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Growing water and land pollution, the possibility of exhaustion of raw materials and resistance of plastics to physical and chemical factors results in increasing importance of synthetic polymers waste recycling, recovery and environmentally friendly ways of disposal. Polyurethanes (PU) are a family of versatile synthetic polymers with highly diver...
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... most significant share of positive biodegradation results can be assigned to the hydrolysis of the polyester fraction of polyester-based polyurethanes by esterases. This reaction results in the formation of carboxylic acid and alcohol (Figure 7). Some studies show that esterases can also be responsible for the hydrolysis of urethane linkage, resulting in the presence of carbamic acid and alcohol chain-ends [103]. ...
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... There are different methods of chemical recycling: hydrolysis, methanolysis, aminolysis, phosphorolysis, acidolysis and glycolysis [5]. Currently, glycolysis is the most commonly used method of chemical recycling of PUR [2,9,16]. Low-molecularweight glycols with a number of carbon atoms not exceeding six (ethylene, propylene, butylene, diethylene, dipropylene glycol) and polyethylene or polypropylene are used in chemolysis of PUR waste [3,8,12]. ...
The primary goal of the research presented here was to evaluate the possibility of chemolysis of polyurethane biofoams synthesized from vegetable oil-based biopolyols with different chemical structures. As a reference material, a foam synthesized in 100 % from a petrochemical polyol was used. Chemolysis of polyurethane foams was conducted by using diethylene glycol as a solvent with a 1.5:1 wt ratio of biopolyurethane scraps to glycol. The reaction was carried out at 180 • C for 100 min in the presence of potassium hydroxide as a catalyst. The results of the chemolysis of different polyurethane foams were evaluated in terms of the hydroxyl number, amine value, viscosity, molecular weight and FTIR analysis of the new rebiopolyols. It can be concluded that the chemical structures of different biopolyols (obtained through the method of transesterification of vegetable oils with two different reagents and a two-step method of epoxidation and oxirane rings opening) that are used to make biopolyurethane foams have an impact on the course of the chemolysis process and the properties of resultant rebiopolyols. In order to verify the application possibilities of the new components obtained in accordance with the idea of circular economy, extreme conditions were applied in the form of complete replacement of the polyol in the reference foam with the rebiopolyols. It was found that replacing the petrochemical polyol with the repolyol results in partial cell opening, and replacing this component with the rebiopolyols results in open-cell foams. Only the rebiopolyol derived from the biofoam with the biopolyol obtained by transesterification of oil with triethanolamine was not suitable for use in a polyurethane system because its reactivity was too high. In conclusion, there is no need to use catalysts to obtain new biofoams from rebiopolyols given the catalytic nature of the new biocomponents.
... Polyurethane (PU) materials rank sixth in terms of global polymer production, boasting an annual output ranging between 18 and 24 million tons [1][2][3]. Among the PU materials, polyurethane foam (PUF), which is made by reacting polyether polyol or polyester polyol with aromatic diisocyanate, constitutes approximately 70% of this impressive figure. ...
Recycling flexible polyurethane foam (F-PUF) scraps is difficult due to the material’s high cross-linking structure. In this work, a wedge-block-reinforced extruder with a considerable enhanced shear extrusion and stretching area between the rotating screw and the stationary wedge blocks was utilized to recycle F-PUF scraps into powder containing surface-active hydroxyl groups. The powder was then utilized for the quantitative replacement of polyol in the foaming process. Characterizations showed that the continuous shear extrusion and stretching during the extrusion process reduced the volume mean diameter (VMD) of the F-PUF powder obtained by extruding it three times at room temperature to reach 54 μm. The -OH number (OHN) of the powder prepared by extruding it three times reached 19.51 mgKOH/g due to the mechanochemical effect of the powdering method. The F-PUF containing recycled powder used to quantitively replace 10 wt.% polyol was similar in microstructure and chemical structure to the original F-PUF, with a compression set of 2%, indentation load deflection of 21.3 lbf, resilience of 43.4%, air permeability of 815.7 L/m2·s, tensile strength of 73.0 Kpa, and tear strength of 2.3 N/cm, indicating that the recycling method has potential for industrial applications.
... Polyurethanes (PU) are prominent polymers globally, owing to their versatility and wide range of applications [1]. Ranked as the sixth most important polymer, PUs are highly favored due to their ability to be tailor-made for specific purposes, well-established synthesis technology, and exceptional properties, such as thermal insulation, diverse densities, and load-bearing capabilities for applications in elastomers, foams, coatings, and adhesives, to name a few [2][3][4]. ...
