Polymers

15 pages, 4399 KiB

Open AccessArticle

Enhanced Electrical Conductivity of Carbon Nanotube-Based Elastomer Nanocomposites Prepared by Microwave Curing

by Blake Herren, Preston Larson, Mrinal C. Saha and Yingtao Liu

Polymers 2019, 11(7), 1212; https://doi.org/10.3390/polym11071212 - 26 Jul 2019

Cited by 22 | Viewed by 6939

Nanocomposites consisting of polydimethylsiloxane (PDMS) and well-dispersed carbon nanotubes (CNT) can be cured by microwave radiation within a minute, forming a conductive network within the cured materials. Microwave irradiation delivers energy directly to the inner core of the nanocomposites by heating CNTs and [...] Read more.

Nanocomposites consisting of polydimethylsiloxane (PDMS) and well-dispersed carbon nanotubes (CNT) can be cured by microwave radiation within a minute, forming a conductive network within the cured materials. Microwave irradiation delivers energy directly to the inner core of the nanocomposites by heating CNTs and initiating rapid polymerization of the elastomer. In this paper, nanocomposites were fabricated with CNT loadings between 0.5 wt.%–2.5 wt.% via microwave irradiation. Key properties of the nanocomposites including electrical conductivity, microstructures, CNT distribution, density, and surface effects were all characterized. The properties of microwave-cured nanocomposites were compared with those manufactured by the thermal method using a conventional oven. The microwave-curing method substantially increased the electrical conductivity of the nanocomposites due to the improved nanoparticle dispersion and likely CNT alignment. Optimal microwave-curing parameters were identified to further improve the conductivity of the nanocomposites with lowest CNT loading. A conductivity enhancement of 142.8% over thermally cured nanocomposites was achieved for nanocomposites with 1 wt.% CNTs cured via one-step microwave irradiation. Full article

(This article belongs to the Special Issue Conducting Polymers)

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12 pages, 2225 KiB

Open AccessArticle

Purification of Polybutylene Terephthalate by Oligomer Removal Using a Compressed CO₂ Antisolvent

by Wen Yu, Jian-Hao Huang and Chung-Sung Tan

Polymers 2019, 11(7), 1230; https://doi.org/10.3390/polym11071230 - 23 Jul 2019

Cited by 2 | Viewed by 3949

Abstract

In this study, the cyclic oligomers in the highly chemically resistant polyester polybutylene terephthalate (PBT) were effectively removed using a compressed CO₂ antisolvent technique in which 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) was used as the solvent. In addition to the oligomers, tetrahydrofuran was completely removed [...] Read more.

In this study, the cyclic oligomers in the highly chemically resistant polyester polybutylene terephthalate (PBT) were effectively removed using a compressed CO₂ antisolvent technique in which 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) was used as the solvent. In addition to the oligomers, tetrahydrofuran was completely removed because of its low molecular weight and liquid state. The effects of the operating variables, including temperature, pressure, and the PBT concentration in HFIP, on the degree of removal of the oligomers were systematically studied using experimental design and the response surface methodology. The most appropriate operating conditions for the purification of PBT were 8.3 MPa and 23.4 °C when using 4.5 wt % PBT in HFIP. Under these conditions, the cyclic trimers and dimers could be removed by up to 81.4% and 95.7%, respectively, in a very short operating time. Full article

(This article belongs to the Special Issue Supercritical Fluid Processing of Polymers)

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11 pages, 2976 KiB

Open AccessArticle

Spatially Engraving Morphological Structure on a Polymeric Surface by Ion Beam Milling

by Ansu Sun, Ding Wang, Honghao Zhou, Yifan Li, Chris Connor, Jie Kong, Jining Sun and Ben Bin Xu

Polymers 2019, 11(7), 1229; https://doi.org/10.3390/polym11071229 - 23 Jul 2019

Cited by 4 | Viewed by 3764

Abstract

Polymer surface patterning and modification at the micro/nano scale has been discovered with great impact in applications such as microfluidics and biomedical technologies. We propose a highly efficient fabricating strategy, to achieve a functional polymer surface, which has control over the surface roughness. [...] Read more.

Polymer surface patterning and modification at the micro/nano scale has been discovered with great impact in applications such as microfluidics and biomedical technologies. We propose a highly efficient fabricating strategy, to achieve a functional polymer surface, which has control over the surface roughness. The key development in this fabrication method is the polymer positive diffusion effect (PDE) for an ion-bombarded polymeric hybrid surface through focused ion beam (FIB) technology. The PDE is theoretically explored by introducing a positive diffusion term into the classic theory. The conductivity-induced PDE constant is discussed as functions of substrates conductivity, ion energy and flux. The theoretical results agree well with the experiential results on the conductivity-induced PDE, and thus yield good control over roughness and patterning milling depth on the fabricated surface. Moreover, we demonstrate a controllable surface wettability in hydrophobic and superhydrophobic surfaces (contact angles (CA) range from 108.3° to 150.8°) with different CA hysteresis values ranging from 31.4° to 8.3°. Full article

(This article belongs to the Special Issue Functional Surfaces/Interfaces Enabled Smart Behaviour in Soft Matter System and Their Engineering Applications)

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12 pages, 3036 KiB

Open AccessArticle

Surface-Induced ARGET ATRP for Silicon Nanoparticles with Fluorescent Polymer Brushes

by Chun-Na Yan, Lin Xu, Qing-Di Liu, Wei Zhang, Rui Jia, Cheng-Zhi Liu, Shuang-Shuang Wang, Li-Ping Wang and Guang Li

Polymers 2019, 11(7), 1228; https://doi.org/10.3390/polym11071228 - 23 Jul 2019

Cited by 13 | Viewed by 5430

Abstract

Well-defined polymer brushes attached to nanoparticles offer an elegant opportunity for surface modification because of their excellent mechanical stability, functional versatility, high graft density as well as controllability of surface properties. This study aimed to prepare hybrid materials with good dispersion in different [...] Read more.

Well-defined polymer brushes attached to nanoparticles offer an elegant opportunity for surface modification because of their excellent mechanical stability, functional versatility, high graft density as well as controllability of surface properties. This study aimed to prepare hybrid materials with good dispersion in different solvents, and to endow this material with certain fluorescence characteristics. Well-defined diblock copolymers poly (styrene)-b-poly (hydroxyethyl methyl acrylate)–co-poly (hydroxyethyl methyl acrylate- rhodamine B) grafted silica nanoparticles (SNPs-g-PS-b-PHEMA-co-PHEMA-RhB) hybrid materials were synthesized via surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP). The SNPs surfaces were modified by 3-aminopropyltriethoxysilane (KH-550) firstly, then the initiators 2-Bromoisobutyryl bromide (BIBB) was attached to SNPs surfaces through the esterification of acyl bromide groups and amidogen groups. The synthetic initiators (SNPs-Br) were further used for the SI-ARGET ATRP of styrene (St), hydroxyethyl methyl acrylate (HEMA) and hydroxyethyl methyl acrylate-rhodamine B (HEMA-RhB). The results indicated that the SI-ARGET ATRP initiator had been immobilized onto SNPs surfaces, the Br atom have located at the end of the main polymer chains, and the polymerization process possessed the characteristic of controlled/“living” polymerization. The SNPs-g-PS-b-PHEMA-co-PHEMA-RhB hybrid materials show good fluorescence performance and good dispersion in water and EtOH but aggregated in THF. This study demonstrates that the SI-ARGET ATRP provided a unique way to tune the polymer brushes structure on silica nanoparticles surface and further broaden the application of SI-ARGET ATRP. Full article

(This article belongs to the Collection Silicon-Containing Polymeric Materials)

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18 pages, 7682 KiB

Open AccessArticle

Solvent-Free Synthesis of Amidated Carboxymethyl Cellulose Derivatives: Effect on the Thermal Properties

by Asja Pettignano, Aurélia Charlot and Etienne Fleury

Polymers 2019, 11(7), 1227; https://doi.org/10.3390/polym11071227 - 23 Jul 2019

Cited by 40 | Viewed by 11907

Abstract

The present work explores the possibility of chemically modifying carboxymethyl cellulose (CMC), a widely diffused commercial cellulose ether, by grafting of hydrophobic moieties. Amidation of CMC, at high temperature and in heterogeneous conditions, was selected as synthetic tool for grafting on CMC a [...] Read more.

