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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Green Chemistry".

Deadline for manuscript submissions: closed (30 September 2017) | Viewed by 56778

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Dr. Sylvain Caillol

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Institut Charles Gerhardt Montpellier (ICGM), University of Montpellier, CNRS, ENSCM, 34095 Montpellier, France
Interests: green and sustainable chemistry; building-blocks from biomass; biobased monomers and polymers
Special Issues, Collections and Topics in MDPI journals

Dr. Guillaume Couture

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Research Scientist, Institute Charles Gerhardt, 34296 Montpellier, France
Interests: thermosets; green chemistry; bio-based monomers and polymers

Special Issue Information

Dear Colleagues,

The price volatility of oil-based monomers and the increasing concern from the civil society for health, environment, and sustainability issues, have urged chemists around the planet to look for alternatives to fossil-based derivatives, especially in the field of polymers. The past fifteen years have seen a booming number of articles and review describing the use of bio-resources as a starting point for original polymer chemistry. Working directly with crude products, such as chitosan, cellulose, or lignin, or using building blocks from biomass, such as terpenes or vanillin derivatives, researchers have developed elegant ways to synthesize functional monomers and polymers for various applications, in binders, coatings, composites and nano- and multi-scale structured-materials. Hence, these latest developments not only created a library of polymeric materials exhibiting a wide range of properties to fulfill the requirements of various industrial applications, but they also improved our knowledge and understanding of the structure and reactivity of the complex biomass.

This Special Issue on "Natural Polymers and Biopolymers" will present on cutting edge research works, focusing on the use of bio-resources for polymeric materials. It will demonstrate that the field of “green polymers” is still gaining increased attention, highlighting that natural and biopolymers, with their interesting and original properties, are destined to replace their oil-based competitors.

Dr. Sylvain Caillol
Dr. Guillaume Couture
Guest Editors

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Keywords

Biopolymers
Bio-based molecules
Chemical functionalization
Thermosets
Structure characterization
Thermal properties
Mechanical properties
Sustainability

Related Special Issues

Natural Polymers and Biopolymers II in Molecules (27 articles)
Natural Polymers and Biopolymers III in Molecules (15 articles)

Published Papers (10 papers)

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Research

17 pages, 4258 KiB

Open AccessArticle

Synthesis and Characterization of a Bioartificial Polymeric System with Potential Antibacterial Activity: Chitosan-Polyvinyl Alcohol-Ampicillin

by Andres Bernal-Ballen, Jorge Lopez-Garcia, Martha-Andrea Merchan-Merchan and Marian Lehocky

Molecules 2018, 23(12), 3109; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23123109 - 28 Nov 2018

Cited by 16 | Viewed by 3564

Abstract

Bio-artificial polymeric systems are a new class of polymeric constituents based on blends of synthetic and natural polymers, designed with the purpose of producing new materials that exhibit enhanced properties with respect to the individual components. In this frame, a combination of polyvinyl alcohol (PVA) and chitosan, blended with a widely used antibiotic, sodium ampicillin, has been developed showing a moderate behavior in terms of antibacterial properties. Thus, aqueous solutions of PVA at 1 wt.% were mixed with acid solutions of chitosan at 1 wt.%, followed by adding ampicillin ranging from 0.3 to 1.0 wt.% related to the total amount of the polymers. The prepared bio-artificial polymeric system was characterized by FTIR, SEM, DSC, contact angle measurements, antibacterial activity against Staphylococcus aureus and Escherichia coli and antibiotic release studies. The statistical significance of the antibacterial activity was determined using a multifactorial analysis of variance with ρ < 0.05 (ANOVA). The characterization techniques did not show alterations in the ampicillin structure and the interactions with polymers were limited to intermolecular forces. Therefore, the antibiotic was efficiently released from the matrix and its antibacterial activity was preserved. The system disclosed moderate antibacterial activity against bacterial strains without adding a high antibiotic concentration. The findings of this study suggest that the system may be effective against healthcare-associated infections, a promising view in the design of novel antimicrobial biomaterials potentially suitable for tissue engineering applications. Full article

(This article belongs to the Special Issue Natural Polymers and Biopolymers)

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16 pages, 3609 KiB

Open AccessFeature PaperArticle

Limonene-Based Epoxy: Anhydride Thermoset Reaction Study

by Guillaume Couture, Lérys Granado, Florent Fanget, Bernard Boutevin and Sylvain Caillol

Molecules 2018, 23(11), 2739; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23112739 - 23 Oct 2018

