Polymers

10 pages, 3304 KB

Open AccessEditor’s ChoiceCommunication

Formulation and Characterization of a SIS-Based Photocrosslinkable Bioink

by Julian A. Serna, Sergio Leonardo Florez, Vivian A. Talero, Juan C. Briceño, Carolina Muñoz-Camargo and Juan C. Cruz

Polymers 2019, 11(3), 569; https://doi.org/10.3390/polym11030569 - 26 Mar 2019

Cited by 34 | Viewed by 6712

Abstract

Decellularized extracellular matrices (dECMs) represent a promising alternative as a source of materials to develop scaffolds that closely mimic the native environment of cells. As a result, dECMs have attracted significant attention for their applications in regenerative medicine and tissue engineering. One such [...] Read more.

Decellularized extracellular matrices (dECMs) represent a promising alternative as a source of materials to develop scaffolds that closely mimic the native environment of cells. As a result, dECMs have attracted significant attention for their applications in regenerative medicine and tissue engineering. One such application is 3D bioprinting, in which dECMs can be used to prepare bioinks with the biomimicry attributes required for regeneration purposes. Formulating bioinks is, however, challenging, due to difficulties in assuring that the printed materials match the mechanical properties of the tissue which is to be regenerated. To tackle this issue, a number of strategies have been devised, including crosslinking methods, the addition of synthetic materials as excipients, and the use of synthetic matrices for casting. We are particularly interested in extrusion-based 3D bioprinting, mainly due to the ease of rapidly conducting tests for adjusting operating conditions such that the required rheological and mechanical properties are met when using it. Here, we propose a novel bioink that consists of an acid-based precipitation of a small intestinal submucosa (SIS) dECM. The formulated bioink also relies on photocrosslinking reactions to attempt to control gelation and ultimately the mechanical properties of the extruded material. Photoinitiation was explored with the aid of varying concentrations of riboflavin (RF). Manual extrusion and rheological flow tests confirmed the printability and shear-thinning behavior of all formulations. Photocrosslinking reactions, however, failed to promote a substantial increase in gelation, which was attributed to considerable entanglement of undigested collagen molecules. As a result, pendant amine groups thought to be involved in the photo-mediated reactions remain largely inaccessible. In silico computational fluid dynamics (CFD) simulations were implemented to determine shear stress values on the bioink along the exit of the printing nozzle. Moreover, we calculated a stability parameter as a means to estimate changes in the bioink stability during the extrusion process. Future studies should be directed toward assessing the role of temperature-induced gelation in the rheological properties of the bioink and the development of strategies to improve the efficiency of photocrosslinking processes. Full article

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18 pages, 1213 KB

Open AccessEditor’s ChoiceReview

Polymeric Antimicrobial Food Packaging and Its Applications

by Tianqi Huang, Yusheng Qian, Jia Wei and Chuncai Zhou

Polymers 2019, 11(3), 560; https://doi.org/10.3390/polym11030560 - 25 Mar 2019

Cited by 258 | Viewed by 20518

Abstract

Food corruption and spoilage caused by food-borne pathogens and microorganisms is a serious problem. As a result, the demand for antibacterial drugs in food packaging is growing. In this review, biodegradable and non-biodegradable materials for food packaging are discussed based on their properties. [...] Read more.

Food corruption and spoilage caused by food-borne pathogens and microorganisms is a serious problem. As a result, the demand for antibacterial drugs in food packaging is growing. In this review, biodegradable and non-biodegradable materials for food packaging are discussed based on their properties. Most importantly, antibacterial agents are essential to inhibit the growth of bacteria in food. To keep food fresh and prolong the shelf life, different kinds of antibacterial agents were used. The composition and application of natural antibacterial agents and synthetic antibacterial agents are discussed. Compared with natural antibacterial agents, synthetic antibacterial agents have the advantages of low cost and high activity, but their toxicity is usually higher than that of natural antibacterial agents. Finally, future development of antimicrobial food packaging is proposed. It is an urgent problem for researchers to design and synthesize antibacterial drugs with high efficiency and low toxicity. Full article

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15 pages, 3240 KB

Open AccessEditor’s ChoiceArticle

Exploring Next-Generation Engineering Bioplastics: Poly(alkylene furanoate)/Poly(alkylene terephthalate) (PAF/PAT) Blends

by Niki Poulopoulou, Nejib Kasmi, Maria Siampani, Zoi N. Terzopoulou, Dimitrios N. Bikiaris, Dimitris S. Achilias, Dimitrios G. Papageorgiou and George Z. Papageorgiou

Polymers 2019, 11(3), 556; https://doi.org/10.3390/polym11030556 - 23 Mar 2019

Cited by 45 | Viewed by 7725

Abstract

Polymers from renewable resources and especially strong engineering partially aromatic biobased polyesters are of special importance for the evolution of bioeconomy. The fabrication of polymer blends is a creative method for the production of tailor-made materials for advanced applications that are able to [...] Read more.

Polymers from renewable resources and especially strong engineering partially aromatic biobased polyesters are of special importance for the evolution of bioeconomy. The fabrication of polymer blends is a creative method for the production of tailor-made materials for advanced applications that are able to combine functionalities from both components. In this study, poly(alkylene furanoate)/poly(alkylene terephthalate) blends with different compositions were prepared by solution blending in a mixture of trifluoroacetic acid and chloroform. Three different types of blends were initially prepared, namely, poly(ethylene furanoate)/poly(ethylene terephthalate) (PEF/PET), poly(propylene furanoate)/poly(propylene terephthalate) (PPF/PPT), and poly(1,4-cyclohenedimethylene furanoate)/poly(1,4-cycloxehane terephthalate) (PCHDMF/PCHDMT). These blends’ miscibility characteristics were evaluated by examining the glass transition temperature of each blend. Moreover, reactive blending was utilized for the enhancement of miscibility and dynamic homogeneity and the formation of copolymers through transesterification reactions at high temperatures. PEF–PET and PPF–PPT blends formed a copolymer at relatively low reactive blending times. Finally, poly(ethylene terephthalate-co-ethylene furanoate) (PETF) random copolymers were successfully introduced as compatibilizers for the PEF/PET immiscible blends, which resulted in enhanced miscibility. Full article

(This article belongs to the Collection Sustainable Polymeric Materials from Renewable Resources)

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19 pages, 8064 KB

Open AccessEditor’s ChoiceArticle

Electrical and Thermal Conductivity of Polylactic Acid (PLA)-Based Biocomposites by Incorporation of Nano-Graphite Fabricated with Fused Deposition Modeling

by Rui Guo, Zechun Ren, Hongjie Bi, Min Xu and Liping Cai

Polymers 2019, 11(3), 549; https://doi.org/10.3390/polym11030549 - 22 Mar 2019

Cited by 105 | Viewed by 8856

Abstract

The aim of the study was to improve the electrical and thermal conductivity of the polylactic acid/wood flour/thermoplastic polyurethane composites by Fused Deposition Modeling (FDM). The results showed that, when the addition amount of nano-graphite reached 25 pbw, the volume resistivity of the [...] Read more.

The aim of the study was to improve the electrical and thermal conductivity of the polylactic acid/wood flour/thermoplastic polyurethane composites by Fused Deposition Modeling (FDM). The results showed that, when the addition amount of nano-graphite reached 25 pbw, the volume resistivity of the composites decreased to 10⁸ Ω·m, which was a significant reduction, indicating that the conductive network was already formed. It also had good thermal conductivity, mechanical properties, and thermal stability. The adding of the redox graphene (rGO) combined with graphite into the composites, compared to the tannic acid-functionalized graphite or the multi-walled carbon nanotubes, can be an effective method to improve the performance of the biocomposites, because the resistivity reduced by one order magnitude and the thermal conductivity increased by 25.71%. Models printed by FDM illustrated that the composite filaments have a certain flexibility and can be printed onto paper or flexible baseplates. Full article

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41 pages, 12661 KB

Open AccessEditor’s ChoiceReview

Kinetics of Alkoxysilanes and Organoalkoxysilanes Polymerization: A Review

by Ahmed A. Issa and Adriaan S. Luyt

Polymers 2019, 11(3), 537; https://doi.org/10.3390/polym11030537 - 21 Mar 2019

Cited by 253 | Viewed by 26267

Abstract

Scientists from various different fields use organo-trialkoxysilanes and tetraalkoxysilanes in a number of applications. The silica-based materials are sometimes synthesized without a good understanding of the underlying reaction kinetics. This literature review attempts to be a comprehensive and more technical article in which [...] Read more.

Scientists from various different fields use organo-trialkoxysilanes and tetraalkoxysilanes in a number of applications. The silica-based materials are sometimes synthesized without a good understanding of the underlying reaction kinetics. This literature review attempts to be a comprehensive and more technical article in which the kinetics of alkoxysilanes polymerization are discussed. The kinetics of polymerization are controlled by primary factors, such as catalysts, water/silane ratio, pH, and organo-functional groups, while secondary factors, such as temperature, solvent, ionic strength, leaving group, and silane concentration, also have an influence on the reaction rates. Experiments to find correlations between these factors and reaction rates are restricted to certain conditions and most of them disregard the properties of the solvent. In this review, polymerization kinetics are discussed in the first two sections, with the first section covering early stage reactions when the reaction medium is homogenous, and the second section covering when phase separation occurs and the reaction medium becomes heterogeneous. Nuclear magnetic resonance (NMR) spectroscopy and other techniques are discussed in the third section. The last section summarizes the study of reaction mechanisms by using ab initio and Density Functional Theory (DFT) methods alone, and in combination with molecular dynamics (MD) or Monte Carlo (MC) methods. Full article

(This article belongs to the Special Issue Kinetics of Polymerization Reactions)

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17 pages, 4233 KB

Open AccessEditor’s ChoiceArticle

The Impact of Lignin Structural Diversity on Performance of Cellulose Nanofiber (CNF)-Starch Composite Films

by Yadong Zhao, Ayumu Tagami, Galina Dobele, Mikael E. Lindström and Olena Sevastyanova

Polymers 2019, 11(3), 538; https://doi.org/10.3390/polym11030538 - 21 Mar 2019

Cited by 40 | Viewed by 6469

Abstract

Lignin fractions having different molecular weights and varied chemical structures isolated from kraft lignins of both softwood and hardwood via a sequential solvent fractionation technique were incorporated into a tunicate cellulose nanofibers (CNF)—starch mixture to prepare 100% bio-based composite films. The aim was [...] Read more.

Lignin fractions having different molecular weights and varied chemical structures isolated from kraft lignins of both softwood and hardwood via a sequential solvent fractionation technique were incorporated into a tunicate cellulose nanofibers (CNF)—starch mixture to prepare 100% bio-based composite films. The aim was to investigate the impact of lignin structural diversity on film performance. It was confirmed that lignin’s distribution in the films was dependent on the polarity of solvents used for fractionation (acetone > methanol > ethanol > ethyl acetate) and influenced the optical properties of the films. The –OH group content and molecular weight of lignin were positively related to film density. In general, the addition of lignin fractions led to decrease in thermal stability and increase in Young’s modulus of the composite films. The modulus of the films was found to decrease as the molecular weight of lignin increased, and a higher amount of carboxyl and phenolic –OH groups in the lignin fraction resulted in films with higher stiffness. The thermal analysis showed higher char content formation for lignin-containing films in a nitrogen atmosphere with increased molecular weight. In an oxygen atmosphere, the phenol content, saturated side chains and short chain structures of lignin had impacts on the maximum decomposition temperature of the films, confirming the relationship between the chemical structure of lignin and thermo-oxidative stability of the corresponding film. This study addresses the importance of lignin diversities on composite film performance, which could be helpful for tailoring lignin’s applications in bio-based materials based on their specific characteristics. Full article

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

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9 pages, 1180 KB

Open AccessEditor’s ChoiceReview

Supramolecular Cyclodextrin-Based Hydrogels for Controlled Gene Delivery

by Ana Rey-Rico and Magali Cucchiarini

Polymers 2019, 11(3), 514; https://doi.org/10.3390/polym11030514 - 19 Mar 2019

Cited by 46 | Viewed by 4895

Abstract

Controlled delivery of gene transfer vectors is a powerful strategy to enhance the temporal and spatial presentation of therapeutic agents in a defined target. Hydrogels are adapted biomaterials for gene delivery capable of acting as a localized depot of genes while maintaining the [...] Read more.

