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Advances in Recycling and Reuse of Polymers

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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: 31 July 2026 | Viewed by 3774

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Special Issue Editor

Dr. Anita Ptiček Siročić

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Guest Editor

Faculty of Geotechnical Engineering, University of Zagreb, Varazdin, Croatia
Interests: polymers; recycling; chemical engineering; preparation of polymers; characterization of polymers

Special Issue Information

Dear Colleagues,

Polymer materials have become indispensable basic materials in modern society due to their excellent processability, durability and versatility. However, the huge amount of waste generated by their large-scale production and consumption (more than 6 billion tons globally) poses a severe challenge to the ecological environment and to resource sustainability. The unsustainability of the linear economic model ("production–use–disposal") has become increasingly prominent, prompting the polymer science and industry to shift their research focus to polymer recycling and reuse, viewing it as a key path to achieve a circular economy transition.

The core challenge of polymer recycling lies in polymers’ inherent chemical and physical properties: long-chain molecular structure, wide molecular weight distribution, diverse additive formulations, and incompatibility between different polymers. These characteristics make it extremely complicated to effectively sort mixed waste, remove contaminants, and maintain or restore material properties during recycling.

Therefore, converting waste polymers into high-value products has become a prominent issue, significant for both economic purposes and environmental protection. Here, the recycling and reuse of waste polymers involves physics, chemistry, engineering.

This Special Issue provides a channel to exchange and share novel ideas and recent research for the recycling and reuse of waste polymers. Both original contributions and comprehensive reviews are welcome.

Dr. Anita Ptiček Siročić
Guest Editor

Manuscript Submission Information

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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

chemically recycled polymers
mechanically recycled polymers
recycling of waste polymers with new approaches
reuse of waste polymers
recycled polymer reprocessing
assessment of present recycling of waste polymers

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Published Papers (5 papers)

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Research

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17 pages, 2037 KB

Open AccessArticle

Solid State Alkaline Depolymerization of Polyester Elastane Textiles in a Laboratory Kneader

by Leonard Both, Isabel Zerfuss, Mandy Paschetag and Stephan Scholl

Polymers 2026, 18(4), 537; https://doi.org/10.3390/polym18040537 - 22 Feb 2026

Viewed by 557

Abstract

Elastane is ubiquitous in polyester-based textiles and complicates depolymerization-based recycling because it can undergo thermal degradation and chemical bond cleavage, consuming reagents and forming low-molecular by-products that may compromise monomer quality. Here, we investigate alkaline PET depolymerization of PET/elastane blends under an intentional base-competition scenario in a laboratory kneader. Pure PET (100/0) and PET/EL blends (95/5 and 85/15, wt/wt) were processed under quasi-solid-state conditions at 140 °C for 5 min using solid NaOH dosed at 2.1 mol per mol PET repeat unit and pelletized feedstocks to ensure scale-relevant mixing and reproducible chamber filling. Torque and bulk-temperature profiles were similar across compositions, and isolated terephthalic acid yields remained in a narrow corridor (68–71%), indicating that PET depolymerization is not measurably impaired by 5–15 wt% elastane within this reaction window. Differential scanning calorimetry of water-insoluble residues revealed pronounced changes in elastane-related thermal transitions, evidencing elastane modification during treatment. Targeted ¹H NMR screening of recovered TA against a 4,4′-methylenedianiline spiked reference showed no detectable co-isolated aromatic diamines. Overall, the study demonstrates robust monomer recovery from mixed PET/EL textiles under solid-NaOH, short-residence, solvent-lean processing, while identifying residue analytics as the key bottleneck for quantifying elastane fate and closing component balances. Full article

(This article belongs to the Special Issue Advances in Recycling and Reuse of Polymers)

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18 pages, 1694 KB

Open AccessArticle

Effects of Repeated Thermo-Mechanical Processing on the Degradation Behavior of Bottle-Grade PET Under Controlled Conditions

by Mária Straková, Slávka Hlaváčiková, Jozef Feranc, Henrieta Suchánková, Zuzana Kramárová, Michal Ďurfina, Leona Omaníková, Mohammadhassan Rahnama Hezaveh, Katarína Tomanová, Zuzana Vanovčanová, Ján Kruželák, Pavol Alexy and Roderik Plavec

Polymers 2026, 18(3), 416; https://doi.org/10.3390/polym18030416 - 5 Feb 2026

Viewed by 817

Abstract

Mechanical recycling of polyethylene terephthalate (PET) is a key strategy for circular packaging applications; however, repeated thermo-mechanical processing leads to progressive polymer degradation. In this study, the effect of controlled repeated extrusion on the degradation behavior of bottle-grade PET was systematically investigated under laboratory conditions. Mechanical recycling was simulated using a co-rotating twin-screw extruder, where PET was subjected to up to four consecutive processing cycles corresponding to a cumulative residence time of 8 min. Progressive processing resulted in chain scission, reflected by a decrease in intrinsic viscosity from approximately 0.80 to 0.65 dL·g⁻¹ and a corresponding reduction in molecular weight. Melt flow rate increased accordingly, indicating a gradual loss of melt strength. Differential scanning calorimetry revealed that the glass transition and melting temperatures remained nearly unchanged, while the degree of crystallinity increased from approximately 23.0% to 29.5%, accompanied by changes in crystallization behavior. These structural changes led to reduced ductility, with elongation at break decreasing from about 84% to 60%. Optical analysis showed systematic material darkening, and a strong linear correlation between lightness (L*) and intrinsic viscosity was observed. By isolating intrinsic thermo-mechanical degradation effects under controlled processing conditions, this study enables a clearer definition of realistic reuse limits for mechanically recycled bottle-grade PET. The results indicate that bottle-grade PET retains properties compatible with demanding applications only after a limited number of thermo-mechanical processing cycles, whereas further processing restricts its usability to less demanding applications such as fibers, films, and non-food packaging. Full article

