An innovative organocatalyst for the recycling of commodity polymers

El contenido del capítulo 3 está sujeto a confidencialidad 252 p.Polymat, Warwick University, IB

An innovative organocatalyst for the chemical recycling of commodity polymers

Over the past century, synthetic plastics have become ubiquitous in our daily life, occupying an ever-expanding range of uses. Their global production has exponentially increased in the past half-century, from 15 to 311 million tons between 1964 and 2014, and is expected to double again by 2035. Many of those materials have extremely short lifetimes and the direct consequence is the tremendous quantities of plastic wastes accumulating in the environment for years. Produce, buy, use and dispose, this linear way of consuming more and more plastics is nowadays raising concerns, not only from governments, interstate institutions and companies but also by citizens themselves. The treatment of plastic wastes is a global problem which requires innovative solutions to collect, sort, degrade, and re-process these materials. Thus, recycling is a crucial matter from an environmental point of view but also taking into account the plastic production and the tremendous income recycling could be for the global economy. Currently, most of the recycled plastics are by means of mechanical methods that involve grinding and re-processing of the material into lower value plastic products. The structural deteriorations lead to recycled product which does not share the same properties as the virgin polymer and also rapidly ends up as waste. Another approach relies on their direct conversion into high calorific value fuels through pyrolysis, but this thermal deterioration only postpones their unsustainable end-of-life since the resulting combustible will typically be burnt releasing mainly green-house gases such as CO2 and potentially affecting to the global warming. In comparison, chemical recycling involves the depolymerisation of polymers into monomers or oligomeric fragments that can then be subsequently polymerised to yield recycled materials, it represents an attractive long-term strategy to create a sustainable polymer supply chain. Recently, the chemical recycling of polymers has attracted a lot of attention among the scientific community, mainly driven by the current public awareness of the plastic pollution problem. However, as a consequence of the high stability of most polymers, depolymerisation processes are generally conducted in very harsh conditions and in the presence of catalysts, principally organometallics, which can present several drawbacks: possible presence of metal in the final product, low monomer yields or challenging purification procedures. Organocatalysts are promising “green” substitutes to classic organometallic catalysts. Although they are currently widely investigated for various polymerisation techniques, they have been much less explored in depolymerisation processes. One of the main reason behind this is that typically organic catalysts show poor thermal stability at temperatures that would be practical for recycling reactions. Thus, the partial or full degradation of the catalyst hinders the perspective of reusing it for several reactions and entails colouration of the final products, low conversion or undesirable side-reactions. In Chapter 1, an innovative series of acid and base mixtures have been explored as catalyst for depolymerisation reactions. Not only these acid-base mixtures displayed unique thermal stability, a tremendous advantage compared to most of organocatalysts which usually degrade at relatively low temperatures, but also reveals very good abilities for the depolymerisation of commodity polymers. Indeed, both poly(ethylene terepthalate) (PET) and Bisphenol A-based polycarbonate (BPA-PC) have been depolymerised using an equimolar mixture of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and methanesulfonic acid (MSA) as catalyst in a solvent-free procedure. The comparison with already reported procedures have demonstrated the superior control of the reaction employing the present organocatalyst. Chapter 2 has explored the influence of different parameters on the PET glycolysis catalysed by TBD:MSA (1:1). Using the adequate amount of reagent and catalyst, over 90% of Bis(hydroxyethyl)terephtalate (BHET) is obtained and easily recovered. Kinetics have emphasised the high selectivity of the reaction to form the desired monomer compared to well-known organocatalyst. Both the reagent and the catalyst can be easily recycled, demonstrating no loss of catalytic activity even after 6 cycles. Finally, it was demonstrated that this catalyst could even be used in the self-condensation of BHET to obtain recycled PET exhibiting good thermal and physical properties, closing the polymer to monomer to polymer loop. In a similar way, Chapter 3 has investigated the same procedure for the depolymerisation of BPA-PC into both Bisphenol A (BPA), its industrial monomer, and valuable building blocks. By wisely choosing the starting reagent and tuning the reaction conditions, 5- and 6-membered cyclic carbonates were obtained in reasonable to excellent yields (up to 97 %), constituting a phosgene-free, 100% atom economy procedure for the ringclosing of valuable carbonates widely reported for the synthesis of highperformance materials. Similarly, innovative linear carbonates and ureas were obtained. Density functional theory (DFT) methodology was employed for determining the mechanisms involved for both reactions – with PET and with BPA-PC. The obtained pathways exhibited similar chemical interactions but with a large energetic difference, inspiring the possibility for these two polymers to be recycled selectively. Thus, in Chapter 4, using different reagents and different reaction conditions investigated in the previous chapters, the simultaneous depolymerisation of BPA-PC and PET was explored using different reagents and in the presence of other plastics (i.e. polyolefins)

