Polymers

Review

33 pages, 5442 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Temperature-Responsive Polymer Brush Coatings for Advanced Biomedical Applications

by Svyatoslav Nastyshyn, Yuriy Stetsyshyn, Joanna Raczkowska, Yuriy Nastishin, Yuriy Melnyk, Yuriy Panchenko and Andrzej Budkowski

Polymers 2022, 14(19), 4245; https://doi.org/10.3390/polym14194245 - 10 Oct 2022

Cited by 40 | Viewed by 4234

Abstract

Modern biomedical technologies predict the application of materials and devices that not only can comply effectively with specific requirements, but also enable remote control of their functions. One of the most prospective materials for these advanced biomedical applications are materials based on temperature-responsive [...] Read more.

Modern biomedical technologies predict the application of materials and devices that not only can comply effectively with specific requirements, but also enable remote control of their functions. One of the most prospective materials for these advanced biomedical applications are materials based on temperature-responsive polymer brush coatings (TRPBCs). In this review, methods for the fabrication and characterization of TRPBCs are summarized, and possibilities for their application, as well as the advantages and disadvantages of the TRPBCs, are presented in detail. Special attention is paid to the mechanisms of thermo-responsibility of the TRPBCs. Applications of TRPBCs for temperature-switchable bacteria killing, temperature-controlled protein adsorption, cell culture, and temperature-controlled adhesion/detachment of cells and tissues are considered. The specific criteria required for the desired biomedical applications of TRPBCs are presented and discussed. Full article

(This article belongs to the Special Issue Polymer Brushes: Synthesis, Properties and Structure)

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30 pages, 1610 KiB

Open AccessEditor’s ChoiceReview

Novel Trends in Hydrogel Development for Biomedical Applications: A Review

by Pablo Sánchez-Cid, Mercedes Jiménez-Rosado, Alberto Romero and Víctor Pérez-Puyana

Polymers 2022, 14(15), 3023; https://doi.org/10.3390/polym14153023 - 26 Jul 2022

Cited by 132 | Viewed by 11731

Abstract

Nowadays, there are still numerous challenges for well-known biomedical applications, such as tissue engineering (TE), wound healing and controlled drug delivery, which must be faced and solved. Hydrogels have been proposed as excellent candidates for these applications, as they have promising properties for [...] Read more.

Nowadays, there are still numerous challenges for well-known biomedical applications, such as tissue engineering (TE), wound healing and controlled drug delivery, which must be faced and solved. Hydrogels have been proposed as excellent candidates for these applications, as they have promising properties for the mentioned applications, including biocompatibility, biodegradability, great absorption capacity and tunable mechanical properties. However, depending on the material or the manufacturing method, the resulting hydrogel may not be up to the specific task for which it is designed, thus there are different approaches proposed to enhance hydrogel performance for the requirements of the application in question. The main purpose of this review article was to summarize the most recent trends of hydrogel technology, going through the most used polymeric materials and the most popular hydrogel synthesis methods in recent years, including different strategies of enhancing hydrogels’ properties, such as cross-linking and the manufacture of composite hydrogels. In addition, the secondary objective of this review was to briefly discuss other novel applications of hydrogels that have been proposed in the past few years which have drawn a lot of attention. Full article

(This article belongs to the Collection Hydrogels)

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42 pages, 4201 KiB

Open AccessEditor’s ChoiceReview

Overoxidation of Intrinsically Conducting Polymers

by Rudolf Holze

Polymers 2022, 14(8), 1584; https://doi.org/10.3390/polym14081584 - 13 Apr 2022

Cited by 30 | Viewed by 4177

Abstract

Intrinsically conducting polymers may undergo significant changes of molecular structure and material properties when exposed to highly oxidizing conditions or very positive electrode potentials, commonly called overoxidation. The type and extent of the changes depend on the experimental conditions and chemical environment. They [...] Read more.

Intrinsically conducting polymers may undergo significant changes of molecular structure and material properties when exposed to highly oxidizing conditions or very positive electrode potentials, commonly called overoxidation. The type and extent of the changes depend on the experimental conditions and chemical environment. They may proceed already at much lower rates at lower electrode potentials because some of the processes associated with overoxidation are closely related to more or less reversible redox processes employed in electrochemical energy conversion and electrochromism. These changes may be welcome for some applications of these polymers in sensors, extraction, and surface functionalization, but in many cases, the change of properties affects the performance of the material negatively, contributing to material and device degradation. This report presents published examples, experimental observations, and their interpretations in terms of both structural and of material property changes. Options to limit and suppress overoxidation are presented, and useful applications are described extensively. Full article

(This article belongs to the Special Issue Electrochemical and Spectroscopic Properties of Conducting Polymers)

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32 pages, 2852 KiB

Open AccessEditor’s ChoiceReview

Towards a Circular Economy of Plastics: An Evaluation of the Systematic Transition to a New Generation of Bioplastics

by Elda M. Melchor-Martínez, Rodrigo Macías-Garbett, Lynette Alvarado-Ramírez, Rafael G. Araújo, Juan Eduardo Sosa-Hernández, Diana Ramírez-Gamboa, Lizeth Parra-Arroyo, Abraham Garza Alvarez, Rosina Paola Benavides Monteverde, Karen Aleida Salazar Cazares, Adriana Reyes-Mayer, Mauricio Yáñez Lino, Hafiz M. N. Iqbal and Roberto Parra-Saldívar

Polymers 2022, 14(6), 1203; https://doi.org/10.3390/polym14061203 - 17 Mar 2022

Cited by 36 | Viewed by 16054

Abstract

Plastics have become an essential part of the modern world thanks to their appealing physical and chemical properties as well as their low production cost. The most common type of polymers used for plastic account for 90% of the total production and are [...] Read more.

Plastics have become an essential part of the modern world thanks to their appealing physical and chemical properties as well as their low production cost. The most common type of polymers used for plastic account for 90% of the total production and are made from petroleum-based nonrenewable resources. Concerns over the sustainability of the current production model and the environmental implications of traditional plastics have fueled the demand for greener formulations and alternatives. In the last decade, new plastics manufactured from renewable sources and biological processes have emerged from research and have been established as a commercially viable solution with less adverse effects. Nevertheless, economic and legislative challenges for biobased plastics hinder their widespread implementation. This review summarizes the history of plastics over the last century, including the most relevant bioplastics and production methods, the environmental impact and mitigation of the adverse effects of conventional and emerging plastics, and the regulatory landscape that renewable and recyclable bioplastics face to reach a sustainable future. Full article

(This article belongs to the Special Issue Bio-Based Materials: Contribution to Advancing Circular Economy)

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35 pages, 10095 KiB

Open AccessEditor’s ChoiceReview

A Review on Current Strategies for the Modulation of Thermomechanical, Barrier, and Biodegradation Properties of Poly (Butylene Succinate) (PBS) and Its Random Copolymers

by Mario Iván Peñas, Ricardo Arpad Pérez-Camargo, Rebeca Hernández and Alejandro J. Müller

Polymers 2022, 14(5), 1025; https://doi.org/10.3390/polym14051025 - 3 Mar 2022

Cited by 37 | Viewed by 5390

Abstract

The impact of plastics on the environment can be mitigated by employing biobased and/or biodegradable materials (i.e., bioplastics) instead of the traditional “commodities”. In this context, poly (butylene succinate) (PBS) emerges as one of the most promising alternatives due to its good mechanical, [...] Read more.

The impact of plastics on the environment can be mitigated by employing biobased and/or biodegradable materials (i.e., bioplastics) instead of the traditional “commodities”. In this context, poly (butylene succinate) (PBS) emerges as one of the most promising alternatives due to its good mechanical, thermal, and barrier properties, making it suitable for use in a wide range of applications. Still, the PBS has some drawbacks, such as its high crystallinity, which must be overcome to position it as a real and viable alternative to “commodities”. This contribution covers the actual state-of-the-art of the PBS through different sections. The first section reviews the different synthesis routes, providing a complete picture regarding the obtained molecular weights and the greener alternatives. Afterward, we examine how different strategies such as random copolymerization and the incorporation of fillers can effectively modulate PBS properties to satisfy the needs for different applications. The impact of these strategies is evaluated in the crystallization behavior, crystallinity, mechanical and barrier properties, and biodegradation. The biodegradation is carefully analyzed, highlighting the wide variety of methodologies existing in the literature to measure PBS degradation through different routes (hydrolytic, enzymatic, and soil). Full article

(This article belongs to the Collection Design and Synthesis of Polymers)

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15 pages, 7414 KiB

Open AccessEditor’s ChoiceReview

Recent Progress on Heparin–Protamine Particles for Biomedical Application

by Yuuki Hata, Hiromi Miyazaki, Masayuki Ishihara and Shingo Nakamura

Polymers 2022, 14(5), 932; https://doi.org/10.3390/polym14050932 - 25 Feb 2022

Cited by 7 | Viewed by 2639

Abstract

Biomolecules are attractive building blocks with self-assembly ability, structural diversity, and excellent functionality for creating artificial materials. Heparin and protamine, a clinically relevant pair of biomolecules used in cardiac and vascular surgery, have been shown to coassemble into particulate polyelectrolyte complexes in vitro. [...] Read more.

Biomolecules are attractive building blocks with self-assembly ability, structural diversity, and excellent functionality for creating artificial materials. Heparin and protamine, a clinically relevant pair of biomolecules used in cardiac and vascular surgery, have been shown to coassemble into particulate polyelectrolyte complexes in vitro. The resulting heparin–protamine particles exhibit adhesive properties that enable advantageous interactions with proteins, cells, and various other substances and have been employed as functional materials for biomedical applications. In this review article, we summarize recent progress in research on the use of heparin–protamine particles as drug carriers, cell adhesives, and cell labels. Studies have demonstrated that heparin–protamine particles are potentially versatile in biomedical fields from drug delivery and regenerative medicine to plastic surgery. Full article

(This article belongs to the Special Issue Biodegradable Polymeric Implants for Drug Delivery and Cell Therapy Applications)

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36 pages, 5474 KiB

Open AccessEditor’s ChoiceReview

Modelling of Environmental Ageing of Polymers and Polymer Composites—Durability Prediction Methods

by Olesja Starkova, Abedin I. Gagani, Christian W. Karl, Iuri B. C. M. Rocha, Juris Burlakovs and Andrey E. Krauklis

Polymers 2022, 14(5), 907; https://doi.org/10.3390/polym14050907 - 24 Feb 2022

Cited by 50 | Viewed by 7434

Abstract

Polymers and polymer composites are negatively impacted by environmental ageing, reducing their service lifetimes. The uncertainty of the material interaction with the environment compromises their superior strength and stiffness. Validation of new composite materials and structures often involves lengthy and expensive testing programs. [...] Read more.

