[go: up one dir, main page]
Next Issue
Volume 11, May
Previous Issue
Volume 11, March
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
8.0
4.7
Journals
Polymers
Volume 11
Issue 4
polymers-logo

Journal Menu

► Journal Menu

Journal Browser

► Journal Browser
share announcement

Polymers, Volume 11, Issue 4 (April 2019) – 174 articles

Cover Story (view full-size image): Volatile organic components pose a significant danger to human health and, especially, formaldehyde (HCHO) is produced in many natural and synthetic processes and is considered a prime household air pollutant. To destroy HCHO at room temperature, platinum–nickel nanoparticles were directly synthesized on polydopamine-coated poly(methyl methacrylate) electrospun fibers without any excessive oxide. These formed a filter-like membrane that was able to decompose 90% of the formaldehyde at very low dosage with high durability. The sheet-like membrane enables facile handling and its low air resistance allows for minimal air flow losses when integrated, for example, in an air conditioning unit. View this paper
  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Reader to open them.
Order results
Result details
Section
Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
35 pages, 3663 KiB  
Review
Polymeric Nanoparticles in Gene Therapy: New Avenues of Design and Optimization for Delivery Applications
by Raj Rai, Saniya Alwani and Ildiko Badea
Polymers 2019, 11(4), 745; https://doi.org/10.3390/polym11040745 - 25 Apr 2019
Cited by 227 | Viewed by 18897
Abstract
The field of polymeric nanoparticles is quickly expanding and playing a pivotal role in a wide spectrum of areas ranging from electronics, photonics, conducting materials, and sensors to medicine, pollution control, and environmental technology. Among the applications of polymers in medicine, gene therapy [...] Read more.
The field of polymeric nanoparticles is quickly expanding and playing a pivotal role in a wide spectrum of areas ranging from electronics, photonics, conducting materials, and sensors to medicine, pollution control, and environmental technology. Among the applications of polymers in medicine, gene therapy has emerged as one of the most advanced, with the capability to tackle disorders from the modern era. However, there are several barriers associated with the delivery of genes in the living system that need to be mitigated by polymer engineering. One of the most crucial challenges is the effectiveness of the delivery vehicle or vector. In last few decades, non-viral delivery systems have gained attention because of their low toxicity, potential for targeted delivery, long-term stability, lack of immunogenicity, and relatively low production cost. In 1987, Felgner et al. used the cationic lipid based non-viral gene delivery system for the very first time. This breakthrough opened the opportunity for other non-viral vectors, such as polymers. Cationic polymers have emerged as promising candidates for non-viral gene delivery systems because of their facile synthesis and flexible properties. These polymers can be conjugated with genetic material via electrostatic attraction at physiological pH, thereby facilitating gene delivery. Many factors influence the gene transfection efficiency of cationic polymers, including their structure, molecular weight, and surface charge. Outstanding representatives of polymers that have emerged over the last decade to be used in gene therapy are synthetic polymers such as poly(l-lysine), poly(l-ornithine), linear and branched polyethyleneimine, diethylaminoethyl-dextran, poly(amidoamine) dendrimers, and poly(dimethylaminoethyl methacrylate). Natural polymers, such as chitosan, dextran, gelatin, pullulan, and synthetic analogs, with sophisticated features like guanidinylated bio-reducible polymers were also explored. This review outlines the introduction of polymers in medicine, discusses the methods of polymer synthesis, addressing top down and bottom up techniques. Evaluation of functionalization strategies for therapeutic and formulation stability are also highlighted. The overview of the properties, challenges, and functionalization approaches and, finally, the applications of the polymeric delivery systems in gene therapy marks this review as a unique one-stop summary of developments in this field. Full article
(This article belongs to the Special Issue Polymers in Gene Delivery)
►▼ Show Figures

Figure 1

Figure 1
<p>Polymeric nanoparticles for the intracellular delivery of DNA and siRNA: (1) complexation of anionic DNA and siRNA with cationic polymers to form polyplexes (2) cellular uptake of polyplexes via different endocytic routes, (3) enclosure and subsequent release of polyplexes from endo-lysosomal compartments, (4) release of free DNA and siRNA from polyplexes leaving behind polymer remnants, and (5) transfer of DNA to the nucleus for expression by nuclear membrane transport proteins and binding of siRNA by RNA-induced silencing complex (RISC).</p> Full article ">Figure 2
<p>Summary of top-down and bottom-up techniques for generating polymeric nanoparticles.</p> Full article ">Figure 3
<p>Schematic representation of the solvent-evaporation technique. Reprinted with permission from Reference [<a href="#B53-polymers-11-00745" class="html-bibr">53</a>]. Copyright 2006 Elsevier.</p> Full article ">Figure 4
<p>Schematic representation of the nanoprecipitation (solvent displacement) technique. Reprinted with permission from Reference [<a href="#B53-polymers-11-00745" class="html-bibr">53</a>]. Copyright 2006 Elsevier.</p> Full article ">Figure 5
<p>Schematic representation of the salting out technique. Reprinted with permission from Reference [<a href="#B53-polymers-11-00745" class="html-bibr">53</a>]. Copyright 2006 Elsevier.</p> Full article ">Figure 6
<p>Schematic representation of an osmosis-based method for the preparation of polymer nanoparticles.</p> Full article ">Figure 7
<p>Experimental set-up for preparation of polymer nanoparticles via the rapid expansion of supercritical fluid solution. Reprinted with permission from Reference [<a href="#B73-polymers-11-00745" class="html-bibr">73</a>]. Copyright 2011 Elsevier.</p> Full article ">Figure 8
<p>Experimental set-up for the rapid expansion of supercritical fluid solution into liquid solvent process. Reprinted with permission from Reference [<a href="#B73-polymers-11-00745" class="html-bibr">73</a>]. Copyright 2011 Elsevier.</p> Full article ">Figure 9
<p>Schematic representation of the emulsification/solvent diffusion technique. Reprinted with permission from Reference [<a href="#B53-polymers-11-00745" class="html-bibr">53</a>]. Copyright 2006 Elsevier.</p> Full article ">Figure 10
<p>Summary of properties and challenges of polymeric nanoparticles for gene delivery and associated factors influencing each of these parameters.</p> Full article ">Figure 11
<p>Schematic illustration of non-invasive or minimally invasive routes of administration and targeting strategies for polymeric nanoparticles. From Reference [<a href="#B191-polymers-11-00745" class="html-bibr">191</a>], open access peer-reviewed edited volume, Copyright (2014) IntechOpen.</p> Full article ">Figure 12
<p>Chemical structure of biocleavable polyrotaxane: (<b>a</b>) polyplex formation and (<b>b</b>) terminal cleavage-triggered de-condensation of the polyplex. Reprinted with permission from Reference [<a href="#B210-polymers-11-00745" class="html-bibr">210</a>]. Copyright 2006 American Chemical Association.</p> Full article ">
14 pages, 3399 KiB  
Article
In vitro Comparative Study of Fibroblastic Behaviour on Polymethacrylate (PMMA) and Lithium Disilicate Polymer Surfaces
by Cristina Herráez-Galindo, María Rizo-Gorrita, Irene Luna-Oliva, María-Ángeles Serrera-Figallo, Raquel Castillo-Oyagüe and Daniel Torres-Lagares
Polymers 2019, 11(4), 744; https://doi.org/10.3390/polym11040744 - 25 Apr 2019
Cited by 13 | Viewed by 3539
Abstract
Polymethyl methacrylate (PMMA) and lithium disilicate are widely used materials in the dental field. PMMA is mainly used for the manufacture of removable prostheses; however, with the incorporation of CAD-CAM technology, new applications have been introduced for this material, including as a provisional [...] Read more.
Polymethyl methacrylate (PMMA) and lithium disilicate are widely used materials in the dental field. PMMA is mainly used for the manufacture of removable prostheses; however, with the incorporation of CAD-CAM technology, new applications have been introduced for this material, including as a provisional implant attachment. Lithium disilicate is considered the gold standard for definitive attachment material. On the other hand, PMMA has begun to be used in clinics as a provisional attachment until the placement of a definitive one occurs. Although there are clinical studies regarding its use, there are few studies on cell reorganization around this type of material. This is why we carried out an in vitro comparative study using discs of both materials in which human gingival fibroblasts (HGFs) were cultured. After processing them, we analyzed various cellular parameters (cell count, cytoskeleton length, core size and coverage area). We analyzed the surface of the discs together with their composition. The results obtained were mostly not statistically significant, which shows that the qualities of PMMA make it a suitable material as an implant attachment. Full article
(This article belongs to the Special Issue Biomedical Polymer Materials)
►▼ Show Figures

Figure 1

Figure 1
<p>Images captured using SEM of the surfaces of IPS e.max CAD discs (<b>left</b>) and Vita CAD-Temp (<b>right</b>) at a magnification of 200×.</p> Full article ">Figure 2
<p>Measurement areas and 20× objective profilometry for each IPS (<b>A</b>) and VITA CAD Temp (<b>B</b>) disc.</p> Full article ">Figure 3
<p>Energy dispersive spectroscopy analysis of IPS e-max CAD.</p> Full article ">Figure 4
<p>Energy dispersive spectroscopy analysis of VITA CAD-Temp.</p> Full article ">Figure 5
<p>The graphs above represent the number of cells, average size, cytoskeleton length and area covered by nuclei on the two types of disc being studied. We obtained these data by averaging the values taken from the five regions of interest of each disc.</p> Full article ">Figure 6
<p>Confocal microscope images of fibroblasts on IPS at 40× and 63× (top left and right, respectively) and VITA CAD Temp (lower images).</p> Full article ">
14 pages, 6214 KiB  
Article
Pluronic F127-Folate Coated Super Paramagenic Iron Oxide Nanoparticles as Contrast Agent for Cancer Diagnosis in Magnetic Resonance Imaging
by Hieu Vu-Quang, Mads Sloth Vinding, Thomas Nielsen, Marcus Görge Ullisch, Niels Chr. Nielsen, Dinh-Truong Nguyen and Jørgen Kjems
Polymers 2019, 11(4), 743; https://doi.org/10.3390/polym11040743 - 25 Apr 2019
Cited by 50 | Viewed by 8518
Abstract
Contrast agents have been widely used in medicine to enhance contrast in magnetic resonance imaging (MRI). Among them, super paramagnetic iron oxide nanoparticles (SPION) have been reported to have low risk in clinical use. In our study, F127-Folate coated SPION was fabricated in [...] Read more.
Contrast agents have been widely used in medicine to enhance contrast in magnetic resonance imaging (MRI). Among them, super paramagnetic iron oxide nanoparticles (SPION) have been reported to have low risk in clinical use. In our study, F127-Folate coated SPION was fabricated in order to efficiently target tumors and provide imaging contrast in MRI. SPION alone have an average core size of 15 nm. After stabilizing with Pluronic F127, the nanoparticles reached a hydrodynamic size of 180 nm and dispersed well in various kinds of media. The F127-Folate coated SPION were shown to specifically target folate receptor expressing cancer cells by flow cytometry analysis, confocal laser scanning microscope, as well as in vitro MRI. Furthermore, in vivo MRI images have shown the enhanced negative contrast from the F127-Folate coated SPION in tumor-bearing mice. In conclusion, our F127-Folate coated SPION have shown great potential as a contrast agent in MRI, as well as in the combination with drug delivery for cancer therapy. Full article
(This article belongs to the Special Issue Intrinsically Biocompatible Polymer Systems)
►▼ Show Figures

Figure 1

Figure 1
<p>Schematic illustration of chemical reaction. (1) Activation of folic acid by 1,1′ Carbonyldiimidazole (CDI) in dry dimethyl sulfoxide (DMSO) and darkness for 24 h, (2) conjugation of CDI-Folate to Pluronic F127, 24 h darkness.</p> Full article ">Figure 2
<p>NMR spectrum of (1) folic acid, (2) Pluronic F127, (3) Pluronic F127 – Folate.</p> Full article ">Figure 3
<p>Coating procedure of F127 onto the oleic-super paramagnetic iron oxide nanoparticles (SPION). (1) Oleic SPION dispersed in n-Hexane, (2) polymer coated SPION after the evaporation of <span class="html-italic">n</span>-Hexane, (3) the dispersion of F127 coated SPION in water.</p> Full article ">Figure 4
<p>TEM images of SPION. (<b>a</b>) Oleic coated SPION, (<b>b</b>) oleic coated SPION at magnification 350k ×, (<b>c</b>) F127 coated SPION. The scale bars are 20 nm, 5 nm, and 20 nm.</p> Full article ">Figure 5
<p>Cell viability of F127 coated SPIO and F127-Folate coated SPION after 24 h of incubation. MTT assay, n = 4, vertical axis: % percentage of viability compares to untreated cells.</p> Full article ">Figure 6
<p>Prussian blue staining of KB cells. Cells were incubated with (<b>a</b>) cells only – negative control, F127 coated SPION (<b>b</b>), and F127-Folate coated SPION (<b>c</b>) for 3 h. Blue color indicates SPION, pink colors indicate cell body, and arrows show the position of iron, scale bar: 50 µL.</p> Full article ">Figure 7
<p>Confocal laser scanning microscope images of particles and KB cells. Cells were incubated with particles for 3 h. (<b>a</b>) Negative control, (<b>b</b>) F127 coated SPION and Nile Red, (<b>c</b>) F127-Folate coated SPION and Nile Red. Green: Wheat germ agglutinin-Alexa fluoro 488, Red: Nile Red, scale bar: 100 µm.</p> Full article ">Figure 8
<p>Iron concentration in KB cells, 3 h after incubation. From the left: Cells, 100, 50, 25, 12.5. 6.25, 3.125 µg/mL. (<span class="html-italic">n</span> = 4), Y axis: µg/well.</p> Full article ">Figure 9
<p>Flow cytometry analysis (FACs). KB cells were incubated with 50 µg/mL iron F127 coated SPION; F127-Folate coated SPION in the media with and without folic acid (5 ng/mL). Histogram (<b>a</b>) shows the cell fluorescent signal, graph (<b>b</b>) presents uptake efficiency. Gate region A was chosen for non-uptake particles, while gate region B indicates the uptake (n = 4, cell counted number: 10,000, iron concentration for incubation 50 µL/mL).</p> Full article ">Figure 10
<p>(<b>a</b>) T2 map of cells in NMR tubes, (1) water, (2) agarose 0.5%, (3) F127- Folate coated SPION in folic acid media,(4) F127-Folate coated SPION in free Folic acid media, (5) F127 coated SPION, (6) cells in 0.5% agarose. (<b>b</b>) T2 and T2* value from T2 map (a) and T2* map (images not show). Number of cells: 4.5 x 10<sup>5</sup> cells/ 200 µL in 0.5 % agarose.</p> Full article ">Figure 11
<p>T2 weighted images of tumor bearing mice pre-injection and post injection. F127 coated SPION (<b>a</b>) and F127-Folate coated SPION (<b>b</b>) nanoparticles. TR/TE 4000/10.16 ms, TH 1 mm, matrix size 128 × 128, number of average: two.</p> Full article ">Figure A1
<p>Diffraction of SPION. Magnetite Fe<sub>3</sub>O<sub>4</sub>: (1) 3; (2) 2.56; (3) 2.11; (4) 1.73; (5) 1.63; (6) 1.49; (7) 1.29. Diffraction pattern confirms the main chemical structure of nanoparticle is Fe<sub>3</sub>O<sub>4</sub>.</p> Full article ">Figure A2
<p>T2 relaxation of F127 coated SPION. F127 coated SPION was diluted in various concentrations, ranging from 100 µg to 1.5625 µg/mL and aliquot to NMR tubes. Next, T2 map was taken by choosing different TE (from 7.76 ms to 62 ms in steps of 10), TR of 5000 ms, number, or average (NA) of 20, matrix size of 256 x 256, field of view (FOV) of 22 × 22 mm<sup>2</sup>, slice thickness (TH) of 0.5 mm. (<b>a</b>) T2 map of F127 coated SPION, (<b>b</b>) R2 relaxation time graph represents the correlation between iron concentration and R2 relaxation time. Numbers in (<b>a</b>) indicate iron concentration (µg/mL).</p> Full article ">
16 pages, 3272 KiB  
Article
Synthesis and Characterization of Covalently Crosslinked pH-Responsive Hyaluronic Acid Nanogels: Effect of Synthesis Parameters
by Sheila Maiz-Fernández, Leyre Pérez-Álvarez, Leire Ruiz-Rubio, Raúl Pérez González, Virginia Sáez-Martínez, Jesica Ruiz Pérez and José Luis Vilas-Vilela
Polymers 2019, 11(4), 742; https://doi.org/10.3390/polym11040742 - 24 Apr 2019
Cited by 37 | Viewed by 6890
Abstract
Stable hyaluronic acid nanogels were obtained following the water-in-oil microemulsion method by covalent crosslinking with three biocompatible crosslinking agents: Divinyl sulfone, 1,4-butanediol diglycidyl ether (BDDE), and poly(ethylene glycol) bis(amine). All nanoparticles showed a pH-sensitive swelling behavior, according to the pKa value of hyaluronic [...] Read more.
Stable hyaluronic acid nanogels were obtained following the water-in-oil microemulsion method by covalent crosslinking with three biocompatible crosslinking agents: Divinyl sulfone, 1,4-butanediol diglycidyl ether (BDDE), and poly(ethylene glycol) bis(amine). All nanoparticles showed a pH-sensitive swelling behavior, according to the pKa value of hyaluronic acid, as a consequence of the ionization of the carboxylic moieties, as it was corroborated by zeta potential measurements. QELS studies were carried out to study the influence of the chemical structure of the crosslinking agents on the particle size of the obtained nanogels. In addition, the effect of the molecular weight of the biopolymer and the degree of crosslinking on the nanogels dimensions was also evaluated for BDDE crosslinked nanoparticles, which showed the highest pH-responsive response. Full article
(This article belongs to the Special Issue Hyaluronic Acid-Based Polymers and Biomaterials)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Pseudothernary phase diagram obtained for the system based on H<sub>2</sub>O/ trimethylpentane (isooctane)/ dioctyl sulfosuccinate sodium salt (Aerosol OT, AOT). The white point corresponds with the employed formulation for hyaluronic acid (HA) nanogel preparation.</p> Full article ">Figure 2
<p>Schemes of crosslinking reactions of HA with (<b>A</b>) divinyl sulfone (DVS) (<b>B</b>) butanediol diglycidyl ether (BDDE), and (<b>C</b>) poly(ethylene glycol) bis(amine) (PEGBNH<sub>2)</sub> followed in the preparation of covalently crosslinked HA nanogels.</p> Full article ">Figure 3
<p>Nuclear magnetic resonance (<sup>1</sup>H-NMR) spectra of hyaluronic acid (2.1 MDA) in D<sub>2</sub>O (<b>A</b>) and HA nanogels prepared by its crosslinking in microemulsion with (<b>B</b>) DVS, (<b>C</b>) PEGBNH<sub>2</sub>, and (<b>D</b>) BDDE in a molar ratio HA: crosslinker of 1:1.</p> Full article ">Figure 4
<p>Transmission electron microscopy (TEM) microphotographs of (<b>A</b>) DVS, (<b>B</b>) BDDE, and (<b>C</b>) PEGBNH<sub>2</sub>, crosslinked (1:1, HA:crosslinker molar ratio) HA (2.1 MDA) nanoparticles, average particle sizes (d<sub>p</sub>), and particle size distributions.</p> Full article ">Figure 5
<p>Variation of the hydrodynamic diameter (●) and the zeta potential (▲) of HA (2.1MDA) nanogels prepared by crosslinking (1:1, HA:crosslinker molar ratio) with (<b>A</b>) DVS, (<b>B</b>) BDDE, and (<b>C</b>) PEGBNH<sub>2</sub>.</p> Full article ">Figure 6
<p>TEM microphotograph of (<b>A</b>) HA (LMW)–BDDE 1:0.2, (<b>B</b>) HA (LMW)–BDDE 1:1, (<b>C</b>) HA (LMW)–BDDE 1:10, (<b>D</b>) HA (HMW)–BDDE 1:0.2, (<b>E</b>) HA (HMW)–BDDE 1:1, and (<b>F</b>) HA (HMW)–BDDE 1:10 nanoparticles average particle sizes (d<sub>p</sub>) and particle size distributions.</p> Full article ">Figure 7
<p>Hydrodynamic diameters (●) and zeta potential (▲) as a function of external pH for HA nanogels obtained by crosslinking with BDDE with (<b>A</b>) high molecular weight and (<b>B</b>) low molecular weight HA.</p> Full article ">Figure 8
<p>Hydrodynamic diameters (●) and zeta potential (▲) as a function of external pH for HA nanogels obtained by the crosslinking of HA (high molecular weight) with BDDE at different ratios: (<b>A</b>) HA (HMW)–BDDE 1:0.2, (<b>B</b>) HA (HMW)–BDDE 1:1, and (<b>C</b>) HA (HMW)–BDDE 1:10 and obtained by crosslinking of HA (low molecular weight) with (<b>D</b>) HA (LMW)– =BDDE 1:0.2, (<b>E</b>) HA (LMW)–BDDE, and (<b>F</b>) HA (LMW)–BDDE 1:10.</p> Full article ">
16 pages, 4204 KiB  
Article
Effect of Silane Treatment on Mechanical Properties of Polyurethane/Mesoscopic Fly Ash Composites
by Chuanrui Qin, Wei Lu, Zhenglong He, Guansheng Qi, Jinliang Li and Xiangming Hu
Polymers 2019, 11(4), 741; https://doi.org/10.3390/polym11040741 - 24 Apr 2019
Cited by 17 | Viewed by 4238
Abstract
In view of the accidents such as rock mass breakage, roof fall and coal slide in coal mines, polyurethane/mesoscopic fly ash (PU/MFA) reinforcement materials were produced from polymethylene polyphenylene isocyanate (PAPI), the polyether polyol, flame retardant, and MFA using stannous octanate as a [...] Read more.
In view of the accidents such as rock mass breakage, roof fall and coal slide in coal mines, polyurethane/mesoscopic fly ash (PU/MFA) reinforcement materials were produced from polymethylene polyphenylene isocyanate (PAPI), the polyether polyol, flame retardant, and MFA using stannous octanate as a catalyst. 3-Glycidoxypropyltrimethoxysilane (GPTMS) was grafted on MFA surface, aiming to improve the mechanical properties of PU/MFA composites. The analyses of infrared spectroscopy and compression resistance reveal that the GPTMS can be successfully attached to the surface of MFA, and the optimum modification dosage of GPTMS to MFA is 2.5 wt. % (weight percent). On this basis, the effect of GPTMS on the mechanical properties of PU/MFA reinforcement materials during the curing process was systematically investigated through a compression test, a fracture toughness test, a three-point bending test, a bond property test, and a dynamic mechanics analysis. The results show that the compression property, fracture toughness, maximum flexural strength, and bond strength of PU/MFA composites increase by 21.6%, 10.1%, 8.8%, and 19.3%, respectively, compared with the values before the modification. Furthermore, the analyses of scanning electron microscope and dynamic mechanics suggest that the coupling agent GPTMS can successfully improve the mechanical properties of PU/MFA composites because it eliminates the stress concentration and exerts a positive effect on the crosslink density and hardness of PU/MFA composites. Full article
(This article belongs to the Collection Silicon-Containing Polymeric Materials)
►▼ Show Figures

