Polymers

15 pages, 4442 KiB

Open AccessArticle

Bagasse Cellulose Grafted with an Amino-Terminated Hyperbranched Polymer for the Removal of Cr(VI) from Aqueous Solution

by Lu Xia, Zhonghang Huang, Lei Zhong, Fengwei Xie, Chak Yin Tang and Chi Pong Tsui

Polymers 2018, 10(8), 931; https://doi.org/10.3390/polym10080931 - 20 Aug 2018

Cited by 33 | Viewed by 5220

Abstract

A novel bio-adsorbent was fabricated via grafting an amino-terminated hyperbranched polymer (HBP-NH₂) onto bagasse cellulose. The morphology and microstructure of the HBP-NH₂-grafted bagasse cellulose (HBP-g-BC) were characterized and its adsorption capacity for Cr(VI) ions in aqueous solutions [...] Read more.

A novel bio-adsorbent was fabricated via grafting an amino-terminated hyperbranched polymer (HBP-NH₂) onto bagasse cellulose. The morphology and microstructure of the HBP-NH₂-grafted bagasse cellulose (HBP-g-BC) were characterized and its adsorption capacity for Cr(VI) ions in aqueous solutions was investigated. The rough surface structure of HBP-g-BC that is beneficial for improving the adsorption capacity was observed by scanning electron microscopy (SEM). The grafting reaction was confirmed by Fourier-transform infrared (FT-IR) spectroscopy. The adsorbent performance was shown to be better with a lower pH value, a higher adsorbent dosage, or a higher initial Cr(VI) concentration. Moreover, the kinetics study revealed that the adsorption behavior followed a pseudo-second-order model. The isotherm results showed that the adsorption data could be well-fitted by the Langmuir, Freundlich, or Temkin models. Moreover, HBP-g-BC could maintain 74.4% of the initial removal rate even after five cycles of regeneration. Thus, the high potential of HBP-g-BC as a bio-adsorbent for heavy metal removal has been demonstrated. Full article

(This article belongs to the Collection Biopolymers and Biobased Polymers: Chemistry and Engineering)

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10 pages, 1303 KiB

Open AccessArticle

Ternary Sulfur/Polyacrylonitrile/SiO₂ Composite Cathodes for High-Performance Sulfur/Lithium Ion Full Batteries

by Yusen He, Zhenzhen Shan, Taizhe Tan, Zhihong Chen and Yongguang Zhang

Polymers 2018, 10(8), 930; https://doi.org/10.3390/polym10080930 - 20 Aug 2018

Cited by 28 | Viewed by 5131

Abstract

In the present study, a novel sulfur/lithium-ion full battery was assembled while using ternary sulfur/polyacrylonitrile/SiO₂ (S/PAN/SiO₂) composite as the cathode and prelithiated graphite as the anode. For anode, Stabilized Lithium Metal Powder (SLMP) was successfully transformed into lithiated graphite anode. [...] Read more.

In the present study, a novel sulfur/lithium-ion full battery was assembled while using ternary sulfur/polyacrylonitrile/SiO₂ (S/PAN/SiO₂) composite as the cathode and prelithiated graphite as the anode. For anode, Stabilized Lithium Metal Powder (SLMP) was successfully transformed into lithiated graphite anode. For cathode, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that SiO₂ was uniformly distributed on S/PAN composites, where SiO₂ served as an effective additive due to its ultra high absorb ability and enhanced ability in trapping soluble polysulfide. The tested half-cell based on S/PAN/SiO₂ composite revealed high discharge capacity of 1106 mAh g⁻¹ after 100 cycles at 0.2 C. The full cell based on prelithiated graphite//S/PAN/SiO₂ composite system delivered a specific capacity of 810 mAh g⁻¹ over 100 cycles. Full article

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22 pages, 6700 KiB

Open AccessArticle

A Network-Theory-Based Comparative Study of Melt-Conveying Models in Single-Screw Extrusion: A. Isothermal Flow

by Christian Marschik, Wolfgang Roland and Jürgen Miethlinger

Polymers 2018, 10(8), 929; https://doi.org/10.3390/polym10080929 - 19 Aug 2018

Cited by 31 | Viewed by 7692

Abstract

In many extrusion processes, the metering section is the rate-controlling part of the screw. In this functional zone, the polymer melt is pressurized and readied to be pumped through the die. We have recently proposed a set of heuristic models for predicting the [...] Read more.

In many extrusion processes, the metering section is the rate-controlling part of the screw. In this functional zone, the polymer melt is pressurized and readied to be pumped through the die. We have recently proposed a set of heuristic models for predicting the flow behavior of power-law fluids in two- and three-dimensional metering channels. These novel theories remove the need for numerical simulations and can be implemented easily in practice. Here we present a comparative study designed to validate these new methods against experimental data. Extensive experiments were performed on a well-instrumented laboratory single-screw extruder, using various materials, screw designs, and processing conditions. A network-theory-based simulation routine was written in MATLAB to replicate the flow in the metering zones in silico. The predictions of the three-dimensional heuristic melt-conveying model for the axial pressure profile along the screw are in excellent agreement with the experimental extrusion data. To demonstrate the usefulness of the novel melt-flow theories, we additionally compared the models to a modified Newtonian pumping model known from the literature. Full article

(This article belongs to the Special Issue Model-Based Polymer Processing)

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17 pages, 1867 KiB

Open AccessArticle

Sulfonated Lignin-g-Styrene Polymer: Production and Characterization

by Nasim Ghavidel Darestani, Adrianna Tikka and Pedram Fatehi

Polymers 2018, 10(8), 928; https://doi.org/10.3390/polym10080928 - 19 Aug 2018

Cited by 11 | Viewed by 7473

Abstract

Among sustainable alternatives for replacing fossil-based chemicals, lignin is widely available on earth, albeit the least utilized component of biomass. In this work, lignin was polymerized with styrene in aqueous emulsion systems. The reaction afforded a yield of 20 wt % under the [...] Read more.