(This article belongs to the Special Issue Advances in Recycling and Reuse of Polymers)

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17 pages, 1222 KB

Open AccessArticle

Investigation into the Reprocessability of Polycarbonate/Organoclay Nanocomposites

by Basak Tuna

Polymers 2026, 18(1), 67; https://doi.org/10.3390/polym18010067 - 26 Dec 2025

Viewed by 617

Abstract

With the rapid expansion in the use of nanomaterials, ensuring their reprocessability has become a critical consideration for the sustainable development of polymer-based nanocomposites. In this study, the effects of repetitive thermo-mechanical processing cycles on the properties of polycarbonate (PC)/organoclay nanocomposites, as well as the impact of reactive extrusion of reprocessed PC/organoclay nanocomposites using a chain extender, were investigated for the first time. The nanocomposites were processed three times using a twin-screw extruder, and a multi-anhydride functional chain extender was incorporated to counteract the thermo-mechanical degradation observed after the third extrusion cycle. Morphological analysis indicated that the delamination of clay nanolayers within the polymer matrix was slightly enhanced with increasing extrusion cycles, while the addition of the chain extender further promoted nanoclay exfoliation. Despite the improved clay dispersion in PC, both rheological and tensile measurements revealed the detrimental effects of repeated reprocessing on the nanocomposites. The chain extender effectively mitigated this degradation by relinking cleaved polymer chains; consequently, the complex viscosity and storage modulus at 0.1 Hz of the three-times-extruded nanocomposite increased by 248% and 426%, respectively, following chain extender incorporation. The effectiveness of the chain extender was further evidenced by a 27% enhancement in tensile strength. The glass transition temperatures of the samples were not significantly affected by either the extrusion cycles or the addition of the chain extender. The thermal stability of the nanocomposites decreased with increasing numbers of extrusion cycles; however, the incorporation of the chain extender imparted enhanced resistance to thermal degradation, as confirmed by thermogravimetric analysis. Full article

(This article belongs to the Special Issue Advances in Recycling and Reuse of Polymers)

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18 pages, 3376 KB

Open AccessArticle

Gate-to-Gate Life Cycle Study and Techno-Economic Analysis of an Industrial Process for Producing Densified Polystyrene from Recycled Expanded Polystyrene

by Eliana Berrio-Mesa, Alba N. Ardila A., Erasmo Arriola-Villaseñor and Santiago A. Bedoya-Betancur

Polymers 2026, 18(1), 34; https://doi.org/10.3390/polym18010034 - 23 Dec 2025

Cited by 2 | Viewed by 797

Abstract

In this study, material and energy losses were systematically assessed, together with a comprehensive economic and environmental evaluation, for an industrial expanded polystyrene (EPS) recycling process implemented under a circular economy framework at a company located in Medellín, Colombia. The system boundaries were clearly defined, and detailed mass and energy balances were performed using operational data collected over a six-month period. The process achieved a yield of 78.09 percent in the production of densified polystyrene from post-consumer EPS, with the main material losses attributed to solid residues and water losses during processing. The total energy consumption was 7350.34 kWh, of which 55.46 percent corresponded to energy losses, predominantly thermal losses associated with the EPS melting stage. Techno-economic evaluation indicated that the process is financially viable over a twelve-year operational horizon. Furthermore, the environmental assessment demonstrated a 68.44 percent reduction in carbon footprint, underscoring the strong potential of this recycling route as a sustainable and effective alternative for the management of recyclable solid waste. Full article

(This article belongs to the Special Issue Advances in Recycling and Reuse of Polymers)

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Review

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26 pages, 2288 KB

Open AccessReview

Toward High-Value Circular Pathways for Polymer Waste: Process–Structure–Property Strategies in Mechanical Recycling, Filament Re-Extrusion, and Additive Manufacturing

by Hanife Bukre Koc Gunessu, Gurcan Atakok and Menderes Kam

Polymers 2026, 18(5), 607; https://doi.org/10.3390/polym18050607 - 28 Feb 2026

Viewed by 481

Abstract

The global polymer waste burden has catalyzed a shift from linear “production–use–disposal” systems to circular models that prioritize recycling, reuse, and value retention. This article proposes an integrated, technology-ready roadmap for mechanical recycling and reuse of commodity and bio-based polymers via filament re-extrusion and Additive Manufacturing (AM). Building upon recent findings on performance envelopes of virgin vs. recycled Polylactic Acid (PLA) filaments processed by Fused Deposition Modeling (FDM), process parameter sensitivities (layer height, infill density) and their statistical optimization, and functional reinforcement routes (aluminum: Al, alumina: Al₂O₃, titanium: Ti, and Nano Boron Nitride: nano-BN), we articulate (1) a process–structure–property (PSP) mapping; (2) a low-defect, low-energy filament re-extrusion protocol; and (3) a graded-value strategy for upcycling mixed polymer streams. Across case analyses, we show that recycled PLA can achieve near-parity with virgin PLA when extrusion quality and printing parameters are controlled, and that ceramic/metal nanofillers enable thermal management and biocompatibility benefits crucial for durable reuse scenarios. Full article

(This article belongs to the Special Issue Advances in Recycling and Reuse of Polymers)

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