Figure 1

Figure 1
<p>Schematic diagram of PU/MFA composites preparation.</p> Full article ">Figure 2
<p>Electronic Universal Testing Machine (<b>a</b>) and Measuring Specimens: (<b>b</b>) Cylindrical Specimens, (<b>c</b>) Three-point Bending/DMA Specimens, (<b>d</b>) Rectangular Specimens, and (<b>e</b>) Bond Specimens of Iron Batten.</p> Full article ">Figure 3
<p>Schematic illustration of the synthesis of PU/MFA composites (<b>a</b>) and the crosslink mechanism of modified MFA by 3-Glycidoxypropyltrimethoxysilane (GPTMS) and PU matrix (<b>b</b>).</p> Full article ">Figure 4
<p>Infrared spectra of coupling agents of GPTMS, unmodified MFA and MFA modified by different contents of GPTMS: (<b>a</b>) GPTMS; (<b>b</b>) unmodified MFA; (<b>c</b>) MFA modified by 0.5 wt. % GPTMS; (<b>d</b>) MFA modified by 1.5 wt. % GPTMS; and (<b>e</b>) MFA modified by 2.5 wt. % GPTMS; (<b>f</b>) MFA modified by 3.5 wt. % GPTMS.</p> Full article ">Figure 5
<p>(<b>a</b>) Compressive strength of specimens under different GPTMS content in MFA; (<b>b</b>) stress-strain curves of PU/MFA composites with different GPTMS contents; and (<b>c</b>) compressive strength of -0.0 wt. % and -2.5 wt. % PU/MFA specimens at different curing times.</p> Full article ">Figure 6
<p>The fracture toughness <span class="html-italic">K</span><sub>c</sub> (<b>a</b>) and the maximum flexural strengths σ<sub>fm</sub> (<b>b</b>) of PU, PU/MFA-0.0 wt. %, and PU/MFA-2.5 wt. % specimens at different curing times.</p> Full article ">Figure 7
<p>Bond strengths of PU, PU/MFA-0.0 wt. %, and PU/MFA-2.5 wt. % specimens at different curing times.</p> Full article ">Figure 8
<p>The SEM micrographs of fracture surface of (<b>A</b>) PU, (<b>B</b>) and (<b>C</b>) PU/MFA-0.0 wt. %, (<b>D</b>) and (<b>E</b>) PU/MFA-2.5 wt. % specimens after fracture toughness test.</p> Full article ">Figure 9
<p>The relationship between storage modulus and temperature of PU, PU/MFA-0.0 wt. %, and PU/MFA-2.5 wt. % specimens at different curing times.</p> Full article ">Figure 10
<p>The relationship between loss factors and temperatures of PU, PU/MFA-0.0 wt. %, and PU/MFA-2.5 wt. % specimens at different curing times.</p> Full article ">
15 pages, 4333 KiB  
Article
Characterization of Reduced and Surface-Modified Graphene Oxide in Poly(Ethylene-co-Butyl Acrylate) Composites for Electrical Applications
by Carmen Cobo Sánchez, Martin Wåhlander, Mattias Karlsson, Diana C. Marin Quintero, Henrik Hillborg, Eva Malmström and Fritjof Nilsson
Polymers 2019, 11(4), 740; https://doi.org/10.3390/polym11040740 - 24 Apr 2019
Cited by 7 | Viewed by 3842
Abstract
Promising electrical field grading materials (FGMs) for high-voltage direct-current (HVDC) applications have been designed by dispersing reduced graphene oxide (rGO) grafted with relatively short chains of poly (n-butyl methacrylate) (PBMA) in a poly(ethylene-co-butyl acrylate) (EBA) matrix. All rGO-PBMA composites [...] Read more.
Promising electrical field grading materials (FGMs) for high-voltage direct-current (HVDC) applications have been designed by dispersing reduced graphene oxide (rGO) grafted with relatively short chains of poly (n-butyl methacrylate) (PBMA) in a poly(ethylene-co-butyl acrylate) (EBA) matrix. All rGO-PBMA composites with a filler fraction above 3 vol.% exhibited a distinct non-linear resistivity with increasing electric field; and it was confirmed that the resistivity could be tailored by changing the PBMA graft length or the rGO filler fraction. A combined image analysis- and Monte-Carlo simulation strategy revealed that the addition of PBMA grafts improved the enthalpic solubility of rGO in EBA; resulting in improved particle dispersion and more controlled flake-to-flake distances. The addition of rGO and rGO-PBMAs increased the modulus of the materials up to 200% and the strain did not vary significantly as compared to that of the reference matrix for the rGO-PBMA-2 vol.% composites; indicating that the interphase between the rGO and EBA was subsequently improved. The new composites have comparable electrical properties as today’s commercial FGMs; but are lighter and less brittle due to a lower filler fraction of semi-conductive particles (3 vol.% instead of 30–40 vol.%). Full article
(This article belongs to the Special Issue Conducting Polymers)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>TGA thermograms of reduced graphene oxide (rGO), after silanization (rGO-Silanized), and after subsequent polymer grafting (rGO-PBMA). PBMA = poly(<span class="html-italic">n</span>-butyl methacrylate).</p> Full article ">Figure 2
<p>Thermal stability increase versus nanofiller fraction at (<b>left</b>) 15% weight loss and (<b>right</b>) 50% weight loss. The data are extracted from TGA thermograms.</p> Full article ">Figure 3
<p>SEM micrographs of cross-sections of the nanocomposites, the arrows indicate the film direction (i.e., perpendicular to the pressing direction). The unmodified rGO sheets are clearly aligned in the film direction (top row). The polymer-grafted rGO gradually develop a more random direction with increasing length of the polymer brushes. All scale bars are 20 µm.</p> Full article ">Figure 4
<p>Young’s Modulus (left) and tensile strain at maximum tensile stress (right) of the rGO-nanocomposites.</p> Full article ">Figure 5
<p>Resistivity measurements for the 2, 3, and 4 vol.% nanocomposites.</p> Full article ">Figure 6
<p>Comparison of non-linear resistivity of rGO-PBMA-9k with literature data. The commercial grade field grading materials (No. 2 and 5 in Greuter et al. [<a href="#B6-polymers-11-00740" class="html-bibr">6</a>]) exhibit a significantly lower resistivity at the lower fields, and higher non-linearity, compared to rGO-PBMA-9k. A field grading material based on 1.5 vol.% rGO in silicone rubber, reported by Hillborg et al. [<a href="#B24-polymers-11-00740" class="html-bibr">24</a>] exhibits a higher resistivity.</p> Full article ">Figure 7
<p>Percolation threshold φ<sub>c</sub> as a function of the degree of isotropy (0 = minimum, 90 = maximum) for simulated nanocomposites with nanofillers having an aspect ratio of 100.</p> Full article ">
10 pages, 7681 KiB  
Article
Jetting Performance of Polyethylene Glycol and Reactive Dye Solutions
by Zhiyuan Tang, Kuanjun Fang, Yawei Song and Fuyun Sun
Polymers 2019, 11(4), 739; https://doi.org/10.3390/polym11040739 - 24 Apr 2019
Cited by 24 | Viewed by 5010
Abstract
The jetting performance of dye inks determines the image quality, production efficiency, and lifetime of the print head. In the present study, we explored the jetting performance of mixed solutions of polyethylene glycol (PEG) and reactive dye by testing the visible absorption spectra, [...] Read more.
The jetting performance of dye inks determines the image quality, production efficiency, and lifetime of the print head. In the present study, we explored the jetting performance of mixed solutions of polyethylene glycol (PEG) and reactive dye by testing the visible absorption spectra, rheological properties, and surface tension, in addition to the observation of droplet formation. The results indicate that PEG macromolecules could change the aggregate groups of Red 218 molecules into smaller ones through hydrophobic interactions and separation effect. The addition of PEG into the dye solution increased the viscosity and decreased the surface tension. In the whole shear rate range tested, the 10% and 20% PEG400, as well as the 30% PEG200 dye solutions, showed good Newtonian fluid behavior. PEG macromolecules improved the droplet formation of the dye solutions. Increasing the PEG400 concentration to 30% and 40% resulted in elimination of the formation of satellites and the formation of ideal droplets at 10,000 Hz jetting frequency. A 30% PEG600-dye solution with the Z value of 4.6 formed the best spherical droplets at 10,000 Hz and produced perfect color images on cotton fabrics. Full article
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Chemical structure of Red 218; (<b>b</b>) Chemical structure of polyethylene glycol (PEG).</p> Full article ">Figure 2
<p>Visible absorption spectra of 7% Red 218 and PEG solutions at 25 °C. (<b>a</b>) For different amounts of PEG400; (<b>b</b>) For PEG200, PEG400, and PEG600 at 30% by weight.</p> Full article ">Figure 3
<p>The hydrophobic interaction of PEG and dye molecules and the separation effect of PEG macromolecules. <a href="#polymers-11-00739-t001" class="html-table">Table 1</a> lists all the peak positions for different dye solutions. It is clear that the maximum absorption peak of the dye solution, λ<sub>1</sub>, changed to λ<sub>2</sub> when PEGs were added to the solution due to the rapid increase of the peak height of λ<sub>2</sub>.</p> Full article ">Figure 4
<p>The rheological properties of Red 218 dye inks at different PEG400 concentrations and PEG molecular weights. (<b>a</b>) At low shear rates; (<b>b</b>) At high shear rates. Red 218 concentration was 7%, and the temperature was 25 °C.</p> Full article ">Figure 5
<p>The surface tension of Red 21 8 dye inks: (<b>a</b>) At different PEG400 concentrations; (<b>b</b>) At different PEG molecular weights. The Red 218 concentration was 7%, and the temperature was 25 °C.</p> Full article ">Figure 6
<p>The arrangement of Red 218 dye (<b>a</b>) and PEG molecules (<b>b</b>) at the air/liquid interface.</p> Full article ">Figure 7
<p>Droplet formation of 7% (<span class="html-italic">w</span>/<span class="html-italic">w</span>) Red 218 dye aqueous solutions at different jetting frequency at 25 °C. (<b>a</b>) 1500 Hz; (<b>b</b>) 5000 Hz; (<b>c</b>) 10,000 Hz; (<b>d</b>) 20,000 Hz.</p> Full article ">Figure 8
<p>Droplet formation of 7% dye solutions with different concentrations of PEG400 at 25 °C and 10,000 Hz. (<b>a</b>) 10% PEG400, (<b>b</b>) 20% PEG400, (<b>c</b>) 30% PEG400, (<b>d</b>) 40% PEG400.</p> Full article ">Figure 9
<p>Droplet formation of 7% Red 218 dye solutions containing 30% PEG400 at different jetting frequency and 25 °C: (<b>a</b>) 1500 Hz; (<b>b</b>) 5000 Hz; (<b>c</b>) 10,000 Hz; (<b>d</b>) 20,000 Hz.</p> Full article ">Figure 10
<p>The influence of PEG molecular weights on the droplet formation of Red 218 dye solutions. (<b>a</b>) PEG200; (<b>b</b>) PEG400; (<b>c</b>) PEG600.The concentrations of Red 218 and PEG were 7% and 30%, respectively, the temperature was 25 °C, and the jet frequency was 10,000 Hz.</p> Full article ">Figure 11
<p>The images of cotton fabrics printed with 30% PEG600–dye solution: (<b>a</b>) The printed fabric, (<b>b</b>) The lines printed.</p> Full article ">
16 pages, 1598 KiB  
Article
Fuzzy Optimization on the Synthesis of Chitosan-Graft-Polyacrylic Acid with Montmorillonite as Filler Material: A Case Study
by Angelo Earvin Sy Choi, Cybelle Morales Futalan and Jurng-Jae Yee
Polymers 2019, 11(4), 738; https://doi.org/10.3390/polym11040738 - 23 Apr 2019
Cited by 7 | Viewed by 3403
Abstract
In this paper, the synthesis of a chitosan–montmorillonite nanocomposite material grafted with acrylic acid is presented based on its function in a case study analysis. Fuzzy optimization is used for a multi-criteria decision analysis to determine the best desirable swelling capacity (Y [...] Read more.
In this paper, the synthesis of a chitosan–montmorillonite nanocomposite material grafted with acrylic acid is presented based on its function in a case study analysis. Fuzzy optimization is used for a multi-criteria decision analysis to determine the best desirable swelling capacity (YQ) of the material synthesis at its lowest possible variable cost. For YQ, the integrating the result’s cumulative uncertainty is an essential element to investigate the feasibility of the developed model equation. The Pareto set analysis is able to set the appropriate boundary limits for YQ and the variable cost. Two case studies are presented in determining the lowest possible cost: Case 1 for maximum YQ, and Case 2 for minimum YQ. These boundary limits were used in the fuzzy optimization to determine its global optimum results that achieved the overall satisfaction ratings of 67.2% (Case 1) and 52.3% (Case 2). The synthesis of the polyacrylic acid/chitosan material for Case 1 resulted in 305 g/g YQ and 10.8 USD/kg, while Case 2 resulted in 97 g/g YQ and 12.3 USD/kg. Thus, the fuzzy optimization approach proves to be a practical method for examining the best possible compromise solution based on the desired function to adequately synthesize a material. Full article
(This article belongs to the Special Issue Polymer Clay Nano-composites)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Fuzzy optimization process diagram.</p> Full article ">Figure 2
<p>Simultaneous analysis of swelling capacity and variable cost at different levels of (<b>a</b>) acrylic acid/chitosan, (<b>b</b>) <span class="html-italic">N</span>,<span class="html-italic">N</span>′-methylenebisacrylamide, and (<b>c</b>) ammonium persulfate.</p> Full article ">Figure 2 Cont.
<p>Simultaneous analysis of swelling capacity and variable cost at different levels of (<b>a</b>) acrylic acid/chitosan, (<b>b</b>) <span class="html-italic">N</span>,<span class="html-italic">N</span>′-methylenebisacrylamide, and (<b>c</b>) ammonium persulfate.</p> Full article ">Figure 3
<p>Pareto plot of variable cost with (<b>a</b>) maximum and (<b>b</b>) minimum conditions on the swelling capacity.</p> Full article ">Figure 3 Cont.
<p>Pareto plot of variable cost with (<b>a</b>) maximum and (<b>b</b>) minimum conditions on the swelling capacity.</p> Full article ">Figure 4
<p>Linear membership function at goals towards (<b>a</b>) maximization and (<b>b</b>) minimization.</p> Full article ">
15 pages, 4589 KiB  
Article
Tethered Semiflexible Polymer under Large Amplitude Oscillatory Shear
by Antonio Lamura and Roland G. Winkler
Polymers 2019, 11(4), 737; https://doi.org/10.3390/polym11040737 - 23 Apr 2019
Cited by 6 | Viewed by 3138
Abstract
The properties of a semiflexible polymer with fixed ends exposed to oscillatory shear flow are investigated by simulations. The two-dimensionally confined polymer is modeled as a linear bead-spring chain, and the interaction with the fluid is described by the Brownian multiparticle collision dynamics [...] Read more.
The properties of a semiflexible polymer with fixed ends exposed to oscillatory shear flow are investigated by simulations. The two-dimensionally confined polymer is modeled as a linear bead-spring chain, and the interaction with the fluid is described by the Brownian multiparticle collision dynamics approach. For small shear rates, the tethering of the ends leads to a more-or-less linear oscillatory response. However, at high shear rates, we found a strongly nonlinear reaction, with a polymer (partially) wrapped around the fixation points. This leads to an overall shrinkage of the polymer. Dynamically, the location probability of the polymer center-of-mass position is largest on a spatial curve resembling a limaçon, although with an inhomogeneous distribution. We found shear-induced modifications of the normal-mode correlation functions, with a frequency doubling at high shear rates. Interestingly, an even-odd asymmetry for the Cartesian components of the correlation functions appears, with rather similar spectra for odd x- and even y-modes and vice versa. Overall, our simulations yielded an intriguing nonlinear behavior of tethered semiflexible polymers under oscillatory shear flow. Full article
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Sketch of the tethered bead-spring polymer exposed to oscillatory linear shear flow.</p> Full article ">Figure 2
<p>Conformations of the polymer at times <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math> (solid line), <math display="inline"><semantics> <mrow> <mn>0.5</mn> <mi>π</mi> <mo>/</mo> <mi>ω</mi> </mrow> </semantics></math> (dashed line), <math display="inline"><semantics> <mrow> <mi>π</mi> <mo>/</mo> <mi>ω</mi> </mrow> </semantics></math> (dotted line), <math display="inline"><semantics> <mrow> <mn>1.5</mn> <mi>π</mi> <mo>/</mo> <mi>ω</mi> </mrow> </semantics></math> (dash-dotted line) after equilibration for <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mi>p</mi> </msub> <mo>/</mo> <mi>L</mi> <mo>=</mo> <mn>0.5</mn> </mrow> </semantics></math> (<b>left</b>), 2 (<b>right</b>), and <math display="inline"><semantics> <mrow> <mi>W</mi> <mi>i</mi> </mrow> </semantics></math> = 10, 25, 50, 100 (<b>from top to bottom</b>). Black dots denote the position of fixed beads.</p> Full article ">Figure 3
