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Polymers, Volume 10, Issue 3 (March 2018)

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Cover Story (view full-size image) A key step in the manufacture of bioresorbable vascular scaffolds (BVSs) for treatment of coronary [...] Read more.
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Open AccessReview Chitosan Derivatives: Introducing New Functionalities with a Controlled Molecular Architecture for Innovative Materials
Polymers 2018, 10(3), 342; https://doi.org/10.3390/polym10030342
Received: 28 February 2018 / Revised: 16 March 2018 / Accepted: 17 March 2018 / Published: 20 March 2018
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Abstract
The functionalization of polymeric substances is of great interest for the development of innovative materials for advanced applications. For many decades, the functionalization of chitosan has been a convenient way to improve its properties with the aim of preparing new materials with specialized
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The functionalization of polymeric substances is of great interest for the development of innovative materials for advanced applications. For many decades, the functionalization of chitosan has been a convenient way to improve its properties with the aim of preparing new materials with specialized characteristics. In the present review, we summarize the latest methods for the modification and derivatization of chitin and chitosan under experimental conditions, which allow a control over the macromolecular architecture. This is because an understanding of the interdependence between chemical structure and properties is an important condition for proposing innovative materials. New advances in methods and strategies of functionalization such as the click chemistry approach, grafting onto copolymerization, coupling with cyclodextrins, and reactions in ionic liquids are discussed. Full article
(This article belongs to the Special Issue Advances in Chitin/Chitosan Characterization and Applications)
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Open AccessArticle Lignocellulose-Chitosan-Multiwalled Carbon Nanotube Composites with Improved Mechanical Strength, Dimensional Stability and Fire Retardancy
Polymers 2018, 10(3), 341; https://doi.org/10.3390/polym10030341
Received: 25 February 2018 / Revised: 12 March 2018 / Accepted: 16 March 2018 / Published: 20 March 2018
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Abstract
A novel composite composed of lignocellulose (LC), glutaraldehyde crosslinked chitosan (GC) and multiwalled carbon nanotube (MWCNT) was fabricated by the hot-pressing process. The effect of the additional GC and MWCNT on the mechanical strength, dimensional stability and fire retardancy of lignocellulose composites was
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A novel composite composed of lignocellulose (LC), glutaraldehyde crosslinked chitosan (GC) and multiwalled carbon nanotube (MWCNT) was fabricated by the hot-pressing process. The effect of the additional GC and MWCNT on the mechanical strength, dimensional stability and fire retardancy of lignocellulose composites was investigated. The results showed that LC/GC/MWCNT composite exhibited the maximum modulus of rupture (MOR) of 35.3 MPa, modulus of elasticity (MOE) of 2789.1 MPa and internal bonding (IB) strength of 1.2 MPa. Meanwhile, the LC/GC/MWCNT composite displayed improved dimensional stability with a thickness swelling (TS) value of 22.4%. Besides, the LC/GC/MWCNT composite exhibited improved fire retardancy with a limiting oxygen index of 29.0%. The peak heat release rate, the total heat release, the total smoke production and the maximum smoke production ratio of LC/GC/MWCNT composite decreased by 15.9%, 10.7%, 45.5% and 20.7% compared with those of LC composite, respectively. Therefore, the LC/GC/MWCNT composite may be a promising candidate for green wood based composites. Full article
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Open AccessArticle Epoxy-Thiol Systems Filled with Boron Nitride for High Thermal Conductivity Applications
Polymers 2018, 10(3), 340; https://doi.org/10.3390/polym10030340
Received: 13 February 2018 / Revised: 9 March 2018 / Accepted: 15 March 2018 / Published: 20 March 2018
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Abstract
An epoxy-thiol system filled with boron nitride (BN), in the form of 80 µm agglomerates, has been investigated with a view to achieving enhanced thermal conductivity. The effect of BN content on the cure reaction kinetics has been studied by differential scanning calorimetry
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An epoxy-thiol system filled with boron nitride (BN), in the form of 80 µm agglomerates, has been investigated with a view to achieving enhanced thermal conductivity. The effect of BN content on the cure reaction kinetics has been studied by differential scanning calorimetry (DSC) and the thermal conductivity of the cured samples has been measured by the transient hot bridge method. The heat of reaction and the glass transition temperature of the fully cured samples are both independent of the BN content, but the cure reaction kinetics is not: with increasing BN content, the reaction first advances and is then delayed, this behaviour being more pronounced than for the same system with 6 µm BN particles, investigated previously. This dependence on BN content is attributed to the effects of heat transfer, and the DSC results can be correlated with the thermal conductivity of the cured systems, which is found to increase with both BN content and BN particle size. For a given BN content, the values of thermal conductivity obtained are significantly higher than many others reported in the literature, and achieve a value of over 4.0 W/mK for a BN content of about 40 vol %. Full article
(This article belongs to the Special Issue Thermosets)
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Open AccessArticle Regulating Dielectric and Ferroelectric Properties of Poly(vinylidene fluoride-trifluoroethylene) with Inner CH=CH Bonds
Polymers 2018, 10(3), 339; https://doi.org/10.3390/polym10030339
Received: 28 February 2018 / Revised: 15 March 2018 / Accepted: 16 March 2018 / Published: 20 March 2018
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Abstract
Poly(vinylidene fluoride) (PVDF) based ferroelectric polymers have attracted considerable attention both academically and industrially due to their tunable ferroelectric properties. By pinning the conformation of the polymer chain and the ferroelectric phase physically or chemically, the ferroelectric behaviors of PVDF based polymers could