Polymers and polymer composites are negatively impacted by environmental ageing, reducing their service lifetimes. The uncertainty of the material interaction with the environment compromises their superior strength and stiffness. Validation of new composite materials and structures often involves lengthy and expensive testing programs. Therefore, modelling is an affordable alternative that can partly replace extensive testing and thus reduce validation costs. Durability prediction models are often subject to conflicting requirements of versatility and minimum experimental efforts required for their validation. Based on physical observations of composite macroproperties, engineering and phenomenological models provide manageable representations of complex mechanistic models. This review offers a systematised overview of the state-of-the-art models and accelerated testing methodologies for predicting the long-term mechanical performance of polymers and polymer composites. Accelerated testing methods for predicting static, creep, and fatig ue lifetime of various polymers and polymer composites under environmental factors’ single or coupled influence are overviewed. Service lifetimes are predicted by means of degradation rate models, superposition principles, and parametrisation techniques. This review is a continuation of the authors’ work on modelling environmental ageing of polymer composites: the first part of the review covered multiscale and modular modelling methods of environmental degradation. The present work is focused on modelling engineering mechanical properties. Full article

(This article belongs to the Special Issue Advances in Polymer Matrix Composites: Synthesis, Characterization and Simulation)

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29 pages, 4065 KiB

Open AccessEditor’s ChoiceReview

Boronic Acid Esters and Anhydrates as Dynamic Cross-Links in Vitrimers

by Mateusz Gosecki and Monika Gosecka

Polymers 2022, 14(4), 842; https://doi.org/10.3390/polym14040842 - 21 Feb 2022

Cited by 32 | Viewed by 8888

Abstract

Growing environmental awareness imposes on polymer scientists the development of novel materials that show a longer lifetime and that can be easily recycled. These challenges were largely met by vitrimers, a new class of polymers that merges properties of thermoplastics and thermosets. This [...] Read more.

Growing environmental awareness imposes on polymer scientists the development of novel materials that show a longer lifetime and that can be easily recycled. These challenges were largely met by vitrimers, a new class of polymers that merges properties of thermoplastics and thermosets. This is achieved by the incorporation of dynamic covalent bonds into the polymer structure, which provides high stability at the service temperature, but enables the processing at elevated temperatures. Numerous types of dynamic covalent bonds have been utilized for the synthesis of vitrimers. Amongst them, boronic acid-based linkages, namely boronic acid esters and boroxines, are distinguished by their quick exchange kinetics and the possibility of easy application in various polymer systems, from commercial thermoplastics to low molecular weight thermosetting resins. This review covers the development of dynamic cross-links. This review is aimed at providing the state of the art in the utilization of boronic species for the synthesis of covalent adaptable networks. We mainly focus on the synthetic aspects of boronic linkages-based vitrimers construction. Finally, the challenges and future perspectives are provided. Full article

(This article belongs to the Special Issue The Frontier of Self-Assembled Polymers and Dendronized Polymers-Based Smart Materials)

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29 pages, 3269 KiB

Open AccessEditor’s ChoiceReview

Lignosulphonates as an Alternative to Non-Renewable Binders in Wood-Based Materials

by Sofia Gonçalves, João Ferra, Nádia Paiva, Jorge Martins, Luísa H. Carvalho and Fernão D. Magalhães

Polymers 2021, 13(23), 4196; https://doi.org/10.3390/polym13234196 - 30 Nov 2021

Cited by 23 | Viewed by 4028

Abstract

Lignin is a widely abundant renewable source of phenolic compounds. Despite the growing interest on using it as a substitute for its petroleum-based counterparts, only 1 to 2% of the global lignin production is used for obtaining value-added products. Lignosulphonates (LS), derived from [...] Read more.

Lignin is a widely abundant renewable source of phenolic compounds. Despite the growing interest on using it as a substitute for its petroleum-based counterparts, only 1 to 2% of the global lignin production is used for obtaining value-added products. Lignosulphonates (LS), derived from the sulphite pulping process, account for 90% of the total market of commercial lignin. The most successful industrial attempts to use lignin for wood adhesives are based on using this polymer as a partial substitute in phenol-formaldehyde or urea-formaldehyde resins. Alternatively, formaldehyde-free adhesives with lignin and lignosulphonates have also been developed with promising results. However, the low number of reactive sites available in lignin’s aromatic ring and high polydispersity have hindered its application in resin synthesis. Currently, finding suitable crosslinkers for LS and decreasing the long pressing time associated with lignin adhesives remains a challenge. Thus, several methods have been proposed to improve the reactivity of lignin molecules. In this paper, techniques to extract, characterize, as well as improve the reactivity of LS are addressed. The most recent advances in the application of LS in wood adhesives, with and without combination with formaldehyde, are also reviewed. Full article

(This article belongs to the Special Issue Recent Developments in Eco-Friendly Wood-Based Composites II)

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51 pages, 3452 KiB

Open AccessEditor’s ChoiceReview

Sustainable Polymers from Recycled Waste Plastics and Their Virgin Counterparts as Bitumen Modifiers: A Comprehensive Review

by Sabzoi Nizamuddin, Yeong Jia Boom and Filippo Giustozzi

Polymers 2021, 13(19), 3242; https://doi.org/10.3390/polym13193242 - 24 Sep 2021

Cited by 52 | Viewed by 10642

Abstract

The failure of bituminous pavements takes place due to heavy traffic loads and weather-related conditions, such as moisture, temperature, and UV radiation. To overcome or minimize such failures, a great effort has been put in recent years to enhance the material properties of [...] Read more.

The failure of bituminous pavements takes place due to heavy traffic loads and weather-related conditions, such as moisture, temperature, and UV radiation. To overcome or minimize such failures, a great effort has been put in recent years to enhance the material properties of bitumen, ultimately improving field performance and increasing the pavement service life. Polymer modification is considered one of the most suitable and by far the most popular approach. Elastomers, chemically functionalised thermoplastics and plastomers * (* Note: notwithstanding the fact that in Polymer Science the word ‘plastomer’ indicates a polymer with the simultaneous behaviour of an elastomer and plastics (thermoplastics), this paper uses the term ‘plastomer’ to indicate a thermoplastic polymer as it is more commonly found in Civil and Pavement Engineering.) are the most commonly used polymers for bitumen modification. Plastomers provide several advantages and are commonly acknowledged to improve high-temperature stiffness, although some of them are more prone to phase separation and consequent storage instability. Nowadays, due to the recent push for recycling, many road authorities are looking at the use of recycled plastics in roads. Hence, some of the available plastomers—in pellet, flakes, or powder form—are coming from materials recycling facilities rather than chemical companies. This review article describes the details of using plastomers as bitumen modifiers—with a specific focus on recycled plastics—and how these can potentially be used to enhance bitumen performance and the road durability. Chemical modifiers for improving the compatibility between plastomers and bitumen are also addressed in this review. Plastomers, either individual or in combination of two or three polymers, are found to offer great stiffness at high temperature. Different polymers including HDPE, LDPE, LLDPE, MDPE, PP, PS, PET, EMA, and EVA have been successfully employed for bitumen modification. However, each of them has its own merit and demerit as thoroughly discussed in the paper. The recent push in using recycled materials in roads has brought new light to the use of virgin and recycled plastomers for bitumen modification as a low-cost and somehow environmental beneficial solution for roads and pavements. Full article

(This article belongs to the Special Issue Advances in Sustainable Polymeric Materials)

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25 pages, 4291 KiB

Open AccessEditor’s ChoiceReview

Advanced Photocatalysts Based on Conducting Polymer/Metal Oxide Composites for Environmental Applications

by Vinh Van Tran, Truong Thi Vu Nu, Hong-Ryun Jung and Mincheol Chang

Polymers 2021, 13(18), 3031; https://doi.org/10.3390/polym13183031 - 8 Sep 2021

Cited by 40 | Viewed by 4969

Abstract

Photocatalysts provide a sustainable method of treating organic pollutants in wastewater and converting greenhouse gases. Many studies have been published on this topic in recent years, which signifies the great interest and attention that this topic inspires in the community, as well as [...] Read more.

Photocatalysts provide a sustainable method of treating organic pollutants in wastewater and converting greenhouse gases. Many studies have been published on this topic in recent years, which signifies the great interest and attention that this topic inspires in the community, as well as in scientists. Composite photocatalysts based on conducting polymers and metal oxides have emerged as novel and promising photoactive materials. It has been demonstrated that conducting polymers can substantially improve the photocatalytic efficiency of metal oxides owing to their superior photocatalytic activities, high conductivities, and unique electrochemical and optical properties. Consequently, conducting polymer/metal oxide composites exhibit a high photoresponse and possess a higher surface area allowing for visible light absorption, low recombination of charge carriers, and high photocatalytic performance. Herein, we provide an overview of recent advances in the development of conducting polymer/metal oxide composite photocatalysts for organic pollutant degradation and CO₂ conversion through photocatalytic processes. Full article

(This article belongs to the Special Issue Conjugated Polymer Nanocomposites: Synthesis, Characterization, and Applications)

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23 pages, 6575 KiB

Open AccessEditor’s ChoiceReview

Greener Pretreatment Approaches for the Valorisation of Natural Fibre Biomass into Bioproducts

by Mohd Nor Faiz Norrrahim, Muhammad Roslim Muhammad Huzaifah, Mohammed Abdillah Ahmad Farid, Siti Shazra Shazleen, Muhammad Syukri Mohamad Misenan, Tengku Arisyah Tengku Yasim-Anuar, Jesuarockiam Naveen, Norizan Mohd Nurazzi, Mohd Saiful Asmal Rani, Mohd Idham Hakimi, Rushdan Ahmad Ilyas and Mohd Azwan Jenol

Polymers 2021, 13(17), 2971; https://doi.org/10.3390/polym13172971 - 31 Aug 2021

Cited by 45 | Viewed by 5208

Abstract

The utilization of lignocellulosic biomass in various applications has a promising potential as advanced technology progresses due to its renowned advantages as cheap and abundant feedstock. The main drawback in the utilization of this type of biomass is the essential requirement for the [...] Read more.

The utilization of lignocellulosic biomass in various applications has a promising potential as advanced technology progresses due to its renowned advantages as cheap and abundant feedstock. The main drawback in the utilization of this type of biomass is the essential requirement for the pretreatment process. The most common pretreatment process applied is chemical pretreatment. However, it is a non-eco-friendly process. Therefore, this review aims to bring into light several greener pretreatment processes as an alternative approach for the current chemical pretreatment. The main processes for each physical and biological pretreatment process are reviewed and highlighted. Additionally, recent advances in the effect of different non-chemical pretreatment approaches for the natural fibres are also critically discussed with a focus on bioproducts conversion. Full article

(This article belongs to the Special Issue Bio and Synthetic Based Polymer Composite Materials)

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15 pages, 1645 KiB

Open AccessEditor’s ChoiceReview

Current Strategies for the Production of Sustainable Biopolymer Composites

by Ehsan Bari, Asghar Sistani, Jeffrey J. Morrell, Antonio Pizzi, Mohammad Reza Akbari and Javier Ribera

Polymers 2021, 13(17), 2878; https://doi.org/10.3390/polym13172878 - 27 Aug 2021

Cited by 29 | Viewed by 4654

Abstract

Rapid global population growth has led to an exponential increase in the use of disposable materials with a short life span that accumulate in landfills. The use of non-biodegradable materials causes severe damage to the environment worldwide. Polymers derived from agricultural residues, wood, [...] Read more.

