, and 12) is presented, applicable for the analysis of polyolefin-recyclates. An HPLC equipped with a drift-tube ion-mobility QTOF-MS was used for the identification and differentiation of compounds originating from the polyamides, which were then used as markers. These marker compounds are specific for each type and can be identified by their corresponding value of the collision cross section (CCS). After a simple sample preparation, all three types of polyamides were identified within one measurement. In particular, the problematic differentiation of polyamide 6 and 6.6 was easily made possible. Full article
(This article belongs to the Section Circular and Green Polymer Science)
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17 pages, 509 KiB  
Article
Orientational Fluctuations and Bimodality in Semiflexible Nunchucks
by Panayotis Benetatos and Mohammadhosein Razbin
Polymers 2021, 13(12), 2031; https://doi.org/10.3390/polym13122031 - 21 Jun 2021
Cited by 4 | Viewed by 2802
Abstract
Semiflexible nunchucks are block copolymers consisting of two long blocks with high bending rigidity jointed by a short block of lower bending stiffness. Recently, the DNA nanotube nunchuck was introduced as a simple nanoinstrument that mechanically magnifies the bending angle of short double-stranded [...] Read more.
Semiflexible nunchucks are block copolymers consisting of two long blocks with high bending rigidity jointed by a short block of lower bending stiffness. Recently, the DNA nanotube nunchuck was introduced as a simple nanoinstrument that mechanically magnifies the bending angle of short double-stranded (ds) DNA and allows its measurement in a straightforward way [Fygenson et al., Nano Lett. 2020, 20, 2, 1388–1395]. It comprises two long DNA nanotubes linked by a dsDNA segment, which acts as a hinge. The semiflexible nunchuck geometry also appears in dsDNA with a hinge defect (e.g., a quenched denaturation bubble or a nick), and in end-linked stiff filaments. In this article, we theoretically investigate various aspects of the conformations and the tensile elasticity of semiflexible nunchucks. We analytically calculate the distribution of bending fluctuations of a wormlike chain (WLC) consisting of three blocks with different bending stiffness. For a system of two weakly bending WLCs end-jointed by a rigid kink, with one end grafted, we calculate the distribution of positional fluctuations of the free end. For a system of two weakly bending WLCs end-jointed by a hinge modeled as harmonic bending spring, with one end grafted, we calculate the positional fluctuations of the free end. We show that, under certain conditions, there is a pronounced bimodality in the transverse fluctuations of the free end. For a semiflexible nunchuck under tension, under certain conditions, there is bimodality in the extension as a function of the hinge position. We also show how steric repulsion affects the bending fluctuations of a rigid-rod nunchuck. Full article
(This article belongs to the Special Issue Semiflexible Polymers II)
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19 pages, 4853 KiB  
Article
Sulfonated Polysulfone/TiO2(B) Nanowires Composite Membranes as Polymer Electrolytes in Fuel Cells
by Maria Jose Martinez-Morlanes, Carmen de la Torre-Gamarra, María Teresa Pérez-Prior, Sara Lara-Benito, Carmen del Rio, Alejandro Várez and Belen Levenfeld
Polymers 2021, 13(12), 2030; https://doi.org/10.3390/polym13122030 - 21 Jun 2021
Cited by 11 | Viewed by 2627
Abstract
New proton conducting membranes based on sulfonated polysulfone (sPSU) reinforced with TiO2(B) nanowires (1, 2, 5 and 10 wt.%) were synthesized and characterized. TiO2(B) nanowires were synthesized by means of a hydrothermal method by mixing TiO2 precursor in [...] Read more.
New proton conducting membranes based on sulfonated polysulfone (sPSU) reinforced with TiO2(B) nanowires (1, 2, 5 and 10 wt.%) were synthesized and characterized. TiO2(B) nanowires were synthesized by means of a hydrothermal method by mixing TiO2 precursor in aqueous solution of NaOH as solvent. The presence of the TiO2(B) nanowires into the polymer were confirmed by means of Field Emission Scanning Electron Microscopy, Fourier transform infrared and X-ray diffraction. The thermal study showed an increase of almost 20 °C in the maximum temperature of sPSU backbone decomposition due to the presence of 10 wt.% TiO2(B) nanowires. Water uptake also is improved with the presence of hydrophilic TiO2(B) nanowires. Proton conductivity of sPSU with 10 wt.% TiO2(B) nanowires was 21 mS cm−1 (at 85 °C and 100% RH). Under these experimental conditions the power density was 350 mW cm−2 similar to the value obtained for Nafion 117. Considering all these obtained results, the composite membrane doped with 10 wt.% TiO2(B) nanowires is a promising candidate as proton exchange electrolyte in fuel cells (PEMFCs), especially those operating at high temperatures. Full article
(This article belongs to the Section Polymer Applications)
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18 pages, 8044 KiB  
Article
On the Mechanical Response of Silicon Dioxide Nanofiller Concentration on Fused Filament Fabrication 3D Printed Isotactic Polypropylene Nanocomposites
by Nectarios Vidakis, Markos Petousis, Emmanouil Velidakis, Lazaros Tzounis, Nikolaos Mountakis, Apostolos Korlos, Peder Erik Fischer-Griffiths and Sotirios Grammatikos
Polymers 2021, 13(12), 2029; https://doi.org/10.3390/polym13122029 - 21 Jun 2021
Cited by 22 | Viewed by 2823
Abstract
Utilization of advanced engineering thermoplastic materials in fused filament fabrication (FFF) 3D printing process is critical in expanding additive manufacturing (AM) applications. Polypropylene (PP) is a widely used thermoplastic material, while silicon dioxide (SiO2) nanoparticles (NPs), which can be found in [...] Read more.
Utilization of advanced engineering thermoplastic materials in fused filament fabrication (FFF) 3D printing process is critical in expanding additive manufacturing (AM) applications. Polypropylene (PP) is a widely used thermoplastic material, while silicon dioxide (SiO2) nanoparticles (NPs), which can be found in many living organisms, are commonly employed as fillers in polymers to improve their mechanical properties and processability. In this work, PP/SiO2 nanocomposite filaments at various concentrations were developed following a melt mixing extrusion process, and used for FFF 3D printing of specimens’ characterization according to international standards. Tensile, flexural, impact, microhardness, and dynamic mechanical analysis (DMA) tests were conducted to determine the effect of the nanofiller loading on the mechanical and viscoelastic properties of the polymer matrix. Scanning electron microscopy (SEM), Raman spectroscopy and atomic force microscopy (AFM) were performed for microstructural analysis, and finally melt flow index (MFI) tests were conducted to assess the melt rheological properties. An improvement in the mechanical performance was observed for silica loading up to 2.0 wt.%, while 4.0 wt.% was a potential threshold revealing processability challenges. Overall, PP/SiO2 nanocomposites could be ideal candidates for advanced 3D printing engineering applications towards structural plastic components with enhanced mechanical performance. Full article
(This article belongs to the Special Issue Polymers in Additive Manufacturing)
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16 pages, 5511 KiB  
Article
Influence of HRGO Nanoplatelets on Behaviour and Processing of PMMA Bone Cement for Surgery
by Jaime Orellana, Ynés Yohana Pastor, Fernando Calle and José Ygnacio Pastor
Polymers 2021, 13(12), 2027; https://doi.org/10.3390/polym13122027 - 21 Jun 2021
Cited by 8 | Viewed by 1926
Abstract
Bone cement, frequently based on poly (methyl methacrylate), is commonly used in different arthroplasty surgical procedures and its use is essential for prosthesis fixation. However, its manufacturing process reaches high temperatures (up to 120 °C), producing necrosis in the patients’ surrounding tissues. To [...] Read more.