<p>Time-dependence of the center-of-mass coordinate along the <span class="html-italic">x</span>-axis for <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mi>p</mi> </msub> <mo>/</mo> <mi>L</mi> <mo>=</mo> <mn>0.5</mn> </mrow> </semantics></math> (<b>left</b>) and 2 (<b>right</b>), and <math display="inline"><semantics> <mrow> <mi>W</mi> <mi>i</mi> </mrow> </semantics></math> = 10, 25, 50, 100 (<b>from top to bottom</b>). The black lines correspond to the externally applied shear flow with arbitrary amplitude.</p> Full article ">Figure 4
<p>Probability distribution of the center-of-mass position of the tethered polymers for <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mi>p</mi> </msub> <mo>/</mo> <mi>L</mi> <mo>=</mo> <mn>0.5</mn> </mrow> </semantics></math> (<b>left</b>) and 2 (<b>right</b>), and <math display="inline"><semantics> <mrow> <mi>W</mi> <mi>i</mi> <mo>=</mo> <mn>10</mn> <mo>,</mo> <mn>25</mn> <mo>,</mo> <mn>50</mn> <mo>,</mo> <mn>100</mn> </mrow> </semantics></math> (<b>from top to bottom</b>). Black dots indicate the position of fixed ends. The lines for <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mi>p</mi> </msub> <mo>/</mo> <mi>L</mi> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math> (right) are limaons according to Equations (5) and (6) for the parameters: (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>a</mi> <mo>/</mo> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>20.48</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>b</mi> <mo>/</mo> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>1.92</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>y</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>, (<b>d</b>) <math display="inline"><semantics> <mrow> <mi>a</mi> <mo>/</mo> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>19.91</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>b</mi> <mo>/</mo> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>2.72</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>y</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>, (<b>f</b>) <math display="inline"><semantics> <mrow> <mi>a</mi> <mo>/</mo> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>17</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>b</mi> <mo>/</mo> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>14</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>y</mi> <mn>0</mn> </msub> <mo>/</mo> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>=</mo> <mo>−</mo> <mn>6</mn> </mrow> </semantics></math>, (<b>h</b>) <math display="inline"><semantics> <mrow> <mi>a</mi> <mo>/</mo> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>16</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>b</mi> <mo>/</mo> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>16</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>y</mi> <mn>0</mn> </msub> <mo>/</mo> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>=</mo> <mo>−</mo> <mn>6</mn> </mrow> </semantics></math>.</p> Full article ">Figure 5
<p>Probability distribution functions of the <span class="html-italic">x</span> (<b>top</b>) and <span class="html-italic">y</span> (<b>bottom</b>) coordinates of the polymer center of mass for <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mi>p</mi> </msub> <mo>/</mo> <mi>L</mi> <mo>=</mo> <mn>0.5</mn> </mrow> </semantics></math> (<b>left</b>), 2 (<b>right</b>) and <math display="inline"><semantics> <mrow> <mi>W</mi> <mi>i</mi> <mo>=</mo> <mn>10</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>•</mo> <mo>)</mo> <mo>,</mo> <mn>25</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>▴</mo> <mo>)</mo> <mo>,</mo> <mn>50</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>⋆</mo> <mo>)</mo> <mo>,</mo> <mn>100</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>▪</mo> <mo>)</mo> </mrow> </semantics></math>.</p> Full article ">Figure 6
<p>Average position along the <span class="html-italic">y</span>-direction of the polymer center of mass as a function of the Weissenberg number for <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mi>p</mi> </msub> <mo>/</mo> <mi>L</mi> <mo>=</mo> <mn>0.5</mn> </mrow> </semantics></math> (•), 2 (▴). Lines are the fits <math display="inline"><semantics> <mrow> <mo>&lt;</mo> <msub> <mi>y</mi> <mrow> <mi>c</mi> <mi>m</mi> </mrow> </msub> <mo>&gt;</mo> <mo>/</mo> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>∼</mo> <mi>β</mi> <mo form="prefix">ln</mo> <mi>W</mi> <mi>i</mi> </mrow> </semantics></math> with <math display="inline"><semantics> <mrow> <mi>β</mi> <mo>=</mo> <mo>−</mo> <mn>4.9</mn> <mo>±</mo> <mn>0.4</mn> </mrow> </semantics></math> (full line) <math display="inline"><semantics> <mrow> <mi>β</mi> <mo>=</mo> <mo>−</mo> <mn>7.6</mn> <mo>±</mo> <mn>0.6</mn> </mrow> </semantics></math> (dashed line).</p> Full article ">Figure 7
<p>Mean (<b>left</b>) and mean square (<b>right</b>) values of the components of the displacement <math display="inline"><semantics> <mi mathvariant="bold-italic">S</mi> </semantics></math> as a function of the bead index, <span class="html-italic">i</span>, of the semiflexible polymer with <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mi>p</mi> </msub> <mo>/</mo> <mi>L</mi> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math> for <math display="inline"><semantics> <mrow> <mi>W</mi> <mi>i</mi> <mo>=</mo> <mn>10</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>∘</mo> <mo>)</mo> <mo>,</mo> </mrow> </semantics></math><math display="inline"><semantics> <mrow> <mn>25</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>▵</mo> <mo>)</mo> <mo>,</mo> <mn>50</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>⋆</mo> <mo>)</mo> <mo>,</mo> <mn>100</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>□</mo> <mo>)</mo> </mrow> </semantics></math>. Open symbols indicate <math display="inline"><semantics> <msub> <mi>S</mi> <mi>x</mi> </msub> </semantics></math> and filled symbols <math display="inline"><semantics> <msub> <mi>S</mi> <mi>y</mi> </msub> </semantics></math>.</p> Full article ">Figure 8
<p>Variance of the mode components <math display="inline"><semantics> <msub> <mi>A</mi> <mrow> <mi>n</mi> <mi>x</mi> </mrow> </msub> </semantics></math> (open symbols with solid lines) and <math display="inline"><semantics> <msub> <mi>A</mi> <mrow> <mi>n</mi> <mi>y</mi> </mrow> </msub> </semantics></math> (solid symbols with dashed lines) as functions of mode number <span class="html-italic">n</span> for <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mi>p</mi> </msub> <mo>/</mo> <mi>L</mi> <mo>=</mo> <mn>0.5</mn> </mrow> </semantics></math> (<b>left</b>), 2 (<b>right</b>) and <math display="inline"><semantics> <mrow> <mi>W</mi> <mi>i</mi> <mo>=</mo> <mn>10</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>•</mo> <mo>)</mo> <mo>,</mo> <mn>25</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>▴</mo> <mo>)</mo> <mo>,</mo> <mn>50</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>⋆</mo> <mo>)</mo> <mo>,</mo> <mn>100</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>▪</mo> <mo>)</mo> </mrow> </semantics></math>. The slope of the solid lines is <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>4</mn> </mrow> </semantics></math>.</p> Full article ">Figure 9
<p>Autocorrelation function of the mode amplitudes for the modes <math display="inline"><semantics> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> </semantics></math> (<b>top</b>) and <math display="inline"><semantics> <mrow> <mi>n</mi> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math> (<b>bottom</b>) as a function of time along the <span class="html-italic">x</span>- (<b>left</b>) and <span class="html-italic">y</span>-direction (<b>right</b>). The polymer stiffness is <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mi>p</mi> </msub> <mo>/</mo> <mi>L</mi> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math> and the Weissenberg numbers <math display="inline"><semantics> <mrow> <mi>W</mi> <mi>i</mi> <mo>=</mo> <mn>10</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>∘</mo> <mo>)</mo> <mo>,</mo> <mn>25</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>▵</mo> <mo>)</mo> <mo>,</mo> <mn>50</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>⋆</mo> <mo>)</mo> <mo>,</mo> <mn>100</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>□</mo> <mo>)</mo> </mrow> </semantics></math>. The black solid lines are fits of a damped sinusoidal oscillation.</p> Full article ">Figure 10
<p>Autocorrelation function of center-of-mass Cartesian coordinates as a function of time along the <span class="html-italic">x</span>- (<b>left</b>) and <span class="html-italic">y</span>-direction (<b>right</b>). The polymer stiffness is <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mi>p</mi> </msub> <mo>/</mo> <mi>L</mi> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math> and the Weissenberg numbers <math display="inline"><semantics> <mrow> <mi>W</mi> <mi>i</mi> <mo>=</mo> <mn>10</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>∘</mo> <mo>)</mo> <mo>,</mo> <mn>25</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>▵</mo> <mo>)</mo> <mo>,</mo> <mn>50</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>⋆</mo> <mo>)</mo> <mo>,</mo> <mn>100</mn> <mspace width="3.33333pt"/> <mo>(</mo> <mo>□</mo> <mo>)</mo> </mrow> </semantics></math>.</p> Full article ">
9 pages, 2274 KiB  
Article
Surface-Controlled Molecular Self-Alignment in Polymer Actuators for Flexible Microrobot Applications
by Minsu Jang, Jun Sik Kim, Ji-Hun Kim, Do Hyun Bae, Min Jun Kim, Donghee Son, Yong-Tae Kim, Soong Ho Um, Yong Ho Kim and Jinseok Kim
Polymers 2019, 11(4), 736; https://doi.org/10.3390/polym11040736 - 23 Apr 2019
Cited by 2 | Viewed by 3740
Abstract
Polymer actuators are important components in lab-on-a-chip and micromechanical systems because of the inherent properties that result from their large and fast mechanical responses induced by molecular-level deformations (e.g., isomerization). They typically exhibit bending movements via asymmetric contraction or expansion with respect to [...] Read more.
Polymer actuators are important components in lab-on-a-chip and micromechanical systems because of the inherent properties that result from their large and fast mechanical responses induced by molecular-level deformations (e.g., isomerization). They typically exhibit bending movements via asymmetric contraction or expansion with respect to changes in environmental conditions. To enhance the mechanical properties of actuators, a strain gradient should be introduced by regulating the molecular alignment; however, the miniaturization of polymer actuators for microscale systems has raised concerns regarding the complexity of such molecular control. Herein, a novel method for the fabrication of micro-actuators using a simple molecular self-alignment method is presented. Amphiphilic molecules that consist of azobenzene mesogens were located between the hydrophilic and hydrophobic surfaces, which resulted in a splayed alignment. Thereafter, molecular isomerization on the surface induced a large strain gradient and bending movement of the actuator under ultraviolet-light irradiation. Moreover, the microelectromechanical systems allowed for the variation of the actuator size below the micron scale. The mechanical properties of the fabricated actuators such as the bending direction, maximum angle, and response time were evaluated with respect to their thicknesses and lengths. The derivatives of the polymer actuator microstructure may contribute to the development of novel applications in the micro-robotics field. Full article
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Chemical structures of the azobenzene liquid crystalline monomers (1-azo and 2-azo) used in this study and their polymerization schemes (the isomerization of the azobenzene group under ultraviolet light irradiation is indicated by the right dotted line).</p> Full article ">Figure 2
<p>Fabrication process of tazobenzene actuators: (<b>a</b>–<b>d</b>) micron-sized mold with microelectromechanical system process, (<b>e</b>,<b>f</b>) monomer pouring and polymerization, and (<b>g</b>) actuator detachment. Fabrication results of (<b>h</b>) the mold on a silicon wafer and (<b>i</b>) the polymer actuators. The red box presents an image of the micro-actuators.</p> Full article ">Figure 3
<p>(<b>a</b>) Schematics of the interaction between amphiphilic azobenzene monomers and mold surface; (<b>b</b>) molecular orientation of the polymerized actuator; and (<b>c</b>) cross-sectional scanning electron microscopy image of the actuator; the fracture shows the molecular alignment (red dotted arrow).</p> Full article ">Figure 4
<p>The relationship between the alignment of illuminated molecules and the bending direction by isomerization; the light exposure to (<b>a</b>,<b>c</b>) homogeneous and (<b>b</b>,<b>d</b>) homeotropic surfaces (depending on whether the surface faces the incident light, the bending direction could be the opposite).</p> Full article ">Figure 5
<p>(<b>a</b>) Maximum bending angle as a function of actuator length and thickness; (<b>b</b>) change in the bending angle with respect to the ultraviolet exposure time. Actuators with thicknesses of 10 μm and 5 μm (solid and dashed lines, respectively) were compared.</p> Full article ">
12 pages, 7487 KiB  
Article
Photo Actuation Performance of Nanotube Sheet Incorporated Azobenzene Crosslinked Liquid Crystalline Polymer Nanocomposite
by Meng Bi, Yifan He, Yuchang Wang, Wenlong Yang, Ban Qin, Jiaojiao Xu, Xiuxiu Wang, Binsong Wang, Yinmao Dong, Yachen Gao and Chensha Li
Polymers 2019, 11(4), 735; https://doi.org/10.3390/polym11040735 - 23 Apr 2019
Cited by 15 | Viewed by 4095
Abstract
Crosslinked liquid crystalline polymers (CLCPs) containing azobenzene (AZO-CLCPs) are a type of promising material due to their significance in the design of light-driven smart actuators. Developing AZO-CLCP composites by incorporating AZO-CLCPs with other materials is an effective way of enhancing their practicability. Herein, [...] Read more.
Crosslinked liquid crystalline polymers (CLCPs) containing azobenzene (AZO-CLCPs) are a type of promising material due to their significance in the design of light-driven smart actuators. Developing AZO-CLCP composites by incorporating AZO-CLCPs with other materials is an effective way of enhancing their practicability. Herein, we report an AZO-CLCP/CNT nanocomposite prepared by the in situ polymerization of diacrylates containing azobenzene chromophores on carbon nanotube (CNT) sheets. The liquid crystal phase structure of CLCP matrix was evidenced by the two-dimensional X-ray scattering. The prepared pure AZO-CLCP films and AZO-CLCP/CNT nanocomposite films demonstrated strong reversible photo-triggered deformation under the irradiation of UV light at 366 nm of wavelength, as a result of photo-induced isomerization of azobenzene moieties in the polymer network. But compared to pure AZO-CLCP films, the AZO-CLCP/CNT nanocomposite films could much more rapidly return to their initial shapes after the UV light irradiation was removed due to the elasticity effect of CNT sheets. The deformation behavior of AZO-CLCP/CNT nanocomposite films under the light irradiation was also different from that of the pure AZO-CLCP films due to the interfacial interaction between a polymer network and CNT sheet. Furthermore, incorporation of a CNT sheet remarkably increased the mechanical strength and robustness of the material. We also used this AZO-CLCP/CNT nanocomposite as a microvalve membrane actuator, which can be controlled by light, for a conceptual device of a microfluidic system. The results showed that this AZO-CLCP/CNT nanocomposite may have great potential in smart actuator applications for biological engineering, medical treatment, environment detection and microelectromechanical systems (MEMS), etc. Full article
(This article belongs to the Special Issue Polymer-CNT Nanocomposites)
►▼ Show Figures