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Poly(vinylidene fluoride) (PVDF) based ferroelectric polymers have attracted considerable attention both academically and industrially due to their tunable ferroelectric properties. By pinning the conformation of the polymer chain and the ferroelectric phase physically or chemically, the ferroelectric behaviors of PVDF based polymers could be finely turned from normal ferroelectric into relaxor ferroelectric, anti-ferroelectric like, and even linear dielectric. Besides high energy electron irradiation and chemical copolymerization with the bulky monomers, in this work, an alternative strategy is presented to regulate the dielectric and ferroelectric performances of PVDF based ferroelectric polymer for the first time. CH=CH bonds with the desired content are inserted by a controlled dehydrofluorination reaction into a poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer (TrFE refers to trifluoroethylene) synthesized from the hydrogenation of P(VDF-CTFE) (CTFE refers to chlorothrifluoroethylene). The influence of the CH=CH bonds along with the fabrication conditions on the crystallization and ferroelectric relaxation of the resultant copolymers (referred to P(VDF-TrFE-DB)) was carefully characterized and discussed. The nonrotatable CH=CH bonds result in depressed dielectric and ferroelectric performances in the as-cast films by confining the orientation of ferroelectric grains in P(VDF-TrFE). The normal ferroelectric performance of P(VDF-TrFE) is turned into anti-ferroelectric like behavior in the resultant P(VDF-TrFE-DB). The cleavage of CH=CH bonds is responsible for the recovery of the ferroelectric behavior in the annealed samples. Uniaxial stretching favors the alignment of the polymer chain and ferroelectric domains, which may address the further regulated ferroelectric characters in the stretched samples. Full article
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Open AccessArticle Optimization of Mechanical Properties for Polyoxymethylene/Glass Fiber/Polytetrafluoroethylene Composites Using Response Surface Methodology
Polymers 2018, 10(3), 338; https://doi.org/10.3390/polym10030338
Received: 9 January 2018 / Revised: 7 February 2018 / Accepted: 28 February 2018 / Published: 20 March 2018
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Abstract
This paper investigated the effects of polytetrafluoroethylene (PTFE) micro-particles on mechanical properties of polyoxymethylene (POM) composites. Since PTFE is immiscible with most polymers, the surface was etched using sodium naphthalene salt in tetrahydrofuran to increase its surface energy. The effects of two variables,
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This paper investigated the effects of polytetrafluoroethylene (PTFE) micro-particles on mechanical properties of polyoxymethylene (POM) composites. Since PTFE is immiscible with most polymers, the surface was etched using sodium naphthalene salt in tetrahydrofuran to increase its surface energy. The effects of two variables, namely PTFE content and PTFE etch time, on the mechanical properties of the composite were studied. Experiments were designed in accordance to response surface methodology (RSM) using central composite design (CCD). Samples were prepared with different compositions of PTFE (1.7, 4.0, 9.5, 15.0, or 17.3 wt %) at different PTFE etch times (2.9, 5.0, 10.0, 15.0, or 17.1 min). Four mechanical properties of the POM/GF/PTFE composites, that is, strength, stiffness, toughness, and hardness, were characterized as a function of two studied variables. The dependency of these mechanical properties on the PTFE etch conditions was analyzed using analysis of variance (ANOVA). Overall desirability, D global index, was computed based on the combination of these mechanical properties for POM/GF/PTFE composites. The D global index was found to be 87.5%, when PTFE content and PTFE etch time were 6.5% and 10 min, respectively. Good correlation between experimental and RSM models was obtained using normal probability plots. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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Open AccessArticle Optical and Thermomechanical Properties of Doped Polyfunctional Acrylate Copolymers
Polymers 2018, 10(3), 337; https://doi.org/10.3390/polym10030337
Received: 9 February 2018 / Revised: 16 March 2018 / Accepted: 16 March 2018 / Published: 19 March 2018
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Abstract
Three different polyfunctional acrylate monomers—trimethylolpropantriacrylate (TMPTA), pentaerythritol triacrylate (PETA) and di(trimethylolpropane) tetraacrylate (DTTA)—have been used as comonomers in combination with a reactive resin consisting of poly(methylmethacrylate), dissolved in its monomer methylmethacrylate. Phenanthrene has been added to form a guest–host system. The level of
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Three different polyfunctional acrylate monomers—trimethylolpropantriacrylate (TMPTA), pentaerythritol triacrylate (PETA) and di(trimethylolpropane) tetraacrylate (DTTA)—have been used as comonomers in combination with a reactive resin consisting of poly(methylmethacrylate), dissolved in its monomer methylmethacrylate. Phenanthrene has been added to form a guest–host system. The level of phenanthrene present may be adjusted to tailor the refractive index in the system. Prior to curing, the shear rate and temperature-dependent viscosity as a function of the composition were measured. It could be demonstrated that, with respect to different shaping methods, a tailor-made flow behaviour can be adjusted. After thermally-induced polymerization, the resulting optical (refractive index, optical transmittance) and thermomechanical (glass transition behavior, Vickers hardness) properties were characterized. A significant refractive index increase—up to a value close to 1.56 (@589 nm)—under the retention of good optical transmittance was able to be obtained. In addition, the photopolymerization behaviour was investigated to overcome the undesirable oxygen inhibition effect during the light-induced radical polymerization of acrylates. The level of acrylate units in the copolymer can compensate for the plasticizing effect of the dopant phenanthrene, enabling higher concentrations of the dopant in the guest–host system and therefore larger refractive index values suitable for polymer waveguide fabrication. Full article
(This article belongs to the Special Issue Polymeric Materials for Optical Applications)
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Open AccessArticle Cargo Release from Polymeric Vesicles under Shear
Polymers 2018, 10(3), 336; https://doi.org/10.3390/polym10030336
Received: 1 January 2018 / Revised: 10 March 2018 / Accepted: 16 March 2018 / Published: 19 March 2018
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Abstract
In this paper we study the release of cargo from polymeric nano-carriers under shear. Vesicles formed by two star block polymers—A12B6C2 (ABC) and A12B6A2 (ABA
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In this paper we study the release of cargo from polymeric nano-carriers under shear. Vesicles formed by two star block polymers— A 12 B 6 C 2 ( A B C ) and A 12 B 6 A 2 ( A B A )—and one linear block copolymer— A 14 B 6 ( A B ), are investigated using dissipative particle dynamics (DPD) simulations. A - and C -blocks are solvophobic and B -block is solvophilic. The three polymers form vesicles of different structures. The vesicles are subjected to shear both in bulk and between solvophobic walls. In bulk shear, the mechanisms of cargo release are similar for all vesicles, with cargo travelling through vesicle membrane with no preferential release location. When sheared between walls, high cargo release rate is only observed with A B C vesicle after it touches the wall. For A B C vesicle, the critical condition for high cargo release rate is the formation of wall-polymersome interface after which the effect of shear rate in promoting cargo release is secondary. High release rate is achieved by the formation of solvophilic pathway allowing cargo to travel from the vesicle cavity to the vesicle exterior. The results in this paper show that well controlled target cargo release using polymersomes can be achieved with polymers of suitable design and can potentially be very useful for engineering applications. As an example, polymersomes can be used as carriers for surface active friction reducing additives which are only released at rubbing surfaces where the additives are needed most. Full article
