Polymers

16 pages, 4703 KB

Open AccessEditor’s ChoiceArticle

AI-Based Soft Module for Safe Human–Robot Interaction towards 4D Printing

by Ali Zolfagharian, Mohammad Reza Khosravani, Hoang Duong Vu, Minh Khoi Nguyen, Abbas Z. Kouzani and Mahdi Bodaghi

Polymers 2022, 14(16), 3302; https://doi.org/10.3390/polym14163302 - 13 Aug 2022

Cited by 12 | Viewed by 3498

Abstract

Soft robotic modules have potential use for therapeutic and educational purposes. To do so, they need to be safe, soft, smart, and customizable to serve individuals’ different preferences and personalities. A safe modular robotic product made of soft materials, particularly silicon, programmed by [...] Read more.

Soft robotic modules have potential use for therapeutic and educational purposes. To do so, they need to be safe, soft, smart, and customizable to serve individuals’ different preferences and personalities. A safe modular robotic product made of soft materials, particularly silicon, programmed by artificial intelligence algorithms and developed via additive manufacturing would be promising. This study focuses on the safe tactile interaction between humans and robots by means of soft material characteristics for translating physical communication to auditory. The embedded vibratory sensors used to stimulate touch senses transmitted through soft materials are presented. The soft module was developed and verified successfully to react to three different patterns of human–robot contact, particularly users’ touches, and then communicate the type of contact with sound. The study develops and verifies a model that can classify different tactile gestures via machine learning algorithms for safe human–robot physical interaction. The system accurately recognizes the gestures and shapes of three-dimensional (3D) printed soft modules. The gestures used for the experiment are the three most common, including slapping, squeezing, and tickling. The model builds on the concept of how safe human–robot physical interactions could help with cognitive and behavioral communication. In this context, the ability to measure, classify, and reflect the behavior of soft materials in robotic modules represents a prerequisite for endowing robotic materials in additive manufacturing for safe interaction with humans. Full article

(This article belongs to the Special Issue Frontiers in 3D and 4D Printing for Polymers and Polymeric Composites)

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17 pages, 9664 KB

Open AccessEditor’s ChoiceArticle

A Sustainable Approach to a Cleaner Production of Antimicrobial and Biocompatible Protein Fibers

by Angela Danila, Mariana Costea, Lenuta Profire, Cristina Mihaela Rimbu, Mihaela Baican, Florentina Lupascu, Simona-Maria Tatarusanu, Bianca-Stefania Profire and Emil-Ioan Muresan

Polymers 2022, 14(15), 3194; https://doi.org/10.3390/polym14153194 - 5 Aug 2022

Cited by 3 | Viewed by 2613

Abstract

This study presents the production, characterization, and application of celandine (Chelidonium majus L.) extracts (aqueous, acidic, alcoholic, and ultrasound) on wool fibers and their characterization. The study aims to obtain an ecologically dyed wool support that possesses biocompatible and antimicrobial activities. The [...] Read more.

This study presents the production, characterization, and application of celandine (Chelidonium majus L.) extracts (aqueous, acidic, alcoholic, and ultrasound) on wool fibers and their characterization. The study aims to obtain an ecologically dyed wool support that possesses biocompatible and antimicrobial activities. The plant extracts were characterized based on pH, total polyphenol content, and berberine content. Ecologically dyed wool supports were characterized based on scanning electron microscopy, levelness index, color measurements, contact angle indirect biocompatibility, and antibacterial analysis. According to the obtained results, celandine extract can be considered a potential candidate for the sustainable dyeing and functionalization of wool fibers. Full article

(This article belongs to the Special Issue Advances in Sustainable Polymers: Processing, Modeling, Properties and Applications)

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16 pages, 6424 KB

Open AccessEditor’s ChoiceArticle

Biochar Particles Obtained from Agricultural Carob Waste as a Suitable Filler for Sustainable Biocomposite Formulations

by Giulia Infurna, Luigi Botta, Marco Maniscalco, Elisabetta Morici, Giuseppe Caputo, Salvatore Marullo, Francesca D’Anna and Nadka Tz. Dintcheva

Polymers 2022, 14(15), 3075; https://doi.org/10.3390/polym14153075 - 29 Jul 2022

Cited by 16 | Viewed by 2940

Abstract

In the context of sustainable and circular economy, the recovery of biowaste for sustainable biocomposites formulation is a challenging issue. The aim of this work is to give a new life to agricultural carob waste after glucose extraction carried out by a local [...] Read more.

In the context of sustainable and circular economy, the recovery of biowaste for sustainable biocomposites formulation is a challenging issue. The aim of this work is to give a new life to agricultural carob waste after glucose extraction carried out by a local factory for carob candy production. A pyrolysis process was carried out on bio-waste to produce biofuel and, later, the solid residual fraction of pyrolysis process was used as interesting filler for biocomposites production. In this work, biochar particles (BC) as a pyrolysis product, after fuels recovery of organic biowaste, specifically, pyrolyzed carobs after glucose extraction, were added on poly(butylene-adipate-co-terephthalate), (PBAT), at two different concentrations, i.e., 10 and 20 wt%. The BC have been produced using three pyrolysis processing temperatures (i.e., 280, 340 and 400 °C) to optimize the compositions of produced solid fractions and biofuels. The resulting particles from the pyrolysis process (BC280, BC340 and BC400) were considered as suitable fillers for PBAT. Firstly, the BC particles properties were characterized by elemental composition and spectroscopy analysis, particle size measurements and evaluation of radical scavenging activity and efficiency. Moreover, PBAT/BC composites were subjected to analysis of their rheological and thermal behavior, morphologies and mechanical properties. In addition, accelerated weathering, monitored by both tensile test and spectroscopic analysis, was carried out, and obtained results show that the biochar particles can exert a beneficial effect on photo-oxidation delay of PBAT matrix. Full article

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

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30 pages, 1610 KB

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 214 | Viewed by 18263

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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22 pages, 7645 KB

Open AccessEditor’s ChoiceArticle

Development of an Injection Molding Process for Long Glass Fiber-Reinforced Phenolic Resins

by Robert Maertens, Wilfried V. Liebig, Kay A. Weidenmann and Peter Elsner

Polymers 2022, 14(14), 2890; https://doi.org/10.3390/polym14142890 - 16 Jul 2022

Cited by 6 | Viewed by 4572

Abstract

Glass fiber-reinforced phenolic resins are well suited to substitute aluminum die-cast materials. They meet the high thermomechanical and chemical demands that are typically found in combustion engine and electric drive train applications. An injection molding process development for further improving their mechanical properties [...] Read more.

Glass fiber-reinforced phenolic resins are well suited to substitute aluminum die-cast materials. They meet the high thermomechanical and chemical demands that are typically found in combustion engine and electric drive train applications. An injection molding process development for further improving their mechanical properties by increasing the glass fiber length in the molded part was conducted. A novel screw mixing element was developed to improve the homogenization of the long fibers in the phenolic resin. The process operation with the mixing element is a balance between the desired mixing action, an undesired preliminary curing of the phenolic resin, and the reduction of the fiber length. The highest mixing energy input leads to a reduction of the initial fiber length L₀ = 5000 μm to a weighted average fiber length of L_p = 571 μm in the molded part. This is an improvement over L_p = 285 μm for a short fiber-reinforced resin under comparable processing conditions. The mechanical characterization shows that for the long fiber-reinforced materials, the benefit of the increased homogeneity outweighs the disadvantages of the reduced fiber length. This is evident from the increase in tensile strength from σ_m = 21 MPa to σ_m = 57 MPa between the lowest and the highest mixing energy input parameter settings. Full article

(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)

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20 pages, 6258 KB

Open AccessEditor’s ChoiceArticle

The Effect of Physical Aging and Degradation on the Re-Use of Polyamide 12 in Powder Bed Fusion

by Benjamin Sanders, Edward Cant, Hoda Amel and Michael Jenkins

Polymers 2022, 14(13), 2682; https://doi.org/10.3390/polym14132682 - 30 Jun 2022

Cited by 27 | Viewed by 5651

Abstract

Powder bed fusion (PBF) is an additive manufacturing (AM) technique which offers efficient part-production, light-weighting, and the ability to create complex geometries. However, during a build cycle, multiple aging and degradation processes occur which may affect the reusability of the Polyamide 12 (PA-12) [...] Read more.

Powder bed fusion (PBF) is an additive manufacturing (AM) technique which offers efficient part-production, light-weighting, and the ability to create complex geometries. However, during a build cycle, multiple aging and degradation processes occur which may affect the reusability of the Polyamide 12 (PA-12) powder. Limited understanding of these phenomena can result in discarding re-usable powder unnecessarily, or the production of parts with insufficient properties, both of which lead to significant amounts of waste. This paper examines the thermal, chemical, and mechanical characteristics of PA-12 via an oven storage experiment that simulates multi jet fusion (MJF) conditions. Changes in the properties of PA-12 powder during oven storage showed two separate, time-dependent trends. Initially, differential scanning calorimetry showed a 4.2 °C increase in melting temperature (T_m) and a rise in crystallinity (X_c). This suggests that secondary crystallisation is occurring instead of, or in addition to, the more commonly reported further polycondensation process. However, with extended storage time, there were substantial reductions in T_m and X_c, whilst an 11.6 °C decrease in crystallisation temperature was observed. Fourier transform infrared spectroscopy, a technique rarely used in PBF literature, shows an increased presence of imide bonds—a key marker of thermo-oxidative degradation. Discolouration of samples, an 81% reduction in strength and severe material embrittlement provided further evidence that thermo-oxidative degradation becomes the dominant process following extended storage times beyond 100 h. An additional pre-drying experiment showed how moisture present within PA-12 can also accelerate degradation via hydrolysis. Full article

(This article belongs to the Special Issue Structure-Property Relationship of Polymer Materials)

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15 pages, 6104 KB

Open AccessEditor’s ChoiceArticle

Chitin Nanocrystal Hydrophobicity Adjustment by Fatty Acid Esterification for Improved Polylactic Acid Nanocomposites

by Ivanna Colijn, Murat Yanat, Geertje Terhaerdt, Karin Molenveld, Carmen G. Boeriu and Karin Schroën

Polymers 2022, 14(13), 2619; https://doi.org/10.3390/polym14132619 - 28 Jun 2022

Cited by 15 | Viewed by 3355

Abstract

Bioplastics may solve environmental issues related to the current linear plastic economy, but they need improvement to be viable alternatives. To achieve this, we aimed to add chitin nanocrystals (ChNC) to polylactic acid (PLA), which is known to alter material properties while maintaining [...] Read more.