Among sustainable alternatives for replacing fossil-based chemicals, lignin is widely available on earth, albeit the least utilized component of biomass. In this work, lignin was polymerized with styrene in aqueous emulsion systems. The reaction afforded a yield of 20 wt % under the conditions of 100 g/L lignin concentration, pH 2.5, 0.35 mol/L sodium dodecyl sulfate concentration, 5 mol/mol styrene/lignin ratio, 5 wt % initiator, 90 °C, and 2 h. The lignin-g-styrene product under the selected conditions had a grafting degree of 31 mol % of styrene, which was determined by quantitative proton nuclear magnetic resonance (NMR). The solvent addition to the reaction mixture and deoxygenation did not improve the yield of the polymerization reaction. The produced lignin-g-styrene polymer was then sulfonated using concentrated sulfuric acid. By introducing sulfonate group on the lignin-g-styrene polymers, the solubility and anionic charge density of 92 wt % (in a 10 g/L solution) and −2.4 meq/g, respectively, were obtained. Fourier-transform infrared (FTIR), static light scattering, two-dimensional COSY NMR, elemental analyses, and differential scanning calorimetry (DSC) were also employed to characterize the properties of the lignin-g-styrene and sulfonate lignin-g-styrene products. Overall, sulfonated lignin-g-styrene polymer with a high anionicity and water solubility was produced. Full article

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16 pages, 4412 KiB

Open AccessArticle

Microbial Conversion of Vegetable Oil to Hydroxy Fatty Acid and Its Application to Bio-Based Polyurethane Synthesis

by Tuan Kiet Tran, Prasun Kumar, Hak-Ryul Kim, Ching T. Hou and Beom Soo Kim

Polymers 2018, 10(8), 927; https://doi.org/10.3390/polym10080927 - 19 Aug 2018

Cited by 16 | Viewed by 7110

Abstract

New polyurethanes were synthesized based on dihydroxy fatty acid obtained by the microbial conversion of olive oil. Monounsaturated 7,10-dihydroxy-8(E)-octadecenoic acid (DOD) was produced from olive oil by Pseudomonas aeruginosa PR3 and reacted with hexamethylene diisocyanate (HMDI) at different ratios to form polyurethanes. Fourier [...] Read more.

New polyurethanes were synthesized based on dihydroxy fatty acid obtained by the microbial conversion of olive oil. Monounsaturated 7,10-dihydroxy-8(E)-octadecenoic acid (DOD) was produced from olive oil by Pseudomonas aeruginosa PR3 and reacted with hexamethylene diisocyanate (HMDI) at different ratios to form polyurethanes. Fourier transform infrared spectroscopy and gas chromatography/mass spectrometry confirmed the synthesis of DOD. The thermal and tensile properties of the polyurethanes were investigated by differential scanning calorimetry, thermogravimetric analysis, and a universal testing machine. At an isocyanate/hydroxyl ratio of 1.4, the polyurethane exhibited an elongation at break of 59.2% and a high tensile strength of 37.9 MPa. DOD was also mixed with polycaprolactone diol or polyethylene glycol at different weight ratios and then reacted with HMDI to produce new polyurethanes of various properties. These polyurethanes displayed higher elongation at break and good thermal stability. This is the first report on the synthesis of polyurethanes based on DOD produced by the microbial conversion of vegetable oil. Full article

(This article belongs to the Special Issue Recent Advances in Bioplastics)

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17 pages, 2520 KiB

Open AccessArticle

Hydrodynamic Shear Effects on Grafted and Non-Grafted Collapsed Polymers

by Richard Schwarzl and Roland R. Netz

Polymers 2018, 10(8), 926; https://doi.org/10.3390/polym10080926 - 18 Aug 2018

Cited by 10 | Viewed by 4393

Abstract

We study collapsed homo-polymeric molecules under linear shear flow conditions using hydrodynamic Brownian dynamics simulations. Tensile force profiles and the shear-rate-dependent globular-coil transition for grafted and non-grafted chains are investigated to shine light on the different unfolding mechanisms. The scaling of the critical [...] Read more.

We study collapsed homo-polymeric molecules under linear shear flow conditions using hydrodynamic Brownian dynamics simulations. Tensile force profiles and the shear-rate-dependent globular-coil transition for grafted and non-grafted chains are investigated to shine light on the different unfolding mechanisms. The scaling of the critical shear rate, at which the globular-coil transition takes place, with the monomer number is inverse for the grafted and non-grafted scenarios. This implicates that for the grafted scenario, larger chains have a decreased critical shear rate, while for the non-grafted scenario higher shear rates are needed in order to unfold larger chains. Protrusions govern the unfolding transition of non-grafted polymers, while for grafted polymers, the maximal tension appears at the grafted end. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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20 pages, 5542 KiB

Open AccessArticle

Electrically Conductive Polyetheretherketone Nanocomposite Filaments: From Production to Fused Deposition Modeling

by Jordana Gonçalves, Patrícia Lima, Beate Krause, Petra Pötschke, Ugo Lafont, José R. Gomes, Cristiano S. Abreu, Maria C. Paiva and José A. Covas

Polymers 2018, 10(8), 925; https://doi.org/10.3390/polym10080925 - 18 Aug 2018

Cited by 77 | Viewed by 11711

Abstract

The present work reports the production and characterization of polyetheretherketone (PEEK) nanocomposite filaments incorporating carbon nanotubes (CNT) and graphite nanoplates (GnP), electrically conductive and suitable for fused deposition modeling (FDM) processing. The nanocomposites were manufactured by melt mixing and those presenting electrical conductivity [...] Read more.

The present work reports the production and characterization of polyetheretherketone (PEEK) nanocomposite filaments incorporating carbon nanotubes (CNT) and graphite nanoplates (GnP), electrically conductive and suitable for fused deposition modeling (FDM) processing. The nanocomposites were manufactured by melt mixing and those presenting electrical conductivity near 10 S/m were selected for the production of filaments for FDM. The extruded filaments were characterized for mechanical and thermal conductivity, polymer crystallinity, thermal relaxation, nanoparticle dispersion, thermoelectric effect, and coefficient of friction. They presented electrical conductivity in the range of 1.5 to 13.1 S/m, as well as good mechanical performance and higher thermal conductivity compared to PEEK. The addition of GnP improved the composites’ melt processability, maintained the electrical conductivity at target level, and reduced the coefficient of friction by up to 60%. Finally, three-dimensional (3D) printed test specimens were produced, showing a Young’s modulus and ultimate tensile strength comparable to those of the filaments, but a lower strain at break and electrical conductivity. This was attributed to the presence of large voids in the part, revealing the need for 3D printing parameter optimization. Finally, filament production was up-scaled to kilogram scale maintaining the properties of the research-scale filaments. Full article

(This article belongs to the Special Issue Polymers: Design, Function and Application)

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16 pages, 6587 KiB

Open AccessArticle

An Experimental Study on the Shear Behaviors of Polymer-Sand Composite Materials after Immersion

by Jin Liu, Yuxia Bai, Ding Li, Qiongya Wang, Wei Qian, Ying Wang, Debi Prasanna Kanungo and Jihong Wei

Polymers 2018, 10(8), 924; https://doi.org/10.3390/polym10080924 - 18 Aug 2018

Cited by 29 | Viewed by 5435

Abstract

Sand mixed with geotextile/fiber/cement/lime or non-traditional chemical additives to form composite materials is recognized as an effective method for improving the sand properties. In this work, the variation in properties of composite materials after immersion is reported which has rarely appeared in the [...] Read more.