(This article belongs to the Special Issue Polymers for Modern and Advanced Engineering Applications)
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Open AccessArticle Preparation of Novel Nano-Sized Hydrogel Microcapsules via Layer-By-Layer Assembly as Delivery Vehicles for Drugs onto Hygiene Paper
Polymers 2018, 10(3), 335; https://doi.org/10.3390/polym10030335
Received: 30 January 2018 / Revised: 27 February 2018 / Accepted: 15 March 2018 / Published: 19 March 2018
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Abstract
Hydrogel microcapsules are improved transplantation delivery vehicles for pharmaceuticals by effectively segregating the active ingredients from the surroundings and delivering them to a certain target site. Layer-by-layer (LbL) assembly is an attractive process to fabricate the nano-sized hydrogel microcapsules. In this study, nano-sized
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Hydrogel microcapsules are improved transplantation delivery vehicles for pharmaceuticals by effectively segregating the active ingredients from the surroundings and delivering them to a certain target site. Layer-by-layer (LbL) assembly is an attractive process to fabricate the nano-sized hydrogel microcapsules. In this study, nano-sized hydrogel microcapsules were prepared through LbL assembly using calcium carbonate nanoparticles (CaCO3 NPs) as the sacrificial inorganic template, sodium alginate (SA) and polyethyleneimine (PEI) as the shell materials. Ciprofloxacin was used to study the encapsulation and release properties of the hydrogel microcapsules. The hydrogel microcapsules were further adsorbed onto the paper to render antimicrobial properties. The results showed that the mean size of the CaCO3 template was reduced after dispersing into sodium n-dodecyl sulfate (SDS) solution under sonication. Transmission electron microscope (TEM) and atomic force microscope (AFM) revealed that some hydrogel microcapsules had a diameter under 200 nm, typical creases and collapses were found on the surface. The nano-sized PEI/SA hydrogel microcapsules showed high loading capacity of ciprofloxacin and a sustained release. PEI/SA hydrogel microcapsules rendered good antimicrobial properties onto the paper by the adsorption of hydrogel microcapsules, however, the mechanical properties of the hygiene paper were decreased. Full article
(This article belongs to the Special Issue Hydrogels in Tissue Engineering and Regenerative Medicine)
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Open AccessArticle Numerical Investigation of Masonry Strengthened with Composites
Polymers 2018, 10(3), 334; https://doi.org/10.3390/polym10030334
Received: 31 January 2018 / Revised: 8 March 2018 / Accepted: 12 March 2018 / Published: 19 March 2018
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Abstract
In this work, two main fiber strengthening systems typically applied in masonry structures have been investigated: composites made of basalt and hemp fibers, coupled with inorganic matrix. Starting from the experimental results on composites, the out-of-plane behavior of the strengthened masonry was assessed
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In this work, two main fiber strengthening systems typically applied in masonry structures have been investigated: composites made of basalt and hemp fibers, coupled with inorganic matrix. Starting from the experimental results on composites, the out-of-plane behavior of the strengthened masonry was assessed according to several numerical analyses. In a first step, the ultimate behavior was assessed in terms of P (axial load)-M (bending moment) domain (i.e., failure surface), changing several mechanical parameters. In order to assess the ductility capacity of the strengthened masonry elements, the P-M domain was estimated starting from the bending moment-curvature diagrams. Key information about the impact of several mechanical parameters on both the capacity and the ductility was considered. Furthermore, the numerical analyses allow the assessment of the efficiency of the strengthening system, changing the main mechanical properties. Basalt fibers had lower efficiency when applied to weak masonry. In this case, the elastic properties of the masonry did not influence the structural behavior under a no tension assumption for the masonry. Conversely, their impact became non-negligible, especially for higher values of the compressive strength of the masonry. The stress-strain curve used to model the composite impacted the flexural strength. Natural fibers provided similar outcomes, but a first difference regards the higher mechanical compatibility of the strengthening system with the substrate. In this case, the ultimate condition is due to the failure mode of the composite. The stress-strain curves used to model the strengthening system are crucial in the ductility estimation of the strengthened masonry. However, the behavior of the composite strongly influences the curvature ductility in the case of higher compressive strength for masonry. The numerical results discussed in this paper provide the base to develop normalized capacity models able to provide important information on the out-of-plane behavior of masonry elements strengthened with inorganic matrix and several kinds of fibers, both synthetic and natural. Full article
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Open AccessArticle Bioinspired Fabrication of Polyurethane/Regenerated Silk Fibroin Composite Fibres with Tubuliform Silk-Like Flat Stress–Strain Behaviour
Polymers 2018, 10(3), 333; https://doi.org/10.3390/polym10030333
Received: 2 January 2018 / Revised: 11 March 2018 / Accepted: 15 March 2018 / Published: 19 March 2018
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Abstract
Tubuliform silk is one of the seven different types of spider silks, which is well known for its unique tensile behaviour with Flat Tensile Stress–Strain (FTSS) curve. It is found that anisotropic microstructure of β-sheets is responsible for this property. In recent years,
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Tubuliform silk is one of the seven different types of spider silks, which is well known for its unique tensile behaviour with Flat Tensile Stress–Strain (FTSS) curve. It is found that anisotropic microstructure of β-sheets is responsible for this property. In recent years, bioinspired approaches to engineer fibres supported by modern manufacturing systems have been attracting considerable interest. The present paper aims to investigate a strategy to biomimic the FTSS behaviour of tubuliform silk in synthetic polymer composite fibres by blending polyurethane (PU) and regenerated silk fibroin (RSF) at different ratios. Wet spinning of composite fibres results in the reconstruction of β-sheets in the synthetic fibre matrix. PU/RSF composite fibre at a ratio of 75/25 produce a tensile curve with FTSS characteristics. Secondary structural changes in RSF and interchain directions of β-sheets within the fibre are studied using Fourier Transform Infra-red (FTIR) spectroscopy and Transmission Electron Microscopy (TEM), respectively. Interestingly, results of TEM patterns confirm transverse anisotropic properties of RSF β-sheets. The composite fibres also display tuneable mechanical properties with respect to RSF contents. Full article
