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Polymers, Volume 12, Issue 2 (February 2020) – 251 articles

Cover Story (view full-size image): The thermophoretic response of a protein is sensitive to ligand binding, provides access to equilibrium binding constants, and is remarkably sensitive to changes in the hydration layer. Systematic thermophoretic measurements of the protein streptavidin and the streptavidin-biotin complex using thermal diffusion forced Rayleigh scattering showed that free streptavidin is more thermophobic and slightly more hydrophilic compared with the streptavidin-biotin complex. The ligand-bound complex most likely forms fewer hydrogen bonds with surrounding water molecules, leading to an entropy increase of the released water molecules, which partially compensates for the conformational entropy loss of streptavidin upon binding biotin. View this paper.
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20 pages, 4085 KiB  
Article
Gelatin Methacryloyl Hydrogels Control the Localized Delivery of Albumin-Bound Paclitaxel
by Margaux Vigata, Christoph Meinert, Stephen Pahoff, Nathalie Bock and Dietmar W. Hutmacher
Polymers 2020, 12(2), 501; https://doi.org/10.3390/polym12020501 - 24 Feb 2020
Cited by 59 | Viewed by 10022
Abstract
Hydrogels are excellent candidates for the sustained local delivery of anticancer drugs, as they possess tunable physicochemical characteristics that enable to control drug release kinetics and potentially tackle the problem of systemic side effects in traditional chemotherapeutic delivery. Yet, current systems often involve [...] Read more.
Hydrogels are excellent candidates for the sustained local delivery of anticancer drugs, as they possess tunable physicochemical characteristics that enable to control drug release kinetics and potentially tackle the problem of systemic side effects in traditional chemotherapeutic delivery. Yet, current systems often involve complicated manufacturing or covalent bonding processes that are not compatible with regulatory or market reality. Here, we developed a novel gelatin methacryloyl (GelMA)-based drug delivery system (GelMA-DDS) for the sustained local delivery of paclitaxel-based Abraxane®, for the prevention of local breast cancer recurrence following mastectomy. GelMA-DDS readily encapsulated Abraxane® with a maximum of 96% encapsulation efficiency. The mechanical properties of the hydrogel system were not affected by drug loading. Tuning of the physical properties, by varying GelMA concentration, allowed tailoring of GelMA-DDS mesh size, where decreasing the GelMA concentration provided overall more sustained cumulative release (significant differences between 5%, 10%, and 15%) with a maximum of 75% over three months of release, identified to be released by diffusion. Additionally, enzymatic degradation, which more readily mimics the in vivo situation, followed a near zero-order rate, with a total release of the cargo at various rates (2–14 h) depending on GelMA concentration. Finally, the results demonstrated that Abraxane® delivery from the hydrogel system led to a dose-dependent reduction of viability, metabolic activity, and live-cell density of triple-negative breast cancer cells in vitro. The GelMA-DDS provides a novel and simple approach for the sustained local administration of anti-cancer drugs for breast cancer recurrence. Full article
(This article belongs to the Special Issue Biopolymers for Medical Applications)
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Figure 1

Figure 1
<p>Gelatin Methacryloyl synthesis and characterization. (<b>A</b>) Gelatin Methacryloyl (GelMA) synthesis by methacrylation at 50 °C produces GelMA and methacrylic acid. (<b>B</b>) Proton nuclear magnetic resonance (<sup>1</sup>H-MNR) spectra of Gelatin and GelMA, confirming the substitution of primary amine groups by methacryloyl groups in GelMA. (<b>C</b>) Degree of GelMA functionalization, as measured by 2,4,6-Trinitrobenzene Sulfonic Acid (TNBS) assay.</p> Full article ">Figure 2
<p>Characterization of the compressive and swelling properties of GelMA-DDS hydrogels for various GelMA concentrations and doses of Abraxane<sup>®</sup>. (<b>A</b>–<b>C</b>) Representative stress-strain curves for 5% <span class="html-italic">w/v</span> (<b>A</b>), 10% <span class="html-italic">w/v</span> (<b>B</b>) and 15% <span class="html-italic">w/v</span> (<b>C</b>) GelMA groups. (<b>D</b>) Compressive modulus. (<b>E</b>) Failure strain. (<b>F</b>) Failure stress. (<b>G</b>) Toughness. (<b>H</b>) Effective swelling. (<b>I</b>) Representative images of hydrogel samples; scale bar = 1 mm. Dose 1 and 2 refer to 37.5 µg and 75 µg Abraxane<sup>®</sup>, respectively. Control refers to no drug loading. Data are shown as box plots, <span class="html-italic">n</span> = 9. Groups with no statistical difference are marked with the same roman numeral.</p> Full article ">Figure 3
<p>Release kinetics of FITC-labeled Abraxane<sup>®</sup> from GelMA hydrogels, as measured in phosphate-buffered saline pH 7.4, under gentle agitation at 37 °C. (<b>A</b>–<b>B</b>) Cumulative release profiles, normalized to encapsulated Dose 1 (37.5 μg) (<b>A</b>) and Dose 2 (75 μg) (B) from 5%, 10%, and 15% w/v GelMA hydrogels. Data are shown as mean ± standard deviation (SD). (<b>C</b>–<b>D</b>) Fraction of FITC-Abraxane<sup>®</sup> released in the first hour (<b>C</b>), and released after 97 days (<b>D</b>), normalized to GelMA encapsulated doses. Data are shown as mean + SD. GelMA Dose 1 and 2 refer to 37.5 µg and 75 µg Abraxane<sup>®</sup>, respectively. Data are shown as mean + SD. Release experiments were repeated three times, n ≥ 5. **** <span class="html-italic">p</span> &lt; 0.0001; *** <span class="html-italic">p</span> &lt; 0.001; ** <span class="html-italic">p</span> &lt; 0.01; * <span class="html-italic">p</span> &lt; 0.05.</p> Full article ">Figure 4
<p>Release kinetics of FITC-labeled Abraxane<sup>®</sup> from GelMA hydrogels via enzymatic (collagenase II) degradation. (<b>A</b>) GelMA degradation over time, as measured by mass loss normalized to initial mass. Data are shown as means ± standard deviation (SD), <span class="html-italic">n</span> = 4. (<b>B</b>) Cumulative release profiles, normalized to respective free doses suspended in collagenase II. Dose 1 and 2 refer to 37.5 µg and 75 µg Abraxane<sup>®</sup>, respectively. Data are shown as mean ± SD, <span class="html-italic">n</span> = 4. **** <span class="html-italic">p</span> &lt; 0.0001; *** <span class="html-italic">p</span> &lt; 0.001; ** <span class="html-italic">p</span> &lt; 0.01; * <span class="html-italic">p</span> &lt; 0.05.</p> Full article ">Figure 5
<p>Aggregation of FITC-labeled Abraxane<sup>®</sup> in GelMA hydrogels. (<b>A</b>) Representative <span class="html-italic">z</span>-stack maximum projections of 10% GelMA releasing FITC-Abraxane<sup>®</sup> for Dose 1 and 2 formulations. Scale bar = 25 µm. (<b>B</b>) Relative average aggregate size normalized to Day 0 and shown as ± standard error of the mean, <span class="html-italic">n</span> ≥ 16,250 aggregates, **** <span class="html-italic">p</span> &lt; 0.0001.</p> Full article ">Figure 6
<p>In vitro evaluation of GelMA-DDS 10% on human MDA-MB-231 breast cancer cells cultured in separate three-dimensional (3D) GelMA hydrogels. (<b>A</b>) Maximum projections of z stacks with live/dead staining using Fluorescein Diacetate (FDA) and Propidium Iodide (PI) of cancer cells for five media conditions; no drug (control), Dose 1 free in solution, Dose 1 in GelMA, Dose 2 free in solution, and Dose 2 in GelMA (from left to right). Green represents live cells, and red represents dead cells. Scale bar = 50 µm. GelMA (<b>B</b>–<b>G</b>) Quantitative in vitro assessment of GelMA-DDS formulations at Day 7; viability (<b>B</b>–<b>C</b>), metabolic activity (<b>D</b>–<b>E</b>), and Live-cell density (<b>F</b>–<b>G</b>) for no drug control, drug in media and drug in GelMA. Data are shown as mean ± standard deviation. The experiment was repeated three times, n=3. **** <span class="html-italic">p</span>&lt;0.0001; *** <span class="html-italic">p</span>&lt;0.001; **<span class="html-italic">p</span>&lt;0.01; * <span class="html-italic">p</span>&lt;0.05.</p> Full article ">
12 pages, 1377 KiB  
Article
Removal of Rhodamine B from Water Using a Solvent Impregnated Polymeric Dowex 5WX8 Resin: Statistical Optimization and Batch Adsorption Studies
by Moonis Ali Khan, Momina, Masoom Raza Siddiqui, Marta Otero, Shareefa Ahmed Alshareef and Mohd Rafatullah
Polymers 2020, 12(2), 500; https://doi.org/10.3390/polym12020500 - 24 Feb 2020
Cited by 60 | Viewed by 4165
Abstract
Herein, commercially available Dowex 5WX8, a cation exchange polymeric resin, was modified through solvent impregnation with t-butyl phosphate (TBP) to produce a solvent impregnated resin (SIR), which was tested for the removal of rhodamine B (RhB) from water in batch adsorption experiments. The [...] Read more.
Herein, commercially available Dowex 5WX8, a cation exchange polymeric resin, was modified through solvent impregnation with t-butyl phosphate (TBP) to produce a solvent impregnated resin (SIR), which was tested for the removal of rhodamine B (RhB) from water in batch adsorption experiments. The effect of SIR dosage, contact time, and pH on RhB adsorption was studied and optimized by response surface methodology (RSM), interaction, Pareto, and surface plots. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were respectively used for characterizing SIR surface morphology and identifying active binding sites before and after RhB adsorption. SEM showed that the pristine SIR surface was covered with irregular size and shape spots with some pores, while RhB saturated SIR surface was non-porous. FTIR revealed the involvement of electrostatic and π–π interactions during RhB adsorption on SIR. Dosage of SIR, contact time, and their interaction significantly affected RhB adsorption on SIR, while pH and its interaction with dosage and contact time did not. The optimum identified experimental conditions were 0.16 g of SIR dose and 27.66 min of contact time, which allowed for 98.45% color removal. Moreover, RhB adsorption equilibrium results fitted the Langmuir isotherm with a maximum monolayer capacity (qmax) of 43.47 mg/g. Full article
(This article belongs to the Special Issue Current Trends and Perspectives in the Application of Polymeric Materials for Wastewater Treatment)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Scanning electron microscopic (SEM) images of raw Dowex 5WX8 polymeric resin (<b>a</b>), pristine SIR (<b>b, c</b>), RhB saturated SIR (<b>d</b>), and Fourier transform infrared (FT-IR) spectra of raw Dowex 5WX8 polymeric resin (<b>i</b>), pristine SIR (<b>ii</b>), and RhB saturated SIR (<b>iii</b>) (<b>e</b>)<b>.</b></p> Full article ">Figure 1 Cont.
<p>Scanning electron microscopic (SEM) images of raw Dowex 5WX8 polymeric resin (<b>a</b>), pristine SIR (<b>b, c</b>), RhB saturated SIR (<b>d</b>), and Fourier transform infrared (FT-IR) spectra of raw Dowex 5WX8 polymeric resin (<b>i</b>), pristine SIR (<b>ii</b>), and RhB saturated SIR (<b>iii</b>) (<b>e</b>)<b>.</b></p> Full article ">Figure 2
<p>Pareto chart showing the effects and interactions of operational variables, namely dosage of resin (g), contact time (min) and pH, on the decolorization efficiency (D.E. (%)) by SIR (<b>a</b>)<b>,</b> and interaction plot of decolorization efficiency (D.E. (%)) by SIR versus contact time (min) for the different dosages of resin, namely 0.1, 0.2, and 0.3 g of SIR (<b>b</b>).</p> Full article ">Figure 3
<p>Surface plot showing the decolorization efficiency (D.E. (%)) as a function of the dosage of resin (g) and contact time (min) under a shaking speed of 230 rpm and pH 3.6 (<b>a</b>), and optimization plot for the determination of the optimum conditions, namely dosage of resin (g) and contact time (min), for a maximum decolorization efficiency (D.E. (%)) by SIR (<b>b</b>).</p> Full article ">Figure 4
<p>Schematic representation of SIR production and RhB adsorption mechanism on SIR.</p> Full article ">
11 pages, 1728 KiB  
Article
Bacterial Natural Disaccharide (Trehalose Tetraester): Molecular Modeling and in Vitro Study of Anticancer Activity on Breast Cancer Cells
by Biliana Nikolova, Georgi Antov, Severina Semkova, Iana Tsoneva, Nelly Christova, Lilyana Nacheva, Proletina Kardaleva, Silvia Angelova, Ivanka Stoineva, Juliana Ivanova, Ivanina Vasileva and Lyudmila Kabaivanova
Polymers 2020, 12(2), 499; https://doi.org/10.3390/polym12020499 - 24 Feb 2020
Cited by 9 | Viewed by 3265
Abstract
Isolation and characterization of new biologically active substances affecting cancer cells is an important issue of fundamental research in biomedicine. Trehalose lipid was isolated from Rhodococcus wratislaviensis strain and purified by liquid chromatography. The effect of trehalose lipid on cell viability and migration, [...] Read more.
Isolation and characterization of new biologically active substances affecting cancer cells is an important issue of fundamental research in biomedicine. Trehalose lipid was isolated from Rhodococcus wratislaviensis strain and purified by liquid chromatography. The effect of trehalose lipid on cell viability and migration, together with colony forming assays, were performed on two breast cancer (MCF7—low metastatic; MDA-MB231—high metastatic) and one “normal” (MCF10A) cell lines. Molecular modeling that details the structure of the neutral and anionic form (more stable at physiological pH) of the tetraester was carried out. The tentative sizes of the hydrophilic (7.5 Å) and hydrophobic (12.5 Å) portions of the molecule were also determined. Thus, the used trehalose lipid is supposed to interact as a single molecule. The changes in morphology, adhesion, viability, migration, and the possibility of forming colonies in cancer cell lines induced after treatment with trehalose lipid were found to be dose and time dependent. Based on the theoretical calculations, a possible mechanism of action and membrane asymmetry between outer and inner monolayers of the bilayer resulting in endosome formation were suggested. Initial data suggest a mechanism of antitumor activity of the purified trehalose lipid and its potential for biomedical application. Full article
(This article belongs to the Special Issue Main Applications of Plant, Fungal and Algal Polysaccharides: Current Vision and Future Horizon)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Number of viable cells after treatment with trehalose lipids (TL) at different concentrations (10, 25, 50, 75, 100 µM), presented as a percentage of control (untreated) cells, analyzed by MTT assay. Presented in (<b>A</b>–<b>C</b>) results are respectively for: MDA–MB23, MCF7 cancer cells, and normal MCF10A cell line; black solid columns present data after 24 h incubation and the striped columns after 48 h. All data are means ±SD from three independent experiments. Statistical analysis: (i) All results are statistically significant versus controls at corresponding incubation time (<span class="html-italic">p</span>-value &lt;0.05); (ii) All presented data from 24 h are statistically significant versus data from 48 h (<span class="html-italic">p</span>-value &lt;0.01); (iii) Cancer lines versus Normal cells: all variations between data in (<b>A</b>) are significant versus data in (<b>C</b>): <span class="html-italic">p</span>-value &lt;0.001 for both 24/24 and 48/48 h type comparison; all variations between data in (<b>B</b>) are significant versus data in (<b>C</b>): <span class="html-italic">p</span>-value &lt;0.05 for 24/24 h and <span class="html-italic">p</span>-value &lt;0.01 for 48/48 h comparison. (iv) Data from cancer cell lines’ comparison were calculated also as a statistically significant result (<span class="html-italic">p</span>-value &lt;0.01 for both 24/24 and 48/48 h variations). (<b>D</b>) GraphPad data calculation of the half-maximal inhibitory concentration (IC<sub>50</sub>)—number of viable cells 48 h after treatment with TL in different concentrations, as a percentage of control (untreated) cells. Values are means ±SD from at least three independent experiments at triplet repetitions.</p> Full article ">Figure 2
<p>(<b>A</b>) Wound closure rate of breast normal/cancer cells 24 h after treatment with subcytotoxic concentration TL (75 µM), analyzed by CytoSelect™—wound healing (WH) assay. Calculated wound area of MCF10A normal cells (green columns), high-metastatic MDA-MB231 cell line (red columns) and low-metastatic MCF7cell line (blue columns) are presented as a percent of initial wound area at the initial zero time. All data are the means ±SD from two independent experiments and three independent calculations via ImageJ software; *<span class="html-italic">p</span> &lt; 0.05 versus MCF10A normal cells, ** <span class="html-italic">p</span> &lt; 0.01 versus MCF10A normal cells; # <span class="html-italic">p</span> &lt; 0.05—all variations versus corresponding controls are statistically significant. (<b>B</b>) Cell migration capacity of normal MCF10A cells (top panel) and cancer cells (high-metastatic MDA-MB231 cells—middle panel; low-metastatic MCF7 cells—bottom panel) after treatment with subcytotoxic concentration (WH assay). Images were obtained after 24 h incubation by phase-contrast microscopy, magnification 10×.</p> Full article ">Figure 3
<p>(<b>A</b>) Clonogenicity of normal MCF10A cells (top panel) and cancer cells (MDA-MB231 cells—middle panel; MCF7 cells—bottom panel) after long-term treatment with subcytotoxic concentration TL concentration (75 µM), analyzed by colony forming cell (CFC) assay. Untreated cells were used as a control. (<b>B</b>) Total number formed colonies of MCF10A, MDA MB231, and MCF7 breast cell lines after long-term treatment with subcytotoxic TL concentration (75 µM). All data are the means ±SD from two independent experiments and three independent enumerations; **<span class="html-italic">p</span> &lt; 0.01 versus MCF10A normal cells, *** <span class="html-italic">p</span> &lt; 0.001 versus MCF10A normal cells; ### <span class="html-italic">p</span> &lt; 0.001—high-metastatic versus low-metastatic cancer cell line.</p> Full article ">Figure 4
<p>Optimized structure of TL. Molecular modeling was performed as described in the text.</p> Full article ">Figure 5
<p>Two (neutral) molecules of TL are shown to depict possible molecular interactions between them. One molecule is presented with sticks for the sake of simplicity.</p> Full article ">Scheme 1
<p>Chemical structure of the <span class="html-italic">Rhodococcus sp</span>. trehalose lipid.</p> Full article ">
15 pages, 4847 KiB  
Article
Oxidation–Responsive Emulsions Stabilized with Poly(Vinyl Pyrrolidone-co-allyl Phenyl Sulfide)
by Seok Ho Park and Jin-Chul Kim
Polymers 2020, 12(2), 498; https://doi.org/10.3390/polym12020498 - 24 Feb 2020
Cited by 4 | Viewed by 3174
Abstract
Oxidation-responsive emulsions were obtained by stabilizing mineral oil droplets using amphiphilic poly(vinyl pyrrolidone-co-allyl phenyl sulfide) (P(VP-APS)). 1H nuclear magnetic resonance (NMR) spectroscopy revealed that P(VP-APS) whose APS content was 0%, 3.28%, 3.43% and 4.58% were successfully prepared by free radical reaction and [...] Read more.