Bioplastics may solve environmental issues related to the current linear plastic economy, but they need improvement to be viable alternatives. To achieve this, we aimed to add chitin nanocrystals (ChNC) to polylactic acid (PLA), which is known to alter material properties while maintaining a fully bio-based character. However, ChNC are not particularly compatible with PLA, and surface modification with fatty acids was used to improve this. We used fatty acids that are different in carbon chain length (C4–C18) and degree of saturation (C18:2). We successfully used Steglich esterification and confirmed covalent attachment of fatty acids to the ChNC with FTIR and solid-state ¹³C NMR. The morphology of the ChNC remained intact after surface modification, as observed by TEM. ChNC modified with C4 and C8 showed higher degrees of substitution compared to fatty acids with a longer aliphatic tail, while particles modified with the longest fatty acid showed the highest hydrophobicity. The addition of ChNC to the PLA matrix resulted in brown color formation that was reduced when using modified particles, leading to higher transparency, most probably as a result of better dispersibility of modified ChNC, as observed by SEM. In general, addition of ChNC provided high UV-protection to the base polymer material, which is an additional feature that can be created through the addition of ChNC, which is not at the expense of the barrier properties, or the mechanical strength. Full article

(This article belongs to the Special Issue Bio-Based and Biodegradable Polymeric Composites: Synthesis, Characterization and Applications)

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19 pages, 4294 KB

Open AccessEditor’s ChoiceArticle

Influence of Thermal Annealing Temperatures on Powder Mould Effectiveness to Avoid Deformations in ABS and PLA 3D-Printed Parts

by Joaquín Lluch-Cerezo, María Desamparados Meseguer, Juan Antonio García-Manrique and Rut Benavente

Polymers 2022, 14(13), 2607; https://doi.org/10.3390/polym14132607 - 27 Jun 2022

Cited by 23 | Viewed by 3775

Abstract

Fused deposition modelling (FDM)-printed parts can be treated with various post-processes to improve their mechanical properties, dimensional accuracy and surface finish. Samples of polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) parts are treated with annealing to study a ceramic powder mould’s effectiveness [...] Read more.

Fused deposition modelling (FDM)-printed parts can be treated with various post-processes to improve their mechanical properties, dimensional accuracy and surface finish. Samples of polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) parts are treated with annealing to study a ceramic powder mould’s effectiveness in order to avoid dimensional part deformation. The variables chosen are annealing temperatures and the usage of a ceramic powder mould to avoid part deformations. A flexural strength test was carried out to evaluate the mould’s influence on the mechanical properties of the part. The effectiveness of the mould has been evaluated mainly attending to the length of the part, because this is the dimension most affected by deformation. A polynomial approximation to a deformation’s length and the effectiveness of the mould allows for their prediction. Results obtained show that effectiveness increases with the annealing temperature. Nevertheless, mould effectiveness decreases when parts are fabricated with PLA, because it is a semi-crystalline thermoplastic, and it suffers a lower shrinkage during thermal post-process than amorphous polymers such as ABS. Attending to the flexural strength test, mould has no significant influence on the mechanical properties of the treated parts in both materials studied. Full article

(This article belongs to the Special Issue New Advances in Polymer Materials for Product Design Processes and Additive Manufacturing)

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12 pages, 1120 KB

Open AccessEditor’s ChoiceArticle

Experimental Investigation of the Different Polyacrylamide Dosages on Soil Water Movement under Brackish Water Infiltration

by Jihong Zhang, Quanjiu Wang, Weiyi Mu, Kai Wei, Yi Guo and Yan Sun

Polymers 2022, 14(12), 2495; https://doi.org/10.3390/polym14122495 - 19 Jun 2022

Cited by 12 | Viewed by 2401

Abstract

The use of soil conditioners in conjunction with brackish water irrigation is critical for the efficient development and use of brackish water as well as the enhancement of the structure of saline soil and stimulating crop growth. This study investigated the effects of [...] Read more.

The use of soil conditioners in conjunction with brackish water irrigation is critical for the efficient development and use of brackish water as well as the enhancement of the structure of saline soil and stimulating crop growth. This study investigated the effects of different polyacrylamide (PAM) dosages (0, 0.02%, 0.04%, and 0.06%) on the water flow properties of sandy loam during brackish water infiltration using one-dimensional vertical and horizontal soil column infiltration experiments. The results showed that: (1) PAM could lower the soil infiltration rate and increase soil water retention performance under brackish water infiltration conditions. (2) PAM had a significant effect on the parameters of the Philip and Kostiakov infiltration models. The soil sorption rate S and the empirical coefficient λ were the smallest, and the empirical index β was the largest when the PAM dosage was 0.04%. (3) PAM dosage displayed a quadratic polynomial connection with the soil saturated water content and the saturated hydraulic conductivity. The soil saturated water content was highest when the PAM dosage was 0.04%, the intake suction h_d of the Brooks-Corey model increased by 15.30%, and the soil water holding capacity was greatly improved. (4) Soil treated with PAM could absorb more water under the same soil water suction, whereas the soil unsaturated hydraulic conductivity and its growth rate decreased. The soil saturated diffusion rate D_s, as well as the soil water diffusion threshold, rose. Finally, the 0.04% PAM dosage could improve soil hydrodynamic characteristics under brackish water infiltration, which is beneficial for the efficient utilization of brackish water. Full article

(This article belongs to the Special Issue Preparation, Structure and Characterization of Polymer/Cement Composites)

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13 pages, 2698 KB

Open AccessEditor’s ChoiceArticle

Synthesis and Thermal Analysis of Non-Covalent PS-b-SC-b-P2VP Triblock Terpolymers via Polylactide Stereocomplexation

by Ameen Arkanji, Viko Ladelta, Konstantinos Ntetsikas and Nikos Hadjichristidis

Polymers 2022, 14(12), 2431; https://doi.org/10.3390/polym14122431 - 15 Jun 2022

Cited by 8 | Viewed by 2739

Abstract

Polylactides (PLAs) are thermoplastic materials known for their wide range of applications. Moreover, the equimolar mixtures of poly(L-Lactide) (PLLA) and poly(D-Lactide) (PDLA) can form stereocomplexes (SCs), which leads to the formation of new non-covalent complex macromolecular architectures. In this work, we report the [...] Read more.

Polylactides (PLAs) are thermoplastic materials known for their wide range of applications. Moreover, the equimolar mixtures of poly(L-Lactide) (PLLA) and poly(D-Lactide) (PDLA) can form stereocomplexes (SCs), which leads to the formation of new non-covalent complex macromolecular architectures. In this work, we report the synthesis and characterization of non-covalent triblock terpolymers of polystyrene-b-stereocomplex PLA-b-poly(2-vinylpyridine) (PS-b-SC-b-P2VP). Well-defined ω-hydroxy-PS and P2VP were synthesized by “living” anionic polymerization high-vacuum techniques with sec-BuLi as initiator, followed by termination with ethylene oxide. The resulting PS-OH and P2VP-OH were used as macroinitiators for the ring-opening polymerization (ROP) of DLA and LLA with Sn(Oct)₂ as a catalyst to afford PS-b-PDLA and P2VP-b-PLLA, respectively. SC formation was achieved by mixing PS-b-PDLA and P2VP-b-PLLA chloroform solutions containing equimolar PLAs segments, followed by precipitation into n-hexane. The molecular characteristics of the resulting block copolymers (BCPs) were determined by ¹H NMR, size exclusion chromatography, and Fourier-transform infrared spectroscopy. The formation of PS-b-SC-b-P2VP and the effect of molecular weight variation of PLA blocks on the resulting polymers, were investigated by differential scanning calorimetry, X-ray powder diffraction, and circular dichroism spectroscopies. Full article

(This article belongs to the Special Issue Advances and Applications of Block Copolymers)

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14 pages, 3187 KB

Open AccessEditor’s ChoiceArticle

Simple, One-Pot Method for Preparing Transparent Ethyl Cellulose Films with Good Mechanical Properties

by Gabrijela Horvat, Klara Žvab, Željko Knez and Zoran Novak

Polymers 2022, 14(12), 2399; https://doi.org/10.3390/polym14122399 - 14 Jun 2022

Cited by 15 | Viewed by 5336

Abstract

In this research, ethyl cellulose films were prepared by a simple, easy, controlled one-pot method using either ethanol or ethyl lactate as solvents, the films being formed at 6 °C. Titanium dioxide nanoparticles were incorporated to improve the oxygen transmission and water vapour [...] Read more.

In this research, ethyl cellulose films were prepared by a simple, easy, controlled one-pot method using either ethanol or ethyl lactate as solvents, the films being formed at 6 °C. Titanium dioxide nanoparticles were incorporated to improve the oxygen transmission and water vapour transmission rates of the obtained films. This method used no plasticizers, and flexible materials with good mechanical properties were obtained. The resulting solvent-free and transparent ethyl cellulose films exhibited good mechanical properties and unique free-shapable properties. The obtained materials had similar properties to those reported in the literature, where plasticizers were incorporated into ethyl cellulose films with an elastic modulus of 528 MPa. Contact angles showed the hydrophobic nature of all the prepared materials, with contact angles between 80 and 108°. Micrographs showed the smooth surfaces of the prepared samples and porous intersections with honeycomb-like structures. The oxygen and water vapor transmission rates were the lowest for the ethyl cellulose films prepared in ethyl lactate, these being 615 cm³·m⁻²·day⁻¹ and 7.8 gm⁻²·day⁻¹, respectively, showing that the films have promise for food packaging applications. Full article

(This article belongs to the Special Issue Smart Polymeric Films and Coatings for Food Packaging Applications)

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14 pages, 4403 KB

Open AccessEditor’s ChoiceArticle

Anisotropic Tensile Characterisation of Eucalyptus nitens Timber above Its Fibre Saturation Point, and Its Application

by Xudong Chen, Yingyao Cheng, Andrew Chan, Damien Holloway and Gregory Nolan

Polymers 2022, 14(12), 2390; https://doi.org/10.3390/polym14122390 - 13 Jun 2022

Cited by 6 | Viewed by 2432

Abstract

Plantation-grown Eucalyptus nitens (E. nitens) has been grown predominantly for the pulp and paper industry. In this study, the suitability of E. nitens as a structural material is examined using static tensile tests in a universal testing machine. The anisotropic tensile [...] Read more.

Plantation-grown Eucalyptus nitens (E. nitens) has been grown predominantly for the pulp and paper industry. In this study, the suitability of E. nitens as a structural material is examined using static tensile tests in a universal testing machine. The anisotropic tensile behaviour of 240 Eucalyptus nitens small clear wood samples with a diversity of grain angles was examined in both dry and wet conditions. The samples had a highly anisotropic tensile characterisation in the context of both a low moisture content (MC = 12%) and a high moisture content (MC > its fibre saturation point, FSP). The results showed that, in a high moisture content condition, the wood showed a lower failure strength and more ductility at all grain angles than in a low moisture content condition. The underlying failure mechanism of Eucalyptusnitens timber in tension was determined in detail from the perspective of the microstructure of wood cellulose polymer composites. The mean tensile failure strengths perpendicular and parallel to the fibre direction were, respectively, 5.6 and 91.6 MPa for the low MC and 3.8 and 62.1 MPa for the high MC condition. This research provides a basis for using E. nitens as a potential structural tensile member. The moisture modification factors of Eucalyptus timber at a mean level are higher than those of the traditional construction material, Pinus radiata, implying that E. nitens is promising as a material to be used for tensile members in water saturated conditions. Full article

(This article belongs to the Special Issue Wood Polymer Composites: Processing, Properties, and Applications)

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16 pages, 4964 KB

Open AccessEditor’s ChoiceArticle

Intrinsically Stretchable Poly(3,4-ethylenedioxythiophene) Conducting Polymer Film for Flexible Electronics

by Lucija Fiket, Marin Božičević, Lana Brkić, Patricia Žagar, Anamarija Horvat and Zvonimir Katančić

Polymers 2022, 14(12), 2340; https://doi.org/10.3390/polym14122340 - 9 Jun 2022

Cited by 3 | Viewed by 3198

Abstract

The aim of this study was to synthesize an intrinsically stretchable conductive polymer (CP) by atom transfer radical polymerization (ATRP). For this purpose, poly(3,4-ethyilenedioxythiophene) (PEDOT) was synthesized as a backbone, while poly(acrylate-urethane) (PAU) was grafted onto the PEDOT backbone to form graft polymers [...] Read more.

