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Overcoming Challenges through Sustainable Polyurethane Based Strategies

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

Deadline for manuscript submissions: closed (31 December 2022) | Viewed by 28195

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Special Issue Editors

Dr. Arantzazu Santamaria-Echart

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Guest Editor

Centro de Investigação de Montanha, Instituto Politecnico de Braganca, Braganca, Portugal
Interests: polyurethane chemistry; polyurethane dispersions; green chemistry; bio-based materials; renewable entities and additives; composite materials; polymers with tailored properties
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Filomena Barreiro

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Guest Editor

Centro de Investigação de Montanha (CIMO) and Laboratório para a Sustentabilidade e Tecnologia em Regiões de Montanha (SusTEC), Instituto Politécnico de Bragança, Campus de Santa Apolónia, 5300-253 Bragança, Portugal
Interests: biobased products; natural functional ingredients and applications; nano and microencapsulation; polyurethane chemistry; hybrid and composite materials
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The need to develop innovative materials in order to satisfy increasingly complex requirements is promoting the emergence of new materials with tailored properties. We are on the right path, but we must keep moving forward! In this context, polyurethanes offer the needed versatility in terms of properties, application forms (e.g., foams or dispersions), and advanced manufacturing strategies, including 3D printing or electrospinning. Based on this, the design of approaches through sustainable strategies is gaining relevance considering environmental concerns, covering green synthesis routes and bio-based reagents, eco-friendly polyurethane-derived materials, preparation methodologies, and recycling pathways after materials’ lifespan. In addition to providing functionalities, the sustainability they provide in their preparation and during/after their lifespan should also be highlighted, helping to promote the circular economy of the systems.

Thus, this Special Issue aims to collect contributions in the field of polyurethane-based alternatives to conventional pathways, yielding reduced toxicity while holding a broad range of properties/functionalities. We welcome manuscripts on polyurethane-derived materials with renewable reinforcements (or additives) and/or (nano)entities incorporated by green pathways providing value-added functionalities. We encourage you to depict your alternative proposals to address the existing challenges in the framework of foams, dispersions, emulsions, hydrogels, or advanced manufacturing strategies.

Dr. Arantzazu Santamaria-Echart
Prof. Dr. Maria Filomena Barreiro
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

Bio-based polyurethanes
Green synthesis strategies
Sustainable preparation methodologies
Polyurethane derived materials
Application forms
Foams
Dispersions
Hydrogels
Advanced properties
Recycling strategies

Published Papers (9 papers)

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Research

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24 pages, 4925 KiB

Open AccessArticle

Development of BioPolyurethane Coatings from Biomass-Derived Alkylphenol Polyols—A Green Alternative

by Tiago A. R. Silva, Ana C. Marques, Rui G. dos Santos, Rana A. Shakoor, Maryna Taryba and Maria Fátima Montemor

Polymers 2023, 15(11), 2561; https://doi.org/10.3390/polym15112561 - 02 Jun 2023

Cited by 1 | Viewed by 1866

Abstract

Bio-based polyols were obtained from the thermochemical liquefaction of two biomass feedstocks, pinewood and Stipa tenacissima, with conversion rates varying between 71.9 and 79.3 wt.%, and comprehensively characterized. They exhibit phenolic and aliphatic moieties displaying hydroxyl (OH) functional groups, as confirmed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and nuclear magnetic resonance spectroscopy (NMR) analysis. The biopolyols obtained were successfully employed as a green raw material to produce bio-based polyurethane (BioPU) coatings on carbon steel substrates, using, as an isocyanate source, a commercial bio-based polyisocyanate—Desmodur^® Eco N7300. The BioPU coatings were analyzed in terms of chemical structure, the extent of the reaction of the isocyanate species, thermal stability, hydrophobicity, and adhesion strength. They show moderate thermal stability at temperatures up to 100 °C, and a mild hydrophobicity, displaying contact angles between 68° and 86°. The adhesion tests reveal similar pull-off strength values (ca. 2.2 MPa) for the BioPU either prepared with pinewood and Stipa-derived biopolyols (BPUI and BPUII). Electrochemical impedance spectroscopy (EIS) measurements were carried out on the coated substrates for 60 days in 0.05 M NaCl solution. Good corrosion protection properties were achieved for the coatings, with particular emphasis on the coating prepared with the pinewood-derived polyol, which exhibited a low-frequency impedance modulus normalized for the coating thickness of 6.1 × 10¹⁰ Ω cm at the end of the 60 days test, three times higher than for coatings prepared with Stipa-derived biopolyols. The produced BioPU formulations show great potential for application as coatings, and for further modification with bio-based fillers and corrosion inhibitors. Full article