Rapid global population growth has led to an exponential increase in the use of disposable materials with a short life span that accumulate in landfills. The use of non-biodegradable materials causes severe damage to the environment worldwide. Polymers derived from agricultural residues, wood, or other fiber crops are fully biodegradable, creating the potential to be part of a sustainable circular economy. Ideally, natural fibers, such as the extremely strong fibers from hemp, can be combined with matrix materials such as the core or hurd from hemp or kenaf to produce a completely renewable biomaterial. However, these materials cannot always meet all of the performance attributes required, necessitating the creation of blends of petroleum-based and renewable material-based composites. This article reviews composites made from natural and biodegradable polymers, as well as the challenges encountered in their production and use. Full article

(This article belongs to the Collection Progress in Polymer Composites and Nanocomposites)

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65 pages, 19388 KiB

Open AccessEditor’s ChoiceReview

Critical Review of Biodegradable and Bioactive Polymer Composites for Bone Tissue Engineering and Drug Delivery Applications

by Shubham Sharma, P. Sudhakara, Jujhar Singh, R. A. Ilyas, M. R. M. Asyraf and M. R. Razman

Polymers 2021, 13(16), 2623; https://doi.org/10.3390/polym13162623 - 6 Aug 2021

Cited by 119 | Viewed by 8617

Abstract

In the determination of the bioavailability of drugs administered orally, the drugs’ solubility and permeability play a crucial role. For absorption of drug molecules and production of a pharmacological response, solubility is an important parameter that defines the concentration of the drug in [...] Read more.

In the determination of the bioavailability of drugs administered orally, the drugs’ solubility and permeability play a crucial role. For absorption of drug molecules and production of a pharmacological response, solubility is an important parameter that defines the concentration of the drug in systemic circulation. It is a challenging task to improve the oral bioavailability of drugs that have poor water solubility. Most drug molecules are either poorly soluble or insoluble in aqueous environments. Polymer nanocomposites are combinations of two or more different materials that possess unique characteristics and are fused together with sufficient energy in such a manner that the resultant material will have the best properties of both materials. These polymeric materials (biodegradable and other naturally bioactive polymers) are comprised of nanosized particles in a composition of other materials. A systematic search was carried out on Web of Science and SCOPUS using different keywords, and 485 records were found. After the screening and eligibility process, 88 journal articles were found to be eligible, and hence selected to be reviewed and analyzed. Biocompatible and biodegradable materials have emerged in the manufacture of therapeutic and pharmacologic devices, such as impermanent implantation and 3D scaffolds for tissue regeneration and biomedical applications. Substantial effort has been made in the usage of bio-based polymers for potential pharmacologic and biomedical purposes, including targeted deliveries and drug carriers for regulated drug release. These implementations necessitate unique physicochemical and pharmacokinetic, microbiological, metabolic, and degradation characteristics of the materials in order to provide prolific therapeutic treatments. As a result, a broadly diverse spectrum of natural or artificially synthesized polymers capable of enzymatic hydrolysis, hydrolyzing, or enzyme decomposition are being explored for biomedical purposes. This summary examines the contemporary status of biodegradable naturally and synthetically derived polymers for biomedical fields, such as tissue engineering, regenerative medicine, bioengineering, targeted drug discovery and delivery, implantation, and wound repair and healing. This review presents an insight into a number of the commonly used tissue engineering applications, including drug delivery carrier systems, demonstrated in the recent findings. Due to the inherent remarkable properties of biodegradable and bioactive polymers, such as their antimicrobial, antitumor, anti-inflammatory, and anticancer activities, certain materials have gained significant interest in recent years. These systems are also actively being researched to improve therapeutic activity and mitigate adverse consequences. In this article, we also present the main drug delivery systems reported in the literature and the main methods available to impregnate the polymeric scaffolds with drugs, their properties, and their respective benefits for tissue engineering. Full article

(This article belongs to the Special Issue Additive Manufacturing of Bio and Synthetic Polymers)

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17 pages, 1859 KiB

Open AccessEditor’s ChoiceReview

Starch–Mucilage Composite Films: An Inclusive on Physicochemical and Biological Perspective

by Mansuri M. Tosif, Agnieszka Najda, Aarti Bains, Grażyna Zawiślak, Grzegorz Maj and Prince Chawla

Polymers 2021, 13(16), 2588; https://doi.org/10.3390/polym13162588 - 4 Aug 2021

Cited by 26 | Viewed by 5685

Abstract

In recent years, scientists have focused on research to replace petroleum-based components plastics, in an eco-friendly and cost-effective manner, with plant-derived biopolymers offering suitable mechanical properties. Moreover, due to high environmental pollution, global warming, and the foreseen shortage of oil supplies, the quest [...] Read more.

In recent years, scientists have focused on research to replace petroleum-based components plastics, in an eco-friendly and cost-effective manner, with plant-derived biopolymers offering suitable mechanical properties. Moreover, due to high environmental pollution, global warming, and the foreseen shortage of oil supplies, the quest for the formulation of biobased, non-toxic, biocompatible, and biodegradable polymer films is still emerging. Several biopolymers from varied natural resources such as starch, cellulose, gums, agar, milk, cereal, and legume proteins have been used as eco-friendly packaging materials for the substitute of non-biodegradable petroleum-based plastic-based packaging materials. Among all biopolymers, starch is an edible carbohydrate complex, composed of a linear polymer, amylose, and amylopectin. They have usually been considered as a favorite choice of material for food packaging applications due to their excellent forming ability, low cost, and environmental compatibility. Although the film prepared from bio-polymer materials improves the shelf life of commodities by protecting them against interior and exterior factors, suitable barrier properties are impossible to attain with single polymeric packaging material. Therefore, the properties of edible films can be modified based on the hydrophobic–hydrophilic qualities of biomolecules. Certain chemical modifications of starch have been performed; however, the chemical residues may impart toxicity in the food commodity. Therefore, in such cases, several plant-derived polymeric combinations could be used as an effective binary blend of the polymer to improve the mechanical and barrier properties of packaging film. Recently, scientists have shown their great interest in underutilized plant-derived mucilage to synthesize biodegradable packaging material with desirable properties. Mucilage has a great potential to produce a stable polymeric network that confines starch granules that delay the release of amylose, improving the mechanical property of films. Therefore, the proposed review article is emphasized on the utilization of a blend of source and plant-derived mucilage for the synthesis of biodegradable packaging film. Herein, the synthesis process, characterization, mechanical properties, functional properties, and application of starch and mucilage-based film are discussed in detail. Full article

(This article belongs to the Special Issue Biopolymers for Medicinal, Macromolecules, and Food Applications II)

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21 pages, 6082 KiB

Open AccessEditor’s ChoiceReview

Graphitic Carbon Nitride as a New Sustainable Photocatalyst for Textile Functionalization

by Jelena Vasiljević, Ivan Jerman and Barbara Simončič

Polymers 2021, 13(15), 2568; https://doi.org/10.3390/polym13152568 - 31 Jul 2021

Cited by 11 | Viewed by 4272

Abstract

As a promising organic semiconducting material, polymeric graphitic carbon nitride (g-C₃N₄) has attracted much attention due to its excellent optical and photoelectrochemical properties, thermal stability, chemical inertness, nontoxicity, abundance, and low cost. Its advantageous visible light-induced photocatalytic activity has [...] Read more.

As a promising organic semiconducting material, polymeric graphitic carbon nitride (g-C₃N₄) has attracted much attention due to its excellent optical and photoelectrochemical properties, thermal stability, chemical inertness, nontoxicity, abundance, and low cost. Its advantageous visible light-induced photocatalytic activity has already been beneficially used in the fields of environmental remediation, biological applications, healthcare, energy conversion and storage, and fuel production. Despite the recognized potential of g-C₃N₄, there is still a knowledge gap in the application of g-C₃N₄ in the field of textiles, with no published reviews on the g-C₃N₄-functionalization of textile materials. Therefore, this review article aims to provide a critical overview of recent advances in the surface and bulk modification of textile fibres by g-C₃N₄ and its composites to tailor photocatalytic self-cleaning, antibacterial, and flame retardant properties as well as to create a textile catalytic platform for water disinfection, the removal of various organic pollutants from water, and selective organic transformations. This paper highlights the possibilities of producing g-C₃N₄-functionalized textile substrates and suggests some future prospects for this research area. Full article

(This article belongs to the Section Polymer Chemistry)

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36 pages, 1580 KiB

Open AccessEditor’s ChoiceReview

Biodegradable Packaging Materials from Animal Processing Co-Products and Wastes: An Overview

by Diako Khodaei, Carlos Álvarez and Anne Maria Mullen

Polymers 2021, 13(15), 2561; https://doi.org/10.3390/polym13152561 - 31 Jul 2021

Cited by 46 | Viewed by 11478

Abstract

Biodegradable polymers are non-toxic, environmentally friendly biopolymers with considerable mechanical and barrier properties that can be degraded in industrial or home composting conditions. These biopolymers can be generated from sustainable natural sources or from the agricultural and animal processing co-products and wastes. Animals [...] Read more.

Biodegradable polymers are non-toxic, environmentally friendly biopolymers with considerable mechanical and barrier properties that can be degraded in industrial or home composting conditions. These biopolymers can be generated from sustainable natural sources or from the agricultural and animal processing co-products and wastes. Animals processing co-products are low value, underutilized, non-meat components that are generally generated from meat processing or slaughterhouse such as hide, blood, some offal etc. These are often converted into low-value products such as animal feed or in some cases disposed of as waste. Collagen, gelatin, keratin, myofibrillar proteins, and chitosan are the major value-added biopolymers obtained from the processing of animal’s products. While these have many applications in food and pharmaceutical industries, a significant amount is underutilized and therefore hold potential for use in the generation of bioplastics. This review summarizes the research progress on the utilization of meat processing co-products to fabricate biodegradable polymers with the main focus on food industry applications. In addition, the factors affecting the application of biodegradable polymers in the packaging sector, their current industrial status, and regulations are also discussed. Full article

(This article belongs to the Special Issue Biopolymers for Food Packaging Films and Coatings)

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22 pages, 6542 KiB

Open AccessEditor’s ChoiceReview

Field-Theoretic Simulations for Block Copolymer Melts Using the Partial Saddle-Point Approximation

by Mark W. Matsen and Thomas M. Beardsley

Polymers 2021, 13(15), 2437; https://doi.org/10.3390/polym13152437 - 24 Jul 2021

Cited by 19 | Viewed by 3276

Abstract

Field-theoretic simulations (FTS) provide an efficient technique for investigating fluctuation effects in block copolymer melts with numerous advantages over traditional particle-based simulations. For systems involving two components (i.e., A and B), the field-based Hamiltonian,

H_{f} [W_{-}, W_{+}]

[...] Read more.