The aim of this study was to synthesize an intrinsically stretchable conductive polymer (CP) by atom transfer radical polymerization (ATRP). For this purpose, poly(3,4-ethyilenedioxythiophene) (PEDOT) was synthesized as a backbone, while poly(acrylate-urethane) (PAU) was grafted onto the PEDOT backbone to form graft polymers PEDOT-g-PAU. Different concentrations of acrylate-urethane (AU) were used to synthesize PAU side chains of different lengths. The successful synthesis of the obtained intermediates and products (PEDOT-g-PAU) was confirmed by infrared spectroscopy and nuclear magnetic resonance. Thermal properties were evaluated by differential scanning calorimetry and thermogravimetric analysis, while conductivity was determined by four-point probe measurement. A simple tensile test was performed to characterize the ductility of the samples. PEDOT-g-PAU has shown high stretchability of up to 500% and, therefore, could potentially be used in skin-worn flexible electronics, while additional subsequent doping is required to improve the deterioration of electrical properties after the addition of the insulating urethane layer. Full article

(This article belongs to the Special Issue Advanced Polymeric Materials for Flexible Electronics Energy Storage Devices and Biosensors)

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15 pages, 2483 KB

Open AccessEditor’s ChoiceArticle

Faraday Instability in Viscous Fluids Covered with Elastic Polymer Films

by Junxiu Liu, Wenqiang Song, Gan Ma and Kai Li

Polymers 2022, 14(12), 2334; https://doi.org/10.3390/polym14122334 - 9 Jun 2022

Cited by 1 | Viewed by 2925

Abstract

Faraday instability has great application value in the fields of controlling polymer processing, micromolding colloidal lattices on structured suspensions, organizing particle layers, and conducting cell culture. To regulate Faraday instability, in this article, we attempt to introduce an elastic polymer film covering the [...] Read more.

Faraday instability has great application value in the fields of controlling polymer processing, micromolding colloidal lattices on structured suspensions, organizing particle layers, and conducting cell culture. To regulate Faraday instability, in this article, we attempt to introduce an elastic polymer film covering the surface of a viscous fluid layer and theoretically study the behaviors of the Faraday instability phenomenon and the effect of the elastic polymer film. Based on hydrodynamic theory, the Floquet theory is utilized to formulate its stability criterion, and the critical acceleration amplitude and critical wave number are calculated numerically. The results show that the critical acceleration amplitude for Faraday instability increases with three increasing bending stiffness of the elastic polymer film, and the critical wave number decreases with increasing bending stiffness. In addition, surface tension and viscosity also have important effects on the critical acceleration amplitude and critical wave number. The strategy of controlling Faraday instability by covering an elastic polymer film proposed in this paper has great application potential in new photonic devices, metamaterials, alternative energy, biology, and other fields. Full article

(This article belongs to the Special Issue Mathematical Modeling and Computer Simulation of Polymer Systems)

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17 pages, 4412 KB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of Porous Chitosan/Saccharomycetes Adsorption Microspheres

by Wei Song, Qingzhu Zhang, Yuxin Guan, Wanyan Li, Siyu Xie, Jin Tong, Mo Li and Lili Ren

Polymers 2022, 14(11), 2292; https://doi.org/10.3390/polym14112292 - 5 Jun 2022

Cited by 12 | Viewed by 3508

Abstract

Porous chitosan/saccharomycetes adsorption microspheres were successfully prepared by using silica gel as porogen. The morphology of porous chitosan/saccharomycetes microspheres was characterized by scanning electron microscopy, the interaction between molecules was characterized by Fourier transform infrared spectroscopy, and the crystallization property of the microspheres [...] Read more.

Porous chitosan/saccharomycetes adsorption microspheres were successfully prepared by using silica gel as porogen. The morphology of porous chitosan/saccharomycetes microspheres was characterized by scanning electron microscopy, the interaction between molecules was characterized by Fourier transform infrared spectroscopy, and the crystallization property of the microspheres was characterized by X-ray diffraction. The results showed that the adsorption sites of amino and hydroxyl groups had been provided by the porous chitosan/saccharomycetes microspheres for the removal of preservatives, pigments, and other additives in food. The surface roughness of microspheres could be improved by increasing the mass ratio of saccharomycetes. The increase in silica gels could make the microsphere structure more compact. The porous chitosan/saccharomycetes microspheres could be used as adsorbents to adsorb doxycycline in wastewater. Full article

(This article belongs to the Section Polymer Chemistry)

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9 pages, 1069 KB

Open AccessEditor’s ChoiceArticle

Meso- and Rac-[bis(3-phenyl-6-tert-butylinden-1-yl)dimethylsilyl]zirconium Dichloride: Precatalysts for the Production of Differentiated Polyethylene Products with Enhanced Properties

by Kaitie A. Giffin, Virginie Cirriez, Orlando Santoro, Alexandre Welle, Evgueni Kirillov and Jean-François Carpentier

Polymers 2022, 14(11), 2217; https://doi.org/10.3390/polym14112217 - 30 May 2022

Cited by 1 | Viewed by 2993

Abstract

Ansa-zirconocene complexes are widely employed as precatalysts for olefin polymerization. Their synthesis generally leads to mixtures of their rac and meso isomers, whose separation is often problematic. In this contribution, we report on the synthesis of a novel silyl-bridged bis(indenyl)-based metallocene, and [...] Read more.

Ansa-zirconocene complexes are widely employed as precatalysts for olefin polymerization. Their synthesis generally leads to mixtures of their rac and meso isomers, whose separation is often problematic. In this contribution, we report on the synthesis of a novel silyl-bridged bis(indenyl)-based metallocene, and on the separation of its rac and meso isomers by simple recrystallization from toluene. The two complexes, activated by methylaluminoxane (MAO), have been used as precatalysts in ethylene/1-hexene copolymerization. Regardless of the reaction conditions, the meso complex outperformed its rac congener. A similar trend was observed by performing the process in the presence of the silica-supported versions of the complexes. This is remarkable, since meso metallocenes generally display lower activities than their rac analogues. Furthermore, the meso isomer generates polymer products that are more in line with the targets for the preparation of a bimodal PE grade made of a lower-MW high-density (HDPE) fraction and a higher-MW linear low-density (LLDPE) fraction. Full article

(This article belongs to the Special Issue Polyolefins: The Ever-Thriving Thermoplastics)

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13 pages, 3423 KB

Open AccessEditor’s ChoiceArticle

Room-Temperature Solid-State UV Cross-Linkable Vitrimer-like Polymers for Additive Manufacturing

by Jian Chen, Ya Wen, Lingyi Zeng, Xinchun Wang, Hongmei Chen, Wei Min Huang, Yuefeng Bai, Wenhao Yu, Keqing Zhao and Ping Hu

Polymers 2022, 14(11), 2203; https://doi.org/10.3390/polym14112203 - 29 May 2022

Cited by 9 | Viewed by 3477

Abstract

In this paper, a UV cross-linkable vitrimer-like polymer, ureidopyrimidinone functionalized telechelic polybutadiene, is reported. It is synthesized in two steps. First, 2(6-isocyanatohexylaminocarbonylamino)-6-methyl-4[1H]-pyrimidinone (UPy-NCO) reacts with hydroxy-functionalized polybutadiene (HTPB) to obtain UPy-HTPB-UPy, and then the resulted UPy-HTPB-UPy is cross-linked under 365 nm UV light [...] Read more.

In this paper, a UV cross-linkable vitrimer-like polymer, ureidopyrimidinone functionalized telechelic polybutadiene, is reported. It is synthesized in two steps. First, 2(6-isocyanatohexylaminocarbonylamino)-6-methyl-4[1H]-pyrimidinone (UPy-NCO) reacts with hydroxy-functionalized polybutadiene (HTPB) to obtain UPy-HTPB-UPy, and then the resulted UPy-HTPB-UPy is cross-linked under 365 nm UV light (photo-initiator: bimethoxy-2-phenylacetophenone, DMPA). Further investigation reveals that the density of cross-linking and mechanical properties of the resulting polymers can be tailored via varying the amount of photo-initiator and UV exposure time. Before UV cross-linking, UPy-HTPB-UPy is found to be vitrimer-like due to the quadruple hydrogen-bonding interactions. The UPy groups at the end of the chain also enable for rapid solidification upon the evaporation of the solvent. The unsaturated double bonds in the HTPB chains enable UPy-HTPB-UPy to be UV cross-linkable in the solid state at room temperature. After cross-linking, the polymers have good shape memory effect (SME). Here, we demonstrate that this type of polymer can have many potential applications in additive manufacturing. In the cases of fused deposition modelling (FDM) and direct ink writing (DIW), not only the strength of the interlayer bonding but also the strength of the polymer itself can be enhanced via UV exposure (from thermoplastic to thermoset) either during printing or after printing. The SME after cross-linking further helps to achieve rapid volumetric additive manufacturing anytime and anywhere. Full article

(This article belongs to the Special Issue Shape Memory Polymers IV)

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10 pages, 3688 KB

Open AccessEditor’s ChoiceArticle

Manipulation of Elastic Instability of Viscoelastic Fluid in a Rhombus Cross Microchannel

by Meng Zhang, Zihuang Wang, Yanhua Zheng, Bifeng Zhu, Bingzhi Zhang, Xiaohui Fang, Wenli Shang and Wu Zhang

Polymers 2022, 14(11), 2152; https://doi.org/10.3390/polym14112152 - 25 May 2022

Cited by 1 | Viewed by 2021

Abstract

This paper reports the manipulation of elastic instability of the viscoelastic fluid in a rhombus cross microchannel (RCM) structure. The bistable instability and unsteady instability of the flow is firstly demonstrated in a standard cross microchannel (SCM) for reference. We then keep the [...] Read more.

