Recycling Innovative
Recycling Innovative Recycling Solutions for Thermoset Plastics PreScouter, a Chicago-based (USA) research intelligence company, has compiled a new Intelligence Brief that looks at the potential impact of recycling thermosets on reducing fossil-based plastic waste and highlights some examples of current options for recycling these materials along with some that are close to being fully developed. Currently, only 10–18 % of all plastics are recycled, in part because not all types of plastic are easy to process. As explained in the brief, plastic materials are generally classified according to their chemical compositions as either thermoplastics, such as polyethylene terephthalate (PET), or thermosets, which consist of the major resin classes of isocyanates, unsaturated polyesters, formaldehydes, epoxies, and alkyds. These resins are widely used as strong, lightweight materials; but the presence of covalent intermolecular cross-links that makes thermoset materials so attractive is precisely what makes them so difficult to recycle as they cvannot be molten anymore like thermoplastics. After outlining the current routes of thermoset recycling, the brief goes on to provide technology overviews of 9 commercially available thermoset material recycling solutions. Companies profiled include several major chemical companies such as Dow Polyurethanes (Midland, MI, USA), BASF (Ludwigshafen, Germany), and Covestro AG (Leverkusen, Germany). The technologies profiled are categorized into polyurethane foam solutions, epoxy composite solutions, and other difficult to recycle plastic solutions. As we already reported on Dow’s Renuva process earlier this year (bM 01/22) it was not considered in the selection for PU recycling solutions. The Intelligence Brief concludes with an exclusive interview with Sudhin Datta, consultant on polymers and retired Senior Research Associate at ExxonMobil Chemical (Houston, TX, United States). bioplastic MAGAZINE selected three examples of the report (one of each category) as well as some insights from Sudhin Datta. Polyurethane foam recycling 1. Rebonding (mechanical recycling) – Moulding and adding a binder to hold it together. Applications include carpet padding, flooring, athletic mats, cushioning, packaging, and acoustical materials 2. Regrinding (mechanical recycling) – Grinding and blending with polyol. Applications in seating materials 3. Glycolysis (chemical recycling) 4. Energy recovery – Recommended when recycling is not technically or economically feasible Solution: N/A Input material: Polyurethane flexible foam from used mattresses Output material: Polyols Steps: Glycolysis (chemical recycling): Reaction with diols at temperatures greater than 200ºC Efficiency: N/A Advantages: Reduces the carbon footprint Disadvantages: Currently at pilot scale Additional information: Covestro’s products include isocyanates and polyols for cellular foams, thermoplastic polyurethane and polycarbonate pellets, and polyurethanebased additives used in the formulation of coatings and adhesives. Covestro polyurethane was used in the 2014 official FIFA World Cup football. Covestro is taking part in the EU-funded PUReSmart together with eight other partners, the project is planned to finish at the end of this year. As part of the PUReSmart research project, Covestro has, in collaboration with Recticel (Brussels, Belgium) and Redwave (a division of Wolfgang Binder GmbH, Eggersdorf bei Graz, Austria), also developed an intelligent sorting solution for separating the different polyurethane foams from postconsumer mattresses. Epoxy recycling Polyurethane recycling tests (Source: Covestro) Covestro has a pilot plant for flexible foam recycling at its Leverkusen, Germany, site. Polyurethane flexible foam recycling/recovery can be done in a few ways: Schematic depicting curing of epoxy resin systems (non-recyclable vs recyclable) (Source: Dubey et al., 2020) 32 bioplastics MAGAZINE [03/22] Vol. 17
Recycling Recyclamine is a technology platform that uses novel polyamine curing agents that contain specifically engineered cleavage points at cross-linking sites, which convert thermosetting epoxies into recyclable thermoplastics under a specific set of conditions. It was developed by the Aditya Birla Group (Mumbai, India) in partnership with Cobra International (Chon Buri, Thailand) for manufacturing surfboards that can be recycled. Solution: Recyclamine Input material: Epoxy thermoset composites (carbon fibre, glass fibre) Output material: Recyclable thermoplastic and recovered fibres Steps: The matrix composed of epoxy resin and Recyclamine hardeners in polymer composites can be cleaved by solvolysis under specific conditions (not disclosed). Efficiency: N/A Advantages: Maintains or exceeds the process and performance characteristics of epoxy matrix used in composites. Recovered fibres are in near virgin form, with nominally reduced mechanical strength. Disadvantages: Recycling process steps are not disclosed. Case study The first industrial-scale implementation of Recyclamine was performed by Siemens Gamesa Renewable Energy (Hamburg, Germany), and commercial operations are expected to commence in 2022. Companies: Siemens Gamesa Renewable Energy Location: German North Sea Input material: A mixture of resin and materials including balsa wood, glass fibre, and carbon fibre Output material: A combination of materials (balsa wood, glass and carbon fibre) cast together with resin to form a strong and flexible lightweight structure Objective: Recyclable wind turbine blade Methods: Heating the material in a mildly acidic solution Results: The chemical structure of this new resin type makes it possible to efficiently separate the resin from the other components at the end of the blade’s working life. This mild process protects the properties of the materials in the blade, in contrast to other existing ways of recycling conventional wind turbine blades. The materials can then be reused in new applications after separation. Additional information: Wind turbine blades have been produced using epoxy systems. With Recyclamine, the blades are recyclable, as are the fibres and epoxy, closing the loop and allowing for a circular economy. This helps solve the difficult issue of disposal of the blades, making the wind turbines truly 100 % recyclable, as well as creating value through the reuse of recovered materials. In the vehicle industry, thermoset composite structural elements like the doors, chassis, and panels can have improved end-of-life characteristics with Recyclamine. Recyclamine was developed by Connora Technologies (Hayward, CA, USA), and Aditya Birla acquired the product and technology rights. This technology is protected by patent number US20130245204A1. All plastics – Difficult to recycle solutions Obtained products after plastic recycling through HydroPRS process (Source: Bioenergy International.) The Hydrothermal Plastic Recycling System (HydroPRS) is a process developed by Mura Technology (London, UK) that utilizes the Cat-HTR technology, which employs supercritical water, heat, and pressure to convert waste plastics into valuable chemicals and oil. This chemical recycling process targets plastics deemed unrecyclable. Solution: HydroPRS Input material: All kinds of end-of-life plastics Output material: Naphtha, distillate gas oil, heavy gas oil, heavy wax residue Steps: 1) Waste plastic cleaned and shredded; 2) Melting and pressurization; 3) Mix with steam; 4) Heat; 5) Cat- HTR reactor; 6) Depressurize; 7) Product separation; 8) Product storage. The first six 81-metre long recyclable blades (Source: FT) bioplastics MAGAZINE [03/22] Vol. 17 33