Figure 1

Figure 1
<p>(<b>a</b>) Chemical structure and <sup>1</sup>H NMR spectrum of DA11AB; (<b>b</b>) Chemical structure and <sup>1</sup>H NMR spectrum of C9A; (<b>c</b>) Illustration of the formation of AZO-CLCP through photopolymerization of DA11AB and C9A; (<b>d</b>) Illustration of AZO-CLCP/CNT nanocomposite.</p> Full article ">Figure 2
<p>(<b>a</b>) A photo image of the prepared AZO-CLCP film (F20) and AZO-CLCP/CNT nanocomposite film (CF20). Size of the films: 12 mm × 6 mm × 20 μm; (<b>b</b>) A SEM image of the CNT sheet; (<b>c</b>) A SEM image of the cross section of AZO-CLCP/CNT nanocomposite film (CF20).</p> Full article ">Figure 3
<p>(<b>a</b>) POMs of the AZO-CLCP film(F20): (I) The rubbing direction is parallel to the vertical polarization direction; (II) The rubbing direction is parallel to the horizontal polarization direction; (III) The angle between the rubbing direction and the polarization direction of either polarizer is −45°; (IV) The angle between the rubbing direction and the polarization direction of either polarizer is 45°. Inserted crossarrows illustrate the polarization directions of the two polarizers, and the pink arrows illustrate the rubbing directions; (<b>b</b>) 2D-WAXS pattern of the AZO-CLCP/CNT nanocomposite film (CF20). Inserted pink arrow illustrates the rubbing direction.</p> Full article ">Figure 4
<p>Photographs that exhibit the photoinduced deformation behavior of the AZO-CLCP films (<b>a</b>), and the AZO-CLCP/CNT nanocomposite films (<b>b</b>). Size of the films: 12 mm × 6 mm × 20 μm. The wavelength and intensity of the used UV light was 366 nm and 1.5 mW/cm<sup>2</sup> respective. The room lamplight kept turning on state constantly.</p> Full article ">Figure 5
<p>(<b>a</b>) Schematic illustration of the experimental setup for measuring the photoinduced stresses of AZO-CLCP films and AZO-CLCP/CNT nanocomposite films under irradiation of UV light. Size of the films: 12 mm × 6 mm × 20 μm. The wavelength and intensity of the used UV light was 366 nm and 1.5 mW/cm<sup>2</sup> respective. The room lamplight kept turning on state constantly; (<b>b</b>) Photoinduced stresses of the AZO-CLCP films; (<b>c</b>) Photoinduced stresses of the AZO-CLCP/CNT nanocomposite films.</p> Full article ">Figure 6
<p>(<b>a</b>) A Photograph of experimental setup of the conceptual device of microfluidic system. A CF20 with the size of 12 mm × 6 mm × 20 μm was used as the microvalve actuator; (<b>b</b>) A Scheme of the PMMA valve chamber with the AZO-CLCP/CNT nanocomposite microvalve actuator set in it without the UV irradiation; (<b>c</b>) A Schematic illustration of the switching on process of the microvalve under irradiation of UV light.</p> Full article ">Figure 7
<p>Photographs that exhibit the simulated switching on process of AZO-CLCP/CNT nanocomposite microvalve under irradiation of UV light (<b>a</b>) and switching off process of AZO-CLCP/CNT nanocomposite microvalve after the UV source was switched off (<b>b</b>). A CF20 with the size of 12 mm × 6 mm × 20 μm was used as microvalve actuator. The wavelength and intensity of the used UV light was 366 nm and 1.5 mW/cm<sup>2</sup> respective. The room lamplight was kept on consistently.</p> Full article ">
11 pages, 4309 KiB  
Article
An Albumin Biopassive Polyallylamine Film with Improved Blood Compatibility for Metal Devices
by Shuang Lin, Xin Li, Kebing Wang, Tengda Shang, Lei Zhou, Lu Zhang, Jin Wang and Nan Huang
Polymers 2019, 11(4), 734; https://doi.org/10.3390/polym11040734 - 23 Apr 2019
Cited by 8 | Viewed by 3448
Abstract
Nowadays, a variety of materials are employed to make numerous medical devices, including metals, polymers, ceramics, and others. Blood-contact devices are one of the major classes of these medical devices, and they have been widely applied in clinical settings. Blood-contact devices usually need [...] Read more.
Nowadays, a variety of materials are employed to make numerous medical devices, including metals, polymers, ceramics, and others. Blood-contact devices are one of the major classes of these medical devices, and they have been widely applied in clinical settings. Blood-contact devices usually need to have good mechanical properties to maintain clinical performance. Metal materials are one desirable candidate to fabricate blood-contact devices due to their excellent mechanical properties and machinability, although the blood compatibility of existing blood-contact devices is better than other medical devices, such as artificial joints and artificial crystals. However, blood coagulation still occurs when these devices are used in clinical settings. Therefore, it is necessary to develop a new generation of blood-contact devices with fewer complications, and the key factor is to develop novel biomaterials with good blood compatibility. In this work, one albumin biopassive polyallylamine film was successfully established onto the 316L stainless steel (SS) surface. The polyallylamine film was prepared by plasma polymerization in the vacuum chamber, and then polyallylamine film was annealed at 150 °C for 1 h. The chemical compositions of the plasma polymerized polyallylamine film (PPAa) and the annealed polyallylamine film (HT-PPAa) were characterized by Fourier transform infrared spectrum (FTIR). Then, the wettability, surface topography, and thickness of the PPAa and HT-PPAa were also evaluated. HT-PPAa showed increased stability when compared with PPAa film. The major amino groups remained on the surface of HT-PPAa after annealing, indicating that this could be a good platform for numerous molecules’ immobilization. Subsequently, the bovine serum albumin (BSA) was immobilized onto the HT-PPAa surface. The successful introduction of the BSA was confirmed by the FTIR and XPS detections. The blood compatibility of these modified films was evaluated by platelets adhesion and activation assays. The number of the platelets that adhered on BSA-modified HT-PPAa film was significantly decreased, and the activation degree of the adhered platelets was also decreased. These data revealed that the blood compatibility of the polyallylamine film was improved after BSA immobilized. This work provides a facile and effective approach to develop novel surface treatment for new-generation blood-contact devices with improved hemocompatibility. Full article
►▼ Show Figures

Figure 1

Figure 1
<p>Fourier transform infrared spectrum (FTIR) results of allylamine, plasma polymerized polyallylamine film (PPAa), and annealed polyallylamine film (HT-PPAa) film.</p> Full article ">Figure 2
<p>Atomic Force Microscopy (AFM) results of the PPAa and HT-PPAa film surface topography.</p> Full article ">Figure 3
<p>The water contact angle of stainless steel (SS), PPAa, and HT-PPAa film. Data are presented as mean ± SD (<span class="html-italic">n</span> = 4) and analyzed using one-way ANOVA (* <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.01, and *** <span class="html-italic">p</span> &lt; 0.001).</p> Full article ">Figure 4
<p>The thickness of PPAa and HT-PPAa film. Data are presented as mean ± SD (<span class="html-italic">n</span> = 4) and analyzed using one-way ANOVA (* <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.01, and *** <span class="html-italic">p</span> &lt; 0.001).</p> Full article ">Figure 5
<p>Surface -NH<sub>2</sub> density of the PPAa and HT-PPAa samples. Data are presented as mean ± SD (<span class="html-italic">n</span> = 4) and analyzed using one-way ANOVA (* <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.01, *** <span class="html-italic">p</span> &lt; 0.001).</p> Full article ">Figure 6
<p>The SEM images of PPAa film and HT-PPAa film immersed into the phosphate-buffered saline (PBS) solution for 30 days.</p> Full article ">Figure 7
<p>High-resolution survey of (<b>A</b>) HT-PPAa film and (<b>B</b>) BSA-HT-PPAa film on C1s.</p> Full article ">Figure 8
<p>FTIR results of HT-PPAa film and BSA-HT-PPAa film.</p> Full article ">Figure 9
<p>The water contact angle of SS, PPAa, and HT-PPAa and BSA-HT-PPAa film. Data are presented as mean ± SD (<span class="html-italic">n</span> = 4) and analyzed using one-way ANOVA (* <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.01, and *** <span class="html-italic">p</span> &lt; 0.001).</p> Full article ">Figure 10
<p>(<b>A</b>) The platelet adhesion rate of SS, PPAa, HT-PPAa, and BSA-HT-PPAa film. (<b>B</b>) Data are presented as mean ± SD (<span class="html-italic">n</span> = 4) and analyzed using one-way ANOVA (* <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.01, and *** <span class="html-italic">p</span> &lt; 0.001).</p> Full article ">
23 pages, 4486 KiB  
Article
Graphene Oxide–Platinum Nanoparticle Nanocomposites: A Suitable Biocompatible Therapeutic Agent for Prostate Cancer
by Sangiliyandi Gurunathan, Muniyandi Jeyaraj, Min-Hee Kang and Jin-Hoi Kim
Polymers 2019, 11(4), 733; https://doi.org/10.3390/polym11040733 - 23 Apr 2019
Cited by 40 | Viewed by 5916
Abstract
Metal nanoparticles and the combination of metal nanoparticles with graphene oxide are widely used in environmental, agriculture, textile, and therapeutic applications. The effect of graphene oxide–green platinum nanoparticles (GO-PtNPs) on human prostate cancer cells (LNCaP) is unclear. Therefore, this study aimed to synthesize [...] Read more.
Metal nanoparticles and the combination of metal nanoparticles with graphene oxide are widely used in environmental, agriculture, textile, and therapeutic applications. The effect of graphene oxide–green platinum nanoparticles (GO-PtNPs) on human prostate cancer cells (LNCaP) is unclear. Therefore, this study aimed to synthesize a nanocomposite of GO-PtNPs and evaluate their effect on prostate cancer cells. Herein, we synthesized GO-PtNPs using vanillin and characterized GO-PtNPs. GO-PtNP cytotoxicity in LNCaP cells was demonstrated by measuring cell viability and proliferation. Both decreased in a dose-dependent manner compared to that by GO or PtNPs alone. GO-PtNP cytotoxicity was confirmed by increased lactate dehydrogenase release and membrane integrity loss. Oxidative stress induced by GO-PtNPs increased malondialdehyde, nitric oxide, and protein carbonyl contents. The effective reactive oxygen species generation impaired the cellular redox balance and eventually impaired mitochondria by decreasing the membrane potential and ATP level. The cytotoxicity to LNCaP cells was correlated with increased expression of proapoptotic genes (p53, p21, Bax, Bak, caspase 9, and caspase 3) and decreased levels of antiapoptotic genes (Bcl2 and Bcl-xl). Activation of the key regulators p53 and p21 inhibited the cyclin-dependent kinases Cdk2 and Cdk4, suggesting that p53 and p21 activation in GO-PtNP-treated cells caused genotoxic stress and apoptosis. The increased expression of genes involved in cell cycle arrest and DNA damage and repair, and increased levels of 8-oxo-deoxyguanosine and 8-oxoguanine suggested that GO-PtNPs potentially induce oxidative damage to DNA. Thus, GO-PtNPs are both cytotoxic and genotoxic. LNCaP cells appear to be more susceptible to GO-PtNPs than to GO or PtNPs. Therefore, GO-PtNPs have potential as an alternate and effective cancer therapeutic agent. Finally, this work shows that the combination of graphene oxide with platinum nanoparticles opens new perspectives in cancer therapy. However further detailed mechanistic studies are required to elucidate the molecular mechanism of GO-PtNPs induced cytotoxicity in prostate cancer. Full article
(This article belongs to the Special Issue Graphene-Polymer Composites II)
►▼ Show Figures

