Glycolysis of flexible polyurethane wastes using stannous octoate as the catalyst: Study on the influence of reaction parameters

Polyurethane Composites Recycling with Styrene-Acrylonitrile and Calcium Carbonate Recovery

The glycolysis process of flexible polyurethane foams containing styrene-acrylonitrile and calcium carbonate as fillers was explored in detail. The use of DABCO as a catalyst allowed us to reduce the catalyst concentration and the polyurethane-to-glycol mass ratio to 0.1% and 1:1, respectively. The glycolysis process allowed us to obtain a high-purity polyol (99%), which can totally replace raw polyols in the synthesis of new flexible polyurethane foams, maintaining the standard mechanical properties of the original one and modifying the ratio of isocyanates employed to correct the closed cell structure caused by the impurities present in the recovered polyol. This isocyanate mixture was also optimized, resulting in a ratio of 30 and 70% of the isocyanates TDI80 and TDI65, respectively. Additionally, the fillers incorporated in the glycolyzed foams were recovered. Both recovered fillers, styrene-acrylonitrile and calcium carbonate, were fully characterized, showing a quality very similar to that of commercial compounds. Finally, the replacement of commercial fillers by the recovered ones in the synthesis of new polyurethane foams was studied, demonstrating the feasibility of using them in the synthesis of new foams without significantly altering their properties.

Polyurethane Glycerolysate as a Modifier of the Properties of Natural Rubber Mixtures and Vulcanizates

Chemical recycling of polyurethanes can be realized in several different ways, but the most important methods are glycolysis and glycerolysis. Both methods permit recovery of polyols (when the process is realized with the mass excess of depolymerizing agent) or substitutes of polyols, which contain urethane moieties in the main chains and terminate mainly in hydroxyl groups (when the process is realized with the mass excess of depolymerized polyurethane). Oligomeric products with urethane groups in the chemical structure can also be used as modifiers of rubber mixtures and vulcanizates. The main aim of the presented work is to study the effect of polyurethane glycerolysate on the performance of natural rubber mixtures and vulcanizates. The influence of the modifier on the vulcanization kinetics and swelling of rubber mixtures, and the thermo-mechanical and mechanical properties of rubber vulcanizates, was studied. The prepared materials were also subjected to accelerated thermal aging in air. It was found that polyurethane glycerolysate affects the vulcanization process of rubber mixtures (for example, promotes the activation of vulcanization) and acts as an antidegradant under thermoxidative conditions (higher stability of mechanical properties was observed in comparison to a reference sample without modifier). The obtained results show that chemical recycling products can be valuable modifiers of natural rubber mixtures and vulcanizates, which extends the possible applications of polyurethane chemical recycling products.

Chemical Recycling of Flexible Polyurethane Foams by Aminolysis to Recover High-Quality Polyols

Polyurethane foams (PUFs) are widely used commodity materials, but most of them end up in landfills at the end of their life, which is not in line with the circular economy approach. Here, we introduce microwave-assisted aminolysis with amine reagents that contain primary and tertiary amino groups in the structure. These reagents enable complete degradation of the urethane groups in the structure of the flexible PUFs with a much lower amount of degradation reagent than is typically required for solvolysis reactions. The purified, recovered polyols are close equivalents to the corresponding virgin polyols in terms of their structural and molar mass characteristics. Therefore, they can be used for the production of high-quality PUFs without having to adapt the synthesis process. The flexible PUFs made from recovered polyols have comparable mechanical properties to those made from virgin polyols.

Determination of End-Group Functionality of Propylene Oxide-Based Polyether Polyols Recovered from Polyurethane Foams by Chemical Recycling

Chemical recycling of polyurethane foams (PUFs) leads to partially aromatic, amino-functionalized polyol chains when the urethane groups in the PUF structure are incompletely degraded. Since the reactivity of amino and hydroxyl groups with isocyanate groups is significantly different, information on the type of the end-group functionality of recycled polyols is important to adjust the catalyst system accordingly to produce PUFs from recycled polyols of suitable quality. Therefore, we present here a liquid adsorption chromatography (LAC) method using a SHARC 1 column that separates polyol chains according to their end-group functionality based on their ability to form hydrogen bonds with the stationary phase. To correlate end-group functionality of recycled polyol with chain size, LAC was coupled with size-exclusion chromatography (SEC) to form a two-dimensional liquid chromatography system. For accurate identification of peaks in LAC chromatograms, the results were correlated with those obtained by characterization of recycled polyols using nuclear magnetic resonance, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and SEC coupled with a multi-detection system. The developed method allows the quantification of fully hydroxyl-functionalized chains in recycled polyols using an evaporative light scattering detector and appropriate calibration curve.