(This article belongs to the Special Issue Overcoming Challenges through Sustainable Polyurethane Based Strategies)

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21 pages, 4222 KiB

Open AccessArticle

Rational Design of a Polyurethane Foam

by Harry Charles Wright, Duncan Drummond Cameron and Anthony John Ryan

Polymers 2022, 14(23), 5111; https://doi.org/10.3390/polym14235111 - 24 Nov 2022

Cited by 1 | Viewed by 2415

Abstract

Polyurethane (PU) foams are exceptionally versatile due to the nature of PU bond formation and the large variety of polymeric backbones and formulation components such as catalysts and surfactants. This versatility introduces a challenge, namely a near unlimited number of variables for formulating foams. In addition to this, PU foam development requires expert knowledge, not only in polyurethane chemistry but also in the art of evaluating the resulting foams. In this work, we demonstrate that a rational experimental design framework in conjunction with a design of experiments (DoE) approach reduces both the number of experiments required to understand the formulation space and reduces the need for tacit knowledge from a PU expert. We focus on an in-depth example where a catalyst and two surfactants of a known formulation are set as factors and foam physical properties are set as responses. An iterative DoE approach is used to generate a set of foams with substantially different cell morphology and hydrodynamic behaviour. We demonstrate that with 23 screening formulations and 16 final formulations, foam physical properties can be modelled from catalyst and surfactant loadings. This approach also allows for the exploration of relationships between the cell morphology of PU foam and its hydrodynamic behaviour. Full article

(This article belongs to the Special Issue Overcoming Challenges through Sustainable Polyurethane Based Strategies)

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17 pages, 3751 KiB

Open AccessArticle

Effect of Cellulose Nanofibers’ Structure and Incorporation Route in Waterborne Polyurethane–Urea Based Nanocomposite Inks

by Izaskun Larraza, Julen Vadillo, Tamara Calvo-Correas, Alvaro Tejado, Loli Martin, Aitor Arbelaiz and Arantxa Eceiza

Polymers 2022, 14(21), 4516; https://doi.org/10.3390/polym14214516 - 25 Oct 2022

Cited by 6 | Viewed by 1498

Abstract

In order to continue the development of inks valid for cold extrusion 3D printing, waterborne, polyurethane–urea (WBPUU) based inks with cellulose nanofibers (CNF), as a rheological modulator, were prepared by two incorporation methods, ex situ and in situ, in which the CNF were added after and during the synthesis process, respectively. Moreover, in order to improve the affinity of the reinforcement with the matrix, modified CNF was also employed. In the ex situ preparation, interactions between CNFs and water prevail over interactions between CNFs and WBPUU nanoparticles, resulting in strong gel-like structures. On the other hand, in situ addition allows the proximity of WBPUU particles and CNF, favoring interactions between both components and allowing the formation of chemical bonds. The fewer amount of CNF/water interactions present in the in situ formulations translates into weaker gel-like structures, with poorer rheological behavior for inks for 3D printing. Stronger gel-like behavior translated into 3D-printed parts with higher precision. However, the direct interactions present between the cellulose and the polyurethane–urea molecules in the in situ preparations, and more so in materials reinforced with carboxylated CNF, result in stronger mechanical properties of the final 3D parts. Full article

(This article belongs to the Special Issue Overcoming Challenges through Sustainable Polyurethane Based Strategies)

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15 pages, 3047 KiB

Open AccessArticle

Synthesis of Polyhydroxyurethanes—Experimental Verification of the Box–Behnken Optimization Model

by Michał J. Zalewski, Mariusz Ł. Mamiński and Paweł G. Parzuchowski

Polymers 2022, 14(21), 4510; https://doi.org/10.3390/polym14214510 - 25 Oct 2022

Cited by 1 | Viewed by 1074

Abstract

Polyurethanes are one of the most important groups of polymers for numerous sectors of industry. Their production involves using dangerous components (diisocyanates), thus, in the search for safer synthetic routes, alternative methods yielding non-isocyanate polyurethanes (NIPU) have been investigated. In this study, the synthesis of polyhydroxyurethane from cyclic carbonates was performed. A three-factor, three-level Box–Behnken experimental design was constructed and the reaction time, temperature and reagents’ molar ratio were the independent variables. The built model revealed that the viscosity was influenced by all three independent factors, while the mechanical properties and glass transition temperature of the PHUs were affected by the reagents’ ratios. An experimental verification of the model proved its accuracy as the mechanical strength and glass transition temperature deviated from the modeled values, by 15% and 7%, respectively. Full article