Oxidation-responsive emulsions were obtained by stabilizing mineral oil droplets using amphiphilic poly(vinyl pyrrolidone-co-allyl phenyl sulfide) (P(VP-APS)). 1H nuclear magnetic resonance (NMR) spectroscopy revealed that P(VP-APS) whose APS content was 0%, 3.28%, 3.43% and 4.58% were successfully prepared by free radical reaction and the sulfide of APS was oxidized by H2O2 treatment. X-ray Photoelectron Spectroscopy (XPS) also disclosed that the sulfide of APS was oxidized to sulfone by the oxidizing agent. The optical density of copolymer solutions and the interfacial activity of the copolymers markedly decreased by H2O2 treatment possibly because the sulfide of APS was oxidized and the amphiphilicity of the copolymers were weakened. The increase rate of the oil droplet diameter of the emulsions was outstandingly promoted when H2O2 solution (10%, v/v) was used as an aqueous phase. The phase separation of the emulsions was also expedited by the oxidizing agent. The oxidation of APS and the weakened interfacial activity were thought to be a main reason for the demulsification of P(VP-APS)-stabilized emulsions. Full article
(This article belongs to the Special Issue Stimuli-Sensitive Amphiphilic Polymers and Their Biomedical Applications)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Schematic representation of oxidation-responsive emulsion. Oxidation-responsive emulsion was prepared by stabilizing mineral oil droplets using an oxidizable amphiphilic copolymer (i.e., poly(vinyl pyrrolidone-co-allyl phenyl sulfide) (P(VP-APS)). When exposed to an oxidizing condition, the sulfide of APS would be oxidized to sulfoxide and sulfone. As a result, the amphiphilicity and the interfacial activity of the copolymer would be weakened and the oil droplets-stabilizing capacity would also fall down, leading to the coalescence of oil droplets and the phase separation of emulsions.</p> Full article ">Figure 2
<p><sup>1</sup>H nuclear magnetic resonance (NMR) spectrum of P(VP-APS)(100/0) (<b>A</b>), Oxi-P(VP-APS)(100/0) (<b>B</b>), P(VP-APS)(98/2) (<b>C</b>) and Oxi-P(VP-APS)(98/2) (<b>D</b>). Inset represents the enlarged signals in 7 to 7.8 ppm.</p> Full article ">Figure 2 Cont.
<p><sup>1</sup>H nuclear magnetic resonance (NMR) spectrum of P(VP-APS)(100/0) (<b>A</b>), Oxi-P(VP-APS)(100/0) (<b>B</b>), P(VP-APS)(98/2) (<b>C</b>) and Oxi-P(VP-APS)(98/2) (<b>D</b>). Inset represents the enlarged signals in 7 to 7.8 ppm.</p> Full article ">Figure 2 Cont.
<p><sup>1</sup>H nuclear magnetic resonance (NMR) spectrum of P(VP-APS)(100/0) (<b>A</b>), Oxi-P(VP-APS)(100/0) (<b>B</b>), P(VP-APS)(98/2) (<b>C</b>) and Oxi-P(VP-APS)(98/2) (<b>D</b>). Inset represents the enlarged signals in 7 to 7.8 ppm.</p> Full article ">Figure 3
<p>XPS spectrum of P(VP-APS)(100/0) (<b>A</b>, solid line), Oxi-P(VP-APS)(100/0) (<b>A</b>, dotted line), P(VP-APS)(96/4) (<b>B</b>, solid line) and Oxi-P(VP-APS)(96/4) (<b>B</b>, dotted line).</p> Full article ">Figure 4
<p>Temperature-dependent optical density change of copolymer solutions (P(VP-APS)(100/0) (▲), Oxi-P(VP-APS)(100/0) (○), P(VP-APS)(98/2) (▼), Oxi-P(VP-APS)(98/2) (▽), P(VP-APS)(97.5/2.5) (■), Oxi-P(VP-APS)(97.5/2.5) (□), P(VP-APS)(96/4) (◆) and Oxi-P(VP-APS)(96/4) (◇)).</p> Full article ">Figure 5
<p>Air/water interfacial tension profiles of copolymer solutions ((P(VP-APS)(100/0) (●) and Oxi-P(VP-APS)(100/0) (○) (<b>A</b>), (P(VP-APS)(98/2) (▼) and Oxi-P(VP-APS)(98/2) (▽) (<b>B</b>), P(VP-APS)(97.5/2.5) (■) and Oxi-P(VP-APS)(97.5/2.5) (□) (<b>C</b>), P(VP-APS)(96/4) (◆) and Oxi-P(VP-APS)(96/4) (◇) (<b>D</b>)).</p> Full article ">Figure 6
<p>Time-dependent droplet diameter of O/W emulsions stabilized with P(VP-APS)(100/0) (●,○), P(VP-APS)(98/2) (▲,△), P(VP-APS)(97.5/2.5) (■,□) and P(VP-APS)(96/4) (◆,◇), when distilled water (<b>A</b>) and H<sub>2</sub>O<sub>2</sub> solution (<b>B</b>) were used as the aqueous phase.</p> Full article ">Figure 7
<p>Stability of O/W emulsions stabilized with P(VP-APS)(100/0) (●,○), P(VP-APS)(98/2) (▲,△), P(VP-APS)(97.5/2.5) (■,□) and P(VP-APS)(96/4) (◆,◇), when distilled water (<b>A</b>) and H<sub>2</sub>O<sub>2</sub> solution (<b>B</b>) were used as the aqueous phase.</p> Full article ">
18 pages, 3918 KiB  
Article
The Incorporation of Carvacrol into Poly (vinyl alcohol) Films Encapsulated in Lecithin Liposomes
by Johana Andrade, Chelo González-Martínez and Amparo Chiralt
Polymers 2020, 12(2), 497; https://doi.org/10.3390/polym12020497 - 24 Feb 2020
Cited by 27 | Viewed by 4445
Abstract
Lecithin-encapsulated carvacrol has been incorporated into poly (vinyl alcohol) (PVA) for the purpose of obtaining active films for food packaging application. The influence of molecular weight (Mw) and degree of hydrolysis (DH) of the polymer on its ability to retain carvacrol has been [...] Read more.
Lecithin-encapsulated carvacrol has been incorporated into poly (vinyl alcohol) (PVA) for the purpose of obtaining active films for food packaging application. The influence of molecular weight (Mw) and degree of hydrolysis (DH) of the polymer on its ability to retain carvacrol has been analysed, as well as the changes in the film microstructure, thermal behaviour, and functional properties as packaging material provoked by liposome incorporation into PVA matrices. The films were obtained by casting the PVA aqueous solutions where liposomes were incorporated until reaching 0 (non-loaded liposomes), 5 or 10 g carvacrol per 100 g polymer. The non-acetylated, high Mw polymer provided films with a better mechanical performance, but less CA retention and a more heterogeneous structure. In contrast, partially acetylated, low Mw PVA gave rise to more homogenous films with a higher carvacrol content. Lecithin enhanced the thermal stability of both kinds of PVA, but reduced the crystallinity degree of non-acetylated PVA films, although it did not affect this parameter in acetylated PVA when liposomes contained carvacrol. The mechanical and barrier properties of the films were modified by liposome incorporation in line with the induced changes in crystallinity and microstructure of the films. Full article
(This article belongs to the Special Issue Polymers in Agriculture and Food Science)
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Figure 1

Figure 1
<p>Field Emission Scanning Electron Microscope (FESEM) micrographs of the cross-section of the poly (vinyl) alcohol (PVA) A and B films with lecithin liposomes (L) and carvacrol loaded liposomes (L-CA) (5 or 10 g/100 g PVA) (magnification: 500X; bar: 10 μm).</p> Full article ">Figure 2
<p>X-Ray diffraction spectra of the PVA films (A: left and B: right) without and with carvacrol (5 or 10 g/100 g PVA) previously encapsulated in lecithin liposomes. Percentages of crystallinity are shown for each sample.</p> Full article ">Figure 3
<p>FTIR spectra of the PVA films (A and B) without and with carvacrol (5 or 10 g/100 g PVA) previously encapsulated in lecithin liposomes (L).</p> Full article ">Figure 4
<p>Thermogravimetric analysis (TGA) (left) and DTGA (right) curves of the PVA films (A and B) without and with carvacrol (5 or 10 g/100 g PVA) previously encapsulated in lecithin liposomes (L).</p> Full article ">Figure 5
<p>Differential scanning calorimetry (DSC) curves of the PVA films (A and B) with and without carvacrol (5 or 10 g/100 g PVA) previously encapsulated in lecithin (L). On the left, the first heating scan and on the right the second heating scan.</p> Full article ">
15 pages, 4707 KiB  
Article
Effects of Zirconium Silicide on the Vulcanization, Mechanical and Ablation Resistance Properties of Ceramifiable Silicone Rubber Composites
by Jiuqiang Song, Zhixiong Huang, Yan Qin, Honghua Wang and Minxian Shi
Polymers 2020, 12(2), 496; https://doi.org/10.3390/polym12020496 - 24 Feb 2020
Cited by 38 | Viewed by 3878
Abstract
Ceramifiable silicone rubber composites play important roles in the field of thermal protection systems (TPS) for rocket motor cases due to their advantages. Ceramifiable silicone rubber composites filled with different contents of ZrSi2 were prepared in this paper. The fffects of ZrSi [...] Read more.
Ceramifiable silicone rubber composites play important roles in the field of thermal protection systems (TPS) for rocket motor cases due to their advantages. Ceramifiable silicone rubber composites filled with different contents of ZrSi2 were prepared in this paper. The fffects of ZrSi2 on the vulcanization, mechanical and ablation resistance properties of the composites were also investigated. The results showed that the introduction of ZrSi2 decreased the vulcanization time of silicone rubber. FTIR spectra showed that ZrSi2 did not participate in reactions of the functional groups of silicone rubber. With the increasing content of ZrSi2, the tensile strength increased first and then decreased. The elongation at break decreased and the permanent deformation increased gradually. The thermal conductivity of the composite increased from 0.553 W/(m·K) to 0.694 W/(m·K) as the content of the ZrSi2 increased from 0 to 40 phr. In addition, the thermal conductivity of the composite decreased with the increase of temperature. Moreover, thermal analysis showed that the addition of ZrSi2 increased the initial decomposition temperature of the composite, but had little effect on the peak decomposition temperature in nitrogen. However, the thermal decomposition temperature of the composite in air was lower than that in nitrogen. The addition of ZrSi2 decreased the linear and mass ablation rate, which improved the ablative resistance of the composite. With the ZrSi2 content of 30 phr, the linear and mass ablation rate were 0.041 mm/s and 0.029 g/s, decreasing by 57.5% and 46.3% compared with the composite without ZrSi2, respectively. Consequently, the ceramifiable silicone rubber composite filled with ZrSi2 is very promising for TPS. Full article
(This article belongs to the Special Issue Synthesis–Processing–Structure–Property Interrelationship of Multifunctional Polymer Nanocomposites)
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<p>Vulcanization curves of the ceramifiable silicone rubber composites with different content of ZrSi<sub>2</sub>.</p> Full article ">Figure 2
<p>FTIR spectra of the ceramifiable silicone rubber composites.</p> Full article ">Figure 3
<p>The tensile strength and elongation at break of ceramifiable silicone rubber composites with different content of ZrSi<sub>2</sub>.</p> Full article ">Figure 4
<p>Thermal conductivity of ceramifiable silicone rubber composites with different content of ZrSi<sub>2</sub>.</p> Full article ">Figure 5
<p>Thermal conductivity of ceramifiable silicone rubber composites with different content of ZrSi<sub>2</sub> at different temperature.</p> Full article ">Figure 6
<p>TG (<b>a</b>) and DTG (<b>b</b>) curves of the ceramifiable silicone rubber composites in N<sub>2</sub>.</p> Full article ">Figure 7
<p>TG (<b>a</b>) and DTG (<b>b</b>) curves of the ceramifiable silicone rubber composites in air.</p> Full article ">Figure 8
<p>Linear and mass ablation rate of ceramifiable silicone rubber composites with different content of ZrSi<sub>2</sub>.</p> Full article ">Figure 9
<p>Photographs of ablated composite: (<b>a</b>) Surface; (<b>b</b>) Cross section.</p> Full article ">Figure 10
<p>SEM images for the residue of the ceramifiable silicone rubber composite after ablation: (<b>a</b>) pyrolysis layer of SRZ3; (<b>b</b>) ceramic layer of SRZ3, (<b>c</b>) ceramic layer of SRZ0.</p> Full article ">Figure 11
<p>XRD patterns for the ablation area of the ceramifiable silicone rubber composite after ablation (<b>a</b>) Pyrolysis layer, (<b>b</b>) Ceramic layer.</p> Full article ">Figure 12
<p>Bending strength of the heat-treatment residue of ceramifiable silicone rubber composites with different content of ZrSi<sub>2</sub>.</p> Full article ">
12 pages, 5866 KiB  
Article
Ionic Liquid as Dispersing Agent of LDH-Carbon Nanotubes into a Biodegradable Vinyl Alcohol Polymer
by Valeria Bugatti, Gianluca Viscusi, Antonio Di Bartolomeo, Laura Iemmo, Daniela Clotilde Zampino, Vittoria Vittoria and Giuliana Gorrasi
Polymers 2020, 12(2), 495; https://doi.org/10.3390/polym12020495 - 24 Feb 2020
Cited by 33 | Viewed by 3774
Abstract
A Zn/Al layered double hydroxides (LDHs) hosting carbon nanotubes (80% of CNTs) was synthesized and dispersed into a commercial biodegradable highly amorphous vinyl alcohol polymer at different loading (i.e., 1; 3; 5; 10 wt %). In order to improve the degree of dispersion [...] Read more.
A Zn/Al layered double hydroxides (LDHs) hosting carbon nanotubes (80% of CNTs) was synthesized and dispersed into a commercial biodegradable highly amorphous vinyl alcohol polymer at different loading (i.e., 1; 3; 5; 10 wt %). In order to improve the degree of dispersion of the filler into the polymer matrix, an ionic liquid (IL) based on 1-hexadecyl-3-methylimidazolium dimethyl-5-sodiosulfoisophthalate was added to the composites’ mixtures. Structural characterization of filler and polymeric composites was carried out. The analysis of thermal, mechanical and electrical properties of the composites, resulted improved compared to the unfilled material, allowed to hypothesize a good dispersion of the LDH-CNTs lamellar filler into the polymer matrix-assisted by the ionic liquid. This was demonstrated comparing electrical conductivity of composite at 5% of LDH-CNTs in the presence and in the absence of IL. The experimental results showed that the electrical conductivity of the sample with IL is four orders of magnitude higher than the one without IL. Furthermore, the percolation threshold of the whole system resulted very low—0.26% of LDH-CNTs loading, which is 0.21% of CNTs. Full article
(This article belongs to the Special Issue State-of-the-Art Polymer Science and Technology in Italy (2019,2020))
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<p>SEM analysis of (<b>a</b>) pristine layered double hydroxides (LDH), (<b>b</b>) pristine CNT and (<b>c</b>) LDH-CNT.</p> Full article ">Figure 2
<p>The TGA curves of LDH in nitrate form, the CNTs and the hybrid LDH-CNTs.</p> Full article ">Figure 3
<p>The XRD of LDH in nitrate form, the CNTs and the hybrid LDH-CNTs.</p> Full article ">Figure 4
<p>FTIR of LDH in nitrate form, the CNTs and the hybrid LDH-CNTs.</p> Full article ">Figure 5
<p>XRD spectra of HVOH and all the composites.</p> Full article ">Figure 6
<p>TGA curves for all the composites and the unfilled polymer.</p> Full article ">Figure 7
<p>Elastic modulus, E (MPa), as a function of filler loading.</p> Full article ">Figure 8
<p>(<b>a</b>) Conductivity as a function of the filler loading. The inset shows the sample and measurement setup; (<b>b</b>) I-V characteristics for different filler loading.</p> Full article ">Figure 9
<p>(<b>a</b>) SEM of the sample filled with 3 wt % of LDH-CNT and IL and (<b>b</b>) SEM of the sample filled with 3 wt % of LDH-CNT without IL.</p> Full article ">Scheme 1
<p>Ionic liquid chemical structure.</p> Full article ">
17 pages, 7102 KiB  
Article
A Novel Approach to Optimize the Fabrication Conditions of Thin Film Composite RO Membranes Using Multi-Objective Genetic Algorithm II
by Fekri Abdulraqeb Ahmed Ali, Javed Alam, Arun Kumar Shukla, Mansour Alhoshan, Basem M. A. Abdo and Waheed A. Al-Masry
Polymers 2020, 12(2), 494; https://doi.org/10.3390/polym12020494 - 24 Feb 2020
Cited by 16 | Viewed by 3630
Abstract
This work focuses on developing a novel method to optimize the fabrication conditions of polyamide (PA) thin film composite (TFC) membranes using the multi-objective genetic algorithm II (MOGA-II) method. We used different fabrication conditions for formation of polyamide layer—trimesoyl chloride (TMC) concentration, reaction [...] Read more.