Controlled delivery of gene transfer vectors is a powerful strategy to enhance the temporal and spatial presentation of therapeutic agents in a defined target. Hydrogels are adapted biomaterials for gene delivery capable of acting as a localized depot of genes while maintaining the long term local availability of DNA vectors at a specific location. Supramolecular hydrogels based on cyclodextrins (CDs) have attracted considerable attention as potential biomaterials in a broad range of drug delivery applications. Their unique characteristics of thixotropicity and low cytotoxicity due to their production under mild conditions make them potential candidates to form injectable delivery systems. This work aims to provide an overview of the use of CD-based polypseudorotaxane hydrogels as controlled gene delivery systems for different applications in regenerative medicine. Full article

(This article belongs to the Special Issue Cyclodextrin-Containing Polymers)

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33 pages, 2846 KB

Open AccessEditor’s ChoiceReview

Nanocelluloses: Natural-Based Materials for Fiber-Reinforced Cement Composites. A Critical Review

by Ana Balea, Elena Fuente, Angeles Blanco and Carlos Negro

Polymers 2019, 11(3), 518; https://doi.org/10.3390/polym11030518 - 19 Mar 2019

Cited by 130 | Viewed by 12686

Abstract

Nanocelluloses (NCs) are bio-based nano-structurated products that open up new solutions for natural material sciences. Although a high number of papers have described their production, properties, and potential applications in multiple industrial sectors, no review to date has focused on their possible use [...] Read more.

Nanocelluloses (NCs) are bio-based nano-structurated products that open up new solutions for natural material sciences. Although a high number of papers have described their production, properties, and potential applications in multiple industrial sectors, no review to date has focused on their possible use in cementitious composites, which is the aim of this review. It describes how they could be applied in the manufacturing process as a raw material or an additive. NCs improve mechanical properties (internal bonding strength, modulus of elasticity (MOE), and modulus of rupture (MOR)), alter the rheology of the cement paste, and affect the physical properties of cements/cementitious composites. Additionally, the interactions between NCs and the other components of the fiber cement matrix are analyzed. The final result depends on many factors, such as the NC type, the dosage addition mode, the dispersion, the matrix type, and the curing process. However, all of these factors have not been studied in full so far. This review has also identified a number of unexplored areas of great potential for future research in relation to NC applications for fiber-reinforced cement composites, which will include their use as a surface treatment agent, an anionic flocculant, or an additive for wastewater treatment. Although NCs remain expensive, the market perspective is very promising. Full article

(This article belongs to the Special Issue Bio-Based Polymers for Engineered Green Materials)

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39 pages, 9472 KB

Open AccessEditor’s ChoiceReview

Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors

by Beata Dudziec, Patrycja Żak and Bogdan Marciniec

Polymers 2019, 11(3), 504; https://doi.org/10.3390/polym11030504 - 16 Mar 2019

Cited by 51 | Viewed by 8006

Abstract

Over the past two decades, organic optoelectronic materials have been considered very promising. The attractiveness of this group of compounds, regardless of their undisputable application potential, lies in the possibility of their use in the construction of organic–inorganic hybrid materials. This class of [...] Read more.

Over the past two decades, organic optoelectronic materials have been considered very promising. The attractiveness of this group of compounds, regardless of their undisputable application potential, lies in the possibility of their use in the construction of organic–inorganic hybrid materials. This class of frameworks also considers nanostructural polyhedral oligomeric silsesquioxanes (POSSs) with “organic coronae” and precisely defined organic architectures between dispersed rigid silica cores. A significant number of papers on the design and development of POSS-based organic optoelectronic as well as photoluminescent (PL) materials have been published recently. In view of the scientific literature abounding with numerous examples of their application (i.e., as OLEDs), the aim of this review is to present efficient synthetic pathways leading to the formation of nanocomposite materials based on silsesquioxane systems that contain organic chromophores of complex nature. A summary of stoichiometric and predominantly catalytic methods for these silsesquioxane-based systems to be applied in the construction of photoactive materials or their precursors is given. Full article

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

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14 pages, 3304 KB

Open AccessEditor’s ChoiceArticle

Robust Superhydrophobic Cellulose Nanofiber Aerogel for Multifunctional Environmental Applications

by Hasan. M., Deepu A. Gopakumar, Vishnu Arumughan, Yasir Beeran Pottathara, Sisanth K. S., Daniel Pasquini, Matej Bračič, Bastien Seantier, Ange Nzihou, Sabu Thomas, Samsul Rizal and Abdul Khalil H. P. S.

Polymers 2019, 11(3), 495; https://doi.org/10.3390/polym11030495 - 14 Mar 2019

Cited by 58 | Viewed by 7953

Abstract

The fabrication of superadsorbent for dye adsorption is a hot research area at present. However, the development of low-cost and highly efficient superadsorbents against toxic textile dyes is still a big challenge. Here, we fabricated hydrophobic cellulose nanofiber aerogels from cellulose nanofibers through [...] Read more.

The fabrication of superadsorbent for dye adsorption is a hot research area at present. However, the development of low-cost and highly efficient superadsorbents against toxic textile dyes is still a big challenge. Here, we fabricated hydrophobic cellulose nanofiber aerogels from cellulose nanofibers through an eco-friendly silanization reaction in liquid phase, which is an extremely efficient, rapid, cheap, and environmentally friendly procedure. Moreover, the demonstrated eco-friendly silanization technique is easy to commercialize at the industrial level. Most of the works that have reported on the hydrophobic cellulose nanofiber aerogels explored their use for the elimination of oil from water. The key novelty of the present work is that the demonstrated hydrophobic cellulose nanofibers aerogels could serve as superadsorbents against toxic textile dyes such as crystal violet dye from water and insulating materials for building applications. Here, we make use of the possible hydrophobic interactions between silane-modified cellulose nanofiber aerogel and crystal violet dye for the removal of the crystal violet dye from water. With a 10 mg/L of crystal violet (CV) aqueous solution, the silane-modified cellulose nanofiber aerogel showed a high adsorption capacity value of 150 mg/g of the aerogel. The reason for this adsorption value was due to the short-range hydrophobic interaction between the silane-modified cellulose nanofiber aerogel and the hydrophobic domains in crystal violet dye molecules. Additionally, the fabricated silane-modified cellulose nanofiber hydrophobic aerogels exhibited a lower thermal conductivity value of 0.037 W·m⁻¹ K⁻¹, which was comparable to and lower than the commercial insulators such as mineral wools (0.040 W·m⁻¹ K⁻¹) and polystyrene foams (0.035 W·m⁻¹ K⁻¹). We firmly believe that the demonstrated silane-modified cellulose nanofiber aerogel could yield an eco-friendly adsorbent that is agreeable to adsorbing toxic crystal violet dyes from water as well as active building thermal insulators. Full article

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24 pages, 3157 KB

Open AccessEditor’s ChoiceArticle

Chitosan Grafted Adsorbents for Diclofenac Pharmaceutical Compound Removal from Single-Component Aqueous Solutions and Mixtures

by Areti Tzereme, Evi Christodoulou, George Z. Kyzas, Margaritis Kostoglou, Dimitrios N. Bikiaris and Dimitra A. Lambropoulou

Polymers 2019, 11(3), 497; https://doi.org/10.3390/polym11030497 - 14 Mar 2019

Cited by 56 | Viewed by 6007

Abstract

The main purpose of this study was to investigate the synthesis of some cross-linked carboxyl-grafted chitosan derivatives to be used as selective adsorbents for diclofenac (DCF) pharmaceutical compounds from aqueous mixtures. Four different materials were synthesized using succinic anhydride (CsSUC), maleic anhydride (CsMAL), [...] Read more.

The main purpose of this study was to investigate the synthesis of some cross-linked carboxyl-grafted chitosan derivatives to be used as selective adsorbents for diclofenac (DCF) pharmaceutical compounds from aqueous mixtures. Four different materials were synthesized using succinic anhydride (CsSUC), maleic anhydride (CsMAL), itaconic acid (CsITA), and trans-aconitic acid (CsTACON) as grafting agents. After synthesis, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were performed before and after DCF adsorption. In addition, a complete adsorption evaluation was carried out for all materials studying some important parameters. The optimum pH was 4; the amino groups of DCF can be protonated at pH = 4 (–NH⁺), so this groups can easily attract the clear negatively carboxyl moieties (–COO⁻) of the chitosan adsorbents. The Q_m for CsTACON was higher than those of the other materials, at all temperatures studied. By altering the temperature from 25 to 35 °C, an increase (16%) of Q_m (from 84.56 to 98.34 mg g⁻¹) was noted, while similar behavior was revealed after a further increase of temperature from 35 to 45 °C, improving by 5% (from 98.34 to 102.75 mg g⁻¹). All isotherms were fitted to Langmuir, Freundlich, and Langmuir-Freundlich (L-F) models). In addition, a kinetic model was proposed taking into account not only the interactions but also the diffusivity of the molecule (DCF) into the polymeric network. The behavior of the prepared chitosan materials in simultaneously removing other compounds (synergetic or antagonistic) was also evaluated by experiments performed in mixtures. DCF presented the highest removal from the mixture in the order: CsTACON (92.8%) > CsITA (89.5%) > CsSUC (80.9%) > CsMAL (66.2%) compared to other pharmaceutical compounds (salicylic acid, ibuprofen and ketoprofen). Desorption was achieved by using different eluants (either water or organic). The highest desorption ability was found for acetone (100% for CsTACON, CsSUC, CsMAL and 77% for CsITA) for all materials. Full article

(This article belongs to the Special Issue Chitin and Chitosan: Properties and Applications)

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15 pages, 4106 KB

Open AccessEditor’s ChoiceArticle

Interaction of Surface Energy Components between Solid and Liquid on Wettability, and Its Application to Textile Anti-Wetting Finish

by Kwanwoo Song, Jinwook Lee, Seong-O Choi and Jooyoun Kim

Polymers 2019, 11(3), 498; https://doi.org/10.3390/polym11030498 - 14 Mar 2019

Cited by 97 | Viewed by 7633

Abstract

With various options of anti-wetting finish methods, this study intends to provide basic information that can be applied in selecting a relevant anti-wetting chemical to grant protection from spreading of liquids with different surface energy profiles. With such an aim, the anti-wetting effectiveness [...] Read more.

With various options of anti-wetting finish methods, this study intends to provide basic information that can be applied in selecting a relevant anti-wetting chemical to grant protection from spreading of liquids with different surface energy profiles. With such an aim, the anti-wetting effectiveness of fluorinated coating and silane coating was investigated for liquids having different surface energy components, water (WA), methylene iodide (MI) and formamide (FA). The wetting thermodynamics was experimentally investigated by analyzing dispersive and polar component surface energies of solids and liquids. The role of surface roughness in wettability was examined for fibrous nonwoven substrates that have varied surface roughness. The presence of roughness enhanced the anti-wetting performance of the anti-wetting treated surfaces. While the effectiveness of different anti-wetting treatments was varied depending on the liquid polarities, the distinction of different treatments was less apparent for the roughened fibrous surfaces than the film surfaces. This study provides experimental validation of wetting thermodynamics and the practical interpretation of anti-wetting finishing. 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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15 pages, 2017 KB

Open AccessEditor’s ChoiceArticle

The Impact of Cross-linking Mode on the Physical and Antimicrobial Properties of a Chitosan/Bacterial Cellulose Composite

by Jun Liang, Rui Wang and Ruipeng Chen

Polymers 2019, 11(3), 491; https://doi.org/10.3390/polym11030491 - 13 Mar 2019

Cited by 84 | Viewed by 8382

Abstract

The bacteriostatic performance of a chitosan film is closely related to its ionic and physical properties, which are significantly influenced by the mode of cross-linking. In the current work, chitosan with or without bacterial cellulose was cross-linked with borate, tripolyphosphate, or the mixture [...] Read more.