Sand mixed with geotextile/fiber/cement/lime or non-traditional chemical additives to form composite materials is recognized as an effective method for improving the sand properties. In this work, the variation in properties of composite materials after immersion is reported which has rarely appeared in the literature. The focus of this study is to evaluate the shear behaviors of polymer-sand composite material after immersion with direct shear tests. Several factors which may influence the shear behaviors after immersion are analyzed. The results demonstrate that this composite material still has good shear behaviors after immersion when compared to the purely sand material. The shear behaviors are improved with an increment in the curing time, polymer content and sand dry density while there is a decrease in the shear behaviors with increasing immersion time. The interaction between sand particles and the polymer are analyzed with Scanning Electron Microscope (SEM). The polymer membranes are formed by polymer enwrapping and connected sand particles to build an elastic and viscous structure in the sand that increases the interlocking forces between sand particles and decreases the void ratio of this material. The membranes are softened in water resulting in a decrease in the shear strength. Moreover, other factors affect the shear behaviors by improving the completeness and stability of this structure. Full article

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14 pages, 3800 KiB

Open AccessArticle

Synthesis and Properties of Silk Fibroin/Konjac Glucomannan Blend Beads

by Carla Giometti França, Vicente Franco Nascimento, Jacobo Hernandez-Montelongo, Daisy Machado, Marcelo Lancellotti and Marisa Masumi Beppu

Polymers 2018, 10(8), 923; https://doi.org/10.3390/polym10080923 - 18 Aug 2018

Cited by 11 | Viewed by 5551

Abstract

Silk fibroin (SF) and konjac glucomannan (KGM) are promising materials in the biomedical field due to their low toxicity, biocompatibility, biodegradability and low immune response. Beads of these natural polymers are interesting scaffolds for biomedical applications, but their fabrication is a challenge due [...] Read more.

Silk fibroin (SF) and konjac glucomannan (KGM) are promising materials in the biomedical field due to their low toxicity, biocompatibility, biodegradability and low immune response. Beads of these natural polymers are interesting scaffolds for biomedical applications, but their fabrication is a challenge due to their low stability and the necessary adaptation of their chemical and mechanical properties to be successfully applied. In that sense, this study aimed to synthesize a blend of silk fibroin and konjac glucomannan (SF/KGM) in the form of porous beads obtained through dripping into liquid nitrogen, with a post-treatment using ethanol. Intermolecular hydrogen bonds promoted the integration of SF and KGM. Treated beads showed higher porous size, crystallinity, and stability than untreated beads. Characterization analyses by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric (TGA), and X-ray diffraction (XDR) evidenced that ethanol treatment allows a conformational transition from silk I to silk II in SF and an increase in the KGM deacetylation. Those chemical changes significantly enhanced the mechanical resistance of SF/KGM beads in comparison to pure SF and KGM beads. Moreover, samples showed cytocompatibility with HaCaT and BALB/c 3T3 cells. Full article

(This article belongs to the Special Issue Intrinsically Biocompatible Polymer Systems)

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13 pages, 19265 KiB

Open AccessArticle

Extrusion 3D Printing of Polybutyrate-Adipate-Terephthalate-Polymer Composites in the Pellet Form

by Sarat Singamneni, Dawn Smith, Marie-Joo LeGuen and Derryn Truong

Polymers 2018, 10(8), 922; https://doi.org/10.3390/polym10080922 - 17 Aug 2018

Cited by 40 | Viewed by 7449

Abstract

Fused deposition modelling is a common 3D printing technique used for the freeform fabrication of complex shapes based on polymers. Acrylonitrile butadiene styrene (ABS) is the common material option, though polylactide (PLA) has also proved to be a successful candidate. There is an [...] Read more.

Fused deposition modelling is a common 3D printing technique used for the freeform fabrication of complex shapes based on polymers. Acrylonitrile butadiene styrene (ABS) is the common material option, though polylactide (PLA) has also proved to be a successful candidate. There is an ever increasing demand to harness new materials as possible candidates for fused deposition. The current research is focused on evaluating polybutyrate-adipate-terephthalate–polymer (PBAT) for fused deposition modelling. Both neat and composite PBAT filled with varying wood flour fillers were experimentally analyzed for 3D printing by extrusion from the pellet forms. The results are positive and the addition of small quantities of the wood flour filler material was found to improve the thixotropic nature of the polymer composite and consequently the inter-strand and inter-layer coalescence. Full article

(This article belongs to the Special Issue Additive Manufacturing of Polymeric Materials)

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12 pages, 2670 KiB

Open AccessCommunication

Embedding Carbon Dots in Superabsorbent Polymers for Additive Manufacturing

by Yiqun Zhou, Keenan J. Mintz, Cagri Y. Oztan, Sajini D. Hettiarachchi, Zhili Peng, Elif S. Seven, Piumi Y. Liyanage, Sabrina De La Torre, Emrah Celik and Roger M. Leblanc

Polymers 2018, 10(8), 921; https://doi.org/10.3390/polym10080921 - 17 Aug 2018

Cited by 47 | Viewed by 7000

Abstract

A type of orange carbon dots (O-CDs) synthesized via an ultrasonication route with citric acid and 1,2-phenylenediamine as precursors was embedded into sodium polyacrylate (SPA) as the ink for 3D printing. Characterizations of these spherical O-CDs revealed an ultra-small size (~2 nm) and [...] Read more.

A type of orange carbon dots (O-CDs) synthesized via an ultrasonication route with citric acid and 1,2-phenylenediamine as precursors was embedded into sodium polyacrylate (SPA) as the ink for 3D printing. Characterizations of these spherical O-CDs revealed an ultra-small size (~2 nm) and excitation-independent, but solvent dependent, emission. The O-CDs were evenly distributed with low degree of aggregation in sodium polyacrylate (SPA), which was achieved due to the property that SPA can absorb water together with O-CDs. The 3D printed photoluminescent objective with the ink revealed a great potential for high yield application of these materials for additive manufacturing. This also represents the first time, bare CDs have been reported as a photoluminescent material in 3D printing, as well as the first time SPA has been reported as a material for 3D printing. Full article

(This article belongs to the Special Issue Polymers in Carbon Dots)

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10 pages, 3375 KiB

Open AccessArticle

Preparation and Characterization of Esterified Bamboo Flour by an In Situ Solid Phase Method

by Yaqi Geng, Xiaohan Pei, Xiaoyu He, Ping Li, Yiqiang Wu and Yingfeng Zuo

Polymers 2018, 10(8), 920; https://doi.org/10.3390/polym10080920 - 16 Aug 2018

Cited by 7 | Viewed by 4087

Abstract

Bamboo plastic composites have become a hot research topic and a key focus of research. However, many strong, polar, hydrophilic hydroxyl groups in bamboo flour (BF) results in poor interfacial compatibility between BF and hydrophobic polymers. Maleic anhydride-esterified (MAH-e-BF) and lactic acid-esterified bamboo [...] Read more.