Field-theoretic simulations (FTS) provide an efficient technique for investigating fluctuation effects in block copolymer melts with numerous advantages over traditional particle-based simulations. For systems involving two components (i.e., A and B), the field-based Hamiltonian,

H_{f} [W_{-}, W_{+}]

, depends on a composition field,

W_{-} (r)

, that controls the segregation of the unlike components and a pressure field,

W_{+} (r)

, that enforces incompressibility. This review introduces researchers to a promising variant of FTS, in which

W_{-} (r)

fluctuates while

W_{+} (r)

tracks its mean-field value. The method is described in detail for melts of AB diblock copolymer, covering its theoretical foundation through to its numerical implementation. We then illustrate its application for neat AB diblock copolymer melts, as well as ternary blends of AB diblock copolymer with its A- and B-type parent homopolymers. The review concludes by discussing the future outlook. To help researchers adopt the method, open-source code is provided that can be run on either central processing units (CPUs) or graphics processing units (GPUs). Full article

(This article belongs to the Special Issue Simulation Methods of Polymers Involving Field Theory)

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42 pages, 4670 KiB

Open AccessEditor’s ChoiceReview

Nanotechnological Manipulation of Nutraceuticals and Phytochemicals for Healthy Purposes: Established Advantages vs. Still Undefined Risks

by Silvana Alfei, Anna Maria Schito and Guendalina Zuccari

Polymers 2021, 13(14), 2262; https://doi.org/10.3390/polym13142262 - 9 Jul 2021

Cited by 10 | Viewed by 3344

Abstract

Numerous foods, plants, and their bioactive constituents (BACs), named nutraceuticals and phytochemicals by experts, have shown many beneficial effects including antifungal, antiviral, anti-inflammatory, antibacterial, antiulcer, anti-cholesterol, hypoglycemic, immunomodulatory, and antioxidant activities. Producers, consumers, and the market of food- and plant-related compounds are increasingly [...] Read more.

Numerous foods, plants, and their bioactive constituents (BACs), named nutraceuticals and phytochemicals by experts, have shown many beneficial effects including antifungal, antiviral, anti-inflammatory, antibacterial, antiulcer, anti-cholesterol, hypoglycemic, immunomodulatory, and antioxidant activities. Producers, consumers, and the market of food- and plant-related compounds are increasingly attracted by health-promoting foods and plants, thus requiring a wider and more fruitful exploitation of the healthy properties of their BACs. The demand for new BACs and for the development of novel functional foods and BACs-based food additives is pressing from various sectors. Unfortunately, low stability, poor water solubility, opsonization, and fast metabolism in vivo hinder the effective exploitation of the potential of BACs. To overcome these issues, researchers have engineered nanomaterials, obtaining food-grade delivery systems, and edible food- and plant-related nanoparticles (NPs) acting as color, flavor, and preservative additives and natural therapeutics. Here, we have reviewed the nanotechnological transformations of several BACs implemented to increase their bioavailability, to mask any unpleasant taste and flavors, to be included as active ingredients in food or food packaging, to improve food appearance, quality, and resistance to deterioration due to storage. The pending issue regarding the possible toxic effect of NPs, whose knowledge is still limited, has also been discussed. Full article

(This article belongs to the Special Issue Polymer-Based Nanocomposites: Processing to Advance Applications)

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47 pages, 7517 KiB

Open AccessEditor’s ChoiceReview

Nanocelluloses: Sources, Pretreatment, Isolations, Modification, and Its Application as the Drug Carriers

by Valentino Bervia Lunardi, Felycia Edi Soetaredjo, Jindrayani Nyoo Putro, Shella Permatasari Santoso, Maria Yuliana, Jaka Sunarso, Yi-Hsu Ju and Suryadi Ismadji

Polymers 2021, 13(13), 2052; https://doi.org/10.3390/polym13132052 - 23 Jun 2021

Cited by 45 | Viewed by 5145

Abstract

The ‘Back-to-nature’ concept has currently been adopted intensively in various industries, especially the pharmaceutical industry. In the past few decades, the overuse of synthetic chemicals has caused severe damage to the environment and ecosystem. One class of natural materials developed to substitute artificial [...] Read more.

The ‘Back-to-nature’ concept has currently been adopted intensively in various industries, especially the pharmaceutical industry. In the past few decades, the overuse of synthetic chemicals has caused severe damage to the environment and ecosystem. One class of natural materials developed to substitute artificial chemicals in the pharmaceutical industries is the natural polymers, including cellulose and its derivatives. The development of nanocelluloses as nanocarriers in drug delivery systems has reached an advanced stage. Cellulose nanofiber (CNF), nanocrystal cellulose (NCC), and bacterial nanocellulose (BC) are the most common nanocellulose used as nanocarriers in drug delivery systems. Modification and functionalization using various processes and chemicals have been carried out to increase the adsorption and drug delivery performance of nanocellulose. Nanocellulose may be attached to the drug by physical interaction or chemical functionalization for covalent drug binding. Current development of nanocarrier formulations such as surfactant nanocellulose, ultra-lightweight porous materials, hydrogel, polyelectrolytes, and inorganic hybridizations has advanced to enable the construction of stimuli-responsive and specific recognition characteristics. Thus, an opportunity has emerged to develop a new generation of nanocellulose-based carriers that can modulate the drug conveyance for diverse drug characteristics. This review provides insights into selecting appropriate nanocellulose-based hybrid materials and the available modification routes to achieve satisfactory carrier performance and briefly discusses the essential criteria to achieve high-quality nanocellulose. Full article

(This article belongs to the Special Issue Cellulose (Nano)Composites)

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49 pages, 7182 KiB

Open AccessEditor’s ChoiceReview

Thiophene-Based Trimers and Their Bioapplications: An Overview

by Lorenzo Vallan, Emin Istif, I. Jénnifer Gómez, Nuria Alegret and Daniele Mantione

Polymers 2021, 13(12), 1977; https://doi.org/10.3390/polym13121977 - 16 Jun 2021

Cited by 16 | Viewed by 4945

Abstract

Certainly, the success of polythiophenes is due in the first place to their outstanding electronic properties and superior processability. Nevertheless, there are additional reasons that contribute to arouse the scientific interest around these materials. Among these, the large variety of chemical modifications that [...] Read more.

Certainly, the success of polythiophenes is due in the first place to their outstanding electronic properties and superior processability. Nevertheless, there are additional reasons that contribute to arouse the scientific interest around these materials. Among these, the large variety of chemical modifications that is possible to perform on the thiophene ring is a precious aspect. In particular, a turning point was marked by the diffusion of synthetic strategies for the preparation of terthiophenes: the vast richness of approaches today available for the easy customization of these structures allows the finetuning of their chemical, physical, and optical properties. Therefore, terthiophene derivatives have become an extremely versatile class of compounds both for direct application or for the preparation of electronic functional polymers. Moreover, their biocompatibility and ease of functionalization make them appealing for biology and medical research, as it testifies to the blossoming of studies in these fields in which they are involved. It is thus with the willingness to guide the reader through all the possibilities offered by these structures that this review elucidates the synthetic methods and describes the full chemical variety of terthiophenes and their derivatives. In the final part, an in-depth presentation of their numerous bioapplications intends to provide a complete picture of the state of the art. Full article

(This article belongs to the Special Issue Applied Conductive Polymer Materials)

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23 pages, 6016 KiB

Open AccessEditor’s ChoiceReview

Biopolymers for Biological Control of Plant Pathogens: Advances in Microencapsulation of Beneficial Microorganisms

by Roohallah Saberi-Riseh, Mojde Moradi-Pour, Reza Mohammadinejad and Vijay Kumar Thakur

Polymers 2021, 13(12), 1938; https://doi.org/10.3390/polym13121938 - 10 Jun 2021

Cited by 61 | Viewed by 6945

Abstract

The use of biofertilizers, including biocontrol agents such as Pseudomonas and Bacillus in agriculture can increase soil characteristics and plant acquisition of nutrients and enhancement the efficiency of manure and mineral fertilizer. Despite the problems that liquid and solid formulations have in maintaining [...] Read more.

The use of biofertilizers, including biocontrol agents such as Pseudomonas and Bacillus in agriculture can increase soil characteristics and plant acquisition of nutrients and enhancement the efficiency of manure and mineral fertilizer. Despite the problems that liquid and solid formulations have in maintaining the viability of microbial agents, encapsulation can improve their application with extended shelf-life, and controlled release from formulations. Research into novel formulation methods especially encapsulation techniques has increased in recent years due to the mounting demand for microbial biological control. The application of polymeric materials in agriculture has developed recently as a replacement for traditional materials and considered an improvement in technological processes in the growing of crops. This study aims to overview of types of biopolymers and methods used for encapsulation of living biological control agents, especially microbial organisms. Full article

(This article belongs to the Special Issue Sustainable Polymers and Composites from Biorenewable Resources)

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26 pages, 2180 KiB

Open AccessEditor’s ChoiceReview

Closing the Loop with Keratin-Rich Fibrous Materials

by Simona Perța-Crișan, Claudiu Ștefan Ursachi, Simona Gavrilaș, Florin Oancea and Florentina-Daniela Munteanu

Polymers 2021, 13(11), 1896; https://doi.org/10.3390/polym13111896 - 7 Jun 2021

Cited by 25 | Viewed by 7691

Abstract

One of the agro-industry’s side streams that is widely met is the-keratin rich fibrous material that is becoming a waste product without valorization. Its management as a waste is costly, as the incineration of this type of waste constitutes high environmental concern. Considering [...] Read more.

One of the agro-industry’s side streams that is widely met is the-keratin rich fibrous material that is becoming a waste product without valorization. Its management as a waste is costly, as the incineration of this type of waste constitutes high environmental concern. Considering these facts, the keratin-rich waste can be considered as a treasure for the producers interested in the valorization of such slowly-biodegradable by-products. As keratin is a protein that needs harsh conditions for its degradation, and that in most of the cases its constitutive amino acids are destroyed, we review new extraction methods that are eco-friendly and cost-effective. The chemical and enzymatic extractions of keratin are compared and the optimization of the extraction conditions at the lab scale is considered. In this study, there are also considered the potential applications of the extracted keratin as well as the reuse of the by-products obtained during the extraction processes. Full article

(This article belongs to the Special Issue Renaissance of Fibers and Fibrous Materials)

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19 pages, 1135 KiB

Open AccessEditor’s ChoiceReview

Embracing Additive Manufacturing Technology through Fused Filament Fabrication for Antimicrobial with Enhanced Formulated Materials

by Waleed Ahmed, Sidra Siraj and Ali H. Al-Marzouqi

Polymers 2021, 13(9), 1523; https://doi.org/10.3390/polym13091523 - 9 May 2021

Cited by 30 | Viewed by 3683

Abstract

Antimicrobial materials produced by 3D Printing technology are very beneficial, especially for biomedical applications. Antimicrobial surfaces specifically with enhanced antibacterial property have been prepared using several quaternary salt-based agents, such as quaternary ammonium salts and metallic nanoparticles (NPs), such as copper and zinc, [...] Read more.