This paper reports the manipulation of elastic instability of the viscoelastic fluid in a rhombus cross microchannel (RCM) structure. The bistable instability and unsteady instability of the flow is firstly demonstrated in a standard cross microchannel (SCM) for reference. We then keep the bi-stable instability over a much wider injection rate range in the RCM, which is attributed to the stabilizing effect of the rhombus structure. A semi-bistable instability was also established in the RCM at a high enough injection rate. In addition, the unsteady elastic instability is realized in the RCM through an asymmetric injection rate condition. Full article

(This article belongs to the Special Issue Microfluidics as a Platform to Manufacture, Manipulate and Test Polymeric Entities)

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17 pages, 5107 KB

Open AccessEditor’s ChoiceArticle

Heat Analysis of Thermal Conductive Polymer Composites: Reference Temperature History in Pure Polymer Matrices

by Fethi Guesmi, Makram Elfarhani, Ali Mkaddem, Sami Ghazali, Abdullah S. Bin Mahfouz and Abdessalem Jarraya

Polymers 2022, 14(10), 2084; https://doi.org/10.3390/polym14102084 - 20 May 2022

Cited by 4 | Viewed by 2679

Abstract

This attempt aims at assessing heat generation in thermal conductive polymer (TCP) composites widely used in aerospace sectors. Temperature histories were investigated in both nonreinforced and glass-fiber-reinforced TCPs during abrasive milling. Glass/epoxy and glass/polyester composites with 30% unidirectional glass fiber content were prepared [...] Read more.

This attempt aims at assessing heat generation in thermal conductive polymer (TCP) composites widely used in aerospace sectors. Temperature histories were investigated in both nonreinforced and glass-fiber-reinforced TCPs during abrasive milling. Glass/epoxy and glass/polyester composites with 30% unidirectional glass fiber content were prepared according to appropriate curing cycles. Type K thermocouples connected to a data acquisition system ensured the recording of temperature history along the trim plan during milling. Unexpectedly, when milling TCP composites parallel to fibers, peak temperature was found to be slightly lower than that recorded in nonreinforced polymers. The lateral surface of fibers acts to favor sliding friction, which limits heat generation at interfaces, while relatively low specific heat capacity and thermal conductivity of glass fiber disadvantage heat transfer. However, when milling perpendicular to fibers, the contact area between the tool and the transverse failure area of fibers increases drastically, hence involving severe friction at interfaces. This yields peak temperatures sensitively higher than those obtained in nonreinforced polymers. SEM inspections highlighted the failure modes dominating the material removal process in both nonreinforced and glass-fiber-reinforced polymers. The microcracks and debris observed at the trim plan explain, in part, the heat generation detected on temperature rate plots. Thus, heat conduction between phases governs sensitive surface finish integrity and tool lifetime and, hence, has great economic impact on the manufacturing steps. Full article

(This article belongs to the Special Issue Advanced Applications of Conductive Polymer Nanocomposites)

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18 pages, 4895 KB

Open AccessEditor’s ChoiceArticle

Bio-Inspired 4D Printing of Dynamic Spider Silks

by Guiwei Li, Qi Tian, Wenzheng Wu, Shida Yang, Qian Wu, Yihang Zhao, Jiaqing Wang, Xueli Zhou, Kunyang Wang, Luquan Ren, Ji Zhao and Qingping Liu

Polymers 2022, 14(10), 2069; https://doi.org/10.3390/polym14102069 - 19 May 2022

Cited by 13 | Viewed by 3406

Abstract

Spider silks exhibit excellent mechanical properties and have promising application prospects in engineering fields. Because natural spider silk fibers cannot be manufactured on a large scale, researchers have attempted to fabricate bio-inspired spider silks. However, the fabrication of bio-inspired spider silks with dynamically [...] Read more.

Spider silks exhibit excellent mechanical properties and have promising application prospects in engineering fields. Because natural spider silk fibers cannot be manufactured on a large scale, researchers have attempted to fabricate bio-inspired spider silks. However, the fabrication of bio-inspired spider silks with dynamically tunable mechanical properties and stimulation–response characteristics remains a challenge. Herein, the 4D printing of shape memory polyurethane is employed to produce dynamic bio-inspired spider silks. The bio-inspired spider silks have two types of energy-absorbing units that can be adjusted, one by means of 4D printing with predefined nodes, and the other through different stimulation methods to make the bio-inspired spider silks contract and undergo spiral deformation. The shape morphing behaviors of bio-inspired spider silks are programmed via pre-stress assemblies enabled by 4D printing. The energy-absorbing units of bio-inspired spider silks can be dynamically adjusted owing to stress release generated with the stimuli of temperature or humidity. Therefore, the mechanical properties of bio-inspired spider silks can be controlled to change dynamically. This can further help in developing applications of bio-inspired spider silks in engineering fields with dynamic changes of environment. Full article

(This article belongs to the Special Issue Advanced Materials in 3D/4D Printing Technology)

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11 pages, 3269 KB

Open AccessEditor’s ChoiceArticle

Relating Amorphous Structure to the Tear Strength of Polylactic Acid Films

by Yutaka Kobayashi, Akira Ishigami and Hiroshi Ito

Polymers 2022, 14(10), 1965; https://doi.org/10.3390/polym14101965 - 11 May 2022

Cited by 6 | Viewed by 2695

Abstract

Compared with polyolefins that are used as single-use plastics, polylactic acid (PLA) has a lower tear strength in films. The relationship between the tear strength and the higher-order structure of films was investigated using PLA films that absorbed moisture at 30 °C and [...] Read more.

Compared with polyolefins that are used as single-use plastics, polylactic acid (PLA) has a lower tear strength in films. The relationship between the tear strength and the higher-order structure of films was investigated using PLA films that absorbed moisture at 30 °C and 95% relative humidity (RH) or that had been annealed under reduced pressure conditions. Although the mobile amorphous (MAm) amount did not change under high humidity, the film became brittle due to enthalpy relaxation. The crystallization by annealing also caused embrittlement, and the MAm amount decreased to 10%. The displacement until tearing is lowered from 2.5 to 0.5 mm in both cases. However, in situ retardation measurements revealed that there was a significant difference in the fracture morphology of the torn tip. When crystallized, the molecular chains and crystals are oriented in the tensile direction of the film, and a fragmented structure is observed in the ligament. Embrittlement due to enthalpy relaxation caused a weak orientation perpendicular to the tensile direction of the film, and cracks occurs along with this orientation. Full article

(This article belongs to the Special Issue Development of Bio-Based Materials: Synthesis, Characterization and Applications)

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15 pages, 7776 KB

Open AccessEditor’s ChoiceArticle

Molecular Dynamics Study of Cellulose Nanofiber Alignment under an Electric Field

by Ruth M. Muthoka, Pooja S. Panicker and Jaehwan Kim

Polymers 2022, 14(9), 1925; https://doi.org/10.3390/polym14091925 - 9 May 2022

Cited by 11 | Viewed by 3750

Abstract

The alignment of cellulose by an electric field is an interesting subject for cellulose material processing and its applications. This paper reports an atomistic molecular dynamics simulation of the crystalline cellulose nanofiber (CNF) model in varying electric field directions and strengths. GROMACS software [...] Read more.

The alignment of cellulose by an electric field is an interesting subject for cellulose material processing and its applications. This paper reports an atomistic molecular dynamics simulation of the crystalline cellulose nanofiber (CNF) model in varying electric field directions and strengths. GROMACS software was used to study crystalline cellulose 1β consisting of 18 chains in an aqueous environment at room temperature, and an electric field was applied along the cellulose chain direction and the perpendicular direction with varying field strength. The root-mean-square displacement, radius of gyration, end-to-end length, and hydrogen bond population of the crystalline CNF model were analyzed to determine the effects of the applied electric field on the structure of the CNF model. The results suggest that the nanosecond electric field can induce the orientation of the CNF along the applied electric field direction. The alignment rate and ability to maintain the alignment depend on the electric field strength. Analysis of the radius of gyration, end-to-end length, and bond lengths for intrachain and interchain hydrogen bonds revealed no significant effect on the cellulose structure. Cellulose alignment in an electric field has the potential to broaden the design of electric field-induced processing techniques for cellulose filaments, thin films, and electro-active cellulose composites. Full article

(This article belongs to the Topic Computational Materials Science for Polymers)

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16 pages, 2916 KB

Open AccessEditor’s ChoiceArticle

pH- and Thermo-Responsive Water-Soluble Smart Polyion Complex (PIC) Vesicle with Polyampholyte Shells

by Thu Thao Pham, Tien Duc Pham and Shin-ichi Yusa

Polymers 2022, 14(9), 1659; https://doi.org/10.3390/polym14091659 - 20 Apr 2022

Cited by 9 | Viewed by 3277

Abstract

A diblock copolymer (P(VBTAC/NaSS)₁₇-b-PAPTAC₅₀; P(VS)₁₇A₅₀) composed of amphoteric random copolymer, poly(vinylbenzyl trimethylammonium chloride-co-sodium p-styrensunfonate) (P(VBTAC/NaSS); P(VS)) and cationic poly(3-(acrylamidopropyl) trimethylammonium chloride) (PAPTAC; A) block, and poly(acrylic acid) (PAAc₄₉) [...] Read more.

A diblock copolymer (P(VBTAC/NaSS)₁₇-b-PAPTAC₅₀; P(VS)₁₇A₅₀) composed of amphoteric random copolymer, poly(vinylbenzyl trimethylammonium chloride-co-sodium p-styrensunfonate) (P(VBTAC/NaSS); P(VS)) and cationic poly(3-(acrylamidopropyl) trimethylammonium chloride) (PAPTAC; A) block, and poly(acrylic acid) (PAAc₄₉) were prepared via a reversible addition−fragmentation chain transfer radical polymerization. Scrips V, S, and A represent VBTAC, NaSS, and PAPTAC blocks, respectively. Water-soluble polyion complex (PIC) vesicles were formed by mixing P(VS)₁₇A₅₀ and PAAc₄₉ in water under basic conditions through electrostatic interactions between the cationic PAPTAC block and PAA_c49 with the deprotonated pendant carboxylate anions. The PIC vesicle collapsed under an acidic medium because the pendant carboxylate anions in PAAc₄₉ were protonated to delete the anionic charges. The PIC vesicle comprises an ionic PAPTAC/PAAc membrane coated with amphoteric random copolymer P(VS)₁₇ shells. The PIC vesicle showed upper critical solution temperature (UCST) behavior in aqueous solutions because of the P(VS)₁₇ shells. The pH- and thermo-responsive behavior of the PIC vesicle were studied using ¹H NMR, static and dynamic light scattering, and percent transmittance measurements. When the ratio of the oppositely charged polymers in PAPTAC/PAAc was equal, the size and light scattering intensity of the PIC vesicle reached maximum values. The hydrophilic guest molecules can be encapsulated into the PIC vesicle at the base medium and released under acidic conditions. It is expected that the PIC vesicles will be applied as a smart drug delivery system. Full article

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

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42 pages, 4201 KB

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 50 | Viewed by 6569

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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15 pages, 3149 KB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of Cyclodextrin-Based Polyhemiaminal Composites with Enhanced Thermal Stability

by Hoque Mohammed Jabedul, Mitsuo Toda and Nobuyuki Mase

Polymers 2022, 14(8), 1562; https://doi.org/10.3390/polym14081562 - 11 Apr 2022

Cited by 3 | Viewed by 2847

Abstract

Polyhemiaminal (PHA) polymers are a new class of thermosetting polymers that have recently gained attention owing to their high mechanical strength and excellent recycling behavior. However, low thermal stability is a common issue in PHA polymers due to the thermally labile crosslinked knots. [...] Read more.