(This article belongs to the Special Issue Overcoming Challenges through Sustainable Polyurethane Based Strategies)

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18 pages, 3847 KiB

Open AccessArticle

Hybrid Films from Blends of Castor Oil and Polycaprolactone Waterborne Polyurethanes

by Gastón Pascual, Mirta I. Aranguren and Verónica Mucci

Polymers 2022, 14(20), 4303; https://doi.org/10.3390/polym14204303 - 13 Oct 2022

Cited by 3 | Viewed by 1609

Abstract

Waterborne polyurethanes (WBPUs) with relatively high biobased content (up to 43.7%) were synthesized, aiming at their use as coatings for metals and woods. The study was performed on self-standing films obtained from anionic polyurethane water dispersions (PUDs). The initially targeted PUD was prepared from castor oil (CO), while tartaric acid (TA), a byproduct of wine production, was utilized as the internal anionic emulsifier. Although the films were cohesive and transparent, they were fragile, and thus blending the CO-TA PUD with other WBPUs was the chosen strategy to obtain films with improved handling characteristics. Two different WBPUs based on polycaprolactone diol (PCL), a biodegradable macrodiol, were prepared with dimethylolpropionic acid (DMPA) and tartaric acid (TA) as synthetic and biobased internal emulsifiers, respectively. The use of blends with PCL-TA and PCL-DMPA allowed for tailoring the moduli of the samples and also varying their transparency and haze. The characterization of the neat and hybrid films was performed by colorimetry, FTIR-ATR, XRD, DMA, TGA, solubility and swelling in toluene, and water contact angle. In general, the addition of PCL-based films increases haze; reduces the storage modulus, G’, which at room temperature can vary in the range of 100 to 350 MPa; and reduces thermal degradation at high temperatures. The results are related to the high gel content of the CO-TA film (93.5 wt.%), which contributes to the cohesion of the blend films and to the crystallization of the PCL segments in the samples. The highest crystallinity values corresponded to the neat PCL-based films (32.3% and 26.9%, for PCL-DMPA and PCL-TA, respectively). The strategy of mixing dispersions is simpler than preparing a new synthesis for each new requirement and opens possibilities for new alternatives in the future. Full article

(This article belongs to the Special Issue Overcoming Challenges through Sustainable Polyurethane Based Strategies)

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10 pages, 6361 KiB

Open AccessArticle

Polyurethane Wood Adhesives Prepared from Modified Polysaccharides

by Reza Hosseinpourpia, Arantxa Eceiza and Stergios Adamopoulos

Polymers 2022, 14(3), 539; https://doi.org/10.3390/polym14030539 - 28 Jan 2022

Cited by 7 | Viewed by 3130

Abstract

This study investigated the performance of polyurethane adhesives prepared with various combinations of wheat starch that had been modified by isophorone diisocyanate (MS), two polyol types (1,3-propanediol (PD) and glycerol (Gly)), native wheat starch (NS), and 4,4′-diphenylmethane diisocyanate (pMDI) at a NCO:OH weight ratio of 1:1. Two more adhesives were also synthesized with NS, PD, or Gly and pMDI blends and served as controls. The thermal behavior of the adhesives before and after the curing process, as well as their rheological performance and lap shear strength, were analyzed. Differential scanning calorimetry (DSC) showed a reduction in curing temperature and heat by adding MS. The thermal stability of the cured adhesives was slightly increased by MS addition. The viscosity of the adhesives that contained MS substantially increased at a linear ascendant ramp of shear, while the controls exhibited relatively low viscosity during the whole shear rate spectrum from 0.1 to 100 s⁻¹. The tensile shear strength of wood veneers was also significantly increased by the incorporation of MS under both dry and wet measuring conditions. The maximum dry shear strength was obtained for the adhesive with Gly polyol and a higher content of MS and was comparable to the control adhesive with pMDI. Full article

(This article belongs to the Special Issue Overcoming Challenges through Sustainable Polyurethane Based Strategies)

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18 pages, 4913 KiB

Open AccessArticle

Preparation of Polyurethane Adhesives from Crude and Purified Liquefied Wood Sawdust

by Wen Jiang, Reza Hosseinpourpia, Vladimirs Biziks, Sheikh Ali Ahmed, Holger Militz and Stergios Adamopoulos