This work focuses on developing a novel method to optimize the fabrication conditions of polyamide (PA) thin film composite (TFC) membranes using the multi-objective genetic algorithm II (MOGA-II) method. We used different fabrication conditions for formation of polyamide layer—trimesoyl chloride (TMC) concentration, reaction time (t), and curing temperature (Tc)—at different levels, and designed the experiment using the factorial design method. Three functions (polynomial, neural network, and radial basis) were used to generate the response surface model (RSM). The results showed that the radial basis predicted good results (R2 = 1) and was selected to generate the RSM that was used as the solver for MOGA-II. The experimental results indicate that TMC concentration and t have the highest influence on water flux, while NaCl rejection is mainly affected by the TMC concentration, t, and Tc. Moreover, the TMC concentration controls the density of the PA, whereas t confers the PA layer thickness. In the optimization run, MOGA-II was used to determine optimal parametric conditions for maximizing water flux and NaCl rejection with constraints on the maximum acceptable levels of Na2SO4, MgSO4, and MgCl2 rejections. The optimized solutions were obtained for longer t, higher Tc, and different TMC concentration levels. Full article
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<p>Protocol steps used to prepare polyamide-thin film composite (PA-TFC) membrane.</p> Full article ">Figure 2
<p>Flow chart of the multi-objective genetic algorithm (MOGA) optimization process.</p> Full article ">Figure 3
<p>Optimization workflow using MOGA-II.</p> Full article ">Figure 4
<p>Scanning electron microscope (SEM) micrographs of the cross section for different PA-TFC membranes; (<b>a</b>–<b>c</b>) 0.1 trimesoyl chloride (TMC) and 15, 30, and 60 s, and (<b>d</b>) 0.2 TMC and 60 s.</p> Full article ">Figure 5
<p>3D topographic atomic force microscope (AFM) images at different fabrication parameters; (<b>a</b>) 0.1 TMC and 15 s, (<b>b</b>) 0.1 TMC and 60 s, and (<b>c</b>) 0.2 TMC and 60 s.</p> Full article ">Figure 6
<p>Differential scanning calorimetric (DSC) curves of polyamide (PA) layers at different reaction times (15, 30, and 60 s).</p> Full article ">Figure 7
<p>ANOVA spline relative strength of input variables and their interactions for all responses.</p> Full article ">Figure 8
<p>Response surface plots, effects of the fabrication parameters on (<b>a</b>) flux, (<b>b</b>,<b>c</b>) NaCl rejection, (<b>d</b>) Na<sub>2</sub>SO<sub>4</sub> rejection, and (<b>e</b>) MgSO<sub>4</sub> rejection.</p> Full article ">Figure 9
<p>Response surface model (RSM) distance charts to used functions (<b>a</b>) polynomial, (<b>b</b>) neural network, and (<b>c</b>) radial basis.</p> Full article ">Figure 10
<p>(<b>a</b>) 3D bubble chart showing the design points obtained with the two objectives (flux and NaCl rejection) and TMC concentration variable; (<b>b</b>) 4D bubble chart showing the design points obtained with two objectives of flux and NaCl rejection and two variables of Tc and t; and (<b>c</b>) 4D bubble chart showing the design points obtained with output variables of flux and NaCl Na<sub>2</sub>SO<sub>4</sub>, and MgSO<sub>4</sub> rejections.</p> Full article ">Figure 11
<p>A parallel coordinate chart for the analysis of fabrication parameters for TFC membrane.</p> Full article ">
11 pages, 2253 KiB  
Article
Experimental Characterization of the Torsional Damping in CFRP Disks by Impact Hammer Modal Testing
by Francesco Cosco, Giuseppe Serratore, Francesco Gagliardi, Luigino Filice and Domenico Mundo
Polymers 2020, 12(2), 493; https://doi.org/10.3390/polym12020493 - 24 Feb 2020
Cited by 10 | Viewed by 3528
Abstract
Composite materials are widely used for their peculiar combination of excellent structural, mechanical, and damping properties. This work presents an experimental study on the dissipation properties of disk-shaped composite specimens exploiting vibration tests. Two different polymer matrix composites with the same number of [...] Read more.
Composite materials are widely used for their peculiar combination of excellent structural, mechanical, and damping properties. This work presents an experimental study on the dissipation properties of disk-shaped composite specimens exploiting vibration tests. Two different polymer matrix composites with the same number of identical laminae, but characterized by different stacking sequences, namely unidirectional and quasi-isotropic configurations, have been evaluated. An ad-hoc steel structure was designed and developed to reproduce an in-plane torsional excitation on the specimen. The main idea of the proposed approach relies on deriving the damping properties of the disks by focusing on the modal damping of the overall vibrating structure and, in particular, using just the first in-plane torsional deformation mode. Experimental torsional damping evaluations were conducted by performing vibrational hammer excitation on the presented setup. Two methods were proposed and compared, both relying on a single-degree-of-freedom (SDOF) approximation of the measured frequency response function (FRF). Full article
(This article belongs to the Section Polymer Analysis and Characterization)
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<p>The experimental test set-up for impact hammer modal testing.</p> Full article ">Figure 2
<p>Drawing of the designed frame setup and disk-shaped sample configurations. CFRP—carbon fiber-reinforced polymer.</p> Full article ">Figure 3
<p>(<b>a</b>) Schematic diagrams of the testing setup: the moment arm behaves as a beam clamped on a rotational compliance; (<b>b</b>) an equivalent damped single degree of freedom system, where <span class="html-italic">M</span>, <span class="html-italic">K</span>, and <span class="html-italic">C</span>, represent the lumped mass, stiffness, and damping, respectively, of the depicted system.</p> Full article ">Figure 4
<p>Modal model as the superposition of different single-degree-of-freedom (SDOF) contributions. FRF—frequency response function.</p> Full article ">Figure 5
<p>Experimental modal analysis of the set-up with the steel disk. The fitted modal model was obtained using five poles, for which the frequencies and damping ratios are reported in <a href="#polymers-12-00493-t002" class="html-table">Table 2</a>.</p> Full article ">Figure 6
<p>Modal shape of the in-plane torsional mode for the steel specimen case.</p> Full article ">Figure 7
<p>Experimental data and best-fit SDOF model for the set-up with (<b>a</b>) the steel specimen, (<b>b</b>) the quasi-isotropic (QI) specimen, (<b>c</b>) the unidirectional configuration (UD)-90° specimen, and (<b>d</b>) the UD-0° specimen.</p> Full article ">
20 pages, 2446 KiB  
Review
Emerging Developments in the Use of Electrospun Fibers and Membranes for Protective Clothing Applications
by Avinash Baji, Komal Agarwal and Sruthi Venugopal Oopath
Polymers 2020, 12(2), 492; https://doi.org/10.3390/polym12020492 - 24 Feb 2020
Cited by 83 | Viewed by 9649
Abstract
There has been increased interest to develop protective fabrics and clothing for protecting the wearer from hazards such as chemical, biological, heat, UV, pollutants etc. Protective fabrics have been conventionally developed using a wide variety of techniques. However, these conventional protective fabrics lack [...] Read more.
There has been increased interest to develop protective fabrics and clothing for protecting the wearer from hazards such as chemical, biological, heat, UV, pollutants etc. Protective fabrics have been conventionally developed using a wide variety of techniques. However, these conventional protective fabrics lack breathability. For example, conventional protective fabrics offer good protection against water but have limited ability in removing the water vapor and moisture. Fibers and membranes fabricated using electrospinning have demonstrated tremendous potential to develop protective fabrics and clothing. These fabrics based on electrospun fibers and membranes have the potential to provide thermal comfort to the wearer and protect the wearer from wide variety of environmental hazards. This review highlights the emerging applications of electrospinning for developing such breathable and protective fabrics. Full article
(This article belongs to the Special Issue Electrospun Nanofibers: Theory and Its Applications)
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<p>Modified electrospinning setup used to collect linear nanofiber assemblies. Reprinted from <span class="html-italic">Macromolecular Materials and Engineering</span>, Vol. 297, Avinash Baji, Yiu-Wing Mai, Xusheng Du, Shing-Chung Wong, Improved tensile strength and ferroelectric phase content of self-assembled polyvinylidene fluoride fiber yarns, 209–213, Copyright (2012), with permission from John Wiley and Sons.</p> Full article ">Figure 2
<p>Conjugated electrospinning setup used to produce nanofiber yarns. Reprinted from <span class="html-italic">RSC Advances</span>, Vol. 5, Zhigang Xie, Haitao Niu, Tong Lin, Continuous polyacrylonitrile nanofiber yarns: preparation and dry-drawing treatment for carbon nanofiber production, 15147–15153, Copyright (2015), with permission from Royal Society of Chemistry.</p> Full article ">Figure 3
<p>Scanning electron microscope (SEM) image of woven structure obtained using the electrospun yarns. Reprinted with permission from John Joseph, Shantikumar V. Nair, Deepthy Menon, Integrating substrateless electrospinning with textile technology for creating biodegradable three-dimensional structures, <span class="html-italic">Nano Letters 2015</span>, Vol 15, 5420–5426. Copyright (2015), American Chemical Society.</p> Full article ">Figure 4
<p>Schematic of the electrofluidodynamic (EFD) process and the corresponding SEM images of the fibers obtained using the EFD process. Reprinted from <span class="html-italic">Journal of Colloid and Interface Science</span>, Vol. 541, Francesca De Falco, Vincenzo Guarino, Gennaro Gentile, Mariacristina Cocca, Veronica Ambrogi, Luigi Ambrosio, Maurizio Avella, Design of functional textile coatings via non-conventional electrofluidodynamic processes, 367–375, Copyright (2019), with permission from Elsevier.</p> Full article ">Figure 5
<p>SEM image shows the microstructure of a woven piezoelectric fabric obtained using the plied yarns. Reprinted with permission from Enlong Yang, Zhe Xu, Lucas K. Chur, Ali Behroozfar, Mahmoud Baniasadi, Salvador Moreno, Jiacheng Huang, Jules Gilligan, Majid Minary-Jolandan, Nanofibrous smart fabrics from twisted yarns of electrospun piezopolymer, <span class="html-italic">ACS Applied Materials and Interfaces 2017</span>, Vol. 9, 24220–24229. Copyright (2017), American Chemical Society.</p> Full article ">Figure 6
<p>(<b>a</b>) Schematic demonstrating the use of yarns for developing electronic fabrics. Briefly, graphene doped polyurethane fibers are deposited on the surface of Ni-coated cotton yarns. These core-shell yarns are then wound around an elastic thread. In the next step, the composite yarns are woven to obtain a fabric. (<b>b</b>) SEM image of the elastic composite yarn. (<b>c</b>) optical microscopy image of the elastic composite yarn. (<b>d</b>) SEM image of the stretched elastic composite yarn. (<b>e</b>) optical microscopy image of the woven electronic fabric. Reprinted from <span class="html-italic">Journal of Materials Chemistry C</span>, Vol. 6, Xiaolu You, Jianxin He, Nan Nan, Xianqiang Sun, Kun Qi, Yuman Zhou, Weili Shao, Fan Liu, Shozhong Cui, Stretchable capacitive fabric electronic skin woven by electrospun nanofiber coated yarns for detecting tactile and multimodal mechanical stimuli, 12981–12991, Copyright (2018), with permission from The Royal Society of Chemistry.</p> Full article ">Figure 7
<p>Waterproof and breathability investigation of an electrospun PAN-modified PDMS membrane. The electrospun PAN modified PDMS membrane is made to cover the beaker with water. Due to the hydrophobicity of the membrane, the water droplets placed on the membrane are restricted from entering the membrane. On the other hand, when the setup is heated, the membrane is permeable to water vapor. Thus, when silica gel is placed on the membrane, it changes its color from blue to pink. Reprinted with permission from Junlu Sheng, Min Zhang, Yue Xu, Jianyong Yu, Bin Ding, Tailoring water-resistant and breathable performance of polyacrylonitrile nanofibrous membranes modified by polydimethylsiloxane, <span class="html-italic">ACS Applied Materials and Interfaces 2016</span>, Vol. 8, 27218–27226. Copyright (2016), American Chemical Society.</p> Full article ">Figure 8
<p>Plot of % survival of bacterial colonies against time for ZnO/TiO<sub>2</sub> composite (red dots) fibers and TiO<sub>2</sub> fibers (black hollow squares) against Staphylococcus aureus in the absence of light. The inset demonstrates the bacterial colonies. Reprinted from <span class="html-italic">Chemical Communications</span>, Vol. 47, Sun Hye Hwang, Jooyoung Song, Yujung Jung, O. Young Kweon, Hee Song, Jyongsik Jang, Electrospun ZnO/TiO<sub>2</sub> composite nanofibers as a bactericidal agent, 9164–9166, Copyright (2011), with permission from The Royal Society of Chemistry.</p> Full article ">Figure 9
<p>Digital photograph demonstrating the flame-retardant ability of the Hec/BBB membrane. Hec/BBB membrane is brought in contact with a flame and a cotton ball is held on the other side of the membrane. The membrane is demonstrated to block the flame and protect the cotton ball. Reprinted with permission from Jian Zhu, Josef Breu, Haoqing Hou, Andreas Greiner, Seema Agarwal, Gradient-structured nonflammable flexible polymer membranes, <span class="html-italic">ACS Applied Materials and Interfaces 2019</span>, Vol. 11, 11876–11883. Copyright (2019), American Chemical Society.</p> Full article ">
17 pages, 5939 KiB  
Article
Effects of Adhesive Coating on the Hygrothermal Aging Performance of Pultruded CFRP Plates
by Xinkai Hao, Guijun Xian, Xiangyu Huang, Meiyin Xin and Haijuan Shen
Polymers 2020, 12(2), 491; https://doi.org/10.3390/polym12020491 - 23 Feb 2020
Cited by 3 | Viewed by 2473
Abstract
Bonding of carbon fiber reinforced polymer (CFRP) plates to a concrete member is a widely used strengthening method. CFRP plates used in construction degrade due to harsh environmental conditions such as high temperature or alkaline solution seepage from concrete. However, the adhesive between [...] Read more.