Bone cement, frequently based on poly (methyl methacrylate), is commonly used in different arthroplasty surgical procedures and its use is essential for prosthesis fixation. However, its manufacturing process reaches high temperatures (up to 120 °C), producing necrosis in the patients’ surrounding tissues. To help avoid this problem, the addition of graphene could delay the polymerisation of the methyl methacrylate as it could, simultaneously, favour the optimisation of the composite material’s properties. In this work, we address the effect of different percentages of highly reduced graphene oxide with different wt.% (0.10, 0.50, and 1.00) and surface densities (150, 300, 500, and 750 m2/g) on the physical, mechanical, and thermal properties of commercial poly (methyl methacrylate)-based bone cement and its processing. It was noted that a lower sintering temperature was achieved with this addition, making it less harmful to use in surgery and reducing its adverse effects. In contrast, the variation of the density of the materials did not introduce significant changes, which indicates that the addition of highly reduced graphene oxide would not significantly increase bone porosity. Lastly, the mechanical properties (strength, elastic modulus, and fracture toughness) were reduced by almost 20%. Nevertheless, their typical values are high enough that these new materials could still fulfil their structural function. In conclusion, this paper presents a way to control the sintering temperature, without significant degradation of the mechanical performance, by adding highly reduced graphene oxide so that local necrosis of bone cement based on poly (methyl methacrylate) used in surgery is avoided. Full article
(This article belongs to the Special Issue Intrinsically Biocompatible Polymer Systems II)
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13 pages, 2734 KiB  
Communication
Bioprinting of Matrigel Scaffolds for Cancer Research
by Paola De Stefano, Francesco Briatico-Vangosa, Elena Bianchi, Alessandro Filippo Pellegata, Ariel Hartung de Hartungen, Pietro Corti and Gabriele Dubini
Polymers 2021, 13(12), 2026; https://doi.org/10.3390/polym13122026 - 21 Jun 2021
Cited by 13 | Viewed by 3133
Abstract
Cancer is one of the most life-threatening diseases worldwide. Despite the huge efforts, the failure rate of therapies remains high due to cells heterogeneity, so physiologically relevant models are strictly necessary. Bioprinting is a technology able to form highly complex 3D tissue models [...] Read more.
Cancer is one of the most life-threatening diseases worldwide. Despite the huge efforts, the failure rate of therapies remains high due to cells heterogeneity, so physiologically relevant models are strictly necessary. Bioprinting is a technology able to form highly complex 3D tissue models and enables the creation of large-scale constructs. In cancer research, Matrigel® is the most widely used matrix, but it is hardly bioprinted pure, without the use of any other bioink as reinforcement. Its complex rheological behavior makes the control with a standard bioprinting process nearly impossible. In this work, we present a customized bioprinting strategy to produce pure Matrigel® scaffolds with good shape fidelity. To this aim, we realized a custom-made volumetric dispensing system and performed printability evaluations. To determine optimal printing parameters, we analyzed fibers spreading ratio on simple serpentines. After identifying an optimal flow rate of 86.68 ± 5.77 µL/min and a printing speed of 10 mm/min, we moved forward to evaluate printing accuracy, structural integrity and other key parameters on single and multi-layer grids. Results demonstrated that Matrigel® was able to maintain its structure in both simple and complex designs, as well as in single and multilayer structures, even if it does not possess high mechanical strength. In conclusion, the use of volumetric dispensing allowed printing pure Matrigel® constructs with a certain degree of shape fidelity on both single and multiple layers. Full article
(This article belongs to the Special Issue Polymeric Materials as Scaffolds for Tissue Engineering)
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16 pages, 18793 KiB  
Article
Ultrafine Friction Grinding of Lignin for Development of Starch Biocomposite Films
by Seyedeh Najmeh Mousavi, Noureddin Nazarnezhad, Ghasem Asadpour, Sunil Kumar Ramamoorthy and Akram Zamani
Polymers 2021, 13(12), 2024; https://doi.org/10.3390/polym13122024 - 21 Jun 2021
Cited by 9 | Viewed by 2520
Abstract
The work demonstrates the utilization of fractionalized lignin from the black liquor of soda pulping for the development of starch-lignin biocomposites. The effect of ultrafine friction grinding on lignin particle size and properties of the biocomposites was investigated. Microscopic analysis and membrane filtration [...] Read more.
The work demonstrates the utilization of fractionalized lignin from the black liquor of soda pulping for the development of starch-lignin biocomposites. The effect of ultrafine friction grinding on lignin particle size and properties of the biocomposites was investigated. Microscopic analysis and membrane filtration confirmed the reduction of lignin particle sizes down to micro and nanoparticles during the grinding process. Field Emission Scanning Electron Microscopy confirmed the compatibility between lignin particles and starch in the composites. The composite films were characterized for chemical structure, ultraviolet blocking, mechanical, and thermal properties. Additional grinding steps led to the reduction of large lignin particles and the produced particles were uniform. The formation of 7.7 to 11.3% lignin nanoparticles was confirmed in the two steps of membrane filtration. The highest tensile strain of the biocomposite films were 5.09 MPa, which displays a 40% improvement compared to starch films. Further, thermal stability of the composite films was better than that of starch films. The results from ultraviolet transmission showed that the composite films could act as an ultraviolet barrier in packaging applications. Full article
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13 pages, 3296 KiB  
Article
Controlled Polyelectrolyte Association of Chitosan and Carboxylated Nano-Fibrillated Cellulose by Desalting
by Sarah Amine, Alexandra Montembault, Matthieu Fumagalli, Anayancy Osorio-Madrazo and Laurent David
Polymers 2021, 13(12), 2023; https://doi.org/10.3390/polym13122023 - 21 Jun 2021
Cited by 12 | Viewed by 2526
Abstract
We prepared chitosan (CHI) hydrogels reinforced with highly charged cellulose nanofibrils (CNF) by the desalting method. To this end, the screening of electrostatic interactions between CHI polycation and CNF polyanion was performed by adding NaCl at 0.4 mol/L to the chitosan acetate solution [...] Read more.
We prepared chitosan (CHI) hydrogels reinforced with highly charged cellulose nanofibrils (CNF) by the desalting method. To this end, the screening of electrostatic interactions between CHI polycation and CNF polyanion was performed by adding NaCl at 0.4 mol/L to the chitosan acetate solution and to the cellulose nanofibrils suspension. The polyelectrolyte complexation between CHI polycation and CNF polyanion was then triggered by desalting the CHI/CNF aqueous mixture by multistep dialysis, in large excess of chitosan. Further gelation of non-complexed CHI was performed by alkaline neutralization of the polymer, yielding high reinforcement effects as probed by the viscoelastic properties of the final hydrogel. The results showed that polyelectrolyte association by desalting can be achieved with a polyanionic nanoparticle partner. Beyond obtaining hydrogel with improved mechanical performance, these composite hydrogels may serve as precursor for dried solid forms with high mechanical properties. Full article
(This article belongs to the Special Issue Chitosan, Chitin, and Cellulose Nanofiber Biomaterials)
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43 pages, 23383 KiB  
Review
Functionalized Particles Designed for Targeted Delivery
by Teresa Basinska, Mariusz Gadzinowski, Damian Mickiewicz and Stanislaw Slomkowski
Polymers 2021, 13(12), 2022; https://doi.org/10.3390/polym13122022 - 21 Jun 2021
Cited by 10 | Viewed by 2880
Abstract
Pure bioactive compounds alone can only be exceptionally administered in medical treatment. Usually, drugs are produced as various forms of active compounds and auxiliary substances, combinations assuring the desired healing functions. One of the important drug forms is represented by a combination of [...] Read more.
