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Advances in Polymer Recycling and Upcycling: Toward a Circular and Sustainable Future

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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Circular and Green Sustainable Polymer Science".

Deadline for manuscript submissions: closed (31 January 2026) | Viewed by 6916

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Special Issue Editors

Dr. Nuno Gama

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Guest Editor

CICECO—Aveiro Institute of Materials and Department of Chemistry, University of Aveiro—Campus Santiago, 3810-193 Aveiro, Portugal
Interests: polymers; polyurethane; polymers recycling; circular polymer economy
Special Issues, Collections and Topics in MDPI journals

Dr. Alessandra Lorenzetti

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Guest Editor

Department of Industrial Engineering, University of Padova, Via Marzolo, 9, 35131 Padova, Italy
Interests: polymer recycling; upcycling; enzymatic recycling; circular economy
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue will explore critical advances and challenges in polymer recycling and upcycling, highlighting innovative strategies to enhance material circularity and reduce environmental impacts. It aims to cover the following topics:

Recycling Technologies: this refers to progress in mechanical, chemical, and biological recycling methods, improved sorting and separation techniques, and innovations to retain polymer properties during processing.
Upcycling Approaches: examples of these approaches include converting plastic waste into higher-value products, developing functionalized polymers, and employing advanced methods like reactive extrusion and catalysis.
Sustainability and Circular Economy: by incorporating life cycle assessments (LCAs), we can gauge environmental impacts, present industrial case studies, and examine policies and market trends driving polymer recycling and upcycling.
Novel Materials and Composites: utilizing recycled content in polymer blends can create biocomposites and biologically derived materials as alternatives to conventional plastics, developing hybrid materials for better performance and recyclability.
The Integration of Safety and Sustainability: from the outset of polymer design and recycling, environmental impact can be minimized, enhancing material performance and supporting circular economy goals through advanced recycling and upcycling innovations.
Challenges and Future Directions: this involves addressing polymer degradation, contamination, and mixed waste streams, leveraging emerging technologies like AI and robotics in waste management, and setting research priorities to improve recycling efficiency and material quality.

This Special Issue aims to foster collaboration among academia, industry, and policymakers, driving innovation in polymer recycling and upcycling for a sustainable future.

Dr. Nuno Gama
Dr. Alessandra Lorenzetti
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 250 words) can be sent to the Editorial Office for assessment.

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

polymer recycling
upcycling
circular economy
sustainable materials
waste valorization
environmental impact

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Published Papers (5 papers)

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Research

22 pages, 4150 KB

Open AccessArticle

Closed-Loop Chemical Recycling of Polylactide via Glycolysis: From Water-Soluble Oligomers to High-Purity Lactide

by Gadir Aliev, Roman Toms, Matvey Marinichev, Daniil Ismailov, Kirill Kirshanov and Alexander Gervald

Polymers 2026, 18(5), 655; https://doi.org/10.3390/polym18050655 - 7 Mar 2026

Viewed by 395

Abstract

Polylactide (PLA) has become widely adopted across biomedical, packaging, and manufacturing sectors due to its biodegradability and renewable sourcing. However, the rapid growth in PLA consumption has created urgent challenges related to waste management and the cleaning of processing equipment. This study investigates glycolysis as a promising chemical depolymerization pathway for PLA recycling and in situ reactor cleaning. A systematic analysis of four glycolysis agents (GA) (ethylene glycol, diethylene glycol, propylene glycol, and glycerol) was performed across molar PLA:GA ratios from 1:0.125 to 1:4 at 220 °C, targeting the efficient conversion of high-molecular-weight PLA (Mn ≈ 165 kDa) into low-molecular-weight oligomers. Gel permeation chromatography (GPC) demonstrated that propylene glycol exhibited the highest depolymerization efficiency, yielding oligomers with Mn as low as 200 g·mol⁻¹ even at minimal glycolysis agent ratios, while glycerol produced hydroxyl-rich oligomers optimal for subsequent lactide synthesis. Hydroxyl value (HV) measurements showed excellent agreement with theoretical values (<5% deviation), allowing us to make an assumption about an approximate, close to near-quantitative con-version. Glycolysis products with Mw below 400 g·mol⁻¹ displayed excellent water solubility, making them particularly attractive for reactor cleaning applications. Using glycerol-derived (GL) oligomers (PLA:GL = 1:0.25), purified L-lactide with a melting point of 98.1 °C and high purity (>99%) was obtained through thermocatalytic depolymerization and five recrystallization cycles, as confirmed by ¹H nuclear magnetic resonance (¹H NMR) and differential scanning calorimetry (DSC) analyses. The recovered lactide’s high purity renders it suitable for ring-opening polymerization, enabling closed-loop PLA recycling schemes. Overall, glycolysis emerges as a highly promising chemical recycling route complementary to hydrolysis and pyrolysis: propylene glycol maximizes depolymerization efficiency for cleaning applications, while glycerol optimizes oligomer functionality for lactide recovery and advanced material synthesis. Our results provide practical guidelines for selecting glycolysis agents and conditions for cleaning and recycling applications. Full article

