Bug-Busting Spandex: Biodegrading Textile Blends for Molecular Recycling

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Waste textiles are a major issue worldwide and recent reports have highlighted that Britons throw away ~ 3 kg textiles each year. While some waste clothing (~10%) is resold or exported, nearly 50% ends up in landfill in the UK which is a missed recycling opportunity. The global polyester fibre market was $74 billion in 2020 and is projected to rise to $124 billion by 2027. Polyester fibre is made from processed polyethylene terephthalate (PET), including virgin fibres, and more recently recycled PET. Spandex, also known as Lycra or Elastane, is an important elastane fibre with production levels of 1 million tonnes/year. It is used in many stretchy fabrics such as activewear as a textile blend with polyesters (e.g. ratio Spandex:PET, 15:85 or less). Such blended textiles are particularly challenging to recycle into useful materials due to the complex structure, however biotechnological approaches have the potential to degrade the polymers into fragments or small molecules for recycling or upgrading into other polymers or materials. This project aims to identify and develop enzymes for the breakdown of polyester/Spandex fabric blends and to recycle the small molecule monomers into either new polymers, for use as a feedstock for biopolymer synthesis, or as a drug precursor. This 'bug-busting' strategy for Spandex textile blends will provide routes to tackle a major problematic textile waste stream. A particular challenge of Spandex is their combination with other textiles into fabric blends, and the carbamate bonds which are hard to hydrolyse under mild conditions. While there have been significant developments recently in generating productive enzymes to break down plastic PET bottles, there has been little work carried on the breakdown of PET polyesters in textiles. There are also currently very few enzymes that cleave the carbamate bond that have been characterized.Several strategies to obtain productive degrading enzymes for polyester/Spandex blends are proposed. Crucial to the rapid success of enzyme discovery and screening will be suitable assays and for this we will synthesise substrates for the development of chromogenic high throughput assays on an automated platform and for subsequent screening on an analytical HPLC machine. The biodegradation of polyesters will be investigated using current in-house PETases and esterases, and available PETases, together with the use of mechanoenzymatic reaction conditions and ionic liquids to enhance textile/enzyme interactions. Then the Spandex biodegradation will be explored via the identification of enzymes that can break down the carbamate bond. This will be through the development of microbial consortia/bacteria from enrichment experiments in hotbins set up two years ago, assays, DNA sequencing and enzyme identification. Also, informatics approaches and the use of databases, and metagenomic strategies including our metagenomics database. The polyester and Spandex degrading enzymes will then be combined and optimised using enzyme mutagenesis approaches and high throughput automated screening platforms. Using the best combination of enzymes, procedures will be tested to isolate the key aromatic acid and amine fragments, while the remaining soft segment components can potentially be used as a carbon feedstock for bioplastic production. A route to enhance the value of the amine fragment will also be explored using in house oxidative enzymes. Throughout the project and through links to the UCL Plastic Waste Innovation Hub we will assess the social, economic, and environmental impact of the technologies developed and gather the data for a life cycle analysis.