Pure bioactive compounds alone can only be exceptionally administered in medical treatment. Usually, drugs are produced as various forms of active compounds and auxiliary substances, combinations assuring the desired healing functions. One of the important drug forms is represented by a combination of active substances and particle-shaped polymer in the nano- or micrometer size range. The review describes recent progress in this field balanced with basic information. After a brief introduction, the paper presents a concise overview of polymers used as components of nano- and microparticle drug carriers. Thereafter, progress in direct synthesis of polymer particles with functional groups is discussed. A section is devoted to formation of particles by self-assembly of homo- and copolymer-bearing functional groups. Special attention is focused on modification of the primary functional groups introduced during particle preparation, including introduction of ligands promoting anchorage of particles onto the chosen living cell types by interactions with specific receptors present in cell membranes. Particular attention is focused on progress in methods suitable for preparation of particles loaded with bioactive substances. The review ends with a brief discussion of the still not answered questions and unsolved problems. Full article
(This article belongs to the Special Issue Polymers and Drug Delivery)
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16 pages, 1994 KiB  
Article
Self-Initiated Butyl Acrylate Polymerizations in Bulk and in Solution Monitored By In-Line Techniques
by Jonas Mätzig, Marco Drache and Sabine Beuermann
Polymers 2021, 13(12), 2021; https://doi.org/10.3390/polym13122021 - 21 Jun 2021
Cited by 9 | Viewed by 2427
Abstract
High-temperature acrylate polymerizations are technically relevant, but yet not fully understood. In particular the mechanism and the kinetics of the thermal self-initiation is a topic of current research. To obtain more detailed information the conversion dependence of the polymerization rate, rbr, [...] Read more.
High-temperature acrylate polymerizations are technically relevant, but yet not fully understood. In particular the mechanism and the kinetics of the thermal self-initiation is a topic of current research. To obtain more detailed information the conversion dependence of the polymerization rate, rbr, is determined via in-line DSC and FT-NIR spectroscopy for reactions in bulk and in solution at temperatures ranging from 80 to 160 °C. Solution polymerizations revealed that dioxane is associated with the highest rbr, while aromatic solvents result in the lowest values of rbr. Interestingly, rbr for polymerizations in solution with dioxane depends on the actual monomer concentration at a given time in the system, but is not depending on the initial monomer concentration. The overall rate of polymerization in bulk and in solution is well represented by an equation with three or four parameters, respectively, being estimated by multiple linear regression and the temperature as additional parameter. Full article
(This article belongs to the Section Polymer Chemistry)
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16 pages, 3686 KiB  
Article
The Influence of Neem Oil and Its Glyceride on the Structure and Characterization of Castor Oil-Based Polyurethane Foam
by Yi-Han Liao, You-Lin Su and Yi-Chun Chen
Polymers 2021, 13(12), 2020; https://doi.org/10.3390/polym13122020 - 21 Jun 2021
Cited by 6 | Viewed by 3196
Abstract
Neem (Azadirachta indica) oil is a non-edible oil that contains azadirachtin, which can be used as a biopesticide. This study synthesizes bio-based polyurethane (PU) foam from neem and castor (Ricinus communis L.) oil at normal temperature and pressure. Neem oil [...] Read more.
Neem (Azadirachta indica) oil is a non-edible oil that contains azadirachtin, which can be used as a biopesticide. This study synthesizes bio-based polyurethane (PU) foam from neem and castor (Ricinus communis L.) oil at normal temperature and pressure. Neem oil can be reacted to narrow-distribution polyol by transesterification of oil and glycerol. Neem oil glyceride (NOG) can be used as polyol for bio-based PU foams and can be blended with castor oil homogeneously to reduce the cost of production. The composition of polyol was castor oil and 0 to 20% molar ratios of NOG. Hexamethylene diisocyanate trimer (Desmodur N) was used as isocyanate. The molar ratios of NCO/OH were set as 1.0, 1.5 and 2.0. The average hydroxyl contents of castor oil, neem oil and NOG were 2.7 mmol/g, 0.1 mmol/g and 5.1 mmol/g, respectively. The reaction time of bio-based PU foam could be adjusted between 5 to 10 min, which is acceptable for manufacturing. The densities of PU foams were between 49.7 and 116.2 kg/m3 and decreased with increasing NCO/OH and NOG ratios and decreasing neem oil. The ranges of specific compressive strength of foams were from 0.0056 to 0.0795 kPa·m3/kg. Increasing the NOG and neem oil ratio significantly enhanced the specific compressive strength in the low NCO/OH ratio. The solvent resistance and thermogravimetric (TG) results showed that the foams have high water and thermal stability. NOG can help to increase solvent resistance. Adding neem oil reduces the solvent resistance. The results indicated that increasing NCO/OH and NOG ratios increases the cross-linking density and hard segment content of PU foams. This investigation demonstrated that castor oil-based PU foams are improved by adding NOG to the polyol mixture. PU foam has excellent properties. Neem oil can be used in manufacturing processes to produce high-performance foams via a green synthesis process. Full article
(This article belongs to the Special Issue Bio-Based Polymers for Industrial Applications)
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16 pages, 4190 KiB  
Article
Flow Characteristics, Mechanical, Thermal, and Thermomechanical Properties, and 3D Printability of Biodegradable Polylactide Containing Boehmite at Different Loadings
by Dimakatso Makwakwa, Vincent Ojijo, Jayita Bandyopadhyay and Suprakas Sinha Ray
Polymers 2021, 13(12), 2019; https://doi.org/10.3390/polym13122019 - 21 Jun 2021
Cited by 7 | Viewed by 2482
Abstract
This work investigates the effects of modification of polylactide (PLA) using dicumyl peroxide (DCP) as a crosslinker and Joncryl as a chain extender on boehmite distribution. The PLA/boehmite (PLA/BA) composites at various concentrations were prepared via a twin-screw extruder. Transmission electron microscopy showed [...] Read more.