(This article belongs to the Special Issue Advances in Polymer Recycling and Upcycling: Toward a Circular and Sustainable Future)

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19 pages, 4219 KB

Open AccessArticle

Mitigating Composition Variability in Post-Industrial PC/ABS Recycling via Targeted Compatibilization

by Silvia Zanatta, Eleonora Dal Lago, Filippo Dall’Amico, Carlo Boaretti, Alessandra Lorenzetti, Martina Roso and Michele Modesti

Polymers 2025, 17(21), 2848; https://doi.org/10.3390/polym17212848 - 25 Oct 2025

Viewed by 1124

Abstract

The growing demand for sustainable solutions in the plastics industry has highlighted the need to reintroduce post-industrial polymer waste into high-performance applications. This study focuses on the mechanical recycling of automotive scraps containing variable proportions of polycarbonate (PC), acrylonitrile–butadiene–styrene (ABS), and a commercial PC/ABS blend. After determining the composition of two representative batches, a screening of seven commercial compatibilizers and impact modifiers was performed to improve impact strength. Among them, an ethylene–methyl acrylate–glycidyl methacrylate (E-MA-GMA) terpolymer was identified as the most effective additive. Its influence was further investigated through a mixture design approach, varying the composition of the three polymer phases and the additive content (0–10 wt.%). The resulting response surface model revealed a significant increase in impact resistance in PC-rich formulations with increasing E-MA-GMA content, while ABS and PC/ABS showed more complex trends. Rheological, mechanical, and thermal analyses supported the observed behavior, suggesting improved matrix compatibility and reduced degradation during processing. The proposed model enables the prediction of impact performance across a wide range of compositions, offering a practical tool for the optimization of recycled blends. These findings support the potential of targeted compatibilization strategies for closed-loop recycling in the automotive sector. Full article

(This article belongs to the Special Issue Advances in Polymer Recycling and Upcycling: Toward a Circular and Sustainable Future)

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16 pages, 2400 KB

Open AccessArticle

Recycling of Polyurethanes via Covalent Adaptable Networks: The Role of Crosslink Density in Performance Recovery

by Edoardo Miravalle, Teodora Andra Olariu, Claudio Cecone, Valentina Brunella, Pierangiola Bracco and Marco Zanetti

