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Polymers from Renewable Sources and Their Mechanical Reinforcement

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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Physics and Theory".

Deadline for manuscript submissions: closed (30 May 2022) | Viewed by 46916

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Special Issue Editors

Dr. Micaela Vannini

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Guest Editor

Department of Civil, Chemical, Environmental and Materials Engineering, University of Bologna, via Terracini 28, 40131 Bologna, Italy
Interests: synthesis and characterization of novel polymeric materials with particular focus on the polymers deriving from renewable materials; composites and nanocomposites; design of polymeric structures characterized by high gas barrier properties

Dr. Laura Sisti

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Guest Editor

Department of Civil, Chemical, Environmental and Materials Engineering, University of Bologna, via Terracini 28, 40131 Bologna, Italy
Interests: synthesis and characterization of new polymer materials; preparation of composites and nanocomposites; polymers from renewable sources and their mechanical reinforcement with natural fibers and inorganic fillers

Special Issue Information

Dear Colleagues,

Currently, the Scientific Community has to face big concerns bound to worldwide plastic pollution and climate change due to the increment in Green House Gas emissions. Even the polymer scientists have been called to put into play their knowledge and expertise to achieve new solutions for the material production that do not impact on the environment. One possible route to answer to this demand is the development of polymers that are deriving from renewable sources, which being renewable are always available and not exhaustible as petroleum, and being usually obtained from biomass are CO₂-neutral materials.

However sometimes, polymers derived from renewable sources display inadequate mechanical properties which limit their potential applications and therefore restrain their development and use. To solve these drawbacks, chemical modifications of the macromolecular structure, the addition of fibers, organic or inorganic additives or the application of physical or thermal treatments could be applied.

This Special Issue aims at highlighting the progress on the mechanical reinforcement of bioderived materials, by focusing on new additives, new blending processes or new technologies.

Dr. Micaela Vannini
Dr. Laura Sisti
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Biocomposites
physical blending
mechanical properties
mechanical reinforcement
renewable sources
bioderived polymers
fillers
nanofillers
fibers

Published Papers (13 papers)

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Research

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11 pages, 1199 KiB

Open AccessArticle

Valorization of Ferulic Acid from Agro-Industrial by-Products for Application in Agriculture

by Maria Pilar Villanueva, Claudio Gioia, Laura Sisti, Laura Martí, Raquel Llorens-Chiralt, Steven Verstichel and Annamaria Celli

Polymers 2022, 14(14), 2874; https://doi.org/10.3390/polym14142874 - 15 Jul 2022

Cited by 5 | Viewed by 1617

Abstract

The use of bioplastic mulch in agriculture has increased dramatically in the last years throughout the world. Nowadays, biodegradable materials for mulching films strive to constitute a reliable and more sustainable alternative to classical materials such as polyethylene (PE). The main challenge is to improve their durability in the soil to meet the required service length for crop farming by using benign and sustainable antioxidant systems. Here, we report the design and fabrication of biodegradable materials based on polybutylene (succinate adipate) (PBSA) for mulching applications, incorporating a fully biobased polymeric antioxidant deriving from ferulic acid, which can be extracted from an industrial by-product. Poly-dihydro (ethylene ferulate) (PHEF) from ferulic acid was synthesized by a two-step polymerization process. It is characterized by improved thermal stability in comparison with ferulic acid monomer and therefore suitable for common industrial processing conditions. Different blends of PBSA and PHEF obtained by melt mixing or by reactive extrusion were prepared and analyzed to understand the effect of the presence of PHEF. The results demonstrate that PHEF, when processed by reactive extrusion, presents a remarkable antioxidant effect, even in comparison with commercial additives, preserving a high level of the mechanical properties of the PBSA matrix without affecting the biodegradable character of the blend. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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16 pages, 9628 KiB

