Glycolysis of high resilience flexible polyurethane foams containing polyurethane dispersion polyol

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.

Sustainable cycloaliphatic polyurethanes: from synthesis to applications

Polyurethanes (PUs) are a versatile and major polymer family, mainly produced via polyaddition between polyols and polyisocyanates. A large variety of fossil-based building blocks is commonly used to develop a wide range of macromolecular architectures with specific properties. Due to environmental concerns, legislation, rarefaction of some petrol fractions and price fluctuation, sustainable feedstocks are attracting significant attention, e.g., plastic waste and biobased resources from biomass. Consequently, various sustainable building blocks are available to develop new renewable macromolecular architectures such as aromatics, linear aliphatics and cycloaliphatics. Meanwhile, the relationship between the chemical structures of these building blocks and properties of the final PUs can be determined. For instance, aromatic building blocks are remarkable to endow materials with rigidity, hydrophobicity, fire resistance, chemical and thermal stability, whereas acyclic aliphatics endow them with oxidation and UV light resistance, flexibility and transparency. Cycloaliphatics are very interesting as they combine most of the advantages of linear aliphatic and aromatic compounds. This original and unique review presents a comprehensive overview of the synthesis of sustainable cycloaliphatic PUs using various renewable products such as biobased terpenes, carbohydrates, fatty acids and cholesterol and/or plastic waste. Herein, we summarize the chemical modification of the main sustainable cycloaliphatic feedstocks, synthesis of PUs using these building blocks and their corresponding properties and subsequently present their major applications in hot-topic fields, including building, transportation, packaging and biomedicine.

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.

Recent Advances in Development of Waste-Based Polymer Materials: A Review

Limited petroleum sources, suitable law regulations, and higher awareness within society has caused sustainable development of manufacturing and recycling of polymer blends and composites to be gaining increasing attention. This work aims to report recent advances in the manufacturing of environmentally friendly and low-cost polymer materials based on post-production and post-consumer wastes. Sustainable development of three groups of materials: wood polymer composites, polyurethane foams, and rubber recycling products were comprehensively described. Special attention was focused on examples of industrially applicable technologies developed in Poland over the last five years. Moreover, current trends and limitations in the future “green” development of waste-based polymer materials were also 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.

Breakthrough in polyurethane bio-recycling: An efficient laccase-mediated system for the degradation of different types of polyurethanes

Development of green, efficient and profitable recycling processes for plastic material will contribute to reduce the expanding plastic pollution and microplastics accumulation in the environment. Polyurethanes (PU) are versatile polymers with a large range of chemical compositions and structures. This variability increases the complexity of PU waste management. Biological recycling researchers have recently demonstrated great interest in polyethylene terephthalate. The adaptation of this route towards producing polyurethanes requires the discovery of enzymes that are able to depolymerize a large variety of PU. A laccase mediated system (LMS) was tested on four representative PU models, with different structures (foams and thermoplastics), and chemical compositions (polyester- and polyether-based PU). Size exclusion chromatography was performed on the thermoplastics and this revealed a significant reduction in the molar masses after 18 days of incubation at 37 °C. Degradation of foams under the same conditions was demonstrated by microscopy and compression assay for both polyester- and polyether-based PU. This study represents a major breakthrough in PU degradation, as it is the first time that enzymatic degradation has been clearly demonstrated on a polyether-based PU foam. This work is a step forward in the development of a sustainable recycling pathway, adapted to a large variety of PU materials.

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.

100th Anniversary of Macromolecular Science Viewpoint: Toward Catalytic Chemical Recycling of Waste (and Future) Plastics

The current global materials economy has long been inefficient due to unproductive reuse and recycling efforts. Within the wider materials portfolio, plastics have been revolutionary to many industries but they have been treated as disposable commodities leading to their increasing accumulation in the environment as waste. The field of chemistry has had significant bearing in ushering in the current plastics industry and will undoubtedly have a hand in transforming it to become more sustainable. Existing approaches include the development of synthetic biodegradable plastics and turning to renewable raw materials in order to produce plastics similar to our current petrol-based materials or to create new polymers. Additionally, chemists are confronting the environmental crisis by developing alternative recycling methods to deal with the legacy of plastic waste. Important emergent technologies, such as catalytic chemical recycling or upcycling, have the potential to alleviate numerous issues related to our current and future refuse and, in doing so, help pivot our materials economy from linearity to circularity.