Bamboo plastic composites have become a hot research topic and a key focus of research. However, many strong, polar, hydrophilic hydroxyl groups in bamboo flour (BF) results in poor interfacial compatibility between BF and hydrophobic polymers. Maleic anhydride-esterified (MAH-e-BF) and lactic acid-esterified bamboo flour (LA-e-BF) were prepared while using an in situ solid-phase esterification method with BF as the raw material and maleic anhydride or lactic acid as the esterifying agent. Fourier transform infrared spectroscopy results confirmed that BF esterification with maleic anhydride and lactic acid was successful, with the esterification degrees of MAH-e-BF and LA-e-BF at 21.04 ± 0.23% and 14.28 ± 0.17%, respectively. Esterified BF was characterized by scanning electron microscopy, contact angle testing, X-ray diffractometry, and thermogravimetric analysis. The results demonstrated that esterified BF surfaces were covered with graft polymer and the surface roughness and bonding degree of MAH-e-BF clearly larger than those of LA-e-BF. The hydrophobicity of esterified BF was significantly higher than BF and the hydrophobicity of MAH-e-BF was better than LA-e-BF. The crystalline structure of esterified BF showed some damage, while MAH-e-BF exhibited a greater decrease in crystallinity than LA-e-BF. Overall, the esterification reaction improved BF thermoplasticity, with the thermoplasticity of MAH-e-BF appearing to be better than LA-e-BF. Full article

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15 pages, 4816 KiB

Open AccessArticle

Investigation on the Properties of PMMA/Reactive Halloysite Nanocomposites Based on Halloysite with Double Bonds

by Shiwei Chen, Zhizhou Yang and Fuzhong Wang

Polymers 2018, 10(8), 919; https://doi.org/10.3390/polym10080919 - 15 Aug 2018

Cited by 17 | Viewed by 7183

Abstract

PMMA/reactive halloysite nanocomposites were firstly prepared using reactive halloysite with double bonds. The halloysite was functionalized to improve its dispersion in the polymer matrix. The reactive halloysite could increase the molecular weight of PMMA. The molecular distribution of PMMA/reactive halloysite nanocomposite was more [...] Read more.

PMMA/reactive halloysite nanocomposites were firstly prepared using reactive halloysite with double bonds. The halloysite was functionalized to improve its dispersion in the polymer matrix. The reactive halloysite could increase the molecular weight of PMMA. The molecular distribution of PMMA/reactive halloysite nanocomposite was more uniform than that of PMMA. The moisture absorption of PMMA/reactive halloysite nanocomposite increased with the addition of the reactive halloysite. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) confirmed that the thermal stability of PMMA/reactive halloysite nanocomposites was greatly enhanced. Significant improvement in the mechanical property of PMMA nanocomposites was achieved by the addition of 3 wt % reactive halloysite. A 31.1% increase in tensile strength and a 64.2% increase in Young’ modulus of the nanocomposites with 3 wt % of the reactive halloysite were achieved. Finally, the formation mechanism of PMMA/reactive halloysites nanocomposites was proposed. This approach demonstrated the potential for general applicability to other polymer nanocomposites. Full article

(This article belongs to the Special Issue Polymer-Clay (Nano)Composites)

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22 pages, 3345 KiB

Open AccessArticle

Composite Biopolymer-Based Wafer Dressings Loaded with Microbial Biosurfactants for Potential Application in Chronic Wounds

by Olufunke Akiyode and Joshua Boateng

Polymers 2018, 10(8), 918; https://doi.org/10.3390/polym10080918 - 15 Aug 2018

Cited by 27 | Viewed by 6330

Abstract

In this study two bioactive polysaccharide polymers kappa-carrageenan (CARR) and sodium alginate (SA) incorporated with microbial biosurfactants (BSs) were formulated as medicated wafer dressings for potential application in chronic wounds. Wafers were loaded with BSs at concentrations of 0.1% and 0.2% rhamnolipids [...] Read more.

In this study two bioactive polysaccharide polymers kappa-carrageenan (CARR) and sodium alginate (SA) incorporated with microbial biosurfactants (BSs) were formulated as medicated wafer dressings for potential application in chronic wounds. Wafers were loaded with BSs at concentrations of 0.1% and 0.2% rhamnolipids (RL) and 0.1% and 5% sophorolipids (SL) and were functionally characterized using scanning electron microscopy (SEM), texture analysis (mechanical strength and in vitro wound adhesion), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray diffraction (XRD) and exudate handling properties (pore analysis, swelling index, water absorption (Aw), equilibrium water content (EWC), evaporative water loss (EWL) and water vapor transmission rate (WVTR). The wafers were tactile and ductile in appearance with a hardness range of 2.7–4.1 N and can withstand normal stresses but are also flexible to prevent damage to newly formed skin tissues. Wafers were porous (SEM) with pore sizes ranging from 78.8 to 141 µm, and BSs were not visible on the wafer surface or pore walls. The BSs enhanced the porosity of the wafers with values above 98%, while the Aw and EWC ranged from 2699–3569% and 96.58–98.00%, respectively. The EWL ranged from 85 to 86% after 24 h while the WVTR ranged from 2702–3080 g/m² day⁻¹. The compatibility of BSs within the CARR-SA matrix was confirmed by seven characteristic functional groups which were consistently transmitted in the ATR-FTIR spectra. These novel medicated dressing prototypes can potentially help to achieve more rapid wound healing. Full article

(This article belongs to the Special Issue Polymeric Materials for Tissue Engineering)

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13 pages, 3920 KiB

Open AccessArticle

New Polyhedral Oligomeric Silsesquioxanes-Based Fluorescent Ionic Liquids: Synthesis, Self-Assembly and Application in Sensors for Detecting Nitroaromatic Explosives

by Wensi Li, Dengxu Wang, Dongdong Han, Ruixue Sun, Jie Zhang and Shengyu Feng

Polymers 2018, 10(8), 917; https://doi.org/10.3390/polym10080917 - 15 Aug 2018

Cited by 10 | Viewed by 4659

Abstract

In this paper, two different models of hybrid ionic liquids (ILs) based on polyhedral oligomeric silsesquioxanes (POSSs) have been prepared. Additionally, these ILs based on POSSs (ILs-POSSs) exhibited excellent thermal stabilities and low glass transition temperatures. ¹H, ¹³C, and ²⁹Si [...] Read more.