Polyhemiaminal (PHA) polymers are a new class of thermosetting polymers that have recently gained attention owing to their high mechanical strength and excellent recycling behavior. However, low thermal stability is a common issue in PHA polymers due to the thermally labile crosslinked knots. Herein, crosslinked PHA polymer composites were synthesized by reacting formaldehyde with a precursor solution of 4,4ʹ-oxydianiline (ODA) and cyclodextrins (CDs) (α-, β-, and γ-). The material obtained under optimal conditions (ODA:CD molar ratio of 1:0.5, 37% aqueous solution of formaldehyde (formalin)) exhibited good film formability and high thermal stability with two characteristic decomposition phenomena and a high char yield. The early decomposition of CDs and char formation led to high thermal stability. Time-resolved NMR analysis was conducted to study hemiaminal bond formation via a condensation reaction between ODA and formaldehyde. Furthermore, PHA matrix formation was confirmed by the dissolution of the deposited CD layer in a solution of N-methyl-2-pyrrolidinone containing 8–9 wt.% LiBr at 80 °C and FTIR analysis. Based on the elemental analysis results, PHA network formation was confirmed by considering a single unit of the PHA network with CD composition, including the solvent and water. Full article

(This article belongs to the Topic Synthesis, Characterization and Performance of Materials for a Sustainable Future)

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15 pages, 3412 KB

Open AccessEditor’s ChoiceArticle

Sequencing Biodegradable and Potentially Biobased Polyesteramide of Sebacic Acid and 3-Amino-1-propanol by MALDI TOF-TOF Tandem Mass Spectrometry

by Paola Rizzarelli, Stefania La Carta, Emanuele Francesco Mirabella, Marco Rapisarda and Giuseppe Impallomeni

Polymers 2022, 14(8), 1500; https://doi.org/10.3390/polym14081500 - 7 Apr 2022

Cited by 4 | Viewed by 3006

Abstract

Biodegradable and potentially biobased polyesteramide oligomers (PEA-Pro), obtained from melt condensation of sebacic acid and 3-amino-1-propanol, were characterized by nuclear magnetic resonance (NMR), matrix assisted laser desorption/ionization-time of flight/time of flight-mass spectrometry/mass spectrometry (MALDI-TOF/TOF-MS/MS), thermogravimetric analysis (TGA), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). NMR [...] Read more.

Biodegradable and potentially biobased polyesteramide oligomers (PEA-Pro), obtained from melt condensation of sebacic acid and 3-amino-1-propanol, were characterized by nuclear magnetic resonance (NMR), matrix assisted laser desorption/ionization-time of flight/time of flight-mass spectrometry/mass spectrometry (MALDI-TOF/TOF-MS/MS), thermogravimetric analysis (TGA), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). NMR analysis showed the presence of hydroxyl and amino terminal groups as well as carboxylic groups of the sebacate moiety. Hydroxyl and carboxyl termination had the same abundance, while the amine termination was 2.7-times less frequent. Information regarding the fragmentation pathways and ester/amide bond sequences was obtained by MALDI-TOF/TOF-MS/MS analysis performed on sodiated adducts of cyclic species and linear oligomers. Different end groups did not influence the observed fragmentation. Three fragmentation pathways were recognized. The β-hydrogen-transfer rearrangement, which leads to the selective scission of the –O–CH₂– bonds, was the main mechanism. Abundant product ions originating from –CH₂–CH₂– (β–γ) bond cleavage in the sebacate moiety and less abundant ions formed by –O–CO– cleavages were also detected. TGA showed a major weight loss (74%) at 381 °C and a second degradation step (22% weight loss) at 447 °C. Py-GC/MS performed in the temperature range of 350–400 °C displayed partial similarity between the degradation products and the main fragments detected in the MALDI-TOF/TOF-MS/MS experiments. Degradation products derived from amide bonds were related to the formation of CN groups, in agreement with the literature. Full article

(This article belongs to the Special Issue Development of Bio-Based Materials: Synthesis, Characterization and Applications)

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16 pages, 6201 KB

Open AccessEditor’s ChoiceArticle

Basalt Fiber Hybridization Effects on High-Performance Sisal-Reinforced Biocomposites

by Bernardo Zuccarello, Francesco Bongiorno and Carmelo Militello

Polymers 2022, 14(7), 1457; https://doi.org/10.3390/polym14071457 - 3 Apr 2022

Cited by 10 | Viewed by 2942

Abstract

The increasing attention given to environmental protection, largely through specific regulations on environmental impact and the recycling of materials, has led to a considerable interest of researchers in biocomposites, materials consisting of bio-based or green polymer matrixes reinforced by natural fibers. Among the [...] Read more.

The increasing attention given to environmental protection, largely through specific regulations on environmental impact and the recycling of materials, has led to a considerable interest of researchers in biocomposites, materials consisting of bio-based or green polymer matrixes reinforced by natural fibers. Among the various reinforcing natural fibers, sisal fibers are particularly promising for their good mechanical properties, low specific weight and wide availability on the current market. As proven in literature by various authors, the hybridization of biocomposites by synthetical fibers or different natural fibers can lead to an interesting improvement of the mechanical properties or, in turn, of the strength against environmental agents. Consequently, this can lead to a significant enlargement of their practical applications, in particular from quite common non-structural applications (dashboards, fillings, soundproofing, etc.) towards semi-structural (panels, etc.) and structural applications (structural elements of civil construction and/or machine components). Hybridizations with natural fibers or with ecofriendly basalt fibers are the most interesting ones, since they permit the improvement of the biocomposite’s performance without an appreciable increment on environmental impact, as occurs instead for synthetic fiber hybridizations that are also widely proposed in the literature. In order to further increase the mechanical performance and, above all, to reduce the aging effects on high-performance sisal-reinforced biocomposites due to environmental agents, the hybridization of such biocomposites with basalt fibers are studied with tensile, compression and delamination tests performed by varying the exposition to environmental agents. In brief, the experimental analysis has shown that hybridization can lead to further enhancements of mechanical performance (strength and stiffness) that increase with basalt volume fraction and can lead to appreciable reductions in the aging effects on mechanical performance by simple hybridization of the surface laminae. Therefore, such a hybridization can be advantageously used in all practical outdoor applications in which high-performance sisal biocomposites can be exposed to significant environmental agents (temperature, humidity, UV). Full article

(This article belongs to the Special Issue High-Performance Biocomposite Reinforced by Natural Fibers)

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15 pages, 2890 KB

Open AccessEditor’s ChoiceArticle

Threonine-Based Stimuli-Responsive Nanoparticles with Aggregation-Induced Emission-Type Fixed Cores for Detection of Amines in Aqueous Solutions

by Keita Kataoka, Kazuhiro Nakabayashi, Chen-Tsyr Lo and Hideharu Mori

Polymers 2022, 14(7), 1362; https://doi.org/10.3390/polym14071362 - 27 Mar 2022

Cited by 2 | Viewed by 2625

Abstract

Stimuli-responsive polymeric nanoparticles (NPs) exhibit reversible changes in the dispersion or aggregation state in response to external stimuli. In this context, we designed and synthesized core-shell NPs with threonine-containing weak polyelectrolyte shells and fluorescent cross-linked cores, which are applicable for the detection of [...] Read more.

Stimuli-responsive polymeric nanoparticles (NPs) exhibit reversible changes in the dispersion or aggregation state in response to external stimuli. In this context, we designed and synthesized core-shell NPs with threonine-containing weak polyelectrolyte shells and fluorescent cross-linked cores, which are applicable for the detection of pH changes and amine compounds in aqueous solution. Stable and uniform NP(dTh) and NP(Fl), consisting of fluorescent symmetric diphenyl dithiophene (dTh) and diphenyl fluorene (Fl) cross-linked cores, were prepared by site-selective Suzuki coupling reactions in self-assembled block copolymer. NP(Fl) with the Fl unit in the core showed a high fluorescence intensity in different solvents, which is regarded as an aggregation-induced emission-type NP showing strong emission in aggregated states in the cross-linked core. Unimodal NPs were observed in water at different pH values, and the diameter of NP(Fl) changed from 122 (pH = 2) to 220 nm (pH = 11). Furthermore, pH-dependent changes of the fluorescence peak positions and intensities were detected, which may be due to the core aggregation derived from the deprotonation of the threonine-based shell fragment. Specific interactions between the threonine-based shell of NP(Fl) and amine compounds (triethylamine and p-phenylenediamine) resulted in fluorescence quenching, suggesting the feasibility of fluorescent amine detection. Full article

(This article belongs to the Special Issue State-of-the-Art Polymer Science and Technology in Japan (2021,2022))

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12 pages, 2178 KB

Open AccessEditor’s ChoiceArticle

Integration of Biofunctional Molecules into 3D-Printed Polymeric Micro-/Nanostructures

by Eider Berganza, Gurunath Apte, Srivatsan K. Vasantham, Thi-Huong Nguyen and Michael Hirtz

Polymers 2022, 14(7), 1327; https://doi.org/10.3390/polym14071327 - 25 Mar 2022

Cited by 6 | Viewed by 4040

Abstract

Three-dimensional printing at the micro-/nanoscale represents a new challenge in research and development to achieve direct printing down to nanometre-sized objects. Here, FluidFM, a combination of microfluidics with atomic force microscopy, offers attractive options to fabricate hierarchical polymer structures at different scales. However, [...] Read more.

Three-dimensional printing at the micro-/nanoscale represents a new challenge in research and development to achieve direct printing down to nanometre-sized objects. Here, FluidFM, a combination of microfluidics with atomic force microscopy, offers attractive options to fabricate hierarchical polymer structures at different scales. However, little is known about the effect of the substrate on the printed structures and the integration of (bio)functional groups into the polymer inks. In this study, we printed micro-/nanostructures on surfaces with different wetting properties, and integrated molecules with different functional groups (rhodamine as a fluorescent label and biotin as a binding tag for proteins) into the base polymer ink. The substrate wetting properties strongly affected the printing results, in that the lateral feature sizes increased with increasing substrate hydrophilicity. Overall, ink modification only caused minor changes in the stiffness of the printed structures. This shows the generality of the approach, as significant changes in the mechanical properties on chemical functionalization could be confounders in bioapplications. The retained functionality of the obtained structures after UV curing was demonstrated by selective binding of streptavidin to the printed structures. The ability to incorporate binding tags to achieve specific interactions between relevant proteins and the fabricated micro-/nanostructures, without compromising the mechanical properties, paves a way for numerous bio and sensing applications. Additional flexibility is obtained by tuning the substrate properties for feature size control, and the option to obtain functionalized printed structures without post-processing procedures will contribute to the development of 3D printing for biological applications, using FluidFM and similar dispensing techniques. Full article

(This article belongs to the Special Issue Advanced Materials in 3D/4D Printing Technology)

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13 pages, 3435 KB

Open AccessEditor’s ChoiceArticle

One-Pot Green Preparation of Fluorescent Cellulose Nanofibers

by Qilin Lu, Jiayin Wu, Hanchen Wang and Biao Huang

Polymers 2022, 14(7), 1313; https://doi.org/10.3390/polym14071313 - 24 Mar 2022

Cited by 7 | Viewed by 3098

Abstract

Fluorescent cellulose nanofibers (FCNFs), with a high yield, were prepared via one-pot hydrolysis and the grafting reaction of cellulose with thiazolipyridine carboxylic acid (TPCA). The hydrolysis and Fischer esterification of cellulose were conducted under microwave-hydrothermal conditions; meanwhile, TPCA formation was induced by the [...] Read more.