Figure 1

Figure 1
<p>Synthesis and characterization of graphene oxide (GO) and graphene oxide–green platinum nanoparticles (GO-PtNPs). Ultraviolet–visible spectroscopy of GO (<b>A</b>) and GO-PtNPs (<b>B</b>). At least three independent experiments were performed for each sample and reproducible results were obtained.</p> Full article ">Figure 2
<p>Characterization of GO and GO-PtNPs by Fourier-transform infrared spectroscopy (FTIR). FTIR images of GO (<b>A</b>) and GO-PtNPs (<b>B</b>). At least three independent experiments were performed for each sample and reproducible results were obtained.</p> Full article ">Figure 3
<p>Characterization of GO and GO-PtNPs by XRD. XRD images of GO (<b>A</b>) and GO-PtNPs (<b>B</b>). At least three independent experiments were performed for each sample and reproducible results were obtained.</p> Full article ">Figure 4
<p>Characterization of GO and GO-PtNPs by Raman spectroscopy. Raman spectroscopy images of GO (<b>A</b>) and GO-PtNPs (<b>B</b>). At least three independent experiments were performed for each sample and reproducible results were obtained.</p> Full article ">Figure 5
<p>Characterization of GO and GO-PtNPs by SEM and TEM. Morphology of GO (<b>A</b>) and GO-PtNPs (<b>B</b>), and size of GO (<b>C</b>) and GO-PtNPs (<b>D</b>) were analyzed by SEM and TEM, respectively. The red circle indicates decoration of PtNPs particles on the surface of graphene sheet (White arrow). The graphene sheet depicted as wrinkled sheet-like structure.</p> Full article ">Figure 6
<p>GO, GO-PtNPs, and PtNPs inhibit cell viability of LNCaP cells. The viability of LNCaP cells was determined after 24-h exposure to different concentrations of GO (<b>A</b>), GO-PtNPs (<b>B</b>), and PtNPs (<b>C</b>) using CCK-8. The treated groups showed statistically significant differences from the control group by the Student’s <span class="html-italic">t</span>-test (* <span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 7
<p>GO, GO-PtNPs, and PtNPs inhibit cell proliferation of LNCaP cells. Cell proliferation of LNCaP cells was determined using BrdU assay after 24-h exposure to different concentrations of GO (<b>A</b>), GO-PtNPs (<b>B</b>), and PtNPs (<b>C</b>). The treated groups showed statistically significant differences from the control group by the Student’s <span class="html-italic">t</span>-test (* <span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 8
<p>GO, GO-PtNPs, and PtNPs increase the leakage of LDH and cell death. LNCaP cells were treated with respective IC50 concentrations of GO, GO-PtNPs, and PtNPs for 24 h, and the LDH activity was measured at 490 nm using the LDH cytotoxicity kit (<b>A</b>). Cell death was determined by trypan blue assay after 24 h of exposure to GO, GO-PtNPs, and PtNPs for 24 h. Cell death was quantified by the ratio of living cells (<b>B</b>). The treated groups showed statistically significant differences from the control group by the Student’s <span class="html-italic">t</span>-test (* <span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 9
<p>GO, GO-PtNPs, and PtNPs increase ROS generation (<b>A</b>), lipid peroxidation (<b>B</b>), and nitric oxide (<b>C</b>) and carbonylated protein content (<b>D</b>) in LNCaP cells. LNCaP cells was exposed to respective IC50 concentrations of GO, GO-PtNPs, and PtNPs for 24 h and then Spectrophotometric analysis of ROS was measured using DCFH-DA (<b>B</b>). The concentration of MDA was measured MDA using a thiobarbituric acid reactive substances assay and expressed as nanomoles per milliliter (<b>C</b>). NO production was quantified spectrophotometrically using the Griess reagent and expressed as micromoles per milliliter (<b>D</b>). Protein carbonyl content was measured and expressed relative to the total protein content. The treated groups showed statistically significant differences from the control group by the Student’s <span class="html-italic">t</span>-test (* <span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 10
<p>GO, GO-PtNPs, and PtNPs decrease mitochondrial membrane potential and ATP content. LNCaP cells were treated with respective IC50 concentration of GO, GO-PtNPs, and PtNPs for 24 h and spectrophotometric determination of JC-1 monomer/aggregate formation using cationic fluorescent indicator JC-1 (<b>A</b>). Intracellular ATP content (<b>B</b>). The treated groups showed statistically significant differences from the control group by the Student’s <span class="html-italic">t</span>-test (* <span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 11
<p>Effect of GO, GO-PtNPs, and PtNPs on antioxidant markers. LNCaP cells were treated with respective IC50 concentration of GO, GO-PtNPs, and PtNPs for 24 h. After incubation, cells were harvested and washed twice with an ice-cold phosphate-buffered saline solution. The cells were collected and disrupted by ultrasonication for 5 min on ice. GSH concentration is expressed as percentage of control (<b>A</b>). GSH:GSSG ratio is expressed as percentage of control (<b>B</b>). SOD concentration is expressed as percentage of control (<b>C</b>). CAT is expressed as percentage of control (<b>D</b>). GPx concentration is expressed as percentage of control (<b>E</b>). TRX is expressed as percentage of control (<b>F</b>). There was a significant difference in treated cells compared to untreated cells with Student’s <span class="html-italic">t</span>-test (* <span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 12
<p>Effect of GO, GO-PtNPs, and PtNPs on the expression of pro- and antiapoptotic genes. LNCaP cells were treated with respective IC50 concentration of GO, GO-PtNPs, and PtNPs for 24 h. The relative messenger RNA(mRNA) expression of P53 (<b>A</b>), P21 (<b>B</b>), Bax (<b>C</b>), Bak (<b>D</b>) Bcl-2 (<b>E</b>), Bcl-xl (<b>F</b>), caspase-9 (<b>G</b>), and caspase-3 (<b>H</b>) was analyzed by quantitative reverse-transcription polymerase chain reaction in LNCaP cells treated for 24 h. After 24-h treatment, expression fold level was determined as fold changes in reference to expression values against GAPDH. Results are expressed as fold changes. There was a significant difference in treated cells compared to untreated cells with Student’s <span class="html-italic">t</span>-test (* <span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 13
<p>GO, GO-PtNPs, and PtNPs increase DNA damage. LNCaP cells were treated with respective IC50 concentration of GO, GO-PtNPs, and PtNPs for 24 h. 8-oxo-dG and 8-oxo-G were measured after 24 h of exposure of LNCaP cells. There was a significant difference in treated cells compared to untreated cells with Student’s <span class="html-italic">t</span>-test (* <span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 14
<p>Effect of GO, GO-PtNPs, and PtNPs on expression cell cycle arrest and DNA damage genes. LNCaP cells were treated with respective IC50 concentrations of GO, GO-PtNPs, and PtNPs for 24 h. Relative messenger RNA(mRNA) expression of CDK2 (<b>A</b>), CDK4 (<b>B</b>), GADD45A (<b>C</b>), OGG1 (<b>D</b>) APEX1 (<b>E</b>), CREB1 (<b>F</b>), POLB (<b>G</b>), and UNG (<b>H</b>) was analyzed by quantitative reverse-transcription polymerase chain reaction in LNCaP cells treated for 24 h. After 24-h treatment, expression fold level was determined as fold changes in reference to expression values against GAPDH. Results are expressed as fold changes. There was a significant difference in treated cells compared to untreated cells with Student’s <span class="html-italic">t</span>-test (* <span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 15
<p>The hypothetical model demonstrates that the impact of GO-PtNPs on oxidative stress induced DNA damage in LnCaP cells.</p> Full article ">
14 pages, 2561 KiB  
Article
Ionic Liquid Composite Polybenzimidazol Membranes for High Temperature PEMFC Applications
by Jorge Escorihuela, Abel García-Bernabé, Álvaro Montero, Óscar Sahuquillo, Enrique Giménez and Vicente Compañ
Polymers 2019, 11(4), 732; https://doi.org/10.3390/polym11040732 - 22 Apr 2019
Cited by 42 | Viewed by 6275
Abstract
A series of proton exchange membranes based on polybenzimidazole (PBI) were prepared using the low cost ionic liquids (ILs) derived from 1-butyl-3-methylimidazolium (BMIM) bearing different anions as conductive fillers in the polymeric matrix with the aim of enhancing the proton conductivity of PBI [...] Read more.
A series of proton exchange membranes based on polybenzimidazole (PBI) were prepared using the low cost ionic liquids (ILs) derived from 1-butyl-3-methylimidazolium (BMIM) bearing different anions as conductive fillers in the polymeric matrix with the aim of enhancing the proton conductivity of PBI membranes. The composite membranes prepared by casting method (containing 5 wt. % of IL) exhibited good thermal, dimensional, mechanical, and oxidative stability for fuel cell applications. The effects of anion, temperature on the proton conductivity of phosphoric acid-doped membranes were systematically investigated by electrochemical impedance spectroscopy. The PBI composite membranes containing 1-butyl-3-methylimidazolium-derived ionic liquids exhibited high proton conductivity of 0.098 S·cm−1 at 120 °C when tetrafluoroborate anion was present in the polymeric matrix. This conductivity enhancement might be attributed to the formed hydrogen-bond networks between the IL molecules and the phosphoric acid molecules distributed along the polymeric matrix. Full article
(This article belongs to the Special Issue Polymer Electrolytes for Energy Storage and Conversion Devices)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Schematic representation of PBI composite membranes containing ionic liquids and photograph of PBI@BMIM-NTf<sub>2</sub> membrane.</p> Full article ">Figure 2
<p>FT–IR spectra of PBI and PBI composite membranes containing different ionic liquids derived from BMIM (5 wt. %).</p> Full article ">Figure 3
<p>Cross-sectional SEM images of (<b>A</b>) PBI, (<b>B</b>) PBI@BMIM-Cl, (<b>C</b>) PBI@BMIM-Br, (<b>D</b>) PBI@BMIM-I, (<b>E</b>) PBI@BMIM-NCS, (<b>F</b>) PBI@BMIM-BF<sub>4</sub>, (<b>G</b>) PBI@BMIM-PF<sub>6</sub>, and (<b>H</b>) PBI@BMIM-NTf<sub>2</sub>.</p> Full article ">Figure 4
<p>TGA curves of (<b>a</b>) undoped and (<b>b</b>) phosphoric acid-doped PBI composite membranes containing different ionic liquids derived from BMIM (5 wt. %) under a N<sub>2</sub> atmosphere.</p> Full article ">Figure 5
<p>Weight loss of the IL composite membranes (containing 5 wt. % of BMIM-X) and PBI after Fenton test.</p> Full article ">Figure 6
<p>Bode diagram for phosphoric acid-doped PBI@BMIM-NTf<sub>2</sub> composite membrane (containing 5 wt. % of BMIM-NTf<sub>2</sub>) under anhydrous conditions. In the top graphical representation, σ′ is plotted against the frequency, whereas in the bottom, the out of phase angle φ is plotted against the frequency.</p> Full article ">Figure 7
<p>Representation of the ln of conductivity (σ<sub>dc</sub>) as a function of the reciprocal of the temperature for phosphoric acid-doped PBI composite membranes containing 5 wt. % of BMIM-X.</p> Full article ">
13 pages, 2599 KiB  
Article
Optimization of Laccase/Mediator System (LMS) Stage Applied in Fractionation of Eucalyptus globulus
by Javier M. Loaiza, Ascensión Alfaro, Francisco López, María T. García and Juan C. García
Polymers 2019, 11(4), 731; https://doi.org/10.3390/polym11040731 - 22 Apr 2019
Cited by 3 | Viewed by 3218
Abstract
In a biorefinery framework, a laccase/mediator system treatment following autohydrolysis was carried out for eucalyptus wood prior to soda-anthraquinone pulping. The enzymatic and autohydrolysis conditions, with a view to maximizing the extraction of hemicelluloses while preserving the integrity of glucan, were optimized. Secondly, [...] Read more.
In a biorefinery framework, a laccase/mediator system treatment following autohydrolysis was carried out for eucalyptus wood prior to soda-anthraquinone pulping. The enzymatic and autohydrolysis conditions, with a view to maximizing the extraction of hemicelluloses while preserving the integrity of glucan, were optimized. Secondly, pulping of solid phase from Eucalyptus globulus wood autohydrolysis and the enzymatic process was carried out and compared with a conventional soda-anthraquinone (AQ) pulping process. The prehydrolysis and enzymatic delignification of the raw material prior to the delignification with soda- Anthraquinone (AQ) results in paper sheets with a lower kappa number and brightness and strength properties close to conventional soda-AQ paper and a liquid fraction rich in hemicellulose compounds that can be used in additional ways. The advantage of this biorefinery scheme is that it requires a lower concentration of chemical reagents, and lower operating times and temperature in the alkaline delignification stage, which represents an economic and environmental improvement over the conventional process. Full article
(This article belongs to the Special Issue Lignocellulosic Fibers and Films)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Scheme of experimental work.</p> Full article ">Figure 2
<p>Variation of the glucan as a function of laccase concentration (<span class="html-italic">X</span><sub>l</sub>) and operation time (<span class="html-italic">X</span><sub>t</sub>) at three HBT concentration levels.</p> Full article ">Figure 3
<p>Variation of the klason lignin as a function of laccase concentration (<span class="html-italic">X</span><sub>l</sub>) and operation time (<span class="html-italic">X</span><sub>t</sub>) at three HBT concentration levels.</p> Full article ">Figure 4
<p>Variation of the acid-soluble lignin as a function of laccase concentration (<span class="html-italic">X</span><sub>l</sub>) and operation time (<span class="html-italic">X</span><sub>t</sub>) at three HBT concentration levels.</p> Full article ">
21 pages, 2384 KiB  
Article
Synthesis and Characterization of Dental Nanocomposite Resins Filled with Different Clay Nanoparticles
by Alexandros K. Nikolaidis, Elisabeth A. Koulaouzidou, Christos Gogos and Dimitris S. Achilias
Polymers 2019, 11(4), 730; https://doi.org/10.3390/polym11040730 - 22 Apr 2019
Cited by 37 | Viewed by 5596
Abstract
Nanotechnology comprises a promising approach towards the update of dental materials.The present study focuses on the reinforcement ofdental nanocomposite resins with diverse organomodified montmorillonite (OMMT) nanofillers. The aim is to investigate whether the presence of functional groups in the chemical structure of the [...] Read more.
Nanotechnology comprises a promising approach towards the update of dental materials.The present study focuses on the reinforcement ofdental nanocomposite resins with diverse organomodified montmorillonite (OMMT) nanofillers. The aim is to investigate whether the presence of functional groups in the chemical structure of the nanoclay organic modifier may virtually influence the physicochemical and/or the mechanical attitude of the dental resin nanocomposites. The structure and morphology of the prepared materials were investigated by means of wide angle X-ray diffraction and scanning electron microscopy analysis. Fourier transform infrared spectroscopy was used to determine the variation of the degree of conversion over time. Measurements of polymerization shrinkage and mechanical properties were conducted with a linear variable displacement transducer apparatus and a dynamometer, respectively. All the obtained nanocomposites revealed intercalated structures and most of them had an extensive filler distribution into the polymer matrix. Polymerization kinetics werefound to be influenced by the variance of the clay organomodifier, whilenanoclays with vinyl groups considerably increased the degree of conversion. Polymerization shrinkage was almost limited up to 50% by incorporating nanoclays. The absence of reactive groups in the OMMT structure may retain setting contraction atlow levels. An enhancement of the flexural modulus was observed, mainly by using clay nanoparticles decorated with methacrylated groups, along with a decrease in the flexural strength at a high filler loading. The overall best performance was found for the nanocomposites with OMMTs containing double bonds. The significance of the current work relies on providing novel information about chemical interactions phenomena between nanofillers and the organic matrix towards the improvement of dental restorative materials. Full article
(This article belongs to the Special Issue Polymer Clay Nano-composites)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Different types of clay organomodifiers used for nanocomposite synthesis (R stands for hydrogenated tallow).</p> Full article ">Figure 2
<p>X-ray diffraction (XRD) patterns of the dental nanocomposite resins and the different incorporated organo modified montmorillonite (OMMT) nanoclays.</p> Full article ">Figure 3
<p>Schematic representation of nanocomposite formation indicating the possible chemical interactions between nanoclayorganomodifier and dental resin monomers.</p> Full article ">Figure 4
<p>Scanning electron microscopy (SEM) images of a series of experimental dental nanocomposite resins containing (<b>a</b>) Nanomer<sup>®</sup> I.34MN; (<b>b</b>) Montmorillonite-dimethylaminooctadecyl methacrylate (MMT-DMAODM); (<b>c</b>) Montmorillonite-dimethylaminohexadecyl methacrylate (MMT-DMAHDM); (<b>d</b>) S.MMT-DMAHDM; (<b>e</b>) Montmorillonite-cetyltrimethylammonium chloride (MMT-CTAC); (<b>f</b>) S.MMT-CTAC at concentration 50 wt %.</p> Full article ">Figure 5
<p>(<b>a</b>) Degree of conversion versus time of 2,2-Bis[p-(2′-hydroxy-3′- methacryloxypropoxy)phenylene]propane/triethylene glycol dimethacrylate(Bis-GMA/TEGDMA) matrix and dental nanocomposite resins filled with different OMMT nanoparticles; (<b>b</b>) FTIR spectra with measured peak areas (1635 and 1582 cm<sup>−1</sup>) used to calculate the percent degree of conversion (DC (%)) for uncured and cured nanocomposites.</p> Full article ">Figure 5 Cont.
<p>(<b>a</b>) Degree of conversion versus time of 2,2-Bis[p-(2′-hydroxy-3′- methacryloxypropoxy)phenylene]propane/triethylene glycol dimethacrylate(Bis-GMA/TEGDMA) matrix and dental nanocomposite resins filled with different OMMT nanoparticles; (<b>b</b>) FTIR spectra with measured peak areas (1635 and 1582 cm<sup>−1</sup>) used to calculate the percent degree of conversion (DC (%)) for uncured and cured nanocomposites.</p> Full article ">Figure 6
<p>Representative DC-time experimental data and the two exponential approximate functions, for pure Bis-GMA/TEGDMA matrix and nanocomposites filled with Nanomer<sup>®</sup> I.34MN, MMT-DMAHDM and S.MMT-DMAHDM. Lines of best fit are drawn through all experimental points of the approximate function.</p> Full article ">Figure 7
<p>(<b>a</b>) Time dependence of polymerization shrinkage strain of Bis-GMA/TEGDMA matrix and dental nanocomposite resins with diverse types of OMMT nanoclays; (<b>b</b>) Apparatus utilized for polymerization shrinkage measurements.</p> Full article ">Figure 7 Cont.
<p>(<b>a</b>) Time dependence of polymerization shrinkage strain of Bis-GMA/TEGDMA matrix and dental nanocomposite resins with diverse types of OMMT nanoclays; (<b>b</b>) Apparatus utilized for polymerization shrinkage measurements.</p> Full article ">Figure 8
<p>(<b>a</b>) Flexural modulus; (<b>b</b>) Flexural resistance; (<b>c</b>) Graphic representation of force against the displacement of flexural properties, for pure Bis-GMA/TEGMA matrix and dental nanocomposite resins filled with different OMMT nanofillers.</p> Full article ">
17 pages, 5094 KiB  
Article
Structure and Properties of a Metallocene Polypropylene Resin with Low Melting Temperature for Melt Spinning Fiber Application
by Renwei Xu, Peng Zhang, Hai Wang, Xu Chen, Jie Xiong, Jinpeng Su, Peng Chen and Zhicheng Zhang
Polymers 2019, 11(4), 729; https://doi.org/10.3390/polym11040729 - 22 Apr 2019
Cited by 4 | Viewed by 5538
Abstract
An isotactic polypropylene (iPP-1) resin with low melting temperature (Tm) is synthesized by a metallocene catalyst and investigated for melt-spun fiber applications. The structure, thermal and mechanical properties, and feasibility of producing fibers of a commercial metallocene iPP (iPP-2) and [...] Read more.
An isotactic polypropylene (iPP-1) resin with low melting temperature (Tm) is synthesized by a metallocene catalyst and investigated for melt-spun fiber applications. The structure, thermal and mechanical properties, and feasibility of producing fibers of a commercial metallocene iPP (iPP-2) and a conventional Ziegler–Natta iPP (iPP-3) are carefully examined for comparison. Tm of iPP-1 is about 10 °C lower than the other two samples, which is well addressed both in the resin and the fiber products. Besides, the newly developed iPP-1 possesses higher isotacticity and crystallinity than the commercial ones, which assures the mechanical properties of the fiber products. Thanks to the addition of calcium stearate, its crystal grain size is smaller than those of the two other commercial iPPs. iPP-1 shows a similar rheological behavior as the commercial ones and good spinnability within a wide range of take-up speeds (1200–2750 m/min). The tensile property of fibers from iPP-1 is better than commercial ones, which can fulfill the application requirement. The formation of the mesomorphic phase in iPP-1 during melt spinning is confirmed by the orientation and crystallization investigation with wide angle X-ray diffraction (WAXD), which is responsible for its excellent processing capability and the mechanical properties of the resultant fibers. The work may provide not only a promising candidate for the high-performance PP fiber but also a deep understanding of the formation mechanism of the mesomorphic phase during fiber spinning. Full article
(This article belongs to the Special Issue Catalytic Olefin Polymerisation and Polyolefins)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>X-ray powder diffraction profiles of as-prepared specimens of the iPP samples.</p> Full article ">Figure 2
<p>DSC curves of the iPP samples.</p> Full article ">Figure 3
<p>Morphologies of (<b>a</b>) iPP-1, (<b>b</b>) iPP-2 and (<b>c</b>) iPP-3 under a polarizing microscope.</p> Full article ">Figure 3 Cont.
<p>Morphologies of (<b>a</b>) iPP-1, (<b>b</b>) iPP-2 and (<b>c</b>) iPP-3 under a polarizing microscope.</p> Full article ">Figure 4
<p>Temperature rising elution fractionation (TREF)curves of the iPP samples.</p> Full article ">Figure 5
<p>Rheological properties of the iPP samples.</p> Full article ">Figure 6
<p>DSC thermograms of (<b>a</b>), (<b>c</b>), (<b>e</b>) as-spun and (<b>b</b>), (<b>d</b>), (<b>f</b>) drawn iPP fibers.</p> Full article ">Figure 7
<p>2D-WAXD patterns of as-spun iPP fibers.</p> Full article ">Figure 8
<p>2D WAXD patterns of drawn iPP fibers (draw ratio: 1.6).</p> Full article ">Figure 8 Cont.
<p>2D WAXD patterns of drawn iPP fibers (draw ratio: 1.6).</p> Full article ">Figure 9
<p>1D WAXD curves of as-spun iPP fibers.</p> Full article ">Figure 10
<p>1D-WAXD curves of drawn iPP fibers (draw ratio: 1.6).</p> Full article ">
9 pages, 3184 KiB  
Article
A Bioinspired Functionalization of Polypropylene Separator for Lithium-Sulfur Battery
by Zhijia Zhang, Xuequan Li, Yawen Yan, Wenyi Zhu, Li-Hua Shao and Junsheng Li
Polymers 2019, 11(4), 728; https://doi.org/10.3390/polym11040728 - 22 Apr 2019
Cited by 17 | Viewed by 4794
Abstract
Lithium-sulfur batteries have received intensive attention, due to their high specific capacity, but the shuttle effect of soluble polysulfide results in a decrease in capacity. In response to this issue, we develop a novel tannic acid and Au nanoparticle functionalized separator. The tannic [...] Read more.
Lithium-sulfur batteries have received intensive attention, due to their high specific capacity, but the shuttle effect of soluble polysulfide results in a decrease in capacity. In response to this issue, we develop a novel tannic acid and Au nanoparticle functionalized separator. The tannic acid and gold nanoparticles were modified onto commercial polypropylene separator through a two-step solution process. Due to a large number of phenolic hydroxyl groups contained in the modified layer and the strong polarity of the gold nanoparticles, the soluble polysulfide generated during battery cycling is well stabilized on the cathode side, slowing down the capacity fade brought by the shuttle effect. In addition, the modification effectively improves the electrolyte affinity of the separator. As a result of these benefits, the novel separator exhibits improved battery performance compared to the pristine polypropylene separator. Full article
(This article belongs to the Special Issue Polymer Based Catalysts and Membranes and Their Composites for Energy Storage and Conversion Applications)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>SEM images of PP-TA/Au separator prepared in HAuCl<sub>4</sub> bath with different pH values: (<b>A</b>) pH 4; (<b>B</b>) pH 6.8; (<b>C</b>) pH 7.6 and (<b>D</b>) pH 8.3.</p> Full article ">Figure 2
<p>(<b>A</b>) picture of pristine polypropylene (PP) separator (left), PP-TA separator (middle) and PP-TA/Au separator (right). (<b>B</b>) TG curve of PP separator, PP-TA separator and PP-TA/Au separator.</p> Full article ">Figure 3
<p>(<b>A</b>) FTIR spectra of pristine PP and PP-TA separator. (<b>B</b>) XRD spectra of PP-TA/Au separator.</p> Full article ">Figure 4
<p>(<b>A</b>) Water contact angle of PP, PP-TA and PP-TA/Au separator. (<b>B</b>) EIS spectra of stainless steel/electrolyte saturated separator/stainless steel cell assembled with PP, PP-TA and PP-TA/Au separator. (<b>C</b>) LSV curve of Li foil/electrolyte saturated separator/stainless steel cell assembled with PP, PP-TA and PP-TA/Au separator.</p> Full article ">Figure 5
<p>(<b>A</b>) Cycling performance of Li-S battery assembled with PP, PP-TA and PP-TA/Au separator. (<b>B</b>) Rate performance of Li-S battery assembled with PP, PP-TA and PP-TA/Au separator. (<b>C</b>) EIS spectra of uncycled Li-S battery assembled with PP, PP-TA and PP-TA/Au separator. (<b>D</b>) EIS spectra of cycled Li-S battery assembled with PP, PP-TA and PP-TA/Au separator.</p> Full article ">Figure 6
<p>Au 4f spectra of PP-TA/Au separator (<b>A</b>) before and (<b>B</b>) after cycling in Li-S battery. S 2p spectra of PP-TA/Au separator (<b>C</b>) before and (<b>D</b>) after cycling in Li-S battery.</p> Full article ">
12 pages, 2836 KiB  
Article
PA12 Powder Recycled from SLS for FDM
by Li Feng, Yan Wang and Qinya Wei
Polymers 2019, 11(4), 727; https://doi.org/10.3390/polym11040727 - 22 Apr 2019
Cited by 65 | Viewed by 8823
Abstract
In this study, Polyamide 12 (PA12) powder recycled after selective laser sintering (SLS) was made into filaments for fused deposition modelling (FDM). Compared with fresh PA12, the melt flow rate (MFR) of the recycled PA12 powder decreased by 77%, but the mechanical properties [...] Read more.
In this study, Polyamide 12 (PA12) powder recycled after selective laser sintering (SLS) was made into filaments for fused deposition modelling (FDM). Compared with fresh PA12, the melt flow rate (MFR) of the recycled PA12 powder decreased by 77%, but the mechanical properties were only slightly reduced. In FDM, the printing speed and building orientation were changed, and the performance of the printed parts was tested. If the printing speed is too fast or too slow, the mechanical properties of the parts will be affected, and there is an optimal speed range. The tensile strength, flexural modulus, and impact strength of a printed test sample made from recycled powder reached 95%, 85%, and 87% of an x-direction test sample made from fresh PA12, respectively. For test samples printed from different orientations, the mechanical properties of the test samples printed in the x-direction were the best, while the crystallization performance was the opposite. Scanning electron microscope (SEM) images show that the printed test sample had good compactness and mechanical properties, and the delamination phenomenon was basically not observed. Full article
(This article belongs to the Special Issue Additive Manufacturing of Polymeric Materials)
►▼ Show Figures