Sustainable Materials and Chemical Processes for Additive Manufacturing

Unformatted postprintAdditive manufacturing (AM) is energizing the fields of chemistry and materials science to develop new inks for new applications within fields such as aerospace, robotics, and healthcare. AM enables the fabrication of innumerable 3D geometries that cannot be easily produced by other means. In spite of the great promise of AM as an advanced form of future manufacturing, there are still fundamental challenges with respect to sustainability that need to be addressed. Some of the material needs for AM include sustainable sources of printing inks, resins, and filaments, as well as pathways for polymer recycling, upcycling, and chemical circularity. Furthermore, the combination of bio-sourced and biodegradable polymers with additive manufacturing could enable the fabrication of objects that can be recycled back into feedstock or degraded into non-toxic products after they have served their function. Herein, we review the recent literature on the design and chemistry of the polymers to that enable sustainability within the field of AM, with a particular focus on biodegradable and bio-sourced polymers. We also discuss some of the sustainability-related applications that have emerged as a result of AM technologies.E.S.-R. thanks the European funding by the Marie Sklodowska-Curie Individual Fellowships (MSCA-IF-GF) 841879-4D Biogel. H.S. and C.J. thank MINECO for funding through MAT2017-83373-R. A.N. thanks the National Science Foundation for support (1752972)

From Plastic Waste to New Materials for Energy Storage

The use of plastic waste to develop high added value materials, also known as upcycling, is a useful strategy towards the development of more sustainable materials. More specifically, the use of plastic waste as a feedstock for synthesising new materials for energy storage devices can not only provide a route to upgrading plastic waste but can also help in the search for sustainable materials. This perspective describes recent strategies for the use of plastic waste as a sustainable, cheap and abundant feedstock in the production of new materials for electrochemical energy storage devices such as lithium batteries, sodium batteries and supercapacitors. Two main strategies are described, the development of conducting carbons by combustion of plastic waste and the depolymerization of plastics into new chemicals and materials. In both cases, catalysis has been key to ensuring high efficiency and performance. Future opportunities and challenges are highlighted and hypotheses are made on how the use of plastic waste could enhance the circularity of current energy storage devices.NG acknowledges the funding from the European Union’s Horizon 2020 framework programme under the Marie Skłodowska-Curie agreement No. 101028682. CJ acknowledges the financial support from el Ministerio de ciencia e innovación from the Juan de la Cierva Program (FJC2020-045872-I). The funding from the European Union’s Horizon 2020 framework programme under the Marie Skłodowska-Curie agreement No. 101028975 and Ministerio de ciencia e innovación under PDC2021-121461-I00 project is acknowledged

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.C.J. acknowledges the financial support from el Ministerio de ciencia e innovación from the Juan de la Cierva Program (FJC2020045872-I). The funding from the European Union’s Horizon 2020 framework programme under the Marie Skłodowska Curie agreement No. 101028975 and Ministerio de ciencia e innovación under PDC2021-121461-I00 project are acknowledged

Organocatalysis for depolymerisation

Polymeric materials have been accumulating in the environment for decades as a result of the linear way of consuming plastics. Unfortunately, the current approaches followed to treat such a large amount of plastic waste, mainly involving physical recycling or pyrolysis, are not efficient enough. Recently, chemical degradation has emerged as a long-term strategy towards reaching completely sustainable cycles where plastics are polymerised, depolymerised, and then re-polymerised with minimal changes in their quantity or final properties. Organocatalysts, which are promising “green” substitutes for traditional organometallic complexes, are able to catalyse depolymerisation reactions yielding highly pure small molecules that are adequate for subsequent polymerisations or other uses. Moreover, by varying several reaction parameters (e.g. solvent, temperature, concentration, co-catalyst, etc.), the depolymerisation products can be tuned in innumerable possibilities, which further evidences the versatility of depolymerisation. In this review, we highlight the recent advances made by applying organocatalysts, such as organic bases, organic acids, and ionic compounds, to chemically degrade the most commonly used commercial polymers. Indeed, organocatalysis is envisaged as a promising tool to reach a circular and environmentally friendly plastic economy.Postprint (published version

An innovative organocatalyst for the recycling of commodity polymers

El contenido del capítulo 3 está sujeto a confidencialidad 252 p.Polymat, Warwick University, IB

An innovative organocatalyst for the recycling of commodity polymers

El contenido del capítulo 3 está sujeto a confidencialidad 252 p.Polymat, Warwick University, IB

Sustainable Green Polymerizations and End-of-Life Treatment of Polymers

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/173121/1/marc202200446.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/173121/2/marc202200446_am.pd