Fluorescent cellulose nanofibers (FCNFs), with a high yield, were prepared via one-pot hydrolysis and the grafting reaction of cellulose with thiazolipyridine carboxylic acid (TPCA). The hydrolysis and Fischer esterification of cellulose were conducted under microwave-hydrothermal conditions; meanwhile, TPCA formation was induced by the dehydration reaction between L-cysteine and citric acid. The effects of the reaction temperature and reaction time on the yield and performance of FCNF were investigated. The morphology and size, surface chemical property, crystal structure, thermostability, and fluorescent performance of FCNF were characterized. The results revealed that the yield of FCNF reached 73.2% under a microwave power of 500 W, reaction temperature of 110 °C, and reaction time of 5 h. The FCNF obtained presents a short rod-like morphology. The crystallinity of the FCNFs is 80%, and their thermal stability did not decline significantly. Additionally, the fluorescent performance of the FCNFs is excellent, which results in them having good sensitivity to chloride ions. The good fluorescent performance and significant responsiveness to chloride ions of FCNFs lead to them having broad prospects in bio-labeling, biosensing, information storage, chloride ion detection, among others. Full article

(This article belongs to the Special Issue Synthesis and Application of Cellulose-Based Composites)

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32 pages, 2852 KB

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 63 | Viewed by 21126

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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17 pages, 4483 KB

Open AccessEditor’s ChoiceArticle

Development and Evaluation of Nanoparticles-in-Film Technology to Achieve Extended In Vivo Exposure of MK-2048 for HIV Prevention

by Xin Tong, Sravan Kumar Patel, Jing Li, Dorothy Patton, Elaine Xu, Peter L. Anderson, Urvi Parikh, Yvonne Sweeney, Julie Strizki, Sharon L. Hillier and Lisa C. Rohan

Polymers 2022, 14(6), 1196; https://doi.org/10.3390/polym14061196 - 16 Mar 2022

Cited by 4 | Viewed by 3043

Abstract

MK-2048 is a second-generation integrase inhibitor active against HIV, which has been applied vaginally using ring formulations. In this work, a nanoparticle-in-film technology was developed as a discrete pre-exposure prophylactic product option against HIV for an extended duration of use. A film platform [...] Read more.

MK-2048 is a second-generation integrase inhibitor active against HIV, which has been applied vaginally using ring formulations. In this work, a nanoparticle-in-film technology was developed as a discrete pre-exposure prophylactic product option against HIV for an extended duration of use. A film platform loaded with poly (lactic-co-glycolic acid) nanoparticles (PNP) encapsulating MK-2048 was engineered. MK-2048 PNPs were loaded into films that were manufactured via the solvent casting method. Physicochemical and mechanical properties, in vitro efficacy, Lactobacillus compatibility, in vitro and ex vivo permeability, and in vivo pharmacokinetics in macaques were evaluated. PNPs with a mean diameter of 382.2 nm and −15.2 mV zeta potential were obtained with 95.2% drug encapsulation efficiency. PNP films showed comparable in vitro efficacy to free MK-2048 (IC₅₀ 0.46 vs. 0.54 nM) and were found to have no impact on Lactobacillus. MK-2048 encapsulated in PNPs showed an increase in permeability (>4-fold) compared to the free MK-2048 in MDCKII cell lines. Furthermore, PNPs had higher ectocervical tissue permeability (1.7-fold) compared to free MK-2048. PNP films showed sustained drug levels for at least 3 weeks in the macaque vaginal fluid. This work demonstrates the synergy of integrating nanomedicine and polymeric film technology to achieve sustained vaginal drug delivery. Full article

(This article belongs to the Special Issue Advances in Natural or Synthetic Biomaterials for Developing Micro or Nano Drug Delivery Systems)

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35 pages, 10095 KB

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 59 | Viewed by 7281

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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16 pages, 2929 KB

Open AccessEditor’s ChoiceArticle

Evaluation of the Performance of a ZnO-Nanoparticle-Coated Hydrocolloid Patch in Wound Healing

by Van Anh Thi Le, Tung X. Trinh, Pham Ngoc Chien, Nguyen Ngan Giang, Xin-Rui Zhang, Sun-Young Nam and Chan-Yeong Heo

Polymers 2022, 14(5), 919; https://doi.org/10.3390/polym14050919 - 25 Feb 2022

Cited by 30 | Viewed by 5049

Abstract

Hydrocolloid dressings are an important method for accelerating wound healing. A combination of a hydrocolloid and nanoparticles (NPs), such as gold (Au), improves the wound healing rate, but Au-NPs are expensive and unable to block ultraviolet (UV) light. Herein, we combined zinc oxide [...] Read more.

Hydrocolloid dressings are an important method for accelerating wound healing. A combination of a hydrocolloid and nanoparticles (NPs), such as gold (Au), improves the wound healing rate, but Au-NPs are expensive and unable to block ultraviolet (UV) light. Herein, we combined zinc oxide nanoparticles (ZnO-NPs) with hydrocolloids for a less expensive and more effective UV-blocking treatment of wounds. Using Sprague–Dawley rat models, we showed that, during 10-day treatment, a hydrocolloid patch covered with ZnO-NPs (ZnO-NPs-HC) macroscopically and microscopically stimulated the wound healing rate and improved wound healing in the inflammation phase as shown by reducing of pro-inflammatory cytokines (CD68, IL-8, TNF-α, MCP-1, IL-6, IL-1β, and M1) up to 50%. The results from the in vitro models (RAW264.7 cells) also supported these in vivo results: ZnO-NPs-HCs improved wound healing in the inflammation phase by expressing a similar level of pro-inflammatory mediators (TNF-α and IL-6) as the negative control group. ZnO-NPs-HCs also encouraged the proliferation phase of the healing process, which was displayed by increasing expression of fibroblast biomarkers (α-SMA, TGF-β3, vimentin, collagen, and M2) up to 60%. This study provides a comprehensive analysis of wound healing by measuring the biomarkers in each phase and suggests a cheaper method for wound dressing. Full article

(This article belongs to the Section Polymer Applications)

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15 pages, 7414 KB

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 8 | Viewed by 3569

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 KB

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 69 | Viewed by 10146

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 KB

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 50 | Viewed by 12439

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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11 pages, 782 KB

Open AccessEditor’s ChoiceArticle

Bioactive Films Based on Starch from White, Red, and Black Rice to Food Application

by Luan Ramos da Silva, José Ignacio Velasco and Farayde Matta Fakhouri

Polymers 2022, 14(4), 835; https://doi.org/10.3390/polym14040835 - 21 Feb 2022

Cited by 10 | Viewed by 4434

Abstract

Packages from renewable sources have been the focus of many studies, due to the consumer needs for high-quality food, environmental concern related to the inadequate discard of packaging, low percentage of packaging recycling, and starch application by a viable method. Thus, this work [...] Read more.

Packages from renewable sources have been the focus of many studies, due to the consumer needs for high-quality food, environmental concern related to the inadequate discard of packaging, low percentage of packaging recycling, and starch application by a viable method. Thus, this work aimed to develop bioactive packages based on white, red, and black rice starch and analyze the influence of macromolecule and plasticizer type, even its blends, on the characteristics of films. Films were characterized by color, opacity, thickness, water solubility, water vapor permeability, and bioactive properties. The use of rice starch in the development of edible and/or biodegradable films was feasible, with all the formulations tested presenting a homogeneous matrix and the films obtained varying in hue, to the naked eye, as a function of the starch used. Variation of the type of starch and plasticizer, as well as the concentrations of the same, resulted in films with differences in all studied properties. Films prepared with 5% of starch and 30% of sorbitol showed phenolic compounds and antioxidant capacity, using the DPPH and ABTS methods, indicating that these can be considered bioactive packages and also suitable for food application. Full article

(This article belongs to the Special Issue Biopolymers from Renewable Sources and Their Applications)

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17 pages, 3431 KB

Open AccessEditor’s ChoiceArticle

Poly(vinyl pyridine) and Its Quaternized Derivatives: Understanding Their Solvation and Solid State Properties

by Katerina Mavronasou, Alexandra Zamboulis, Panagiotis Klonos, Apostolos Kyritsis, Dimitrios N. Bikiaris, Raffaello Papadakis and Ioanna Deligkiozi

Polymers 2022, 14(4), 804; https://doi.org/10.3390/polym14040804 - 19 Feb 2022

Cited by 34 | Viewed by 11661

Abstract

A series of N-methyl quaternized derivatives of poly(4-vinylpyridine) (PVP) were synthesized in high yields with different degrees of quaternization, obtained by varying the methyl iodide molar ratio and affording products with unexplored optical and solvation properties. The impact of quaternization on the physicochemical [...] Read more.

A series of N-methyl quaternized derivatives of poly(4-vinylpyridine) (PVP) were synthesized in high yields with different degrees of quaternization, obtained by varying the methyl iodide molar ratio and affording products with unexplored optical and solvation properties. The impact of quaternization on the physicochemical properties of the copolymers, and notably the solvation properties, was further studied. The structure of the synthesized polymers and the quaternization degrees were determined by infrared and nuclear magnetic spectroscopies, while their thermal characteristics were studied by differential scanning calorimetry and their thermal stability and degradation by thermogravimetric analysis (TG-DTA). Attention was given to their optical properties, where UV-Vis and diffuse reflectance spectroscopy (DRS) measurements were carried out. The optical band gap of the polymers was calculated and correlated with the degree of quaternization. The study was further orientated towards the solvation properties of the polymers in binary solvent mixtures that strongly depend on the degree of quaternization, enabling a better understanding of the key polymer (solute)-solvent interactions. The assessment of the underlying solvation phenomena was performed in a system of different ratios of DMSO/H₂O and the solvatochromic indicator used was Reichardt’s dye. Solvent polarity parameters have a significant effect on the visible spectra of the nitrogen quaternization of PVP studied in this work and a detailed path towards this assessment is presented. Full article

(This article belongs to the Special Issue Advances and Applications of Block Copolymers)

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13 pages, 2135 KB

Open AccessEditor’s ChoiceArticle

Thermally Degradable Poly(n-butyl acrylate) Model Networks Prepared by PhotoATRP and Radical Trap-Assisted Atom Transfer Radical Coupling

by Michael R. Martinez, Ziye Zhuang, Megan Treichel, Julia Cuthbert, Mingkang Sun, Joanna Pietrasik and Krzysztof Matyjaszewski

Polymers 2022, 14(4), 713; https://doi.org/10.3390/polym14040713 - 12 Feb 2022

Cited by 2 | Viewed by 4127

Abstract

Model poly(n-butyl acrylate) (PBA) networks were prepared by photoinduced atom transfer radical polymerization (photoATRP), followed by curing of polymer stars via atom transfer radical coupling (ATRC) with a nitrosobenzene radical trap. The resulting nitroxyl radical installed thermally labile alkoxyamine functional groups [...] Read more.