The present work explores the possibility of chemically modifying carboxymethyl cellulose (CMC), a widely diffused commercial cellulose ether, by grafting of hydrophobic moieties. Amidation of CMC, at high temperature and in heterogeneous conditions, was selected as synthetic tool for grafting on CMC a panel of commercially available amines (bearing long aliphatic chains, alkyl aromatic and heteroaromatic groups, more or less spaced from the cellulose backbone). The reaction was successfully carried out in absence of solvents, catalysts and coupling agents, providing a promising and more sustainable alternative to conventional amidation procedures. Relationships between the chemical structure of the obtained CMC derivatives and their thermal properties were carefully studied, with a particular attention to the thermal behavior. Grafting of aromatic and heteroaromatic alkyl amines, presenting a linear alkyl chain between CMC backbone and a terminal bulky moiety, allowed for efficiently separating the polysaccharide chains, improving their mobility and resulting in a consequent lowering of the glass transition temperature (T_g). The T_g values obtained (90–147 °C) were found to be closely dependent on both the size of the aliphatic spacer, the structure of the aromatic ring and the extent of amidation. Full article

(This article belongs to the Special Issue Nanostructured Polymers and Nanocomposites)

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10 pages, 1127 KiB

Open AccessArticle

Adsorption of Vi Capsular Antigen of Salmonella Typhi in Chitosan–Poly (Methacrylic Acid) Nanoparticles

by Raimundo Lopes da Silva, Jaqueline Rodrigues da Silva, Anivaldo Pereira Duarte Júnior, Patrícia Santana Barbosa Marinho, Lourivaldo Silva Santos, Francisco Martins Teixeira, José Otávio Carréra Silva Júnior and Roseane Maria Ribeiro Costa

Polymers 2019, 11(7), 1226; https://doi.org/10.3390/polym11071226 - 23 Jul 2019

Cited by 6 | Viewed by 4600

Abstract

The development of a nanoparticulate system for the carrier antigen is now an important tool in the vaccination process, since a smaller number of doses is necessary for effective immunization. Thus, in this work a nanoparticulate system using polymers of chitosan and poly [...] Read more.

The development of a nanoparticulate system for the carrier antigen is now an important tool in the vaccination process, since a smaller number of doses is necessary for effective immunization. Thus, in this work a nanoparticulate system using polymers of chitosan and poly (methacrylic acid) (CS–PMAA) to adsorb the Vi antigen of Salmonella Typhi was developed. CS–PMAA nanoparticles with different proportions of chitosan and poly (methacrylic acid) were obtained and reached sizes from 123.9 ± 2.48 to 234.9 ± 2.66 nm, and spherical shapes were seen in transmission microscopy. At pH 7.2, the nanoparticles had a cationic surface charge that contributed to the adsorption of the Vi antigen. Qualitative analyses of the isolated Vi antigen were performed using Fourier-transform infrared spectroscopy, which indicated the presence of all the characteristic bands of the capsular polysaccharide, and nuclear magnetic resonance, which showed signals for the five hydrogens and the N-acetyl and O-acetyl groups which are characteristic of the Vi antigen structure. In the adsorption kinetics study, the Vi capsular antigen, contained in a phosphate buffer solution of pH 7.2, experienced 55% adsorption on the 1–1% (CS–PMAA) nanoparticles. The adsorption kinetics results showed the ability of the nanoparticulate system to adsorb the Vi antigen. Full article

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10 pages, 2080 KiB

Open AccessCommunication

Controlled Shape and Porosity of Polymeric Colloids by Photo-Induced Phase Separation

by Elad Hadad, Eitan Edri and Hagay Shpaisman

Polymers 2019, 11(7), 1225; https://doi.org/10.3390/polym11071225 - 23 Jul 2019

Viewed by 4181

Abstract

The shape and porosity of polymeric colloids are two properties that highly influence their ability to accomplish specific tasks. For micro-sized colloids, the control of both properties was demonstrated by the photo-induced phase separation of droplets of NOA81—a thiol-ene based UV-curable adhesive—mixed with [...] Read more.

The shape and porosity of polymeric colloids are two properties that highly influence their ability to accomplish specific tasks. For micro-sized colloids, the control of both properties was demonstrated by the photo-induced phase separation of droplets of NOA81—a thiol-ene based UV-curable adhesive—mixed with acetone, water, and polyethylene glycol. The continuous phase was perfluoromethyldecalin, which does not promote phase separation prior to UV activation. A profound influence of the polymer concentration on the particle shape was observed. As the photo-induced phase separation is triggered by UV radiation, polymerization drives the extracted solution out of the polymeric matrix. The droplets of the extracted solution coalesce until they form a dimple correlated to the polymer concentration, significantly changing the shape of the formed solid colloids. Moreover, control could be gained over the porosity by varying the UV intensity, which governs the kinetics of the reaction, without changing the chemical composition; the number of nanopores was found to increase significantly at higher intensities. Full article

(This article belongs to the Special Issue Micro- and Nano-Fabrication Approaches for Polymers)

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14 pages, 6402 KiB

Open AccessArticle

Competition in Coordination Assemblies: 1D-Coordination Polymer or 2D-Nets Based on Co(NCS)₂ and 4′-(4-methoxyphenyl)-3,2′:6′,3″-terpyridine

by Dalila Rocco, Alessandro Prescimone, Y. Maximilian Klein, Dariusz J. Gawryluk, Edwin C. Constable and Catherine E. Housecroft

Polymers 2019, 11(7), 1224; https://doi.org/10.3390/polym11071224 - 23 Jul 2019

Cited by 12 | Viewed by 3589 | Correction

Abstract

The synthesis and characterization of 4′-(4-methoxyphenyl)-3,2′:6′,3″-terpyridine (2) (IUPAC PIN 2⁴-(4-methoxyphenyl)-1²,2²:2⁶,3²-terpyridine) are described, and its coordination behaviour with cobalt(II) thiocyanate has been investigated. In a series of experiments, crystals were grown at [...] Read more.