... The synthesis of polyurethane prepolymer involves an exothermic reaction between isocyanates and polyol, as shown in Figure 1a. First, isocyanates react with the reactive hydrogen of polyols to form polyurethane prepolymer [1]. For the reaction of traditional polyol (hydroxyl-based polyol) and isocyanates, polyurethanes are formed exclusively. ...
... Blowing proceeds as the isocyanate reacts with the water present to form an unstable product, carbamic acid, which, consequently, decomposes to amine and carbon dioxide, as shown in Figure 1b. General polyurethane (a) prepolymerization reactions of traditional and hybrid polyols with isocyanate where the OH moieties react with isocyanates to form urethane, and the NH moieties react with isocyanates to form urea.and (b) foaming reaction via water blowing with isocyanate schemes [1,53]. ...
The pursuit of sustainable polyurethane (PU) product development necessitates a profound understanding of precursor materials. Particularly, polyol plays a crucial role, since PU properties are heavily influenced by the type of polyol employed during production. While traditional PUs are solely derived from hydroxyl functionalized polyols, the emergence of amine-hydroxyl hybrid polyols has garnered significant attention due to their potential for enhancing PU product properties. These hybrid polyols are characterized by the presence of both amine and hydroxyl functional groups. However, characterizing these polyols remains a daunting challenge due to the lack of established experimental testing standards for properties, such as fractional hydroxyl and amine moieties and thermo-kinetic parameters for amine reactions with isocyanates. Additionally, characterization methods demand extensive time and resources and pose risks to health and the environment. To bridge these gaps, this study employed computational simulation via MATLAB to determine the moieties’ fractions and thermo-kinetic parameters for hybrid polyols. The computational method integrated energy balance and reaction kinetics analysis for various polyols to elucidate the influence of functional moieties on the thermo-kinetic behavior of PU formations. Validation of the simulated results was conducted by comparing their experimental and simulated prepolymer and foam temperature profiles, highlighting the direct influence of fractional moieties on PU formations. The comparisons revealed an average relative error of less than 5%, indicating the accuracy and credibility of the simulation. Thus, this study represents a pivotal opportunity for advancing knowledge and driving sustainable developments in bio-based polyol characterization for PU production streamlining and formulation optimization.
... 7,9 Virtually all chemical recycling methods for thermoset polyurethanes result in the recovery of the parent polyol aer solvolysis (glycolysis, acidolysis, hydrolysis or aminolysis) of the urethane hard domains, while further depolymerisation of the polyether is never pursued. [9][10][11][12] Silicones are organosiloxane polymers that are ubiquitous in our daily lives, widely used in household appliances and many technical sectors. 13 The estimated global production of silicones in 2020 was over 8 million tonnes, 10 which although only about a third of the global production of PET, 7 is still an amount that should not be overlooked. ...
... [9][10][11][12] Silicones are organosiloxane polymers that are ubiquitous in our daily lives, widely used in household appliances and many technical sectors. 13 The estimated global production of silicones in 2020 was over 8 million tonnes, 10 which although only about a third of the global production of PET, 7 is still an amount that should not be overlooked. It is important to note that the driving force behind the recycling of silicones is not the environmental impact they may cause at the end of their life, but rather the nature of their raw materials and how they are produced. ...
... 29,31 The Jitsukawa group has reported using montmorillonite as a heterogeneous catalyst to synthesise chloroesters by depolymerising polyethers. 33 [7][8][9][10][11][12]. In terms of yield, H-mordenite is superior to the other solid acid catalysts. ...
Plastics have become ubiquitous and indispensable in our daily lives since their invention at the beginning of the 20th century. As a result, millions of tonnes of plastic waste are produced every year and efforts to reduce their environmental impact are increasing. Most of the efforts have logically been devoted to tackling the plastic wastes with the highest volume, namely polyolefins and polyesters, as is reflected in the scientific and patent literature. In this review we have focused on a less studied class of polymer wastes, polyethers and polysiloxanes, both consisting of monomeric units linked by oxygen atoms. The most representative examples of chemical degradation of these materials at laboratory and industrial scales are presented and their reaction mechanisms are discussed.
... Efforts are being made to address this challenge by developing alternative recycling methods, including chemical recycling, depolymerization and conversion into bio-based materials. These approaches aim to recover valuable materials from PU waste, diverting it from landfills and promoting a more sustainable approach to polyurethane waste management [15][16][17][18]. The focus of this study is on a novel material produced using a circular economy approach. ...