Polymers 2021, 13(19), 3267; https://doi.org/10.3390/polym13193267 - 25 Sep 2021

Cited by 17 | Viewed by 4106

Abstract

Polyurethane (PU) adhesives were prepared with bio-polyols obtained via acid-catalyzed polyhydric alcohol liquefaction of wood sawdust and polymeric diphenylmethane diisocyanate (pMDI). Two polyols, i.e., crude and purified liquefied wood (CLW and PLW), were obtained from the liquefaction process with a high yield of 99.7%. PU adhesives, namely CLWPU and PLWPU, were then prepared by reaction of CLW or PLW with pMDI at various isocyanate to hydroxyl group (NCO:OH) molar ratios of 0.5:1, 1:1, 1.5:1, and 2:1. The chemical structure and thermal behavior of the bio-polyols and the cured PU adhesives were analyzed by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Performance of the adhesives was evaluated by single-lap joint shear tests according to EN 302-1:2003, and by adhesive penetration. The highest shear strength was found at the NCO:OH molar ratio of 1.5:1 as 4.82 ± 1.01 N/mm² and 4.80 ± 0.49 N/mm² for CLWPU and PLWPU, respectively. The chemical structure and thermal properties of the cured CLWPU and PLWPU adhesives were considerably influenced by the NCO:OH molar ratio. Full article

(This article belongs to the Special Issue Overcoming Challenges through Sustainable Polyurethane Based Strategies)

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21 pages, 4838 KiB

Open AccessArticle

Glycolysis of Polyurethanes Composites Containing Nanosilica

by Jesus del Amo, Ana Maria Borreguero, Maria Jesus Ramos and Juan Francisco Rodríguez

Polymers 2021, 13(9), 1418; https://doi.org/10.3390/polym13091418 - 27 Apr 2021

Cited by 5 | Viewed by 3712

Abstract

Rigid polyurethane (RPU) foams have been successfully glycolyzed by using diethylene glycol (DEG) and crude glycerol (CG) as transesterification agents. However, DEG did not allow to achieve a split-phase process, obtaining a product with low polyol purity (61.7 wt %). On contrary, CG allowed to achieve a split-phase glycolysis improving the recovered polyol purity (76.5%). This is an important novelty since, up to now, RPUs were glycolyzed in single-phase processes giving products of low polyol concentration, which reduced the further applications. Moreover, the nanosilica used as filler of the glycolyzed foams was recovered completely pure. The recovered polyol successfully replaced up to 60% of the raw polyol in the synthesis of RPU foams and including the recovered nanosilica in the same concentration than in glycolyzed foam. Thus, the feasibility of the chemical recycling of this type of polyurethane composites has been demonstrated. Additionally, PU foams were synthesized employing fresh nanosilica to evaluate whether the recovered nanosilica has any influence on the RPU foam properties. These foams were characterized structurally, mechanically and thermally with the aim of proving that they met the specifications of commercial foams. Finally, the feasibility of recovering the of CG by vacuum distillation has been demonstrated. Full article

(This article belongs to the Special Issue Overcoming Challenges through Sustainable Polyurethane Based Strategies)

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Review

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31 pages, 3200 KiB

Open AccessReview

Advances in Waterborne Polyurethane and Polyurethane-Urea Dispersions and Their Eco-friendly Derivatives: A Review

by Arantzazu Santamaria-Echart, Isabel Fernandes, Filomena Barreiro, Maria Angeles Corcuera and Arantxa Eceiza

Polymers 2021, 13(3), 409; https://doi.org/10.3390/polym13030409 - 27 Jan 2021

Cited by 61 | Viewed by 7569

Abstract

Polyurethanes and polyurethane-ureas, particularly their water-based dispersions, have gained relevance as an extremely versatile area based on environmentally friendly approaches. The evolution of their synthesis methods, and the nature of the reactants (or compounds involved in the process) towards increasingly sustainable pathways, has positioned these dispersions as a relevant and essential product for diverse application frameworks. Therefore, in this work, it is intended to show the progress in the field of polyurethane and polyurethane-urea dispersions over decades, since their initial synthesis approaches. Thus, the review covers from the basic concepts of polyurethane chemistry to the evolution of the dispersion’s preparation strategies. Moreover, an analysis of the recent trends of using renewable reactants and enhanced green strategies, including the current legislation, directed to limit the toxicity and potentiate the sustainability of dispersions, is described. The review also highlights the strengths of the dispersions added with diverse renewable additives, namely, cellulose, starch or chitosan, providing some noteworthy results. Similarly, dispersion’s potential to be processed by diverse methods is shown, evidencing, with different examples, their suitability in a variety of scenarios, outstanding their versatility even for high requirement applications. Full article

(This article belongs to the Special Issue Overcoming Challenges through Sustainable Polyurethane Based Strategies)

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