Bonding of carbon fiber reinforced polymer (CFRP) plates to a concrete member is a widely used strengthening method. CFRP plates used in construction degrade due to harsh environmental conditions such as high temperature or alkaline solution seepage from concrete. However, the adhesive between CFRP plates and concrete may have a positive effect on the durability performance of CFRP plates. In this paper, the long-term performance of both naked and adhesive coated CFRP pultruded plates subjected to different-temperature water or alkaline solution (20, 40 and 60 °C) are investigated to evaluate the protective effect of adhesive on CFRP plates. It is found that the adhesive coating can slow the deterioration of mechanical properties especially the tensile properties and fiber-matrix interfacial properties. The water absorption mechanism of CFRP plates was also investigated. Full article
(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers II: Procedures and Reliability)
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<p>Coating CFRP plate.</p> Full article ">Figure 2
<p>Adhesive coated CFRP plate.</p> Full article ">Figure 3
<p>Specimens immersed in: (<b>a</b>) Water; (<b>b</b>) Alkaline solution.</p> Full article ">Figure 4
<p>In-plane shear test: (<b>a</b>) Realistic diagram; (<b>b</b>) Schematic diagram.</p> Full article ">Figure 5
<p>Water uptake of: (<b>a</b>) Naked plate immersed in water; (<b>b</b>) Naked plate immersed in alkaline solution; (<b>c</b>) Coated plate immersed in water; (<b>d</b>) Coated plate immersed in alkaline solution. In <a href="#polymers-12-00491-f005" class="html-fig">Figure 5</a>a,b the solid lines represent the two-stage model curve fittings.</p> Full article ">Figure 6
<p>Coated specimen (left side) and naked specimen (right side) immersed in 60 °C alkaline solution for 135 days.</p> Full article ">Figure 7
<p>Cross-Section of (<b>a</b>) Coated CFRP plate; (<b>b</b>) Naked CFRP plate.</p> Full article ">Figure 8
<p>Water uptake of T1 adhesive.</p> Full article ">Figure 9
<p>Thermogravimetric analysis of specimens immersed for 135 days.</p> Full article ">Figure 10
<p>Variation of T<sub>g</sub> for: (<b>a</b>) Naked plate immersed in water; (<b>b</b>) Naked plate immersed in Alkaline solution; (<b>c</b>) Coated plate immersed in water; (<b>d</b>) Coated plate immersed in Alkaline solution.</p> Full article ">Figure 11
<p>Comparison of tan δ between initial specimens and those immersed for three months.</p> Full article ">Figure 12
<p>Tensile strength of: (<b>a</b>) Naked plate immersed in water; (<b>b</b>) Naked plate immersed in alkaline solution; (<b>c</b>) Coated plate immersed in water; (<b>d</b>) Coated plate immersed in alkaline solution.</p> Full article ">Figure 13
<p>Tensile strength retention of specimens immersed for three months.</p> Full article ">Figure 14
<p>Tensile stress/strain relationship of naked CFRP plate immersed in alkaline solution for 90 days.</p> Full article ">Figure 15
<p>Tensile modulus of: (<b>a</b>) Naked plate immersed in water; (<b>b</b>) Naked plate immersed in alkaline solution; (<b>c</b>) Coated plate immersed in water; (<b>d</b>) Coated plate immersed in alkaline solution.</p> Full article ">Figure 16
<p>Tensile modulus retention of specimens immersed for three months.</p> Full article ">Figure 17
<p>FTIR of the initial CFRP plate and that immersed for 135 days (numbers in the figure shows the specific value of the spectrum of absorption).</p> Full article ">Figure 18
<p>In-Plane shear strength of: (<b>a</b>) Naked plate immersed in water; (<b>b</b>) Naked plate immersed in alkaline solution; (<b>c</b>) Coated plate immersed in water; (<b>d</b>) Coated plate immersed in alkaline solution.</p> Full article ">Figure 19
<p>In-Plane shear strength retention of specimens immersed for three months.</p> Full article ">
11 pages, 4358 KiB  
Article
Effect of Phenolic Resin Oligomer Motion Ability on Energy Dissipation of Poly (Butyl Methacrylate)/Phenolic Resins Composites
by Xing Huang, Songbo Chen, Songhan Wan, Ben Niu, Xianru He and Rui Zhang
Polymers 2020, 12(2), 490; https://doi.org/10.3390/polym12020490 - 23 Feb 2020
Cited by 8 | Viewed by 3190
Abstract
Poly (butyl methacrylate) (PBMA) was blended with a series of phenolic resins (PR) to study the effect of PR molecular weight on dynamic mechanical properties of PBMA/PR composites. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) found a similar variation of glass [...] Read more.
Poly (butyl methacrylate) (PBMA) was blended with a series of phenolic resins (PR) to study the effect of PR molecular weight on dynamic mechanical properties of PBMA/PR composites. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) found a similar variation of glass transition temperature (Tg). The maximum loss peak (tanδmax) improved in all PBMA/PR blends compared with the pure PBMA. However, tanδmax reduced as the molecular weight increased. This is because PR with higher molecular weight is more rigid in the glass transition zone of blends. The hydrogen bonding between PBMA and PR was characterized by Fourier transform infrared spectroscopy (FTIR). Lower molecular weight PR formed more hydrogen bonds with the matrix and it had weaker temperature dependence. Combined with the results from DMA, we studied how molecular weight affected hydrogen bonding and thus further affected tanδmax. Full article
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<p>Chemical structures of (<b>a</b>) poly (butyl methacrylate); (<b>b</b>) phenolic resin.</p> Full article ">Figure 2
<p>Infrared spectra of poly (butyl methacrylate) (PBMA) and B01.</p> Full article ">Figure 3
<p>The differential scanning calorimetry (DSC) thermograms of PBMA, (<b>a</b>) PR with different molecular weights and (<b>b</b>) PBMA/PR blends.</p> Full article ">Figure 4
<p>Tg of five hybrid systems with different molecular weights.</p> Full article ">Figure 5
<p>Temperature dependence of tanδ for (<b>a</b>) PBMA/A04 with different loadings, (<b>b</b>) PBMA, B01,B02, B03 B04, and B05.</p> Full article ">Figure 6
<p>Schematic diagram of the recombination of hydrogen bonds as strain occurs.</p> Full article ">Figure 7
<p>Temperature dependence of storage modulus for (<b>a</b>) PBMA/A04 with different loadings, (<b>b</b>) PBMA, B02, B03, B04, and B05.</p> Full article ">Figure 8
<p>Temperature dependence of fourier transform infrared spectroscopy (FTIR) spectra in the carbonyl stretching region: (<b>a</b>) B04; (<b>b</b>) B01.</p> Full article ">Figure 9
<p>Curve fitting results in the carbonyl stretching region of B04 at 170 °C.</p> Full article ">Figure 10
<p>The fraction of hydrogen bonded carbonyl of the samples as a function of temperature.</p> Full article ">
20 pages, 3482 KiB  
Article
Multi-Trigger Thermo-Electro-Mechanical Soft Actuators under Large Deformations
by Ebrahim Yarali, Reza Noroozi, Armin Yousefi, Mahdi Bodaghi and Mostafa Baghani
Polymers 2020, 12(2), 489; https://doi.org/10.3390/polym12020489 - 23 Feb 2020
Cited by 18 | Viewed by 3872
Abstract
Dielectric actuators (DEAs), because of their exceptional properties, are well-suited for soft actuators (or robotics) applications. This article studies a multi-stimuli thermo-dielectric-based soft actuator under large bending conditions. In order to determine the stress components and induced moment (or stretches), a nominal Helmholtz [...] Read more.
Dielectric actuators (DEAs), because of their exceptional properties, are well-suited for soft actuators (or robotics) applications. This article studies a multi-stimuli thermo-dielectric-based soft actuator under large bending conditions. In order to determine the stress components and induced moment (or stretches), a nominal Helmholtz free energy density function with two types of hyperelastic models are employed. Non-linear electro-elasticity theory is adopted to derive the governing equations of the actuator. Total deformation gradient tensor is multiplicatively decomposed into electro-mechanical and thermal parts. The problem is solved using the second-order Runge-Kutta method. Then, the numerical results under thermo-mechanical loadings are validated against the finite element method (FEM) outcomes by developing a user-defined subroutine, UHYPER in a commercial FEM software. The effect of electric field and thermal stimulus are investigated on the mean radius of curvature and stresses distribution of the actuator. Results reveal that in the presence of electric field, the required moment to actuate the actuator is smaller. Finally, due to simplicity and accuracy of the present boundary problem, the proposed thermally-electrically actuator is expected to be used in future studies and 4D printing of artificial thermo-dielectric-based beam muscles. Full article
(This article belongs to the Special Issue Polymer-Based Soft Electronics)
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<p>Experimental data [<a href="#B57-polymers-12-00489" class="html-bibr">57</a>] and the model prediction for VHB 4910 in two parts, (<b>a</b>) relativedielectric constant at frequency of 100Hz; (<b>b</b>) hyperelastic response at strain rate of 0.01 s.</p> Full article ">Figure 2
<p>A schematic of plane-strain bending of a soft dielectric-based actuator under a thermo-electro-mechanical loading.</p> Full article ">Figure 3
<p>Variation of analytical and finite element method (FEM) (<b>a</b>) radial; (<b>b</b>) hoop stresses through the beam thickness with <span class="html-italic">ρ</span> = 0.5 m for two hyperelastic models. Analytical (ANL) stands for semi-analytical solution results.</p> Full article ">Figure 4
<p>Variation of analytical and FEM (<b>a</b>) radial; (<b>b</b>) hoop stress through the beam thickness under <span class="html-italic">ρ</span> = 0.5 m and Δ<span class="html-italic">T</span> = 50 °C for two types of strain energy functions.</p> Full article ">Figure 5
<p>The effect of temperature gradients on (<b>a</b>) radial stress; (<b>b</b>) hoop stress; (<b>c</b>) induced moment for Mooney-Rivlin model in the absence of electric field at <span class="html-italic">ρ</span> = 0.3 m.</p> Full article ">Figure 6
<p>The effect of the electric field on (<b>a</b>) radial stress; (<b>b</b>) hoop stress; (<b>c</b>) induced moment for Mooney-Rivlin model with <span class="html-italic">ρ</span> = 0.5 m in the absence of temperature differences.</p> Full article ">Figure 7
<p>The effect of applied mean radius of curvature on (<b>a</b>) radial stress; (<b>b</b>) hoop stress; (<b>c</b>) induced moment for the exp-exp model at <span class="html-italic">E</span><sub>1</sub> = 20 MV·m<sup>−1</sup> and Δ<span class="html-italic">T</span> = 0 °C.</p> Full article ">Figure 8
<p>The effect of electric field on (<b>a</b>) radial stress; (<b>b</b>) hoop stress; (<b>c</b>) induced moment for Mooney-Rivlin model with <span class="html-italic">ρ</span> = 0.5 m and Δ<span class="html-italic">T</span> = 40 °C.</p> Full article ">Figure 9
<p>The effect of applied mean radius of curvature on (<b>a</b>) radial stress; (<b>b</b>) hoop stress; (<b>c</b>) induced moment for exp-exp model with <span class="html-italic">E</span><sub>1</sub> = 20 MV·m<sup>−1</sup> and Δ<span class="html-italic">T</span> = 40 °C.</p> Full article ">Figure 10
<p>Variations of electric induction for exp-exp model with different (<b>a</b>) temperature gradients at <span class="html-italic">E</span><sub>1</sub> = 10 MV·m<sup>−1</sup><span class="html-italic">, ρ</span> = 0.4 m; (<b>b</b>) electric fields at Δ<span class="html-italic">T</span> = 0 °C, <span class="html-italic">ρ</span> = 0.4 m; (<b>c</b>) applied mean radius of curvature at Δ<span class="html-italic">T</span> = 0 °C and <span class="html-italic">E</span><sub>1</sub> = 10 MV·m<sup>−1</sup>.</p> Full article ">
16 pages, 2882 KiB  
Article
Dynamic Compression Induced Solidification
by Benedikt Roth, Wolfgang Wildner and Dietmar Drummer
Polymers 2020, 12(2), 488; https://doi.org/10.3390/polym12020488 - 22 Feb 2020
Cited by 3 | Viewed by 2910
Abstract
This study presents a method for the determination of the dynamic pressure-dependent solidification of polycarbonate (PC) during flow using high pressure capillary rheometer (HPC) measurements. In addition, the pressure-dependent solidification was determined by isothermal pressure-volume-temperature (pvT) measurements under static conditions without shear. Independent [...] Read more.
This study presents a method for the determination of the dynamic pressure-dependent solidification of polycarbonate (PC) during flow using high pressure capillary rheometer (HPC) measurements. In addition, the pressure-dependent solidification was determined by isothermal pressure-volume-temperature (pvT) measurements under static conditions without shear. Independent of the compression velocity, a linear increase of the solidification pressure with temperature could be determined. Furthermore, the results indicate that the relaxation time at a constant temperature and compression rate can increase to such an extent that the material can no longer follow within the time scale specified by the compression rate. Consequently, the flow through the capillary stops at a specific pressure, with higher compression rates resulting in lower solidification pressures. Consequently, in regard to HPC measurements, it could be shown that the evaluation of the pressure via a pressure hole can lead to measurement errors in the limit range. Since the filling process in injection molding usually takes place under such transient conditions, the results are likely to be relevant for modelling the flow processes of thin-walled and microstructures with high aspect ratios. Full article
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<p>Melt flow during compression in pressure-induced solidification (CIS); <b>1</b>: No Compression; <b>2</b>: Beginning compression; <b>3</b>: End of Compression; black arrows indicates the compression direction.</p> Full article ">Figure 2
<p>Schematic drawing of the counter pressure Rheograph 75 with the pressure sensor behind the pressure hole; adapted according to [<a href="#B53-polymers-12-00488" class="html-bibr">53</a>]; <span class="html-italic">r</span><sub>p</sub>: piston radius; <span class="html-italic">v</span><sub>P</sub>: piston velocity; <span class="html-italic">r</span><sub>c</sub>: capillary radius; <span class="html-italic">l<sub>c</sub></span>: capillary length.</p> Full article ">Figure 3
<p>Calculated isothermal compressibility for evaluation of solidification pressure in pvT measurements, adapted according to [<a href="#B54-polymers-12-00488" class="html-bibr">54</a>]; <span class="html-italic">p</span><sub>g,E</sub>: pressure of ending solidification; <span class="html-italic">p</span><sub>g,B</sub>: pressure of beginning solidification.</p> Full article ">Figure 4
<p>Determination of the solidification by evaluation of the pressure difference in HPC measurements; p1: Pressure transducer measuring cavity p2: Pressure transducer counter pressure chamber p<sub>p</sub>: Pressure calculated from piston force; (<b>a</b>) pressure signals as a function of time; (<b>b</b>) pressure difference p<sub>p</sub>-p1 as a function of p<sub>p</sub>; (<b>c</b>) first derivation of (<b>b</b>) with respect to p<sub>p</sub>.</p> Full article ">Figure 5
<p>Isothermal pvT-measurements (<b>a</b>) and calculated specific compressibility according to Equation (1) (<b>b</b>).</p> Full article ">Figure 6
<p>Second derivative of the specific volume (<b>a</b>) and evaluation of the temperature dependent glass transition (<b>b</b>); <span class="html-italic">p</span><sub>g,B</sub>: pressure of beginning solidification; <span class="html-italic">p</span><sub>g,E</sub>: pressure of ending solidification; <span class="html-italic">T</span><sub>g,B</sub>: temperature of beginning solidification; <span class="html-italic">T</span><sub>g;E</sub>: temperature of ending solidification.</p> Full article ">Figure 7
<p>Pressures p1, p2 and p<sub>p</sub> for the Temperatures 220 (<b>a</b>), 230 (<b>b</b>), 240 (<b>c</b>) and 250 °C (<b>d</b>); the velocity of the piston was 0.0056 mm/s.</p> Full article ">Figure 8
<p>Evaluation of the beginning of solidification at different compression velocities. The ordinates of the graphs show the first derivative of the difference of the pressure signals p1 and p<sub>p</sub>. The vertical red lines indicate the range for building the linear fit. The crosses mark the intersections with the x-axis for the different temperatures; (<b>a</b>): 0.0028 mm/s; (<b>b</b>): 0.0056 mm/s; (<b>c</b>): 0.028 mm/s.</p> Full article ">Figure 9
<p>Pressure of solidification <span class="html-italic">P</span><sub>g</sub> in relation to the temperature for the four different measurements: isothermal pvT-measurement, dynamic solidification with a closed counter pressure chamber and a piston velocity of 0.0028 mm/s, 0.0056 mm/s and 0.028 mm/s.</p> Full article ">Figure 10
<p>HPC measurements as a function of a measurement instrument independent compression rate ψ (<b>a</b>); calculation of a master curve by shifting the measurements with a shift factor α (<b>b</b>); logarithmic shift factor α as a function of the temperature difference to the reference temperature of 250 °C (<b>c</b>).</p> Full article ">
15 pages, 3914 KiB  
Article
Doubly Dynamic Hydrogel Formed by Combining Boronate Ester and Acylhydrazone Bonds
by Yusheng Liu, Yigang Liu, Qiuxia Wang, Yugui Han, Hao Chen and Yebang Tan
Polymers 2020, 12(2), 487; https://doi.org/10.3390/polym12020487 - 21 Feb 2020
Cited by 25 | Viewed by 5596
Abstract
The incorporation of double dynamic bonds into hydrogels provides an effective strategy to engineer their performance on demand. Herein, novel hydrogels were PREPARED by combining two kinetically distinct dynamic covalent bonds, boronate ester and acylhydrazone bonds, and the synergistic properties of the hydrogels [...] Read more.