(This article belongs to the Special Issue Textile and Textile-Based Materials)
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Open AccessArticle Appropriate Donor-Acceptor Phase Separation Structure for the Enhancement of Charge Generation and Transport in Polymer Solar Cells
Polymers 2018, 10(3), 332; https://doi.org/10.3390/polym10030332
Received: 15 February 2018 / Revised: 13 March 2018 / Accepted: 16 March 2018 / Published: 18 March 2018
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Abstract
The morphology of active layer for polymer solar cells is critical to enhance the performance especially for fill factor of the devices. To investigate the relationship between active layer morphology and performance of polymer solar cells (PSCs), 1,8-diiodooctane (DIO) additive, and [6,6]-phenyl-C71
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The morphology of active layer for polymer solar cells is critical to enhance the performance especially for fill factor of the devices. To investigate the relationship between active layer morphology and performance of polymer solar cells (PSCs), 1,8-diiodooctane (DIO) additive, and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) electron acceptor were used to regulate the aggregation morphology of copolymer poly(thieno[3,4-b]-thiophene/benzodithiophene) (PTB7) electron donor from solution state to solid state. Atom force microscopy (AFM), steady-state absorption (UV-Vis), time-resolved absorption (TA), spectroelectrochemistry (SEC) and current-voltage (J-V) measurements were employed to characterize the morphology, optical and electrical characteristics of active layers and to reveal the relationship among the morphology, photophysical property, and performance of PTB7-based devices. The results show that DIO can refine the aggregation scale of PTB7 during the dissolution process, whereas both the aggregation scale and aggregation behaviors of PTB7 donor are affected by PC71BM acceptor molecules. Furthermore, the bulk heterojunction structure (BHJ) morphology of active layer can be optimized during the DIO evaporation process. TA kinetic data indicate that the population and lifetime of charged species are improved in the DIO-treated BHJ active layer. Moreover, the active layers with DIO treatment have a relative low highest occupied molecular orbital (HOMO) energy level, which makes hole transport more easily in PTB7 donor phase. As a result, the performance of PTB7-based PSCs is enhanced. Full article
(This article belongs to the Special Issue Polymers for Energy Applications)
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Open AccessArticle Synthesis and Photovoltaic Properties of 2D-Conjugated Polymers Based on Alkylthiothienyl-Substituted Benzodithiophene and Different Accepting Units
Polymers 2018, 10(3), 331; https://doi.org/10.3390/polym10030331
Received: 24 February 2018 / Revised: 14 March 2018 / Accepted: 15 March 2018 / Published: 18 March 2018
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Abstract
Two new low bandgap conjugated polymers, PBDTS-ID and PBDTS-DTNT, containing isoindigo (ID) and naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NT), respectively, as an electron-deficient unit and alkylthiothienyl-substituted benzodithiophene (BDTS) as an electron-rich unit, were designed and synthesized by palladium-catalyzed Stille polycondensation. Both polymers showed
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Two new low bandgap conjugated polymers, PBDTS-ID and PBDTS-DTNT, containing isoindigo (ID) and naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NT), respectively, as an electron-deficient unit and alkylthiothienyl-substituted benzodithiophene (BDTS) as an electron-rich unit, were designed and synthesized by palladium-catalyzed Stille polycondensation. Both polymers showed good thermal stability up to 330 °C and broad absorption ranging from 300 to 842 nm. Electrochemical measurement revealed that PBDTS-ID and PBDTS-DTNT exhibited relatively low-lying highest occupied molecular orbital energy levels at −5.40 and −5.24 eV, respectively. These features might be beneficial for obtaining reasonable high open-circuit voltage and high short-circuit current. Polymer solar cells (PSCs) were fabricated with an inverted structure of indium-tin oxide/poly(ethylenimine ethoxylate)/polymer:PC71BM/MoO3/Ag. As a preliminary result, the PSCs based on PBDTS-ID and PBDTS-DTNT exhibited moderate power conversion efficiencies of 2.70% and 2.71%, respectively. Full article
(This article belongs to the Special Issue Polymeric Materials for Optical Applications)
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Open AccessArticle On-Demand Multi-Resolution Liquid Alloy Printing Based on Viscoelastic Flow Squeezing
Polymers 2018, 10(3), 330; https://doi.org/10.3390/polym10030330
Received: 23 February 2018 / Revised: 15 March 2018 / Accepted: 16 March 2018 / Published: 16 March 2018
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Abstract
Recently, high-resolution patterning techniques of stretchable electronics advanced extensively. An important trend is to fabricate complex circuits with varied sizes in a small area, which is a technical challenge to current conductive ink printing technologies. Here, we introduce a new strategy for multi-resolution
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Recently, high-resolution patterning techniques of stretchable electronics advanced extensively. An important trend is to fabricate complex circuits with varied sizes in a small area, which is a technical challenge to current conductive ink printing technologies. Here, we introduce a new strategy for multi-resolution liquid alloy printing, which can tune the resolution of printed liquid alloy trace in real time with the squeezing effect of compound viscoelastic flow. A newly developed coaxial nozzle with the inner nozzle extension (CNINE) is used to wrap and squeeze liquid alloy steadily and effectively. By controlling the working parameters and compound flow properties, liquid alloy patterns with different widths are obtained continuously. This work offers a new way to rapidly manufacture complex stretchable electronics patterning in multi-resolution. Full article
(This article belongs to the Special Issue Soft Materials and Systems)
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Open AccessArticle Tumbling-Snake Model for Polymeric Liquids Subjected to Biaxial Elongational Flows with a Focus on Planar Elongation
Polymers 2018, 10(3), 329; https://doi.org/10.3390/polym10030329
Received: 6 March 2018 / Revised: 14 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
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Abstract
We have recently solved the tumbling-snake model for concentrated polymer solutions and entangled melts in the presence of both steady-state and transient shear and uniaxial elongational flows, supplemented by a variable link tension coefficient. Here, we provide the transient and stationary solutions of
[...] Read more.