The bacteriostatic performance of a chitosan film is closely related to its ionic and physical properties, which are significantly influenced by the mode of cross-linking. In the current work, chitosan with or without bacterial cellulose was cross-linked with borate, tripolyphosphate, or the mixture of borate and tripolyphosphate, and the composite films were obtained by a casting of dispersion. Mechanical measurements indicated that different modes of cross-linking led to varying degrees of film strength and elongation increases, while the films treated with the borate and tripolyphosphate mixture showed the best performance. Meanwhile, changes in the fractured sectional images showed a densified texture induced by cross-linkers, especially for the borate and tripolyphosphate mixture. Measurements of Fourier transform infrared showed the enhanced interaction between the matrix polymers treated by borate, confirmed by a slight increase in the glass transitional temperature and a higher surface hydrophobicity. However, the reduced antimicrobial efficiency of composite films against E. coli, B. cinerea, and S. cerevisiae was obtained in cross-linked films compared with chitosan/bacterial cellulose films, indicating that the impact on the antimicrobial function of chitosan is a noteworthy issue for cross-linking. Full article

(This article belongs to the Special Issue Antimicrobial Polymer-Based Materials for Food Packaging Applications)

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23 pages, 3263 KB

Open AccessEditor’s ChoiceArticle

Shock-Driven Decomposition of Polymers and Polymeric Foams

by Dana M. Dattelbaum and Joshua D. Coe

Polymers 2019, 11(3), 493; https://doi.org/10.3390/polym11030493 - 13 Mar 2019

Cited by 41 | Viewed by 5548

Abstract

Polymers and foams are pervasive in everyday life, as well as in specialized contexts such as space exploration, industry, and defense. They are frequently subject to shock loading in the latter cases, and will chemically decompose to small molecule gases and carbon (soot) [...] Read more.

Polymers and foams are pervasive in everyday life, as well as in specialized contexts such as space exploration, industry, and defense. They are frequently subject to shock loading in the latter cases, and will chemically decompose to small molecule gases and carbon (soot) under loads of sufficient strength. We review a body of work—most of it performed at Los Alamos National Laboratory—on polymers and foams under extreme conditions. To provide some context, we begin with a brief review of basic concepts in shockwave physics, including features particular to transitions (chemical reaction or phase transition) entailing an abrupt reduction in volume. We then discuss chemical formulations and synthesis, as well as experimental platforms used to interrogate polymers under shock loading. A high-level summary of equations of state for polymers and their decomposition products is provided, and their application illustrated. We then present results including temperatures and product compositions, thresholds for reaction, wave profiles, and some peculiarities of traditional modeling approaches. We close with some thoughts regarding future work. Full article

(This article belongs to the Special Issue Polymeric Foams)

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17 pages, 5879 KB

Open AccessEditor’s ChoiceArticle

Isothermal Crystallization Kinetics Study of Fully Aliphatic PA6 Copolyamides: Effect of Novel Long-Chain Polyamide Salt as a Comonomer

by Syang-Peng Rwei, Palraj Ranganathan and Yi-Huan Lee

Polymers 2019, 11(3), 472; https://doi.org/10.3390/polym11030472 - 12 Mar 2019

Cited by 39 | Viewed by 7657

Abstract

N¹, N⁶-bis (4-aminobutyl) adipamide (BABA) diamine and sebacic acid (SA), also called BABA/SA polyamide salt, were used in a typical melt polymerization processes of polyamide 6 (PA6) to form a series of PA6-BABA/SA copolyamides. The effects of BABA/SA on [...] Read more.

N¹, N⁶-bis (4-aminobutyl) adipamide (BABA) diamine and sebacic acid (SA), also called BABA/SA polyamide salt, were used in a typical melt polymerization processes of polyamide 6 (PA6) to form a series of PA6-BABA/SA copolyamides. The effects of BABA/SA on the isothermal crystallization kinetics of PA6-BABA/SA were studied for the first time. An isothermal crystallization analysis demonstrates that the PA6-BABA/SA matrix provided a higher crystallization rate and shorter half-crystallization time than virgin PA6 did. The degree of crystallization of the PA6-BABA/SA₃₀ matrix was also the lowest among all of the samples considered herein. This result is attributed to the high nucleation efficacy of a small amount of BABA/SA in the crystallization of PA6. Values of the Avrami exponent (n) from 1.84 to 3.91 were observed for all of the polyamide samples, suggesting that the crystallization was involved via a two- to three-dimensional growth mechanism. These findings deepen our understanding of the structure–property relationship of PA6-BABA/SA copolyamides, favoring their practical application. Full article

(This article belongs to the Special Issue Thermal Properties and Applications of Polymers)

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25 pages, 7605 KB

Open AccessEditor’s ChoiceArticle

Individual Molecular Dynamics of an Entangled Polyethylene Melt Undergoing Steady Shear Flow: Steady-State and Transient Dynamics

by Mohammad Hadi Nafar Sefiddashti, Brian J. Edwards and Bamin Khomami

Polymers 2019, 11(3), 476; https://doi.org/10.3390/polym11030476 - 12 Mar 2019

Cited by 51 | Viewed by 5095

Abstract

The startup and steady shear flow properties of an entangled, monodisperse polyethylene liquid (C₁₀₀₀H₂₀₀₂) were investigated via virtual experimentation using nonequilibrium molecular dynamics. The simulations revealed a multifaceted dynamical response of the liquid to the imposed flow field in [...] Read more.

The startup and steady shear flow properties of an entangled, monodisperse polyethylene liquid (C₁₀₀₀H₂₀₀₂) were investigated via virtual experimentation using nonequilibrium molecular dynamics. The simulations revealed a multifaceted dynamical response of the liquid to the imposed flow field in which entanglement loss leading to individual molecular rotation plays a dominant role in dictating the bulk rheological response at intermediate and high shear rates. Under steady shear conditions, four regimes of flow behavior were evident. In the linear viscoelastic regime (

\dot{γ} < τ_{d}^{- 1}

), orientation of the reptation tube network dictates the rheological response. Within the second regime (

τ_{d}^{- 1} < \dot{γ} < τ_{R}^{- 1}

), the tube segments begin to stretch mildly and the molecular entanglement network begins to relax as flow strength increases; however, the dominant relaxation mechanism in this region remains the orientation of the tube segments. In the third regime (

τ_{R}^{- 1} < \dot{γ} < τ_{e}^{- 1}

), molecular disentangling accelerates and tube stretching dominates the response. Additionally, the rotation of molecules become a significant source of the overall dynamic response. In the fourth regime (

\dot{γ} > τ_{e}^{- 1}

), the entanglement network deteriorates such that some molecules become almost completely unraveled, and molecular tumbling becomes the dominant relaxation mechanism. The comparison of transient shear viscosity,

η^{+}

, with the dynamic responses of key variables of the tube model, including the tube segmental orientation,

S

, and tube stretch,

λ

, revealed that the stress overshoot and undershoot in steady shear flow of entangled liquids are essentially originated and dynamically controlled by the

S_{x y}

component of the tube orientation tensor, rather than the tube stretch, over a wide range of flow strengths. Full article

(This article belongs to the Special Issue Theory and Simulations of Entangled Polymers)

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18 pages, 4793 KB

Open AccessEditor’s ChoiceReview

Thermal Conductivity of Protein-Based Materials: A Review

by Ye Xue, Samuel Lofland and Xiao Hu

Polymers 2019, 11(3), 456; https://doi.org/10.3390/polym11030456 - 11 Mar 2019

Cited by 56 | Viewed by 12483

Abstract

Fibrous proteins such as silks have been used as textile and biomedical materials for decades due to their natural abundance, high flexibility, biocompatibility, and excellent mechanical properties. In addition, they also can avoid many problems related to traditional materials such as toxic chemical [...] Read more.

Fibrous proteins such as silks have been used as textile and biomedical materials for decades due to their natural abundance, high flexibility, biocompatibility, and excellent mechanical properties. In addition, they also can avoid many problems related to traditional materials such as toxic chemical residues or brittleness. With the fast development of cutting-edge flexible materials and bioelectronics processing technologies, the market for biocompatible materials with extremely high or low thermal conductivity is growing rapidly. The thermal conductivity of protein films, which is usually on the order of 0.1 W/m·K, can be rather tunable as the value for stretched protein fibers can be substantially larger, outperforming that of many synthetic polymer materials. These findings indicate that the thermal conductivity and the heat transfer direction of protein-based materials can be finely controlled by manipulating their nano-scale structures. This review will focus on the structure of different fibrous proteins, such as silks, collagen and keratin, summarizing factors that can influence the thermal conductivity of protein-based materials and the different experimental methods used to measure their heat transfer properties. Full article

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17 pages, 5923 KB

Open AccessEditor’s ChoiceArticle

Enhancing the Mechanical and Thermal Properties of Epoxy Resin via Blending with Thermoplastic Polysulfone

by Zeyu Sun, Lei Xu, Zhengguo Chen, Yuhao Wang, Rogers Tusiime, Chao Cheng, Shuai Zhou, Yong Liu, Muhuo Yu and Hui Zhang

Polymers 2019, 11(3), 461; https://doi.org/10.3390/polym11030461 - 11 Mar 2019

Cited by 115 | Viewed by 8188

Abstract

Efficient enhancement of the toughness of epoxy resins has been a bottleneck for expanding their suitability for advanced applications. Here, polysulfone (PSF) was adopted to toughen and modify the epoxy. The influences of PSF on the mechanical and thermal properties of the epoxy [...] Read more.

Efficient enhancement of the toughness of epoxy resins has been a bottleneck for expanding their suitability for advanced applications. Here, polysulfone (PSF) was adopted to toughen and modify the epoxy. The influences of PSF on the mechanical and thermal properties of the epoxy resin were systematically studied by optical microscopy, Fourier transform infrared spectrometer (FT-IR), differential scanning calorimetry (DSC), thermogravimetric analyzer (TG), dynamic mechanical thermal analyzer (DMA), mechanical tests and scanning electron microscope (SEM). The dissolution experimental results showed that PSF presents a good compatibility with the epoxy resin and could be well dissolved under controlled conditions. The introduction of PSF was found to promote the curing reaction of the epoxy resin without participating in the curing reaction and changing the curing mechanism as revealed by the FT-IR and DSC studies. The mechanical properties of PSF/epoxy resin blends showed that the fracture toughness and impact strength were significantly improved, which could be attributed to the bicontinuous phase structure of PSF/epoxy blends. Representative phase structures resulted from the reaction induced phase separation process were clearly observed in the PSF/epoxy blends during the curing process of epoxy resin, which presented dispersed particles, bicontinuous and phase inverted structures with the increase of the PSF content. Our work further confirmed that the thermal stability of the PSF/epoxy blends was slightly increased compared to that of the pure epoxy resin, mainly due to the good heat resistance of the PSF component. Full article

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15 pages, 2308 KB

Open AccessEditor’s ChoiceArticle

Characterization of Highly Filled PP/Graphite Composites for Adhesive Joining in Fuel Cell Applications

by Piotr Rzeczkowski, Beate Krause and Petra Pötschke

Polymers 2019, 11(3), 462; https://doi.org/10.3390/polym11030462 - 11 Mar 2019

Cited by 60 | Viewed by 6944

Abstract

In order to evaluate the suitability of graphite composite materials for use as bipolar plates in fuel cells, polypropylene (PP) was melt compounded with expanded graphite as conductive filler to form composites with different filler contents of 10–80 wt %. Electrical resistivity, thermal [...] Read more.