The synthesis and characterization of 4′-(4-methoxyphenyl)-3,2′:6′,3″-terpyridine (2) (IUPAC PIN 2⁴-(4-methoxyphenyl)-1²,2²:2⁶,3²-terpyridine) are described, and its coordination behaviour with cobalt(II) thiocyanate has been investigated. In a series of experiments, crystals were grown at room temperature by layering a MeOH solution of Co(NCS)₂ over a CHCl₃ solution of 2 using 1:1, 1:2 or 2:1 molar ratios of metal salt-to-ligand. Crystals harvested within 2–3 weeks proved to be the 1D-coordination polymer [Co(2)(NCS)₂(MeOH)₂]_n and powder X-ray diffraction (PXRD) confirmed that the crystals selected for single-crystal X-ray diffraction were representative of the bulk samples. Longer crystallization times with a Co(NCS)₂ to 2 molar ratio of 1:1 yielded crystals of [Co(2)(NCS)₂(MeOH)₂]_n (1D-chain) and the pseudopolymorphs [{Co(2)₂(NCS)₂}·3MeOH]_n and [{Co(2)₂(NCS)₂}·2.2CHCl₃]_n ((4,4)-nets), each type of crystal originating from a different zone in the crystallization tube. PXRD for this last experiment confirmed that the dominant product in the bulk sample was the 1D-coordination polymer. Full article

(This article belongs to the Special Issue Metallopolymer, supramolecular chemistry and materials)

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20 pages, 6852 KiB

Open AccessArticle

Computational Investigations on Soundproof Applications of Foam-Formed Cellulose Materials

by Carmen Debeleac, Petronela Nechita and Silviu Nastac

Polymers 2019, 11(7), 1223; https://doi.org/10.3390/polym11071223 - 23 Jul 2019

Cited by 21 | Viewed by 4712

Abstract

Recent studies have highlighted an innovative way to produce highly porous materials based on cellulose fibers. These studies have focused on the foam-forming process, where the cellulose fibers and other components are mixed with foam. In the authors’ previous research, the foam-formed cellulose [...] Read more.

Recent studies have highlighted an innovative way to produce highly porous materials based on cellulose fibers. These studies have focused on the foam-forming process, where the cellulose fibers and other components are mixed with foam. In the authors’ previous research, the foam-formed cellulose materials (FCM) were obtained by mixing a surfactant with cellulose fibers, taken from virgin pulp and recovered papers. In the present paper, the authors performed additional experimental and computational analyses in order to evaluate the sound insulation capabilities of these FCM beyond the initial impedance of tube investigations. The poroacoustics computational methodology parameters—i.e., airflow resistivity, porosity, tortuosity, viscous, and thermal characteristic lengths—were herein evaluated. This analysis was performed using both a theoretical/empirical approach from the specialized literature and an experimental investigation developed by the authors. The computational investigations were conducted in two stages: First, we evaluated the approximation of the experimentally gained normal incidence parameters, in terms of absorption and reflection, respectively, relative to the estimated ones. The second stage of analysis consists of a parametrical estimation of sound insulation characteristics concerning the incidence angle of sound hitting the porous layer. The results presented in this paper are in agreement with the computational experimental results, providing extended soundproof characteristics to the incidence angle of the acoustic field. Further, this study supplies additional information useful for future analyses regarding the influences of random geometry air inclusions into the FCM layer. Full article

(This article belongs to the Special Issue Lignocellulosic Fibers and Films)

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11 pages, 2572 KiB

Open AccessArticle

Influence of Co-Catalysts and Polymerization Conditions on Properties of Poly(anhydride-alt-epoxide)s from ROCOP Using Salen Complexes with Different Metals

by Matteo Proverbio, Nella Galotto Galotto, Simona Losio, Incoronata Tritto and Laura Boggioni

Polymers 2019, 11(7), 1222; https://doi.org/10.3390/polym11071222 - 22 Jul 2019

Cited by 17 | Viewed by 4106

Abstract

Cyclohexene oxide (CHO) and phthalic anhydride (PA) have been reacted in the presence of commercial salen–type complexes with different metals Cr (1), Al (2), and Mn (3) in combination with 4-(dimethylamino) pyridine (DMAP), bis-(triphenylphosphorydine) ammonium chloride (PPNCl) [...] Read more.

Cyclohexene oxide (CHO) and phthalic anhydride (PA) have been reacted in the presence of commercial salen–type complexes with different metals Cr (1), Al (2), and Mn (3) in combination with 4-(dimethylamino) pyridine (DMAP), bis-(triphenylphosphorydine) ammonium chloride (PPNCl) and bis-(triphenylphosphoranylidene)ammonium azide (PPNN₃) as co-catalysts to obtain alternating poly(PA-alt-CHO)s by ring-opening copolymerization (ROCOP). The effect of different reaction conditions (pre-contact between catalyst and co-catalyst, polymerization time) on the productivity, molecular weight and glass transition temperature has been evaluated. By using a 24 h pre-contact, the aliphatic polyesters obtained were characterized by high molecular weight (M_n > 15 kg/mol) and glass transition temperature (T_g) up to 146 °C; the more sustainable metals Al and Mn in the presence of PPNCl give comparable results to Cr. Moreover, biodegradability data of these polyesters and the study of the microstructure reveal that the biodegradability is influenced more by the type of chain linkages rather than by the molecular weight of the polyesters. Full article

(This article belongs to the Special Issue Polymerizations Promoted by Metal Complexes)

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12 pages, 2636 KiB

Open AccessArticle

Anionic Polymerization of β-Butyrolactone Initiated with Sodium Phenoxides. The Effect of the Initiator Basicity/Nucleophilicity on the ROP Mechanism

by Adrian Domiński, Tomasz Konieczny, Magdalena Zięba, Magdalena Klim and Piotr Kurcok

Polymers 2019, 11(7), 1221; https://doi.org/10.3390/polym11071221 - 22 Jul 2019

Cited by 17 | Viewed by 4915

Abstract

It was shown that selected sodium phenoxide derivatives with different basicity and nucleophilicity, such as sodium p-nitrophenoxide, p-chlorophenoxide, 1-napthoxide, phenoxide and p-methoxyphenoxide, are effective initiators in anionic ring-opening polymerization (AROP) of β-butyrolactone in mild conditions. It was found that [...] Read more.

It was shown that selected sodium phenoxide derivatives with different basicity and nucleophilicity, such as sodium p-nitrophenoxide, p-chlorophenoxide, 1-napthoxide, phenoxide and p-methoxyphenoxide, are effective initiators in anionic ring-opening polymerization (AROP) of β-butyrolactone in mild conditions. It was found that phenoxides as initiators in anionic ring-opening polymerization of β-butyrolactone behave as strong nucleophiles, or weak nucleophiles, as well as Brønsted bases. The resulting polyesters possessing hydroxy, phenoxy and crotonate initial groups are formed respectively by the attack of phenoxide anion at (i) C2 followed by an elimination reaction with hydroxide formation, (ii) C4 and (iii) abstraction of acidic proton at C3. The obtained poly(3-hydroxybutyrate) possesses carboxylate growing species. The ratio of the observed initial groups strongly depends on the basicity and nucleophilicity of the sodium phenoxide derivative used as initiator. The proposed mechanism of this polymerization describes the reactions leading to formation of observed end groups. Moreover, the possibility of formation of a crotonate group during the propagation step of this polymerization is also discussed. Full article

(This article belongs to the Special Issue Biodegradable Polymers - Where We Are and Where to Going)

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16 pages, 16875 KiB

Open AccessArticle

Printability and Tensile Performance of 3D Printed Polyethylene Terephthalate Glycol Using Fused Deposition Modelling

by Sofiane Guessasma, Sofiane Belhabib and Hedi Nouri

Polymers 2019, 11(7), 1220; https://doi.org/10.3390/polym11071220 - 22 Jul 2019

Cited by 60 | Viewed by 10082

Abstract

Polyethylene terephthalate glycol (PETG) is a thermoplastic formed by polyethylene terephthalate (PET) and ethylene glycol and known for his high impact resistance and ductility. The printability of PETG for fused deposition modelling (FDM) is studied by monitoring the filament temperature using an infra-red [...] Read more.