Antimicrobial materials produced by 3D Printing technology are very beneficial, especially for biomedical applications. Antimicrobial surfaces specifically with enhanced antibacterial property have been prepared using several quaternary salt-based agents, such as quaternary ammonium salts and metallic nanoparticles (NPs), such as copper and zinc, which are incorporated into a polymeric matrix mainly through copolymerization grafting and ionic exchange. This review compared different materials for their effectiveness in providing antimicrobial properties on surfaces. This study will help researchers choose the most suitable method of developing antimicrobial surfaces with the highest efficiency, which can be applied to develop products compatible with 3D Printing Technology. Full article

(This article belongs to the Special Issue Additive Manufacturing of Bio and Synthetic Polymers)

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44 pages, 5087 KiB

Open AccessEditor’s ChoiceReview

Dynamics & Spectroscopy with Neutrons—Recent Developments & Emerging Opportunities

by Kacper Drużbicki, Mattia Gaboardi and Felix Fernandez-Alonso

Polymers 2021, 13(9), 1440; https://doi.org/10.3390/polym13091440 - 29 Apr 2021

Cited by 8 | Viewed by 5557

Abstract

This work provides an up-to-date overview of recent developments in neutron spectroscopic techniques and associated computational tools to interrogate the structural properties and dynamical behavior of complex and disordered materials, with a focus on those of a soft and polymeric nature. These have [...] Read more.

This work provides an up-to-date overview of recent developments in neutron spectroscopic techniques and associated computational tools to interrogate the structural properties and dynamical behavior of complex and disordered materials, with a focus on those of a soft and polymeric nature. These have and continue to pave the way for new scientific opportunities simply thought unthinkable not so long ago, and have particularly benefited from advances in high-resolution, broadband techniques spanning energy transfers from the meV to the eV. Topical areas include the identification and robust assignment of low-energy modes underpinning functionality in soft solids and supramolecular frameworks, or the quantification in the laboratory of hitherto unexplored nuclear quantum effects dictating thermodynamic properties. In addition to novel classes of materials, we also discuss recent discoveries around water and its phase diagram, which continue to surprise us. All throughout, emphasis is placed on linking these ongoing and exciting experimental and computational developments to specific scientific questions in the context of the discovery of new materials for sustainable technologies. Full article

(This article belongs to the Special Issue Polymers and Soft Matter: From Synthesis to Structure & Dynamics)

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31 pages, 5569 KiB

Open AccessEditor’s ChoiceReview

Polymer-Based Smart Drug Delivery Systems for Skin Application and Demonstration of Stimuli-Responsiveness

by Louise Van Gheluwe, Igor Chourpa, Coline Gaigne and Emilie Munnier

Polymers 2021, 13(8), 1285; https://doi.org/10.3390/polym13081285 - 15 Apr 2021

Cited by 61 | Viewed by 9455

Abstract

Progress in recent years in the field of stimuli-responsive polymers, whose properties change depending on the intensity of a signal, permitted an increase in smart drug delivery systems (SDDS). SDDS have attracted the attention of the scientific community because they can help meet [...] Read more.

Progress in recent years in the field of stimuli-responsive polymers, whose properties change depending on the intensity of a signal, permitted an increase in smart drug delivery systems (SDDS). SDDS have attracted the attention of the scientific community because they can help meet two current challenges of the pharmaceutical industry: targeted drug delivery and personalized medicine. Controlled release of the active ingredient can be achieved through various stimuli, among which are temperature, pH, redox potential or even enzymes. SDDS, hitherto explored mainly in oncology, are now developed in the fields of dermatology and cosmetics. They are mostly hydrogels or nanosystems, and the most-used stimuli are pH and temperature. This review offers an overview of polymer-based SDDS developed to trigger the release of active ingredients intended to treat skin conditions or pathologies. The methods used to attest to stimuli-responsiveness in vitro, ex vivo and in vivo are discussed. Full article

(This article belongs to the Special Issue Smart-Polymer-Based Systems for Drug Delivery)

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13 pages, 11050 KiB

Open AccessEditor’s ChoiceReview

Advances in Liquid Crystalline Epoxy Resins for High Thermal Conductivity

by Younggi Hong and Munju Goh

Polymers 2021, 13(8), 1302; https://doi.org/10.3390/polym13081302 - 15 Apr 2021

Cited by 31 | Viewed by 6361

Abstract

Epoxy resin (EP) is one of the most famous thermoset materials. In general, because EP has a three-dimensional random network, it possesses thermal properties similar to those of a typical heat insulator. Recently, there has been substantial interest in controlling the network structure [...] Read more.

Epoxy resin (EP) is one of the most famous thermoset materials. In general, because EP has a three-dimensional random network, it possesses thermal properties similar to those of a typical heat insulator. Recently, there has been substantial interest in controlling the network structure of EP to create new functionalities. Indeed, the modified EP, represented as liquid crystalline epoxy (LCE), is considered promising for producing novel functionalities, which cannot be obtained from conventional EPs, by replacing the random network structure with an oriented one. In this paper, we review the current progress in the field of LCEs and their application to highly thermally conductive composite materials. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials)

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42 pages, 7541 KiB

Open AccessEditor’s ChoiceReview

Exploring the Potential Application of Matrimid^® and ZIFs-Based Membranes for Hydrogen Recovery: A Review

by Pablo Fernández-Castro, Alfredo Ortiz and Daniel Gorri

Polymers 2021, 13(8), 1292; https://doi.org/10.3390/polym13081292 - 15 Apr 2021

Cited by 13 | Viewed by 3288

Abstract

Hydrogen recovery is at the center of the energy transition guidelines promoted by governments, owing to its applicability as an energy resource, but calls for energetically nonintensive recovery methods. The employment of polymeric membranes in selective gas separations has arisen as a potential [...] Read more.

Hydrogen recovery is at the center of the energy transition guidelines promoted by governments, owing to its applicability as an energy resource, but calls for energetically nonintensive recovery methods. The employment of polymeric membranes in selective gas separations has arisen as a potential alternative, as its established commercial availability demonstrates. However, enhanced features need to be developed to achieve adequate mechanical properties and the membrane performance that allows the obtention of hydrogen with the required industrial purity. Matrimid^®, as a polyimide, is an attractive material providing relatively good performance to selectively recover hydrogen. As a consequence, this review aims to study and summarize the main results, mechanisms involved and advances in the use of Matrimid^® as a selective material for hydrogen separation to date, delving into membrane fabrication procedures that increase the effectiveness of hydrogen recovery, i.e., the addition of fillers (within which ZIFs have acquired extraordinary importance), chemical crosslinking or polymeric blending, among others. Full article

(This article belongs to the Section Polymer Applications)

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23 pages, 1698 KiB

Open AccessEditor’s ChoiceReview

Near-Field Electrospinning and Melt Electrowriting of Biomedical Polymers—Progress and Limitations

by William E. King and Gary L. Bowlin

Polymers 2021, 13(7), 1097; https://doi.org/10.3390/polym13071097 - 30 Mar 2021

Cited by 31 | Viewed by 5517

Abstract

Near-field electrospinning (NFES) and melt electrowriting (MEW) are the process of extruding a fiber due to the force exerted by an electric field and collecting the fiber before bending instabilities occur. When paired with precise relative motion between the polymer source and the [...] Read more.

Near-field electrospinning (NFES) and melt electrowriting (MEW) are the process of extruding a fiber due to the force exerted by an electric field and collecting the fiber before bending instabilities occur. When paired with precise relative motion between the polymer source and the collector, a fiber can be directly written as dictated by preprogrammed geometry. As a result, this precise fiber control results in another dimension of scaffold tailorability for biomedical applications. In this review, biomedically relevant polymers that to date have manufactured fibers by NFES/MEW are explored and the present limitations in direct fiber writing of standardization in published setup details, fiber write throughput, and increased ease in the creation of complex scaffold geometries are discussed. Full article

(This article belongs to the Section Polymer Applications)

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26 pages, 4253 KiB

Open AccessEditor’s ChoiceReview

A Review of Wet Compounding of Cellulose Nanocomposites

by Craig Clemons and Ronald Sabo

Polymers 2021, 13(6), 911; https://doi.org/10.3390/polym13060911 - 16 Mar 2021

Cited by 14 | Viewed by 4092

Abstract

Cellulose nanomaterials (CNs) are an emerging class of materials with numerous potential applications, including as additives or reinforcements for thermoplastics. Unfortunately, the preparation of CNs typically results in dilute, aqueous suspensions, and the lack of efficient water removal methods has hindered commercialization. However, [...] Read more.

Cellulose nanomaterials (CNs) are an emerging class of materials with numerous potential applications, including as additives or reinforcements for thermoplastics. Unfortunately, the preparation of CNs typically results in dilute, aqueous suspensions, and the lack of efficient water removal methods has hindered commercialization. However, water may also present opportunities for improving overall efficiencies if its potential is better understood and if it is better managed through the various stages of CN and composite production. Wet compounding represents one such possible opportunity by leveraging water’s ability to aid in CN dispersion, act as a transport medium for metering and feeding of CNs, plasticize some polymers, or potentially facilitate the preparation of CNs during compounding. However, there are also considerable challenges and much investigation remains. Here, we review various wet compounding approaches used in the preparation of cellulose nanocomposites as well as the related concepts of wet feeding and wet extrusion fibrillation of cellulose. We also discuss potential opportunities, remaining challenges, and research and development needs with the ultimate goal of developing a more integrated approach to cellulose nanocomposite preparation and a more sophisticated understanding of water’s role in the compounding process. Full article

(This article belongs to the Special Issue Nanocellulose: Polymer Nanocomposites and all-Cellulose Materials)

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22 pages, 3126 KiB

Open AccessEditor’s ChoiceReview

What Fate for Plastics in Artworks? An Overview of Their Identification and Degradative Behaviour

by Massimo Lazzari and Daniela Reggio

Polymers 2021, 13(6), 883; https://doi.org/10.3390/polym13060883 - 13 Mar 2021

Cited by 12 | Viewed by 4296

Abstract

This review is conceived as a guide for material science researchers and conservators aiming to face the problem of deterioration of contemporary artworks entirely or partially made of plastics. It initially illustrates the analytical approaches for identifying polymeric material components in 3D art [...] Read more.

This review is conceived as a guide for material science researchers and conservators aiming to face the problem of deterioration of contemporary artworks entirely or partially made of plastics. It initially illustrates the analytical approaches for identifying polymeric material components in 3D art objects, such as sculptures and installations, and provides a perspective of their limits and advantages. Subsequently, the methodologies used for studying the deterioration of contemporary art plastics are reviewed, emphasising the main effects of the different types of degradation (i.e., migration of additives, oxidation and hydrolysis) and suggesting the appropriate techniques for their detection. Finally, the application of artificial ageing tests is critically assessed. All the concepts are elaborated through case studies and examples. Full article

(This article belongs to the Special Issue Historical Synthetic Polymers: Recent Advances in the Characterization and Preservation of Cultural Heritage)

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18 pages, 64135 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in Natural Functional Biopolymers and Their Applications of Electronic Skins and Flexible Strain Sensors

by Ziying Wang, Zongtao Ma, Jingyao Sun, Yuhua Yan, Miaomiao Bu, Yanming Huo, Yun-Fei Li and Ning Hu

Polymers 2021, 13(5), 813; https://doi.org/10.3390/polym13050813 - 6 Mar 2021

Cited by 49 | Viewed by 7054

Abstract

In order to replace nonrenewable resources and decrease electronic waste disposal, there is a rapidly rising demand for the utilization of reproducible and degradable biopolymers in flexible electronics. Natural biopolymers have many remarkable characteristics, including light weight, excellent mechanical properties, biocompatibility, non-toxicity, low [...] Read more.