This work investigates the effects of modification of polylactide (PLA) using dicumyl peroxide (DCP) as a crosslinker and Joncryl as a chain extender on boehmite distribution. The PLA/boehmite (PLA/BA) composites at various concentrations were prepared via a twin-screw extruder. Transmission electron microscopy showed more agglomerations of BA particles when Joncryl and DCP were added individually to the PLA matrix, with lesser agglomeration upon simultaneous addition of DCP and Joncryl, which led to an enhancement of 10.7% of the heat distortion temperature and 8.8% of the modulus. The existence of fine dispersed BA particles in the BA3 sample improved the cold crystallization by 4 °C. Moreover, the maximum reinforcing effect in increasing the storage modulus of the prepared system was observed upon concurrent addition of DCP and Joncryl, with minimum reinforcing effect upon individual addition of DCP and Joncryl. In general, a bio-based PLA composite base BA with enhanced properties was successfully prepared for various applications. Full article
(This article belongs to the Special Issue Mechanical Performance of Sustainable Bio-Based Compounds)
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9 pages, 1074 KiB  
Article
The Effect of Stereocomplex Polylactide Particles on the Stereocomplexation of High Molecular Weight Polylactide Blends
by Muhammad Samsuri, Ihsan Iswaldi and Purba Purnama
Polymers 2021, 13(12), 2018; https://doi.org/10.3390/polym13122018 - 21 Jun 2021
Cited by 6 | Viewed by 1942
Abstract
Stereocomplexation is one of several approaches for improving polylactide (PLA) properties. The high molecular weight of poly L-lactide (PLLA) and poly D-lactide (PDLA) homopolymers are a constraint during the formation of stereocomplex PLAs (s-PLAs). The presence of s-PLA particles in PLA PLLA/PDLA blends [...] Read more.
Stereocomplexation is one of several approaches for improving polylactide (PLA) properties. The high molecular weight of poly L-lactide (PLLA) and poly D-lactide (PDLA) homopolymers are a constraint during the formation of stereocomplex PLAs (s-PLAs). The presence of s-PLA particles in PLA PLLA/PDLA blends can initiate the formation of s-PLA crystalline structures. We used the solution casting method to study the utilization of s-PLA materials from high molecular weight PLLA/PDLA blends for increasing s-PLA formation. The s-PLA particles initiated the formation of high molecular weight PLLA/PDLA blends, obtaining 49.13% s-PLA and 44.34% of the total crystalline fraction. In addition, the mechanical properties were enhanced through s-PLA crystalline formation and the increasing of total crystallinity of the PLLA/PDLA blends. The s-PLA particles supported initiation for s-PLA formation and acted as a nucleating agent for PLA homopolymers. These unique characteristics of s-PLA particles show potential to overcome the molecular weight limitation for stereocomplexation of PLLA/PDLA blends. Full article
(This article belongs to the Special Issue Advanced Polymer-Based Biomaterials)
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24 pages, 4671 KiB  
Review
Synergic Effect of TiO2 Filler on the Mechanical Properties of Polymer Nanocomposites
by Cristina Cazan, Alexandru Enesca and Luminita Andronic
Polymers 2021, 13(12), 2017; https://doi.org/10.3390/polym13122017 - 20 Jun 2021
Cited by 74 | Viewed by 8739
Abstract
Nanocomposites with polymer matrix offer excellent opportunities to explore new functionalities beyond those of conventional materials. TiO2, as a reinforcement agent in polymeric nanocomposites, is a viable strategy that significantly enhanced their mechanical properties. The size of the filler plays an [...] Read more.
Nanocomposites with polymer matrix offer excellent opportunities to explore new functionalities beyond those of conventional materials. TiO2, as a reinforcement agent in polymeric nanocomposites, is a viable strategy that significantly enhanced their mechanical properties. The size of the filler plays an essential role in determining the mechanical properties of the nanocomposite. A defining feature of polymer nanocomposites is that the small size of the fillers leads to an increase in the interfacial area compared to traditional composites. The interfacial area generates a significant volume fraction of interfacial polymer, with properties different from the bulk polymer even at low loadings of the nanofiller. This review aims to provide specific guidelines on the correlations between the structures of TiO2 nanocomposites with polymeric matrix and their mechanical properties. The correlations will be established and explained based on interfaces realized between the polymer matrix and inorganic filler. The paper focuses on the influence of the composition parameters (type of polymeric matrix, TiO2 filler with surface modified/unmodified, additives) and technological parameters (processing methods, temperature, time, pressure) on the mechanical strength of TiO2 nanocomposites with the polymeric matrix. Full article
(This article belongs to the Special Issue Advances in Sustainable Polymeric Materials)
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15 pages, 2740 KiB  
Article
Thermal and Chemical Characterization of Kenaf Fiber (Hibiscus cannabinus) Reinforced Epoxy Matrix Composites
by Thuane Teixeira da Silva, Pedro Henrique Poubel Mendonça da Silveira, Matheus Pereira Ribeiro, Maurício Ferrapontoff Lemos, Ana Paula da Silva, Sergio Neves Monteiro and Lucio Fabio Cassiano Nascimento
Polymers 2021, 13(12), 2016; https://doi.org/10.3390/polym13122016 - 20 Jun 2021
Cited by 26 | Viewed by 3772
Abstract
Kenaf (Hibiscus cannabinus L.) is one of the most investigated and industrially applied natural fibers for polymer composite reinforcement. However, relatively limited information is available regarding its epoxy composites. In this work, both thermal and chemical properties were, for the first [...] Read more.
Kenaf (Hibiscus cannabinus L.) is one of the most investigated and industrially applied natural fibers for polymer composite reinforcement. However, relatively limited information is available regarding its epoxy composites. In this work, both thermal and chemical properties were, for the first time, determined in kenaf fiber reinforced epoxy matrix composites. Through XRD analysis, a microfibrillar angle of 7.1° and crystallinity index of 44.3% was obtained. The FTIR analysis showed the functional groups normally found for natural lignocellulosic fibers. TMA analysis of the composites with 10 vol% and 20 vol% of kenaf fibers disclosed a higher coefficient of thermal expansion. The TG/DTG results of the epoxy composites revealed enhanced thermal stability when compared to plain epoxy. The DSC results corroborated the results obtained by TGA, which indicated a higher mass loss in the first stage for kenaf when compared to its composites. These results might contribute to kenaf fiber composite applications requiring superior performance. Full article
(This article belongs to the Section Polymer Applications)
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18 pages, 4533 KiB  
Article
Lawsone Derivatives as Efficient Photopolymerizable Initiators for Free-Radical, Cationic Photopolymerizations, and Thiol—Ene Reactions
by Christine Elian, Vlasta Brezová, Pauline Sautrot-Ba, Martin Breza and Davy-Louis Versace
Polymers 2021, 13(12), 2015; https://doi.org/10.3390/polym13122015 - 20 Jun 2021
Cited by 10 | Viewed by 2568
Abstract
Two new photopolymerizable vinyl (2-(allyloxy) 1,4-naphthoquinone, HNQA) and epoxy (2-(oxiran-2yl methoxy) 1,4-naphthoquinone, HNQE) photoinitiators derived from lawsone were designed in this paper. These new photoinitiators can be used as one-component photoinitiating systems for the free-radical photopolymerization of acrylate bio-based monomer without [...] Read more.