The incorporation of double dynamic bonds into hydrogels provides an effective strategy to engineer their performance on demand. Herein, novel hydrogels were PREPARED by combining two kinetically distinct dynamic covalent bonds, boronate ester and acylhydrazone bonds, and the synergistic properties of the hydrogels were studied comprehensively. The functional diblock copolymers P(N-isopropyl acrylamide-co-N-acryloyl-3-aminophenylboronic acid)-b-(N-isopropyl acrylamide-co-diacetone acrylamide) (PAD) were prepared via reversible addition−fragmentation chain transfer (RAFT) polymerization. The hydrogel was constructed by exploiting dynamic reaction of phenyboronic acid moieties with polyvinyl alcohol (PVA) and ketone moieties with adipic dihydrazide (ADH) without any catalyst. The active boronate ester linkage endows the hydrogel with fast gelation kinetics and self-healing ability, and the stable acylhydrazone linkage can enhance the mechanical property of the hydrogel. The difference in kinetics endows that the contribution of each linkage to mechanical strength of the hydrogel can be accurately estimated. Moreover, the mechanical property of the hydrogel can be readily engineered by changing the composition and solid content, as well as by controlling the formation or dissociation of the dynamic linkages. Thus, we provide a promising strategy to design and prepare multi-responsive hydrogels with tunable properties. Full article
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<p><sup>1</sup>H NMR spectra of (<b>a</b>) PAD and (<b>c</b>) PA in CD<sub>3</sub>OD, and (<b>b</b>) PD in D<sub>2</sub>O.</p> Full article ">Figure 2
<p>Storage and loss modulus of (<b>a</b>) singly acylhydrazone-crosslinked hydrogels with varying molar ratios of ketone to hydrazine and (<b>b</b>) singly boronate ester-crosslinked hydrogels with varying mass ratios of PVA to PAD2. The concentration of PAD2 is fixed to 10 wt%. The data were obtained with a strain of 1.0% and a frequency of 1 Hz.</p> Full article ">Figure 3
<p>Oscillatory time sweep experiments of the (<b>a</b>) single acylhydrazone-crosslinked hydrogels with different polymer concentrations, the molar ratios of ketone to hydrazine are fixed to 1.0; (<b>b</b>) single boronate ester-crosslinked hydrogels and double DCBs-crosslinked hydrogels (the PAD concentration is fixed to 10 wt%, the mass ratios of PAD to polyvinyl alcohol (PVA) are fixed to 0.5 and the molar ratios of ketone to hydrazine are fixed to 1.0); (<b>c</b>) storage modulus of the doubly DCBs-crosslinked hydrogels at different time during the gelation. All the experiments were performed at a frequency of 1.0 Hz and a strain of 1.0%.</p> Full article ">Figure 4
<p>(<b>a</b>) frequency sweeps with a strain of 1.0% of the single/double DCBs-crosslinked hydrogels; storage modulus of double DCBs-crosslinked hydrogels at 2 h (bottom) and 48 h (whole) during the gelation with different composition and copolymer concentrations, the molar ratios of ketone to hydrazine is fixed to 1.0, (<b>b</b>) mass ratios of PVA to PAD are fixed to 0.5 and (<b>c</b>) mass ratios of PVA to PAD are fixed to 0.1. All the experiments were performed at a frequency of 1.0 Hz and a strain of 1.0%; (<b>d</b>) tensile tests of single/double DCBs-crosslinked hydrogels. The stretching rate of the samples is 50 mm min<sup>−1</sup>.</p> Full article ">Figure 5
<p>(<b>a</b>) self-healing behaviour of single/double DCBs-crosslinked hydrogels, (a1) PAD2@ADH, (a2) PAD2@PVA, (a3) PAD2@PVA@ADH. The hydrogels were coloured by carmine (red) or methylene blue (blue). Repeated dynamic strain sweep tests with a frequency of 1.0 Hz, (<b>b</b>) PAD2@ADH, (<b>c</b>) PAD2@PVA, (<b>d</b>) PAD2@PVA@ADH.</p> Full article ">Figure 6
<p>Photographs of phase transitions of PAD2@PVA@ADH hydrogel, (<b>a</b>) pH-triggered gel-sol-gel and (<b>b</b>) fructose and ADH; (<b>c</b>) storage/loss modulus of the hydrogel under different chemical stimuli.</p> Full article ">Figure 7
<p>(<b>a</b>) storage modulus PAD2@PVA@ADH hydrogels with different malar ratios of ketone to acyhydrazine; (<b>b</b>) storage modulus of PAD2@PVA@ADH hydrogel treated with fructose.</p> Full article ">Scheme 1
<p>(<b>a</b>) synthesis route for the preparation of diblock copolymer P(<span class="html-italic">N</span>-isopropyl acrylamide-co-<span class="html-italic">N</span>-acryloyl-3-aminophenylboronic acid)-b-(<span class="html-italic">N</span>-isopropyl acrylamide-co-diacetone acrylamide) (PAD) via reversible addition−fragmentation chain transfer (RAFT) polymerization; (<b>b</b>) schematic for the preparation of the double DCB-based hydrogel.</p> Full article ">
12 pages, 5521 KiB  
Article
Temperature and pH-Dependent Response of Poly(Acrylic Acid) and Poly(Acrylic Acid-co-Methyl Acrylate) in Highly Concentrated Potassium Chloride Aqueous Solutions
by Aleksander Sinek, Maria Kupczak, Anna Mielańczyk, Marcin Lemanowicz, Shin-ichi Yusa, Dorota Neugebauer and Andrzej Gierczycki
Polymers 2020, 12(2), 486; https://doi.org/10.3390/polym12020486 - 21 Feb 2020
Cited by 7 | Viewed by 6199
Abstract
In this study, the phase transition phenomena of linear poly(acrylic acid) (PAA) and linear or star-shaped poly(acrylic acid-co-methyl acrylate) (P(AA-co-MA)) in highly concentrated KCl solutions were investigated. The effects of polymer molecular weight, topology, and composition on their phase [...] Read more.
In this study, the phase transition phenomena of linear poly(acrylic acid) (PAA) and linear or star-shaped poly(acrylic acid-co-methyl acrylate) (P(AA-co-MA)) in highly concentrated KCl solutions were investigated. The effects of polymer molecular weight, topology, and composition on their phase transition behavior in solution were investigated. The cloud point temperature (TCP) of polymers drastically increased as the KCl concentration (CKCl) and solution pH increased. CKCl strongly influenced the temperature range at which the phase transition of PAA occurred: CKCl of 1.0–2.2 M allowed the phase transition to occur between 30 and 75 °C. Unfortunately, at CKCl above 2.6 M, the TCP of PAA was too high to theoretically trigger the crystallization of KCl. The addition of hydrophobic methyl acrylate moieties decreased the TCP into a temperature region where KCl crystallization could occur. Additionally, the hydrodynamic diameters (Dh) and zeta potentials of commercial PAA samples were examined at room temperature and at their TCP using dynamic light scattering. The salt concentration (from 1 to 3 M) did not impact the hydrodynamic diameter of the molecules. Dh values were 1500 and 15 nm at room temperature and at TCP, respectively. Full article
(This article belongs to the Section Polymer Processing and Engineering)
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<p>The cloud point temperature (<span class="html-italic">T</span><sub>CP</sub>) curves for 0.25% L1 in KCl solutions with different concentrations without HCl (<b>a</b>) and after the addition of 140 μL HCl (<b>b</b>).</p> Full article ">Figure 2
<p><span class="html-italic">T</span><sub>CP</sub> curves for 0.25% L1 in a 3 M KCl solution (<b>a</b>) and 2.2 M KCl (<b>b</b>); the linear decrease of <span class="html-italic">T</span><sub>CP</sub> of 0.25% L1 as the volume of 0.01 M HCl increased in 3.0 M KCl (<b>c</b>) and 2.2 M KCl solutions (<b>d</b>).</p> Full article ">Figure 3
<p>Comparison between the KCl solubility curve and <span class="html-italic">T</span><sub>CP</sub> of L1 at different pH values.</p> Full article ">Figure 4
<p>Hydrodynamic diameters (<span class="html-italic">D</span><sub>h</sub>) of 0.25% L1 for various KCl concentrations at 25 °C (dots) and at <span class="html-italic">T</span><sub>CP</sub> (triangles) (<b>a</b>); particle size distribution of 0.25% L1 in 3 M KCl solution at different temperatures (<b>b</b>); zeta potential (ZP) of 1% L1 in water at 25 °C (<b>c</b>).</p> Full article ">Figure 5
<p>Scanning electron microscopy (SEM) micrographs of pure KCl (<b>A</b>,<b>B</b>) and L1 in 3 M KCl (<b>C</b>,<b>D</b>).</p> Full article ">Figure 6
<p>The influence of KCl concentration on the transmittance (%<span class="html-italic">T</span>) of the L4 solution (0.25% <span class="html-italic">w</span>/<span class="html-italic">w</span>).</p> Full article ">Figure 7
<p><sup>1</sup>H nuclear magnetic resonance (NMR) (600 MHz) spectra of star-shaped P(<span class="html-italic">t</span>BuA-<span class="html-italic">co</span>-MA) in CDCl<sub>3</sub> (<b>a</b>) and the product of its acidolysis S1 in CD<sub>3</sub>OD (<b>b</b>).</p> Full article ">Figure 8
<p><span class="html-italic">T</span><sub>CP</sub> values of poly(acrylic acid) (PAA) (L1), linear poly(acrylic acid-<span class="html-italic">co</span>-methyl acrylate) (P(AA-<span class="html-italic">co</span>-MA)) (L6), and star-shaped P(AA-<span class="html-italic">co</span>-MA) (S1) with different concentrations as a function of pH.</p> Full article ">Scheme 1
<p>The two-step procedure used to obtain linear and star-shaped acrylic acid (AA)/MA copolymers.</p> Full article ">
12 pages, 1949 KiB  
Article
Structural Changes of Oak Wood Main Components Caused by Thermal Modification
by Ivan Kubovský, Danica Kačíková and František Kačík
Polymers 2020, 12(2), 485; https://doi.org/10.3390/polym12020485 - 21 Feb 2020
Cited by 198 | Viewed by 7370
Abstract
Thermal modification of wood causes chemical changes that significantly affect the physical, mechanical and biological properties of wood; thus, it is essential to investigate these changes for better utilization of products. Fourier transform infrared spectroscopy and size exclusion chromatography were used for evaluation [...] Read more.
Thermal modification of wood causes chemical changes that significantly affect the physical, mechanical and biological properties of wood; thus, it is essential to investigate these changes for better utilization of products. Fourier transform infrared spectroscopy and size exclusion chromatography were used for evaluation of chemical changes at thermal treatment of oak wood. Thermal modification was applied according to Thermowood process at the temperatures of 160, 180 and 210 °C, respectively. The results showed that hemicelluloses are less thermally stable than cellulose. Chains of polysaccharides split to shorter ones leading to a decrease of the degree of polymerization and an increase of polydispersity. At the highest temperature of the treatment (210 °C), also crosslinking reactions take place. At lower temperatures degradation reactions of lignin predominate, higher temperatures cause mainly condensation reactions and a molecular weight increase. Chemical changes in main components of thermally modified wood mainly affect its mechanical properties, which should be considered into account especially when designing various timber constructions. Full article
(This article belongs to the Special Issue Degradation of Wood-Based Materials)
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<p>FTIR spectra of the thermally treated lignin from oak wood.</p> Full article ">Figure 2
<p>FTIR spectra of the thermally treated holocellulose from oak wood.</p> Full article ">Figure 3
<p>FTIR spectra of the thermally treated cellulose from oak wood.</p> Full article ">Figure 4
<p>Molecular weight distribution of oak wood lignin before and after thermal treatment.</p> Full article ">Figure 5
<p>Molecular weight distribution of oak wood holocellulose before and after thermal treatment.</p> Full article ">Figure 6
<p>Molecular weight distribution of oak wood cellulose before and after thermal treatment.</p> Full article ">
18 pages, 4006 KiB  
Article
Drying of the Natural Fibers as A Solvent-Free Way to Improve the Cellulose-Filled Polymer Composite Performance
by Stefan Cichosz and Anna Masek
Polymers 2020, 12(2), 484; https://doi.org/10.3390/polym12020484 - 21 Feb 2020
Cited by 20 | Viewed by 4634
Abstract
When considering cellulose (UFC100) modification, most of the processes employ various solvents in the role of the reaction environment. The following article addresses a solvent-free method, thermal drying, which causes a moisture content decrease in cellulose fibers. Herein, the moisture content in UFC100 [...] Read more.
When considering cellulose (UFC100) modification, most of the processes employ various solvents in the role of the reaction environment. The following article addresses a solvent-free method, thermal drying, which causes a moisture content decrease in cellulose fibers. Herein, the moisture content in UFC100 was analyzed with spectroscopic methods, thermogravimetric analysis, and differential scanning calorimetry. During water desorption, a moisture content drop from approximately 6% to 1% was evidenced. Moreover, drying may bring about a specific variation in cellulose’s chemical structure. These changes affected the cellulose-filled polymer composite’s properties, e.g., an increase in tensile strength from 17 MPa for the not-dried UFC100 to approximately 30 MPa (dried cellulose; 24 h, 100 °C) was observed. Furthermore, the obtained tensile test results were in good correspondence with Payne effect values, which changed from 0.82 MPa (not-dried UFC100) to 1.21 MPa (dried fibers). This raise proves the reinforcing nature of dried UFC100, as the Payne effect is dependent on the filler structure’s development within a polymer matrix. This finding paves new opportunities for natural fiber applications in polymer composites by enabling a solvent-free and efficient cellulose modification approach that fulfils the sustainable development rules. Full article
(This article belongs to the Special Issue Cellulose and Renewable Materials)
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<p>Ethylene–norbornene copolymer structure.</p> Full article ">Figure 2
<p>FT-IR spectra of the cellulose fibers that were dried for 1440 min at 100 °C and then left to adsorb moisture for different times. Characteristic absorption bands: 3334 cm<sup>−1</sup> (O–H, water), 2894 cm<sup>−1</sup> (C–H), 1200–900 cm<sup>−1</sup> (O–H, C–O, –COO, CO–O–CO), and 558 cm<sup>−1</sup> (C–OH, C–C).</p> Full article ">Figure 3
<p>FT-IR spectra of the cellulose fibers that were dried for 45, 90, 180, and 1440 min at 100 °C. Characteristic absorption bands: 3334 cm<sup>−1</sup> (O–H, water), 2894 cm<sup>−1</sup> (C–H), 1200–900 cm<sup>−1</sup> (O–H, C–O, –COO, CO–O–CO), and 558 cm<sup>−1</sup> (C–OH, C–C).</p> Full article ">Figure 4
<p>Moisture content changes during the water adsorption and desorption processes. (<b>a</b>) Normalized moisture level variations in time according to the sample mass changes and (<b>b</b>) Fischer titration experiment results.</p> Full article ">Figure 5
<p>Thermogravimetric analysis (TGA) curves of the dried (1440 min, 100 °C) and not-dried cellulose fibers.</p> Full article ">Figure 6
<p>Images of (<b>a</b>) the polymer matrix (ethylene–norbornene copolymer), (<b>b</b>) the cellulose powder, and (<b>c</b>) the polymer composite sample.</p> Full article ">Figure 7
<p>Mechanical properties of the investigated composite samples. (<b>a</b>) Tensile strength and (<b>b</b>) elongation at break.</p> Full article ">Figure 8
<p>Storage modulus, loss modulus, and tanδ changes of the ethylene–norbornene copolymer (TOPAS) that was filled with cellulose fibers and dried for different times. (<b>a</b>) Not-dried, (<b>b</b>) dried for 45 min, (<b>c</b>) dried for 180 min, (<b>d</b>) and dried for 1440 min.</p> Full article ">
15 pages, 17232 KiB  
Article
Effect of PEW and CS on the Thermal, Mechanical, and Shape Memory Properties of UHMWPE
by Run Zhang, Suwei Wang, Jing Tian, Ke Chen, Ping Xue, Yihui Wu and Weimin Chou
Polymers 2020, 12(2), 483; https://doi.org/10.3390/polym12020483 - 21 Feb 2020
Cited by 20 | Viewed by 3663
Abstract
Modified ultra-high-molecular-weight polyethylene (UHMWPE) with calcium stearate (CS) and polyethylene wax (PEW) is a feasible method to improve the fluidity of materials because of the tense entanglement network formed by the extremely long molecular chains of UHMWPE, and a modified UHMWPE sheet was [...] Read more.
Modified ultra-high-molecular-weight polyethylene (UHMWPE) with calcium stearate (CS) and polyethylene wax (PEW) is a feasible method to improve the fluidity of materials because of the tense entanglement network formed by the extremely long molecular chains of UHMWPE, and a modified UHMWPE sheet was fabricated by compression molding technology. A Fourier-transform infrared spectroscopy test found that a new chemical bond was generated at 1097 cm−1 in the materials. Besides, further tests on the thermal, thermomechanical, mechanical, and shape memory properties of the samples were also conducted, which indicates that all properties are affected by the dimension and distribution of crystal regions. Moreover, the experimental results indicate that the addition of PEW and CS can effectively improve the mechanical properties. Additionally, the best comprehensive performance of the samples was obtained at the PEW content of 5 wt % and the CS content of 1 wt %. In addition, the effect of temperature on the shape memory properties of the samples was investigated, and the results indicate that the shape fixity ratio (Rf) and the shape recovery ratio (Rr) can reach 100% at 115 °C and 79% at 100 °C, respectively, which can contribute to the development of UHMWPE-based shape memory polymers. Full article
(This article belongs to the Special Issue Functional Polymers in Additive Manufacturing)
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<p>Schematic diagram of the quantitative analysis of shape memory behavior in a bending test.</p> Full article ">Figure 2
<p>FTIR spectra of UHMWPE, PEW, CS, 5PW, and 5CS.</p> Full article ">Figure 3
<p>Thermal properties of UHMWPE with different contents of PEW and CS: (<b>a</b>) DSC curves; (<b>b</b>) TGA curves.</p> Full article ">Figure 4
<p>The Vicat softening temperature (VST) curves of UHMWPE with different contents of PEW and CS.</p> Full article ">Figure 5
<p>Storage modulus–temperature curves of UHMWPE with different contents of PEW and CS.</p> Full article ">Figure 6
<p>Tensile tests of the samples: (<b>a</b>) representative stress–elongation curves; (<b>b</b>) tensile strength; (<b>c</b>) elongation at break.</p> Full article ">Figure 7
<p>Schematic representation of the effect of CS addition to UHMWPE. This figure highlights the possible ways in which the increase in the size of calcium ionic clusters reduces their strength.</p> Full article ">Figure 8
<p>Mechanical properties of the samples: (<b>a</b>) flexural strength; (<b>b</b>) flexural modulus; (<b>c</b>) notched impact strength.</p> Full article ">Figure 8 Cont.