This study details the synthesis and performance evaluation of a novel lightweight thermal and acoustic insulation material, resulting from the combination of a scleroglucan-based hydrogel and recycled rigid polyurethane waste powder. Through a sublimation-driven water-removal process, a porous three-dimensional network structure is formed, showcasing notable thermal and acoustic insulation properties. Experimental data are presented to highlight the material’s performance, including comparisons with commercially available mineral wool and polymeric foams. This material versatility is demonstrated through tunable mechanical, thermal and acoustic characteristics, achieved by strategically adjusting the concentration of the biopolymer and additives. This adaptability positions the material as a promising candidate for different insulation applications. Addressing environmental concerns related to rigid polyurethane waste disposal, the study contributes to the circular economy.
... Polyurethanes (PU), which account for approximately 8% of plastics [1], are highly versatile materials and hold a prominent position among the world's most adaptable substances. In 2018, polyurethane secured the sixth position in global polymer production (20 million tons [2]), with a thriving market valued at 65.5 billion dollars. ...
... The composition of PU can be widespread allowing it to cover numerous fields. The most important part of polyurethane is the urethane bond, which is formed during the reaction between isocyanate and alcohol groups [1]. The stability of the urethane linkage is a major issue in the recycling of polyurethane-based plastics. ...
... One of the earliest investigated reactions mainly for flexible polyurethane foam (PUF) waste recycling is hydrolysis, which yields polyol, amine intermediates, and carbon dioxide [1,3]. The process is conducted in an anaerobic environment and at high temperatures (above 150-320 • C). ...
A sudden increase in polyurethane (PU) production necessitates viable recycling methods for the waste generated. PU is one of the most important plastic materials with a wide range of applications; however, the stability of the urethane linkage is a major issue in chemical recycling. In this work, termination reactions of a model urethane molecule, namely methyl N-phenyl carbamate (MPCate), are investigated using G3MP2B3 composite quantum chemical method. Our main goal was to gain insights into the energetic profile of urethane bond termination and find an applicable chemical recycling method. Hydrogenation, hydrolysis, methanolysis, peroxidation, glycolysis, ammonolysis, reduction with methylamine and termination by dimethyl phosphite were explored in both gas and condensed phases. Out of these chemicals, degradation by H2, H2O2 and CH3NH2 revealed promising results with lower activation barriers and exergonic pathways, especially in water solvation. Implementing these effective PU recycling methods can also have significant economic benefits since the obtained products from the reactions are industrially relevant substances. For example, aniline and dimethyl carbonate could be reusable in polymer technologies serving as potential methods for circular economy. As further potential transformations, several ionizations of MPCate were also examined including electron capture and detachment, protonation/deprotonation and reaction with OH−. Alkaline digestion against the model urethane MPCate was found to be promising due to the relatively low activation energy. In an ideal case, the transformation of the urethane bond could be an enzymatic process; therefore, potential enzymes, such as lipoxygenase, were also considered for the catalysis of peroxidation, and lipases for methanolysis.
... 18,21 In contrast to mechanical routes, thermochemical recycling involves the depolymerization/deconstruction of used PU into monomers or other valuable small molecules that can potentially be repolymerized into virgin-grade products, yet none lead to recovery of all original starting components. 12,13,22,23 The most common PU chemical recycling methods are hydrolysis, aminolysis, hydrogenolysis, and glycolysis, 22,24 although other techniques that leverage transcarbamoylation/transurethanization reactions have been reported recently. 12,13,23,25−27 Glycolysis is the most mature chemical recycling route, in which PU waste is deconstructed by reacting the polymer with an alcohol, typically a diol or triol (e.g., ethylene glycol or glycerol), at ∼240°C to form polyols that can be incorporated into second-generation PUs. ...
We report a depolymerization strategy to nearly quantitatively regenerate isocyanates from thermoplastic and thermoset polyurethanes (PUs) and then resynthesize PUs using the recovered isocyanates. To date, chemical/advanced recycling of PUs has focused primarily on the recovery of polyols and diamines under comparatively harsh conditions (e.g., high pressure and temperature), and the recovery of isocyanates has been difficult. Our approach leverages an organoboron Lewis acid to depolymerize PUs directly to isocyanates under mild conditions (e.g., ∼80 °C in toluene) without the need for phosgene or other harsh reagents, and we show that both laboratory-synthesized and commercially sourced PUs can be depolymerized. Furthermore, we demonstrate the utility of the recovered isocyanate in the production of second-generation PUs with thermal properties and molecular weights similar to those of the virgin PUs. Overall, this route uniquely provides an opportunity for circularity in PU materials and can add significant value to end-of-life PU products.