In order to replace nonrenewable resources and decrease electronic waste disposal, there is a rapidly rising demand for the utilization of reproducible and degradable biopolymers in flexible electronics. Natural biopolymers have many remarkable characteristics, including light weight, excellent mechanical properties, biocompatibility, non-toxicity, low cost, etc. Thanks to these superior merits, natural functional biopolymers can be designed and optimized for the development of high-performance flexible electronic devices. Herein, we provide an insightful overview of the unique structures, properties and applications of biopolymers for electronic skins (e-skins) and flexible strain sensors. The relationships between properties and sensing performances of biopolymers-based sensors are also investigated. The functional design strategies and fabrication technologies for biopolymers-based flexible sensors are proposed. Furthermore, the research progresses of biopolymers-based sensors with various functions are described in detail. Finally, we provide some useful viewpoints and future prospects of developing biopolymers-based flexible sensors. Full article

(This article belongs to the Special Issue Functional Polymer Composites)

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15 pages, 2746 KiB

Open AccessEditor’s ChoiceReview

A Review: Research Progress in Modification of Poly (Lactic Acid) by Lignin and Cellulose

by Sixiang Zhai, Qingying Liu, Yuelong Zhao, Hui Sun, Biao Yang and Yunxuan Weng

Polymers 2021, 13(5), 776; https://doi.org/10.3390/polym13050776 - 3 Mar 2021

Cited by 25 | Viewed by 4730

Abstract

With the depletion of petroleum energy, the possibility of prices of petroleum-based materials increasing, and increased environmental awareness, biodegradable materials as a kind of green alternative have attracted more and more research attention. In this context, poly (lactic acid) has shown a unique [...] Read more.

With the depletion of petroleum energy, the possibility of prices of petroleum-based materials increasing, and increased environmental awareness, biodegradable materials as a kind of green alternative have attracted more and more research attention. In this context, poly (lactic acid) has shown a unique combination of properties such as nontoxicity, biodegradability, biocompatibility, and good workability. However, examples of its known drawbacks include poor tensile strength, low elongation at break, poor thermal properties, and low crystallization rate. Lignocellulosic materials such as lignin and cellulose have excellent biodegradability and mechanical properties. Compounding such biomass components with poly (lactic acid) is expected to prepare green composite materials with improved properties of poly (lactic acid). This paper is aimed at summarizing the research progress of modification of poly (lactic acid) with lignin and cellulose made in in recent years, with emphasis on effects of lignin and cellulose on mechanical properties, thermal stability and crystallinity on poly (lactic acid) composite materials. Development of poly (lactic acid) composite materials in this respect is forecasted. Full article

(This article belongs to the Special Issue Design and Modification of Bio-Based Polymers, Blends and Composites)

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18 pages, 3268 KiB

Open AccessEditor’s ChoiceReview

Review of Technologies and Materials Used in High-Voltage Film Capacitors

by Olatoundji Georges Gnonhoue, Amanda Velazquez-Salazar, Éric David and Ioana Preda

Polymers 2021, 13(5), 766; https://doi.org/10.3390/polym13050766 - 28 Feb 2021

Cited by 43 | Viewed by 9946

Abstract

High-voltage capacitors are key components for circuit breakers and monitoring and protection devices, and are important elements used to improve the efficiency and reliability of the grid. Different technologies are used in high-voltage capacitor manufacturing process, and at all stages of this process [...] Read more.

High-voltage capacitors are key components for circuit breakers and monitoring and protection devices, and are important elements used to improve the efficiency and reliability of the grid. Different technologies are used in high-voltage capacitor manufacturing process, and at all stages of this process polymeric films must be used, along with an encapsulating material, which can be either liquid, solid or gaseous. These materials play major roles in the lifespan and reliability of components. In this paper, we present a review of the different technologies used to manufacture high-voltage capacitors, as well as the different materials used in fabricating high-voltage film capacitors, with a view to establishing a bibliographic database that will allow a comparison of the different technologies Full article

(This article belongs to the Special Issue Dielectric Polymers)

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31 pages, 3339 KiB

Open AccessEditor’s ChoiceReview

Polymeric Nanoparticles for Antimicrobial Therapies: An up-to-date Overview

by Vera Alexandra Spirescu, Cristina Chircov, Alexandru Mihai Grumezescu and Ecaterina Andronescu

Polymers 2021, 13(5), 724; https://doi.org/10.3390/polym13050724 - 27 Feb 2021

Cited by 102 | Viewed by 5936

Abstract

Despite the many advancements in the pharmaceutical and medical fields and the development of numerous antimicrobial drugs aimed to suppress and destroy pathogenic microorganisms, infectious diseases still represent a major health threat affecting millions of lives daily. In addition to the limitations of [...] Read more.

Despite the many advancements in the pharmaceutical and medical fields and the development of numerous antimicrobial drugs aimed to suppress and destroy pathogenic microorganisms, infectious diseases still represent a major health threat affecting millions of lives daily. In addition to the limitations of antimicrobial drugs associated with low transportation rate, water solubility, oral bioavailability and stability, inefficient drug targeting, considerable toxicity, and limited patient compliance, the major cause for their inefficiency is the antimicrobial resistance of microorganisms. In this context, the risk of a pre-antibiotic era is a real possibility. For this reason, the research focus has shifted toward the discovery and development of novel and alternative antimicrobial agents that could overcome the challenges associated with conventional drugs. Nanotechnology is a possible alternative, as there is significant evidence of the broad-spectrum antimicrobial activity of nanomaterials and nanoparticles in particular. Moreover, owing to their considerable advantages regarding their efficient cargo dissolving, entrapment, encapsulation, or surface attachment, the possibility of forming antimicrobial groups for specific targeting and destruction, biocompatibility and biodegradability, low toxicity, and synergistic therapy, polymeric nanoparticles have received considerable attention as potential antimicrobial drug delivery agents. In this context, the aim of this paper is to provide an up-to-date overview of the most recent studies investigating polymeric nanoparticles designed for antimicrobial therapies, describing both their targeting strategies and their effects. Full article

(This article belongs to the Special Issue Biopolymers for Biomedical Applications II)

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28 pages, 7637 KiB

Open AccessEditor’s ChoiceReview

Nature of Carbon Black Reinforcement of Rubber: Perspective on the Original Polymer Nanocomposite

by Christopher G. Robertson and Ned J. Hardman

Polymers 2021, 13(4), 538; https://doi.org/10.3390/polym13040538 - 12 Feb 2021

Cited by 139 | Viewed by 18873

Abstract

Adding carbon black (CB) particles to elastomeric polymers is essential to the successful industrial use of rubber in many applications, and the mechanical reinforcing effect of CB in rubber has been studied for nearly 100 years. Despite these many decades of investigations, the [...] Read more.

Adding carbon black (CB) particles to elastomeric polymers is essential to the successful industrial use of rubber in many applications, and the mechanical reinforcing effect of CB in rubber has been studied for nearly 100 years. Despite these many decades of investigations, the origin of stiffness enhancement of elastomers from incorporating nanometer-scale CB particles is still debated. It is not universally accepted whether the interactions between polymer chains and CB surfaces are purely physical adsorption or whether some polymer–particle chemical bonds are also introduced in the process of mixing and curing the CB-filled rubber compounds. We review key experimental observations of rubber reinforced with CB, including the finding that heat treatment of CB can greatly reduce the filler reinforcement effect in rubber. The details of the particle morphology and surface chemistry are described to give insights into the nature of the CB–elastomer interfaces. This is followed by a discussion of rubber processing effects, the influence of CB on crosslinking, and various chemical modification approaches that have been employed to improve polymer–filler interactions and reinforcement. Finally, we contrast various models that have been proposed for rationalizing the CB reinforcement of elastomers. Full article

(This article belongs to the Special Issue Rubber Materials: Processes, Structures and Applications)

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24 pages, 4041 KiB

Open AccessEditor’s ChoiceReview

Greener, Faster, Stronger: The Benefits of Deep Eutectic Solvents in Polymer and Materials Science

by Yeasmin Nahar and Stuart C. Thickett

Polymers 2021, 13(3), 447; https://doi.org/10.3390/polym13030447 - 30 Jan 2021

Cited by 93 | Viewed by 11391

Abstract

Deep eutectic solvents (DESs) represent an emergent class of green designer solvents that find numerous applications in different aspects of chemical synthesis. A particularly appealing aspect of DES systems is their simplicity of preparation, combined with inexpensive, readily available starting materials to yield [...] Read more.

Deep eutectic solvents (DESs) represent an emergent class of green designer solvents that find numerous applications in different aspects of chemical synthesis. A particularly appealing aspect of DES systems is their simplicity of preparation, combined with inexpensive, readily available starting materials to yield solvents with appealing properties (negligible volatility, non-flammability and high solvation capacity). In the context of polymer science, DES systems not only offer an appealing route towards replacing hazardous volatile organic solvents (VOCs), but can serve multiple roles including those of solvent, monomer and templating agent—so called “polymerizable eutectics.” In this review, we look at DES systems and polymerizable eutectics and their application in polymer materials synthesis, including various mechanisms of polymer formation, hydrogel design, porous monoliths, and molecularly imprinted polymers. We provide a comparative study of these systems alongside traditional synthetic approaches, highlighting not only the benefit of replacing VOCs from the perspective of environmental sustainability, but also the materials advantage with respect to mechanical and thermal properties of the polymers formed. Full article

(This article belongs to the Special Issue Sustainable Monomers, Catalysts, Polymers and Polymer-Based Materials)

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13 pages, 4449 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Responsive Nanostructured Polymer Particles

by Kang Hee Ku

Polymers 2021, 13(2), 273; https://doi.org/10.3390/polym13020273 - 15 Jan 2021

Cited by 7 | Viewed by 4301

Abstract

Responsive polymer particles with switchable properties are of great importance for designing smart materials in various applications. Recently, the self-assembly of block copolymers (BCPs) and polymer blends within evaporative emulsions has led to advances in the shape-controlled synthesis of polymer particles. Despite extensive [...] Read more.