Open AccessArticle

Relationships between the Decomposition Behaviour of Renewable Fibres and Their Reinforcing Effect in Composites Processed at High Temperatures

by Janez Slapnik, Thomas Lucyshyn and Gerald Pinter

Polymers 2021, 13(24), 4448; https://doi.org/10.3390/polym13244448 - 18 Dec 2021

Cited by 5 | Viewed by 2112

Abstract

Engineering polymers reinforced with renewable fibres (RF) are an attractive class of materials, due to their excellent mechanical performance and low environmental impact. However, the successful preparation of such composites has proven to be challenging due to the low thermal stability of RF. The aim of the present study was to investigate how different RF behaves under increased processing temperatures and correlate the thermal properties of the fibres to the mechanical properties of composites. For this purpose, hemp, flax and Lyocell fibres were compounded into polypropylene (PP) using a co-rotating twin screw extruder and test specimens were injection moulded at temperatures ranging from 180 °C to 260 °C, with 20 K steps. The decomposition behaviour of fibres was characterised using non-isothermal and isothermal simultaneous thermogravimetric analysis/differential scanning calorimetry (TGA/DSC). The prepared composites were investigated using optical microscopy (OM), colorimetry, tensile test, Charpy impact test, dynamic mechanical analysis (DMA) and melt flow rate (MFR). Composites exhibited a decrease in mechanical performance at processing temperatures above 200 °C, with a steep decrease observed at 240 °C. Lyocell fibres exhibited the best reinforcement effect, especially at elevated processing temperatures, followed by flax and hemp fibres. It was found that the retention of the fibre reinforcement effect at elevated temperatures can be well predicted using isothermal TGA measurements. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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19 pages, 4703 KiB

Open AccessArticle

The Influence of Chosen Plant Fillers in PHBV Composites on the Processing Conditions, Mechanical Properties and Quality of Molded Pieces

by Wiesław Frącz, Grzegorz Janowski, Robert Smusz and Marek Szumski

Polymers 2021, 13(22), 3934; https://doi.org/10.3390/polym13223934 - 14 Nov 2021

Cited by 11 | Viewed by 1896

Abstract

This work is inspired by the current European policies that aim to reduce plastic waste. This is especially true of the packaging industry. The biocomposites developed in the work belong to the group of environmentally friendly plastics that can reduce the increasing costs of environmental fees in the future. Three types of short fibers (flax, hemp and wood) with a length of 1 mm each were selected as fillers (30% mass content in PHBV). The biocomposites were extruded and then processed by the injection molding process with the same technical parameters. The samples obtained in this way were tested for mechanical properties and quality of the molded pieces. A significant improvement of some mechanical properties of biocomposites containing hemp and flax fibers and quality of molded pieces was obtained in comparison with pure PHBV. Only in the case of wood–PHBV biocomposites was no significant improvement of properties obtained compared to biocomposites with other fillers used in this research. The use of natural fibers, in particular hemp fibers as a filler in the PHBV matrix, in most cases has a positive effect on improving the mechanical properties and quality of molded pieces. In addition, it should be remembered that the obtained biocomposites are of natural origin and are fully biodegradable, which are interesting and desirable properties that are a part of the current trend regarding the production and commercialization of modern biomaterials. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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16 pages, 4311 KiB

Open AccessArticle

Bio-Based Furan-Polyesters/Graphene Nanocomposites Prepared by In Situ Polymerization

by Laura Sisti, Grazia Totaro, Annamaria Celli, Loris Giorgini, Simone Ligi and Micaela Vannini

Polymers 2021, 13(9), 1377; https://doi.org/10.3390/polym13091377 - 23 Apr 2021

Cited by 4 | Viewed by 2031

Abstract

In situ intercalative polymerization has been investigated as a strategic way to obtain poly(propylene 2,5-furandicarboxylate) (PPF) and poly(hexamethylene 2,5-furandicarboxylate) (PHF) nanocomposites with different graphene types and amounts. Graphene (G) has been dispersed in surfactant stabilized water suspensions. The loading range in composites was 0.25–0.75 wt %. For the highest composition, a different type of graphene (XT500) dispersed in 1,3 propanediol, containing a 6% of oxidized graphene and without surfactant has been also tested. The results showed that the amorphous PPF is able to crystallize during heating scan in DSC and graphene seems to affect such capability: G hinders the polymer chains in reaching an ordered state, showing even more depressed cold crystallization and melting. On the contrary, such hindering effect is absent with XT500, which rather induces the opposite. Concerning the thermal stability, no improvement has been induced by graphene, even if the onset degradation temperatures remain high for all the materials. A moderate enhancement in mechanical properties is observed in PPF composite with XT500, and especially in PHF composite, where a significative increase of 10–20% in storage modulus E’ is maintained in almost all the temperature range. Such an increase is also reflected in a slightly higher heat distortion temperature. These preliminary results can be useful in order to further address the field of application of furan-based polyesters; in particular, they could be promising as packaging materials. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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18 pages, 6237 KiB