Figure 1

Figure 1
<p>Build orientation.</p> Full article ">Figure 2
<p>Test sample printed by fresh PA12.</p> Full article ">Figure 3
<p>Test sample printed by recycled PA12.</p> Full article ">Figure 4
<p>Tensile strength of test samples in different printing orientations.</p> Full article ">Figure 5
<p>Flexural modulus of test samples in different printing orientations.</p> Full article ">Figure 6
<p>Impact strength of test samples in different printing orientations.</p> Full article ">Figure 7
<p>X-direction (<b>a</b>), <span class="html-italic">y</span>-direction (<b>c</b>), and <span class="html-italic">z</span>-direction (<b>e</b>) test samples printed from filament made of fresh pellets; <span class="html-italic">x</span>-direction (<b>b</b>), <span class="html-italic">y</span>-direction (<b>d</b>), and <span class="html-italic">z</span>-direction (<b>f</b>) test samples printed from filament made of recycled powder.</p> Full article ">Figure 8
<p>XRD pattern of different build orientations printed from filaments made of recycled PA12 powder and fresh PA12 pellets.</p> Full article ">
41 pages, 6258 KiB  
Review
Nanomaterials in Advanced, High-Performance Aerogel Composites: A Review
by Elizabeth Barrios, David Fox, Yuen Yee Li Sip, Ruginn Catarata, Jean E. Calderon, Nilab Azim, Sajia Afrin, Zeyang Zhang and Lei Zhai
Polymers 2019, 11(4), 726; https://doi.org/10.3390/polym11040726 - 20 Apr 2019
Cited by 123 | Viewed by 16884
Abstract
Aerogels are one of the most interesting materials of the 21st century owing to their high porosity, low density, and large available surface area. Historically, aerogels have been used for highly efficient insulation and niche applications, such as interstellar particle capture. Recently, aerogels [...] Read more.
Aerogels are one of the most interesting materials of the 21st century owing to their high porosity, low density, and large available surface area. Historically, aerogels have been used for highly efficient insulation and niche applications, such as interstellar particle capture. Recently, aerogels have made their way into the composite universe. By coupling nanomaterial with a variety of matrix materials, lightweight, high-performance composite aerogels have been developed for applications ranging from lithium-ion batteries to tissue engineering materials. In this paper, the current status of aerogel composites based on nanomaterials is reviewed and their application in environmental remediation, energy storage, controlled drug delivery, tissue engineering, and biosensing are discussed. Full article
(This article belongs to the Special Issue Polymer and Composite Aerogels)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Comparison of aerogel fabrication strategies showing typical transitions into an aerogel. (<b>a</b>) shows the supercritical drying process where precursor materials undergo gelation prior to supercritical drying. Often, these processes include a solvent exchange step after gelation to provide better fluids for supercritical drying. (<b>b</b>) shows a standard freeze-drying technique where an aqueous solution is frozen and the ice crystal formation dictates the alignment of the precursor materials and thus, the resulting pore structure of the dried aerogel.</p> Full article ">Figure 2
<p>A typical phase diagram for pure compounds. Two methods are shown for the gel to aerogel transition, indicated by I → II. The solid-gas transition depicts the transition from a frozen gel (I) to the dried porous gel (II) during freeze-drying (<a href="#sec2dot2-polymers-11-00726" class="html-sec">Section 2.2</a>). The transition from a liquid to gas during supercritical drying requires a rise in temperature and pressure (curved arrow from I → II) to avoid crossing the liquid-gas phase boundary (<a href="#sec2dot1-polymers-11-00726" class="html-sec">Section 2.1</a>). This pass into the supercritical region eliminates surface tension and capillary forces.</p> Full article ">Figure 3
<p>Schematic depiction of the three main 3D-printing techniques employed for the fabrication of aerogels. (<b>a</b>) Stereolithography, where a laser is used to transform the sol to a gel during the printing process; (<b>b</b>) ink-jet printing, where a solution is printed into its desired structure prior to observing gelation; and (<b>c</b>) direct ink writing, where the gel is formed prior to printing and the gel is extruded in order to achieve the desired structure.</p> Full article ">Figure 4
<p>(<b>a</b>) Fabrication of CNT aerogels using (P3HT-b-PTMSPMA), (<b>b</b>) scanning electron microscopy (SEM) image of the macroporous honeycomb structure of the aerogel with ~100-nm-thick walls, and (<b>c</b>) SEM image of the aerogel walls with entangled CNTs. Reprinted from [<a href="#B56-polymers-11-00726" class="html-bibr">56</a>] with permission, copyright American Chemical Society, 2010.</p> Full article ">Figure 5
<p>The DIW of aerogels in two distinct macrostructures, (<b>a</b>) a cube and (<b>b</b>) an ear. (<b>c</b>) The structural porosity, accounting for pores in the range of 600 μm (green box) and the aerogel porosity, accounting for pores in the range of 20 to 800 μm. Reprinted from [<a href="#B90-polymers-11-00726" class="html-bibr">90</a>] under open access license.</p> Full article ">Figure 6
<p>Depiction of the DIW of CNF aerogels (<b>a</b>) and four different methods of drying (<b>b</b>). From left to right, the CNF hydrogel drying procedures are (i) air drying), (ii) air drying in the presence of surfactants, (iii) solvent exchange before drying, and (iv) freeze-drying. (<b>c</b>) SEM micrographs of the resulting microstructures of such dried CNF aerogels. Adapted from [<a href="#B92-polymers-11-00726" class="html-bibr">92</a>] with permission, copyright John Wiley &amp; Sons, 2016.</p> Full article ">Figure 7
<p>The processing schematic of aerogel fabrication via the electrospinning of nanofiber mats. Reprinted from [<a href="#B102-polymers-11-00726" class="html-bibr">102</a>] with permission, copyright American Chemical Society, 2018.</p> Full article ">Figure 8
<p>(<b>a</b>) HTC synthesis of nitrogen-doped carbon nanofiber aerogels; (<b>b</b>) image of large-scale quantities of such a product, and (<b>c</b>) and (<b>d</b>) SEM micrographs of images at different magnifications. Reproduced from [<a href="#B107-polymers-11-00726" class="html-bibr">107</a>], copyright Elsevier, 2015.</p> Full article ">Figure 9
<p>Schematics and images from the radially grown GO aerogels. (<b>a</b>) Illustrates the ice-templating process, (<b>b</b>) shows scanning electron microscopy (SEM) images of the radially aligned aerogel, (<b>c</b>) illustrates the decreasing width of the radial channels, which decrease from edge to center, and (<b>d</b>–<b>f</b>) show SEM micrographs of the sections outlined in (<b>c</b>). Adapted from [<a href="#B22-polymers-11-00726" class="html-bibr">22</a>] with permission, copyright American Chemical Society, 2018.</p> Full article ">Figure 10
<p>Reversible compressibility of various graphene aerogels created via DIW. Image (<b>a</b>) shows the behavior of a bulk graphene aerogel (31 mg cm<sup>−3</sup>), (<b>b</b>) 3D-printed graphene aerogel (16 mg cm<sup>−3</sup>), (<b>c</b>) bulk graphene aerogel (123 mg cm<sup>−3</sup>), and (<b>d</b>) 3D-printed graphene aerogel (53 mg cm<sup>−3</sup>) using resorcinol-formaldehyde. Reprinted from [<a href="#B130-polymers-11-00726" class="html-bibr">130</a>] under open access license.</p> Full article ">Figure 11
<p>Schematic of 3D graphene lattice fabrication with photocurable hollow polymer architecture. Adapted from [<a href="#B31-polymers-11-00726" class="html-bibr">31</a>] with permission, copyright American Chemical Society, 2018.</p> Full article ">Figure 12
<p>Structure design and fabrication of the ceramic aerogel metamaterial. (<b>a</b>) Illustration of the metastructure design of ceramic aerogels. The units of the colored scale bars are as follows: kilopascals for NPR and percentage (with strain zoomed by 30 times) for NTEC. (<b>b</b>) Illustration of the CVD synthesis process of the double-paned hyperbolic ceramicaerogels. (<b>c</b>) An optical image showing an h-BNAG sample resting on the stamen of a flower. (<b>d</b>) SEM image of h-BNAG. (<b>e</b>) SEM images of the double-pane wall structure of h-BNAGs. Scale bars, 20 nm. Adapted from [<a href="#B138-polymers-11-00726" class="html-bibr">138</a>] with permission, copyright the American Association for the Advancement of Science, 2019.</p> Full article ">Figure 13
<p>(<b>a</b>) A schematic illustration of fabricating hydrophobic cellulose aerogels. (<b>b</b>) A picture showing water droplets on the aerogels. (<b>c</b>) Pictures showing recovering of an aerogel from compression. Adapted from [<a href="#B152-polymers-11-00726" class="html-bibr">152</a>] with permission, copyright the American Chemical Society, 2019.</p> Full article ">Figure 14
<p>Optical interrogation of aerogel fabrics’ gross and fine structure. Image of a dyed-green water droplet and Iraq oil on the surface of (<b>a</b>) TW (6 mm thick) and (<b>d</b>) SL (10 mm thick). Insets are images from the WCA measurements. Please note that the TW used is thinner than SL. SEM images of the surfaces of (<b>b</b> and <b>c</b>) TW and (<b>e</b> and <b>f</b>) SL, where aerogel particles are visible on the fibers in high-resolution. Reprinted from [<a href="#B153-polymers-11-00726" class="html-bibr">153</a>] with permission, copyright American Chemical Society, 2016.</p> Full article ">Figure 15
<p>(<b>a</b>) Schematic illustration showing the fabrication process of P-GA. (<b>b,c</b>) SEM images of the GA (<b>b</b>) and P-GA (<b>c</b>). (<b>d</b>) HRTEM images of P-GA. (<b>e</b>) Schematic showing ASC device construction using MnO<sub>2</sub> and P-GA electrodes. (<b>f</b>) Ragone plot reflecting the superiority of P-GA nanostructures over other electrode materials. The inset shows a red LED powered by using two devices connected in series. Reprinted from [<a href="#B167-polymers-11-00726" class="html-bibr">167</a>] with permission, copyright American Chemical Society, 2015.</p> Full article ">Figure 16
<p>Schematic of the processing of 3D-printed graphene-based composites for supercapacitors. Reproduced from [<a href="#B174-polymers-11-00726" class="html-bibr">174</a>] with permission, copyright John Wiley &amp; Sons, 2018.</p> Full article ">Figure 17
<p>Scanning electron microscopy (SEM) images of microgel particles printed via IJP of aqueous alginate solutions into baths of CaCl<sub>2</sub> with (<b>a</b>,<b>c</b>–<b>e</b>) direct or (<b>b</b>) sequential solvent exchange. Reproduced from [<a href="#B200-polymers-11-00726" class="html-bibr">200</a>] with permission, copyright Elsevier B.V., 2018.</p> Full article ">Figure 18
<p>Schematic illustration of the fabrication of 3D hybrid aerogels from polymer nanofibers and bioglass nanofibers. Reprinted from [<a href="#B192-polymers-11-00726" class="html-bibr">192</a>] with permission, copyright John Wiley &amp; Sons, 2018.</p> Full article ">Figure 19
<p>(<b>A</b>) Wound healing study where a–f (top row) show the collagen control aerogel at day 0, 3, 9, 12, 15, and 18 and g−l (bottom row) show the 12% collagen-wheat grass aerogel at day 0, 3, 9, 12, 15, and 18. Image (<b>B</b>) shows the wound healing as a percent of wound reduction. Adapted from [<a href="#B205-polymers-11-00726" class="html-bibr">205</a>] with permission, copyright American Chemical Society, 2017.</p> Full article ">
8 pages, 488 KiB  
Article
NMR Analysis of Poly(Lactic Acid) via Statistical Models
by Koto Suganuma, Tetsuo Asakura, Miyuki Oshimura, Tomohiro Hirano, Koichi Ute and H. N. Cheng
Polymers 2019, 11(4), 725; https://doi.org/10.3390/polym11040725 - 19 Apr 2019
Cited by 20 | Viewed by 7160
Abstract
The physical properties of poly(lactic acid) (PLA) are influenced by its stereoregularity and stereosequence distribution, and its polymer stereochemistry can be effectively studied by NMR spectroscopy. In previously published NMR studies of PLA tacticity, the NMR data were fitted to pair-addition Bernoullian models. [...] Read more.
The physical properties of poly(lactic acid) (PLA) are influenced by its stereoregularity and stereosequence distribution, and its polymer stereochemistry can be effectively studied by NMR spectroscopy. In previously published NMR studies of PLA tacticity, the NMR data were fitted to pair-addition Bernoullian models. In this work, we prepared several PLA samples with a tin catalyst at different L,L-lactide and D,D-lactide ratios. Upon analysis of the tetrad intensities with the pair-addition Bernoullian model, we found substantial deviations between observed and calculated intensities due to the presence of transesterification and racemization during the polymerization processes. We formulated a two-state (pair-addition Bernoullian and single-addition Bernoullian) model, and it gave a better fit to the observed data. The use of the two-state model provides a quantitative measure of the extent of transesterification and racemization, and potentially yields useful information on the polymerization mechanism. Full article
(This article belongs to the Special Issue NMR in Polymer Science)
►▼ Show Figures