Two new photopolymerizable vinyl (2-(allyloxy) 1,4-naphthoquinone, HNQA) and epoxy (2-(oxiran-2yl methoxy) 1,4-naphthoquinone, HNQE) photoinitiators derived from lawsone were designed in this paper. These new photoinitiators can be used as one-component photoinitiating systems for the free-radical photopolymerization of acrylate bio-based monomer without the addition of any co-initiators. As highlighted by the electron paramagnetic resonance (EPR) spin-trapping results, the formation of carbon-centered radicals from an intermolecular H abstraction reaction was evidenced and can act as initiating species. Interestingly, the introduction of iodonium salt (Iod) used as a co-initiator has led to (1) the cationic photopolymerization of epoxy monomer with high final conversions and (2) an increase of the rates of free-radical polymerization of the acrylate bio-based monomer; we also demonstrated the concomitant thiol–ene reaction and cationic photopolymerizations of a limonene 1,2 epoxide/thiol blend mixture with the HNQA/Iod photoinitiating system. Full article
(This article belongs to the Special Issue Photoinitiators and Photopolymerization Technology)
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13 pages, 4458 KiB  
Article
Viscoelasticity, Mechanical Properties, and In Vitro Bioactivity of Gelatin/Borosilicate Bioactive Glass Nanocomposite Hydrogels as Potential Scaffolds for Bone Regeneration
by Asmaa M. Abd El-Aziz, Ahmed Abd El-Fattah, Azza El-Maghraby, Doaa A. Ghareeb and Sherif Kandil
Polymers 2021, 13(12), 2014; https://doi.org/10.3390/polym13122014 - 20 Jun 2021
Cited by 11 | Viewed by 2783
Abstract
Chemical cross-linking was used to create nanocomposite hydrogels made up of gelatin (G) and borosilicate bioactive glass (BBG) with different content (0, 3, and 5 wt.%). The G/BBG nanocomposite hydrogels were studied for their morphology, mechanical properties, and viscoelasticity. SEM images revealed a [...] Read more.
Chemical cross-linking was used to create nanocomposite hydrogels made up of gelatin (G) and borosilicate bioactive glass (BBG) with different content (0, 3, and 5 wt.%). The G/BBG nanocomposite hydrogels were studied for their morphology, mechanical properties, and viscoelasticity. SEM images revealed a macroporous interconnected structure with particles scattered across the pore walls. Studies of water absorption and degradation confirmed that the nanocomposite scaffolds were hydrophilic and biodegradable. The addition of 5% BBG to the scaffold formulations increased the compressive modulus by 413% and the compressive intensity by 20%, respectively. At all frequency ranges tested, the storage modulus (G′) was greater than the loss modulus (G″), revealing a self-standing elastic nanocomposite hydrogel. The nanocomposite scaffolds facilitated apatite formation while immersed in simulated body fluid (SBF). According to the findings, G/BBG nanocomposite scaffolds could be a promising biomaterial for bone regeneration. Full article
(This article belongs to the Special Issue Hydrogel-Based Composites for Biomedical Applications)
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11 pages, 3669 KiB  
Article
Conductive Polymer (Graphene/PPy)–BiPO4 Composite Applications in Humidity Sensors
by Zhen Zhu, Wang-De Lin, Zhi-Yi Lin, Ming-Hong Chuang, Ren-Jang Wu and Murthy Chavali
Polymers 2021, 13(12), 2013; https://doi.org/10.3390/polym13122013 - 20 Jun 2021
Cited by 7 | Viewed by 2136
Abstract
In this particular experiment, a chain of conductive polymer graphene/polypyrrole (Gr/PPy) and BiPO4—or (Gr/PPy)–BiPO4—materials were prepared and used as moisture-sensitive materials. The structure and morphology of the conductive polymer (Gr/PPy)–BiPO4 materials were analyzed using an X-ray diffractometer, scanning [...] Read more.
In this particular experiment, a chain of conductive polymer graphene/polypyrrole (Gr/PPy) and BiPO4—or (Gr/PPy)–BiPO4—materials were prepared and used as moisture-sensitive materials. The structure and morphology of the conductive polymer (Gr/PPy)–BiPO4 materials were analyzed using an X-ray diffractometer, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Moreover, properties such as hysteresis loop, impedance, sensing response, and response and recovery time were calculated and evaluated using an inductance–capacitance–resistance analyzer. The data expressed that PPy/BiPO4, as prepared in this study, exhibited excellent sensing properties, with impedance changing by only a few orders of range. Furthermore, the response time and time of recovery were 340 s and 60 s, respectively, and negligible humidity hysteresis occurred at different relative humidities. Therefore, conductive PPy/BiPO4, as prepared in the present study, is an excellent candidate for application in humidity sensors. Full article
(This article belongs to the Section Polymer Applications)
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26 pages, 16241 KiB  
Article
Antifungal Activities of Wood and Non-Wood Kraft Handsheets Treated with Melia azedarach Extract Using SEM and HPLC Analyses
by Mohamed Z. M. Salem, Saqer S. Alotaibi, Wael A. A. Abo Elgat, Ayman S. Taha, Yahia G. D. Fares, Ahmed M. El-Shehawi and Rehab Y. Ghareeb
Polymers 2021, 13(12), 2012; https://doi.org/10.3390/polym13122012 - 20 Jun 2021
Cited by 4 | Viewed by 2436
Abstract
The main objective of this work was to evaluate pulp produced by kraft cooking for wood materials (WMT) (Bougainvillea spectabilis, Ficus altissima, and F. elastica) and non-wood materials (NWMT) (Sorghum bicolor and Zea mays stalks) and to study [...] Read more.
The main objective of this work was to evaluate pulp produced by kraft cooking for wood materials (WMT) (Bougainvillea spectabilis, Ficus altissima, and F. elastica) and non-wood materials (NWMT) (Sorghum bicolor and Zea mays stalks) and to study the fungal activity of handsheets treated with Melia azedarach heartwood extract (MAHE) solutions. Through the aforementioned analyses, the ideal cooking conditions were determined for each raw material based on the lignin percentage present. After cooking, pulp showed a decrease in the Kappa number produced from WMT, ranging from 16 to 17. This was in contrast with NWMT, which had Kappa numbers ranging from 31 to 35. A difference in the optical properties of the pulp produced from WMT was also observed (18 to 29%) compared with pulp produced from NWMT (32.66 to 35.35%). As for the evaluation of the mechanical properties, the tensile index of the pulp ranged from 30.5 to 40 N·m/g for WMT and from 44.33 to 47.43 N·m/g for NWMT; the tear index ranged from 1.66 to 2.55 mN·m2/g for WMT and from 4.75 to 5.87 mN·m2/g for NWMT; and the burst index ranged from 2.35 to 2.85 kPa·m2/g for WMT and from 3.92 to 4.76 kPa·m2/g for NWMT. Finally, the double fold number was 3 compared with that of pulp produced from pulp, which showed good values ranging from 36 to 55. In the SEM examination, sheets produced from treated handsheets with extract from MAHE showed no growth of Aspergillus fumigatus over paper discs manufactured from B. speclabilis pulp wood. Pulp paper produced from Z. mays and S. bicolor stalks was treated with 1% MAHE, while pulp paper from F. elastica was treated with 0.50% and 1% MAHE. With the addition of 0.5 or 1% MAHE, Fusarium culmorum showed no increase in growth over the paper manufactured from B. speclabilis, F. altissima, F. elastica and Zea mays pulps with visual inhibition zones found. There was almost no growth of S. solani in paper discs manufactured from pulps treated with 1% MAHE. This is probably due to the phytochemical compounds present in the extract. The HPLC analysis of MAHE identified p-hydroxybenzoic acid, caffeine, rutin, chlorogenic acid, benzoic acid, quinol, and quercetin as the main compounds, and these were present in concentrations of 3966.88, 1032.67, 834.13, 767.81, 660.64, 594.86, and 460.36 mg/Kg extract, respectively. Additionally, due to the importance of making paper from agricultural waste (stalks of S. bicolor and Z. mays), the development of sorghum and corn with high biomass is suggested. Full article
(This article belongs to the Special Issue Lignocellulosic Composites: Processing and Applications)
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18 pages, 7077 KiB  
Article
Evaluation of the Photocatalytic Activity and Anticorrosion Performance of Electrospun Fibers Doped with Metallic Oxides
by Ainhoa Albistur, Pedro J. Rivero, Joseba Esparza and Rafael Rodríguez
Polymers 2021, 13(12), 2011; https://doi.org/10.3390/polym13122011 - 20 Jun 2021
Cited by 13 | Viewed by 2269
Abstract
This paper reports the development and characterization of a multifunctional coating that combines anticorrosion and photocatalytic properties, deposited by means of the electrospinning technique. In the first step, a functional electrospun fiber mat composed of poly(acrylic acid) (PAA) and β-cyclodextrin (β-CD) was obtained, [...] Read more.