We have recently solved the tumbling-snake model for concentrated polymer solutions and entangled melts in the presence of both steady-state and transient shear and uniaxial elongational flows, supplemented by a variable link tension coefficient. Here, we provide the transient and stationary solutions of the tumbling-snake model under biaxial elongation both analytically, for small and large elongation rates, and via Brownian dynamics simulations, for the case of planar elongational flow over a wide range of rates, times, and the model parameters. We show that both the steady-state and transient first planar viscosity predictions are similar to their uniaxial counterparts, in accord with recent experimental data. The second planar viscosity seems to behave in all aspects similarly to the shear viscosity, if shear rate is replaced by elongation rate. Full article
(This article belongs to the Special Issue Polymer Dynamics)
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Open AccessArticle Antibacterial Capability, Physicochemical Properties, and Biocompatibility of nTiO2 Incorporated Polymeric Scaffolds
Polymers 2018, 10(3), 328; https://doi.org/10.3390/polym10030328
Received: 29 January 2018 / Revised: 12 March 2018 / Accepted: 13 March 2018 / Published: 16 March 2018
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Abstract
Postoperative infection is a common risk which brings about failure in bone transplantation. In this study, nano titanium dioxide (nTiO2) was incorporated into Polyetheretherketone/polyglycolicacid (PEEK/PGA) blends to construct antibacterial scaffolds via selective laser sintering. Antibacterial capability was assessed using Escherichia coli
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Postoperative infection is a common risk which brings about failure in bone transplantation. In this study, nano titanium dioxide (nTiO2) was incorporated into Polyetheretherketone/polyglycolicacid (PEEK/PGA) blends to construct antibacterial scaffolds via selective laser sintering. Antibacterial capability was assessed using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The results demonstrated that the scaffolds with nTiO2 presented an effective antibacterial activity, which might be attributed to that nTiO2 would do the mechanical and oxidative damage to bacteria by occurring contact actions and generating reactive oxygen species (ROS), and thus killed bacteria from structure and function. Moreover, nTiO2 could enhance the tensile strength and modulus of scaffolds due to the reinforcing effect and its uniform disperse. And the cell culture experiments showed that nTiO2 stimulated cellular attachment and proliferation. Besides, it also elevated the hydrophily and thermal stability of scaffolds. These results suggested that the polymeric scaffolds incorporated nTiO2 had potential application in bone tissue engineering. Full article
(This article belongs to the Special Issue Polymer Hybrid Materials)
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Open AccessArticle Amphiphilic Quantum Dots with Asymmetric, Mixed Polymer Brush Layers: From Single Core-Shell Nanoparticles to Salt-Induced Vesicle Formation
Polymers 2018, 10(3), 327; https://doi.org/10.3390/polym10030327
Received: 1 March 2018 / Revised: 9 March 2018 / Accepted: 12 March 2018 / Published: 16 March 2018
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Abstract
A mixed micelle approach is used to produce amphiphilic brush nanoparticles (ABNPs) with cadmium sulfide quantum dot (QD) cores and surface layers of densely grafted (σ = ~1 chain/nm2) and asymmetric (fPS = 0.9) mixed polymer brushes that contain
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A mixed micelle approach is used to produce amphiphilic brush nanoparticles (ABNPs) with cadmium sulfide quantum dot (QD) cores and surface layers of densely grafted (σ = ~1 chain/nm2) and asymmetric (fPS = 0.9) mixed polymer brushes that contain hydrophobic polystyrene (PS) and hydrophilic poly(methyl methacrylate) (PMAA) chains (PS/PMAA-CdS). In aqueous media, the mixed brushes undergo conformational rearrangements that depend strongly on prior salt addition, giving rise to one of two pathways to fluorescent and morphologically disparate QD-polymer colloids. (A) In the absence of salt, centrosymmetric condensation of PS chains forms individual core-shell QD-polymer colloids. (B) In the presence of salt, non-centrosymmetric condensation of PS chains forms Janus particles, which trigger anisotropic interactions and amphiphilic self-assembly into the QD-polymer vesicles. To our knowledge, this is the first example of an ABNP building block that can form either discrete core-shell colloids or self-assembled superstructures in water depending on simple changes to the chemical conditions (i.e., salt addition). Such dramatic and finely tuned morphological variation could inform numerous applications in sensing, biolabeling, photonics, and nanomedicine. Full article
(This article belongs to the Special Issue Polymeric Materials for Optical Applications)
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Open AccessArticle Engineering Polyzwitterion and Polydopamine Decorated Doxorubicin-Loaded Mesoporous Silica Nanoparticles as a pH-Sensitive Drug Delivery
Polymers 2018, 10(3), 326; https://doi.org/10.3390/polym10030326
Received: 22 January 2018 / Revised: 13 March 2018 / Accepted: 14 March 2018 / Published: 15 March 2018
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Abstract
Multifunctional drug carriers have great applications in biomedical field. In this study, we introduced both polydopamine (PDA) and zwitterionic polymer of poly(3-(3-methacrylamidopropyl-(dimethyl)-ammonio)propane-1-sulfonate) (PSPP) onto the surface of mesoporous silica nanoparticles (MSNs) to develop a novel nanoparticle ([email protected]), which was employed as a new
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Multifunctional drug carriers have great applications in biomedical field. In this study, we introduced both polydopamine (PDA) and zwitterionic polymer of poly(3-(3-methacrylamidopropyl-(dimethyl)-ammonio)propane-1-sulfonate) (PSPP) onto the surface of mesoporous silica nanoparticles (MSNs) to develop a novel nanoparticle ([email protected]), which was employed as a new kind of drug carrier for the delivery of doxorubicin (DOX). The PDA coating, as a gatekeeper, could endow the drug carrier with pH-sensitive drug release performance. The outermost PSPP layer would make the drug carrier possess protein resistance performance. The chemical structure and properties were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS) and thermogravimetric analysis (TGA). [email protected] could keep good colloidal stability within 72 h in phosphate buffered saline (PBS) and protein solutions. Meanwhile, [email protected] exhibited a high drug loading for DOX. In vitro drug release experiments suggested [email protected] exhibited pH-dependent drug release behaviors. Besides, [email protected] had no cytotoxicity to human hepatocellular carcinoma cells (HepG2 cells) even at a concentration of 125 µg/mL. More importantly, cellular uptake and in vitro anticancer activity tests suggested that [email protected] could be taken up by HepG2 cells and DOX could be successfully released and delivered into the cell nuclei. Taken together, [email protected] have great potential in the biomedical field. Full article
(This article belongs to the Special Issue Polymer Hybrid Materials)
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Open AccessArticle Exploring Poly(ethylene glycol)-Polyzwitterion Diblock Copolymers as Biocompatible Smart Macrosurfactants Featuring UCST-Phase Behavior in Normal Saline Solution
Polymers 2018, 10(3), 325; https://doi.org/10.3390/polym10030325
Received: 31 January 2018 / Revised: 12 March 2018 / Accepted: 13 March 2018 / Published: 15 March 2018
Cited by 4 | Viewed by 1410 | PDF Full-text (3229 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Nonionic-zwitterionic diblock copolymers are designed to feature a coil-to-globule collapse transition with an upper critical solution temperature (UCST) in aqueous media, including physiological saline solution. The block copolymers that combine presumably highly biocompatible blocks are synthesized by chain extension of a poly(ethylene glycol)