Cited by 27 | Viewed by 5512

Abstract

The development of epoxy thermosets from renewable resources is of paramount importance in a sustainable development context. In this paper, a novel bio-based epoxy monomer derived from limonene was synthesized without epichlorohydrine and characterized. In fact, this paper depicts the synthesis of bis-limonene oxide (bis-LO). However, intern epoxy rings generally exhibit a poor reactivity and allow reaction with anhydride. Therefore, we used a reaction model with hexahydro-4-methylphthalic anhydride to compare reactivity of terminal and interepoxy functions. We also studied the influence of methyl group on intern epoxy functions. Furthermore, the influence of epoxy:anhydride stoichiometry and initiator amount was studied. These studies allow to propose an optimized formulation of bis-LO. Finally, a bis-LO-based thermoset was obtained and characterized. Full article

(This article belongs to the Special Issue Natural Polymers and Biopolymers)

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18 pages, 6797 KiB

Open AccessArticle

Synthesis and Characterization of Poly(Vinyl Alcohol)-Chitosan-Hydroxyapatite Scaffolds: A Promising Alternative for Bone Tissue Regeneration

by Sergio Pineda-Castillo, Andrés Bernal-Ballén, Cristian Bernal-López, Hugo Segura-Puello, Diana Nieto-Mosquera, Andrea Villamil-Ballesteros, Diana Muñoz-Forero and Lukas Munster

Molecules 2018, 23(10), 2414; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23102414 - 20 Sep 2018

Cited by 29 | Viewed by 4735

Abstract

Scaffolds can be considered as one of the most promising treatments for bone tissue regeneration. Herein, blends of chitosan, poly(vinyl alcohol), and hydroxyapatite in different ratios were used to synthesize scaffolds via freeze-drying. Mechanical tests, FTIR, swelling and solubility degree, DSC, morphology, and cell viability were used as characterization techniques. Statistical significance of the experiments was determined using a two-way analysis of variance (ANOVA) with p < 0.05. Crosslinked and plasticized scaffolds absorbed five times more water than non-crosslinked and plasticized ones, which is an indicator of better hydrophilic features, as well as adequate resistance to water without detriment of the swelling potential. Indeed, the tested mechanical properties were notably higher for samples which were undergone to crosslinking and plasticized process. The presence of chitosan is determinant in pore formation and distribution which is an imperative for cell communication. Uniform pore size with diameters ranging from 142 to 519 µm were obtained, a range that has been described as optimal for bone tissue regeneration. Moreover, cytotoxicity was considered as negligible in the tested conditions, and viability indicates that the material might have potential as a bone regeneration system. Full article

(This article belongs to the Special Issue Natural Polymers and Biopolymers)

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17 pages, 3176 KiB

Open AccessFeature PaperArticle

Enzymatic Synthesis of Amino Acids Endcapped Polycaprolactone: A Green Route Towards Functional Polyesters

by Stéphane W. Duchiron, Eric Pollet, Sébastien Givry and Luc Avérous

Molecules 2018, 23(2), 290; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23020290 - 30 Jan 2018

Cited by 10 | Viewed by 5681

Abstract

ε-caprolactone (CL) has been enzymatically polymerized using α-amino acids based on sulfur (methionine and cysteine) as (co-)initiators and immobilized lipase B of Candida antarctica (CALB) as biocatalyst. In-depth characterizations allowed determining the corresponding involved mechanisms and the polymers thermal properties. Two synthetic strategies were tested, a first one with direct polymerization of CL with the native amino acids and a second one involving the use of an amino acid with protected functional groups. The first route showed that mainly polycaprolactone (PCL) homopolymer could be obtained and highlighted the lack of reactivity of the unmodified amino acids due to poor solubility and affinity with the lipase active site. The second strategy based on protected cysteine showed higher monomer conversion, with the amino acids acting as (co-)initiators, but their insertion along the PCL chains remained limited to chain endcapping. These results thus showed the possibility to synthesize enzymatically polycaprolactone-based chains bearing amino acids units. Such cysteine endcapped PCL materials could then find application in the biomedical field. Indeed, subsequent functionalization of these polyesters with drugs or bioactive molecules can be obtained, by derivatization of the amino acids, after removal of the protecting group. Full article

(This article belongs to the Special Issue Natural Polymers and Biopolymers)

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2031 KiB

Open AccessArticle

Characterization of Non-Derivatized Cellulose Samples by Size Exclusion Chromatography in Tetrabutylammonium Fluoride/Dimethylsulfoxide (TBAF/DMSO)

by Jérémy Rebière, Antoine Rouilly, Vanessa Durrieu and Frédéric Violleau

Molecules 2017, 22(11), 1985; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22111985 - 16 Nov 2017