This paper reports the development and characterization of a multifunctional coating that combines anticorrosion and photocatalytic properties, deposited by means of the electrospinning technique. In the first step, a functional electrospun fiber mat composed of poly(acrylic acid) (PAA) and β-cyclodextrin (β-CD) was obtained, showing high water insolubility and great adhesion increased by means of a thermal crosslinking process (denoted as PAA + β-CD). In the second step, the fibers were doped with particles of titanium dioxide (denoted as PAA + β-CD/TiO2) and titanium dioxide plus iron oxide (denoted as PAA + β-CD/TiO2/Fe2O3). The morphology and fiber diameter of the electrospun mats were evaluated by using confocal microscopy, whereas the presence of the metal oxides in the electrospun fibers was corroborated by scanning electron microscopy (SEM) and X-ray fluorescence (XRF), respectively. In addition, electrochemical tests in saline solution revealed that the sample composed of PAA + β-CD/TiO2/Fe2O3 showed the highest corrosion protection efficiency of all the samples, which was directly associated to lower corrosion current density and higher corrosion potential. Furthermore, the paper reports a novel approach to in situ determination of methylene blue (MB) degradation onto the coating. The results revealed complete degradation of MB, which is perfectly appreciated by total discoloration of the film in the irradiated zone (from bluish to a white spot). The main conclusions of this research are the efficiency of the electrospun system PAA + β-CD/TiO2/Fe2O3 for developing photocatalytic activity and corrosion protection and the utility of the dry MB discoloration tests to evaluate photocatalytic activity. Full article
(This article belongs to the Section Polymer Applications)
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13 pages, 30036 KiB  
Article
Electrical Heating Performance of Graphene/PLA-Based Various Types of Auxetic Patterns and Its Composite Cotton Fabric Manufactured by CFDM 3D Printer
by Hyelim Kim and Sunhee Lee
Polymers 2021, 13(12), 2010; https://doi.org/10.3390/polym13122010 - 19 Jun 2021
Cited by 3 | Viewed by 2019
Abstract
To evaluate the electrical heating performance by auxetic pattern, re-entrant honeycomb (RE), chiral truss (CT), honeycomb (HN), and truss (TR), using graphene/PLA (Polylactic acid) filament, were manufactured by CFDM (conveyor fused deposition modelling) 3D printer. In addition, HN and TR, which was indicated [...] Read more.
To evaluate the electrical heating performance by auxetic pattern, re-entrant honeycomb (RE), chiral truss (CT), honeycomb (HN), and truss (TR), using graphene/PLA (Polylactic acid) filament, were manufactured by CFDM (conveyor fused deposition modelling) 3D printer. In addition, HN and TR, which was indicated to have an excellent electrical heating property, were selected to verify the feasibility of applying fabric heating elements. The result of morphology was that the number of struts constituting the unit cell and the connected points were TR < HN < CT < RE. It was also influenced by the surface resistivity and electrical heating performance. RE, which has the highest number of struts constituting the unit cell and the relative density, had the highest value of surface resistivity, and the lowest value was found in the opposite TR. In the electrical heating performance of samples, the heat distribution of RE was limited even when the applied voltage was increased. However, HN and TR were diffused throughout the sample. In addition, the surface temperature of RE, CT, HN, and TR was about 72.4 °C, 83.1 °C, 94.9 °C, and 85.9, respectively as applied at 30 V. When the HN and TR were printed on cotton fabric, the surface resistivity of HN/cotton and TR/cotton was about 103 Ω/sq, which showed conductive material. The results of electrical heating properties indicated that the heat distribution of HN/cotton showed only in the region where power was supplied, but the TR/cotton was gradually expanded and presented stable electric heating properties. When 30 V was applied, the surface temperature of both samples showed more than 80 °C, and the shape was maintained stably due to the high thermal conductivity of the cotton fabric. Therefore, this study ensured that HN and TR show excellent electrical heating performance among four types of auxetic patterns with continuity. Full article
(This article belongs to the Special Issue Innovative Functional Textiles)
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21 pages, 12157 KiB  
Article
Facile Synthesis of Natural Anise-Based Nanoemulsions and Their Antimicrobial Activity
by Ola A. Abu Ali, Mehrez E. El-Naggar, Mohamed S. Abdel-Aziz, Dalia I. Saleh, Mohamed. A. Abu-Saied and Wael A. El-Sayed
Polymers 2021, 13(12), 2009; https://doi.org/10.3390/polym13122009 - 19 Jun 2021
Cited by 8 | Viewed by 2285
Abstract
Anise oil was prepared in its nanoemulsion form to facilitate the penetration of microbial walls, causing microbe mortality. The penetration occurred easily owing to the reduction in its size (nm). Nanoemulsions with different concentrations of anise oil were prepared using lecithin as an [...] Read more.
Anise oil was prepared in its nanoemulsion form to facilitate the penetration of microbial walls, causing microbe mortality. The penetration occurred easily owing to the reduction in its size (nm). Nanoemulsions with different concentrations of anise oil were prepared using lecithin as an emulsifying agent with the aid of an ultra-sonification process. Their morphological and chemical properties were then characterized. The promising constituents were l-Menthone (11.22%), Gurjunene (6.78%), Geranyl acetate (4.03%), Elemene (3.93%), Geranyl tiglate (3.53%), geraniol (3.48%), linalool (0.17%) as well as camphene (0.12%). Different concentrations of prepared anise oil in micro and nanoemulsions were tested as antimicrobial agents against Gram-positive bacteria (Staphylococcus aureus), Gram-negative bacteria (Escherichia coli), yeast (Candida albicans) and fungi (Asperigillus niger). The findings illustrated that the anise oil-based nanoemulsion exhibited better results. Different biochemical and biological evaluations of anise oil nanoemulsions were conducted, including determining killing times, antioxidant activities (using three different methods), and total phenolics. A trial to estimate the mode of action of anise oil-based nanoemulsion as an antimicrobial agent against S. aureus and C. albicans was performed via studying the release of reducing sugars and protein and conducting scanning electron microscopy. Full article
(This article belongs to the Section Polymer Networks)
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10 pages, 1548 KiB  
Communication
Surface Crystal Nucleation and Growth in Poly (ε-caprolactone): Atomic Force Microscopy Combined with Fast Scanning Chip Calorimetry
by Rui Zhang, Mengxue Du, Evgeny Zhuravlev, René Androsch and Christoph Schick
Polymers 2021, 13(12), 2008; https://doi.org/10.3390/polym13122008 - 19 Jun 2021
Cited by 2 | Viewed by 1955
Abstract
By using an atomic force microscope (AFM) coupled to a fast scanning chip calorimeter (FSC), AFM-tip induced crystal nucleation/crystallization in poly (ε-caprolactone) (PCL) has been studied at low melt-supercooling, that is, at a temperature typically not assessable for melt-crystallization studies. Nanogram-sized PCL was [...] Read more.