In order to evaluate the suitability of graphite composite materials for use as bipolar plates in fuel cells, polypropylene (PP) was melt compounded with expanded graphite as conductive filler to form composites with different filler contents of 10–80 wt %. Electrical resistivity, thermal conductivity, and mechanical properties were measured and evaluated as a function of filler content. The electrical and thermal conductivities increased with filler content. Tensile and flexural strengths decreased with the incorporation of expanded graphite in PP. With higher graphite contents, however, both strength values remained more or less unchanged and were below the values of pure PP. Young’s-modulus and flexural modulus increased almost linearly with increasing filler content. The results of the thermogravimetric analysis confirmed the actual filler content in the composite materials. In order to evaluate the wettability and suitability for adhesive joining of graphite composites, contact angle measurements were conducted and surface tensions of composite surfaces were calculated. The results showed a significant increase in the surface tension of graphite composites with increasing filler content. Furthermore, graphite composites were adhesively joined and the strength of the joints was evaluated in the lap-shear test. Increasing filler content in the substrate material resulted in higher tensile lap-shear strength. Additionally, the influence of surface treatment (plasma and chemical) on surface tension and tensile lap-shear strength was investigated. The surface treatment led to a significant improvement of both properties. Full article

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

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13 pages, 3745 KB

Open AccessEditor’s ChoiceArticle

Multifunctional Silicone Rubber Nanocomposites by Controlling the Structure and Morphology of Graphene Material

by Ruben Sanchez-Hidalgo, Clara Blanco, Rosa Menendez, Raquel Verdejo and Miguel A. Lopez-Manchado

Polymers 2019, 11(3), 449; https://doi.org/10.3390/polym11030449 - 8 Mar 2019

Cited by 27 | Viewed by 5180

Abstract

Multifunctional elastomer nanocomposites have been applied in several high-tech fields. The design of materials with tailored properties capable of tuning their performance is a topical challenge. Here, we demonstrate that it is possible to modulate the mechanical and transport properties of silicone rubber [...] Read more.

Multifunctional elastomer nanocomposites have been applied in several high-tech fields. The design of materials with tailored properties capable of tuning their performance is a topical challenge. Here, we demonstrate that it is possible to modulate the mechanical and transport properties of silicone rubber nanocomposites by controlling the structure, chemical composition and morphology of the graphene material. Intrinsic graphene properties, such as remaining oxygen groups, specific surface area, and aspect ratio, among others, have a profound effect on the final properties of the nanocomposite. Thus, the thermal conductivity benefits from larger filler size and high aromatic restoration. Whereas mechanical properties and electrical conductivity require a proper balance between filler/polymer matrix interaction and a partial aromatic restoration. Full article

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

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15 pages, 5327 KB

Open AccessEditor’s ChoiceReview

Advances in Conjugated Polymer Lasers

by Hongyan Xia, Chang Hu, Tingkuo Chen, Dan Hu, Muru Zhang and Kang Xie

Polymers 2019, 11(3), 443; https://doi.org/10.3390/polym11030443 - 7 Mar 2019

Cited by 27 | Viewed by 6470

Abstract

This paper provides a review of advances in conjugated polymer lasers. High photoluminescence efficiencies and large stimulated emission cross-sections coupled with wavelength tunability and low-cost manufacturing processes make conjugated polymers ideal laser gain materials. In recent years, conjugated polymer lasers have become an [...] Read more.

This paper provides a review of advances in conjugated polymer lasers. High photoluminescence efficiencies and large stimulated emission cross-sections coupled with wavelength tunability and low-cost manufacturing processes make conjugated polymers ideal laser gain materials. In recent years, conjugated polymer lasers have become an attractive research direction in the field of organic lasers and numerous breakthroughs based on conjugated polymer lasers have been made in the last decade. This paper summarizes the recent progress of the subject of laser processes employing conjugated polymers, with a focus on the photoluminescence principle and excitation radiation mechanism of conjugated polymers. Furthermore, the effect of conjugated polymer structures on the laser threshold is discussed. The most common polymer laser materials are also introduced in detail. Apart from photo-pumped conjugated polymer lasers, a direction for the future development of electro-pumped conjugated polymer lasers is proposed. Full article

(This article belongs to the Special Issue Laser processing in polymer research)

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13 pages, 3072 KB

Open AccessEditor’s ChoiceArticle

Different Dependence of Tear Strength on Film Orientation of LLDPE Made with Different Co-Monomer

by Yi Ren, Ying Shi, Xuerong Yao, Yujing Tang and Li-Zhi Liu

Polymers 2019, 11(3), 434; https://doi.org/10.3390/polym11030434 - 6 Mar 2019

Cited by 20 | Viewed by 10644

Abstract

Crystal orientations, tear strength and shrinkage of Linear Low-Density PolyEthylene (LLDPE) films made with different processes (compressed, cast and blown) were investigated. The films were made with three different LLDPE resins, respectively, which have similar density and molecular weight but are made with [...] Read more.

Crystal orientations, tear strength and shrinkage of Linear Low-Density PolyEthylene (LLDPE) films made with different processes (compressed, cast and blown) were investigated. The films were made with three different LLDPE resins, respectively, which have similar density and molecular weight but are made with different comonomers (1-butene, 1-hexene and 1-octene), in order to investigate if tear strength in Machine Direction (MD) of the LLDPE films made with different comonomer has similar dependence on crystal orientation. Our study indicates that the films made of 1-hexene and 1-octene based LLDPE resins have significantly higher intrinsic tear strength and less decrease in MD tear strength for a given film orientation. That is, for a given orientation in MD, the MD tear drops dramatically for films made with butene-based resin but much less decrease for the films made with hexene and octene-based resins. The shrinkage property at high temperature shows a good correlation with crystal orientation and the fraction of the crystals melted at this temperature. Full article

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25 pages, 3196 KB

Open AccessEditor’s ChoiceArticle

Solid-State Polymerization of Poly(Ethylene Furanoate) Biobased Polyester, III: Extended Study on Effect of Catalyst Type on Molecular Weight Increase

by Yosra Chebbi, Nejib Kasmi, Mustapha Majdoub, George Z. Papageorgiou, Dimitris S. Achilias and Dimitrios N. Bikiaris

Polymers 2019, 11(3), 438; https://doi.org/10.3390/polym11030438 - 6 Mar 2019

Cited by 31 | Viewed by 7582

Abstract

In this study, the synthesis of poly(ethylene furanoate) (PEF), catalyzed by five different catalysts—antimony acetate (III) (Sb Ac), zirconium (IV) isopropoxide isopropanal (Zr Is Ip), antimony (III) oxide (Sb Ox), zirconium (IV) 2,4-pentanedionate (Zr Pe) and germanium (IV) oxide (Ge Ox)—via an industrially [...] Read more.

In this study, the synthesis of poly(ethylene furanoate) (PEF), catalyzed by five different catalysts—antimony acetate (III) (Sb Ac), zirconium (IV) isopropoxide isopropanal (Zr Is Ip), antimony (III) oxide (Sb Ox), zirconium (IV) 2,4-pentanedionate (Zr Pe) and germanium (IV) oxide (Ge Ox)—via an industrially common combination of melt polymerization and subsequent solid-state polymerization (SSP) is presented. In all reactions, proper amounts of 2,5-dimethylfuran-dicarboxylate (DMFD) and ethylene glycol (EG) in a molar ratio of DMFD/EG= 1/2 and 400 ppm of catalyst were used. Polyester samples were subjected to SSP procedure, under vacuum application, at different reaction times (1, 2, 3.5, and 5 h) and temperatures of 190, 200, and 205 °C. Carboxyl end-groups concentration (–COOH), intrinsic viscosity (IV), and thermal properties, via differential scanning calorimetry (DSC), were measured for all resultant polymers to study the effect of the used catalysts on the molecular weight increase of PEF during SSP process. As was expected, it was found that with increasing the SSP time and temperature, the intrinsic viscosity and the average molecular weight of PEF steadily increased. In contrast, the number of carboxyl end-groups content showed the opposite trend as intrinsic viscosity, that is, gradually decreasing during SSP time and temperature increase. It is worthy to note that thanks to the SSP process an obvious and continuous enhancement in the thermal properties of the prepared PEF samples was attained, in which their melting temperatures (T_m) and degree of crystallinity (X_c) increase progressively with increasing of reaction time and temperature. To predict the time evolution of polymers IV, as well as the hydroxyl and carboxyl content of PEF polyesters during the SSP, a simple kinetic model was developed. From both the theoretical simulation results and the experimental measurements, it was demonstrated that surely the Zr Is Ip catalyst shows the best catalytic characteristics compared to all other used catalysts herein, that is, leading in reducing—in a spectacular way—the activation energy of the involved both transesterification and esterification reactions during SSP. Full article

(This article belongs to the Special Issue Biodegradable and Biobased Polyesters)

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14 pages, 6716 KB

Open AccessEditor’s ChoiceArticle

Microfluidic Based Fabrication and Characterization of Highly Porous Polymeric Microspheres

by Benzion Amoyav and Ofra Benny

Polymers 2019, 11(3), 419; https://doi.org/10.3390/polym11030419 - 5 Mar 2019

Cited by 76 | Viewed by 12412

Abstract

Polymeric porous particles are currently used for various applications in biotechnology, tissue engineering and pharmaceutical science, e.g., floating drug delivery systems and inhaled formulations. Particle shape and size depend on variable parameters; among them, polymer type and concentration, stirring speed, pH and type [...] Read more.

Polymeric porous particles are currently used for various applications in biotechnology, tissue engineering and pharmaceutical science, e.g., floating drug delivery systems and inhaled formulations. Particle shape and size depend on variable parameters; among them, polymer type and concentration, stirring speed, pH and type of solvent. In this study, porous poly(lactic-co-glycolic) acid (PLGA) and poly(d,l-lactide) (PLA) microspheres (MPs), with varying sizes and morphologies, were synthesized and optimized using both batch formulation and a flow-focusing microfluidic device. A well-established method of preparation utilizing solvent evaporation and the double emulsion technique was performed. Similar to other batch encapsulation methods, this technique is time and reagent consuming and consists of several steps. Hence, although porous structures provide tremendous opportunity in the design of new applications for tissue engineering and as improved controlled-release carriers, the synthesis of these particles with predefined properties remains challenging. We demonstrated the fabrication of porous MPs using a simple microfluidic device, compared to batch synthesis fabrication; and the effect of solvent, polymer concentration and type, post-hydrolysis treatment, on porosity degree. Moreover, a kinetic release study of fluorescent molecule was conducted for non-porous in comparison to porous particles. An overview of future prospects and the potential of these porous beads in this scientific area are discussed. Full article

(This article belongs to the Special Issue Polymer-Based Systems for Controlled Release and Targeting of Drugs)

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11 pages, 2537 KB

Open AccessEditor’s ChoiceArticle

Two-Step Separation of Chitin from Shrimp Shells Using Citric Acid and Deep Eutectic Solvents with the Assistance of Microwave

by Dandan Zhao, Wen-Can Huang, Na Guo, Shuye Zhang, Changhu Xue and Xiangzhao Mao

Polymers 2019, 11(3), 409; https://doi.org/10.3390/polym11030409 - 3 Mar 2019

Cited by 119 | Viewed by 10930

Abstract

In this research, a two-step extraction approach was developed for chitin preparation from shrimp shells by utilizing citric acids and deep eutectic solvents (DESs), which effectively removed minerals and proteins. In the first step, minerals of shrimp shells were removed by citric acid, [...] Read more.