<p>Mechanical properties of the samples: (<b>a</b>) flexural strength; (<b>b</b>) flexural modulus; (<b>c</b>) notched impact strength.</p> Full article ">Figure 9
<p>Representative shape recovery processes of 13PEW5CS over time at different T<sub>SW</sub>: (<b>a</b>) T<sub>SW</sub> = 85 °C; (<b>b</b>) T<sub>SW</sub> = 100 °C; (<b>c</b>) T<sub>SW</sub> = 115 °C.</p> Full article ">Figure 10
<p>Shape memory properties of the samples: (<b>a</b>) shape fixity ratio; (<b>b</b>) shape recovery ratio.</p> Full article ">
19 pages, 5574 KiB  
Article
Evaluation of Carbon Dioxide-Based Urethane Acrylate Composites for Sealers of Root Canal Obturation
by Hao-Hueng Chang, Yi-Ting Tseng, Sheng-Wun Huang, Yi-Fang Kuo, Chun-Liang Yeh, Chien-Hsin Wu, Ying-Chi Huang, Ru-Jong Jeng, Jiang-Jen Lin and Chun-Pin Lin
Polymers 2020, 12(2), 482; https://doi.org/10.3390/polym12020482 - 21 Feb 2020
Cited by 8 | Viewed by 3409
Abstract
A new root canal sealer was developed based on urethane acrylates using polycarbonate polyol (PCPO), a macrodiol prepared in the consumption of carbon dioxide as feedstock. The superior mechanical properties and biostability nature of PCPO-based urethane acrylates were then co-crosslinked with a difunctional [...] Read more.
A new root canal sealer was developed based on urethane acrylates using polycarbonate polyol (PCPO), a macrodiol prepared in the consumption of carbon dioxide as feedstock. The superior mechanical properties and biostability nature of PCPO-based urethane acrylates were then co-crosslinked with a difunctional monomer of tripropylene glycol diarylate (TPGDA) as sealers for resin matrix. Moreover, nanoscale silicate platelets (NSPs) immobilized with silver nanoparticles (AgNPs) and/or zinc oxide nanoparticles (ZnONPs) were introduced to enhance the antibacterial effect for the sealers. The biocompatibility and the antibacterial effect were investigated by Alamar blue assay and LDH assay. In addition, the antibacterial efficiency was performed by using Enterococcus faecalis (E. faecalis) as microbial response evaluation. These results demonstrate that the PCPO-based urethane acrylates with 50 ppm of both AgNP and ZnONP immobilized on silicate platelets, i.e., Ag/ZnO@NSP, exhibited great potential as an antibacterial composite for the sealer of root canal obturation. Full article
(This article belongs to the Special Issue Advanced Polymer Nanocomposites)
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<p>The illustration of filling materials for root canal therapy.</p> Full article ">Figure 2
<p>The preparation of urethane acrylate (UA).</p> Full article ">Figure 3
<p>The test method for curing depths according to ISO 4049:2009 [<a href="#B33-polymers-12-00482" class="html-bibr">33</a>].</p> Full article ">Figure 4
<p>The process of antibacterial evaluation.</p> Full article ">Figure 5
<p>FTIR spectra of UAC50 and UAC50/TPGDA.</p> Full article ">Figure 6
<p>Thermogravimetric analysis (TGA) thermograms of UAC50- and UAC50-based composites.</p> Full article ">Figure 7
<p>Flow analysis of UA resins with various weight ratios of UAT65/tripropylene glycol diacrylate (TPGDA) or UAC50/TPGDA according to ISO 4049:2009.</p> Full article ">Figure 8
<p>Viscosity analysis of UA resins with various weight ratios of UAT65/TPGDA or UAC50/TPGDA according to ISO 4049:2009.</p> Full article ">Figure 9
<p>Curing depths of UAT65/TPGDA resins (<span class="html-italic">w/w</span> = 70/30) and UAC50/TPGDA resins (<span class="html-italic">w/w</span> = 70/30) with various Ag@NSP contents (ppm).</p> Full article ">Figure 10
<p>Curing depths of UAT65/TPGDA resins (<span class="html-italic">w/w</span> = 70/30) and UAC50/TPGDA resins (<span class="html-italic">w/w</span> = 70/30) with various ZnO@NSP contents (ppm).</p> Full article ">Figure 11
<p>Curing depths of UAT65/TPGDA resins (<span class="html-italic">w/w</span> = 70/30) and UAC50/TPGDA resins (<span class="html-italic">w/w</span> = 70/30) with various Ag/ZnO@NSP contents (ppm).</p> Full article ">Figure 12
<p>Alamar blue assay of (<b>a</b>) UAT65/TPGDA (<span class="html-italic">w/w</span> = 70/30) and (<b>b</b>) UAC50/TPGDA (<span class="html-italic">w/w</span> = 70/30) resins with various concentrations of Ag@NSP, ZnO@NSP, or Ag/ZnO@NSP (<span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 12 Cont.
<p>Alamar blue assay of (<b>a</b>) UAT65/TPGDA (<span class="html-italic">w/w</span> = 70/30) and (<b>b</b>) UAC50/TPGDA (<span class="html-italic">w/w</span> = 70/30) resins with various concentrations of Ag@NSP, ZnO@NSP, or Ag/ZnO@NSP (<span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 13
<p>Lactate dehydrogenase (LDH) assay of (<b>a</b>) UAT65/TPGDA (<span class="html-italic">w/w</span> = 70/30) and (<b>b</b>) UAC50/TPGDA (<span class="html-italic">w/w</span> = 70/30) with various concentrations of Ag@NSP, ZnO@NSP, or Ag/ZnO@NSP (<span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 13 Cont.
<p>Lactate dehydrogenase (LDH) assay of (<b>a</b>) UAT65/TPGDA (<span class="html-italic">w/w</span> = 70/30) and (<b>b</b>) UAC50/TPGDA (<span class="html-italic">w/w</span> = 70/30) with various concentrations of Ag@NSP, ZnO@NSP, or Ag/ZnO@NSP (<span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 14
<p>SEM images (2500x) of <span class="html-italic">E. faecalis</span> on the surfaces of UAC50/TPGDA = (<span class="html-italic">w/w</span> = 70/30) with various antibacterial agents: control (<b>a</b>,<b>e</b>); 50 ppm Ag@NSP (<b>b</b>,<b>f</b>); 75 ppm Ag@NSP (<b>c</b>,<b>g</b>); 50 ppm Ag/ZnO@NSP (<b>d</b>,<b>h</b>) for 6 h and 24 h, respectively.</p> Full article ">
13 pages, 7558 KiB  
Article
Analysis of Thermal–Mechanical Properties of Silicon Dioxide/Polyvinylidene Fluoride Reinforced Non-Woven Fabric (Polypropylene) Composites
by Fangyun Kong, Mengzhou Chang and Zhenqing Wang
Polymers 2020, 12(2), 481; https://doi.org/10.3390/polym12020481 - 21 Feb 2020
Cited by 4 | Viewed by 3917
Abstract
In this paper, solution casting method is used to prepare the PP (polypropylene) non-woven fabric based composite film filled with silicon dioxide/polyvinylidene fluoride (SiO2/PVDF). The mechanical and thermodynamic properties of PP/SiO2/PVDF composites were studied by a uniaxial tensile test [...] Read more.
In this paper, solution casting method is used to prepare the PP (polypropylene) non-woven fabric based composite film filled with silicon dioxide/polyvinylidene fluoride (SiO2/PVDF). The mechanical and thermodynamic properties of PP/SiO2/PVDF composites were studied by a uniaxial tensile test under different temperature and combustion experiment. It is found that the stress of PP/SiO2/PVDF composite film with 4 wt % SiO2 is the maximum value, reaching 18.314 MPa, 244.42% higher than that of pure PP non-woven. Meanwhile, the thermal–mechanical coupling tests indicate that with the increase of temperature, the ultimate stress and strain of the composite decrease. At the same time, the thermal shrinkage property of the composite during the heating process is studied. The modified composite has good thermal stability under 180 °C. Scanning electron microscope (SEM), X-ray diffraction (XRD) and thermogravimetric (TG) were used to characterize the pore shape, distribution and crystal phase change of the composite. The modified PP/SiO2/PVDF composite film structure shows high strength and good thermal stability, and can better meet the requirements of strength and thermal performance of lithium-ion battery during the charging and discharging process. Full article
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<p>Composite material production flow chart.</p> Full article ">Figure 2
<p>Samples before and after the tensile test.</p> Full article ">Figure 3
<p>Stress strain curve and bar chart of tensile test: (<b>a</b>) stress strain curve and (<b>b</b>) maximum stress bar chart.</p> Full article ">Figure 4
<p>The stress–strain curves of composites at different temperatures: (<b>a</b>) 50 °C and (<b>b</b>) 80 °C.</p> Full article ">Figure 5
<p>Thermal shrinkage properties of the film: (<b>a</b>) thermal shrinkage of PP non-woven materials under different heat treatment temperature; (<b>b</b>) PVDF; (<b>c</b>) PP/SiO<sub>2</sub>/PVDF (4%); (<b>d</b>) SiO<sub>2</sub>/PVDF (4%) and (<b>e</b>) SiO<sub>2</sub>/PVDF (8%).</p> Full article ">Figure 6
<p>Combustion behavior of the materials: (<b>a</b>) PP; (<b>b</b>) PP/SiO<sub>2</sub>/PVDF and (<b>c</b>) SiO<sub>2</sub>/PVDF.</p> Full article ">Figure 7
<p>Thermal analysis curve of the PP/SiO<sub>2</sub>/PVDF and SiO<sub>2</sub>/PVDF composite.</p> Full article ">Figure 8
<p>SEM of the composite surface: (<b>a</b>) PP non-woven at 100×; (<b>b</b>) PP non-woven at 1000×; (<b>c</b>) PP/SiO<sub>2</sub>/PVDF composite with 4 wt % SiO<sub>2</sub> and (<b>d</b>) PP/SiO<sub>2</sub>/PVDF (4 wt %) magnified by 5000×.</p> Full article ">Figure 9
<p>SEM of the cross section: (<b>a</b>) PP/SiO<sub>2</sub>/PVDF (4 wt %) magnified by 20,000×; (<b>b</b>) PP/SiO<sub>2</sub>/PVDF (4 wt %) magnified by 500×; (<b>c</b>) SiO<sub>2</sub>/PVDF (6 wt %) magnified by 500× and (<b>d</b>) SiO<sub>2</sub>/PVDF (4 wt %) magnified by 500×.</p> Full article ">Figure 10
<p>Energy dispersive spectrometer (EDS) analysis diagram of the PP/SiO<sub>2</sub>/PVDF composite with 4 wt % SiO<sub>2</sub>: (<b>a</b>) EDS mapping of O, C, Si and F and (<b>b</b>) elemental EDS analysis.</p> Full article ">Figure 11
<p>XRD analysis of samples: (<b>a</b>) Jade (XRD analysis software) and (<b>b</b>) curve of XRD.</p> Full article ">
21 pages, 1883 KiB  
Article
Optical and Nonlinear Properties of Photonic Polymer Nanocomposites and Holographic Gratings Modified with Noble Metal Nanoparticles
by Oksana Sakhno, Pavel Yezhov, Volodymyr Hryn, Valentyn Rudenko and Tatiana Smirnova
Polymers 2020, 12(2), 480; https://doi.org/10.3390/polym12020480 - 21 Feb 2020
Cited by 29 | Viewed by 4116
Abstract
Nanocomposites based on transparent polymer matrices containing nanoparticles (NPs) of noble metals are modern-day materials that can be specially designed for photonics, linear and nonlinear optics, laser physics and sensing applications. We present the improved photosensitive nanocomposites doped with Au and Ag NPs [...] Read more.
Nanocomposites based on transparent polymer matrices containing nanoparticles (NPs) of noble metals are modern-day materials that can be specially designed for photonics, linear and nonlinear optics, laser physics and sensing applications. We present the improved photosensitive nanocomposites doped with Au and Ag NPs allowing fabrication of high effective submicrometer dimensional diffraction structures using holographic method. A general approach for the fabrication of holographic structures using a two-component mixture of the monomers of different reactivity was developed. Two different methods, ex situ and in situ, were studied to introduce Au and Ag NPs in the polymer matrix. The diffusion model of the grating formation upon holographic exposure as well as the process of Ag NP synthesis in a polymer matrix is considered. The influence of the NP size on the polymerization process, material dynamic range and nonlinear properties were investigated. The mechanisms and characteristics of the nanocomposite nonlinear optical response are discussed. Full article
(This article belongs to the Special Issue Polymeric and Polymer Nanocomposite Materials for Photonic Applications)
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Figure 1
<p>The sample preparation (<b>a</b>). Holographic setup for transmission gratings recording (<b>b</b>). Mr is the mirror; Sh is the shutter; SpF is the collimator with the spatial filter; BSp is the beam splitter; 2<math display="inline"><semantics> <mi>α</mi> </semantics></math> is the angle between the recording laser beams; “sample” is the cell filled with the nanocomposite.</p> Full article ">Figure 2
<p>Scheme of the Z-scan setup, D1, D2, D3 are the photodetectors.</p> Full article ">Figure 3
<p>The structures of the monomers used in the nanocomposites and their refractive indices (<b>a</b>–<b>c</b>). Optical spectra of the layers (<b>d</b>): Without Au nanoparticles (NPs) (curve 1), and with different concentrations of Au NPs : 1.5 wt. % Au1 (curve 2); 2 wt. % Au1 (curve 3); 1.3 wt. % Au2 (curve 4); TEM image and histogram of the size distribution of Au1 NPs (area is 0.17 µm × 0.17 µm; average diameter is 1.7 nm; standard deviation is 0.36 nm) (<b>e</b>) and Au2 NPs (area is 0.19 µm × 0.17 µm; average diameter is 2.7 nm; standard deviation is 0.94 nm) (<b>f</b>).</p> Full article ">Figure 4
<p>(<b>a</b>) Photo of the grating in the nanocomposite with Au NPs. (<b>b</b>) Maximum values of <math display="inline"><semantics> <msub> <mi>n</mi> <mn>1</mn> </msub> </semantics></math> as a function of the Au NPs concentration for Au1 (black squares) and Au2 (red circles).</p> Full article ">Figure 5
<p>The model under consideration: (<b>a</b>) A two-component mixture, without Au NPs; (<b>b</b>–<b>d</b>) a three-component mixture containing Au NPs.</p> Full article ">Figure 6
<p>Conversion of: The monomer mixture (1); the nanocomposite with 1.5 wt. % Au1 (2) and 2 wt. % Au1 (3); the nanocomposite with 1.3 wt. % Au2 (4).</p> Full article ">Figure 7
<p>Chemical structure of the mixture components (<b>a</b>). Absorption spectra of a solution of AgNO<sub>3</sub> in acetonitrile (<b>b</b>), and mixture before (red) and after (black) polymerization (<b>c</b>).</p> Full article ">Figure 8
<p>Photo of the grating polymer–Ag NPs (<b>a</b>). The dependence of <math display="inline"><semantics> <msub> <mi>n</mi> <mn>1</mn> </msub> </semantics></math> of the grating before (black squares) and after (red circles) the treatment on the AgNO<sub>3</sub> concentration in a precursor solution (<b>b</b>).</p> Full article ">Figure 9
<p>(<b>a</b>) TEM image of the grating with the <span class="html-italic">in situ</span> formed Ag NPs and histogram of the NP size distribution (the area is 3.5 µm × 3.5 µm; the average diameter is 5.25 nm; the standard deviation is 1.3 nm); (<b>b</b>) optical spectrum of the nanocomposite film containing Ag NPs.</p> Full article ">Figure 10
<p>Nonlinear refractometry of Au NP nanocomposites containing Au1 (<b>a</b>) and Au2 (<b>b</b>) NPs.</p> Full article ">Figure 11
<p>Energy level diagram explaining the mechanism of Au-nanocomposite optical nonlinearity.</p> Full article ">Figure 12
<p>Normalized open-aperture (blue squares) and limited-aperture (red circles) Z-scan traces of Ag-nanocomposite at 532 nm excitation (<math display="inline"><semantics> <msub> <mi>τ</mi> <mi>p</mi> </msub> </semantics></math> = 20 ns, f = 0.5 Hz, <math display="inline"><semantics> <msub> <mi>I</mi> <mn>0</mn> </msub> </semantics></math> = 5.11 MW/cm<sup>2</sup>). The lines are the theoretical fits (<b>a</b>). Energy level diagram explaining the mechanism of Ag-nanocomposite optical nonlinearity (<b>b</b>).</p> Full article ">
15 pages, 4099 KiB  
Article
CD133 Targeted PVP/PMMA Microparticle Incorporating Levamisole for the Treatment of Ovarian Cancer
by Yu-Chi Wang, Meng-Yi Bai, Ying-Ting Yeh, Sung-Ling Tang and Mu-Hsien Yu
Polymers 2020, 12(2), 479; https://doi.org/10.3390/polym12020479 - 20 Feb 2020
Cited by 4 | Viewed by 3056
Abstract
Levamisole (LEVA) is used to treat worm infections, but it can also inhibit cancer cell growth by inhibiting the aldehyde dehydrogenase pathway. Therefore, here, we developed a drug carrier targeting CD133, a biomarker overexpressed in ovarian cancer cells. The particle structure and cytotoxicity [...] Read more.