Upgrading Polyurethanes into Functional Ureas through the Asymmetric Chemical Deconstruction of Carbamates

The importance of systematic and efficient recycling of all forms of plastic is no longer a matter for debate. Constituting the sixth most produced polymer family worldwide, polyurethanes, which are used in a broad variety of applications (buildings, electronics, adhesives, sealants, etc.), are particularly important to recycle. In this study, polyurethanes are selectively recycled to obtain high value-added molecules. It is demonstrated that depolymerization reactions performed with secondary amines selectively cleave the C-O bond of the urethane group, while primary amines unselectively break C-O and C-N bonds. The selective cleavage of C-O bonds, catalyzed by an acid:base mixture, led to the initial polyol and a functional diurea in several hours to a few minutes for both model polyurethanes and commercial polyurethane foams. Different secondary amines were employed as nucleophiles to synthesize a small library of diureas obtained in good to excellent yields. This study not only targets the recovery of the initial polyol but also aims to form new diureas which are useful building blocks for the polymerization of innovative materials.

Study on Green Degradation Process of Polyurethane Foam Based on Integral Utilization and Performance of Recycled Polyurethane Oil-Absorbing Foam

Ester exchange glycolysis of flexible polyurethane foam (PU) usually results in split-phase products, and the recovered polyether polyols are obtained after separation and purification, which can easily cause secondary pollution and redundancy. In this paper, we propose a green recycling process for the degradation of waste polyurethane foam by triblock polyether, and the degradation product can be used directly as a whole. The polyurethane foam can be completely degraded at a minimum mass ratio of 1.5:1. The secondary full utilization of the degradation product as a whole was directly synthesized into recycled polyurethane foam, and the compression cycle test proved that the excess glycolysis agent had less effect on the resilience of the recycled foam. The hydrophobic modification of the recycled foam was carried out, and the oil absorption performance of the recycled foam before and after the hydrophobic modification was compared. The oil absorption capacity for diesel oil ranged from 4.3 to 6.7, while the oil absorption performance of the hydrophobic modified recycled foam was significantly improved and had excellent reusability (absorption–desorption oil processes can be repeated at least 25 times). This economical and green process has large-scale application prospects, and the hydrophobic recycling foam can be applied to the field of oil and water separation.

Thermochemical Conversion of Plastic Waste into Fuels, Chemicals, and Value-Added Materials: A Critical Review and Outlooks

Plastic waste is an emerging environmental issue for our society. Critical action to tackle this problem is to upcycle plastic waste as valuable feedstock. Thermochemical conversion of plastic waste has received growing attention. Although thermochemical conversion is promising for handling mixed plastic waste, it typically occurs at high temperatures (300-800 °C). Catalysts can play a critical role in improving the energy efficiency of thermochemical conversion, promoting targeted reactions, and improving product selectivity. This Review aims to summarize the state-of-the-art of catalytic thermochemical conversions of various types of plastic waste. First, general trends and recent development of catalytic thermochemical conversions including pyrolysis, gasification, hydrothermal processes, and chemolysis of plastic waste into fuels, chemicals, and value-added materials were reviewed. Second, the status quo for the commercial implementation of thermochemical conversion of plastic waste was summarized. Finally, the current challenges and future perspectives of catalytic thermochemical conversion of plastic waste including the design of sustainable and robust catalysts were discussed.