In this research, a two-step extraction approach was developed for chitin preparation from shrimp shells by utilizing citric acids and deep eutectic solvents (DESs), which effectively removed minerals and proteins. In the first step, minerals of shrimp shells were removed by citric acid, and the demineralization efficiency reached more than 98%. In the second step, the removal of protein was carried out using deep eutectic solvents with the assistance of microwave, and the deproteinization efficiency was more than 88%. The results of scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction analysis (XRD), and thermogravimetric analysis (TGA) showed that the quality of DES-prepared chitin was comparable to that of traditional acid/alkali-prepared chitin. These results were realized without utilizing hazardous chemicals, which are detrimental to the environment. This research indicates that a DES-based preparation approach has the potential for application in the recovery of biopolymers from natural resources. Full article

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10 pages, 1399 KB

Open AccessEditor’s ChoiceCommunication

Flame Retardancy Index for Thermoplastic Composites

by Henri Vahabi, Baljinder K. Kandola and Mohammad Reza Saeb

Polymers 2019, 11(3), 407; https://doi.org/10.3390/polym11030407 - 1 Mar 2019

Cited by 255 | Viewed by 8213

Abstract

Flame Retardancy Index, FRI, was defined as a simple yet universal dimensionless criterion born out of cone calorimetry data on thermoplastic composites and then put into practice for quantifying the flame retardancy performance of different polymer composites on a set of reliable [...] Read more.

Flame Retardancy Index, FRI, was defined as a simple yet universal dimensionless criterion born out of cone calorimetry data on thermoplastic composites and then put into practice for quantifying the flame retardancy performance of different polymer composites on a set of reliable data. Four types of thermoplastic composites filled with a wide variety of flame retardant additives were chosen for making comparative evaluations regardless of the type and loading level of the additive as well as the irradiance flux. The main features of cone calorimetry including peak of Heat Release Rate (pHRR), Total Heat Release (THR), and Time-To-Ignition (TTI) served to calculate a dimensionless measure that reflects an improvement in the flame retardancy of nominated thermoplastic composites with respect to the neat thermoplastic, quantitatively. A meaningful trend was observed among well-classified ranges of FRI quantities calculated for the studied dataset on thermoplastic composites by which “Poor”, “Good”, and “Excellent” flame retardancy performances were explicitly defined and exhibited on logarithmic scales of FRI axis. The proposed index remains adaptable to thermoplastic systems whatever the polymer or additive is. Full article

(This article belongs to the Special Issue Flame Retardancy of Polymeric Materials)

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21 pages, 3631 KB

Open AccessEditor’s ChoiceArticle

Kinetic Analysis of the Curing of a Partially Biobased Epoxy Resin Using Dynamic Differential Scanning Calorimetry

by Diego Lascano, Luis Quiles-Carrillo, Rafael Balart, Teodomiro Boronat and Nestor Montanes

Polymers 2019, 11(3), 391; https://doi.org/10.3390/polym11030391 - 27 Feb 2019

Cited by 45 | Viewed by 6765

Abstract

This research presents a cure kinetics study of an epoxy system consisting of a partially bio-sourced resin based on diglycidyl ether of bisphenol A (DGEBA) with amine hardener and a biobased reactive diluent from plants representing 31 wt %. The kinetic study has [...] Read more.

This research presents a cure kinetics study of an epoxy system consisting of a partially bio-sourced resin based on diglycidyl ether of bisphenol A (DGEBA) with amine hardener and a biobased reactive diluent from plants representing 31 wt %. The kinetic study has been carried out using differential scanning calorimetry (DSC) under non-isothermal conditions at different heating rates. Integral and derivative isoconversional methods or model free kinetics (MFK) have been applied to the experimental data in order to evaluate the apparent activation energy, E_a, followed by the application of the appropriate reaction model. The bio-sourced system showed activation energy that is independent of the extent of conversion, with E_a values between 57 and 62 kJ·mol⁻¹, corresponding to typical activation energies of conventional epoxy resins. The reaction model was studied by comparing the calculated y(α) and z(α) functions with standard master plot curves. A two-parameter autocatalytic kinetic model of Šesták–Berggren [SB(m,n)] was assessed as the most suitable reaction model to describe the curing kinetics of the epoxy resins studied since it showed an excellent agreement with the experimental data. Full article

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16 pages, 3916 KB

Open AccessEditor’s ChoiceArticle

Modeling of High-Efficiency Multi-Junction Polymer and Hybrid Solar Cells to Absorb Infrared Light

by Jobeda J. Khanam and Simon Y. Foo

Polymers 2019, 11(2), 383; https://doi.org/10.3390/polym11020383 - 22 Feb 2019

Cited by 30 | Viewed by 7548

Abstract

In this paper, we present our work on high-efficiency multi-junction polymer and hybrid solar cells. The transfer matrix method is used for optical modeling of an organic solar cell, which was inspired by the McGehee Group in Stanford University. The software simulation calculates [...] Read more.

In this paper, we present our work on high-efficiency multi-junction polymer and hybrid solar cells. The transfer matrix method is used for optical modeling of an organic solar cell, which was inspired by the McGehee Group in Stanford University. The software simulation calculates the optimal thicknesses of the active layers to provide the best short circuit current (J_SC) value. First, we show three designs of multi-junction polymer solar cells, which can absorb sunlight beyond the 1000 nm wavelengths. Then we present a novel high-efficiency hybrid (organic and inorganic) solar cell, which can absorb the sunlight with a wavelength beyond 2500 nm. Approximately 12% efficiency was obtained for the multi-junction polymer solar cell and 20% efficiency was obtained from every two-, three- and four-junction hybrid solar cell under 1 sun AM1.5 illumination. Full article

(This article belongs to the Special Issue Polymer-Based Solar Cells)

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28 pages, 3597 KB

Open AccessEditor’s ChoiceReview

Emergence of Flexible White Organic Light-Emitting Diodes

by Dongxiang Luo, Qizan Chen, Baiquan Liu and Ying Qiu

Polymers 2019, 11(2), 384; https://doi.org/10.3390/polym11020384 - 22 Feb 2019

Cited by 46 | Viewed by 9646

Abstract

Flexible white organic light-emitting diodes (FWOLEDs) have considerable potential to meet the rapidly growing requirements of display and lighting commercialization. To achieve high-performance FWOLEDs, (i) the selection of effective flexible substrates, (ii) the use of transparent conducting electrodes, (iii) the introduction of efficient [...] Read more.

Flexible white organic light-emitting diodes (FWOLEDs) have considerable potential to meet the rapidly growing requirements of display and lighting commercialization. To achieve high-performance FWOLEDs, (i) the selection of effective flexible substrates, (ii) the use of transparent conducting electrodes, (iii) the introduction of efficient device architectures, and iv) the exploitation of advanced outcoupling techniques are necessary. In this review, recent state-of-the-art strategies to develop FWOLEDs have been summarized. Firstly, the fundamental concepts of FWOLEDs have been described. Then, the primary approaches to realize FWOLEDs have been introduced. Particularly, the effects of flexible substrates, conducting electrodes, device architectures, and outcoupling techniques in FWOLEDs have been comprehensively highlighted. Finally, issues and ways to further enhance the performance of FWOLEDs have been briefly clarified. Full article

(This article belongs to the Special Issue Polymer-Based Flexible Printed Electronics and Sensors)

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13 pages, 2124 KB

Open AccessEditor’s ChoiceArticle

Enhancing X-ray Attenuation of 3D Printed Gelatin Methacrylate (GelMA) Hydrogels Utilizing Gold Nanoparticles for Bone Tissue Engineering Applications

by Nehar Celikkin, Simone Mastrogiacomo, X. Frank Walboomers and Wojciech Swieszkowski

Polymers 2019, 11(2), 367; https://doi.org/10.3390/polym11020367 - 20 Feb 2019

Cited by 53 | Viewed by 7203

Abstract

Bone tissue engineering is a rapidly growing field which is currently progressing toward clinical applications. Effective imaging methods for longitudinal studies are critical to evaluating the new bone formation and the fate of the scaffolds. Computed tomography (CT) is a prevailing technique employed [...] Read more.

Bone tissue engineering is a rapidly growing field which is currently progressing toward clinical applications. Effective imaging methods for longitudinal studies are critical to evaluating the new bone formation and the fate of the scaffolds. Computed tomography (CT) is a prevailing technique employed to investigate hard tissue scaffolds; however, the CT signal becomes weak in mainly-water containing materials, which hinders the use of CT for hydrogels-based materials. Nevertheless, hydrogels such as gelatin methacrylate (GelMA) are widely used for tissue regeneration due to their optimal biological properties and their ability to induce extracellular matrix formation. To date, gold nanoparticles (AuNPs) have been suggested as promising contrast agents, due to their high X-ray attenuation, biocompatibility, and low toxicity. In this study, the effects of different sizes and concentrations of AuNPs on the mechanical properties and the cytocompatibility of the bulk GelMA-AuNPs scaffolds were evaluated. Furthermore, the enhancement of CT contrast with the cytocompatible size and concentration of AuNPs were investigated. 3D printed GelMA and GelMA-AuNPs scaffolds were obtained and assessed for the osteogenic differentiation of mesenchymal stem cells (MSC). Lastly, 3D printed GelMA and GelMA-AuNPs scaffolds were scanned in a bone defect utilizing µCT as the proof of concept that the GelMA-AuNPs are good candidates for bone tissue engineering with enhanced visibility for µCT imaging. Full article

(This article belongs to the Special Issue Functional Polymers for Biomedicine)

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13 pages, 2300 KB

Open AccessEditor’s ChoiceArticle

Spray-Formed Layered Polymer Microneedles for Controlled Biphasic Drug Delivery

by Seok Chan Park, Min Jung Kim, Seung-Ki Baek, Jung-Hwan Park and Seong-O Choi

Polymers 2019, 11(2), 369; https://doi.org/10.3390/polym11020369 - 20 Feb 2019

Cited by 59 | Viewed by 9730

Abstract

In this study we present polymeric microneedles composed of multiple layers to control drug release kinetics. Layered microneedles were fabricated by spraying poly(lactic-co-glycolic acid) (PLGA) and polyvinylpyrrolidone (PVP) in sequence, and were characterized by mechanical testing and ex vivo skin insertion [...] Read more.

In this study we present polymeric microneedles composed of multiple layers to control drug release kinetics. Layered microneedles were fabricated by spraying poly(lactic-co-glycolic acid) (PLGA) and polyvinylpyrrolidone (PVP) in sequence, and were characterized by mechanical testing and ex vivo skin insertion tests. The compression test demonstrated that no noticeable layer separation occurred, indicating good adhesion between PLGA and PVP layers. Histological examination confirmed that the microneedles were successfully inserted into the skin and indicated biphasic release of dyes incorporated within microneedle matrices. Structural changes of a model protein drug, bovine serum albumin (BSA), in PLGA and PVP matrices were examined by circular dichroism (CD) and fluorescence spectroscopy. The results showed that the tertiary structure of BSA was well maintained in both PLGA and PVP layers while the secondary structures were slightly changed during microneedle fabrication. In vitro release studies showed that over 60% of BSA in the PLGA layer was released within 1 h, followed by continuous slow release over the course of the experiments (7 days), while BSA in the PVP layer was completely released within 0.5 h. The initial burst of BSA from PLGA was further controlled by depositing a blank PLGA layer prior to forming the PLGA layer containing BSA. The blank PLGA layer acted as a diffusion barrier, resulting in a reduced initial burst. The formation of the PLGA diffusion barrier was visualized using confocal microscopy. Our results suggest that the spray-formed multilayer microneedles could be an attractive transdermal drug delivery system that is capable of modulating a drug release profile. Full article

(This article belongs to the Special Issue Materials and Methods for New Technologies in Polymer Processing)

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13 pages, 2716 KB

Open AccessEditor’s ChoiceArticle

Formation of Polyaniline and Polypyrrole Nanocomposites with Embedded Glucose Oxidase and Gold Nanoparticles

by Natalija German, Almira Ramanaviciene and Arunas Ramanavicius

Polymers 2019, 11(2), 377; https://doi.org/10.3390/polym11020377 - 20 Feb 2019

Cited by 62 | Viewed by 6164

Abstract

Several types of polyaniline (PANI) and polypyrrole (Ppy) nanocomposites with embedded glucose oxidase (GOx) and gold nanoparticles (AuNPs) were formed by enzymatic polymerization of corresponding monomers (aniline and pyrrole) in the presence of 6 and 13 nm diameter colloidal gold nanoparticles (AuNPs_(6nm) [...] Read more.