Polymers 2025, 17(20), 2778; https://doi.org/10.3390/polym17202778 - 17 Oct 2025

Cited by 1 | Viewed by 1241

Abstract

Thermoset polyurethanes invite industrial interest for their versatility and chemical and mechanical resistance due to their permanently crosslinked networks; yet this structural feature severely limits their recyclability. Recent advances in Covalent Adaptable Networks (CANs), enabled by Dynamic Covalent Chemistry (DCC), have demonstrated promising pathways toward reprocessability through bond-exchange mechanisms. However, no clear link has yet been identified between material properties and the retention of performance after reprocessing. This work investigates the role of crosslink density as a key factor in determining the reprocessability of polyurethane networks. Two model systems with comparable compositions but distinct crosslink densities were synthesised, reprocessed, and compared. Relaxation analysis based on the Maxwellian approach proved insufficient to predict reprocessing outcomes. Only the highly crosslinked network yielded homogeneous reprocessable films with significant retention of mechanical performance, whereas the less crosslinked network resulted in incoherent materials with markedly reduced properties. The application of Kohlrausch–Williams–Watts (KWW) fitting revealed that dynamic covalent exchange dominates relaxation in the highly crosslinked system, while in the looser network, relaxation is governed by soft segment mobility, hindering effective network reformation. These findings underscore the pivotal role of crosslink density in determining the recyclability of thermoset polyurethanes and provide new insights for the rational design of reprocessable materials. Full article

(This article belongs to the Special Issue Advances in Polymer Recycling and Upcycling: Toward a Circular and Sustainable Future)

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22 pages, 2631 KB

Open AccessArticle

Arabinoxylan-Based Bioplastic from Wheat Bran: A Promising Replacement for Synthetic Plastics

by Md Abdur Rahim Badsha, Michael Kjelland, Chad Ulven and Khwaja Hossain

Polymers 2025, 17(18), 2488; https://doi.org/10.3390/polym17182488 - 15 Sep 2025

Cited by 1 | Viewed by 1384

Abstract

The milling process of wheat annually generates over 150 million tons of wheat bran (WB), which has significant potential for bioplastic production. However, the production of bioplastics from these resources has never been explored until now. Wheat bran (WB) polymer was evaluated for its potential as an environmentally friendly biodegradable plastic, exhibiting a tensile strength of 2.3 MPa, elongation exceeding 100%, and resistance to diluted mineral acids, thereby highlighting its suitability for food packaging and related applications. The biodegradable plastic films were prepared through a molding process that involved three steps: (1) extraction of arabinoxylan from wheat bran, (2) hydrolysis and plasticization with glycerol, and (3) blending with polyvinyl alcohol (PVA) in varying proportions. The resulting bioplastic exhibits competitive mechanical properties and biodegradability. Furthermore, the biodegradable plastic developed in this research contributes to agricultural waste management, the development of value-added products, and the reduction of carbon emissions incurred from plastic industries. Additionally, it can replace and reduce reliance on synthetic plastics, which are non-degradable and a source of severe environmental pollution. Full article

(This article belongs to the Special Issue Advances in Polymer Recycling and Upcycling: Toward a Circular and Sustainable Future)

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13 pages, 5041 KB

Open AccessArticle

A Sustainable Microwave-Assisted Process for Chemical Recycling and the Reuse of Epoxy Resin Matrices

by Fabrizio Cafaro, Francesca Ferrari, Gloria Anna Carallo, Antonio Greco and Alfonso Maffezzoli

Polymers 2025, 17(7), 989; https://doi.org/10.3390/polym17070989 - 5 Apr 2025

Cited by 6 | Viewed by 2280

Abstract

This work presents an optimized and sustainable chemical recycling method for epoxy resin matrices, which uses microwave-assisted reactions to achieve the complete recovery of the matrix without generating waste byproducts. The proposed method employs a green chemistry approach, with hydrogen peroxide (H₂O₂) and tartaric acid (TA) as the eco-friendly reagents. Microwaves are used to activate the chemical reaction, ensuring localized heating, reduced energy consumption, and shorter processing times compared to conventional thermal methods. Unlike most existing recycling processes, which focus on fiber recovery, this study emphasizes the recovery and reuse of the matrix, transforming it into a valuable resource for producing new thermosetting materials. The recovered matrix was characterized using FTIR and H-NMR analyses, confirming the presence of reactive functional groups that enable its reintegration into new composite matrix formulations. The process has also demonstrated environmental benefits and economic advantages due to the absence of any waste and the reduced need for virgin raw materials. This method addresses a critical gap in composite material recycling, paving the way for a circular lifecycle and advancing the principles of sustainability in materials engineering. Full article

(This article belongs to the Special Issue Advances in Polymer Recycling and Upcycling: Toward a Circular and Sustainable Future)

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