In this paper, two different models of hybrid ionic liquids (ILs) based on polyhedral oligomeric silsesquioxanes (POSSs) have been prepared. Additionally, these ILs based on POSSs (ILs-POSSs) exhibited excellent thermal stabilities and low glass transition temperatures. ¹H, ¹³C, and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were used to confirm the structures of the IL-POSSs. Furthermore, the spherical vesicle structures of two IL-POSSs were observed and were caused by self-assembly behaviors. In addition, we found it very meaningful that these two ILs showed lower detection limits of 2.57 × 10⁻⁶ and 3.98 × 10⁻⁶ mol/L for detecting picric acid (PA). Moreover, the experimental data revealed that the products have high sensitivity for detecting a series of nitroaromatic compounds—including 4-nitrophenol, 2,4-dinitrophenol, and PA—and relatively comprehensive explosive detection in all of the tests of IL-POSSs with nitroaromatic compounds thus far. Additionally, the data indicate that these two new ILs have great potential for the detection of explosives. Therefore, our work may provide new materials including ILs as fluorescent sensors in detecting nitroaromatic explosives. Full article

(This article belongs to the Special Issue POSS-Based Polymers)

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6 pages, 6092 KiB

Open AccessCommunication

Elucidating Tricin-Lignin Structures: Assigning Correlations in HSQC Spectra of Monocot Lignins

by Wu Lan, Fengxia Yue, Jorge Rencoret, José Carlos Del Río, Wout Boerjan, Fachuang Lu and John Ralph

Polymers 2018, 10(8), 916; https://doi.org/10.3390/polym10080916 - 15 Aug 2018

Cited by 32 | Viewed by 6915

Abstract

Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one] is a flavone that has been found to be incorporated in grass lignin polymers via 4′–O–β coupling. Herein, we investigated the tricin-lignin structure using nuclear magnetic resonance (NMR) methods by comparing the 1H–13C heteronuclear correlation (HSQC) NMR spectra of the isolated [...] Read more.

Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one] is a flavone that has been found to be incorporated in grass lignin polymers via 4′–O–β coupling. Herein, we investigated the tricin-lignin structure using nuclear magnetic resonance (NMR) methods by comparing the 1H–13C heteronuclear correlation (HSQC) NMR spectra of the isolated lignin with a series of dimeric and trimeric tricin-4′–O–β-ether model compounds. Results showed that the tricin moiety significantly affects the chemical shift of the Cβ/Hβ of 4′–O–β unit, producing peaks at around δC/δH 82.5–83.5/4.15–4.45, that differ from the Cβ/Hβ correlations from normal 4–O–β units formed solely by monolignols, and that have to date been unassigned. Full article

(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)

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14 pages, 2545 KiB

Open AccessFeature PaperArticle

Responsive Protein Hydrogels Assembled from Spider Silk Carboxyl-Terminal Domain and Resilin Copolymers

by Fang Luo, Zhi-Gang Qian and Xiao-Xia Xia

Polymers 2018, 10(8), 915; https://doi.org/10.3390/polym10080915 - 14 Aug 2018

Cited by 15 | Viewed by 5198

Abstract

Responsive protein hydrogels are known to respond to target external stimuli that cause changes in their properties, attracting considerable attention for diverse applications. Here we report the design and recombinant biosynthesis of protein copolymers via genetic fusion of repeating units of resilin with [...] Read more.

Responsive protein hydrogels are known to respond to target external stimuli that cause changes in their properties, attracting considerable attention for diverse applications. Here we report the design and recombinant biosynthesis of protein copolymers via genetic fusion of repeating units of resilin with spider silk carboxyl-terminal (CT) domain. The resulting copolymers were thermoresponsive in aqueous solutions, and formed reversible hydrogels at low temperatures and irreversible hydrogels at high temperatures within minutes, a peculiar dual thermogelation feature endowed by the CT domain. The incorporation of resilin blocks upshifted the temperature range of reversible gelation and hydrogel stiffness, whereas the temperature of irreversible gelation was differentially affected by the length of the resilin blocks. In addition, sodium chloride and potassium phosphate at moderate concentrations downregulated both the reversible and irreversible gelation temperatures and hydrogel mechanical properties, proving the salts as another level of control over dual thermogelation. Surprisingly, the copolymers were prone to gelate at body temperature in a time-dependent manner, and the resulting hydrogels were pH-responsive to release a highly polar model drug in vitro. The newly developed resilin-CT copolymers and the multistimuli-responsive hydrogels may be potentially useful in biomedicine, such as for drug delivery. Full article

(This article belongs to the Special Issue Protein Biopolymer)

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17 pages, 2785 KiB

Open AccessArticle

Bioglass-Incorporated Methacrylated Gelatin Cryogel for Regeneration of Bone Defects

by Song Kwon, Seunghun S. Lee, A. Sivashanmugam, Janet Kwon, Seung Hyun L. Kim, Mi Yeon Noh, Seong Keun Kwon, R. Jayakumar and Nathaniel S. Hwang

Polymers 2018, 10(8), 914; https://doi.org/10.3390/polym10080914 - 14 Aug 2018

Cited by 53 | Viewed by 8967

Abstract

Cryogels have recently gained interest in the field of tissue engineering as they inherently possess an interconnected macroporous structure. Considered to be suitable for scaffold cryogel fabrication, methacrylated gelatin (GelMA) is a modified form of gelatin valued for its ability to retain cell [...] Read more.

Cryogels have recently gained interest in the field of tissue engineering as they inherently possess an interconnected macroporous structure. Considered to be suitable for scaffold cryogel fabrication, methacrylated gelatin (GelMA) is a modified form of gelatin valued for its ability to retain cell adhesion site. Bioglass nanoparticles have also attracted attention in the field due to their osteoinductive and osteoconductive behavior. Here, we prepare methacrylated gelatin cryogel with varying concentration of bioglass nanoparticles to study its potential for bone regeneration. We demonstrate that an increase in bioglass concentration in cryogel leads to improved mechanical property and augmented osteogenic differentiation of mesenchymal cells during in vitro testing. Furthermore, in vivo testing in mice cranial defect model shows that highest concentration of bioglass nanoparticles (2.5 w/w %) incorporated in GelMA cryogel induces the most bone formation compared to the other tested groups, as studied by micro-CT and histology. The in vitro and in vivo results highlight the potential of bioglass nanoparticles incorporated in GelMA cryogel for bone regeneration. Full article

(This article belongs to the Special Issue Polymeric Micro/Nanoparticles for Bio-Medical Applications)

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19 pages, 4122 KiB

Open AccessArticle

Preparation and Identification of Optimal Synthesis Conditions for a Novel Alkaline Anion-Exchange Membrane

by Aitor Marcos-Madrazo, Clara Casado-Coterillo, Leticia García-Cruz, Jesús Iniesta, Laura Simonelli, Víctor Sebastián, María Del Mar Encabo-Berzosa, Manuel Arruebo and Ángel Irabien

Polymers 2018, 10(8), 913; https://doi.org/10.3390/polym10080913 - 13 Aug 2018

Cited by 12 | Viewed by 5246

Abstract

The physicochemical and mechanical properties of new alkaline anion-exchange membranes (AAEMs) based on chitosan (CS) and poly(vinyl alcohol) (PVA) polymers doped with unsupported copper nanoparticles (NPs) and copper exchanged over different porous materials were investigated regarding ion-exchange capacity (IEC), OH⁻ conductivity, water [...] Read more.