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Nonionic-zwitterionic diblock copolymers are designed to feature a coil-to-globule collapse transition with an upper critical solution temperature (UCST) in aqueous media, including physiological saline solution. The block copolymers that combine presumably highly biocompatible blocks are synthesized by chain extension of a poly(ethylene glycol) (PEG) macroinitiator via atom transfer radical polymerization (ATRP) of sulfobetaine and sulfabetaine methacrylates. Their thermoresponsive behavior is studied by variable temperature turbidimetry and 1H NMR spectroscopy. While the polymers with polysulfobetaine blocks exhibit phase transitions in the physiologically interesting window of 30–50 °C only in pure aqueous solution, the polymers bearing polysulfabetaine blocks enabled phase transitions only in physiological saline solution. By copolymerizing a pair of structurally closely related sulfo- and sulfabetaine monomers, thermoresponsive behavior can be implemented in aqueous solutions of both low and high salinity. Surprisingly, the presence of the PEG blocks can affect the UCST-transitions of the polyzwitterions notably. In specific cases, this results in “schizophrenic” thermoresponsive behavior displaying simultaneously an UCST and an LCST (lower critical solution temperature) transition. Exploratory experiments on the UCST-transition triggered the encapsulation and release of various solvatochromic fluorescent dyes as model “cargos” failed, apparently due to the poor affinity even of charged organic compounds to the collapsed state of the polyzwitterions. Full article
(This article belongs to the Special Issue Stimuli Responsive Polymers)
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Open AccessArticle Surface Segregation of Cyclic Chains in Binary Melts of Thin Polymer Films: The Influence of Constituent Concentration
Polymers 2018, 10(3), 324; https://doi.org/10.3390/polym10030324
Received: 31 December 2017 / Revised: 21 February 2018 / Accepted: 2 March 2018 / Published: 15 March 2018
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Abstract
We carry out extensive molecular dynamics simulations of thin films of bead-spring models of binary mixtures composed of cyclic and linear polymer chains. We study the equilibrium behavior of the polymer chains for two very different chain lengths, which resemble short (10-mers) and
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We carry out extensive molecular dynamics simulations of thin films of bead-spring models of binary mixtures composed of cyclic and linear polymer chains. We study the equilibrium behavior of the polymer chains for two very different chain lengths, which resemble short (10-mers) and long (100-mers) chains, at different concentrations of the binary mixture. We clearly show how the concentration variable affects the enrichment of either of the two polymer species at the interface, and also how the chain length influences this process. Full article
(This article belongs to the Special Issue Polymerizations from Surfaces)
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Open AccessArticle A Simple, Green Method to Fabricate Composite Membranes for Effective Oil-in-Water Emulsion Separation
Polymers 2018, 10(3), 323; https://doi.org/10.3390/polym10030323
Received: 21 December 2017 / Revised: 9 March 2018 / Accepted: 13 March 2018 / Published: 15 March 2018
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Abstract
Most factories discharge untreated wastewater to reduce costs, causing serious environmental problems. Low-cost, biological, environmentally friendly and highly effective materials for the separation of emulsified oil/water mixtures are thus in great demand. In this study, a simple, green method was developed for separating
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Most factories discharge untreated wastewater to reduce costs, causing serious environmental problems. Low-cost, biological, environmentally friendly and highly effective materials for the separation of emulsified oil/water mixtures are thus in great demand. In this study, a simple, green method was developed for separating oil-in-water emulsions. A corn straw powder (CSP)-nylon 6,6 membrane (CSPNM) was fabricated by a phase inversion process without any further chemical modification. The CSPNM showed superhydrophilic and underwater superoleophobic properties and could be used for the separation of oil-in-water emulsion with high separation efficiency and flux. The CSPNM maintained excellent separation ability after 20 cycles of separation with an oil rejection >99.60%, and the oil rejection and flux have no obvious change with an increasing number of cycles, suggesting a good antifouling property and the structural stability of CSPNM. In addition, the CSPNM exhibited excellent thermal and chemical stability under harsh conditions of high temperature and varying pH. Full article
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Open AccessArticle Hydrophobicity Tuning by the Fast Evolution of Mold Temperature during Injection Molding
Polymers 2018, 10(3), 322; https://doi.org/10.3390/polym10030322
Received: 2 February 2018 / Revised: 26 February 2018 / Accepted: 9 March 2018 / Published: 15 March 2018
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Abstract
The surface topography of a molded part strongly affects its functional properties, such as hydrophobicity, cleaning capabilities, adhesion, biological defense and frictional resistance. In this paper, the possibility to tune and increase the hydrophobicity of a molded polymeric part was explored. An isotactic
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The surface topography of a molded part strongly affects its functional properties, such as hydrophobicity, cleaning capabilities, adhesion, biological defense and frictional resistance. In this paper, the possibility to tune and increase the hydrophobicity of a molded polymeric part was explored. An isotactic polypropylene was injection molded with fast cavity surface temperature evolutions, obtained adopting a specifically designed heating system layered below the cavity surface. The surface topology was characterized by atomic force microscopy (AFM) and, concerning of hydrophobicity, by measuring the water static contact angle. Results show that the hydrophobicity increases with both the temperature level and the time the cavity surface temperature was kept high. In particular, the contact angle of the molded sample was found to increase from 90°, with conventional molding conditions, up to 113° with 160 °C of cavity surface temperature kept for 18 s. This increase was found to be due to the presence of sub-micro and nano-structures characterized by high values of spatial frequencies which could be more accurately replicated by adopting high heating temperatures and times. The surface topography and the hydrophobicity resulted therefore tunable by selecting appropriate injection molding conditions. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle Copolymerization of Phenylselenide-Substituted Maleimide with Styrene and Its Oxidative Elimination Behavior
Polymers 2018, 10(3), 321; https://doi.org/10.3390/polym10030321
Received: 9 February 2018 / Revised: 9 March 2018 / Accepted: 10 March 2018 / Published: 15 March 2018
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Abstract
Selenium-containing monomer monophenyl maleimide selenide (MSM) was synthesized and copolymerized with styrene (St) using reversible addition-fragmentation chain transfer (RAFT) polymerization. Copolymers with controlled molecular weight and narrow molecular weight distribution were obtained. The structure of the copolymer was characterized by nuclear magnetic resonance,