Insight into Chemical Recycling of Flexible Polyurethane Foams by Acidolysis

Acidolysis is emerging as a promising method for recycling polyurethane foam (PUF) waste. Here, we present highly efficient acidolysis of PUFs with adipic acid (AA) by heating the reaction mixtures with microwaves. The influence of experimental conditions, such as reaction temperature, time, and amount of the degradation reagent, on the polyol functionality, molecular weight characteristics, the presence of side products, and the degree of degradation of the remaining PUF hard segments was studied by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS), nuclear magnetic resonance (NMR), size-exclusion chromatography (SEC) coupled to a multidetection system, and Fourier transform infrared (FT-IR) spectroscopy. The purified recycled polyols were used for the synthesis of flexible PUFs. The morphology and mechanical properties of the PUFs show that the degree of functionalization of the polyol by the carboxylic end groups, which is higher for larger amounts of AA used to degrade the PUFs, significantly affects the quality and performance of the flexible PUFs from the recycled polyols.

Glycolysis of Polyurethanes Composites Containing Nanosilica

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.

Catalytic methods for chemical recycling or upcycling of commercial polymers

Polymers (plastics) have transformed our lives by providing access to inexpensive and versatile materials with a variety of useful properties. While polymers have improved our lives in many ways, their longevity has created some unintended consequences. The extreme stability and durability of most commercial polymers, combined with the lack of equivalent degradable alternatives and ineffective collection and recycling policies, have led to an accumulation of polymers in landfills and oceans. This problem is reaching a critical threat to the environment, creating a demand for immediate action. Chemical recycling and upcycling involve the conversion of polymer materials into their original monomers, fuels or chemical precursors for value-added products. These approaches are the most promising for value-recovery of post-consumer polymer products; however, they are often cost-prohibitive in comparison to current recycling and disposal methods. Catalysts can be used to accelerate and improve product selectivity for chemical recycling and upcycling of polymers. This review aims to not only highlight and describe the tremendous efforts towards the development of improved catalysts for well-known chemical recycling processes, but also identify new promising methods for catalytic recycling or upcycling of the most abundant commercial polymers.

Multistage Chemical Recycling of Polyurethanes and Dicarbamates: A Glycolysis–Hydrolysis Demonstration

The use of polyurethanes and, therefore, the quantity of its scrap are increasing. Considering the thermoset characteristic of most polyurethanes, the most circular recycling method is by means of chemical depolymerization, for which glycolysis is finding its way into the industry. The main goal of polyurethane glycolysis is to recover the polyols used, but only limited attempts were made toward recovering the aromatic dicarbamate residues and derivates from the used isocyanates. By the split-phase glycolysis method, the recovered polyols form a top-layer phase and the bottom layer contain transreacted carbamates, excess glycol, amines, urea, and other side products. The hydrolysis of carbamates results in amines and CO2 as the main products. Consequently, the carbamates in the bottom layer of polyurethane split-phase glycolysis can also be hydrolyzed in a separate process, generating amines, which can serve as feedstock for isocyanate production to complete the polyurethane material cycle. In this paper, the full recycling of polyurethanes is reviewed and experimentally studied. As a matter of demonstration, combined glycolysis and hydrolysis led to an amine production yield of about 30% for model systems. With this result, we show the high potential for further research by future optimization of reaction conditions and catalysis.

Recycling Polyurethanes through Transcarbamoylation

In this paper, we describe a new strategy to recycle polyurethanes (PUs) using base-catalyzed transcarbamoylation. PUs were depolymerized qualitatively in the presence of MeOH (methanol)/tetrahydrofuran as a solvent and tert-butoxide as a base catalyst. The resulting depolymerized mixture constituted by O-dimethylcarbamates and polyols can either be used as the starting material to synthesize new PUs with the transcarbamoylation approach or be purified to recover polyols and diisocyanates. The versatility and easy scaling-up of the experimental procedures and high depolymerization outcomes of the presented method make this strategy very attractive for PU recycling.