Several types of polyaniline (PANI) and polypyrrole (Ppy) nanocomposites with embedded glucose oxidase (GOx) and gold nanoparticles (AuNPs) were formed by enzymatic polymerization of corresponding monomers (aniline and pyrrole) in the presence of 6 and 13 nm diameter colloidal gold nanoparticles (AuNPs_(6nm) or AuNPs_(13nm), respectively) or chloroaurate ions (AuCl₄⁻). Glucose oxidase in the presence of glucose generated H₂O₂, which acted as initiator of polymerization reaction. The influence of polymerization bulk composition and pH on the formation of PANI- and Ppy-based nanocomposites was investigated spectrophotometrically. The highest formation rate of PANI- and Ppy-based nanocomposites with embedded glucose oxidase and gold nanoparticles (PANI/AuNPs-GOx and Ppy/AuNPs-GOx, respectively) was observed in the solution of sodium acetate buffer, pH 6.0. It was determined that the presence of AuNPs or AuCl₄⁻ ions facilitate enzymatic polymerization of aniline and pyrrole. Full article

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15 pages, 8571 KB

Open AccessEditor’s ChoiceArticle

Comparative Study on Kinetics of Ethylene and Propylene Polymerizations with Supported Ziegler–Natta Catalyst: Catalyst Fragmentation Promoted by Polymer Crystalline Lamellae

by Zhen Zhang, Baiyu Jiang, Feng He, Zhisheng Fu, Junting Xu and Zhiqiang Fan

Polymers 2019, 11(2), 358; https://doi.org/10.3390/polym11020358 - 19 Feb 2019

Cited by 23 | Viewed by 7892

Abstract

The kinetic behaviors of ethylene and propylene polymerizations with the same MgCl₂-supported Ziegler–Natta (Z–N) catalyst containing an internal electron donor were compared. Changes of polymerization activity and active center concentration ([C*]) with time in the first 10 min were determined. Activity [...] Read more.

The kinetic behaviors of ethylene and propylene polymerizations with the same MgCl₂-supported Ziegler–Natta (Z–N) catalyst containing an internal electron donor were compared. Changes of polymerization activity and active center concentration ([C*]) with time in the first 10 min were determined. Activity of ethylene polymerization was only 25% of that of propylene, and the polymerization rate (R_p) quickly decayed with time (t_p) in the former system, in contrast to stable R_p in the latter. The ethylene system showed a very low [C*]/[Ti] ratio (<0.6%), in contrast to a much higher [C*]/[Ti] ratio (1.5%–4.9%) in propylene polymerization. The two systems showed noticeably different morphologies of the nascent polymer/catalyst particles, with the PP/catalyst particles being more compact and homogeneous than the PE/catalyst particles. The different kinetic behaviors of the two systems were explained by faster and more sufficient catalyst fragmentation in propylene polymerization than the ethylene system. The smaller lamellar thickness (<20 nm) in nascent polypropylene compared with the size of nanopores (15–25 nm) in the catalyst was considered the key factor for efficient catalyst fragmentation in propylene polymerization, as the PP lamellae may grow inside the nanopores and break up the catalyst particles. Full article

(This article belongs to the Special Issue Catalytic Polymerization)

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16 pages, 6338 KB

Open AccessEditor’s ChoiceArticle

Characterization of Polyurethane Foam Waste for Reuse in Eco-Efficient Building Materials

by Raúl Gómez-Rojo, Lourdes Alameda, Ángel Rodríguez, Verónica Calderón and Sara Gutiérrez-González

Polymers 2019, 11(2), 359; https://doi.org/10.3390/polym11020359 - 19 Feb 2019

Cited by 66 | Viewed by 11035

Abstract

In the European Union, the demand for polyurethane is continually growing. In 2017, the estimated value of polyurethane production was 700,400 Tn, of which 27.3% is taken to landfill, which causes an environmental problem. In this paper, the behaviour of various polyurethane foams [...] Read more.

In the European Union, the demand for polyurethane is continually growing. In 2017, the estimated value of polyurethane production was 700,400 Tn, of which 27.3% is taken to landfill, which causes an environmental problem. In this paper, the behaviour of various polyurethane foams from the waste of different types of industries will be analyzed with the aim of assessing their potential use in construction materials. To achieve this, the wastes were chemically tested by means of CHNS, TGA, and leaching tests. They were tested microstructurally by means of SEM. The processing parameters of the waste was calculated after identifying its granulometry and its physical properties i.e., density and water absorption capacity. In addition, the possibility of incorporating these wastes in plaster matrices was studied by determining their rendering in an operational context, finding out their mechanical resistance to flexion and compression at seven days, their reaction to fire as well as their weight per unit of area, and their thermal behaviour. The results show that in all cases, the waste is inert and does not undergo leaching. The generation process of the waste determines the foam’s microstructure in addition to its physical-chemical properties, which directly affect building materials in which they are included, thus offering different ways in which they can be applied. Full article

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12 pages, 4094 KB

Open AccessEditor’s ChoiceArticle

Study on Soy-Based Adhesives Enhanced by Phenol Formaldehyde Cross-Linker

by Zhigang Wu, Xuedong Xi, Hong Lei, Jiankun Liang, Jingjing Liao and Guanben Du

Polymers 2019, 11(2), 365; https://doi.org/10.3390/polym11020365 - 19 Feb 2019

Cited by 46 | Viewed by 4060

Abstract

To find the effects of cross-linker phenol-formaldehyde (PF) resin on the performance of soy-based adhesives, the reaction between model compounds hydroxymethyl phenol (HPF) and glutamic acid were studied in this paper. HPF prepared in laboratory conditions showed higher content of hydroxymethyl groups than [...] Read more.

To find the effects of cross-linker phenol-formaldehyde (PF) resin on the performance of soy-based adhesives, the reaction between model compounds hydroxymethyl phenol (HPF) and glutamic acid were studied in this paper. HPF prepared in laboratory conditions showed higher content of hydroxymethyl groups than normal PF resin, which was proved by the results of Electrospray Ionization Mass Spectrometry (ESI-MS) and ¹³C Nuclear Magnetic Resonance (¹³C-NMR). The results of ESI-MS, Fourier transform infrared spectroscopy (FT-IR), and ¹³C-NMR based on resultant products obtained from model compounds showed better water resistance of the soy protein-based adhesive modified by PF-based resin, which indicated the reaction between PF resin and soy protein. However, it seemed that the soy-based adhesive cross-linked by HPF with the maximum content of hydroxymethyl groups did not show the best water resistance. Full article

(This article belongs to the Special Issue Renewable Phenolics for Innovative Composites)

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14 pages, 4151 KB

Open AccessEditor’s ChoiceArticle

Antimony Removal from Water by a Chitosan-Iron(III)[ChiFer(III)] Biocomposite

by Byron Lapo, Hary Demey, Tanya Carchi and Ana María Sastre

Polymers 2019, 11(2), 351; https://doi.org/10.3390/polym11020351 - 18 Feb 2019

Cited by 28 | Viewed by 5704

Abstract

The presence of antimony(III) in water represents a worldwide concern, mainly due to its high toxicity and carcinogenicity potential. It can be separated from water by the use of sustainable biopolymers such as chitosan or its derivatives. The present study applied chitosan modified [...] Read more.

The presence of antimony(III) in water represents a worldwide concern, mainly due to its high toxicity and carcinogenicity potential. It can be separated from water by the use of sustainable biopolymers such as chitosan or its derivatives. The present study applied chitosan modified with iron(III) beads to Sb(III) removal from aqueous solutions. The resulting material performed with a high adsorption capacity of 98.68 mg/g. Material characterization consisted of Raman spectroscopy (RS), X-ray diffraction (XRD), scanning electron microscope observations (SEM-EDX), Fourier transform infrared spectroscopy (FTIR) and point of zero charge (pH_pzc). The adsorption study included pH study, effect of initial concentration, kinetics, ion effect, and reusability assessment. The RS, XRD, and FTIR results indicated that the main functional groups in the composite were related to hydroxyl and amino groups, and iron oxyhydroxide species of α-FeO(OH). The pH_pzc was found to be 7.41. The best adsorption efficiency was set at pH 6. The equilibrium isotherms were better fitted with a non-linear Langmuir model, and the kinetics data were fitted with a pseudo-second order rate equation. The incorporation of iron into the chitosan matrix improved the Sb(III) uptake by 47.9%, compared with neat chitosan (CS). The material did not exhibit an impact in its performance in the presence of other ions, and it could be reused for up to three adsorption–desorption cycles. Full article

(This article belongs to the Special Issue Polysaccharides)

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13 pages, 2739 KB

Open AccessEditor’s ChoiceArticle

3D-Printable PP/SEBS Thermoplastic Elastomeric Blends: Preparation and Properties

by Shib Shankar Banerjee, Stephen Burbine, Nischay Kodihalli Shivaprakash and Joey Mead

Polymers 2019, 11(2), 347; https://doi.org/10.3390/polym11020347 - 17 Feb 2019

Cited by 111 | Viewed by 12772

Abstract

Currently, material extrusion 3D printing (ME3DP) based on fused deposition modeling (FDM) is considered a highly adaptable and efficient additive manufacturing technique to develop components with complex geometries using computer-aided design. While the 3D printing process for a number of thermoplastic materials using [...] Read more.

Currently, material extrusion 3D printing (ME3DP) based on fused deposition modeling (FDM) is considered a highly adaptable and efficient additive manufacturing technique to develop components with complex geometries using computer-aided design. While the 3D printing process for a number of thermoplastic materials using FDM technology has been well demonstrated, there still exists a significant challenge to develop new polymeric materials compatible with ME3DP. The present work reports the development of ME3DP compatible thermoplastic elastomeric (TPE) materials from polypropylene (PP) and styrene-(ethylene-butylene)-styrene (SEBS) block copolymers using a straightforward blending approach, which enables the creation of tailorable materials. Properties of the 3D printed TPEs were compared with traditional injection molded samples. The tensile strength and Young’s modulus of the 3D printed sample were lower than the injection molded samples. However, no significant differences could be found in the melt rheological properties at higher frequency ranges or in the dynamic mechanical behavior. The phase morphologies of the 3D printed and injection molded TPEs were correlated with their respective properties. Reinforcing carbon black was used to increase the mechanical performance of the 3D printed TPE, and the balancing of thermoplastic elastomeric and mechanical properties were achieved at a lower carbon black loading. The preferential location of carbon black in the blend phases was theoretically predicted from wetting parameters. This study was made in order to get an insight to the relationship between morphology and properties of the ME3DP compatible PP/SEBS blends. Full article

(This article belongs to the Special Issue Polymer Matrix Composites for Advanced Applications)

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36 pages, 4158 KB

Open AccessEditor’s ChoiceReview

Conducting Polymers, Hydrogels and Their Composites: Preparation, Properties and Bioapplications

by Monika Tomczykowa and Marta Eliza Plonska-Brzezinska

Polymers 2019, 11(2), 350; https://doi.org/10.3390/polym11020350 - 17 Feb 2019

Cited by 163 | Viewed by 23025

Abstract

This review is focused on current state-of-the-art research on electroactive-based materials and their synthesis, as well as their physicochemical and biological properties. Special attention is paid to pristine intrinsically conducting polymers (ICPs) and their composites with other organic and inorganic components, well-defined micro- [...] Read more.