Model poly(n-butyl acrylate) (PBA) networks were prepared by photoinduced atom transfer radical polymerization (photoATRP), followed by curing of polymer stars via atom transfer radical coupling (ATRC) with a nitrosobenzene radical trap. The resulting nitroxyl radical installed thermally labile alkoxyamine functional groups at the junctions of the network. The alkoxyamine crosslinks of the network were degraded back to star-like products upon exposure to temperatures above 135 °C. Characterization of the degraded products via gel permeation chromatography (GPC) confirmed the inversion of polymer topology after thermal treatment. Full article

(This article belongs to the Collection State-of-the-Art Polymer Science and Technology in Poland)

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24 pages, 59957 KB

Open AccessEditor’s ChoiceArticle

Multi-Analytical Investigations of Andy Warhol’s “Orange Car Crash”: Polymeric Materials in Modern Paints

by Valentina Pintus, Anthony J. Baragona, Federica Cappa, Christa Haiml, Christina Hierl, Katja Sterflinger and Manfred Schreiner

Polymers 2022, 14(3), 633; https://doi.org/10.3390/polym14030633 - 7 Feb 2022

Cited by 6 | Viewed by 4151

Abstract

This work presents strategic multi-analytical investigations performed on “Orange Car Crash” by Andy Warhol in order to make a well-informed conservation decision. For determining the type of binding medium used in the artwork, Pyrolysis–Gas Chromatography/Mass Spectrometry (Py–GC/MS) and Thermally Assisted Hydrolysis [...] Read more.

This work presents strategic multi-analytical investigations performed on “Orange Car Crash” by Andy Warhol in order to make a well-informed conservation decision. For determining the type of binding medium used in the artwork, Pyrolysis–Gas Chromatography/Mass Spectrometry (Py–GC/MS) and Thermally Assisted Hydrolysis and Methylation of GC/MS (THM–GC/MS) were employed. The presence of a coating was investigated by Py–GC/MS. Moreover, the comprehension and elucidation of the paint stratigraphy were studied by examining cross-sections of samples taken from both canvases with Optical Microscopy (OM) under reflected visible (Vis) and ultraviolet light (UV) and by Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM–EDX). The investigation of possible synthetic organic pigments (SOPs) and extenders was performed by µ-Raman spectroscopy, while micro-Attenuated Total Reflection of Fourier-Transform Attenuated Total Reflection (µ-ATR–FTIR) allowed us to assign each component detected by Py–GC/MS or THM–GC/MS to a specific layer. The data collected from “Orange Car Crash” show mostly the application of acrylic-based paint as well as alkyd with rosin acids-based ink, thus providing fundamental information about the paint stratigraphy and chemical composition of each layer. In addition to the goal of informing an appropriate conservation–restoration strategy, this work represents a rare scientific study of a work by Andy Warhol. Full article

(This article belongs to the Special Issue Polymeric Materials in Modern-Contemporary Art)

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12 pages, 1357 KB

Open AccessEditor’s ChoiceArticle

Enhancing Mechanical Properties of Graft-Type Nanocomposites Using Organically Modified SiO₂ and Polypropylene Containing Reactive Methoxy Groups

by Dongzhi Zhu, Eiji Kurahashi, Hui You, Toru Wada, Patchanee Chammingkwan and Toshiaki Taniike

Polymers 2022, 14(3), 563; https://doi.org/10.3390/polym14030563 - 30 Jan 2022

Cited by 13 | Viewed by 3980

Abstract

In situ grafting of a reactive matrix and nanofillers is a promising strategy to fabricate graft-type polypropylene (PP)-based nanocomposites, where the grafting efficiency is affected by the initial dispersion of nanofillers in the matrix. In this work, influences of surface organic modification of [...] Read more.

In situ grafting of a reactive matrix and nanofillers is a promising strategy to fabricate graft-type polypropylene (PP)-based nanocomposites, where the grafting efficiency is affected by the initial dispersion of nanofillers in the matrix. In this work, influences of surface organic modification of nanofillers were investigated on properties of PP/SiO₂ nanocomposites using poly(propylene-co-octenyltrimethoxysilane) as a reactive matrix. The surface modification of SiO₂, especially with longer alkyl chains, led to improved dispersion of nanoparticles, thus promoting the grafting reaction and mechanical properties. The combination of in situ grafting and surface modification of nanofillers provided several benefits, most notably in balancing the strength and the toughness, which could not be achieved by the grafting alone. Full article

(This article belongs to the Special Issue Polyolefins: The Ever-Thriving Thermoplastics)

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17 pages, 2730 KB

Open AccessEditor’s ChoiceArticle

Core-Shell Magnetoactive PHB/Gelatin/Magnetite Composite Electrospun Scaffolds for Biomedical Applications

by Artyom S. Pryadko, Vladimir V. Botvin, Yulia R. Mukhortova, Igor Pariy, Dmitriy V. Wagner, Pavel P. Laktionov, Vera S. Chernonosova, Boris P. Chelobanov, Roman V. Chernozem, Maria A. Surmeneva, Andrei L. Kholkin and Roman A. Surmenev

Polymers 2022, 14(3), 529; https://doi.org/10.3390/polym14030529 - 28 Jan 2022

Cited by 38 | Viewed by 4827

Abstract

Novel hybrid magnetoactive composite scaffolds based on poly(3-hydroxybutyrate) (PHB), gelatin, and magnetite (Fe₃O₄) were fabricated by electrospinning. The morphology, structure, phase composition, and magnetic properties of composite scaffolds were studied. Fabrication procedures of PHB/gelatin and PHB/gelatin/Fe₃O₄ [...] Read more.

Novel hybrid magnetoactive composite scaffolds based on poly(3-hydroxybutyrate) (PHB), gelatin, and magnetite (Fe₃O₄) were fabricated by electrospinning. The morphology, structure, phase composition, and magnetic properties of composite scaffolds were studied. Fabrication procedures of PHB/gelatin and PHB/gelatin/Fe₃O₄ scaffolds resulted in the formation of both core-shell and ribbon-shaped structure of the fibers. In case of hybrid PHB/gelatin/Fe₃O₄ scaffolds submicron-sized Fe₃O₄ particles were observed in the surface layers of the fibers. The X-ray photoelectron spectroscopy results allowed the presence of gelatin on the fiber surface (N/C ratio–0.11) to be revealed. Incubation of the composite scaffolds in saline for 3 h decreased the amount of gelatin on the surface by more than ~75%. The differential scanning calorimetry results obtained for pure PHB scaffolds revealed a characteristic melting peak at 177.5 °C. The presence of gelatin in PHB/gelatin and PHB/gelatin/Fe₃O₄ scaffolds resulted in the decrease in melting temperature to 168–169 °C in comparison with pure PHB scaffolds due to the core-shell structure of the fibers. Hybrid scaffolds also demonstrated a decrease in crystallinity from 52.3% (PHB) to 16.9% (PHB/gelatin) and 9.2% (PHB/gelatin/Fe₃O₄). All the prepared scaffolds were non-toxic and saturation magnetization of the composite scaffolds with magnetite was 3.27 ± 0.22 emu/g, which makes them prospective candidates for usage in biomedical applications. Full article

(This article belongs to the Topic Advances in Biomaterials)

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16 pages, 3852 KB

Open AccessEditor’s ChoiceArticle

Synthesis of Polyacids by Copolymerization of l-Lactide with MTC-COOH Using Zn[(acac)(L)H₂O] Complex as an Initiator

by Joanna Jaworska, Michał Sobota, Małgorzata Pastusiak, Michał Kawalec, Henryk Janeczek, Piotr Rychter, Kamila Lewicka and Piotr Dobrzyński

Polymers 2022, 14(3), 503; https://doi.org/10.3390/polym14030503 - 27 Jan 2022

Cited by 4 | Viewed by 2927

Abstract

This work presents the results of research on the preparation of bioresorbable functional polyestercarbonates containing side carboxyl groups. These copolymers were synthesized in two ways: the classic two-step process involving the copolymerization of l-lactide and a cyclic carbonate containing a blocked side [...] Read more.

This work presents the results of research on the preparation of bioresorbable functional polyestercarbonates containing side carboxyl groups. These copolymers were synthesized in two ways: the classic two-step process involving the copolymerization of l-lactide and a cyclic carbonate containing a blocked side carboxylate group in the form of a benzyl ester (MTC-Bz) and its subsequent deprotection, and a new way involving the one-step copolymerization of l-lactide with this same carbonate, but containing an unprotected carboxyl group (MTC-COOH). Both reactions were carried out under identical conditions in the melt, using a specially selected zinc chelate complex, with Zn[(acac)(L)H₂O] (where: L—N-(pyridin-4-ylmethylene) phenylalaninate ligand) as an initiator. The differences in the kinetics of both reactions and their courses were pictured. The reactivity of the MTC-COOH monomer without a blocking group in the studied co-polymerization was much higher, even slightly higher than l-lactide, which allowed the practically complete conversion of the comonomers in a much shorter time. The basic final properties of the obtained copolymers and the microstructures of their chains were determined. The single-step synthesis of biodegradable polyacids was much simpler. Contrary to the conventional method, this made it possible to obtain copolymers containing all carbonate units with carboxyl groups, without even traces of the heavy metals used in the deprotection of the carboxyl groups, the presence of which is known to be very difficult to completely remove from the copolymers obtained in the two-step process. Full article

(This article belongs to the Topic Advances in Biomaterials)

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12 pages, 2227 KB

Open AccessEditor’s ChoiceArticle

Lignin Distribution on Cell Wall Micro-Morphological Regions of Fibre in Developmental Phyllostachys pubescens Culms

by Bo Liu, Lina Tang, Qian Chen, Liming Zhu, Xianwu Zou, Botao Li, Qin Zhou, Yuejin Fu and Yun Lu

Polymers 2022, 14(2), 312; https://doi.org/10.3390/polym14020312 - 13 Jan 2022

Cited by 15 | Viewed by 2547

Abstract

Bamboo is a natural fibre reinforced composite with excellent performance which is, to a certain extent, an alternative to the shortage of wood resources. The heterogeneous distribution and molecular structure of lignin is one of the factors that determines its performance, and it [...] Read more.