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Selenium-containing monomer monophenyl maleimide selenide (MSM) was synthesized and copolymerized with styrene (St) using reversible addition-fragmentation chain transfer (RAFT) polymerization. Copolymers with controlled molecular weight and narrow molecular weight distribution were obtained. The structure of the copolymer was characterized by nuclear magnetic resonance, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrum, Fourier transform infrared spectroscopy (FT-IR) and Ultraviolet–visible spectroscopy (UV-vis) spectroscopy. The copolymer can be oxidized by H2O2 to form carbon-carbon double bonds within the main chain due to the unique sensitivity of selenide groups in the presence of oxidants. Such structure changing resulted in an interesting concentration-related photoluminescence emission enhancement. Full article
(This article belongs to the Special Issue Tailored Polymer Synthesis by Advanced Polymerization Techniques)
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Open AccessArticle Isolation and Rheological Characterization of Cellulose Nanofibrils (CNFs) from Coir Fibers in Comparison to Wood and Cotton
Polymers 2018, 10(3), 320; https://doi.org/10.3390/polym10030320
Received: 13 February 2018 / Revised: 11 March 2018 / Accepted: 13 March 2018 / Published: 14 March 2018
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Abstract
In this report, the isolation and rheological characterization of cellulose nanofibrils from coir (CNFs-1) were studied and compared with the CNFs from wood (CNFs-2) and cotton (CNFs-3). Cellulose nanofibrils were isolated successfully from coir fibers by chemical treatments followed by ultrasonic fibrillation. During
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In this report, the isolation and rheological characterization of cellulose nanofibrils from coir (CNFs-1) were studied and compared with the CNFs from wood (CNFs-2) and cotton (CNFs-3). Cellulose nanofibrils were isolated successfully from coir fibers by chemical treatments followed by ultrasonic fibrillation. During ultrasonic processing, the size and the crystal structure of the CNFs were influenced by the raw materials. In comparison to CNFs-2 and CNFs-3, CNFs-1 from coir fibers presented diverse advantages, such as sufficient fibrillation with a low diameter distribution, in the range of 2–4 nm and high crystallinity. In the dynamic rheology study of CNFs-1, elastic behavior was observed and maintained due to the formation of gel-like steady network structures, which could not be easily deconstructured by frequency shearing and temperature changing. All results indicated that coir fibers could be used as a valuable resource for the preparation of CNFs, which exhibited comparable properties with those isolated from wood, in regard to morphology and rheological properties. This work provides a basis for further advanced applications using the CNFs isolated from coir fibers. Full article
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Open AccessArticle Novel Dual-Component Microencapsulated Hydrophobic Amine and Microencapsulated Isocyanate Used for Self-Healing Anti-Corrosion Coating
Polymers 2018, 10(3), 319; https://doi.org/10.3390/polym10030319
Received: 15 February 2018 / Revised: 9 March 2018 / Accepted: 12 March 2018 / Published: 14 March 2018
Cited by 3 | Viewed by 1109 | PDF Full-text (11777 KB) | HTML Full-text | XML Full-text
Abstract
Dual component microencapsulated hydrophobic amine and microencapsulated isocyanate were designed and fabricated for self-healing anti-corrosion coating. In this system, novel hydrophobic polyaspartic acid ester (PAE) and isophorone diisocyanate (IPDI) were microencapsulated respectively with melamine-formaldehyde (MF) as shell via in situ polymerization. To reduce
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Dual component microencapsulated hydrophobic amine and microencapsulated isocyanate were designed and fabricated for self-healing anti-corrosion coating. In this system, novel hydrophobic polyaspartic acid ester (PAE) and isophorone diisocyanate (IPDI) were microencapsulated respectively with melamine-formaldehyde (MF) as shell via in situ polymerization. To reduce the reaction activity between shell-forming MF prepolymer and PAE, another self-healing agent tung oil (TO) was dissolved in PAE and subsequently employed as core material. With field-emission scanning electron microscopy (FE-SEM) and optical microscopy (OM), the resultant microencapsulated IPDI with diameter of 2–5 μm showed a spherical shape and smooth surface. More importantly, both the morphology and microstructure of microencapsulated PAE enhanced significantly after addition of TO. Fourier transform infrared spectra (FTIR) analysis confirmed the molecular structure of chemical structure of the microcapsules. Thermal gravimetric analysis (TGA) indicated that both kinds of microcapsules exhibit excellent thermal resistance with the protection of MF shell. Furthermore, the self-healing epoxy coating system containing microencapsulated IPDI and microencapsulated PAE/TO was prepared and investigated. From the micrographs of true color confocal microscope (TCCM), the self-healing coating containing dual-component microcapsules showed excellent self-repairing performance compared to single microencapsulated IPDI system, and the optimal content of dual-component microcapsules in epoxy coating was 20 wt % approximately. Full article
(This article belongs to the Special Issue Surface Modification and Functional Coatings for Polymers)
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Open AccessReview Recent Advances in RAFT Polymerization: Novel Initiation Mechanisms and Optoelectronic Applications
Polymers 2018, 10(3), 318; https://doi.org/10.3390/polym10030318
Received: 24 February 2018 / Revised: 9 March 2018 / Accepted: 12 March 2018 / Published: 14 March 2018
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Abstract
Reversible addition-fragmentation chain transfer (RAFT) is considered to be one of most famous reversible deactivation radical polymerization protocols. Benefiting from its living or controlled polymerization process, complex polymeric architectures with controlled molecular weight, low dispersity, as well as various functionality have been constructed,
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Reversible addition-fragmentation chain transfer (RAFT) is considered to be one of most famous reversible deactivation radical polymerization protocols. Benefiting from its living or controlled polymerization process, complex polymeric architectures with controlled molecular weight, low dispersity, as well as various functionality have been constructed, which could be applied in wide fields, including materials, biology, and electrology. Under the continuous research improvement, main achievements have focused on the development of new RAFT techniques, containing fancy initiation methods (e.g., photo, metal, enzyme, redox and acid), sulfur-free RAFT system and their applications in many fields. This review summarizes the current advances in major bright spot of novel RAFT techniques as well as their potential applications in the optoelectronic field, especially in the past a few years. Full article
(This article belongs to the Special Issue RAFT Living Radical Polymerization and Self-Assembly)
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Open AccessArticle Preparation and Application of Phosphorylated Xylan as a Flocculant for Cationic Ethyl Violet Dye
Polymers 2018, 10(3), 317; https://doi.org/10.3390/polym10030317
Received: 10 February 2018 / Revised: 10 March 2018 / Accepted: 12 March 2018 / Published: 14 March 2018
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Abstract
In this study, phosphorylated birchwood xylan was produced under alkali conditions using trisodium trimetaphosphate. Three single-factor experiments were used to explore the influences of time, temperature, and the molar ratio of trisodium trimetaphosphate to xylan on the degree of substitution (DS) and charge