Open AccessArticle

Integrated Efforts for the Valorization of Sweet Potato By-Products within a Circular Economy Concept: Biocomposites for Packaging Applications Close the Loop

by Micaela Vannini, Paola Marchese, Laura Sisti, Andrea Saccani, Taihua Mu, Hongnan Sun and Annamaria Celli

Polymers 2021, 13(7), 1048; https://doi.org/10.3390/polym13071048 - 27 Mar 2021

Cited by 14 | Viewed by 6075

Abstract

With the aim to fully exploit the by-products obtained after the industrial extraction of starch from sweet potatoes, a cascading approach was developed to extract high-value molecules, such as proteins and pectins, and to valorize the solid fraction, rich in starch and fibrous components. This fraction was used to prepare new biocomposites designed for food packaging applications. The sweet potato residue was added to poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in various amounts up to 40 wt % by melt mixing, without any previous treatment. The composites are semicrystalline materials, characterized by thermal stability up to 260 °C. For the composites containing up to 10 wt % of residue, the tensile strength remains over 30 MPa and the strain stays over 3.2%. A homogeneous dispersion of the sweet potato waste into the bio-polymeric matrix was achieved but, despite the presence of hydrogen bond interactions between the components, a poor interfacial adhesion was detected. Considering the significant percentage of sweet potato waste used, the biocomposites obtained show a low economic and environmental impact, resulting in an interesting bio-alternative to the materials commonly used in the packaging industry. Thus, according to the principles of a circular economy, the preparation of the biocomposites closes the loop of the complete valorization of sweet potato products and by-products. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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14 pages, 3526 KiB

Open AccessArticle

Effect of Mineral Fillers on the Mechanical Properties of Commercially Available Biodegradable Polymers

by Wouter Post, Lambertus J. Kuijpers, Martin Zijlstra, Maarten van der Zee and Karin Molenveld

Polymers 2021, 13(3), 394; https://doi.org/10.3390/polym13030394 - 27 Jan 2021

Cited by 18 | Viewed by 5128

Abstract

In the successful transition towards a circular materials economy, the implementation of biobased and biodegradable plastics is a major prerequisite. To prevent the accumulation of plastic material in the open environment, plastic products should be both recyclable and biodegradable. Research and development actions in the past few decades have led to the commercial availability of a number of polymers that fulfil both end-of-life routes. However, these biobased and biodegradable polymers typically have mechanical properties that are not on par with the non-biodegradable plastic products they intend to replace. This can be improved using particulate mineral fillers such as talc, calcium carbonate, kaolin, and mica. This study shows that composites thereof with polybutylene succinate (PBS), polyhydroxybutyrate-hexanoate (PHBH), polybutylene succinate adipate (PBSA), and polybutylene adipate terephthalate (PBAT) as matrix polymers result in plastic materials with mechanical properties ranging from tough elastic towards strong and rigid. It is demonstrated that the balance between the Young’s modulus and the impact resistance for this set of polymer composites is subtle, but a select number of investigated compositions yield a combination of industrially relevant mechanical characteristics. Finally, it is shown that the inclusion of mineral fillers into biodegradable polymers does not negate the microbial disintegration of these polymers, although the nature of the filler does affect the biodegradation rate of the matrix polymer. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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Graphical abstract

14 pages, 19988 KiB

Open AccessArticle

Comparing the Influence of Residual Stress on Composite Materials Made of Polyhydroxybutyrate (PHB) and Amorphous Hydrogenated Carbon (a-C:H) Layers: Differences Caused by Single Side and Full Substrate Film Attachment during Plasma Coating

by Torben Schlebrowski, Rachida Ouali, Barbara Hahn, Stefan Wehner and Christian B. Fischer

Polymers 2021, 13(2), 184; https://doi.org/10.3390/polym13020184 - 06 Jan 2021

Cited by 3 | Viewed by 1817

Abstract

Polyhydroxybutyrate (PHB) is a bio-based, biodegradable and commercially used polymer, which in its native form is unfortunately not generally applicable. A widely used technique to adapt polymers to a wider range of applications is the surface modification with amorphous hydrogenated carbon (a-C:H) layers, realized by plasma-enhanced chemical vapor deposition (PE-CVD). However, this process creates intrinsic stress in the layer–polymer system which can even lead to full layer failure. The aim of this study was to investigate how the carbon layer is affected when the basic polymer film to be coated can follow the stress and bend (single side attachment) and when it cannot do so because it is firmly clamped (full attachment). For both attachment methods, the a-C:H layers were simultaneously deposited on PHB samples. Ex-situ characterization was performed using a scanning electron microscope (SEM) for surface morphology and contact angle (CA) measurements for wettability. In addition, the stress prevailing in the layer was calculated using the Stoney equation. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) measurements were used to investigate the chemical composition of the coating surface. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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21 pages, 2735 KiB