The physicochemical and mechanical properties of new alkaline anion-exchange membranes (AAEMs) based on chitosan (CS) and poly(vinyl alcohol) (PVA) polymers doped with unsupported copper nanoparticles (NPs) and copper exchanged over different porous materials were investigated regarding ion-exchange capacity (IEC), OH⁻ conductivity, water uptake (WU), water vapor permeability (WVP), and thermal and mechanical resistance. The influence of the type of filler included in different morphologies and filler loading has been explored using copper exchanged materials such as the layered porous titanosilicate AM-4, layered stannosilicate UZAR-S3, and zeolites Y, MOR, and BEA. Compared to commercially available anion-exchange membranes, the best performing membranes in terms of WU, IEC, OH⁻ conductivity and WVP in this study were those containing 10 wt % of Cu-AM-4 and Cu-UZAR-S3, although 10 wt % Cu-MOR provided better mechanical strength at close values of WVP and anion conductivity. It was also observed that when Cu was exchanged in a porous silicate matrix, its oxidation state was lower than when embedded as unsupported metal NPs. In addition, the statistical analysis of variance determined that the electrochemical properties of the membranes were noticeably affected by both the type and filler loading, and influenced also by the copper oxidation state and content in the membrane, but their hydrophilic properties were more affected by the polymers. The largest significant effects were noticed on the water sorption and transport properties, which gives scope for the design of AAEMs for electrochemical and water treatment applications. Full article

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19 pages, 6192 KiB

Open AccessArticle

New Pyridinium Type Poly(Ionic Liquids) as Membranes for CO₂ Separation

by Aristofanis Vollas, Thanasis Chouliaras, Valadoula Deimede, Theophilos Ioannides and Joannis Kallitsis

Polymers 2018, 10(8), 912; https://doi.org/10.3390/polym10080912 - 13 Aug 2018

Cited by 39 | Viewed by 6076

Abstract

New pyridinium based PILs have been prepared by modification of their precursors based on high molecular weight aromatic polyethers bearing main chain pyridine units. The proposed methodology involves the conversion of the precursors to their ionic analogues via N-methylation reaction, followed by [...] Read more.

New pyridinium based PILs have been prepared by modification of their precursors based on high molecular weight aromatic polyethers bearing main chain pyridine units. The proposed methodology involves the conversion of the precursors to their ionic analogues via N-methylation reaction, followed by anion exchange methathesis reaction to result in PILs with the desirable anions (tetrafluoroborate and bis(trifluoromethylsulfonyl)imide). These PILs show excellent thermal stability, excellent mechanical properties, and most importantly can form very thin, free standing films with minimum thickness of 3 μm. As expected, the PIL containing the TFSI⁻ anion showed improved CO₂ and CH₄ permeabilities compared to its analogue containing the BF₄⁻. PIL-IL composites membranes have also been prepared using the same PIL and different percentages of pyridinium based IL where it was shown that the membrane with the highest IL weight percentage (45 wt %) showed the highest CO₂ permeability (11.8 Barrer) and a high CO₂/CH₄ ideal selectivity of 35 at room temperature. Full article

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3 pages, 179 KiB

Open AccessEditorial

Host–Guest Polymer Complexes

by Alan E. Tonelli, Ganesh Narayanan and Alper Gurarslan

Polymers 2018, 10(8), 911; https://doi.org/10.3390/polym10080911 - 13 Aug 2018

Cited by 4 | Viewed by 3520

Abstract

n/a Full article

(This article belongs to the Special Issue Host-Guest Polymer Complexes)

12 pages, 507 KiB

Open AccessReview

Role of PhaC Type I and Type II Enzymes during PHA Biosynthesis

by Valeria Mezzolla, Oscar Fernando D’Urso and Palmiro Poltronieri

Polymers 2018, 10(8), 910; https://doi.org/10.3390/polym10080910 - 13 Aug 2018

Cited by 47 | Viewed by 7722

Abstract

PHA synthases (PhaC) are grouped into four classes based on the kinetics and mechanisms of reaction. The grouping of PhaC enzymes into four classes is dependent on substrate specificity, according to the preference in forming short-chain-length (scl) or medium-chain-length (mcl) polymers: Class I, [...] Read more.

PHA synthases (PhaC) are grouped into four classes based on the kinetics and mechanisms of reaction. The grouping of PhaC enzymes into four classes is dependent on substrate specificity, according to the preference in forming short-chain-length (scl) or medium-chain-length (mcl) polymers: Class I, Class III and Class IV produce scl-PHAs depending on propionate, butyrate, valerate and hexanoate precursors, while Class II PhaC synthesize mcl-PHAs based on the alkane (C6 to C14) precursors. PHA synthases of Class I, in particular PhaC_Cs from Chromobacterium USM2 and PhaC_Cn/RePhaC1 from Cupriavidus necator/Ralstonia eutropha, have been analysed and the crystal structures of the C-domains have been determined. PhaC_Cn/RePhaC1 was also studied by X-ray absorption fine-structure (XAFS) analysis. Models have been proposed for dimerization, catalysis mechanism, substrate recognition and affinity, product formation, and product egress route. The assays based on amino acid substitution by mutagenesis have been useful to validate the hypothesis on the role of amino acids in catalysis and in accommodation of bulky substrates, and for the synthesis of PHB copolymers and medium-chain-length PHA polymers with optimized chemical properties. Full article

(This article belongs to the Special Issue Recent Advances in Bioplastics)

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14 pages, 2482 KiB

Open AccessArticle

A High-Performance and Low-Cost Soy Flour Adhesive with a Hydroxymethyl Melamine Prepolymer

by Meng Zhang, Yi Zhang, Mingsong Chen, Qiang Gao and Jianzhang Li

Polymers 2018, 10(8), 909; https://doi.org/10.3390/polym10080909 - 13 Aug 2018

Cited by 23 | Viewed by 3848

Abstract

To improve the performance of a soy flour (SF)-based adhesive, a low-cost hydroxymethyl melamine prepolymer (HMP) was synthesized and then used to modify the SF-based adhesive. The HMP was characterized, and the performance of the adhesive was evaluated, including its residual rate, functions, [...] Read more.