Recycling of Flexible Polyurethane Foam by Split-Phase Alcoholysis: Identification of Additives and Alcoholyzing Agents to Reach Higher Efficiencies

Split-phase alcoholysis of flexible polyurethane (PU) foam yields an apolar phase containing the recycled polyether polyol, and a lower, polar phase of the alcoholyzing agent and aromatic compounds. However, multiple purification steps are required to render the polyether polyol suitable for synthesis of new flexible PU foams; the unfavorable mass balance limits industrial applications. In this work, 2-pyrrolidone was identified as a performant additive for accelerating the dissolution and depolymerization process. By applying a lactam to PU foam in a weight ratio of 0.1:1, the glycol to PU foam weight ratio can be decreased from 1.5:1 to only 0.5:1, without loss of purity or yield of the recycled polyether polyol. Diglycerol was discovered as a novel, promising alcoholyzing agent; it allows the recycling of the polyether polyol in high purity (97 %) and excellent yields (98 %), and after a single washing with diglycerol, a sufficiently low hydroxyl value (61 mgKOH  g-1 ) is reached. The recycled polyether polyol can replace the virgin polyether polyol (48 mgKOH  g-1 ) for up to 50 % in the synthesis of new flexible PU foams with effects on the foam quality that stay within the limits of generally accepted specifications. A first step towards the valorization of the lower phase was also taken by applying hydrolysis of the newly formed carbamates to toluenediamines, which are readily reintegrated in new PU foams.

Recovery of Flexible Polyurethane Foam Waste for Efficient Reuse in Industrial Formulations

Ester polyurethane (PU) foam waste was reacted at atmospheric pressure in an autoclave and using microwaves with diethylene glycol (DEG) at different PU/DEG ratios in the presence of diethanolamine as a catalyst to find the glycolysis conditions that allow for the improved recovery of the PU foam waste and enable the recycling of the whole glycolysis product in foam formulations suitable for industrial application. The recycled polyol was characterized by dynamic viscosity, hydroxyl number, water content, and density, while thermal stability was assessed using thermogravimetric analysis. In the PU foam formulation, 1% and 5% of the glycolyzed material was reused. The relationship between the reuse level of the recycled polyol and the physical properties of the foam was thoroughly investigated. It was observed that both hardness and air flow decreased with increasing recycled polyol content, particularly for the polyester type foam, while tensile strength and compression strength increased. Depending on the amount of recycled polyol and catalyst used, polyether-based foams could be obtained with a low air permeability, needed in special applications as sealed foams, or with higher air permeability desirable for comfort PU foams. The results open the way for further optimization studies of industrial polyurethane foam formulations using a glycolysis process without any separation stage.

Soundproofing flexible polyurethane foams: Effect of chemical structure of chain extenders on micro-phase separation and acoustic damping

In this study, a new high-performance acoustic damping flexible polyurethane foam (FPUF) was successfully designed and fabricated using synthesized linear saturated aliphatic polyester resin as polyol, methylene diphenyl diisocyanate, and ethylene glycol, monoethanolamine, and ethylenediamine as chain extenders and other reagents by one-shot bulk polymerization (isocyanate index = 100 and water content = 2.5%). The effect of the chemical structure of different chain extenders on micro-phase separation and acoustic damping properties of FPUFs were investigated using comprehensive characterization techniques such as atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), compressive strength, optical microscope, and‏ ‏impedance tube. It was indicated that the micro-phase separation degree of the FPUF matrix increased with increasing amine content in the chain extender structure due to the more bidentate hydrogen bondings formation between urea-urea groups. Also, by increasing micro-phase separation, average cell sizes decreased and compressive strength, open-cell contents%, cell walls roughness, and cell size distribution of FPUFs increased. According to the sound absorption spectra, it was found that sound absorption efficiency of FPUF containing DEA was higher than FPUF manufactured by EG by 13.23% in the range of 1500–4000 Hz due to the increase of the amine content of chain extenders. These results indicate that the acoustic properties of FPUFs can be explained with the synergistic actions of micro-phase separation including the viscoelastic behavior of hard-soft segments and increasing of airflow pathway leading to dissipating of the kinetic energy of sound waves. Finally, the results revealed that soundproofing FPUFs with an optimum condition for micro-phase separation and drainage flow can be a promising candidate for using as sound insulating materials in transportation industries such as airplanes, trains, etc.

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.

Renewable polyols for advanced polyurethane foams from diverse biomass resources

This review highlights recent advances in the synthesis of renewable polyols, used for making polyurethane foams, from biomass.