Cited by 6 | Viewed by 4815

Abstract

This paper deals with the use of tetrabutylammonium fluoride/dimethylsulfoxide (TBAF/DMSO) to characterize the molar mass distribution of non-derivatized cellulosic samples by size exclusion chromatography (SEC). Different cellulose samples with various average degree of polymerization (DP) were first solubilized in this solvent system, with increasing TBAF rates, and then analyzed by SEC coupled to a refractive index detector (RID), using DMSO as mobile phase. The Molar Masses (MM) obtained by conventional calibration were then discussed and compared with suppliers’ data and MM determined by viscosimetry measurements. By this non-classic method, molar mass of low DP samples (Avicel^® and cotton fibers) have been determined. For high DP samples (α-cellulose and Vitacel^®), dissolution with TBAF concentration of 10 mg/mL involved elution of cellulose aggregates in the exclusion volume, related to an incomplete dissolution or the dilution of TBAF molecules in elution solvent, preventing the correct evaluation of their molar mass. Full article

(This article belongs to the Special Issue Natural Polymers and Biopolymers)

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7926 KiB

Open AccessArticle

Characteristics of Multifunctional, Eco-Friendly Lignin-Al₂O₃ Hybrid Fillers and Their Influence on the Properties of Composites for Abrasive Tools

by Łukasz Klapiszewski, Artur Jamrozik, Beata Strzemiecka, Iwona Koltsov, Bartłomiej Borek, Danuta Matykiewicz, Adam Voelkel and Teofil Jesionowski

Molecules 2017, 22(11), 1920; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22111920 - 07 Nov 2017

Cited by 24 | Viewed by 4822

Abstract

The main aim of the present study was the preparation and comprehensive characterization of innovative additives to abrasive materials based on functional, pro-ecological lignin-alumina hybrid fillers. The behavior of lignin, alumina and lignin-Al₂O₃ hybrids in a resin matrix was explained on the basis of their surface and application properties determined by inverse gas chromatography, the degree of adhesion/cohesion between components, thermomechanical and rheological properties. On the basis of the presented results, a hypothetical mechanism of interactions between lignin and Al₂O₃ as well as between lignin-Al₂O₃ hybrids and phenolic resins was proposed. It was concluded that lignin compounds can provide new, promising properties for a phenolic binder combining the good properties of this biopolymer as a plasticizer and of alumina as a filler improving mechanical and thermal properties. The use of such materials may be relatively non-complicated and efficient way to improve the performance of bonded abrasive tools. Full article

(This article belongs to the Special Issue Natural Polymers and Biopolymers)

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1869 KiB

Open AccessArticle

Single Actin Bundle Rheology

by Dan Strehle, Paul Mollenkopf, Martin Glaser, Tom Golde, Carsten Schuldt, Josef A. Käs and Jörg Schnauß

Molecules 2017, 22(10), 1804; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22101804 - 24 Oct 2017

Cited by 11 | Viewed by 4600

Abstract

Bundled actin structures play an essential role in the mechanical response of the actin cytoskeleton in eukaryotic cells. Although responsible for crucial cellular processes, they are rarely investigated in comparison to single filaments and isotropic networks. Presenting a highly anisotropic structure, the determination of the mechanical properties of individual bundles was previously achieved through passive approaches observing bending deformations induced by thermal fluctuations. We present a new method to determine the bending stiffness of individual bundles, by measuring the decay of an actively induced oscillation. This approach allows us to systematically test anisotropic, bundled structures. Our experiments revealed that thin, depletion force-induced bundles behave as semiflexible polymers and obey the theoretical predictions determined by the wormlike chain model. Thickening an individual bundle by merging it with other bundles enabled us to study effects that are solely based on the number of involved filaments. These thicker bundles showed a frequency-dependent bending stiffness, a behavior that is inconsistent with the predictions of the wormlike chain model. We attribute this effect to internal processes and give a possible explanation with regard to the wormlike bundle theory. Full article

(This article belongs to the Special Issue Natural Polymers and Biopolymers)

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2912 KiB

Open AccessArticle

Development, Optimization and In Vitro/In Vivo Characterization of Collagen-Dextran Spongious Wound Dressings Loaded with Flufenamic Acid

by Mihaela Violeta Ghica, Mădălina Georgiana Albu Kaya, Cristina-Elena Dinu-Pîrvu, Dumitru Lupuleasa and Denisa Ioana Udeanu

Molecules 2017, 22(9), 1552; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22091552 - 15 Sep 2017