To improve the performance of a soy flour (SF)-based adhesive, a low-cost hydroxymethyl melamine prepolymer (HMP) was synthesized and then used to modify the SF-based adhesive. The HMP was characterized, and the performance of the adhesive was evaluated, including its residual rate, functions, thermal stability, and fracture section. Plywood was fabricated to measure wet shear strength. The results indicated that the HMP preferentially reacted with polysaccharose in SF and formed a cross-linking network to improve the water resistance of the adhesive. This polysaccharose-based network also combined with the HMP self-polycondensation network and soy protein to form an interpenetrating network, which further improved the water resistance of the adhesive. With the addition of 9% HMP, the wet shear strength (63 °C) of the plywood was 1.21 MPa, which was 9.3 times that of the SF adhesive. With the HMP additive increased to 15%, the shear strength (100 °C) of the plywood was 0.79 MPa, which met the plywood requirement for exterior use (≥0.7 MPa) in accordance with Chinese National Standard (GB/T 9846.3-2004). With the addition of 9% and 15% HMP, the residual rates of the adhesive improved by 5.1% and 8.5%, respectively. The dense interpenetrating network structure improved the thermal stability of the resultant adhesive and created a compact fracture to prevent moisture intrusion, which further increased the water resistance of the adhesive. Full article

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18 pages, 998 KiB

Open AccessArticle

Efficient Determination of Slip-Link Parameters from Broadly Polydisperse Linear Melts

by Néstor E. Valadez-Pérez, Konstantin Taletskiy, Jay D. Schieber and Maksim Shivokhin

Polymers 2018, 10(8), 908; https://doi.org/10.3390/polym10080908 - 12 Aug 2018

Cited by 10 | Viewed by 4703

Abstract

We investigate the ability of a coarse-grained slip-link model and a simple double reptation model to describe the linear rheology of polydisperse linear polymer melts. Our slip-link model is a well-defined mathematical object that can describe the equilibrium dynamics and non-linear rheology of [...] Read more.

We investigate the ability of a coarse-grained slip-link model and a simple double reptation model to describe the linear rheology of polydisperse linear polymer melts. Our slip-link model is a well-defined mathematical object that can describe the equilibrium dynamics and non-linear rheology of flexible polymer melts with arbitrary polydispersity and architecture with a minimum of inputs: the molecular weight of a Kuhn step, the entanglement activity, and Kuhn step friction. However, this detailed model is computationally expensive, so we also examine predictions of the cheaper double reptation model, which is restricted to only linear rheology near the terminal zone. We report the storage and loss moduli for polydisperse polymer melts and compare with experimental measurements from small amplitude oscillatory shear. We examine three chemistries: polybutadiene, polypropylene and polyethylene. We also use a simple double reptation model to estimate parameters for the slip-link model and examine under which circumstances this simplified model works. The computational implementation of the slip-link model is accelerated with the help of graphics processing units, which allow us to simulate in parallel large ensembles made of up to 50,000 chains. We show that our simulation can predict the dynamic moduli for highly entangled polymer melts over nine decades of frequency. Although the double reptation model performs well only near the terminal zone, it does provide a convenient and inexpensive way to estimate the entanglement parameter for the slip-link model from polydisperse data. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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14 pages, 3761 KiB

Open AccessArticle

Acylation of Lignin with Different Acylating Agents by Mechanical Activation-Assisted Solid Phase Synthesis: Preparation and Properties

by Xiaohong Zhao, Yanjuan Zhang, Mei Yang, Zuqiang Huang, Huayu Hu, Aimin Huang and Zhenfei Feng

Polymers 2018, 10(8), 907; https://doi.org/10.3390/polym10080907 - 12 Aug 2018

Cited by 25 | Viewed by 5229

Abstract

Acylated lignins with substituents consisting of different lengths of carbon chains were prepared by a mechanical activation-assisted solid phase synthesis (MASPS) technology with a customized stirring ball mill as a reactor. The structures and properties were analyzed by UV/Vis, FTIR, NMR, SEM, DSC, [...] Read more.

Acylated lignins with substituents consisting of different lengths of carbon chains were prepared by a mechanical activation-assisted solid phase synthesis (MASPS) technology with a customized stirring ball mill as a reactor. The structures and properties were analyzed by UV/Vis, FTIR, NMR, SEM, DSC, and TG. The results showed that the acylated lignins were successfully prepared with either non-cyclic or cyclic anhydrides as the acylating agents. Both aliphatic hydroxyl and phenolic hydroxyl groups of lignin reacted with non-cyclic anhydrides, and different reactivity of acylating agents resulted in different relative contents of phenolic and aliphatic substituents in the products. The reactivity of the cyclic anhydrides was weaker than that of the non-cyclic anhydrides, and the reactivity of the acylating agents decreased with increasing carbon chain length and unsaturated bonds of acyl groups. All of the acylated lignins except maleylated lignin had a lower glass transition temperature (T_g) than the original lignin. The acylated lignins prepared with non-cyclic anhydrides had better thermal stability than original lignin, and the thermal stability increased, but T_g decreased with an increasing chain length of the acyl groups. The acylated lignins prepared with cyclic anhydrides had higher a T_g than those with non-cyclic anhydrides with the same carbon number, and the thermal stability was not obviously improved. Full article

(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)

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9 pages, 3556 KiB

Open AccessArticle

Polyurethane/Red Mud Composites with Flexibility, Stretchability, and Flame Retardancy for Grouting

by Chunjing Zhang, Bo Shuai, Xuefeng Zhang, Xinxin Hu, Hui Zhang, Yuanheng Jia, Zhengpeng Yang and Xuemao Guan

Polymers 2018, 10(8), 906; https://doi.org/10.3390/polym10080906 - 12 Aug 2018

Cited by 18 | Viewed by 4711

Abstract

Flexibility, stretchability, and flame retardancy are of ever increasing importance in constructing grouting materials. Herein, a simple and effective strategy to make organic-inorganic composite grouting material in a “flexible, stretchable, and flame retardant” way was based on the excellent synergistic interactions among polyurethane [...] Read more.