Polyethylene terephthalate glycol (PETG) is a thermoplastic formed by polyethylene terephthalate (PET) and ethylene glycol and known for his high impact resistance and ductility. The printability of PETG for fused deposition modelling (FDM) is studied by monitoring the filament temperature using an infra-red camera. The microstructural arrangement of 3D printed PETG is analysed by means of X-ray micro-tomography and tensile performance is investigated in a wide range of printing temperatures from 210 °C to 255 °C. A finite element model is implemented based on 3D microstructure of the printed material to reveal the deformation mechanisms and the role of the microstructural defects on the mechanical performance. The results show that PETG can be printed within a limited range of printing temperatures. The results suggest a significant loss of the mechanical performance due to the FDM processing and particularly a substantial reduction of the elongation at break is observed. The loss of this property is explained by the inhomogeneous deformation of the PETG filament. X-ray micro-tomography results reveal a limited amount of process-induced porosity, which only extends through the sample thickness. The FE predictions point out the combination of local shearing and inhomogeneous stretching that are correlated to the filament arrangement within the plane of construction. Full article

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15 pages, 3672 KiB

Open AccessArticle

Neutral Polysaccharide from the Leaves of Pseuderanthemum carruthersii: Presence of 3-O-Methyl Galactose and Anti-Inflammatory Activity in LPS-Stimulated RAW 264.7 Cells

by Vo Hoai Bac, Berit Smestad Paulsen, Le Van Truong, Andreas Koschella, Tat Cuong Trinh, Christian Winther Wold, Suthajini Yogarajah and Thomas Heinze

Polymers 2019, 11(7), 1219; https://doi.org/10.3390/polym11071219 - 22 Jul 2019

Cited by 5 | Viewed by 4288

Abstract

Pseuderanthemum carruthersii (Seem.) Guillaumin is a native tree in Vietnam. The water extract of the leaves from this tree gives a highly viscous product that has been used to heal wounds and treat inflammations. Our previous studies showed that the leaves of P. [...] Read more.

Pseuderanthemum carruthersii (Seem.) Guillaumin is a native tree in Vietnam. The water extract of the leaves from this tree gives a highly viscous product that has been used to heal wounds and treat inflammations. Our previous studies showed that the leaves of P. carruthersii have a high content of polysaccharides. In this study, the structure and influence of the neutral polysaccharide from Pseuderanthemum carruthersii (PCA1) on lipopolysaccharide (LPS)-stimulated RAW264.7 cells were investigated. The PCA1 isolated from P. carruthersii is a galactan-type polysaccharide, containing galactose (77.0%), 3-O-methyl galactose (20.0%), and arabinose (3.0%). Linkage analysis of PCA1 showed that both the 3-O-methyl galactose and galactose were 1,4-linked. The presence of 3-O-methyl galactose units as part of the polysaccharide is important and can be used as a chemotaxonomic marker. The molecular weight of the PCA1 was 170 kDa. A PCA1 concentration of 30–40 μg/mL strongly inhibited TNFα, IL-1β, and IL-6 inflammatory cytokine production, and reactive oxygen species (ROS) release. PCA1 had inhibitory activities on pro-inflammatory cytokine and ROS release in LPS-stimulated mouse macrophages in vitro through MAPK signaling. Full article

(This article belongs to the Collection Polysaccharides)

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14 pages, 4641 KiB

Open AccessArticle

The Effect of Degradation of Soda Lignin Using Pd/SO₄²⁻/ZrO₂ as a Catalyst: Improved Reactivity and Antioxidant Activity

by Shengming Zhang, Guizhen Fang, Haitao Chen and Qian Lang

Polymers 2019, 11(7), 1218; https://doi.org/10.3390/polym11071218 - 21 Jul 2019

Cited by 6 | Viewed by 3015

Abstract

To the value-added application of the soda lignin by improving its reactivity and antioxidant activity, a self-made Pd/SO₄²⁻/ZrO₂ catalyst was used to catalyze the degradation reaction of soda lignin. The catalyst was loaded with the palladium of 1.47 [...] Read more.

To the value-added application of the soda lignin by improving its reactivity and antioxidant activity, a self-made Pd/SO₄²⁻/ZrO₂ catalyst was used to catalyze the degradation reaction of soda lignin. The catalyst was loaded with the palladium of 1.47 wt.% while retaining the super acidity of SO₄²⁻/ZrO₂. The reaction condition was determined as follows: the dioxane-water solution was selected as the reaction solution, the addition amount of the catalyst was 5 wt.% of the soda lignin, the system was heated at 100 °C for 4 h under a hydrogen pressure of 3 MPa. The reactivity of the catalyzed-soda lignin compared to the soda lignin before the reaction was significantly improved: the values of phenolic hydroxyl groups and total hydroxyl groups were increased by 35.3% and 97.1%, respectively, and the value of methoxy groups was decreased by 13%. Approximately 63.3% of the β-O-4 bonds were cleaved, which resulted in a reduction of the weight average molecular weight from 8200 g·mol⁻¹ to 4900 g·mol⁻¹. At the same time, the EC₅₀ values of the catalyzed-soda lignin on DPPH (1,1-diphenyl-2-picrylhydrazyl) and ABTS⁺ (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) radicals scavenging were decreased by 20.6% and 32.6%, respectively, and the reducing power of catalyzed-soda lignin at the absorption value of 0.5 was increased by 10.5%. The Pd/SO₄²⁻/ZrO₂ catalyst works by breaking the β-O-4 linkages and degrading the methoxy groups. The catalyzed-soda lignin exhibits the possibility of being used as the antioxidants, grafting precursors, adhesive additives, and raw materials for lignin/polymer composites. Full article

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23 pages, 5524 KiB

Open AccessArticle

Preparation and Characterization of Cellulose Acetate Propionate Films Functionalized with Reactive Ionic Liquids

by Joanna Kujawa, Edyta Rynkowska, Kateryna Fatyeyeva, Katarzyna Knozowska, Andrzej Wolan, Krzysztof Dzieszkowski, Guoqiang Li and Wojciech Kujawski

Polymers 2019, 11(7), 1217; https://doi.org/10.3390/polym11071217 - 20 Jul 2019

Cited by 24 | Viewed by 6362

Abstract

1-(1,3-diethoxy-1,3-dioxopropan-2-ylo)-3-methylimidazolium bromide (RIL1_Br), 1-(2-etoxy-2-oxoethyl)-3-methylimidazolium bromide (RIL2_Br), 1-(2-etoxy-2-oxoethyl)-3-methylimidazolium tetrafluoroborate (RIL3_BF4) ionic liquids were synthesized. Subsequently, the dense cellulose acetate propionate (CAP)-based materials containing from 9 to 28.6 wt % of these reactive ionic liquids were elaborated. Reactive ionic liquids (RILs) were immobilized in CAP [...] Read more.

1-(1,3-diethoxy-1,3-dioxopropan-2-ylo)-3-methylimidazolium bromide (RIL1_Br), 1-(2-etoxy-2-oxoethyl)-3-methylimidazolium bromide (RIL2_Br), 1-(2-etoxy-2-oxoethyl)-3-methylimidazolium tetrafluoroborate (RIL3_BF4) ionic liquids were synthesized. Subsequently, the dense cellulose acetate propionate (CAP)-based materials containing from 9 to 28.6 wt % of these reactive ionic liquids were elaborated. Reactive ionic liquids (RILs) were immobilized in CAP as a result of the transesterification reaction. The yield of this reaction was over 90% with respect to the used RIL. The physicochemical properties of resultant films were studied using nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), atomic force microscopy (AFM), and thermogravimetric analysis (TGA). The RIL incorporation influenced the morphology of films by increasing their surface roughness with the rise of RIL content. The thermal stability of CAP-based membranes was dependent on the nature of the ionic liquid. Nevertheless, it was proven that CAP films containing RILs were stable up to 120–150 °C. Transport properties were characterized by water permeation tests. It was found that the type and the amount of the ionic liquid in the CAP matrix substantially influenced the transport properties of the prepared hybrid materials. Full article

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18 pages, 10431 KiB

Open AccessArticle

Complementary Assessment of Commercial Photoluminescent Pigments Printed on Cotton Fabric

by Selestina Gorgieva, Natalija Virant and Alenka Ojstršek

Polymers 2019, 11(7), 1216; https://doi.org/10.3390/polym11071216 - 20 Jul 2019

Cited by 11 | Viewed by 4148

Abstract

The presented study focuses on photoluminescent pigments applied on cotton fabric by a screen-printed procedure using polydimethylsiloxane (PDMS) as a binder. Microscopic data depicts irregular shapes and relatively wide size distribution (3–80 µm) of pigments. Regarding composition, the Energy-Dispersive X-ray (EDX) and Fourier [...] Read more.