Figure 1

Figure 1
<p>(<b>a</b>) <sup>13</sup>C and (<b>b</b>) <sup>1</sup>H NMR spectra of the CH groups of the PLA samples (from the top to the bottom: LL/DD = 50/50, 60/40, 70/30, 80/20, 90/10).</p> Full article ">Scheme 1
<p>Conversion of lactides into PLA</p> Full article ">
2 pages, 651 KiB  
Erratum
Erratum: Electrostatic-Interaction-Driven Assembly of Binary Hybrids towards Fire-Safe Epoxy Resin Nanocomposites. Polymers 2019, 11, 229.
by Lu Liu, Wei Wang, Yongqian Shi, Libi Fu, Lulu Xu and Bin Yu
Polymers 2019, 11(4), 724; https://doi.org/10.3390/polym11040724 - 19 Apr 2019
Cited by 1 | Viewed by 2333
Abstract
The authors wish to make a change to the published paper [...] Full article
►▼ Show Figures

Figure 1

Figure 1
<p>SEM images of fracture surfaces cryogenically broken after immersion in liquid nitrogen of (<b>a</b>) pure EP, (<b>b</b>) EP/MnO<sub>2</sub> 2%, (<b>c</b>) EP/MnO<sub>2</sub>@ZHS 0.5%, (<b>d</b>) EP/MnO<sub>2</sub>@ZHS 1%, and<b> e)</b> EP/MnO<sub>2</sub>@ZHS 2%.</p> Full article ">
13 pages, 3264 KiB  
Article
Improved Aging Stability of Ethylene-Norbornene Composites Filled with Lawsone-Based Hybrid Pigment
by Anna Marzec and Bolesław Szadkowski
Polymers 2019, 11(4), 723; https://doi.org/10.3390/polym11040723 - 19 Apr 2019
Cited by 18 | Viewed by 4147
Abstract
In this study, we produced a new organic-inorganic hybrid pigment based on a natural chromophore. Lawsone was selected as the active organic compound and incorporated into aluminum-magnesium hydroxycarbonate (LH). The hydroxynaphthoquinone derivative lawsone (Lawsonia inermis L.) is a naturally occurring dye, [...] Read more.
In this study, we produced a new organic-inorganic hybrid pigment based on a natural chromophore. Lawsone was selected as the active organic compound and incorporated into aluminum-magnesium hydroxycarbonate (LH). The hydroxynaphthoquinone derivative lawsone (Lawsonia inermis L.) is a naturally occurring dye, which is commonly used as a colorant because of its nontoxicity and biological functions. The structure and stability of the hybrid colorant were investigated using 27-Al solid-state nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), secondary ion mass spectrometry (TOF-SIMS), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and UV-Vis spectroscopy. TOF-SIMS and 27Al NMR spectroscopy revealed interactions between the dye molecules and metal ions present in the LH host, confirming successful formation of an LH-based hybrid (LH/lawsone). In the next part of the study, we examined the effect of the hybrid pigment on the mechanical and thermal properties of ethylene-norbornene (EN) materials, as well as the aging resistance of the colored composites to irradiation across the full solar spectrum. Dynamic mechanical analysis (DMA) and the results of tensile break tests revealed that the EN+LH/lawsone composite had significantly better resistance to solar irradiation in comparison to EN and EN with an unmodified carrier. Full article
(This article belongs to the Special Issue Eurofillers Polymer Blends)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Digital photographs of the EN composites filled with LH, lawsone and LH/lawsone hybrid.</p> Full article ">Figure 2
<p>TOF-SIMS spectra of the LH (black line) and LH/lawsone pigment (blue line).</p> Full article ">Figure 3
<p><sup>27</sup>Al MAS NMR spectra of the LH and LH/lawsone pigments.</p> Full article ">Figure 4
<p>Powder XRD patterns for LH (<b>a</b>), LH/lawsone (<b>b</b>) and lawsone (<b>c</b>).</p> Full article ">Figure 5
<p>SEM micrographs of lawson (<b>a</b>,<b>b</b>), LH (<b>c</b>) and LH/lawson pigment (<b>d</b>).</p> Full article ">Figure 6
<p>TGA/DTG curves for LH, LH/lawsone and lawsone.</p> Full article ">Figure 7
<p>Color changes in lawsone (<b>a</b>) and lawsone pigment (<b>b</b>) after thermal aging at different temperatures.</p> Full article ">Figure 8
<p>Tensile strength (<b>a</b>), aging factor (<b>b</b>) and carbonyl index (<b>c</b>) as a function of the aging time of EN, EN+LH and EN+LH/lawsone composites.</p> Full article ">Figure 9
<p>Temperature dependence of the storage modulus (E’) logarithm at 5 Hz for EN, EN+LH and EN+LH/lawsone composites before (<b>a</b>) and after (<b>b</b>) 350 h of aging.</p> Full article ">Figure 10
<p>Temperature dependence of tanδ at 5 Hz for EN, EN+LH and EN+LH/lawsone composites before (<b>a</b>) and after (<b>b</b>) 350 h of aging.</p> Full article ">Figure 11
<p>The TGA (<b>a</b>) and DTG (<b>b</b>) curves for EN, EN+LH and EN+LH/lawsone composites.</p> Full article ">
11 pages, 2268 KiB  
Article
Preparation and Characterization of Whey Protein-Based Polymers Produced from Residual Dairy Streams
by Bushra Chalermthai, Wui Yarn Chan, Juan-Rodrigo Bastidas-Oyanedel, Hanifa Taher, Bradley D. Olsen and Jens Ejbye Schmidt
Polymers 2019, 11(4), 722; https://doi.org/10.3390/polym11040722 - 19 Apr 2019
Cited by 28 | Viewed by 8129
Abstract
The wide use of non-biodegradable, petroleum-based plastics raises important environmental concerns, which urges finding alternatives. In this study, an alternative way to produce polymers from a renewable source—milk proteins—was investigated with the aim of replacing polyethylene. Whey protein can be obtained from whey [...] Read more.
The wide use of non-biodegradable, petroleum-based plastics raises important environmental concerns, which urges finding alternatives. In this study, an alternative way to produce polymers from a renewable source—milk proteins—was investigated with the aim of replacing polyethylene. Whey protein can be obtained from whey residual, which is a by-product in the cheese-making process. Two different sources of whey protein were tested: Whey protein isolate (WPI) containing 91% protein concentration and whey protein concentrate (WPC) containing 77% protein concentration. These were methacrylated, followed by free radical polymerization with co-polymer poly(ethylene glycol) methyl ether methacrylate (PEGMA) to obtain polymer sheets. Different protein concentrations in water (11–14 w/v%), at two protein/PEGMA mass-ratios, 20:80 and 30:70, were tested. The polymers made from WPI and WPC at a higher protein/PEGMA ratio of 30:70 had significantly better tensile strength than the one with lower protein content, by about 1–2 MPa (the best 30:70 sample exhibited 3.8 ± 0.2 MPa and the best 20:80 sample exhibited 1.9 ± 0.4 MPa). This indicates that the ratio between the hard (protein) and soft (copolymer PEGMA) domains induce significant changes to the tensile strengths of the polymer sheets. Thermally, the WPI-based polymer samples are stable up to 277.8 ± 6.2 °C and the WPC-based samples are stable up to 273.0 ± 3.4 °C. Full article
(This article belongs to the Special Issue Natural Compounds for Natural Polymers)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Methacrylation reaction of protein (adapted from Chan et al. [<a href="#B24-polymers-11-00722" class="html-bibr">24</a>]).</p> Full article ">Figure 2
<p>Copolymerization of the methacrylated protein with PEGMA in presence of initiator APS and catalyst TEMED (adapted from Chan et al. [<a href="#B24-polymers-11-00722" class="html-bibr">24</a>]).</p> Full article ">Figure 3
<p>(<b>a</b>) Sample plastic sheet post drying, (<b>b</b>) Sample plastic sheet breakage at the ultimate tensile strength, (<b>c</b>) Stress-strain curve of a sample.</p> Full article ">Figure 4
<p>Average (<b>a</b>) tensile strength (<b>b</b>) modulus and (<b>c</b>) tensile strain, of all polymer samples, all with error bars at 95% confidence level. Each group of bars color/pattern is a set of 4 different protein concentrations in water from 11–14 <span class="html-italic">w</span>/<span class="html-italic">v</span>%.</p> Full article ">Figure 5
<p>20:80 vs. 30:70: Average (<b>a</b>) tensile strength (<b>b</b>) modulus and (<b>c</b>) tensile strain, all with error bars at 95% confidence level.</p> Full article ">Figure 6
<p>Five percent mass loss temperatures (T<sub>5%</sub>) and maximum mass loss temperatures (DTG<sub>max</sub>) of WPI and WPC-based polymer samples.</p> Full article ">Figure 7
<p>Mass loss curve (black curve) with its first derivative (blue curve) of a representative polymer sample. Moisture loss occurs until about 110 °C. After that, the polymer sample is thermally stable up to about 275 °C (where 5% mass loss occurs post-moisture loss) and the maximum mass loss is observed at the peak of the derivative, i.e., about 390 °C.</p> Full article ">
20 pages, 4725 KiB  
Article
Synthesis and Characterization of Clay Polymer Nanocomposites of P(4VP-co-AAm) and Their Application for the Removal of Atrazine
by Jorge A. Ramírez-Gómez, Javier Illescas, María del Carmen Díaz-Nava, Claudia Muro-Urista, Sonia Martínez-Gallegos and Ernesto Rivera
Polymers 2019, 11(4), 721; https://doi.org/10.3390/polym11040721 - 19 Apr 2019
Cited by 8 | Viewed by 3831
Abstract
Atrazine (ATZ) is an herbicide which is applied to the soil, and its mechanism of action involves the inhibition of photosynthesis. One of its main functions is to control the appearance of weeds in crops, primarily in corn, sorghum, sugar cane, and wheat; [...] Read more.
Atrazine (ATZ) is an herbicide which is applied to the soil, and its mechanism of action involves the inhibition of photosynthesis. One of its main functions is to control the appearance of weeds in crops, primarily in corn, sorghum, sugar cane, and wheat; however, it is very toxic for numerous species, including humans. Therefore, this work deals with the adsorption of ATZ from aqueous solutions using nanocomposite materials, synthesized with two different types of organo-modified clays. Those were obtained by the free radical polymerization of 4-vinylpyridine (4VP) and acrylamide (AAm) in different stoichiometric ratios, using tetrabutylphosphonium persulfate (TBPPS) as a radical initiator and N,N′-methylenebisacrylamide (BIS) as cross-linking agent. The structural, morphological, and textural characteristics of clays, copolymers, and nanocomposites were determined through different analytical and instrumental techniques, i.e., X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Adsorption kinetics experiments of ATZ were determined with the modified and synthesized materials, and the effect of the ratio between 4VP and AAm moieties on the removal capacities of the obtained nanocomposites was evaluated. Finally, from these sets of experiments, it was demonstrated that the synthesized nanocomposites with higher molar fractions of 4VP obtained the highest removal percentages of ATZ. Full article
(This article belongs to the Special Issue Polymer Clay Nano-composites)
►▼ Show Figures