This review is focused on current state-of-the-art research on electroactive-based materials and their synthesis, as well as their physicochemical and biological properties. Special attention is paid to pristine intrinsically conducting polymers (ICPs) and their composites with other organic and inorganic components, well-defined micro- and nanostructures, and enhanced surface areas compared with those of conventionally prepared ICPs. Hydrogels, due to their defined porous structures and being filled with aqueous solution, offer the ability to increase the amount of immobilized chemical, biological or biochemical molecules. When other components are incorporated into ICPs, the materials form composites; in this particular case, they form conductive composites. The design and synthesis of conductive composites result in the inheritance of the advantages of each component and offer new features because of the synergistic effects between the components. The resulting structures of ICPs, conducting polymer hydrogels and their composites, as well as the unusual physicochemical properties, biocompatibility and multi-functionality of these materials, facilitate their bioapplications. The synergistic effects between constituents have made these materials particularly attractive as sensing elements for biological agents, and they also enable the immobilization of bioreceptors such as enzymes, antigen-antibodies, and nucleic acids onto their surfaces for the detection of an array of biological agents. Currently, these materials have unlimited applicability in biomedicine. In this review, we have limited discussion to three areas in which it seems that the use of ICPs and materials, including their different forms, are particularly interesting, namely, biosensors, delivery of drugs and tissue engineering. Full article

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18 pages, 2266 KB

Open AccessEditor’s ChoiceArticle

Sorption and Desorption Studies of Pb(II) and Ni(II) from Aqueous Solutions by a New Composite Based on Alginate and Magadiite Materials

by Keltoum Attar, Hary Demey, Djamila Bouazza and Ana Maria Sastre

Polymers 2019, 11(2), 340; https://doi.org/10.3390/polym11020340 - 15 Feb 2019

Cited by 57 | Viewed by 5460

Abstract

A new composite material based on alginate and magadiite/Di-(2-ethylhexyl) phosphoric acid (CAM-D2EHPA) was successfully prepared by previous impregnation of layered magadiite with D2EHPA extractant, and then immobilized into the alginate matrix. Air dried beads of CAM-D2EHPA were characterized by FTIR and SEM–EDX techniques. [...] Read more.

A new composite material based on alginate and magadiite/Di-(2-ethylhexyl) phosphoric acid (CAM-D2EHPA) was successfully prepared by previous impregnation of layered magadiite with D2EHPA extractant, and then immobilized into the alginate matrix. Air dried beads of CAM-D2EHPA were characterized by FTIR and SEM–EDX techniques. The sorbent was used for the separation of lead and nickel from nitrate solutions; the main parameters of sorption such as contact time, pH of the solution, and initial metal concentration were studied. The beads recovered 94% of Pb(II) and 65% of Ni(II) at pH 4 from dilute solutions containing 10 mg L⁻¹ of metal (sorbent dosage, S.D. 1 g L⁻¹). The equilibrium data gave a better fit using the Langmuir model, and kinetic profiles were fitted using a pseudo-second order rate equation. The maximum sorption capacities obtained (at pH 4) were 197 mg g⁻¹ and 44 mg g⁻¹ for lead and nickel, respectively. The regeneration of the sorbent was efficiently carried out with a dilute solution of HNO₃ (0.5 M). The composite material was reused in 10 sorption–elution cycles with no significant differences on sorption uptake. A study with synthetic effluents containing an equimolar concentration of both metals indicated a better selectivity towards lead ions. Full article

(This article belongs to the Special Issue Polysaccharides)

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11 pages, 7414 KB

Open AccessEditor’s ChoiceArticle

Controlled Self-Assembly of Conjugated Polymers via a Solvent Vapor Pre-Treatment for Use in Organic Field-Effect Transistors

by Gyounglyul Jo, Jaehan Jung and Mincheol Chang

Polymers 2019, 11(2), 332; https://doi.org/10.3390/polym11020332 - 14 Feb 2019

Cited by 41 | Viewed by 6432

Abstract

A facile solution-processing strategy toward well-ordered one-dimensional nanostructures of conjugated polymers via a non-solvent vapor treatment was demonstrated, which resulted in enhancements to the charge transport characteristics of the polymers. The amount of crystalline poly(3-hexylthiophene) (P3HT) nanofibers was precisely controlled by simply varying [...] Read more.

A facile solution-processing strategy toward well-ordered one-dimensional nanostructures of conjugated polymers via a non-solvent vapor treatment was demonstrated, which resulted in enhancements to the charge transport characteristics of the polymers. The amount of crystalline poly(3-hexylthiophene) (P3HT) nanofibers was precisely controlled by simply varying the exposure time of solutions of P3HT solutions to non-solvent vapor. The effects of non-solvent vapor exposure on the molecular ordering and morphologies of the resultant P3HT films were systematically investigated using ultraviolet-visible (UV-vis) spectroscopy, polarized optical microscopy (POM), grazing incidence X-ray diffraction (GIXRD), and atomic force microscopy (AFM). The non-solvent vapor facilitates the π–π stacking in P3HT to minimize unfavorable interactions between the poor solvent molecules and P3HT chains. P3HT films deposited from the non-solvent vapor-treated P3HT solutions exhibited an approximately 5.6-fold improvement in charge carrier mobility as compared to that of pristine P3HT films (7.8 × 10⁻² cm² V⁻¹ s⁻¹ vs. 1.4 × 10⁻² cm² V⁻¹ s⁻¹). The robust and facile strategy presented herein would be applicable in various opto-electronics applications requiring precise control of the molecular assembly, such as organic photovoltaic cells, field-effect transistors, light-emitting diodes, and sensors. Full article

(This article belongs to the Special Issue Conductive Polymers III)

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19 pages, 7871 KB

Open AccessEditor’s ChoiceArticle

Composites of Rigid Polyurethane Foams Reinforced with POSS

by Sylwia Członka, Anna Strąkowska, Krzysztof Strzelec, Agnieszka Adamus-Włodarczyk, Agnė Kairytė and Saulius Vaitkus

Polymers 2019, 11(2), 336; https://doi.org/10.3390/polym11020336 - 14 Feb 2019

Cited by 44 | Viewed by 5705

Abstract

Rigid polyurethane foams (RPUFs) were successfully modified with different weight ratios (0.5 wt%, 1.5 wt% and 5 wt%) of APIB-POSS and AEAPIB-POSS. The resulting foams were evaluated by their processing parameters, morphology (Scanning Electron Microscopy analysis, SEM), mechanical properties (compressive test, three-point bending [...] Read more.

Rigid polyurethane foams (RPUFs) were successfully modified with different weight ratios (0.5 wt%, 1.5 wt% and 5 wt%) of APIB-POSS and AEAPIB-POSS. The resulting foams were evaluated by their processing parameters, morphology (Scanning Electron Microscopy analysis, SEM), mechanical properties (compressive test, three-point bending test and impact strength), viscoelastic behavior (Dynamic Mechanical Analysis, DMA), thermal properties (Thermogravimetric Analysis, TGA, and thermal conductivity) and application properties (contact angle, water absorption and dimensional analysis). The results showed that the morphology of modified foams is significantly affected by the type of the filler and filler content, which resulted in inhomogeneous, irregular, large cell shapes and further affected the physical and mechanical properties of resulting materials. RPUFs modified with APIB-POSS represent better mechanical and thermal properties compared to the RPUFs modified with AEAPIB-POSS. The results showed that the best results were obtained for RPUFs modified with 0.5 wt% of APIB-POSS. For example, in comparison with unfilled foam, compositions modified with 0.5 wt% of APIB-POSS provide greater compression strength, better flexural strength and lower water absorption. Full article

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

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10 pages, 2001 KB

Open AccessEditor’s ChoiceArticle

Effect of Ultrasonic Vibration on Interlayer Adhesion in Fused Filament Fabrication 3D Printed ABS

by Alireza Tofangchi, Pu Han, Julio Izquierdo, Adithya Iyengar and Keng Hsu

Polymers 2019, 11(2), 315; https://doi.org/10.3390/polym11020315 - 13 Feb 2019

Cited by 103 | Viewed by 11319

Abstract

One of the fundamental issues in the Fused Filament Fabrication (FFF) additive manufacturing process lies in the mechanical property anisotropy where the strength of the FFF-3D printed part in the build-direction can be significantly lower than that in other directions. The physical phenomenon [...] Read more.

One of the fundamental issues in the Fused Filament Fabrication (FFF) additive manufacturing process lies in the mechanical property anisotropy where the strength of the FFF-3D printed part in the build-direction can be significantly lower than that in other directions. The physical phenomenon that governs this issue is the coupled effect of macroscopic thermal mechanical issues associated with the thermal history of the interface, and the microscopic effect of the polymer microstructure and mass transfer across interfaces. In this study it was found that the use of 34.4 kHz ultrasonic vibrations during FFF-3D printing results in an increase of up to 10% in the interlayer adhesion in Acrylonitrile Butadiene Styrene (ABS), comparing the printing in identical thermal conditions to that in conventional FFF printing. This increase in the interlayer adhesion strength is attributed to the increase in polymer reptation due to ultrasonic vibration-induced relaxation of the polymer chains from secondary interactions in the interface regions. Full article

(This article belongs to the Special Issue Materials and Methods for New Technologies in Polymer Processing)

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14 pages, 1163 KB

Open AccessEditor’s ChoiceArticle

Study Rheological Behavior of Polymer Solution in Different-Medium-Injection-Tools

by Bin Huang, Xiaohui Li, Cheng Fu, Ying Wang and Haoran Cheng

Polymers 2019, 11(2), 319; https://doi.org/10.3390/polym11020319 - 13 Feb 2019

Cited by 29 | Viewed by 4997

Abstract

Previous studies showed the difficulty during polymer flooding and the low producing degree for the low permeability layer. To solve the problem, Daqing, the first oil company, puts forward the polymer-separate-layer-injection-technology which separates mass and pressure in a single pipe. This technology mainly [...] Read more.

Previous studies showed the difficulty during polymer flooding and the low producing degree for the low permeability layer. To solve the problem, Daqing, the first oil company, puts forward the polymer-separate-layer-injection-technology which separates mass and pressure in a single pipe. This technology mainly increases the control range of injection pressure of fluid by using the annular de-pressure tool, and reasonably distributes the molecular weight of the polymer injected into the thin and poor layers through the shearing of the different-medium-injection-tools. This occurs, in order to take advantage of the shearing thinning property of polymer solution and avoid the energy loss caused by the turbulent flow of polymer solution due to excessive injection rate in different injection tools. Combining rheological property of polymer and local perturbation theory, a rheological model of polymer solution in different-medium-injection-tools is derived and the maximum injection velocity is determined. The ranges of polymer viscosity in different injection tools are mainly determined by the structures of the different injection tools. However, the value of polymer viscosity is mainly determined by the concentration of polymer solution. So, the relation between the molecular weight of polymer and the permeability of layers should be firstly determined, and then the structural parameter combination of the different-medium-injection-tool should be optimized. The results of the study are important for regulating polymer injection parameters in the oilfield which enhances the oil recovery with reduced the cost. Full article

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17 pages, 3658 KB

Open AccessEditor’s ChoiceArticle

Anti-Fouling and Anti-Bacterial Modification of Poly(vinylidene fluoride) Membrane by Blending with the Capsaicin-Based Copolymer

by Xiang Shen, Peng Liu, Shubiao Xia, Jianjun Liu, Rui Wang, Hua Zhao, Qiuju Liu, Jiao Xu and Fan Wang

Polymers 2019, 11(2), 323; https://doi.org/10.3390/polym11020323 - 13 Feb 2019

Cited by 30 | Viewed by 4712

Abstract

Membrane fouling induced by the adsorption of organic matter, and adhesion and propagation of bacteria onto the surfaces, is the major obstacle for the wide application of membrane technology. In this work, the capsaicin-based copolymer (PMMA-PACMO-Capsaicin) was synthesized via radical copolymerization using methyl [...] Read more.