Flexibility, stretchability, and flame retardancy are of ever increasing importance in constructing grouting materials. Herein, a simple and effective strategy to make organic-inorganic composite grouting material in a “flexible, stretchable, and flame retardant” way was based on the excellent synergistic interactions among polyurethane prepolymer, red mud, polyethylene glycol, and trimethylolpropane. The resultant polyurethane/red mud composite grouting material with three-dimensional network structure presented a favorable flexibility, desirable compressive strength of 29.2 MPa at 50% compression state, and a good elongation at 15.1%. The grouting material was mainly composed of amorphous polyurethane and crystalline red mud, and its probable formation mechanism was reaction of prepolymer with H₂O, polyethylene glycol and trimethylolpropane under vigorous stirring in the presence of catalyst. Furthermore, the grouting material possessed favorable thermal stability, flame retardancy and repairment performance for roadway cracks. This work may open a simple and convenient avenue for the massive engineering application of red mud and preparation of flexible organic-inorganic hybrid grouting material. Full article

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11 pages, 4517 KiB

Open AccessArticle

Dentine Surface Morphology after Chlorhexidine Application—SEM Study

by Barbara Lapinska, Leszek Klimek, Jerzy Sokolowski and Monika Lukomska-Szymanska

Polymers 2018, 10(8), 905; https://doi.org/10.3390/polym10080905 - 11 Aug 2018

Cited by 22 | Viewed by 5554

Abstract

Chlorhexidine (CHX) is a widely known and a very popular antibacterial agent that decreases the level of cariogenic bacteria. CHX applied on the cavity surface of dentine may influence adhesive bond strength. The aim of the study was to evaluate the dentine surface [...] Read more.

Chlorhexidine (CHX) is a widely known and a very popular antibacterial agent that decreases the level of cariogenic bacteria. CHX applied on the cavity surface of dentine may influence adhesive bond strength. The aim of the study was to evaluate the dentine surface after different chlorhexidine digluconate (CHG) application protocols. Different CHG application protocols were introduced. A concentration of 0.2% or 2.0% CHG was applied on the etched or unetched dentine surface for 15 or 30 s, then water rinsed or drained. Scanning electron microscopy (SEM) observations and energy disperse spectrometer (EDS) analysis of the dentine surfaces were performed. The application of 0.2% CHG for 15 s, followed by draining, on either etched or unetched dentine surface effectively removed the smear layer, leaving the surface enriched with CHG deposits. Conclusions: The concentration of CHG and its application time influenced the amount of CHG deposits and the degree of smear layer removal from the dentine surface. Full article

(This article belongs to the Special Issue Surface Modification and Functional Coatings for Polymers)

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10 pages, 1937 KiB

Open AccessArticle

The Rediscovery of POSS: A Molecule Rather than a Filler

by Ignazio Blanco

Polymers 2018, 10(8), 904; https://doi.org/10.3390/polym10080904 - 11 Aug 2018

Cited by 82 | Viewed by 6395

Abstract

The use of polyhedral oligomeric silsesquioxanes (POSSs) for making polymer composites has grown exponentially since the last few years of the 20th century. In comparison with the other most commonly used fillers, POSSs possess the advantage of being molecules. Thus, this allows us [...] Read more.

The use of polyhedral oligomeric silsesquioxanes (POSSs) for making polymer composites has grown exponentially since the last few years of the 20th century. In comparison with the other most commonly used fillers, POSSs possess the advantage of being molecules. Thus, this allows us to combine their nano-sized cage structures, which have dimensions that are similar to those of most polymer segments and produce a particular and exclusive chemical composition. These characteristics linked with their hybrid (inorganic–organic) nature allow researchers to modify POSS according to particular needs or original ideas, before incorporating them into polymers. In this present study, we first start with a brief introduction about the reasons for the rediscovery of these nanoparticles over the last 25 years. Starting from the form of POSS that is most widely used in literature (octaisobutyl POSS), this present study aims to evaluate how the reduction of symmetry through the introduction of organic groups favors their dispersion in polystyrene matrix without compromising their solubility. Full article

(This article belongs to the Special Issue POSS-Based Polymers)

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13 pages, 6884 KiB

Open AccessArticle

Nonlinear Material Model for Quasi-Unidirectional Woven Composite Accounting for Viscoelastic, Viscous Deformation, and Stiffness Reduction

by Zhanyu Zhai, Bingyan Jiang and Dietmar Drummer

Polymers 2018, 10(8), 903; https://doi.org/10.3390/polym10080903 - 11 Aug 2018

Cited by 4 | Viewed by 4628

Abstract

To clarify the individual contribution of viscoelastic and viscous deformation to the global nonlinear response of composites, multilevel cyclic loading-unloading recovery tensile tests were carried out. The experimental results show that there is a linear relationship between the viscous strain and viscoelastic strain [...] Read more.

To clarify the individual contribution of viscoelastic and viscous deformation to the global nonlinear response of composites, multilevel cyclic loading-unloading recovery tensile tests were carried out. The experimental results show that there is a linear relationship between the viscous strain and viscoelastic strain of composites, regardless of the off-axis angle or loading stress level. On the basis of experimental results, a coupled damage-plasticity constitutive model was proposed. In this model, the plasticity theory was adopted to assess the evolution of viscous strains. The viscoelastic strain was represented as a linear function of viscous strains. Moreover, the Weibull function of the effective stress was introduced to evaluate the damage variables in terms of stiffness reduction. The tensile stress-strain curves, predicted by the proposed model, showed a good agreement with experimental results. Full article

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10 pages, 2629 KiB

Open AccessArticle

Influence of the Cross-Link Density on the Rate of Crystallization of Poly(ε-Caprolactone)

by Igor Sedov, Timur Magsumov, Albert Abdullin, Egor Yarko, Timur Mukhametzyanov, Alexander Klimovitsky and Christoph Schick

Polymers 2018, 10(8), 902; https://doi.org/10.3390/polym10080902 - 11 Aug 2018

Cited by 22 | Viewed by 5955

Abstract

Cross-linked poly(ε-caprolactone) (PCL) is a smart biocompatible polymer exhibiting two-way shape memory effect. PCL samples with different cross-link density were synthesized by heating the polymer with various amounts of radical initiator benzoyl peroxide (BPO). Non-isothermal crystallization kinetics was characterized by means of conventional [...] Read more.

Cross-linked poly(ε-caprolactone) (PCL) is a smart biocompatible polymer exhibiting two-way shape memory effect. PCL samples with different cross-link density were synthesized by heating the polymer with various amounts of radical initiator benzoyl peroxide (BPO). Non-isothermal crystallization kinetics was characterized by means of conventional differential scanning calorimetry (DSC) and fast scanning calorimetry (FSC). The latter technique was used to obtain the dependence of the degree of crystallinity on the preceding cooling rate by following the enthalpies of melting for each sample. It is shown that the cooling rate required to keep the cooled sample amorphous decreases with increasing cross-link density, i.e., crystallization process slows down monotonically. Covalent bonds between polymer chains impede the crystallization process. Consequently, FSC can be used as a rather quick and low sample consuming method to estimate the degree of cross-linking of PCL samples. Full article

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Polymers, Volume 10, Issue 8 (August 2018) – 124 articles

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