Assessment of the economic recycling potential of a glycolysis treatment of rigid polyurethane foam waste: A case study from Thailand

This research assessed the economic feasibility of recovering polyol from rigid polyurethane foam (RPUF) waste, collected from dismantled, discarded refrigerators, by a single-phase glycolysis recycling process using domestic crude glycerol (a byproduct of biodiesel production) as a transesterification agent. The study, conducted in Thailand, took into account benefits from the added value of the recovered product, the investment and related operating costs of the process, demand (the need for the recovered product) and supply (the amount of RPUF waste). The results showed that the production of recovered polyol from RPUF waste is economically feasible, with a net present value of 1,113,018 USD, an internal rate of return (IRR) of 22.9%, and a payback period of 4.4 years. Due to the high IRR, project investment should be attractive to both the government and private sector investors. In addition, a sensitivity analysis was conducted to assess the economic resilience of the process to uncertainties in key factors, including the prices of the machinery, recovered polyol, crude glycerol and stannous octoate, and the amount of RPUF waste available. The sensitivity analysis showed that the economic feasibility was most sensitive to the price of the recovered polyol, followed by the amount of RPUF waste and the prices of the machinery, crude glycerol and stannous octoate. Based on these results, technological, operational, financial, and regulatory policy recommendations were also presented.

Recycling of polyurethanes from laboratory to industry, a journey towards the sustainability

The recycling of any kind of plastic to convert it in valuable products is one of the main challenges of today's society. Besides, if the recycling process is itself green, then it would be a great achievement. This paper reviews the way covered from the first attempts of reusing the polyurethane (PU) scraps as a filler for cushions to the last chemical routes employing green recycling agents. Polyurethane is the 6th most used polymer all over the world with a production of 18 millions tons per year, which means a daily production of PU specialties greater than 1 million of cubic meters, equivalent to the volume of the Empire State Building. The thermostable nature of the majority of the polyurethanes specialties has made that the preferred solution for their recycling are the chemical recycling processes. Among them, glycolysis is the one that receives a greater attention from an industrial point of view, so this review puts the spotlight on it. However, the existing reviews in literature do not paid a special attention on glycolysis and only give a superficial description of the process. Nevertheless, in the present review, the scientific literature relative to glycolysis is completely reviewed, updated and ordered according the type of PU specialty recycled. Additionally, the other main chemical recycling processes are also revisited in a more extended and deeper way than in the previous approaches to this topic. Moreover, it is crucial to take into account that some of these technologies, which were described in the literature as promising technologies at laboratory scale are now commercial processes running at industrial scale. For that reason, it is essential to remark that the present review comprises not only a detailed state of art of the scientific literature on the subject, also includes a detailed revision of the past and running on pilot plants and industrial facilities, including several patents, which has never been covered in the current literature. Moreover, this review also describes the most recent studies employing crude glycerol (biodiesel subproduct) as an economic, sustainable and environmental friendly cleavage agent, which should lead the way to the industrial implantation of split-phase glycolysis in a near future, providing high quality recovered products, susceptible of replacing raw ones in the synthesis of new PU specialties. What is more, this review intends that any reader could know and understand the reactions involved in the polyurethane chemistry and recycling, the main polyurethanes types and the fundamentals of the recycling strategies in order to comprehend what are the advantages and drawbacks of each recycling process as starting point for looking for new advantageous alternatives from an environmental, technical and economic point of view. Broader context. This paper reviews the main advances in the polyurethane (PU) recycling field, from laboratory and academia processes to pilot plant and industrial scale ones, including the most relevant patents in the subject. Opposite to other common used plastics, PUs are not polymerization but condensation polymers, synthesized from polyols and isocyanates. The wide diversity of polyols and isocyanates allows the synthesis of numerous different compounds covering a huge range of applications. As a direct consequence of their commercial success, an increasing quantity of PU waste is being disposed by landfilling in the last decades. Such waste comprises not only post-consumer products but also scrap from slabstock manufacturing, which can reach the 10% of the total foam production. However, the massive enforcement of the environmental laws is pointing out a new route in the polymer waste removal sector based in the polymer recycling, and this fact has placed the research in waste treatment as one of the most prolific topics nowadays. In fact, polymer recycling processes have experienced a growing attention from the research and industrial worlds as a direct result of the enforcement of the environmental legislations. Hence, it is essential to develop new environmental sustainable recycling processes with the aim of conserving the natural resources, reducing the amount of waste disposed in landfills and enhancing the sustainability for forthcoming generation.