Levamisole (LEVA) is used to treat worm infections, but it can also inhibit cancer cell growth by inhibiting the aldehyde dehydrogenase pathway. Therefore, here, we developed a drug carrier targeting CD133, a biomarker overexpressed in ovarian cancer cells. The particle structure and cytotoxicity of the prepared LEVA-containing particles—called LEVA/PVP/PMMA microparticles (MPs) (because it used matrix material polyvinylpyrrolidone (PVP) and poly(methylmethacrylate) (PMMA))—were investigated in the ovarian cancer cell lines SKOV-3 and CP70. The particle size of the MPs was determined to be 1.0–1.5 µm and to be monodispersed. The hydrophilic property of PVP created a porous MP surface after the MPs were soaked in water for 20 min, which aided the leaching of the hydrophilic LEVA out of the MPs. The encapsulation efficiency of LEVA/PVP/PMMA MPs could reach up to 20%. Free-form LEVA released 50% of drugs in <1 h and 90% of drugs in 1 day, whereas the drug release rate of LEVA/PVP/PMMA MPs was much slower; 50% released in 4 h and only 70% of drugs released in 1 day. In the in vitro cell model test, 5 mM free-form LEVA and 0.1 g/mL CD133 targeted LEVA/PVP/PMMA MPs reduced SKOV-3 cell viability by 60%; 0.1 g/mL LEVA/PVP/PMMA MPs was equivalent to a similar dosage of the free drug. In addition, the cytotoxicity of CD133-conjugated LEVA/PVP/PMMA MPs shows a different cytotoxicity response toward cell lines. For SKOV-3 cells, treatment with free-form LEVA or CD133-conjugated LEVA/PVP/PMMA MPs exerted dose-dependent cytotoxic effects on SKOV-3 cell viability. However, CD133-conjugated LEVA/PVP/PMMA MPs demonstrated no significant dose-dependent cytotoxic efficacy toward CP70 cells. Full article
(This article belongs to the Special Issue Polymeric Colloidal Materials for Biomedical Applications)
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<p>SEM images of the blank polyvinylpyrrolidone (PVP)/poly(methylmethacrylate) (PMMA) microparticle produced from (<b>A</b>–<b>C</b>) in the Ace/DMF = 1/2 cosolvent system; (<b>D</b>–<b>F</b>) in the Ace/DMF = 1/1 cosolvent system; (<b>G</b>–<b>I</b>) in the Ace/DMF = 2/1 cosolvent system.</p> Full article ">Figure 2
<p>SEM images of particles produced from a series of 10 wt% stock solutions containing the different ratio of PVP and PMMA: (<b>A</b>,<b>B</b>) 8:2, (<b>C</b>,<b>D</b>) 5:5 and (<b>E</b>,<b>F</b>) 2:8 (PVP:PMMA; w/w).</p> Full article ">Figure 3
<p>SEM images of levamisole (LEVA)/PVP/PMMA microparticles produced from a series of different concentrations of LEVA: (<b>A</b>) 1250 µg/mL, (<b>B</b>) 625 µg/mL, (<b>C</b>) 312.5 µg/mL, (<b>D</b>) 156.25 µg/mL, (<b>E</b>) 78.125 µg/mL, (<b>F</b>) 39.0625 µg/mL.</p> Full article ">Figure 4
<p>UV–vis spectrum of (<b>A</b>) a standard curve constructed from a series of LEVA solutions with known concentrations; (<b>B</b>) in vitro cumulative release profile of free form LEVA drug and (<b>C</b>) in vitro cumulative release profile of a suspension of LEVA/PVP/PMMA microparticles.</p> Full article ">Figure 5
<p>SEM images of LEVA/PVP/PMMA microparticles infiltrated in distilled water at the time points of (<b>A</b>) 0, (<b>B</b>) 20, (<b>C</b>) 40, (<b>D</b>) 90 min and (<b>E</b>) 24 h.</p> Full article ">Figure 6
<p>(<b>A</b>) Schematic illustration of facile protocol for synthesizing CD133-conjugated LEVA/PVP/PMMA microparticles. (<b>B</b>) Standard curve of Bradford assays established by using the BSA standard protein to determine the conjugation amount of antibody on the particle’s surface.</p> Full article ">Figure 7
<p>(<b>top</b>) FT-IR spectrum of LEVA/PVP/PMMA microparticles before hydrolysis. (<b>bottom</b>) FT-IR spectrum of LEVA/PVP/PMMA microparticles after hydrolysis.</p> Full article ">Figure 8
<p>(<b>A</b>) SEM image of CD133-conjugated LEVA/PVP/PMMA MPs. (<b>B</b>) EDX spectrum acquired from the selected area on the CD133-conjugated LEVA/PVP/PMMA MPs.</p> Full article ">Figure 9
<p>Cell viability of SKOV-3 and CP70 after being treated with a series of different concentration of (<b>A</b>,<b>B</b>) free form LEVA toward SKOV-3 and CP70, respectively. (<b>C</b>,<b>D</b>) CD133-conjugated Leva/PVP/PMMA MPs toward SKOV-3 and CP70, respectively. The results of quantitative analyses of the cytotoxicity of the aforementioned formulations against SKOV-3 and CP70 were determined by the MTT assays.</p> Full article ">
10 pages, 2823 KiB  
Article
Study of POSS on the Properties of Novel Inorganic Dental Composite Resin
by Jiahui Wang, Yizhi Liu, Jianxin Yu, Yi Sun and Weili Xie
Polymers 2020, 12(2), 478; https://doi.org/10.3390/polym12020478 - 20 Feb 2020
Cited by 18 | Viewed by 3556
Abstract
Various amounts of methacryl polyhedral oligomeric silsesquioxane (POSS) were explored to be incorporated into novel nano SiO2 dental resin composites using light curing method. The scanning electron microscopy (SEM), optical microscopy, fourier transform infrared spectroscopy (FTIR), nanoindentation, nanoscratch and three-point flexure tests [...] Read more.
Various amounts of methacryl polyhedral oligomeric silsesquioxane (POSS) were explored to be incorporated into novel nano SiO2 dental resin composites using light curing method. The scanning electron microscopy (SEM), optical microscopy, fourier transform infrared spectroscopy (FTIR), nanoindentation, nanoscratch and three-point flexure tests were performed. The volumetric shrinkage and mechanical properties such as hardness, elastic modulus, resistance, flexural strength and fracture energy were analyzed. With the additions of POSS, the volume shrinkage decreased and the mechanical properties initially increased. The effects of POSS on these properties were studied to provide a reference for clinically selecting a composite resin with excellent properties. Full article
(This article belongs to the Special Issue Silsesquioxane (POSS) Polymers, Copolymers and Nanoparticles)
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<p>The molecule structure of methacryl polyhedral oligomeric silsesquioxane (POSS).</p> Full article ">Figure 2
<p>FTIR spectra of composite resins with different POSS additions.</p> Full article ">Figure 3
<p>Hardness and elastic modulus of composite resins with different POSS additions.</p> Full article ">Figure 4
<p>The effective penetration depth curves of neat dental resin matrix under load.</p> Full article ">Figure 5
<p>Average scratch depth of composite resins with different POSS additions.</p> Full article ">Figure 6
<p>Flexural strength and fracture energy of composite resins with different POSS additions.</p> Full article ">Figure 7
<p>Scanning electron microscopy (SEM) images of the fracture topography of (<b>a</b>) organic dental composite resin and (<b>b</b>) POSS hybrid dental composite resin.</p> Full article ">
16 pages, 3933 KiB  
Article
Quantitative Structural Analysis of Polystyrene Nanoparticles Using Synchrotron X-ray Scattering and Dynamic Light Scattering
by Jia Chyi Wong, Li Xiang, Kuan Hoon Ngoi, Chin Hua Chia, Kyeong Sik Jin and Moonhor Ree
Polymers 2020, 12(2), 477; https://doi.org/10.3390/polym12020477 - 19 Feb 2020
Cited by 8 | Viewed by 4246
Abstract
A series of polystyrene nanoparticles (PS-1, PS-2, PS-3, and PS-4) in aqueous solutions were investigated in terms of morphological structure, size, and size distribution. Synchrotron small-angle X-ray scattering analysis (SAXS) was carried out, providing morphology details, size and size distribution on the particles. [...] Read more.
A series of polystyrene nanoparticles (PS-1, PS-2, PS-3, and PS-4) in aqueous solutions were investigated in terms of morphological structure, size, and size distribution. Synchrotron small-angle X-ray scattering analysis (SAXS) was carried out, providing morphology details, size and size distribution on the particles. PS-1, PS-2, and PS-3 were confirmed to behave two-phase (core and shell) spherical shapes, whereas PS-4 exhibited a single-phase spherical shape. They all revealed very narrow unimodal size distributions. The structural parameter details including radial density profile were determined. In addition, the presence of surfactant molecules and their assemblies were detected for all particle solutions, which could originate from their surfactant-assisted emulsion polymerizations. In addition, dynamic light scattering (DLS) analysis was performed, finding only meaningful hydrodynamic size and intensity-weighted mean size information on the individual PS solutions because of the particles’ spherical nature. In contrast, the size distributions were extracted unrealistically too broad, and the volume- and number-weighted mean sizes were too small, therefore inappropriate to describe the particle systems. Furthermore, the DLS analysis could not detect completely the surfactant and their assemblies present in the particle solutions. Overall, the quantitative SAXS analysis confirmed that the individual PS particle systems were successfully prepared with spherical shape in a very narrow unimodal size distribution. Full article
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<p>X-ray scattering analysis of PS-1. (<b>a</b>) SAXS profile measured at room temperature and corrected for water as the solution medium: (<b>b</b>) pair distance distribution functions <span class="html-italic">p</span>(<span class="html-italic">r</span>) obtained from the scattering profile using the IFT method; (<b>c</b>) data analysis results; (<b>d</b>) radius distribution obtained by the data analysis in (<b>c</b>); (<b>e</b>) density distribution obtained by the data analysis in (<b>c</b>). (<b>f</b>) SAXS profile measured at room temperature and corrected for the supernatant as a solution medium: (<b>g</b>) pair distance distribution functions <span class="html-italic">p</span>(<span class="html-italic">r</span>) obtained from the scattering profile using the IFT method; (<b>h</b>) data analysis results; (<b>i</b>) radius distribution obtained by the data analysis in (<b>h</b>); (<b>j</b>) density distribution obtained by the data analysis in (<b>h</b>). (<b>c</b>, <b>h</b>) the open symbols are the measured data and the red solid line represents the sum of the profiles obtained by fitting the data using two-phase ellipsoid model (blue line) and local random two-phase contributions (purple line) and the background (green line).</p> Full article ">Figure 2
<p>DLS analyses of PS nanoparticles at 25 °C: (<b>a-1</b> to <b>a-4</b>) autocorrelation profiles measured; (<b>b-1</b> to <b>b-4</b>) data analysis results, where the symbols are the measured data and the red solid lines were obtained by fitting the data using the cumulant method in the Zetasizer program package; (<b>c-1</b> to <b>c-4</b>) data analysis results, where the symbols are the measured data and the red solid lines were obtained by fitting the data using the non-negatively constrained least square (NNLS) deconvolution algorithm included in the Zetasizer program package; (<b>d</b>-1 to <b>d-4</b>) intensity-weighted radius distributions obtained by the data analyses; (<b>e</b>) volume-weighted radius distributions obtained from the radius distributions in (<b>d-1</b> to <b>d-4</b>) and (<b>f</b>) number-weighted radius distributions obtained from the radius distributions in <b>(e-1</b> to <b>e-4</b>).</p> Full article ">Figure 3
<p>Radius distributions of PS particles determined by X-ray scattering and DLS analyses: (<b>a-1</b>) PS-1 (<span class="html-italic">σ</span> = 0.8 nm), from X-ray scattering; (<b>a-2</b>) PS-1 (<span class="html-italic">σ</span> = 14.7 nm), from DLS; (<b>b-1</b>) PS-2 (<span class="html-italic">σ</span> = 1.0 nm), from X-ray scattering; (<b>b-2</b>) PS-2 (<span class="html-italic">σ</span> = 7.4 nm), from DLS; (<b>c-1</b>) PS-3 (<span class="html-italic">σ</span> = 1.3 nm), from X-ray scattering; (<b>c-2</b>) PS-3 (<span class="html-italic">σ</span> = 4.7 nm), from DLS; (<b>d-1</b>) PS-4 (<span class="html-italic">σ</span> = 1.8 nm), from X-ray scattering; (<b>d-2</b>) PS-4 (<span class="html-italic">σ</span> = 3.9 nm), from DLS. Here, it is noted that the radius distributions based on the scattering intensities in (<b>a-1</b>), (<b>b-1</b>), (<b>c-1</b>), and (<b>d-1</b>) were obtained from the radius distribution based on the number populations in <a href="#polymers-12-00477-f001" class="html-fig">Figure 1</a>i, <a href="#polymers-12-00477-f004" class="html-fig">Figure 4</a>i, <a href="#polymers-12-00477-f005" class="html-fig">Figure 5</a>i, and <a href="#polymers-12-00477-f006" class="html-fig">Figure 6</a>i using a relation of the scattering intensity and the volume of the particles in population; such relation is given in <a href="#app1-polymers-12-00477" class="html-app">Supporting Information</a>. The X-ray scattering analyses were conducted for the scattering data corrected with the supernatant media.</p> Full article ">Figure 4
<p>X-ray scattering data analysis of PS-2 particle. (<b>a</b>) SAXS profile measured at room temperature and corrected for water as the solution medium: (<b>b</b>) pair distance distribution functions <span class="html-italic">p</span>(<span class="html-italic">r</span>) obtained from the scattering profile using the IFT method; (<b>c</b>) data analysis results; (<b>d</b>) radius distribution obtained by the data analysis in (<b>c</b>); (<b>e</b>) density distribution obtained by the data analysis in (<b>c</b>). (<b>f</b>) SAXS profile measured at room temperature and corrected for the supernatant as a solution medium: (<b>g</b>) pair distance distribution functions <span class="html-italic">p</span>(<span class="html-italic">r</span>) obtained from the scattering profile using the IFT method; (<b>h</b>) data analysis results; (<b>i</b>) radius distribution obtained by the data analysis in (<b>h</b>); (<b>j</b>) density distribution obtained by the data analysis in (<b>h</b>). (<b>c</b>, <b>h</b>) the open symbols are the measured data and the red solid line represents the sum of the profiles obtained by fitting the data using two-phase ellipsoid model (blue line) and local random two-phase contributions (purple line) and the background (green line).</p> Full article ">Figure 5
<p>X-ray scattering data analysis of PS-3 particle. (<b>a</b>) SAXS profile measured at room temperature and corrected for water as the solution medium: (<b>b</b>) pair distance distribution functions <span class="html-italic">p</span>(<span class="html-italic">r</span>) obtained from the scattering profile using the IFT method; (<b>c</b>) data analysis results; (<b>d</b>) radius distribution obtained by the data analysis in (<b>c</b>); (<b>e</b>) density distribution obtained by the data analysis in (<b>c</b>). (<b>f</b>) SAXS profile measured at room temperature and corrected for the supernatant as a solution medium: (<b>g</b>) pair distance distribution functions <span class="html-italic">p</span>(<span class="html-italic">r</span>) obtained from the scattering profile using the IFT method; (<b>h</b>) data analysis results; (<b>i</b>) radius distribution obtained by the data analysis in (<b>h</b>); (<b>j</b>) density distribution obtained by the data analysis in (<b>h</b>). (<b>c</b>, <b>h</b>) the open symbols are the measured data and the red solid line represents the sum of the profiles obtained by fitting the data using two-phase ellipsoid model (blue line) and local random two-phase contributions (purple line) and the background (green line).</p> Full article ">Figure 6
<p>X-ray scattering data analysis of PS-4 particle. (<b>a</b>) SAXS profile measured at room temperature and corrected for water as the solution medium: (<b>b</b>) pair distance distribution functions <span class="html-italic">p</span>(<span class="html-italic">r</span>) obtained from the scattering profile using the IFT method; (<b>c</b>) data analysis results; (<b>d</b>) radius distribution obtained by the data analysis in (<b>c</b>); (<b>e</b>) density distribution obtained by the data analysis in (<b>c</b>). (<b>f</b>) SAXS profile measured at room temperature and corrected for the supernatant as a solution medium: (<b>g</b>) pair distance distribution functions <span class="html-italic">p</span>(<span class="html-italic">r</span>) obtained from the scattering profile using the IFT method; (<b>h</b>) data analysis results; (<b>i</b>) radius distribution obtained by the data analysis in (<b>h</b>); (<b>j</b>) density distribution obtained by the data analysis in (<b>h</b>). (<b>c</b>, <b>h</b>) the open symbols are the measured data and the red solid line represents the sum of the profiles obtained by fitting the data using two-phase ellipsoid model (blue line) and local random two-phase contributions (purple line) and the background (green line).</p> Full article ">
17 pages, 3864 KiB  
Article
Experimental Cold-Cured Nanostructured Epoxy-Based Hybrid Formulations: Properties and Durability Performance
by Mariaenrica Frigione, Mariateresa Lettieri, Francesca Lionetto and Leno Mascia
Polymers 2020, 12(2), 476; https://doi.org/10.3390/polym12020476 - 19 Feb 2020
Cited by 15 | Viewed by 3214
Abstract
Different hybrid epoxy formulations were produced and cold-cured, monitoring the properties development during low temperature curing and aging. All systems were based on silane functionalized bis-phenol A (DGEBA) resins (Part A), cured at ambient temperature with two amine hardeners (Part B). The different [...] Read more.