The presented study focuses on photoluminescent pigments applied on cotton fabric by a screen-printed procedure using polydimethylsiloxane (PDMS) as a binder. Microscopic data depicts irregular shapes and relatively wide size distribution (3–80 µm) of pigments. Regarding composition, the Energy-Dispersive X-ray (EDX) and Fourier Transform Infrared (FTIR) spectroscopy data complement findings suggesting the presence of Eu-doped strontium aluminate in the yellow-green, calcium aluminate in the violet pigment, and metal oxides in the blue pigment. The optical properties of pigment-enriched PDMS-coated cotton fabric were assessed and reflectance intensity was found to be concentration-dependent only in the blue pigment. The luminescence decay data show that luminescence intensity decreased with the reduction of pigment concentration in the following order, yellow-green > blue > violet pigments. Relying on absorption and emission data of powdered pigments, the confocal microscopy enables visualization of the pigments’ distribution within a 3D image projection. This identifies the most homogeneous distribution in the case of the blue pigment, as well as the presence of a continuous fluorescing signal in the z projection when 5% pigment was used. This was, for the first time, presented as a powerful tool for non-destructive visualization of photoluminescent pigments’ spatial distribution when printed on textile (cotton) fabric. Finally, the photoluminescent PDMS coating demonstrates high washing and abrasion resistance, contributing to overall functionality of printed cotton fabrics when commercial types of pigments are applied. Full article

(This article belongs to the Special Issue Innovative Functional Textiles)

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12 pages, 5064 KiB

Open AccessArticle

Long-Term Creep Behavior Prediction of Sol-Gel Derived SiO₂- and TiO₂-Wood Composites Using the Stepped Isostress Method

by Ke-Chang Hung, Tung-Lin Wu and Jyh-Horng Wu

Polymers 2019, 11(7), 1215; https://doi.org/10.3390/polym11071215 - 20 Jul 2019

Cited by 10 | Viewed by 3355

Abstract

In this study, methyltrimethoxysilane (MTMOS), methyltriethoxysilane (MTEOS), tetraethoxysilane (TEOS), and titanium(IV) isopropoxide (TTIP) were used as precursor sols to prepare wood-inorganic composites (WICs) by a sol-gel process, and subsequently, the long-term creep behavior of these composites was estimated by application of the stepped [...] Read more.

In this study, methyltrimethoxysilane (MTMOS), methyltriethoxysilane (MTEOS), tetraethoxysilane (TEOS), and titanium(IV) isopropoxide (TTIP) were used as precursor sols to prepare wood-inorganic composites (WICs) by a sol-gel process, and subsequently, the long-term creep behavior of these composites was estimated by application of the stepped isostress method (SSM). The results revealed that the flexural modulus of wood and WICs were in the range of 9.8–10.5 GPa, and there were no significant differences among them. However, the flexural strength of the WICs (93–103 MPa) was stronger than that of wood (86 MPa). Additionally, based on the SSM processes, smooth master curves were obtained from different SSM testing parameters, and they fit well with the experimental data. These results demonstrated that the SSM was a useful approach to evaluate the long-term creep behavior of wood and WICs. According to the Eyring equation, the activation volume of the WICs prepared from MTMOS (0.825 nm³) and TEOS (0.657 nm³) was less than that of the untreated wood (0.832 nm³). Furthermore, the WICs exhibited better performance on the creep resistance than that of wood, except for the WIC_MTEOS. The reduction of time-dependent modulus for the WIC prepared from MTMOS was 26% at 50 years, which is the least among all WICs tested. These findings clearly indicate that treatment with suitable metal alkoxides could improve the creep resistance of wood. Full article

(This article belongs to the Special Issue Advances in Wood Composites)

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12 pages, 4834 KiB

Open AccessArticle

Gamma-Irradiation-Prepared Low Molecular Weight Hyaluronic Acid Promotes Skin Wound Healing

by Yu-Chih Huang, Kuen-Yu Huang, Wei-Zhen Lew, Kang-Hsin Fan, Wei-Jen Chang and Haw-Ming Huang

Polymers 2019, 11(7), 1214; https://doi.org/10.3390/polym11071214 - 19 Jul 2019

Cited by 30 | Viewed by 5089

Abstract

In this study, we prepared low-molecular-weight hyaluronic acid (LMWHA) powder by γ-irradiation. The chemical and physical properties of γ-irradiated LMWHA and the in vitro cellular growth experiments with γ-irradiated LMWHA were analyzed. Then, hyaluronic acid exposed to 20 kGy of γ-irradiation was used [...] Read more.

In this study, we prepared low-molecular-weight hyaluronic acid (LMWHA) powder by γ-irradiation. The chemical and physical properties of γ-irradiated LMWHA and the in vitro cellular growth experiments with γ-irradiated LMWHA were analyzed. Then, hyaluronic acid exposed to 20 kGy of γ-irradiation was used to fabricate a carboxymethyl cellulose (CMC)/LMWHA fabric for wound dressing. Our results showed that γ-irradiated LMWHA demonstrated a significant alteration in carbon–oxygen double bonding and can be detected using nuclear magnetic resonance and ultraviolet (UV)-visible (Vis) spectra. The γ-irradiated LMWHA exhibited strain rate-dependent Newton/non-Newton fluid biphasic viscosity. The viability of L929 skin fibroblasts improved upon co-culture with γ-irradiated LMWHA. In the in vivo animal experiments, skin wounds covered with dressings prepared by γ-irradiation revealed acceleration of wound healing after two days of healing. The results suggest that γ-irradiated LMWHA could be a potential source for the promotion of skin wound healing. Full article

(This article belongs to the Special Issue Medical Application of Polymer-Based Composites)

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16 pages, 2189 KiB

Open AccessArticle

Amphiphilic Acrylic Nanoparticles Containing the Poloxamer Star Bayfit® 10WF15 as Ophthalmic Drug Carriers

by Miguel Gómez-Ballesteros, Vanessa Andrés-Guerrero, Francisco Jesús Parra, Jorge Marinich, Beatriz de-las-Heras, Irene Teresa Molina-Martínez, Blanca Vázquez-Lasa, Julio San Román and Rocío Herrero-Vanrell

Polymers 2019, 11(7), 1213; https://doi.org/10.3390/polym11071213 - 19 Jul 2019

Cited by 7 | Viewed by 3425

Abstract

Topical application of drops containing ocular drugs is the preferred non-invasive route to treat diseases that affect the anterior segment of the eye. However, the formulation of eye drops is a major challenge for pharmacists since the access of drugs to ocular tissues [...] Read more.