Cited by 42 | Viewed by 6157

Abstract

The aim of this study was the development and optimization of some topical collagen-dextran sponges with flufenamic acid, designed to be potential dressings for burn wounds healing. The sponges were obtained by lyophilization of hydrogels based on type I fibrillar collagen gel extracted from calf hide, dextran and flufenamic acid, crosslinked and un-crosslinked, and designed according to a 3-factor, 3-level Box-Behnken experimental design. The sponges showed good fluid uptake ability quantified by a high swelling ratio. The flufenamic acid release profiles from sponges presented two stages—burst effect resulting in a rapid inflammation reduction, and gradual delivery ensuring the anti-inflammatory effect over a longer burn healing period. The resistance to enzymatic degradation was monitored through a weight loss parameter. The optimization of the sponge formulations was performed based on an experimental design technique combined with response surface methodology, followed by the Taguchi approach to select those formulations that are the least affected by the noise factors. The treatment of experimentally induced burns on animals with selected sponges accelerated the wound healing process and promoted a faster regeneration of the affected epithelial tissues compared to the control group. The results generated by the complex sponge characterization indicate that these formulations could be successfully used for burn dressing applications. Full article

(This article belongs to the Special Issue Natural Polymers and Biopolymers)

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6335 KiB

Open AccessArticle

Phase Behaviour and Miscibility Studies of Collagen/Silk Fibroin Macromolecular System in Dilute Solutions and Solid State

by Ima Ghaeli, Mariana A. De Moraes, Marisa M. Beppu, Katarzyna Lewandowska, Alina Sionkowska, Frederico Ferreira-da-Silva, Maria P. Ferraz and Fernando J. Monteiro

Molecules 2017, 22(8), 1368; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22081368 - 18 Aug 2017

Cited by 22 | Viewed by 6146

Abstract

Miscibility is an important issue in biopolymer blends for analysis of the behavior of polymer pairs through the detection of phase separation and improvement of the mechanical and physical properties of the blend. This study presents the formulation of a stable and one-phase mixture of collagen and regenerated silk fibroin (RSF), with the highest miscibility ratio between these two macromolecules, through inducing electrostatic interactions, using salt ions. For this aim, a ternary phase diagram was experimentally built for the mixtures, based on observations of phase behavior of blend solutions with various ratios. The miscibility behavior of the blend solutions in the miscible zones of the phase diagram was confirmed quantitatively by viscosimetric measurements. Assessing the effects of biopolymer mixing ratio and salt ions, before and after dialysis of blend solutions, revealed the importance of ion-specific interactions in the formation of coacervate-based materials containing collagen and RSF blends that can be used in pharmaceutical, drug delivery, and biomedical applications. Moreover, the conformational change of silk fibroin from random coil to beta sheet, in solution and in the final solid films, was detected by circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR), respectively. Scanning electron microscopy (SEM) exhibited alterations of surface morphology for the biocomposite films with different ratios. Surface contact angle measurement illustrated different hydrophobic properties for the blended film surfaces. Differential scanning calorimetry (DSC) showed that the formation of the beta sheet structure of silk fibroin enhances the thermal stability of the final blend films. Therefore, the novel method presented in this study resulted in the formation of biocomposite films whose physico-chemical properties can be tuned by silk fibroin conformational changes by applying different component mixing ratios. Full article

(This article belongs to the Special Issue Natural Polymers and Biopolymers)

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3883 KiB

Open AccessArticle

Polyurethane Foams for Thermal Insulation Uses Produced from Castor Oil and Crude Glycerol Biopolyols

by Camila S. Carriço, Thaís Fraga, Vagner E. Carvalho and Vânya M. D. Pasa

Molecules 2017, 22(7), 1091; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22071091 - 02 Jul 2017

Cited by 49 | Viewed by 9704

Abstract

Rigid polyurethane foams were synthesized using a renewable polyol from the simple physical mixture of castor oil and crude glycerol. The effect of the catalyst (DBTDL) content and blowing agents in the foams’ properties were evaluated. The use of physical blowing agents (cyclopentane and n-pentane) allowed foams with smaller cells to be obtained in comparison with the foams produced with a chemical blowing agent (water). The increase of the water content caused a decrease in density, thermal conductivity, compressive strength, and Young’s modulus, which indicates that the increment of CO₂ production contributes to the formation of larger cells. Higher amounts of catalyst in the foam formulations caused a slight density decrease and a small increase of thermal conductivity, compressive strength, and Young’s modulus values. These green foams presented properties that indicate a great potential to be used as thermal insulation: density (23–41 kg·m⁻³), thermal conductivity (0.0128–0.0207 W·m⁻¹·K⁻¹), compressive strength (45–188 kPa), and Young’s modulus (3–28 kPa). These biofoams are also environmentally friendly polymers and can aggregate revenue to the biodiesel industry, contributing to a reduction in fuel prices. Full article

(This article belongs to the Special Issue Natural Polymers and Biopolymers)

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