Open AccessArticle

Adenine as Epoxy Resin Hardener for Sustainable Composites Production with Recycled Carbon Fibers and Cellulosic Fibers

by Stefano Merighi, Laura Mazzocchetti, Tiziana Benelli and Loris Giorgini

Polymers 2020, 12(12), 3054; https://doi.org/10.3390/polym12123054 - 20 Dec 2020

Cited by 4 | Viewed by 2868

Abstract

In this work, Adenine is proposed, for the first time, as a cross-linker for epoxy resins. Adenine is an amino-substituted purine with heterocyclic aromatic structure showing both proton donors, and hydrogen bonding ability. DSC studies show that adenine is able to positively cross-link a biobased DGEBA-like commercial epoxy precursor with good thermal performance and a reaction mechanism based on a ¹H NMR investigation has been proposed. The use of such a formulation to produce composite with recycled short carbon fibers (and virgin ones for the sake of comparison), as well as jute and linen natural fibers as sustainable reinforcements, leads to materials with high compaction and fiber content. The curing cycle was optimized for both carbon fiber and natural fiber reinforced materials, with the aim to achieve the better final properties. All composites produced display good thermal and mechanical properties with glass transition in the range of HT resins (T_g > 150 °C, E’ =26 GPa) for the carbon fiber-based composites. The natural fiber-based composites display slightly lower performance that is nonetheless good compared with standard composite performance (T_g about 115–120 °C, E’ = 7–9 GPa). The present results thus pave the way to the application of adenine as hardener system for composites production. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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18 pages, 7362 KiB

Open AccessArticle

On the Use of Biobased Waxes to Tune Thermal and Mechanical Properties of Polyhydroxyalkanoates–Bran Biocomposites

by Vito Gigante, Patrizia Cinelli, Maria Cristina Righetti, Marco Sandroni, Giovanni Polacco, Maurizia Seggiani and Andrea Lazzeri

Polymers 2020, 12(11), 2615; https://doi.org/10.3390/polym12112615 - 06 Nov 2020

Cited by 16 | Viewed by 2714

Abstract

In this work, processability and mechanical performances of bio-composites based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) containing 5, 10, and 15 wt % of bran fibers, untreated and treated with natural carnauba and bee waxes were evaluated. Wheat bran, the main byproduct of flour milling, was used as filler to reduce the final cost of the PHBV-based composites and, in the same time, to find a potential valorization to this agro-food by-product, widely available at low cost. The results showed that the wheat bran powder did not act as reinforcement, but as filler for PHBV, due to an unfavorable aspect ratio of the particles and poor adhesion with the polymeric matrix, with consequent moderate loss in mechanical properties (tensile strength and elongation at break). The surface treatment of the wheat bran particles with waxes, and in particular with beeswax, was found to improve the mechanical performance in terms of tensile properties and impact resistance of the composites, enhancing the adhesion between the PHBV-based polymeric matrix and the bran fibers, as confirmed by predictive analytic models and dynamic mechanical analysis results. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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17 pages, 3310 KiB

Open AccessArticle

Eco-Conversion of Two Winery Lignocellulosic Wastes into Fillers for Biocomposites: Vine Shoots and Wine Pomaces

by Grégoire David, Micaela Vannini, Laura Sisti, Paola Marchese, Annamaria Celli, Nathalie Gontard and Hélène Angellier-Coussy

Polymers 2020, 12(7), 1530; https://doi.org/10.3390/polym12071530 - 10 Jul 2020

Cited by 19 | Viewed by 2773

Abstract

Two winery residues, namely vine shoots (ViSh) and wine pomace (WiPo), were up-cycled as fillers in PHBV-based biocomposites. Answering a biorefinery approach, the impact of a preliminary polyphenols extraction step using an acetone/water mixture on the reinforcing effect of fillers was assessed. Biocomposites (filler content up to 20 wt%) were prepared by melt-mixing and compared in terms of final performance (thermal, mechanical and barrier). It was shown that the reinforcing effect was slightly better in the case of vine shoots, while it was not significantly affected by the pre-treatment, demonstrating that these two winery residues could be perfectly used as fillers in composite materials even after an extraction process to maximize their potential of valorization. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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Review