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In this study, phosphorylated birchwood xylan was produced under alkali conditions using trisodium trimetaphosphate. Three single-factor experiments were used to explore the influences of time, temperature, and the molar ratio of trisodium trimetaphosphate to xylan on the degree of substitution (DS) and charge density of xylan. The response surface methodology was used to explore the interaction of these three factors. Phosphorylated xylan with a maximum DS of 0.79 and a charge density of −3.40 mmol/g was produced under the optimal conditions of 80 °C, 4 h, and a molar ratio of xylan/sodium trimetaphosphate (STMP) of 1/3. Fourier transform infrared (FTIR), ascorbic acid method analyses, and inductively coupled plasma–atomic emission spectrometer (ICP-AES) analyses confirmed that the phosphate groups were successfully attached to xylan. Thermogravimetric analysis confirmed that phosphorylated xylan was less stable than birchwood xylan. Furthermore, the phosphorylated xylan was applied as a flocculant for removing ethyl violet dye from a simulated dye solution. The results indicated that more than 95% of the dye was removed from the solution. The theoretical and experimental values of charge neutralization for the dye removal were close to one another, confirming that charge neutralization was the main mechanism for the interaction of dye and phosphorylated xylan. The impacts of salts on the flocculation efficiency of phosphorylated xylan were also analyzed. Full article
(This article belongs to the Special Issue Polymers for Modern and Advanced Engineering Applications)
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Open AccessArticle Comparative Study of Ex Vivo Transmucosal Permeation of Pioglitazone Nanoparticles for the Treatment of Alzheimer’s Disease
Polymers 2018, 10(3), 316; https://doi.org/10.3390/polym10030316
Received: 27 February 2018 / Revised: 11 March 2018 / Accepted: 13 March 2018 / Published: 14 March 2018
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Abstract
Pioglitazone has been reported in the literature to have a substantial role in the improvement of overall cognition in a mouse model. With this in mind, the aim of this study was to determine the most efficacious route for the administration of Pioglitazone
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Pioglitazone has been reported in the literature to have a substantial role in the improvement of overall cognition in a mouse model. With this in mind, the aim of this study was to determine the most efficacious route for the administration of Pioglitazone nanoparticles (PGZ-NPs) in order to promote drug delivery to the brain for the treatment of Alzheimer’s disease. PGZ-loaded NPs were developed by the solvent displacement method. Parameters such as mean size, polydispersity index, zeta potential, encapsulation efficacy, rheological behavior, and short-term stability were evaluated. Ex vivo permeation studies were then carried out using buccal, sublingual, nasal, and intestinal mucosa. PGZ-NPs with a size around of 160 nm showed high permeability in all mucosae. However, the permeation and prediction parameters revealed that lag-time and vehicle/tissue partition coefficient of nasal mucosa were significantly lower than other studied mucosae, while the diffusion coefficient and theoretical steady-state plasma concentration of the drug were higher, providing biopharmaceutical results that reveal more favorable PGZ permeation through the nasal mucosa. The results suggest that nasal mucosa represents an attractive and non-invasive pathway for PGZ-NPs administration to the brain since the drug permeation was demonstrated to be more favorable in this tissue. Full article
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Open AccessArticle Photo-Polymerization in Chiral Dopant Liquid Crystal Cells via Holographic Exposure to Fabricate Polarization-Independent Phase Modulator with Fast Optical Response
Polymers 2018, 10(3), 315; https://doi.org/10.3390/polym10030315
Received: 21 January 2018 / Revised: 12 March 2018 / Accepted: 12 March 2018 / Published: 14 March 2018
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Abstract
Small liquid crystal domains with random director distributions were obtained to show novel optical isotropy using a holographic exposure processes to treat chiral dopant liquid crystal cells in the isotropic phase (i.e., polymer-stabilized isotropic liquid crystal cells). The cells used to fabricate phase
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Small liquid crystal domains with random director distributions were obtained to show novel optical isotropy using a holographic exposure processes to treat chiral dopant liquid crystal cells in the isotropic phase (i.e., polymer-stabilized isotropic liquid crystal cells). The cells used to fabricate phase modulators showed unique performances, including low light scattering, polarization-independence, and fast optical response. Furthermore, an extra fluoro-surfactant dopant in cells showed that the phase modulators retained their performance but with considerable reduction of operating voltages, from 180 Vrms to 100 Vrms. Full article
(This article belongs to the Special Issue Polymeric Materials for Optical Applications)
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Open AccessArticle 3D Printable Filaments Made of Biobased Polyethylene Biocomposites
Polymers 2018, 10(3), 314; https://doi.org/10.3390/polym10030314
Received: 21 February 2018 / Revised: 9 March 2018 / Accepted: 10 March 2018 / Published: 13 March 2018
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Abstract
Two different series of biobased polyethylene (BioPE) were used for the manufacturing of biocomposites, complemented with thermomechanical pulp (TMP) fibers. The intrinsic hydrophilic character of the TMP fibers was previously modified by grafting hydrophobic compounds (octyl gallate and lauryl gallate) by means of
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Two different series of biobased polyethylene (BioPE) were used for the manufacturing of biocomposites, complemented with thermomechanical pulp (TMP) fibers. The intrinsic hydrophilic character of the TMP fibers was previously modified by grafting hydrophobic compounds (octyl gallate and lauryl gallate) by means of an enzymatic-assisted treatment. BioPE with low melt flow index (MFI) yielded filaments with low void fraction and relatively low thickness variation. The water absorption of the biocomposites was remarkably improved when the enzymatically-hydrophobized TMP fibers were used. Importantly, the 3D printing of BioPE was improved by adding 10% and 20% TMP fibers to the composition. Thus, 3D printable biocomposites with low water uptake can be manufactured by using fully biobased materials and environmentally-friendly processes. Full article
(This article belongs to the Special Issue Polymers from Renewable Resources)
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Open AccessArticle Strength of PLA Components Fabricated with Fused Deposition Technology Using a Desktop 3D Printer as a Function of Geometrical Parameters of the Process
Polymers 2018, 10(3), 313; https://doi.org/10.3390/polym10030313
Received: 5 February 2018 / Revised: 19 February 2018 / Accepted: 9 March 2018 / Published: 13 March 2018
Cited by 4 | Viewed by 1611 | PDF Full-text (2365 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The current paper studies the influence of geometrical parameters of the fused deposition modeling (FDM)—fused filament fabrication (FFF) 3D printing process on printed part strength for open source desktop 3D printers and the most popular material used for that purpose—i.e., polylactic acid (PLA).
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The current paper studies the influence of geometrical parameters of the fused deposition modeling (FDM)—fused filament fabrication (FFF) 3D printing process on printed part strength for open source desktop 3D printers and the most popular material used for that purpose—i.e., polylactic acid (PLA). The study was conducted using a set of different nozzles (0.4, 0.6, and 0.8 mm) and a range of layer heights from the minimum to maximum physical limits of the machine. To assess print strength, a novel assessment method is proposed. A tubular sample is loaded in the weakest direction (across layers) in a three-point bending fixture. Mesostructure evaluation through scanning electronic microscopy (SEM) scans of the samples was used to explain the obtained results. We detected a significant influence of geometric process parameters on sample mesostructure, and consequently, on sample strength. Full article
(This article belongs to the Special Issue Polymers for Modern and Advanced Engineering Applications)
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