Topical application of drops containing ocular drugs is the preferred non-invasive route to treat diseases that affect the anterior segment of the eye. However, the formulation of eye drops is a major challenge for pharmacists since the access of drugs to ocular tissues is restricted by several barriers. Acetazolamide (ACZ) is a carbonic anhydrase inhibitor used orally for the treatment of ocular hypertension in glaucoma. However, large ACZ doses are needed which results in systemic side effects. Recently, we synthesized copolymers based on 2-hydroxyethyl methacrylate (HEMA) and a functionalized three-arm poloxamer star (Bayfit-MA). The new material (HEMA/Bayfit-MA) was engineered to be transformed into nanoparticles without the use of surfactants, which represents a significant step forward in developing new ophthalmic drug delivery platforms. Acetazolamide-loaded nanocarriers (ACZ-NPs) were prepared via dialysis (224 ± 19 nm, −17.2 ± 0.4 mV). The in vitro release rate of ACZ was constant over 24 h (cumulative delivery of ACZ: 83.3 ± 8.4%). Following standard specifications, ACZ-NPs were not cytotoxic in vitro in cornea, conjunctiva, and macrophages. In normotensive rabbits, ACZ-NPs generated a significant intraocular pressure reduction compared to a conventional solution of ACZ (16.4% versus 9.6%) with the same dose of the hypotensive drug (20 µg). In comparison to previously reported studies, this formulation reduced intraocular pressure with a lower dose of ACZ. In summary, HEMA:Bayfit-MA nanoparticles may be a promising system for ocular topical treatments, showing an enhanced ocular bioavailability of ACZ after a single instillation on the ocular surface. Full article

(This article belongs to the Special Issue Polymeric Thin Films and Membranes)

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11 pages, 2464 KiB

Open AccessArticle

Synergistic Flame-Retardant Mechanism of Dicyclohexenyl Aluminum Hypophosphite and Nano-Silica

by Heng Zhang, Junliang Lu, Hongyan Yang, Heng Yang, Jinyan Lang and Qinqin Zhang

Polymers 2019, 11(7), 1211; https://doi.org/10.3390/polym11071211 - 19 Jul 2019

Cited by 14 | Viewed by 4574

Abstract

The flame retardant dicyclohexenyl aluminum hypophosphite (ADCP) and nano-silica are added to PA66 to improve flame retardant property of the composite. The flame-retardant property of the composite is tested via oxygen index test, vertical burning test, and cone calorimetry test. Combustion residues are [...] Read more.

The flame retardant dicyclohexenyl aluminum hypophosphite (ADCP) and nano-silica are added to PA66 to improve flame retardant property of the composite. The flame-retardant property of the composite is tested via oxygen index test, vertical burning test, and cone calorimetry test. Combustion residues are tested using scanning electron microscopy, EDS spectroscopy, and Fourier infrared analysis. Results show that flame-retardant ADCP can effectively promote the formation of a porous carbon layer on the combustion surface of PA66. Nano-silica easily migrates to the material surface to improve the oxidation resistance of the carbon layer and the density of the carbon layer’s structure. It can also effectively prevent heat, flammable gases, and oxygen from entering the flame zone and enhance the flame retardant properties of ADCP. Full article

(This article belongs to the Special Issue Thermal Insulating and Fire-Resistant Polymer Composites)

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14 pages, 2649 KiB

Open AccessArticle

Magnetic Fluorescence Molecularly Imprinted Polymer Based on FeO_x/ZnS Nanocomposites for Highly Selective Sensing of Bisphenol A

by Xin Zhang, Shu Yang, Weijie Chen, Yansong Li, Yuping Wei and Aiqin Luo

Polymers 2019, 11(7), 1210; https://doi.org/10.3390/polym11071210 - 19 Jul 2019

Cited by 30 | Viewed by 4254

Abstract

In this study, magnetic fluorescence molecularly imprinted polymers were fabricated and used for the selective separation and fluorescence sensing of trace bisphenol A (BPA) in environmental water samples. The carboxyl-functionalized FeO_x magnetic nanoparticles were conjugated with mercaptoethylamine-capped Mn²⁺ doped ZnS quantum [...] Read more.

In this study, magnetic fluorescence molecularly imprinted polymers were fabricated and used for the selective separation and fluorescence sensing of trace bisphenol A (BPA) in environmental water samples. The carboxyl-functionalized FeO_x magnetic nanoparticles were conjugated with mercaptoethylamine-capped Mn²⁺ doped ZnS quantum dots to prepare magnetic FeO_x and ZnS quantum dot nanoparticles (FeO_x/ZnS NPs). Additionally, molecular imprinting on the FeO_x/ZnS NPs was employed to synthesize core-shell molecularly imprinted polymers. The resulting nanoparticles were well characterized using transmission electron microscopy, Fourier transform infrared spectra, vibrating sample magnetometer and fluorescence spectra, and the adsorption behavior was investigated. Binding experiments showed that the molecularly imprinted FeO_X/ZnS NPs (FeO_x/ZnS@MIPs) exhibited rapid fluorescent and magnetic responses, and high selectivity and sensitivity for the detection of bisphenol A (BPA). The maximum adsorption capacity of FeO_x/ZnS@MIPs was 50.92 mg·g⁻¹ with an imprinting factor of 11.19. Under optimal conditions, the constructed fluorescence magnetic molecularly imprinted polymers presented good linearity from 0 to 80 ng mL⁻¹ with a detection limit of 0.3626 ng mL⁻¹ for BPA. Moreover, the proposed fluorescence magnetic polymers were successfully applied to on-site magnetic separation and real-time fluorescence analysis of target molecule in real samples. Full article

(This article belongs to the Special Issue Fluorescent polymers for sensing and imaging)

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16 pages, 3686 KiB

Open AccessArticle

Improvement of Mechanical Properties and Self-Healing Efficiency by Ex-Situ Incorporation of TiO₂ Nanoparticles to a Waterborne Poly(Urethane-Urea)

by Iñigo Díez-García, Arantxa Eceiza and Agnieszka Tercjak

Polymers 2019, 11(7), 1209; https://doi.org/10.3390/polym11071209 - 19 Jul 2019

Cited by 10 | Viewed by 3614

Abstract

This research work was focused on the incorporation of TiO₂ nanoparticles into synthesized solvent-free waterborne poly(urethane-urea) (WPUU) based on hydrophilic poly(ethylene oxide) (PU0) in order to improve both the mechanical properties and self-healing effectiveness of a polymer matrix. The incorporation of TiO [...] Read more.

This research work was focused on the incorporation of TiO₂ nanoparticles into synthesized solvent-free waterborne poly(urethane-urea) (WPUU) based on hydrophilic poly(ethylene oxide) (PU0) in order to improve both the mechanical properties and self-healing effectiveness of a polymer matrix. The incorporation of TiO₂ nanoparticles resulted in a successful enhancement of the mechanical properties of nanocomposite films when compared to PU0. Simultaneously, the obtained nanocomposite films did not only maintain the self-healing ability of the PU0 film, measured by means of mechanical properties after successive cutting/recovery cycles, but they also showed a higher self-healing efficiency than the PU0 film. Moreover, the well-dispersed TiO₂ nanoparticles, visualized by atomic force microscopy (AFM), kept their conductive properties when embedded in the PU0 matrix, as was confirmed by electrostatic force microscopy (EFM). This research work described a simple and industrially appealing way to control the dispersion of commercially available TiO₂ nanoparticles in waterborne poly(urethane-urea) for the designing of inorganic/organic hybrid nanocomposites with enhanced mechanical properties and self-healing efficiency, in which TiO₂ nanoparticles preserved their conductive properties within the polymer matrix. Full article

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12 pages, 3051 KiB

Open AccessArticle

Synthesis of Double-Shelled Hollow Inorganic Nanospheres through Block Copolymer-Metal Coordination and Atomic Layer Deposition

by Nina Yan, Qingbao Guan, Zhiming Yang, Min Feng, Xizhi Jiang, Jun Liu and Lei Xu

Polymers 2019, 11(7), 1208; https://doi.org/10.3390/polym11071208 - 19 Jul 2019

Cited by 2 | Viewed by 3184

Abstract

Double-shelled hollow (DSH) structures with varied inorganic compositions are confirmed to have improved performances in diverse applications, especially in lithium ion battery. However, it is still of great challenge to obtain these complex nanostructures with traditional hard templates and solution-based route. Here we [...] Read more.