... Polyurethanes (PU) are the sixth most used polymers with an annual consumption of more than 20 million metric tons, which are mainly used to produce flexible foams (e.g., mattresses and furniture) or rigid foams (e.g., insulation and construction materials) (Eling et al. 2020;Kemona and Piotrowska 2020). Polyurethane is composed of the carbamate-linked isocyanate and a polyester-(polyester PU) or polyether-containing diol (polyether PU), which comprise the hard and soft regions of the polymer, respectively (Fig. 1). ...
Plastic pollution is becoming a major health issue due to the recent discovery of microplastics and nanoplastics in living organisms and the environment, calling for advanced technologies to remove plastic waste. Here we review enzymes that degrade plastics with focus on plastic properties, protein engineering and polymers such as poly(ethylene terephthalate), poly(butylene adipate-co-terephthalate), poly(lactic acid), polyamide and polyurethane. The mechanism of action of natural and engineered enzymes has been probed by experimental and computation approaches. The performance of polyester-degrading enzymes has been improved via directed evolution, structure-guided rational design and machine learning-aided strategies. The improved enzymes display higher stability at elevated temperatures, and tailored substrate-binding sites.
... The breakdown of polyester PU by fungi and bacteria has been linked to the activities of proteases, ureases, and esterases (Kemona and Piotrowska, 2020;Saravanan et al., 2021;Skleničková et al., 2022). Pseudomonas fluorescens and Pseudomonas chlororaphis have both been shown to produce polyurethanase protease (Zhou et al., 2022). ...
... Pseudomonas fluorescens and Pseudomonas chlororaphis have both been shown to produce polyurethanase protease (Zhou et al., 2022). Bacillus subtilis strains have been found to have polyurethanase lipase activity (Shah et al., 2016;Kemona and Piotrowska, 2020;Sadeer et al., 2022). Biodegradation of synthetic polyester PU particles by Candida rugosa lipase in an aqueous medium was successful (Datta et al., 2013;Aggarwal et al., 2021;Gricajeva et al., 2022). ...
... Biodegradation of synthetic polyester PU particles by Candida rugosa lipase in an aqueous medium was successful (Datta et al., 2013;Aggarwal et al., 2021;Gricajeva et al., 2022). Comamonas acidovorans TB-35, Corynebacterium sp. and Pseudomonas chlororaphis have all been found to have PU esterase activity (Kemona and Piotrowska, 2020;Ali et al., 2021;Liu et al., 2021). PU esterase enzymes of two different types were extracted, characterised and demonstrated to be a cell-associated membrane attached and an extracellular PU esterase (Khan et al., 2017;Joshi et al., 2019). ...
... The diamine can then be converted to isocyanate starting materials with phosgene and re-polymerized with the polyols obtained to regenerate the original PU. 71,72 Hydrolysis processes in superheated water under 250°C (ref. 74 and 75) have shown great promise in converting PUF wastes within 30 minutes to give a two-phase liquid with a polyol phase and an aqueous phase that contains toluene diamines (72-86% yield). ...
Plastics are indispensable and ubiquitous materials in oral healthcare and dental applications, favored for their diversity in structure and properties, low cost, durability, chemical and water resistance, ease of processing, and shaping. However, ancillary plastics are used for short periods or even once due to hygiene concerns and convenience, and insufficient attention has been given to their unsustainable current usage and end-of-life. Thus, the amount of plastic waste generated by consumers and clinicians is staggering and projected to increase unabatedly for the foreseeable future. With recent advances in plastics recycling and sustainable polymers, it is time to consider alternatives to tackle dentistry's growing plastic waste problem. This Perspectives article highlights the sources and scale of dental plastic wastage, followed by a multi-pronged consideration of material and practical interventions for this issue. On the materials front, we discuss emerging approaches and alternative sustainable polymers to address the unsustainable end-of-life of existing petroleum-based dental plastics/polymers and enable material circularity. On the practical front, we discuss strategies for sustainable plastic usage, which must be implemented alongside complementary material approaches. These approaches highlight the abundant unrealized opportunities for developing a circular economy around dental plastics while reducing the environmental footprint of modern dentistry.