Development of Styrene-Grafted Polyurethane by Radiation-Based Techniques

Polyurethane (PU) is the fifth most common polymer in the general consumer market, following Polypropylene (PP), Polyethylene (PE), Polyvinyl chloride (PVC), and Polystyrene (PS), and the most common polymer for thermosetting resins. In particular, polyurethane has excellent hardness and heat resistance, is a widely used material for electronic products and automotive parts, and can be used to create products of various physical properties, including rigid and flexible foams, films, and fibers. However, the use of polar polymer polyurethane as an impact modifier of non-polar polymers is limited due to poor combustion resistance and impact resistance. In this study, we used gamma irradiation at 25 and 50 kGy to introduce the styrene of hydrophobic monomer on the polyurethane as an impact modifier of the non-polar polymer. To verify grafted styrene, we confirmed the phenyl group of styrene at 690 cm⁻¹ by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) and at 6.4–6.8 ppm by ¹H-Nuclear Magnetic Resonance (¹H-NMR). Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), Thermogravimetric Analysis (TGA) and contact angle analysis were also used to confirm styrene introduction. This study has confirmed the possibility of applying high-functional composite through radiation-based techniques.

Radiation-Induced Grafting with One-Step Process of Waste Polyurethane onto High-Density Polyethylene

The recycling of waste polyurethane (PU) using radiation-induced grafting was investigated. The grafting of waste PU onto a high-density polyethylene (HDPE) matrix was carried out using a radiation technique with maleic anhydride (MAH). HDPE pellets and PU powders were immersed in a MAH-acetone solution. Finally, the prepared mixtures were irradiated with an electron beam accelerator. The grafted composites were characterized by Fourier transformed infrared spectroscopy (FT-IR), surface morphology, and mechanical properties. To make a good composite, the improvement in compatibility between HDPE and PU is an important factor. Radiation-induced grafting increased interfacial adhesion between the PU domain and the HDPE matrix. When the absorbed dose was 75 kGy, the surface morphology of the irradiated PU/HDPE composite was nearly a smooth and single phase, and the elongation at break increased by approximately three times compared with that of non-irradiated PU/HDPE composite.

Preparation of High Density Polyethylene/Waste Polyurethane Blends Compatibilized with Polyethylene-Graft-Maleic Anhydride by Radiation

Polyurethane (PU) is a very popular polymer that is used in a variety of applications due to its good mechanical, thermal, and chemical properties. However, PU recycling has received significant attention due to environmental issues. In this study, we developed a recycling method for waste PU that utilizes the radiation grafting technique. Grafting of waste PU was carried out using a radiation technique with polyethylene-graft-maleic anhydride (PE-g-MA). The PE-g-MA-grafted PU/high density polyethylene (HDPE) composite was prepared by melt-blending at various concentrations (0–10 phr) of PE-g-MA-grafted PU. The composites were characterized using fourier transform infrared spectroscopy (FT-IR), and their surface morphology and thermal/mechanical properties are reported. For 1 phr PU, the PU could be easily introduced to the HDPE during the melt processing in the blender after the radiation-induced grafting of PU with PE-g-MA. PE-g-MA was easily reacted with PU according to the increasing radiation dose and was located at the interface between the PU and the HDPE during the melt processing in the blender, which improved the interfacial interactions and the mechanical properties of the resultant composites. However, the elongation at break for a PU content >2 phr was drastically decreased.

Glycolysis recycling of rigid waste polyurethane foam from refrigerators

Rapid growth of rigid waste polyurethane (WPUR) foam from refrigerators attracts the attention all over the world. In this study, glycolysis was chosen to treat WPUR from scrapped refrigerators collected in Shanghai, China. Glycolysis reagents and catalysts were selected. The results indicated that the glycolysis efficiency of ethylene glycol (EG) was higher than that of diethylene glycol, and the catalytic efficiency of alkali metal salts (NaOH) was more excellent than that of triethanolamine and organic salts of alkali metal (NaAc). When EG was 100%WPUR as a glycolysis reagent and NaOH was 1%WPUR as a catalyst at a constant temperature of 197.85°C for 2 h, the glycolysis product had the highest glycolysis conversion rate. In order to maximize the recycling of WPUR, regenerative Polyurethane was performed by adding 10% distilled mixed polyol, which conformed to the QB/T 26689-2011 requirements.