Figure 1

Figure 1
<p>Structure of the atrazine (ATZ) herbicide.</p> Full article ">Figure 2
<p>X-ray diffraction (XRD) patterns of the (<b>a</b>) raw clay mineral, the organo-modified with hexadecyltrimethylammonium bromide (OMH), and the hexadecyltrimethylammonium bromide (HDTMA-Br) cationic surfactant. (<b>b</b>) The raw clay mineral, the organo-modified with phenyltrimethylammonium chloride (OMP) and the phenyltrimethylammonium chloride (PTMA-Cl) cationic surfactant.</p> Full article ">Figure 3
<p>Equilibrium swelling time of different systems: (<b>a</b>) CC01, CC04, and CC07; (<b>b</b>) CCH01, CCH04, and CCH07 nanocomposites modified with HDTMA; (<b>c</b>) CCP01, CCP04, and CCP07 nanocomposites modified with PTMA.</p> Full article ">Figure 4
<p>Critical pH value of different systems: (<b>a</b>) CC01, CC04, and CC07 copolymers; (<b>b</b>) CCH01, CCH04, and CCH07 nanocomposites modified with HDTMA; (<b>c</b>) CCP01, CCP04, and CCP07 nanocomposites modified with PTMA.</p> Full article ">Figure 5
<p>pH reversibility for different systems: (<b>a</b>) CCH01, CCH04, and CCH07 nanocomposites modified with HDTMA; (<b>b</b>) CCP01, CCP04, and CCP07 nanocomposites modified with PTMA.</p> Full article ">Figure 6
<p>Fourier-transform infrared (FTIR) spectra of (<b>a</b>) raw clay mineral, OMH, and HDTMA-Br cationic surfactant; (<b>b</b>) raw clay mineral, OMP, and PTMA-Cl cationic surfactant.</p> Full article ">Figure 7
<p>FTIR spectra of CC01, CC04, and CC07 copolymer matrices.</p> Full article ">Figure 8
<p>SEM micrographs of (<b>a</b>) raw clay mineral (sepiolite), and (<b>b</b>) OMH- and (<b>c</b>) OMP-modified clays.</p> Full article ">Figure 9
<p>SEM micrographs of (<b>a</b>) CC04 copolymer, and (<b>b</b>) CCH04 and (<b>c</b>) CCP04 nanocomposites.</p> Full article ">Figure 10
<p>Adsorption kinetics for the synthesized materials: CC04 copolymer, and CCH04 and CCP04 nanocomposites.</p> Full article ">Figure 11
<p>Kinetics models of the different synthesized materials: (<b>a</b>) CC04 copolymer, and (<b>b</b>) CCH04 and (<b>c</b>) CCP04 nanocomposites.</p> Full article ">Figure 12
<p>Removal capacities of the synthesized copolymers, with different of 4-vinylpyridine (4VP)/ acrylamide (AAm) co-monomer ratios in their structures.</p> Full article ">Figure 13
<p>Adsorption experiments varying the mass–volume ratio and the initial concentration of atrazine in the prepared solutions.</p> Full article ">
15 pages, 5080 KiB  
Article
Preparation and Characteristics of an Environmentally Friendly Hyperbranched Flame-Retardant Polyurethane Hybrid Containing Nitrogen, Phosphorus, and Silicon
by Chin-Hsing Chen and Chin-Lung Chiang
Polymers 2019, 11(4), 720; https://doi.org/10.3390/polym11040720 - 19 Apr 2019
Cited by 22 | Viewed by 4726
Abstract
The NCO functional group of 3-isocyanatoproplytriethoxysilane (IPTS) and the OH functional group of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phospha-phenantbrene-10-oxide (DOPO-BQ) were used to conduct an addition reaction. Following completion of the reaction, triglycidyl isocyanurate (TGIC) was introduced to conduct a ring-opening reaction. Subsequently, a sol–gel method was used [...] Read more.
The NCO functional group of 3-isocyanatoproplytriethoxysilane (IPTS) and the OH functional group of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phospha-phenantbrene-10-oxide (DOPO-BQ) were used to conduct an addition reaction. Following completion of the reaction, triglycidyl isocyanurate (TGIC) was introduced to conduct a ring-opening reaction. Subsequently, a sol–gel method was used to initiate a hydrolysis–condensation reaction on TGIC–IPTS–DOPO-BQ to form a hyperbranched nitrogen–phosphorous–silicon (HBNPSi) flame retardant. This flame retardant was incorporated into a polyurethane (PU) matrix to prepare a hybrid material. Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), limiting oxygen index (LOI), UV-VIS spectrophotometry, and Raman analysis were conducted to characterize the structure and analyze the transparency, thermal stability, flame retardancy, and residual char to understand the flame retardant mechanism of the prepared hybrid material. After the flame retardant was added, the maximum degradation rate decreased from −36 to −17 wt.%/min, the integral procedural decomposition temperature (IPDT) increased from 348 to 488 °C, and the char yield increased from 0.7 to 8.1 wt.%. The aforementioned results verified that the thermal stability of PU can be improved after adding HBNPSi. The LOI analysis indicated that the pristine PU was flammable because the LOI of pristine PU was only 19. When the content of added HBNPSi was 40%, the LOI value was 26; thus the PU hybrid became nonflammable. Full article
(This article belongs to the Special Issue Thermal Insulating and Fire-Resistant Polymer Composites)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>FTIR spectra of DOPO-BQ, IPTS, TGIC, and HBNPSi.</p> Full article ">Figure 2
<p>FTIR spectra of prepolymer, HBNPSi, 1,4-BD, and PU/HBNPSi.</p> Full article ">Figure 3
<p>UV-VIS spectrum of pristine PU and PU/HBNPSi hybrid.</p> Full article ">Figure 4
<p>TGA curves of PU/HBNPSi hybrid in N<sub>2</sub>.</p> Full article ">Figure 5
<p>DTG curves of PU/HBNPSi hybrid in N<sub>2</sub>.</p> Full article ">Figure 6
<p>TGA curve for the composite.</p> Full article ">Figure 7
<p>The IPDT data of pristine PU and PU/HBNPSi hybrid.</p> Full article ">Figure 8
<p>Dependence of the interaction TGΔ on the degradation time for PU/HBNPSi (<b>a</b>) 10%, (<b>b</b>) 20%, (<b>c</b>) 30%, and (<b>d</b>) 40%.</p> Full article ">Figure 9
<p>Effect of various HBPSi contents on the limiting oxygen index (LOI) of PU/HBNPSi hybrid.</p> Full article ">Figure 10
<p>The Raman spectra of char products from PU/HBNPSi 10% at 800 °C (<b>a</b>) 1 min and (<b>b</b>) 5 min.</p> Full article ">Figure 11
<p>The Raman spectra of char products from PU/HBNPSi 40% at 800 °C (<b>a</b>) 1 min and (<b>b</b>) 5 min.</p> Full article ">Scheme 1
<p>The reaction of hyperbranched nitrogen–phosphorous–silicon (HBNPSi).</p> Full article ">Scheme 2
<p>The reaction of polyurethane (PU)/HBNPSi.</p> Full article ">
13 pages, 3540 KiB  
Article
Enhancing Saltiness Perception Using Chitin Nanomaterials
by Wan-Chen Tsai, Shang-Ta Wang, Ke-Liang Bruce Chang and Min-Lang Tsai
Polymers 2019, 11(4), 719; https://doi.org/10.3390/polym11040719 - 19 Apr 2019
Cited by 28 | Viewed by 4628
Abstract
In the present study, we prepared and characterized chitin nanomaterials with different diameters, lengths, and degree of deacetylation (DD), and investigated their capability for enhancing saltiness perception. Chitin was isolated from squid pens and transformed into chitin nanofiber (CNF), deacetylated chitin nanofiber (DACNF), [...] Read more.
In the present study, we prepared and characterized chitin nanomaterials with different diameters, lengths, and degree of deacetylation (DD), and investigated their capability for enhancing saltiness perception. Chitin was isolated from squid pens and transformed into chitin nanofiber (CNF), deacetylated chitin nanofiber (DACNF), and chitin nanocrystal (CNC) by ultrasonication, alkali treatment followed by ultrasonication and acid hydrolysis, respectively. The diameters of CNF, CNC and DACNF were 17.24 nm, 16.05 nm and 15.01 nm while the lengths were 1725.05 nm, 116.91 nm, and 1806.60 nm, respectively. The aspect ratios of CNF and DACNF were much higher than that of CNC. The crystalline indices of CNF and CNC were lower than that of original β-chitin, suggesting that ultrasonication and acid hydrolysis might change the molecular arrangement in crystalline region of chitin. The zeta-potentials were between 19.73 nV and 30.08 mV of chitin nanomaterials in distilled water. Concentrations of chitin nanomaterials (40–74 μg/mL) showed minimal effect on zeta-potential, whereas increasing the level of NaCl reduced the zeta-potential of solution. Moreover, NaCl solution (0.3%) with chitin nanomaterials addition produced significant higher saltiness perception than that of solution with NaCl alone. Therefore, chitin nanomaterials may be promising saltiness enhancers in the food industry. Full article
(This article belongs to the Special Issue Modifications and Applications of Chitin/Chitosan for Biomedical, Pharmaceutical, Cosmetic, Biotechnology and Related Applications)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>TEM micrograph of (<b>A</b>) chitin nanofibers after 1 h ultrasonication; (<b>B</b>) after 2 h ultrasonication; (<b>C</b>) deacetylated chitin nanofibers; and (<b>D</b>) chitin nanocrystals from squid pen.</p> Full article ">Figure 2
<p>The width and length distribution from TEM of (<b>A</b>) width of chitin nanofibers; (<b>B</b>) length of chitin nanofibers; (<b>C</b>) width of deacetylated chitin nanofibers; (<b>D</b>) length of deacetylated chitin nanofibers; (<b>E</b>) width of chitin nanocrystals; and (<b>F</b>) length of chitin nanocrystals.</p> Full article ">Figure 3
<p>FTIR spectra of chitin, deacetylated chitin (DACTN), chitin nanofibers (CNF), deacetylated chitin nanofibers (DACNF), and chitin nanocrystals (CNC).</p> Full article ">Figure 4
<p>X-ray diffraction patterns of chitin, deacetylated chitin (DACTN), chitin nanofibers (CNF), deacetylated chitin nanofibers (DACNF), and chitin nanocrystals (CNC).</p> Full article ">Figure 5
<p>Zeta potentials of different concentrations of chitin nanofibers (CNF), deacetylated chitin nanofibers (DACNF), and chitin nanocrystals (CNC). <sup>a–d</sup> Value for each sample with different superscripts are significantly different (<span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 6
<p>The effect of NaCl concentration on the zeta potentials of 74 μg/mL chitin nanofibers (CNF), deacetylated chitin nanofibers (DACNF), and chitin nanocrystals (CNC). <sup>a–g</sup> Value for each sample with different superscripts are significantly different (<span class="html-italic">p</span> &lt; 0.05).</p> Full article ">
20 pages, 5042 KiB  
Article
The Use of Lanthanum Ions and Chitosan for Boron Elimination from Aqueous Solutions
by Joanna Kluczka, Gabriela Dudek, Alicja Kazek-Kęsik, Małgorzata Gnus, Maciej Krzywiecki, Krzysztof Mitko and Katarzyna Krukiewicz
Polymers 2019, 11(4), 718; https://doi.org/10.3390/polym11040718 - 19 Apr 2019
Cited by 9 | Viewed by 4590
Abstract
Boron is an essential element for plants and living organisms; however, it can be harmful if its concentration in the environment is too high. In this paper, lanthanum(III) ions were introduced to the structure of chitosan via an encapsulation technique and the obtained [...] Read more.
Boron is an essential element for plants and living organisms; however, it can be harmful if its concentration in the environment is too high. In this paper, lanthanum(III) ions were introduced to the structure of chitosan via an encapsulation technique and the obtained hydrogel (La-CTS) was used for the elimination of the excess of B(III) from modelling solutions. The reaction between boric acid and hydroxyl groups bound to the lanthanum coordinated by chitosan active centres was the preponderant mechanism of the bio-adsorption removal process. The results demonstrated that La-CTS removed boric acid from the aqueous solution more efficiently than either lanthanum hydroxide or native chitosan hydrogel, respectively. When the initial boron concentration was 100 mg/dm3, the maximum adsorption capacity of 11.1 ± 0.3 mg/g was achieved at pH 5 and the adsorption time of 24 h. The successful introduction of La(III) ions to the chitosan backbone was confirmed by Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy, Fourier-Transform Infrared Spectroscopy, X-Ray Diffraction, X-ray Photoelectron Spectroscopy, and Inductively Coupled Plasma Optical Emission Spectroscopy. Due to its high-performance boron adsorption-desorption cycle and convenient form, La-CTS seems to be a promising bio-adsorbent for water treatment. Full article
(This article belongs to the Special Issue Chitin and Chitosan: Properties and Applications)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>The FTIR spectra of unmodified chitosan (CTS); chitosan attached with La(III) before (La-CTS) and after (LA-CTS-B) boron adsorption.</p> Full article ">Figure 2
<p>The SEM images of cross-section of chitosan hydrogel beads attached with La(III): (<b>a</b>) La-CTS before adsorption and (<b>b</b>) La-CTS-B after boron adsorption.</p> Full article ">Figure 3
<p>The XRD patterns of the hydrogel beads attached with lanthanum (La-CTS) and hydrogel beads attached with lanthanum after boron adsorption (La-CTS-B).</p> Full article ">Figure 4
<p>Hi-resolution XPS scans taken for representative XPS regions: (<b>a</b>) the La 3d<sub>5/2</sub> XPS region recorded for La-CTS sample; (<b>b</b>) the La 3d<sub>5/2</sub> XPS region recorded for La-CTS-B sample; (<b>c</b>) the B 1s XPS region recorded for La-CTS-B sample. Component assignment (given in Arabic numbers): (1) La–NH<sub>2</sub>; (2) La–OH/La–OH(H<sub>2</sub>O); (3) La–O–B; (4) La–O–B; (5) B–OH (6) is the plasmon energy loss feature.</p> Full article ">Figure 5
<p><b>The</b> pH<sub>i</sub> versus ΔpH for unmodified chitosan (CTS) and chitosan attached with lanthanum (La-CTS).</p> Full article ">Figure 6
<p>Boron speciation at different pH of aqueous solution.</p> Full article ">Figure 7
<p>Boron removal efficiency on La(OH)<sub>3</sub> (graph 1) and boron adsorption capacity on La-CTS beads (graph 2) as a function of initial pH value at temperature of 20 ± 1 °C.</p> Full article ">Figure 8
<p>Effect of contact time on boron adsorption capacity of La-CTS hydrogel beads. The inserted figure is the effect of contact time when initial boron concentrations were 20 and 200 mg/dm<sup>3</sup>, respectively.</p> Full article ">Figure 9
<p>Boron adsorption isotherms on La-CTS hydrogel beads: experimental curve and Langmuir, Freundlich, Dubinin–Radushkevich, and Temkin models at 20 ± 1 °C and time of 24 h.</p> Full article ">Figure 10
<p>The influence of the initial boron concentration and time on the elution of lanthanum ions from the La-CTS hydrogel beads (graph 1) and on the content of lanthanum in the La-CTS bio-adsorbent (graph 2) during adsorption.</p> Full article ">Figure 11
<p>The influence of the NaOH concentration on boron desorption efficiency and on lanthanum elution from La-CTS hydrogel beads.</p> Full article ">Scheme 1
<p>Formation of La-CTS hydrogel beads.</p> Full article ">Scheme 2
<p>The assumed interaction of La-CTS hydrogel beads with boric acid.</p> Full article ">
13 pages, 4236 KiB  
Article
Manifestation of Interactions of Nano-Silica in Silicone Rubber Investigated by Low-Frequency Dielectric Spectroscopy and Mechanical Tests
by Chao Wu, Yanfeng Gao, Xidong Liang, Stanislaw M. Gubanski, Qian Wang, Weining Bao and Shaohua Li
Polymers 2019, 11(4), 717; https://doi.org/10.3390/polym11040717 - 19 Apr 2019
Cited by 28 | Viewed by 5140
Abstract
Silicone rubber composites filled with nano-silica are currently widely used as high voltage insulating materials in power transmission and substation systems. We present a systematic study on the dielectric and mechanical performance of silicone rubber filled with surface modified and unmodified fumed nano-silica. [...] Read more.
Silicone rubber composites filled with nano-silica are currently widely used as high voltage insulating materials in power transmission and substation systems. We present a systematic study on the dielectric and mechanical performance of silicone rubber filled with surface modified and unmodified fumed nano-silica. The results indicate that the different interfaces between the silicone rubber and the two types of nano-silica introduce changes in their dielectric response when electrically stressed by a sinusoidal excitation in the frequency range of 10−4–1 Hz. The responses of pure silicone rubber and the composite filled with modified silica can be characterized by a paralleled combination of Maxwell-Wagner-Sillars interface polarization and DC conduction. In contrast, the silicone rubber composite with the unmodified nano-silica exhibits a quasi-DC (Q-DC) transport process. The mechanical properties of the composites (represented by their stress-strain characteristics) reveal an improvement in the mechanical strength with increasing filler content. Moreover, the strain level of the composite with a modified filler is improved. Full article
(This article belongs to the Collection Silicon-Containing Polymeric Materials)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>TEM images representing the morphology of unmodified (<b>a</b>) and modified (<b>b</b>) silica, SEM images representing the morphology of unmodified (<b>c</b>) and modified (<b>d</b>) silica filled silicone rubber composites.</p> Full article ">Figure 2
<p>Chemical groups on the surface of unmodified and modified fumed nano-silica fillers investigated by FTIR.</p> Full article ">Figure 3
<p>Chemical elements on the surface of unmodified and modified fumed nano-silica fillers obtained by XPS.</p> Full article ">Figure 4
<p>Frequency dependence of complex capacitance and susceptibility of pure silicone rubber (<b>a</b>) and (<b>b</b>), silicone rubber with unmodified nano-silica (<b>c</b>) and (<b>d</b>), silicone rubber with modified nano-silica (<b>e</b>) and (<b>f</b>).</p> Full article ">Figure 4 Cont.
<p>Frequency dependence of complex capacitance and susceptibility of pure silicone rubber (<b>a</b>) and (<b>b</b>), silicone rubber with unmodified nano-silica (<b>c</b>) and (<b>d</b>), silicone rubber with modified nano-silica (<b>e</b>) and (<b>f</b>).</p> Full article ">Figure 5
<p>Equivalent circuits of silicone rubber filled with unmodified nano-silica (<b>a</b>). Equivalent circuits of pure silicone rubber and silicone rubber filled with modified fumed nano-silica (<b>b</b>).</p> Full article ">Figure 6
<p>Equivalent circuit fittings for silicone rubber filled with unmodified fumed nano-silica (<b>a</b>) and modified fumed nano-silica (<b>b</b>) at 353 K.</p> Full article ">Figure 7
<p>Master curves of silicone rubber composites filled with unmodified (<b>a</b>) and modified fumed nano-silica (<b>b</b>) at different temperature.</p> Full article ">Figure 8
<p>Tensile stress-strain curves (<b>a</b>) and mechanical strength (<b>b</b>) of silicone rubber composites filled with unmodified and modified nano-silica filler.</p> Full article ">Figure 9
<p>Schematic views of charge interactions in unmodified and modified silica filled silicone rubber composites.</p> Full article ">
13 pages, 3732 KiB  
Article
Preparation of Hydrogel/Silver Nanohybrids Mediated by Tunable-Size Silver Nanoparticles for Potential Antibacterial Applications
by Yeray A. Rodríguez Nuñez, Ricardo I. Castro, Felipe A. Arenas, Zoraya E. López-Cabaña, Gustavo Carreño, Verónica Carrasco-Sánchez, Adolfo Marican, Jorge Villaseñor, Esteban Vargas, Leonardo S. Santos and Esteban F. Durán-Lara
Polymers 2019, 11(4), 716; https://doi.org/10.3390/polym11040716 - 19 Apr 2019
Cited by 35 | Viewed by 6500
Abstract
In this study, a versatile synthesis of silver nanoparticles of well-defined size by using hydrogels as a template and stabilizer of nanoparticle size is reported. The prepared hydrogels are based on polyvinyl alcohol and maleic acid as crosslinker agents. Three hydrogels with the [...] Read more.
In this study, a versatile synthesis of silver nanoparticles of well-defined size by using hydrogels as a template and stabilizer of nanoparticle size is reported. The prepared hydrogels are based on polyvinyl alcohol and maleic acid as crosslinker agents. Three hydrogels with the same nature were synthesized, however, the crosslinking degree was varied. The silver nanoparticles were synthesized into each prepared hydrogel matrix achieving three significant, different-sized nanoparticles that were spherical in shape with a narrow size distribution. It is likely that the polymer network stabilized the nanoparticles. It was determined that the hydrogel network structure can control the size and shape of the nanoparticles. The hydrogel/silver nanohybrids were characterized by swelling degree, Thermal Gravimetric Analysis (TGA), Fourier Transform Infrared (FT-IR), Scanning Electron Microscopy (SEM) and Transmission Electron Microscope (TEM). Antibacterial activity against Staphylococcus aureus was evaluated, confirming antimicrobial action of the encapsulated silver nanoparticles into the hydrogels. Full article
(This article belongs to the Special Issue Hydrogels and Gels for Biomedical and Sustainable Applications)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Scheme of synthesis of PMALH Hydrogels. Esterification reaction of PVA with MAL at three different ratios.</p> Full article ">Figure 2
<p>Preparation scheme of hydrogel/silver nanohybrids (PMALH-AgNPs).</p> Full article ">Figure 3
<p>Swelling index of (<b>a</b>) PMALH10, (<b>b</b>) PMALH20, and (<b>c</b>) PMALH30 in two different buffers (pH 3.0, 7.4) with respect to time. (<b>d</b>) %ESR of PMALH10, PMALH20, and PMALH30 at pH 7.4 and 3.0 with respect to time.</p> Full article ">Figure 4
<p>TGA (Thermogravimetric) thermogram for polyvinilalcohol (PVA) crosslinker with MAL.</p> Full article ">Figure 5
<p>DTG between 280 and 500 °C and possible crosslinking. (<b>A</b>) fraction PVA-AM and (<b>B</b>) fraction PVA-AM-PVA.</p> Full article ">Figure 6
<p>Typical FT-IR spectra of PMALHs.</p> Full article ">Figure 7
<p>SEM images of (<b>A</b>) PMALH10, (<b>B</b>) PMALH20, (<b>C</b>) PMALH30 hydrogels, (<b>D</b>) PMALH10-AgNPs, (<b>E</b>) PMALH20-AgNPs, and (F) PMALH30-AgNPs nanohybrids.</p> Full article ">Figure 8
<p>TEM images of (<b>A</b>) PMALH10-AgNPs, (<b>B</b>) PMALH20-AgNPs, and (<b>C</b>) PMALH30-AgNPs nanohybrids and their respective histogram.</p> Full article ">Figure 9
<p>Screening of antibacterial effect of (<b>A</b>) PMALH10-AgNPs, (<b>B</b>) PMALH20-AgNPs, and (<b>C</b>) PMALH30-AgNPs nanohybrids against <span class="html-italic">S. aureus</span>.</p> Full article ">
Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
 
Displaying articles 1-174
Previous Issue
Next Issue
Back to TopTop