Bamboo is a natural fibre reinforced composite with excellent performance which is, to a certain extent, an alternative to the shortage of wood resources. The heterogeneous distribution and molecular structure of lignin is one of the factors that determines its performance, and it is the key and most difficult component in the basic research into the chemistry of bamboo and in bamboo processing and utilization. In this study, the distribution of lignin components and lignin content in micro-morphological regions were measured in semi-quantitative level by age and radial location by means of visible-light microspectrophotometry (VLMS) coupled with the Wiesner and Maule reaction. There as guaiacyl lignin and syringyl lignin in the cell wall of the fibre. Lignin content of the secondary cell wall and cell corner increased at about 10 days, reached a maximum at 1 year, and then decreased gradually. From 17 days to 4 years, the lignin content of the secondary cell wall in the outer part of bamboo is higher than that in the middle part (which is, in turn, higher than that in the inner part of the bamboo). VLSM results of the micro-morphological regions showed that bamboo lignification developed by aging. Guaiacyl and syringl lignin units can be found in the cell wall of the fibre, parenchyma, and vessel. There was a difference in lignin content among different ages, different radial location, and different micro-morphological regions of the cell wall. The fibre walls were rich in guaiacyl lignin in the early stage of lignification and rich in syringyl units in the later stage of lignification. The guaiacyl and syringyl lignin deposition of bamboo green was earlier than that of the middle part of bamboo culm, and that of the middle part of bamboo culm was earlier than that of bamboo yellow. The single molecule lignin content of the thin layer is higher than that of thick layers, while the primary wall is higher than the secondary cell wall, showing that lignin deposition is consistent with the rules of cell wall formation. The obtained cytological information is helpful to understand the origin of the anisotropic, physical, mechanical, chemical, and machining properties of bamboo. Full article

(This article belongs to the Special Issue Eco Polymeric Materials and Natural Polymer)

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15 pages, 2138 KB

Open AccessEditor’s ChoiceArticle

Anomalous Thermal Characteristics of Poly(ionic liquids) Derived from 1-Butyl-2,3-dimethyl-4-vinylimidazolium Salts

by Fan Yang, Meng Zhao, Darren Smith, Peggy Cebe, Sam Lucisano, Thomas Allston and Thomas W. Smith

Polymers 2022, 14(2), 254; https://doi.org/10.3390/polym14020254 - 8 Jan 2022

Cited by 1 | Viewed by 2761

Abstract

The synthesis of 1-butyl-2,3-dimethyl-4-vinylimidazolium triflate, its polymerization, and ion exchange to yield a trio of 1-butyl-2,3-dimethyl-4-vinylimidazolium polymers is described. Irrespective of the nature of the anion, substitution at the 2-position of the imidazolium moiety substantially increases the distance between the anion and cation. [...] Read more.

The synthesis of 1-butyl-2,3-dimethyl-4-vinylimidazolium triflate, its polymerization, and ion exchange to yield a trio of 1-butyl-2,3-dimethyl-4-vinylimidazolium polymers is described. Irrespective of the nature of the anion, substitution at the 2-position of the imidazolium moiety substantially increases the distance between the anion and cation. The methyl substituent at the 2-position also served to expose the importance of H-bonding for the attractive potential between imidazolium moiety and anions in polymers without a methyl group at the 2-position. The thermal characteristics of poly(1-butyl-2,3-dimethyl-4-vinylimidazolium) salts and corresponding poly(1-ethyl-3-methyl-4-vinylimidazolium) salts were evaluated. While the mid-point glass transition temperatures, T_g-mid, for 1-ethyl-3-methyl-4-vinylimidazolium polymers with CF₃SO₃⁻, (CF₃SO₂)₂N⁻ and PF₆⁻ counterions, were 153 °C, 88 °C and 200 °C, respectively, the T_g-mid values for 1-butyl-2,3-dimethyl-4vinylimidazolium polymers with corresponding counter-ions were tightly clustered at 98 °C, 99 °C and 84 °C, respectively. This dramatically reduced influence of the anion type on the glass transition temperature was attributed to the increased distance between the center of the anions and cations in the 1-butyl-2,3-dimethyl-4-vinylimidazolium polymer set, and minimal H-bonding interactions between the respective anions and the 1-butyl-2,3-dimethyl-4-vinylimidazolium moiety. It is believed that this is the first observation of substantial independence of the glass transition of an ionic polymer on the nature of its counterion. Full article

(This article belongs to the Section Polymer Processing and Engineering)

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13 pages, 13478 KB

Open AccessEditor’s ChoiceArticle

Construction of a (NNN)Ru-Incorporated Porous Organic Polymer with High Catalytic Activity for β-Alkylation of Secondary Alcohols with Primary Alcohols

by Yao Cui, Jixian Wang, Lei Yu, Ying Xu, David J. Young, Haiyan Li and Hongxi Li

Polymers 2022, 14(2), 231; https://doi.org/10.3390/polym14020231 - 7 Jan 2022

Cited by 5 | Viewed by 2658

Abstract

Solid supports functionalized with molecular metal catalysts combine many of the advantages of heterogeneous and homogeneous catalysis. A (NNN)Ru-incorporated porous organic polymer (POP-bp/bbpRuCl₃) exhibited high catalytic efficiency and broad functional group tolerance in the C–C cross-coupling of secondary and primary alcohols [...] Read more.

Solid supports functionalized with molecular metal catalysts combine many of the advantages of heterogeneous and homogeneous catalysis. A (NNN)Ru-incorporated porous organic polymer (POP-bp/bbpRuCl₃) exhibited high catalytic efficiency and broad functional group tolerance in the C–C cross-coupling of secondary and primary alcohols to give β-alkylated secondary alcohols. This catalyst demonstrated excellent durability during successive recycling without leaching of Ru which is ascribed to the strong binding of the pincer ligands to the metal ions. Full article

(This article belongs to the Special Issue High Performance Porous Polymers)

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14 pages, 6932 KB

Open AccessEditor’s ChoiceArticle

Analysis of the Parameters Affecting the Stiffness of Short Sisal Fiber Biocomposites Manufactured by Compression-Molding

by Antonio Pantano, Carmelo Militello, Francesco Bongiorno and Bernardo Zuccarello

Polymers 2022, 14(1), 154; https://doi.org/10.3390/polym14010154 - 31 Dec 2021

Cited by 23 | Viewed by 2520

Abstract

The use of natural fiber-based composites is on the rise in many industries. Thanks to their eco-sustainability, these innovative materials make it possible to adapt the production of components, systems and machines to the increasingly stringent regulations on environmental protection, while at the [...] Read more.

The use of natural fiber-based composites is on the rise in many industries. Thanks to their eco-sustainability, these innovative materials make it possible to adapt the production of components, systems and machines to the increasingly stringent regulations on environmental protection, while at the same time reducing production costs, weight and operating costs. Optimizing the mechanical properties of biocomposites is an important goal of applied research. In this work, using a new numerical approach, the effects of the volume fraction, average length, distribution of orientation and curvature of fibers on the Young’s modulus of a biocomposite reinforced with short natural fibers were studied. Although the proposed approach could be applied to any biocomposite, sisal fibers and an eco-sustainable thermosetting matrix (green epoxy) were considered in both simulations and the associated experimental assessment. The results of the simulations showed the following effects of the aforementioned parameters on Young’s modulus: a linear growth with the volume fraction, nonlinear growth as the length of the fibers increased, a reduction as the average curvature increased and an increase in stiffness in the x-y plane as the distribution of fiber orientation in the z direction decreased. Full article

(This article belongs to the Special Issue High-Performance Biocomposite Reinforced by Natural Fibers)

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11 pages, 3830 KB

Open AccessEditor’s ChoiceArticle

Study on the Flame Retardancy and Hazard Evaluation of Poly(acrylonitrile-co-vinylidene chloride) Fibers by the Addition of Antimony-Based Flame Retardants

by Hyelim Kim, Ji-Su Kim and Wonyoung Jeong

Polymers 2022, 14(1), 42; https://doi.org/10.3390/polym14010042 - 23 Dec 2021

Cited by 7 | Viewed by 3492

Abstract

Antimony oxide (ATO) is used mainly as a flame retardant, but it is classified as a hazardous substance. Therefore, regulations on the use of antimony trioxide (ATO(3)) and antimony pentoxide (ATO(5)) in textile products are being developed. Accordingly, there is a need for [...] Read more.

Antimony oxide (ATO) is used mainly as a flame retardant, but it is classified as a hazardous substance. Therefore, regulations on the use of antimony trioxide (ATO(3)) and antimony pentoxide (ATO(5)) in textile products are being developed. Accordingly, there is a need for alternative flame retardants. In this study, antimony tetroxide (ATO(4)), which has higher thermal stability and resistance to acids and alkalis than ATO(3) or ATO(5), was selected to assess its use as an alternative flame retardant. First, ATO(3) or ATO(4) were added to poly(acrylonitrile-co-vinylidene chloride) (PANVDC), and the film and wet-spun fiber were prepared. The PANVDC film with flame retardants was prepared to evaluate the flame retardancy and the mechanism of action of the flame retardants. Flame retardancy analysis showed that a limiting oxygen index of 31.2% was obtained when ATO(4) was added, which was higher than when ATO(3) was used. Subsequently, PANVDC fibers with antimony oxide were manufactured and showed improved mechanical and thermal properties when ATO(4) was used, compared to when ATO(3) was tested. In addition, migration analysis due to antimony in the fiber confirmed that the elution amount was below the acceptable standard when PANVDC fibers with ATO(4) were added. Therefore, based on these results, the flame-retardant and thermal properties of antimony tetroxide were superior to antimony trioxide, and it was confirmed that ATO(4) could be used as an alternative flame retardant to ATO(3). Full article

(This article belongs to the Special Issue Fire-Safe Polymer Composites: Structure and Application)

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17 pages, 4555 KB

Open AccessEditor’s ChoiceArticle

Chitosan Membrane Containing Copaiba Oil (Copaifera spp.) for Skin Wound Treatment

by Sheila Barbosa Paranhos, Elisângela da Silva Ferreira, Caio Augusto de Almeida Canelas, Simone Patrícia Aranha da Paz, Marcele Fonseca Passos, Carlos Emmerson Ferreira da Costa, Alisson Clay Rios da Silva, Sergio Neves Monteiro and Verônica Scarpini Candido

Polymers 2022, 14(1), 35; https://doi.org/10.3390/polym14010035 - 23 Dec 2021

Cited by 14 | Viewed by 4614

Abstract

The interaction of copaiba oil in the polymer matrix of chitosan can produce a favorable synergistic effect and potentiate properties. Indeed, the bioactive principles present in copaiba oil have anti-inflammatory and healing action. In the present work, chitosan membranes containing different contents of [...] Read more.

The interaction of copaiba oil in the polymer matrix of chitosan can produce a favorable synergistic effect and potentiate properties. Indeed, the bioactive principles present in copaiba oil have anti-inflammatory and healing action. In the present work, chitosan membranes containing different contents of copaiba oil copaíba (0.1, 0.5, 1.0 and 5.0% (v/v)) were for the first time investigated. The membranes were developed by the casting method and analyzed for their morphology, degree of intumescence, moisture content, contact angle, Scanning Electron Microscope, and X-ray diffractometry. These chitosan/copaiba oil porous membranes disclosed fluid absorption capacity, hydrophilic surface, and moisture. In addition, the results showed that chitosan membranes with the addition of 1.0% (v/v) of copaiba oil presented oil drops with larger diameters, around 123.78 μm. The highest fluid absorption indexes were observed in chitosan membranes containing 0.1 and 0.5% (v/v) of copaiba oil. In addition, the copaiba oil modified the crystalline structure of chitosan. Such characteristics are expected to favor wound treatment. However, biological studies are necessary for the safe use of chitosan/copaiba oil membrane as a biomaterial. Full article

(This article belongs to the Special Issue Advanced Hybrid Composite Materials for Engineering and Biomedical Applications)

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