Double-shelled hollow (DSH) structures with varied inorganic compositions are confirmed to have improved performances in diverse applications, especially in lithium ion battery. However, it is still of great challenge to obtain these complex nanostructures with traditional hard templates and solution-based route. Here we report an innovative pathway for the preparation of the DSH nanospheres based on block copolymer self-assembly, metal–ligand coordination and atomic layer deposition. Polymeric composite micelles derived from amphiphilic block copolymers and ferric ions were prepared with heating-enabled micellization and metal–ligand coordination. The DSH nanospheres with Fe₂O₃ stands inner and TiO₂ outer the structures can be obtained with atomic layer deposition of a thin layer of TiO₂ followed with calcination in air. The coordination was carried out at room temperature and the deposition was performed at the low temperature of 80 °C, thus providing a feasible fabrication strategy for DSH structures without destruction of the templates. The cavity and the outer layer of the structures can also be simply tuned with the utilized block copolymers and the deposition cycles. These DSH inorganic nanospheres are expected to find vital applications in battery, catalysis, sensing and drug delivery, etc. Full article

(This article belongs to the Special Issue Self-assembly of Block Copolymers)

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16 pages, 6770 KiB

Open AccessEditor’s ChoiceArticle

Chitosan/Glycosaminoglycan Scaffolds: The Role of Silver Nanoparticles to Control Microbial Infections in Wound Healing

by Giuseppina Sandri, Dalila Miele, Angela Faccendini, Maria Cristina Bonferoni, Silvia Rossi, Pietro Grisoli, Angelo Taglietti, Marco Ruggeri, Giovanna Bruni, Barbara Vigani and Franca Ferrari

Polymers 2019, 11(7), 1207; https://doi.org/10.3390/polym11071207 - 19 Jul 2019

Cited by 59 | Viewed by 4641

Abstract

Cutaneous wounds represent a major issue in medical care, with approximately 300 million chronic and 100 million traumatic wound patients worldwide, and microbial infections slow the healing process. The aim of this work was to develop electrospun scaffolds loaded with silver nanoparticles (AgNPs) [...] Read more.

Cutaneous wounds represent a major issue in medical care, with approximately 300 million chronic and 100 million traumatic wound patients worldwide, and microbial infections slow the healing process. The aim of this work was to develop electrospun scaffolds loaded with silver nanoparticles (AgNPs) to enhance cutaneous healing, preventing wound infections. AgNPs were directly added to polymeric blends based on chitosan (CH) and pullulan (PUL) with hyaluronic acid (HA) or chondroitin sulfate (CS) to be electrospun obtaining nanofibrous scaffolds. Moreover, a scaffold based on CH and PUL and loaded with AgNPs was prepared as a comparison. The scaffolds were characterized by chemico–physical properties, enzymatic degradation, biocompatibility, and antimicrobial properties. All the scaffolds were based on nanofibers (diameters about 500 nm) and the presence of AgNPs was evidenced by TEM and did not modify their morphology. The scaffold degradation was proven by means of lysozyme. Moreover, the AgNPs loaded scaffolds were characterized by a good propensity to promote fibroblast proliferation, avoiding the toxic effect of silver. Furthermore, scaffolds preserved AgNP antimicrobial properties, although silver was entrapped into nanofibers. Chitosan/chondroitin sulfate scaffold loaded with AgNPs demonstrated promotion of fibroblast proliferation and to possess antimicrobial properties, thus representing an interesting tool for the treatment of chronic wounds. Full article

(This article belongs to the Special Issue Biomedical Polymer Materials)

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15 pages, 1484 KiB

Open AccessArticle

Two-Step Energy Transfer Dynamics in Conjugated Polymer and Dye-Labeled Aptamer-Based Potassium Ion Detection Assay

by Inhong Kim, Ji-Eun Jung, Woojin Lee, Seongho Park, Heedae Kim, Young-Dahl Jho, Han Young Woo and Kwangseuk Kyhm

Polymers 2019, 11(7), 1206; https://doi.org/10.3390/polym11071206 - 19 Jul 2019

Cited by 4 | Viewed by 5120

Abstract

We recently implemented highly sensitive detection systems for photo-sensitizing potassium ions (K⁺) based on two-step Förster resonance energy transfer (FRET). As a successive study for quantitative understanding of energy transfer processes in terms of the exciton population, we investigated the fluorescence [...] Read more.

We recently implemented highly sensitive detection systems for photo-sensitizing potassium ions (K⁺) based on two-step Förster resonance energy transfer (FRET). As a successive study for quantitative understanding of energy transfer processes in terms of the exciton population, we investigated the fluorescence decay dynamics in conjugated polymers and an aptamer-based 6-carboxyfluorescein (6-FAM)/6-carboxytetramethylrhodamine (TAMRA) complex. In the presence of K⁺ ions, the Guanine-rich aptamer enabled efficient two-step resonance energy transfer from conjugated polymers to dyed pairs of 6-FAM and TAMRA through the G-quadruplex phase. Although the fluorescence decay time of TAMRA barely changed, the fluorescence intensity was significantly increased. We also found that 6-FAM showed a decreased exciton population due the compensation of energy transfer to TAMRA by FRET from conjugated polymers, but a fluorescence quenching also occurred concomitantly. Consequently, the fluorescence intensity of TAMRA showed a 4-fold enhancement, where the initial transfer efficiency (~300%) rapidly saturated within ~0.5 ns and the plateau of transfer efficiency (~230%) remained afterward. Full article

(This article belongs to the Special Issue Fluorescent polymers for sensing and imaging)

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19 pages, 5973 KiB

Open AccessEditor’s ChoiceArticle

Water Resistant Self-Extinguishing Low Frequency Soundproofing Polyvinylpyrrolidone Based Electrospun Blankets

by Jessica Passaro, Paolo Russo, Aurelio Bifulco, Maria Teresa De Martino, Veronica Granata, Bonaventura Vitolo, Gino Iannace, Antonio Vecchione, Francesco Marulo and Francesco Branda

Polymers 2019, 11(7), 1205; https://doi.org/10.3390/polym11071205 - 19 Jul 2019

Cited by 25 | Viewed by 5193

Abstract

This paper shows that an eco-friendly electrospinning process allows us to produce water resistant sound absorbers with reduced thickness and excellent sound-absorption properties in the low and medium frequency range (250–1600 Hz) for which which human sensitivity is high and traditional materials struggle [...] Read more.