Responsive polymer particles with switchable properties are of great importance for designing smart materials in various applications. Recently, the self-assembly of block copolymers (BCPs) and polymer blends within evaporative emulsions has led to advances in the shape-controlled synthesis of polymer particles. Despite extensive recent progress on BCP particles, the responsive shape tuning of BCP particles and their applications have received little attention. This review provides a brief overview of recent approaches to developing non-spherical polymer particles from soft evaporative emulsions based on the physical principles affecting both particle shape and inner structure. Special attention is paid to the stimuli-responsive, shape-changing nanostructured polymer particles, i.e., design of polymers and surfactant pairs, detailed experimental results, and their applications, including the state-of-the-art progress in this field. Finally, the perspectives on current challenges and future directions in this research field are presented, including the development of surfactants with higher reversibility to multiple stimuli and polymers with unique structural functionality, and diversification of polymer architectures. Full article

(This article belongs to the Special Issue Self-Assembled Functional Macromolecular Materials)

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30 pages, 5422 KiB

Open AccessEditor’s ChoiceReview

Insight into the Structure and Dynamics of Polymers by Neutron Scattering Combined with Atomistic Molecular Dynamics Simulations

by Arantxa Arbe, Fernando Alvarez and Juan Colmenero

Polymers 2020, 12(12), 3067; https://doi.org/10.3390/polym12123067 - 21 Dec 2020

Cited by 18 | Viewed by 3842

Abstract

Combining neutron scattering and fully atomistic molecular dynamics simulations allows unraveling structural and dynamical features of polymer melts at different length scales, mainly in the intermolecular and monomeric range. Here we present the methodology developed by us and the results of its application [...] Read more.

Combining neutron scattering and fully atomistic molecular dynamics simulations allows unraveling structural and dynamical features of polymer melts at different length scales, mainly in the intermolecular and monomeric range. Here we present the methodology developed by us and the results of its application during the last years in a variety of polymers. This methodology is based on two pillars: (i) both techniques cover approximately the same length and time scales and (ii) the classical van Hove formalism allows easily calculating the magnitudes measured by neutron scattering from the simulated atomic trajectories. By direct comparison with experimental results, the simulated cell is validated. Thereafter, the information of the simulations can be exploited, calculating magnitudes that are experimentally inaccessible or extending the parameters range beyond the experimental capabilities. We show how detailed microscopic insight on structural features and dynamical processes of various kinds has been gained in polymeric systems with different degrees of complexity, and how intriguing questions as the collective behavior at intermediate length scales have been faced. Full article

(This article belongs to the Special Issue State-of-the-Art Polymer Science and Technology in Spain (2020,2021))

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23 pages, 4723 KiB

Open AccessEditor’s ChoiceReview

Advancements in the Blood–Brain Barrier Penetrating Nanoplatforms for Brain Related Disease Diagnostics and Therapeutic Applications

by Suresh Thangudu, Fong-Yu Cheng and Chia-Hao Su

Polymers 2020, 12(12), 3055; https://doi.org/10.3390/polym12123055 - 20 Dec 2020

Cited by 44 | Viewed by 8010

Abstract

Noninvasive treatments to treat the brain-related disorders have been paying more significant attention and it is an emerging topic. However, overcoming the blood brain barrier (BBB) is a key obstacle to most of the therapeutic drugs to enter into the brain tissue, which [...] Read more.

Noninvasive treatments to treat the brain-related disorders have been paying more significant attention and it is an emerging topic. However, overcoming the blood brain barrier (BBB) is a key obstacle to most of the therapeutic drugs to enter into the brain tissue, which significantly results in lower accumulation of therapeutic drugs in the brain. Thus, administering the large quantity/doses of drugs raises more concerns of adverse side effects. Nanoparticle (NP)-mediated drug delivery systems are seen as potential means of enhancing drug transport across the BBB and to targeted brain tissue. These systems offer more accumulation of therapeutic drugs at the tumor site and prolong circulation time in the blood. In this review, we summarize the current knowledge and advancements on various nanoplatforms (NF) and discusses the use of nanoparticles for successful cross of BBB to treat the brain-related disorders such as brain tumors, Alzheimer’s disease, Parkinson’s disease, and stroke. Full article

(This article belongs to the Special Issue Intelligent Polymeric Delivery System for Biomedical Applications)

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18 pages, 2685 KiB

Open AccessEditor’s ChoiceReview

Photo-Crosslinked Silk Fibroin for 3D Printing

by Xuan Mu, Jugal Kishore Sahoo, Peggy Cebe and David L. Kaplan

Polymers 2020, 12(12), 2936; https://doi.org/10.3390/polym12122936 - 9 Dec 2020

Cited by 65 | Viewed by 9828

Abstract

Silk fibroin in material formats provides robust mechanical properties, and thus is a promising protein for 3D printing inks for a range of applications, including tissue engineering, bioelectronics, and bio-optics. Among the various crosslinking mechanisms, photo-crosslinking is particularly useful for 3D printing with [...] Read more.

Silk fibroin in material formats provides robust mechanical properties, and thus is a promising protein for 3D printing inks for a range of applications, including tissue engineering, bioelectronics, and bio-optics. Among the various crosslinking mechanisms, photo-crosslinking is particularly useful for 3D printing with silk fibroin inks due to the rapid kinetics, tunable crosslinking dynamics, light-assisted shape control, and the option to use visible light as a biocompatible processing condition. Multiple photo-crosslinking approaches have been applied to native or chemically modified silk fibroin, including photo-oxidation and free radical methacrylate polymerization. The molecular characteristics of silk fibroin, i.e., conformational polymorphism, provide a unique method for crosslinking and microfabrication via light. The molecular design features of silk fibroin inks and the exploitation of photo-crosslinking mechanisms suggest the exciting potential for meeting many biomedical needs in the future. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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36 pages, 7444 KiB

Open AccessEditor’s ChoiceReview

Polysaccharide-Based In Situ Self-Healing Hydrogels for Tissue Engineering Applications

by Sheila Maiz-Fernández, Leyre Pérez-Álvarez, Leire Ruiz-Rubio, Jose Luis Vilas-Vilela and Senentxu Lanceros-Mendez

Polymers 2020, 12(10), 2261; https://doi.org/10.3390/polym12102261 - 1 Oct 2020

Cited by 38 | Viewed by 6054

Abstract

In situ hydrogels have attracted increasing interest in recent years due to the need to develop effective and practical implantable platforms. Traditional hydrogels require surgical interventions to be implanted and are far from providing personalized medicine applications. However, in situ hydrogels offer a [...] Read more.

In situ hydrogels have attracted increasing interest in recent years due to the need to develop effective and practical implantable platforms. Traditional hydrogels require surgical interventions to be implanted and are far from providing personalized medicine applications. However, in situ hydrogels offer a wide variety of advantages, such as a non-invasive nature due to their localized action or the ability to perfectly adapt to the place to be replaced regardless the size, shape or irregularities. In recent years, research has particularly focused on in situ hydrogels based on natural polysaccharides due to their promising properties such as biocompatibility, biodegradability and their ability to self-repair. This last property inspired in nature gives them the possibility of maintaining their integrity even after damage, owing to specific physical interactions or dynamic covalent bonds that provide reversible linkages. In this review, the different self-healing mechanisms, as well as the latest research on in situ self-healing hydrogels, is presented, together with the potential applications of these materials in tissue regeneration. Full article

(This article belongs to the Special Issue In-Situ Forming and Self-Healing Hydrogels)

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36 pages, 4245 KiB

Open AccessEditor’s ChoiceReview

Fish Collagen: Extraction, Characterization, and Applications for Biomaterials Engineering

by Hafez Jafari, Alberto Lista, Manuela Mafosso Siekapen, Pejman Ghaffari-Bohlouli, Lei Nie, Houman Alimoradi and Amin Shavandi

Polymers 2020, 12(10), 2230; https://doi.org/10.3390/polym12102230 - 28 Sep 2020

Cited by 235 | Viewed by 36206

Abstract

The utilization of marine-based collagen is growing fast due to its unique properties in comparison with mammalian-based collagen such as no risk of transmitting diseases, a lack of religious constraints, a cost-effective process, low molecular weight, biocompatibility, and its easy absorption by the [...] Read more.

The utilization of marine-based collagen is growing fast due to its unique properties in comparison with mammalian-based collagen such as no risk of transmitting diseases, a lack of religious constraints, a cost-effective process, low molecular weight, biocompatibility, and its easy absorption by the human body. This article presents an overview of the recent studies from 2014 to 2020 conducted on collagen extraction from marine-based materials, in particular fish by-products. The fish collagen structure, extraction methods, characterization, and biomedical applications are presented. More specifically, acetic acid and deep eutectic solvent (DES) extraction methods for marine collagen isolation are described and compared. In addition, the effect of the extraction parameters (temperature, acid concentration, extraction time, solid-to-liquid ratio) on the yield of collagen is investigated. Moreover, biomaterials engineering and therapeutic applications of marine collagen have been summarized. Full article

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

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44 pages, 9288 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in the Synthesis and Application of Polymer Compartments for Catalysis

by Tai-Lam Nghiem, Deniz Coban, Stefanie Tjaberings and André H. Gröschel

Polymers 2020, 12(10), 2190; https://doi.org/10.3390/polym12102190 - 24 Sep 2020

Cited by 30 | Viewed by 8458

Abstract

Catalysis is one of the most important processes in nature, science, and technology, that enables the energy efficient synthesis of essential organic compounds, pharmaceutically active substances, and molecular energy sources. In nature, catalytic reactions typically occur in aqueous environments involving multiple catalytic sites. [...] Read more.

Catalysis is one of the most important processes in nature, science, and technology, that enables the energy efficient synthesis of essential organic compounds, pharmaceutically active substances, and molecular energy sources. In nature, catalytic reactions typically occur in aqueous environments involving multiple catalytic sites. To prevent the deactivation of catalysts in water or avoid unwanted cross-reactions, catalysts are often site-isolated in nanopockets or separately stored in compartments. These concepts have inspired the design of a range of synthetic nanoreactors that allow otherwise unfeasible catalytic reactions in aqueous environments. Since the field of nanoreactors is evolving rapidly, we here summarize—from a personal perspective—prominent and recent examples for polymer nanoreactors with emphasis on their synthesis and their ability to catalyze reactions in dispersion. Examples comprise the incorporation of catalytic sites into hydrophobic nanodomains of single chain polymer nanoparticles, molecular polymer nanoparticles, and block copolymer micelles and vesicles. We focus on catalytic reactions mediated by transition metal and organocatalysts, and the separate storage of multiple catalysts for one-pot cascade reactions. Efforts devoted to the field of nanoreactors are relevant for catalytic chemistry and nanotechnology, as well as the synthesis of pharmaceutical and natural compounds. Optimized nanoreactors will aid in the development of more potent catalytic systems for green and fast reaction sequences contributing to sustainable chemistry by reducing waste of solvents, reagents, and energy. Full article

(This article belongs to the Collection The Next Generation in Polymer Research)

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25 pages, 2124 KiB

Open AccessEditor’s ChoiceReview

The Potential for Bio-Sustainable Organobromine-Containing Flame Retardant Formulations for Textile Applications—A Review

by A Richard Horrocks

Polymers 2020, 12(9), 2160; https://doi.org/10.3390/polym12092160 - 22 Sep 2020

Cited by 36 | Viewed by 4955

Abstract

This review considers the challenge of developing sustainable organobromine flame retardants (BrFRs) and alternative synergists to the predominantly used antimony III oxide. Current BrFR efficiencies are reviewed for textile coatings and back-coatings with a focus on furnishing and similar fabrics covering underlying flammable [...] Read more.