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14 pages, 3889 KiB

Open AccessReview

A Brief Review on the Influence of Ionic Liquids on the Mechanical, Thermal, and Chemical Properties of Biodegradable Polymer Composites

by Ahmad Adlie Shamsuri, Siti Nurul Ain Md. Jamil and Khalina Abdan

Polymers 2021, 13(16), 2597; https://doi.org/10.3390/polym13162597 - 05 Aug 2021

Cited by 16 | Viewed by 2600

Abstract

Biodegradable polymers are an exceptional class of polymers that can be decomposed by bacteria. They have received significant interest from researchers in several fields. Besides this, biodegradable polymers can also be incorporated with fillers to fabricate biodegradable polymer composites. Recently, a variety of ionic liquids have also been applied in the fabrication of the polymer composites. In this brief review, two types of fillers that are utilized for the fabrication of biodegradable polymer composites, specifically organic fillers and inorganic fillers, are described. Three types of synthetic biodegradable polymers that are commonly used in biodegradable polymer composites, namely polylactic acid (PLA), polybutylene succinate (PBS), and polycaprolactone (PCL), are reviewed as well. Additionally, the influence of two types of ionic liquid, namely alkylimidazolium- and alkylphosphonium-based ionic liquids, on the mechanical, thermal, and chemical properties of the polymer composites, is also briefly reviewed. This review may be beneficial in providing insights into polymer composite investigators by enhancing the properties of biodegradable polymer composites via the employment of ionic liquids. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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23 pages, 5262 KiB

Open AccessReview

Recycling of Chrome-Tanned Leather and Its Utilization as Polymeric Materials and in Polymer-Based Composites: A Review

by Mariafederica Parisi, Alessandro Nanni and Martino Colonna

Polymers 2021, 13(3), 429; https://doi.org/10.3390/polym13030429 - 29 Jan 2021

Cited by 43 | Viewed by 5661

Abstract

Tanneries generate large amounts of solid and liquid wastes, which contain harmful chemical compounds in the environment, such as chromium, that is used in the tanning process. Until now, they have been almost completely dumped in landfills. Thus, finding eco-sustainable and innovative alternatives for the management and disposal of these wastes is becoming a huge challenge for tanneries and researchers around the world. In particular, the scientific and industrial communities have started using wastes to produce new materials exploiting the characteristics of leather, which are strongly connected with the macromolecular structure of its main component, collagen. None of the reviews on leather waste management actually present in the scientific literature report in detail the use of leather to make composite materials and the mechanical properties of the materials obtained, which are of fundamental importance for an effective industrial exploitation of leather scraps. This comprehensive review reports for the first time the state of the art of the strategies related to the recovery and valorization of both hydrolyzed collagen and leather waste for the realization of composite materials, reporting in detail the properties and the industrial applications of the materials obtained. In the conclusion section, the authors provide practical implications for industry in relation to sustainability and identify research gaps that can guide future authors and industries in their work. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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29 pages, 3401 KiB

Open AccessReview

Wine By-Products as Raw Materials for the Production of Biopolymers and of Natural Reinforcing Fillers: A Critical Review

by Alessandro Nanni, Mariafederica Parisi and Martino Colonna

Polymers 2021, 13(3), 381; https://doi.org/10.3390/polym13030381 - 26 Jan 2021

Cited by 31 | Viewed by 8203

Abstract

The plastic industry is today facing a green revolution; however, biopolymers, produced in low amounts, expensive, and food competitive do not represent an efficient solution. The use of wine waste as second-generation feedstock for the synthesis of polymer building blocks or as reinforcing fillers could represent a solution to reduce biopolymer costs and to boost the biopolymer presence in the market. The present critical review reports the state of the art of the scientific studies concerning the use of wine by-products as substrate for the synthesis of polymer building blocks and as reinforcing fillers for polymers. The review has been mainly focused on the most used bio-based and biodegradable polymers present in the market (i.e., poly(lactic acid), poly(butylene succinate), and poly(hydroxyalkanoates)). The results present in the literature have been reviewed and elaborated in order to suggest new possibilities of development based on the chemical and physical characteristics of wine by-products. Full article

(This article belongs to the Special Issue Polymers from Renewable Sources and Their Mechanical Reinforcement)

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