Membrane fouling induced by the adsorption of organic matter, and adhesion and propagation of bacteria onto the surfaces, is the major obstacle for the wide application of membrane technology. In this work, the capsaicin-based copolymer (PMMA-PACMO-Capsaicin) was synthesized via radical copolymerization using methyl methacrylate (MMA), N-acrylomorpholine (ACMO) and 8-methyl-N-vanillyl-6-nonenamide (capsaicin) as monomers. Subsequently, the capsaicin-based copolymer was readily blended with PVDF to fabricate PVDF/PMMA-PACMO-Capsaicin flat sheet membrane via immersed phase inversion method. The effects of copolymer concentration on the structure and performance of resultant membranes were evaluated systematically. With increase of PMMA-PACMO-Capsaicin copolymer concentration in the casting solution, the sponge-like layer at the membrane cross-section transfers to macroviod, and the pore size and porosity of membranes increase remarkably. The adsorbed bovine serum albumin protein (BSA) amounts to PVDF/PMMA-PACMO-Capsaicin membranes decrease significantly because of the enhanced surface hydrophilicty. During the cycle filtration of pure water and BSA solution, the prepared PVDF/PMMA-PACMO-Capsaicin membranes have a higher flux recovery ratio (FFR) and lower irreversible membrane fouling ratio (R_ir), as compared with pristine PVDF membrane. PVDF/PMMA-PACMO-Capsaicin membrane is found to suppress the growth and propagation of Staphylococcus aureus bacteria, achieving an anti-bacterial efficiency of 88.5%. These results confirm that the anti-fouling and anti-bacterial properties of PVDF membrane are enhanced obviously by blending with the PMMA-PACMO-Capsaicin copolymer. Full article

(This article belongs to the Special Issue Advanced Engineering Plastics)

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16 pages, 5060 KB

Open AccessEditor’s ChoiceArticle

Lightweight High-Performance Polymer Composite for Automotive Applications

by Valentina Volpe, Sofia Lanzillo, Giovanni Affinita, Beniamino Villacci, Innocenzo Macchiarolo and Roberto Pantani

Polymers 2019, 11(2), 326; https://doi.org/10.3390/polym11020326 - 13 Feb 2019

Cited by 84 | Viewed by 8634

Abstract

The automotive industry needs to produce plastic products with high dimensional accuracy and reduced weight, and this need drives the research toward less conventional industrial processes. The material that was adopted in this work is a glass-fiber-reinforced polyamide 66 (PA66), a material of [...] Read more.

The automotive industry needs to produce plastic products with high dimensional accuracy and reduced weight, and this need drives the research toward less conventional industrial processes. The material that was adopted in this work is a glass-fiber-reinforced polyamide 66 (PA66), a material of great interest for the automotive industry because of its excellent properties, although being limited in application because of its relatively high cost. In order to reduce the cost of the produced parts, still preserving the main properties of the material, the possibility of applying microcellular injection molding process was explored in this work. In particular, the influence of the main processing parameters on morphology and performance of PA66 + 30% glass-fiber foamed parts was investigated. An analysis of variance (ANOVA) was employed to identify the significant factors that influence the morphology of the molded parts. According to ANOVA results, in order to obtain homogeneous foamed parts with good mechanical properties, an injection temperature of 300 °C, a high gas injection pressure, and a large thickness of the parts should be adopted. Full article

(This article belongs to the Special Issue Foaming and Injection Moulding in Polymer Processing)

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14 pages, 4623 KB

Open AccessEditor’s ChoiceArticle

Chitosan-Modified PLGA Nanoparticles for Control-Released Drug Delivery

by Boting Lu, Xikun Lv and Yuan Le

Polymers 2019, 11(2), 304; https://doi.org/10.3390/polym11020304 - 12 Feb 2019

Cited by 278 | Viewed by 19675

Abstract

Poly (lactic-co-glycolic acid) nanoparticles (PLGA NPs) are well recognized as an ideal drug delivery carrier for their biocompatibility and biodegradability. In order to overcome the disadvantage of drug burst release, chitosan (CS) was used to modify the PLGA nanoparticles. In this [...] Read more.

Poly (lactic-co-glycolic acid) nanoparticles (PLGA NPs) are well recognized as an ideal drug delivery carrier for their biocompatibility and biodegradability. In order to overcome the disadvantage of drug burst release, chitosan (CS) was used to modify the PLGA nanoparticles. In this work, CS-PLGA nanoparticles with different ratio of CS to PLGA were prepared using high-gravity rotating packed bed (RPB). With the increase of amount of CS, the particle size increased from 132.8 ± 1.5 nm to 172.7 ± 3.2 nm, zeta potential increased from −20.8 ± 1.1 mV to 25.6 ± 0.6 mV, and drug encapsulation efficiency increased from 65.8% to 87.1%. The initial burst release of PLGA NPs reduced after being modified by CS, and the cumulative release was 66.9%, 41.9%, 23.8%, and 14.3%, after 2 h, respectively. The drug release of CS-modified PLGA NPs was faster at pH5.5 than that at pH 7.4. The cellular uptake of CS-modified PLGA NPs increased compared with PLGA NPs, while cell viability was reduced. In conclusion, these results indicated that CS-modified, PTX-loaded PLGA NPs have the advantages of sustained drug release and enhanced drug toxicity, suggesting that CS-modified NPs can be used as carriers of anticancer drugs. Full article

(This article belongs to the Special Issue Modifications and Applications of Chitin/Chitosan for Biomedical, Pharmaceutical, Cosmetic, Biotechnology and Related Applications)

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18 pages, 3753 KB

Open AccessEditor’s ChoiceArticle

Hydrolyzable Additive-Based Silicone Elastomers: A New Approach for Antifouling Coatings

by Laure Gevaux, Marlène Lejars, André Margaillan, Jean-François Briand, Robert Bunet and Christine Bressy

Polymers 2019, 11(2), 305; https://doi.org/10.3390/polym11020305 - 12 Feb 2019

Cited by 38 | Viewed by 7241

Abstract

Fouling Release Coatings are marine antifouling coatings based on silicone elastomers. Contrary to commonly used biocide-based antifouling coatings, they do not release biocides into the marine environment, however, they suffer from poor antifouling efficacy during idle periods. To improve their antifouling performances in [...] Read more.

Fouling Release Coatings are marine antifouling coatings based on silicone elastomers. Contrary to commonly used biocide-based antifouling coatings, they do not release biocides into the marine environment, however, they suffer from poor antifouling efficacy during idle periods. To improve their antifouling performances in static conditions, various amounts of hydrolyzable polymers were incorporated within a silicone matrix. These hydrolyzable polymers were chosen for the well-known hydrolytic degradation mechanism of their main chain, e.g. poly(ε-caprolactone) (PCL), or of their ester pending groups, e.g. poly(bis(trimethylsilyloxy)methylsilyl methacrylate) (PMATM2). The degradation kinetics of such hydrolyzable silicone coatings were assessed by mass loss measurements during immersion in deionized water. Coatings containing PMATM2 exhibited a maximum mass loss after 12 weeks, whereas PCL-based coatings showed no significant mass loss after 24 weeks. Dynamic contact angle measurements revealed the modifications of the coatings surface chemistry with an amphiphilic behavior after water exposure. The attachment of macrofoulers on these coatings were evaluated by field tests in the Mediterranean Sea, demonstrating the short or long-term antifouling effect of these hydrolyzable polymers embedded in the silicone matrix. The settlement of A. amphitrite barnacles on the different coatings indicated inhospitable behaviors towards larval barnacles for coatings with at least 15 wt % of additives. Full article

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

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39 pages, 9641 KB

Open AccessEditor’s ChoiceReview

Chemical Modification and Foam Processing of Polylactide (PLA)

by Tobias Standau, Chunjing Zhao, Svenja Murillo Castellón, Christian Bonten and Volker Altstädt

Polymers 2019, 11(2), 306; https://doi.org/10.3390/polym11020306 - 12 Feb 2019

Cited by 171 | Viewed by 26937

Abstract

Polylactide (PLA) is known as one of the most promising biopolymers as it is derived from renewable feedstock and can be biodegraded. During the last two decades, it moved more and more into the focus of scientific research and industrial use. It is [...] Read more.

Polylactide (PLA) is known as one of the most promising biopolymers as it is derived from renewable feedstock and can be biodegraded. During the last two decades, it moved more and more into the focus of scientific research and industrial use. It is even considered as a suitable replacement for standard petroleum-based polymers, such as polystyrene (PS), which can be found in a wide range of applications—amongst others in foams for packaging and insulation applications—but cause strong environmental issues. PLA has comparable mechanical properties to PS. However, the lack of melt strength is often referred to as a drawback for most foaming processes. One way to overcome this issue is the incorporation of chemical modifiers which can induce chain extension, branching, or cross-linking. As such, a wide variety of substances were studied in the literature. This work should give an overview of the most commonly used chemical modifiers and their effects on rheological, thermal, and foaming behavior. Therefore, this review article summarizes the research conducted on neat and chemically modified PLA foamed with the conventional foaming methods (i.e., batch foaming, foam extrusion, foam injection molding, and bead foaming). Full article

(This article belongs to the Special Issue Foaming and Injection Moulding in Polymer Processing)

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31 pages, 2775 KB

Open AccessEditor’s ChoiceReview

Grubbs’ and Schrock’s Catalysts, Ring Opening Metathesis Polymerization and Molecular Brushes—Synthesis, Characterization, Properties and Applications

by Ioannis Choinopoulos

Polymers 2019, 11(2), 298; https://doi.org/10.3390/polym11020298 - 11 Feb 2019

Cited by 66 | Viewed by 13914

Abstract

In this review, molecular brushes and other macromolecular architectures bearing a bottlebrush segment where the main chain is synthesized by ring opening metathesis polymerization (ROMP) mediated by Mo or Ru metal complexes are considered. A brief review of metathesis and ROMP is presented [...] Read more.

In this review, molecular brushes and other macromolecular architectures bearing a bottlebrush segment where the main chain is synthesized by ring opening metathesis polymerization (ROMP) mediated by Mo or Ru metal complexes are considered. A brief review of metathesis and ROMP is presented in order to understand the problems and the solutions provided through the years. The synthetic strategies towards bottlebrush copolymers are demonstrated and each one discussed separately. The initiators/catalysts for the synthesis of the backbone with ROMP are discussed. Syntheses of molecular brushes are presented. The most interesting properties of the bottlebrushes are detailed. Finally, the applications studied by different groups are presented. Full article

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

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13 pages, 4121 KB

Open AccessEditor’s ChoiceArticle

Thermal Healing, Reshaping and Ecofriendly Recycling of Epoxy Resin Crosslinked with Schiff Base of Vanillin and Hexane-1,6-Diamine

by Van-Dung Mai, Se-Ra Shin, Dai-Soo Lee and Ilho Kang

Polymers 2019, 11(2), 293; https://doi.org/10.3390/polym11020293 - 10 Feb 2019

Cited by 96 | Viewed by 11137

Abstract

A bio-derived dihydroxylimine hardener, Van2HMDA, for the curing of epoxy resin was prepared from vanillin (Van) and hexamethylene-1,6-diamine (HMDA) by Schiff base formation. The epoxy resin of diglycidyl ether of bisphenol A was cured with Van2HMDA in the presence of the catalyst, 2-ethyl-4-methylimidazole [...] Read more.

A bio-derived dihydroxylimine hardener, Van2HMDA, for the curing of epoxy resin was prepared from vanillin (Van) and hexamethylene-1,6-diamine (HMDA) by Schiff base formation. The epoxy resin of diglycidyl ether of bisphenol A was cured with Van2HMDA in the presence of the catalyst, 2-ethyl-4-methylimidazole (EMI). The crosslinked epoxy resin showed thermal-healing properties at elevated temperatures. Moreover, the crosslinked epoxy resin can be reshaped by heating via imine metathesis of the hardener units. The imine metathesis of Van2HMDA was confirmed experimentally. Stress-relaxation properties of the epoxy resin crosslinked with Van2HMDA were investigated, and the activation energy obtained from Arrhenius plots of the relaxation times was 44 kJ/mol. The imine bonds in the epoxy polymer matrix did not undergo hydrolysis after immersing in water at room temperature for one week. However, in the presence of acid, the crosslinked polymer was easily decomposed due to the hydrolysis of imine bonds. The hydrolysis of imine bonds was used for the ecofriendly recycling of crosslinked polymer. It is inferred that thermal-healing, reshaping, and reprocessing properties can be implemented in the various crosslinked epoxy resins with the bio-derived dihydroxylimine hardener, albeit the recycled epoxy resin is of inevitably lower quality than the original material. Full article

(This article belongs to the Special Issue Dynamic Chemistry in Polymer Science)

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