This review considers the challenge of developing sustainable organobromine flame retardants (BrFRs) and alternative synergists to the predominantly used antimony III oxide. Current BrFR efficiencies are reviewed for textile coatings and back-coatings with a focus on furnishing and similar fabrics covering underlying flammable fillings, such as flexible polyurethane foam. The difficulty of replacing them with non-halogen-containing systems is also reviewed with major disadvantages including their extreme specificity with regard to a given textile type and poor durability.The possibility of replacing currently used BrFRs for textiles structures that mimic naturally occurring organobromine-containing species is discussed, noting that of the nearly 2000 such species identified in both marine and terrestrial environments, a significant number are functionalised polybrominated diphenyl ethers, which form part of a series of little understood biosynthetic biodegradation cycles.The continued use of antimony III oxide as synergist and possible replacement by alternatives, such as the commercially available zinc stannates and the recently identified zinc tungstate, are discussed. Both are effective as synergists and smoke suppressants, but unlike Sb₂0₃, they have efficiencies dependent on BrFR chemistry and polymer matrix or textile structure. Furthermore, their effectiveness in textile coatings has yet to be more fully assessed.In conclusion, it is proposed that the future of sustainable BrFRs should be based on naturally occurring polybrominated structures developed in conjunction with non-toxic, smoke-suppressing synergists such as the zinc stannates or zinc tungstate, which have been carefully tailored for given polymeric and textile substrates. Full article

(This article belongs to the Special Issue Advances in Flame Retardant Polymeric Materials)

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21 pages, 883 KiB

Open AccessEditor’s ChoiceReview

A Review on Citric Acid as Green Modifying Agent and Binder for Wood

by Seng Hua Lee, Paridah Md Tahir, Wei Chen Lum, Li Peng Tan, Paiman Bawon, Byung-Dae Park, Syeed SaifulAzry Osman Al Edrus and Ummi Hani Abdullah

Polymers 2020, 12(8), 1692; https://doi.org/10.3390/polym12081692 - 29 Jul 2020

Cited by 65 | Viewed by 9963

Abstract

Citric acid (CA) can be found naturally in fruits and vegetables, particularly citrus fruit. CA is widely used in many fields but its usage as a green modifying agent and binder for wood is barely addressed. Esterification is one of the most common [...] Read more.

Citric acid (CA) can be found naturally in fruits and vegetables, particularly citrus fruit. CA is widely used in many fields but its usage as a green modifying agent and binder for wood is barely addressed. Esterification is one of the most common chemical reactions applied in wood modification. CA contains three carboxyl groups, making it possible to attain at least two esterification reactions that are required for crosslinking when reacting with the hydroxyl groups of the cell wall polymers. In addition, the reaction could form ester linkages to bring adhesivity and good bonding characteristics, and therefore CA could be used as wood binder too. This paper presents a review concerning the usage of CA as a wood modifying agent and binder. For wood modification, the reaction mechanism between wood and CA and the pros and cons of using CA are discussed. CA and its combination with various reactants and their respective optimum parameters are also compiled in this paper. As for the major wood bonding component, the bonding mechanism and types of wood composites bonded with CA are presented. The best working conditions for the CA in the fabrication of wood-based panels are discussed. In addition, the environmental impacts and future outlook of CA-treated wood and bonded composite are also considered. Full article

(This article belongs to the Special Issue Recent Developments in Eco-Friendly Wood-Based Composites)

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17 pages, 3339 KiB

Open AccessEditor’s ChoiceReview

Bio-Polyethylene (Bio-PE), Bio-Polypropylene (Bio-PP) and Bio-Poly(ethylene terephthalate) (Bio-PET): Recent Developments in Bio-Based Polymers Analogous to Petroleum-Derived Ones for Packaging and Engineering Applications

by Valentina Siracusa and Ignazio Blanco

Polymers 2020, 12(8), 1641; https://doi.org/10.3390/polym12081641 - 23 Jul 2020

Cited by 279 | Viewed by 42594

Abstract

In recent year, there has been increasing concern about the growing amount of plastic waste coming from daily life. Different kinds of synthetic plastics are currently used for an extensive range of needs, but in order to reduce the impact of petroleum-based plastics [...] Read more.

In recent year, there has been increasing concern about the growing amount of plastic waste coming from daily life. Different kinds of synthetic plastics are currently used for an extensive range of needs, but in order to reduce the impact of petroleum-based plastics and material waste, considerable attention has been focused on “green” plastics. In this paper, we present a broad review on the advances in the research and development of bio-based polymers analogous to petroleum-derived ones. The main interest for the development of bio-based materials is the strong public concern about waste, pollution and carbon footprint. The sustainability of those polymers, for general and specific applications, is driven by the great progress in the processing technologies that refine biomass feedstocks in order to obtain bio-based monomers that are used as building blocks. At the same time, thanks to the industrial progress, it is possible to obtain more versatile and specific chemical structures in order to synthetize polymers with ad-hoc tailored properties and functionalities, with engineering applications that include packaging but also durable and electronic goods. In particular, three types of polymers were described in this review: Bio-polyethylene (Bio-PE), bio-polypropylene (Bio-PP) and Bio-poly(ethylene terephthalate) (Bio-PET). The recent advances in their development in terms of processing technologies, product development and applications, as well as their advantages and disadvantages, are reported. Full article

(This article belongs to the Special Issue Biopolymer Modifications and Characterization)

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18 pages, 5197 KiB

Open AccessEditor’s ChoiceReview

Application of Synchrotron Radiation X-ray Scattering and Spectroscopy to Soft Matter

by Atsushi Takahara, Yuji Higaki, Tomoyasu Hirai and Ryohei Ishige

Polymers 2020, 12(7), 1624; https://doi.org/10.3390/polym12071624 - 21 Jul 2020

Cited by 16 | Viewed by 6402

Abstract

Light produced by synchrotron radiation (SR) is much brighter than that produced by conventional laboratory X-ray sources. The photon energy of SR X-ray ranges from soft and tender X-rays to hard X-rays. Moreover, X-rays become element sensitive with decreasing photon energy. By using [...] Read more.

Light produced by synchrotron radiation (SR) is much brighter than that produced by conventional laboratory X-ray sources. The photon energy of SR X-ray ranges from soft and tender X-rays to hard X-rays. Moreover, X-rays become element sensitive with decreasing photon energy. By using a wide energy range and high-quality light of SR, different scattering and spectroscopic methods were applied to various soft matters. We present five of our recent studies performed using specific light properties of a synchrotron facility, which are as follows: (1) In situ USAXS study to understand the deformation behavior of colloidal crystals during uniaxial stretching; (2) structure characterization of semiconducting polymer thin films along the film thickness direction by grazing-incidence wide-angle X-ray scattering using tender X-rays; (3) X-ray absorption fine structure (XAFS) analysis of the formation mechanism of poly(3-hexylthiophene) (P3HT); (4) soft X-ray absorption and emission spectroscopic analysis of water structure in polyelectrolyte brushes; and (5) X-ray photon correlation spectroscopic analysis of the diffusion behavior of polystyrene-grafted nanoparticles dispersed in a polystyrene matrix. Full article

(This article belongs to the Collection The Next Generation in Polymer Research)

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20 pages, 8186 KiB

Open AccessEditor’s ChoiceReview

Structural Polymorphism of Single pDNA Condensates Elicited by Cationic Block Polyelectrolytes

by Kensuke Osada

Polymers 2020, 12(7), 1603; https://doi.org/10.3390/polym12071603 - 19 Jul 2020

Cited by 8 | Viewed by 3811

Abstract

DNA folding is a core phenomenon in genome packaging within a nucleus. Such a phenomenon is induced by polyelectrolyte complexation between anionic DNA and cationic proteins of histones. In this regard, complexes formed between DNA and cationic polyelectrolytes have been investigated as models [...] Read more.

DNA folding is a core phenomenon in genome packaging within a nucleus. Such a phenomenon is induced by polyelectrolyte complexation between anionic DNA and cationic proteins of histones. In this regard, complexes formed between DNA and cationic polyelectrolytes have been investigated as models to gain insight into genome packaging. Upon complexation, DNA undergoes folding to reduce its occupied volume, which often results in multi-complex associated aggregates. However, when cationic copolymers comprising a polycation block and a neutral hydrophilic polymer block are used instead, DNA undergoes folding as a single molecule within a spontaneously formed polyplex micelle (PM), thereby allowing the observation of the higher-order structures that DNA forms. The DNA complex forms polymorphic structures, including globular, rod-shaped, and ring-shaped (toroidal) structures. This review focuses on the polymorphism of DNA, particularly, to elucidate when, how, and why DNA organizes into these structures with cationic copolymers. The interactions between DNA and the copolymers, and the specific nature of DNA in rigidity; i.e., rigid but foldable, play significant roles in the observed polymorphism. Moreover, PMs serve as potential gene vectors for systemic application. The significance of the controlled DNA folding for such an application is addressed briefly in the last part. Full article

(This article belongs to the Special Issue Bio-Based Polyelectrolytes: Development and Applications)

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29 pages, 13876 KiB

Open AccessEditor’s ChoiceReview

Separation of Semiconducting Carbon Nanotubes Using Conjugated Polymer Wrapping

by Jingyi Wang and Ting Lei

Polymers 2020, 12(7), 1548; https://doi.org/10.3390/polym12071548 - 13 Jul 2020

Cited by 36 | Viewed by 7089

Abstract

In the past two decades, single-walled carbon nanotubes (SWNTs) have been explored for electronic applications because of their high charge carrier mobility, low-temperature solution processability and mechanical flexibility. Semiconducting SWNTs (s-SWNTs) are also considered an alternative to traditional silicon-based semiconductors. However, large-scale, as-produced [...] Read more.

In the past two decades, single-walled carbon nanotubes (SWNTs) have been explored for electronic applications because of their high charge carrier mobility, low-temperature solution processability and mechanical flexibility. Semiconducting SWNTs (s-SWNTs) are also considered an alternative to traditional silicon-based semiconductors. However, large-scale, as-produced SWNTs have poor solubility, and they are mixtures of metallic SWNTs (m-SWNTs) and s-SWNTs, which limits their practical applications. Conjugated polymer wrapping is a promising method to disperse and separate s-SWNTs, due to its high selectivity, high separation yield and simplicity of operation. In this review, we summarize the recent progress of the conjugated polymer wrapping method, and discuss possible separation mechanisms for s-SWNTs. We also discuss various parameters that may affect the selectivity and sorting yield. Finally, some electronic applications of polymer-sorted s-SWNTs are introduced. The aim of this review is to provide polymer chemist a basic concept of polymer based SWNT separation, as well as some polymer design strategies, influential factors and potential applications. Full article

(This article belongs to the Special Issue Conjugated Polymers and Polymer Networks with Unconventional Structural and Functional Features)

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