By using an atomic force microscope (AFM) coupled to a fast scanning chip calorimeter (FSC), AFM-tip induced crystal nucleation/crystallization in poly (ε-caprolactone) (PCL) has been studied at low melt-supercooling, that is, at a temperature typically not assessable for melt-crystallization studies. Nanogram-sized PCL was placed on the active/heatable area of the FSC chip, melted, and then rapidly cooled to 330 K, which is 13 K below the equilibrium melting temperature. Subsequent isothermal crystallization at this temperature was initiated by a soft-tapping AFM-tip nucleation event. Crystallization starting at such surface nucleus led to formation of a single spherulite within the FSC sample, as concluded from the radial symmetry of the observed morphology. The observed growth rate in the sub-micron thin FSC sample, nucleated at its surface, was found being much higher than in the case of bulk crystallization, emphasizing a different growth mechanism. Moreover, distinct banding/ring-like structures are observed, with the band period being less than 1 µm. After crystallization, the sample was melted for gaining information about the achieved crystallinity and the temperature range of melting, both being similar compared to much slower bulk crystallization at the same temperature but for a much longer time. Full article
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12 pages, 1931 KiB  
Article
Use of Organic Acids in Bamboo Fiber-Reinforced Polypropylene Composites: Mechanical Properties and Interfacial Morphology
by Lety del Pilar Fajardo Cabrera de Lima, Cristian David Chamorro Rodríguez and José Herminsul Mina Hernandez
Polymers 2021, 13(12), 2007; https://doi.org/10.3390/polym13122007 - 19 Jun 2021
Cited by 9 | Viewed by 2107
Abstract
In obtaining wood polymer composites (WPCs), a weak interfacial bonding can cause problems during the processing and affect the mechanical properties of the resulting composites. A coupling agent (CA) is commonly used to solving this limitation. To improve the interfacial bonding between bamboo [...] Read more.
In obtaining wood polymer composites (WPCs), a weak interfacial bonding can cause problems during the processing and affect the mechanical properties of the resulting composites. A coupling agent (CA) is commonly used to solving this limitation. To improve the interfacial bonding between bamboo fiber (BF) and a polypropylene matrix, the effect of three organic acids on the mechanical properties and interfacial morphology were investigated. The BF/PP composites were prepared in five families: the first without CA, the second using a maleic anhydride-grafted polypropylene coupling agent, and the third, fourth, and fifth families with the addition of organic acids (OA) tricarboxylic acid (TRIA), hexadecanoic acid (HEXA), and dodecanoic acid (DODA), respectively. The use of OA in BF/PP improved the interfacial adhesion with the PP matrix, and it results in better mechanical performance than composites without CA. Composites coupled with MAPP, TRIA, DODA, and HEXA showed an increase in Young’s modulus of about 26%, 23%, 15%, and 16% respectively compared to the composite without CA incorporation. In tensile strength, the increase in composites with CA was about 190%, while in the flexural modulus, the coupled composites showed higher values, and the increase was more in composites with TRIA: about 46%. The improvement caused by tricarboxylic acid was similar to that promoted by the addition of maleic anhydride-grafted polypropylene (MAPP). Full article
(This article belongs to the Special Issue Mechanical Properties of Polymer Composites)
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10 pages, 1381 KiB  
Article
Effect of Thermal Ageing on the Mechanical Strength of Carbon Fibre Reinforced Epoxy Composites
by Nicola Zavatta, Francesco Rondina, Maria Pia Falaschetti and Lorenzo Donati
Polymers 2021, 13(12), 2006; https://doi.org/10.3390/polym13122006 - 19 Jun 2021
Cited by 26 | Viewed by 2565
Abstract
Applications of Carbon Fibre Reinforced Polymers (CFRP) at temperatures over 150–200 °C are becoming common in aerospace and automotive applications. Exposure of CFRP to these temperatures can lead to permanent changes in their mechanical properties. In this work, we investigated the effect of [...] Read more.
Applications of Carbon Fibre Reinforced Polymers (CFRP) at temperatures over 150–200 °C are becoming common in aerospace and automotive applications. Exposure of CFRP to these temperatures can lead to permanent changes in their mechanical properties. In this work, we investigated the effect of thermal ageing in air on the strength of carbon fabric/epoxy composites. To this end, accelerated artificial ageing at different temperatures was performed on carbon fabric/epoxy specimens. The flexural and interlaminar shear strengths of the aged specimens were assessed by three-point bending and short beam shear tests, respectively, and compared to those of unaged samples. For ageing at temperatures below the glass transition temperature of the resin, Tg, a moderate reduction of strength was found, with a maximum decrease of 25% for 2160 h at 75% Tg. On the other hand, a rapid strength decrease was observed for ageing temperatures above Tg. This was attributed to degradation of the epoxy matrix and of the fibre/epoxy interface. In particular, a 30% strength decrease was found for less than 6 h at 145% Tg. Therefore, it was concluded that even a short exposure to operating temperatures above Tg could substantially impair the load-carrying capability of CFRP components. Full article
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17 pages, 6214 KiB  
Article
The Effect of Alkali Treatment on Physical, Mechanical and Thermal Properties of Kenaf Fiber and Polymer Epoxy Composites
by Nur Farhani Ismail, Nabilah Afiqah Mohd Radzuan, Abu Bakar Sulong, Norhamidi Muhamad and Che Hassan Che Haron
Polymers 2021, 13(12), 2005; https://doi.org/10.3390/polym13122005 - 19 Jun 2021
Cited by 31 | Viewed by 3457
Abstract
The use of kenaf fiber as a reinforcement material for polymer composites is gaining popularity, especially in the production of automotive components. The main objective of this current work is to relate the effect of alkali treatment on the single fiber itself and [...] Read more.