Different hybrid epoxy formulations were produced and cold-cured, monitoring the properties development during low temperature curing and aging. All systems were based on silane functionalized bis-phenol A (DGEBA) resins (Part A), cured at ambient temperature with two amine hardeners (Part B). The different components of the formulations were selected on their potential capability to bring about enhancements in the glass transition temperature. The durability of the produced hybrids was probed in comparison to the corresponding neat epoxies by monitoring changes in glass transition temperature (Tg) and flexural mechanical properties after exposure to different levels of humidity and immersion in water and at temperatures slightly higher than the local ambient temperature, in order to simulate the conditions encountered during summer seasons in very humid environments. The thermal degradation resistance of the hybrid systems was also evaluated by thermogravimetric analysis. Full article
(This article belongs to the Special Issue State-of-the-Art Polymer Science and Technology in Italy (2019,2020))
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Figure 1

Figure 1
<p>Glass transition temperature (<span class="html-italic">T</span><sub>g</sub>) values at different cold-curing times for hybrid and control epoxy systems: (<b>a</b>) B0, BSi, BSiMo; (<b>b</b>) Control bis-phenol A (DGEBA), Hybrid DGEBA, Hyb-L-B samples; (<b>c</b>) Control Epoxy A, Hyb-L-A samples.</p> Full article ">Figure 2
<p>Typical differential scanning calorimetry (DSC) curves found for: (<b>a</b>) B0 and BSiMo; (<b>b</b>) Control DGEBA, Hybrid DGEBA, Hyb-L-B samples; (<b>c</b>) Control Epoxy-A, Hyb-L-A samples. All the systems were cold-cured for prolonged (greater than two months) curing times.</p> Full article ">Figure 3
<p>Final (<b>a</b>) glass transition temperatures (<span class="html-italic">T</span><sub>g</sub>) and (<b>b</b>) residual heat of reaction, (ΔH<sub>res</sub>), measured on cold-cured systems: B0, BSi, and BSiMo; Control DGEBA, Hybrid DGEBA, Hyb-L-B; Control Epoxy-A, Hyb-L-A systems.</p> Full article ">Figure 4
<p>SEM micrographs of the different hybrid systems produced, compared with control systems. For some hybrid systems, EDS spectra or maps are also reported.</p> Full article ">Figure 5
<p>Results ((<b>a</b>) tanδ and (<b>b</b>) storage modulus) of the hybrids cold-cured in presence of PACM or TETA hardeners and of the Control DGEBA.</p> Full article ">Figure 6
<p>Variations in glass transition temperatures and in flexural mechanical properties (modulus and yield strength) for systems B0, BSi, and BSiMo subjected to different aging procedures for up to approximately three months.</p> Full article ">Figure 7
<p>TGA curves of the hybrids cold-cured in presence of PACM amine and of the relative control. In the inset the derivative of the TGA curves obtained for the same systems is shown.</p> Full article ">Scheme 1
<p>Chemical structures of all the components employed.</p> Full article ">Scheme 2
<p>Schematic presentation of steps involved in the production of the epoxy-silica hybrids.</p> Full article ">
14 pages, 3571 KiB  
Article
Fabrication of Porous Recycled HDPE Biocomposites Foam: Effect of Rice Husk Filler Contents and Surface Treatments on the Mechanical Properties
by Farah Atiqah Abdul Azam, Nishata Royan Rajendran Royan, Nor Yuliana Yuhana, Nabilah Afiqah Mohd Radzuan, Sahrim Ahmad and Abu Bakar Sulong
Polymers 2020, 12(2), 475; https://doi.org/10.3390/polym12020475 - 19 Feb 2020
Cited by 22 | Viewed by 4339
Abstract
In this study, a biodegradable, cheap and durable recycled high-density polyethylene (rHDPE) polymer reinforced with rice husk (RH) fibre was fabricated into a foam structure through several processes, including extrusion, internal mixing and hot pressing. The effect of filler loading on the properties [...] Read more.
In this study, a biodegradable, cheap and durable recycled high-density polyethylene (rHDPE) polymer reinforced with rice husk (RH) fibre was fabricated into a foam structure through several processes, including extrusion, internal mixing and hot pressing. The effect of filler loading on the properties of the foam and the influence of RH surface treatments on the filler–matrix adhesion and mechanical properties of the composite foam were investigated. The morphological examination shows that 50 wt.% filler content resulted in an effective dispersion of cells with the smallest cell size (58.3 µm) and the highest density (7.62 × 1011 sel/cm3). This small cell size benefits the mechanical properties. Results indicate that the tensile strength and the Young’s modulus of the alkali-treated RH/rHDPE composite foam are the highest amongst the treatments (10.83 MPa and 858 MPa, respectively), followed by UV/O3, which has shown considerable increments compared with the untreated composite. The flexural and impact tests also show the increment in strength for the composite foam after chemical treatment. Although the UV/O3 surface treatment has minor influence on the mechanical enhancement of the composite foam, this method may be a reliable surface treatment of the fibre-reinforced composite. Full article
(This article belongs to the Special Issue Durability of Natural Fibers and Plastics)
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Figure 1
<p>Fabrication of rice husk (RH)/recycled high-density polyethylene (rHDPE) polymer composite foam.</p> Full article ">Figure 2
<p>SEM micrographs of RH/rHDPE composite foam with different contents of untreated rice husk (RH) filler: (<b>a</b>) 10, (<b>b</b>) 30 and (<b>c</b>) 50 wt.%.</p> Full article ">Figure 3
<p>(<b>a</b>) Tensile strength and (<b>b</b>) Young’s modulus of untreated, alkali- and UV-treated RH with 50 wt.% RH.</p> Full article ">Figure 4
<p>(<b>a</b>) Flexural strength and (<b>b</b>) modulus of elasticity of untreated RH, UV-, alkali- and acid-treated RH with 50 wt.% RH loading.</p> Full article ">Figure 5
<p>Impact strength of untreated, UV-, alkali- and acid-treated RH with 50 wt.% RH loading.</p> Full article ">Figure 6
<p>SEM morphology of (<b>a</b>) untreated, (<b>b</b>) UV/O<sub>3</sub>-, (<b>c</b>) alkali- and (<b>d</b>) acid-treated RH/rHDPE composite foam of 50 wt.% rice husk filler.</p> Full article ">
18 pages, 5128 KiB  
Article
Improvement of Peptide Affinity and Stability by Complexing to Cyclodextrin-Grafted Ammonium Chitosan
by Andrea Cesari, Alessandra Recchimurzo, Angela Fabiano, Federica Balzano, Nicolò Rossi, Chiara Migone, Gloria Uccello-Barretta, Ylenia Zambito and Anna Maria Piras
Polymers 2020, 12(2), 474; https://doi.org/10.3390/polym12020474 - 19 Feb 2020
Cited by 12 | Viewed by 3503
Abstract
Cyclodextrin-grafted polymers are attractive biomaterials that could bring together the host–guest complexing capability of pristine cyclodextrin and the pharmaceutical features of the polymeric backbone. The present paper is aimed at characterizing the potential application of ammonium–chitosan grafted with 2-methyl-β-cyclodextrin (N+-rCh-MCD) as [...] Read more.
Cyclodextrin-grafted polymers are attractive biomaterials that could bring together the host–guest complexing capability of pristine cyclodextrin and the pharmaceutical features of the polymeric backbone. The present paper is aimed at characterizing the potential application of ammonium–chitosan grafted with 2-methyl-β-cyclodextrin (N+-rCh-MCD) as the functional macromolecular complexing agent for the oral administration of the neuropeptide dalargin (DAL). Specific NMR characterization procedures, along with UV and fluorescence techniques, as well as biological in vitro assessments have been performed. The results indicate that N+-rCh-MCD forms water-soluble complexes with DAL, with a prevalent involvement of Tyr or Phe over Leu and Ala residues. The association constant of DAL with the polymeric derivative is one order of magnitude higher than that with the pristine cyclodextrin (Ka: 2600 M−1 and 120 M−1, respectively). Additionally, N+-rCh-MCD shields DAL from enzymatic degradation in gastrointestinal in vitro models with a three-fold time delay, suggesting a future pharmaceutical exploitation of the polymeric derivative. Therefore, the greater affinity of N+-rCh-MCD for DAL and its protective effect against enzymatic hydrolysis can be attributed to the synergistic cooperation between cyclodextrin and the polymer, which is realized only when the former is covalently linked to the latter. Full article
(This article belongs to the Special Issue State-of-the-Art Polymer Science and Technology in Italy (2019,2020))
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Figure 1

Figure 1
<p>(<b>a</b>) 2-methyl-β-cyclodextrin conjugates of ammonium chitosan (N<sup>+</sup>-rCh-MCD) and (<b>b</b>) dalargin (DAL).</p> Full article ">Figure 2
<p><sup>1</sup>H NMR spectrum (600 MHz, D<sub>2</sub>O, 37 °C) of N<sup>+</sup>-rCh-MCD (3.7 mg/mL). Black and white dots, squares and triangles refer to the corresponding protons marked on the structure.</p> Full article ">Figure 3
<p>Complex titration by UV and fluorescence spectrometry. (<b>A</b>) Overlay of UV second derivative spectra; (<b>B</b>) Overlay of emission spectra collected by excitation at λ 275 nm.</p> Full article ">Figure 3 Cont.
<p>Complex titration by UV and fluorescence spectrometry. (<b>A</b>) Overlay of UV second derivative spectra; (<b>B</b>) Overlay of emission spectra collected by excitation at λ 275 nm.</p> Full article ">Figure 4
<p>One-dimensional (1D) Rotating-frame Overhauser Effect SpectroscopY (ROESY) spectra (600 MHz, D<sub>2</sub>O, 25 °C) of H<sub>2</sub><sup>Tyr</sup> and H<sub>2</sub><sup>Ala</sup> of DAL (9.8 mM).</p> Full article ">Figure 5
<p>ROESY map (600 MHz, D<sub>2</sub>O, 25 °C, 9.8 mM) of DAL/MCD mixture between 6.6–7.3 ppm and 2.8–4.4 ppm.</p> Full article ">Figure 6
<p>α-chymotrypsin (CHT) hydrolysis of DAL: Residual DAL % after 5 min of CHT activity on solutions (<span class="html-fig-inline" id="polymers-12-00474-i001"> <img alt="Polymers 12 00474 i001" src="/polymers/polymers-12-00474/article_deploy/html/images/polymers-12-00474-i001.png"/></span>); on lyophilized complexes (<span class="html-fig-inline" id="polymers-12-00474-i002"> <img alt="Polymers 12 00474 i002" src="/polymers/polymers-12-00474/article_deploy/html/images/polymers-12-00474-i002.png"/></span>). Error bars indicate the SD values of three independent experiments.</p> Full article ">Figure 7
<p><sup>1</sup>H NMR spectra (600 MHz, D<sub>2</sub>O, phosphate buffer, pH = 6.8, 37 °C) of pure DAL (0.68 mM, (<b>a</b>) and of the DAL/CHT after 5 min (<b>b</b>) and 14 min (<b>c</b>).</p> Full article ">Figure 8
<p>Caco-2 cells cell viability assay. Error bars indicating SD values of eight replicates.</p> Full article ">Figure 9
<p>Percentage of DAL remaining in the apical chamber after 3 h of incubation on Caco-2 monolayers. Error bars indicate the SD values of three experiments.</p> Full article ">
13 pages, 1878 KiB  
Article
Development of Interfacial Adhesive Property by Novel Anti-Stripping Composite between Acidic Aggregate and Asphalt
by Guohong Zhang, Jianhui Qiu, Jingzhuo Zhao, Dingbang Wei and Hui Wang
Polymers 2020, 12(2), 473; https://doi.org/10.3390/polym12020473 - 19 Feb 2020
Cited by 12 | Viewed by 2701
Abstract
Studies on control of and preventive measures against asphalt pavement moisture damage have important economic and social significance due to the multiple damage and repair of pavements, the reasons for which include the poor interfacial adhesive ability between acidic aggregates and asphalts. Anti-stripping [...] Read more.
Studies on control of and preventive measures against asphalt pavement moisture damage have important economic and social significance due to the multiple damage and repair of pavements, the reasons for which include the poor interfacial adhesive ability between acidic aggregates and asphalts. Anti-stripping agent is used in order to improve the poor adhesion, and decomposition temperature is regarded as being important for lots of anti-stripping products, because they always decompose and lose their abilities under the high temperature in the mixing plant before application to the pavement. A novel anti-stripping composite, montmorillonoid/Polyamide (OMMT/PAR), which possesses excellent thermal stability performance and is effective in preventing moisture damage, especially for acidic aggregates, was prepared. Moreover, the modification mechanisms and pavement properties were also investigated with reference to the composites. The results show that OMMT/PAR was prepared successfully, improving the interfacial adhesion between the acidic aggregate and the modified asphalt. Due to the nanostructure of OMMT/PAR, the thermal stability was enhanced dramatically and the interfacial adhesion properties were also improved. Furthermore, asphalts modified with OMMT/PAR and their mixtures showed excellent properties. Finally, the moisture damage process and the mechanisms by which OMMT/PAR improves the interfacial adhesion properties are explained through adhesion mechanism analyses. Full article
(This article belongs to the Special Issue Processing and Molding of Polymers)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>OMMT/PAR preparation of polymer intercalated by OMMT.</p> Full article ">Figure 2
<p>TG curves of the anti-stripping composites of MAS, ASA-1 and ASA-2.</p> Full article ">Figure 3
<p>FT IR curves of OMMT, PAR and OMMT/PAR composites.</p> Full article ">Figure 4
<p>TG curves of OMMT, PAR and their composites.</p> Full article ">Figure 5
<p>Adhesion test results between acidic aggregates and (<b>a</b>) matrix asphalt of SK-90#, (<b>b</b>) SK-90-OMMT/PAR, (<b>c</b>) SK-90-ASA-1 and (<b>d</b>) SK-90-ASA-2.</p> Full article ">Figure 6
<p>(<b>a</b>) Freeze–thaw splitting strength and (<b>b</b>) TSR of asphalt mixture, where Empty represents asphalt mixtures employed with matrix asphalts, and MAS, ASA-1 and ASA-2 are the asphalt mixtures prepared using the asphalts modified with MAS, ASA-1 and ASA-2, respectively.</p> Full article ">Figure 7
<p>Schematic representation of interfacial adhesion mechanism between asphalt modified by OMMT/PAR and acidic aggregate.</p> Full article ">
11 pages, 6460 KiB  
Article
Comparison and Impact of Different Fiber Debond Techniques on Fiber Reinforced Flexible Composites
by Julia Beter, Bernd Schrittesser, Boris Maroh, Essi Sarlin, Peter Filipp Fuchs and Gerald Pinter
Polymers 2020, 12(2), 472; https://doi.org/10.3390/polym12020472 - 18 Feb 2020
Cited by 14 | Viewed by 4107
Abstract
The focus of this paper is the realization and verification of a modified fiber bundle pull-out test setup to estimate the adhesion properties between threads and elastic matrix materials with a more realistic failure mode than single fiber debond techniques. This testing device [...] Read more.
The focus of this paper is the realization and verification of a modified fiber bundle pull-out test setup to estimate the adhesion properties between threads and elastic matrix materials with a more realistic failure mode than single fiber debond techniques. This testing device including a modified specimen holder provides the basis for an adequate estimation of the interlaminar adhesion of fiber bundles including the opportunity of a faster, easier, and more economic handling compared to single fiber tests. The verification was done with the single-fiber and microbond test. Overall, the modified test setup showed the typical pull-out behavior, and the relative comparability between different test scales is given. Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Manufacturing tool including main components (<b>a</b>) with specimen (<b>b</b>) and schematical test procedure with the modified specimen holder (<b>c</b>) with test setup for FBPO test (<b>d</b>).</p> Full article ">Figure 2
<p>Schematic test procedure (<b>a</b>) and a typical force-displacement graph (<b>b</b>) of the SFPO test [<a href="#B13-polymers-12-00472" class="html-bibr">13</a>,<a href="#B22-polymers-12-00472" class="html-bibr">22</a>] with schematical test setup (<b>c</b>) and typical test graphs (<b>d</b>,<b>e</b>) of a microbond test [<a href="#B29-polymers-12-00472" class="html-bibr">29</a>,<a href="#B30-polymers-12-00472" class="html-bibr">30</a>].</p> Full article ">Figure 3
<p>Force-displacement curves obtained from FBPO test on GF with PDMS matrix (<b>a</b>) with the separation process (<b>b</b>) during pull-out and microscopic images of a FBPO specimen (GF with PDMS) after the test: part of embedded area of GF- bundle (<b>c</b>) and SEM of GF- bundle (<b>d</b>) and image of cross-section area of embedded GF bundle (<b>e</b>).</p> Full article ">Figure 4
<p>Influence of the parameters on the pull-out force for GF and PDMS matrix (<b>a</b>) and on different reinforcement-matrix material combinations tested on reference setting (<b>b</b>).</p> Full article ">Figure 5
<p>Comparison of the relative pull-out force for FBPO, SFPO and microbond tests performed with different fiber-matrix combinations with GF (<b>a</b>) and PETF (<b>b</b>).</p> Full article ">
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