This paper shows that an eco-friendly electrospinning process allows us to produce water resistant sound absorbers with reduced thickness and excellent sound-absorption properties in the low and medium frequency range (250–1600 Hz) for which which human sensitivity is high and traditional materials struggle to match, that also pass the fire tests which are mandatory in many engineering areas. The structure and composition were studied through Scanning Electron Microscopy (SEM), Fourier Transform InfraRed (FTIR) Spectroscopy and ThermoGravimetric Analysis (TGA). The density, porosity and flow resistivity were measured. Preliminary investigation of the thermal conductivity through Differential Scanning Calorimetry (DSC) shows that they have perspectives also for thermal insulation. The experimental results indicate that the achievements are to be ascribed to the chemical nature of Polyvinylpyrrolidone (PVP). PVP is, in fact, a polymeric lactam with a side polar group that may be easily released by a thermooxidative process. The side polar groups allow for using ethanol for electrospinning than relying on a good dispersion of silica gel particles. The silica particles dimensionally stabilize the mats upon thermal treatments and confer water resistance while strongly contributing to the self-extinguishing property of the materials. Full article

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18 pages, 3187 KiB

Open AccessArticle

Melt-Mixed Thermoplastic Nanocomposite Containing Carbon Nanotubes and Titanium Dioxide for Flame Retardancy Applications

by C. Cabello-Alvarado, P. Reyes-Rodríguez, M. Andrade-Guel, G. Cadenas-Pliego, M. Pérez-Alvarez, V.J. Cruz-Delgado, L. Melo-López, Z.V. Quiñones-Jurado and C.A. Ávila-Orta

Polymers 2019, 11(7), 1204; https://doi.org/10.3390/polym11071204 - 19 Jul 2019

Cited by 24 | Viewed by 4255

Abstract

The study of polymeric nanocomposites is a possible alternative to conventional flame retardants. The aim of the present work is to investigate the effects of carbon-nanotubes (CNT) and TiO₂ nanoparticles (NPs) on the thermo-mechanical, flammability, and electrical properties of polypropylene (PP). In [...] Read more.

The study of polymeric nanocomposites is a possible alternative to conventional flame retardants. The aim of the present work is to investigate the effects of carbon-nanotubes (CNT) and TiO₂ nanoparticles (NPs) on the thermo-mechanical, flammability, and electrical properties of polypropylene (PP). In this work, PP-TiO₂/CNT nanocomposites were obtained with TiO₂/CNT mixtures (ratio 1:2) through the melt extrusion process, with different weight percentage of nanoparticles (1, 5, and 10 wt %). The PP-TiO₂/CNT nanocomposites were characterized by DSC, TGA, MFI, FTIR, XRD, and SEM. It was possible to determine that the thermal stability of the PP increases when increasing the content of NPs. A contrary situation is observed in the degree of crystallinity and thermo-oxidative degradation, which decreased with respect to pure PP. The TiO₂ NPs undergo coalition and increase their size at a lower viscosity of the nanocomposite (1 and 5 wt %). The mechanical properties decreased slightly, however, the Young’s modulus presented an improvement of 10% as well as electrical conductivity, this behavior was noted in nanocomposites of 10 wt % of NPs. Flammability properties were measured with a cone calorimeter, and a reduction in the peak heat release rate was observed in nanocomposites with contents of nanoparticles of 5 and 10 wt % Full article

(This article belongs to the Special Issue Carbon-Based Polymer Nanocomposites for High-Performance Applications)

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10 pages, 3422 KiB

Open AccessArticle

A Multilayer Emitter Close to Ideal Solar Reflectance for Efficient Daytime Radiative Cooling

by Yeqing Zhu, Dong Wang, Cheng Fang, Ping He and Yong-Hong Ye

Polymers 2019, 11(7), 1203; https://doi.org/10.3390/polym11071203 - 18 Jul 2019

Cited by 30 | Viewed by 4889

Abstract

A passive radiative cooling method has a significant influence on thermal management applications because it can cool without any energy input. This work both experimentally and theoretically demonstrates a multilayer thin film structure with high solar reflectance, which can be applied to passive [...] Read more.

A passive radiative cooling method has a significant influence on thermal management applications because it can cool without any energy input. This work both experimentally and theoretically demonstrates a multilayer thin film structure with high solar reflectance, which can be applied to passive daytime radiative cooling. The combination of physical vapor deposition and spin-coating prepared the samples, which were also characterized experimentally by spectrometers. On-site measured results show that the emitter can effectively achieve daytime radiative cooling, and the cooling performance can be further improved with the increase of the ambient air temperature. When the emitter is exposed to direct solar radiation (AM1.5) of about 880 W/m² on a rooftop under dry air conditions, it can achieve an average temperature reduction of about 12.6 °C from the ambient air temperature with nonradiative heat transfer (11 a.m.–1 p.m.). Theoretical simulations reveal that the emitter can still have a certain cooling performance in the presence of significant nonradiative heat exchange and nonideal atmospheric conditions. The influence of ambient air temperature on the cooling performance of the emitter is also theoretically analyzed. Full article

(This article belongs to the Special Issue Polymers for Energy Storage and Conversion)

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21 pages, 2638 KiB

Open AccessEditor’s ChoiceReview

Lignin-Based Polyurethanes: Opportunities for Bio-Based Foams, Elastomers, Coatings and Adhesives

by Mona Alinejad, Christián Henry, Saeid Nikafshar, Akash Gondaliya, Sajad Bagheri, Nusheng Chen, Sandip K. Singh, David B. Hodge and Mojgan Nejad

Polymers 2019, 11(7), 1202; https://doi.org/10.3390/polym11071202 - 18 Jul 2019

Cited by 169 | Viewed by 19284

Abstract

Polyurethane chemistry can yield diverse sets of polymeric materials exhibiting a wide range of properties for various applications and market segments. Utilizing lignin as a polyol presents an opportunity to incorporate a currently underutilized renewable aromatic polymer into these products. In this work, [...] Read more.

Polyurethane chemistry can yield diverse sets of polymeric materials exhibiting a wide range of properties for various applications and market segments. Utilizing lignin as a polyol presents an opportunity to incorporate a currently underutilized renewable aromatic polymer into these products. In this work, we will review the current state of technology for utilizing lignin as a polyol replacement in different polyurethane products. This will include a discussion of lignin structure, diversity, and modification during chemical pulping and cellulosic biofuels processes, approaches for lignin extraction, recovery, fractionation, and modification/functionalization. We will discuss the potential of incorporation of lignins into polyurethane products that include rigid and flexible foams, adhesives, coatings, and elastomers. Finally, we will discuss challenges in incorporating lignin in polyurethane formulations, potential solutions and approaches that have been taken to resolve those issues. Full article

(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)

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7 pages, 1727 KiB

Open AccessEditor’s ChoiceArticle

Determination of Surface Accessibility of the Cellulose Substrate According to Enzyme Sorption

by Ekaterina M. Podgorbunskikh, Aleksey L. Bychkov and Oleg I. Lomovsky

Polymers 2019, 11(7), 1201; https://doi.org/10.3390/polym11071201 - 18 Jul 2019

Cited by 20 | Viewed by 3425

Abstract

As a heterogeneous process, enzymatic hydrolysis depends on the contact area between enzymes and the cellulose substrate. The surface area of a substrate is typically evaluated through the sorption of gases (nitrogen, argon, or water vapor) or sorption of high-molecular-weight pigments or proteins. [...] Read more.

As a heterogeneous process, enzymatic hydrolysis depends on the contact area between enzymes and the cellulose substrate. The surface area of a substrate is typically evaluated through the sorption of gases (nitrogen, argon, or water vapor) or sorption of high-molecular-weight pigments or proteins. However, lignocellulosic biomass uninvolved in the reaction because of inefficient binding or even the complete inhibition of the enzymes on the surface consisting of lignin or inorganic compounds is erroneously taken into account under these conditions. The initial rate of enzymatic hydrolysis will directly depend on the number of enzymes efficiently sorbed onto cellulose. In this study, the sorption of cellulolytic enzymes was used to evaluate the surface accessibility of the cellulose substrate and its changes during mechanical pretreatment. It was demonstrated that for pure cellulose, mechanical activation did not alter the chemical composition of the surface and the initial rate of hydrolysis increased, which was inconsistent with the data on the thermal desorption of nitrogen. New active cellulose sorption sites were shown to be formed upon. the mechanical activation of plant biomass (wheat straw), and the ultimate initial rate of hydrolysis corresponding to saturation of the accessible surface area with enzyme molecules was determined. Full article

(This article belongs to the Special Issue Cellulose and Renewable Materials)

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