The use of kenaf fiber as a reinforcement material for polymer composites is gaining popularity, especially in the production of automotive components. The main objective of this current work is to relate the effect of alkali treatment on the single fiber itself and the composite material simultaneously. The effect of temperature condition during mechanical testing is also investigated. Composite materials with discontinuous natural kenaf fibers and epoxy resin were fabricated using a compression moulding process. The epoxy composites were reinforced with 50 wt% untreated and treated kenaf fibers. The kenaf fiber was treated with NaOH solution (6% by weight) for 24 h at room temperature. Kenaf fiber treated with NaOH treatment had a clean surface and no impurities. For the first time we can see that alkali treatment had a damaging effect on the mechanical properties of kenaf fibers itself and the treated kenaf/epoxy composites. The composite reinforced with untreated kenaf fiber and treated kenaf fiber showed increased tensile strength (72.85% and 12.97%, respectively) compared to the neat epoxy. Reinforcement of the composite with treated kenaf fiber decreased the tensile strength due to the fiber pull out and the formation of voids which weakens the adhesion between the fibers and matrix. The temperature conditions also play an important role in composites with a significant impact on the deterioration of composite materials. Treated kenaf fiber has thermal stability and is not sensitive to temperature and as a result reinforcement with treated kenaf gives a lower loss value of 76%. Full article
(This article belongs to the Special Issue High-Performance Biocomposite Reinforced by Natural Fibers)
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11 pages, 2990 KiB  
Article
Transparent, Conductive Hydrogels with High Mechanical Strength and Toughness
by Xiuru Xu, Chubin He, Feng Luo, Hao Wang and Zhengchun Peng
Polymers 2021, 13(12), 2004; https://doi.org/10.3390/polym13122004 - 18 Jun 2021
Cited by 13 | Viewed by 2517
Abstract
Transparent, conductive hydrogels with good mechanical strength and toughness are in great demand of the fields of biomedical and future wearable smart electronics. We reported a carboxymethyl chitosan (CMCS)–calcium chloride (CaCl2)/polyacrylamide (PAAm)/poly(N-methylol acrylamide (PNMA) transparent, tough and conductive hydrogel containing a [...] Read more.
Transparent, conductive hydrogels with good mechanical strength and toughness are in great demand of the fields of biomedical and future wearable smart electronics. We reported a carboxymethyl chitosan (CMCS)–calcium chloride (CaCl2)/polyacrylamide (PAAm)/poly(N-methylol acrylamide (PNMA) transparent, tough and conductive hydrogel containing a bi-physical crosslinking network through in situ free radical polymerization. It showed excellent light transmittance (>90%), excellent toughness (10.72 MJ/m3), good tensile strength (at break, 2.65 MPa), breaking strain (707%), and high elastic modulus (0.30 MPa). The strain sensing performance is found with high sensitivity (maximum gauge factor 9.18, 0.5% detection limit), wide strain response range, fast response and recovery time, nearly zero hysteresis and good repeatability. This study extends the transparent, tough, conductive hydrogels to provide body-surface wearable devices that can accurately and repeatedly monitor the movement of body joints, including the movements of wrists, elbows and knee joints. This study provided a broad development potential for tough, transparent and conductive hydrogels as body-surface intelligent health monitoring systems and implantable soft electronics. Full article
(This article belongs to the Section Polymer Applications)
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46 pages, 10396 KiB  
Review
Preparations, Properties, and Applications of Polyaniline and Polyaniline Thin Films—A Review
by Mahnoush Beygisangchin, Suraya Abdul Rashid, Suhaidi Shafie, Amir Reza Sadrolhosseini and Hong Ngee Lim
Polymers 2021, 13(12), 2003; https://doi.org/10.3390/polym13122003 - 18 Jun 2021
Cited by 203 | Viewed by 20661
Abstract
Polyaniline (PANI) is a famous conductive polymer, and it has received tremendous consideration from researchers in the field of nanotechnology for the improvement of sensors, optoelectronic devices, and photonic devices. PANI is doped easily by different acids and dopants because of its easy [...] Read more.
Polyaniline (PANI) is a famous conductive polymer, and it has received tremendous consideration from researchers in the field of nanotechnology for the improvement of sensors, optoelectronic devices, and photonic devices. PANI is doped easily by different acids and dopants because of its easy synthesis and remarkable environmental stability. This review focuses on different preparation processes of PANI thin film by chemical and physical methods. Several features of PANI thin films, such as their magnetic, redox, and antioxidant, anti-corrosion, and electrical and sensing properties, are discussed in this review. PANI is a highly conductive polymer. Given its unique properties, easy synthesis, low cost, and high environmental stability in various applications such as electronics, drugs, and anti-corrosion materials, it has attracted extensive attention. The most important PANI applications are briefly reviewed at the end of this review. Full article
(This article belongs to the Collection Progress in Polymer Applications)
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15 pages, 6834 KiB  
Article
Dielectric Spectroscopy of Hybrid Magnetoactive Elastomers
by Vitaliy G. Shevchenko, Gennady V. Stepanov and Elena Yu. Kramarenko
Polymers 2021, 13(12), 2002; https://doi.org/10.3390/polym13122002 - 18 Jun 2021
Cited by 7 | Viewed by 2210
Abstract
Dielectric properties of two series of magnetoactive elastomers (MAEs) based on a soft silicone matrix containing 35 vol% of magnetic particles were studied experimentally in a wide temperature range. In the first series, a hybrid filler representing a mixture of magnetically hard NdFeB [...] Read more.
Dielectric properties of two series of magnetoactive elastomers (MAEs) based on a soft silicone matrix containing 35 vol% of magnetic particles were studied experimentally in a wide temperature range. In the first series, a hybrid filler representing a mixture of magnetically hard NdFeB particles of irregular shape and an average size of 50 μm and magnetically soft carbonyl iron (CI) of 4.5 μm in diameter was used for MAE fabrication. MAEs of the second series contained only NdFeB particles. The presence of magnetically hard NdFeB filler made it possible to passively control MAE dielectric response by magnetizing the samples. It was shown that although the hopping mechanism of MAEs conductivity did not change upon magnetization, a significant component of DC conductivity appeared in the magnetized MAEs presumably due to denser clustering of interacting particles resulting in decreasing interparticle distances. The transition from a non-conducting to a conducting state was more pronounced for hybrid MAEs containing both NdFeB and Fe particles with a tenfold size mismatch. Hybrid MAEs also demonstrated a considerable increase in the real part of the complex relative permittivity upon magnetization and its asymmetric behavior in external magnetic fields of various directions. The effects of magnetic filler composition and magnetization field on the dielectric properties of MAEs are important for practical applications of MAEs as elements with a tunable dielectric response. Full article
(This article belongs to the Special Issue Magnetic Polymer Composites: Design and Application)
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19 pages, 4426 KiB  
Article
Sophorolipid-Based Oligomers as Polyol Components for Polyurethane Systems
by Maresa Sonnabend, Suzanne G. Aubin, Annette M. Schmidt and Marc C. Leimenstoll
Polymers 2021, 13(12), 2001; https://doi.org/10.3390/polym13122001 - 18 Jun 2021
Cited by 3 | Viewed by 2294
Abstract
Due to reasons of sustainability and conservation of resources, polyurethane (PU)-based systems with preferably neutral carbon footprints are in increased focus of research and development. The proper design and development of bio-based polyols are of particular interest since such polyols may have special [...] Read more.
Due to reasons of sustainability and conservation of resources, polyurethane (PU)-based systems with preferably neutral carbon footprints are in increased focus of research and development. The proper design and development of bio-based polyols are of particular interest since such polyols may have special property profiles that allow the novel products to enter new applications. Sophorolipids (SL) represent a bio-based toolbox for polyol building blocks to yield diverse chemical products. For a reasonable evaluation of the potential for PU chemistry, however, further investigations in terms of synthesis, derivatization, reproducibility, and reactivity towards isocyanates are required. It was demonstrated that SL can act as crosslinker or as plasticizer in PU systems depending on employed stoichiometry. (ω-1)-hydroxyl fatty acids can be derived from SL and converted successively to polyester polyols and PU. Additionally, (ω-1)-hydroxyl fatty acid azides can be prepared indirectly from SL and converted to A/B type PU by Curtius rearrangement. Full article
(This article belongs to the Collection Polyurethanes)
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