The circular economy of equine surfaces : investigating the recyclability of surfaces produced by Equestrian Surfaces LTD.

Nicholson, Steven and Doulcet, Julien and Ashton, Mark (2024) The circular economy of equine surfaces : investigating the recyclability of surfaces produced by Equestrian Surfaces LTD. PhD thesis, Lancaster University.

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Abstract

As an ever-growing sector, the equestrian industry is constantly developing, with a range of synthetic surfaces available in the market. Typically, synthetic equine surfaces comprise three major components – sand, wax, and fibre. Currently, most equine surfaces are disposed of in landfill when they reach the end of their life. This is an unsustainable waste solution; hence alternative strategies need to be explored. This project has been completed in collaboration with Equestrian Surfaces LTD, with the main aim of this research being the development of a more sustainable end-of-life (EOL) solution for equine surfaces that allows the individual components to be recovered and potentially recycled into new surfaces. Equestrian Surfaces LTD are a company specialising in the production and installation of synthetic equine surfaces, offering a range of surfaces suitable for indoor and outdoor use in all weathers and for all disciplines. The research presented in this thesis focusses on the small-scale extraction and separation of the individual surface components (sand, wax, and fibre) as well as identification of any changes to the quality and physio-chemical properties of the separated materials compared to their composition at time of manufacturing. After presenting the general context for this work (chapter 1), the results section is comprised of 4 chapters focusing on the following aspects: experimental methods (chapter 2), wax extraction (chapter 3), sand and fibre separation (chapter 4), and conclusion and future work (chapter 5) as well as an appendix containing additional experimental detail. Results discussed in chapter 3 show that wax can be extracted efficiently from used surfaces using a range of organic solvents, with ethyl acetate identified as a suitable non-toxic, high-yielding green solvent. Alternative green extraction routes were also explored, with microemulsion extraction proving promising for removal of wax from surfaces. The major obstacle with this technique was the recovery of organic material from the aqueous solution, with this highlighted as an important area for further research. Analysis of extracted wax using a range of analytical techniques (GC-MS, IR, DSC, and CHNS elemental analysis) showed that wax decomposes rapidly and is lost from surfaces progressively over time. The extracted wax can be purified (silica gel column chromatography) however, since a considerable mass of wax is lost during usage, and the yield of reusable wax recovered following purification was as low as 9.5%, this was deemed an unsustainable solution. Chapter 4 focussed on utilising size-based separation techniques to isolate the sand and fibre from surfaces. Results discussed in this chapter revealed that surfaces, in both the waxed and dewaxed forms, can be separated in this way, with sand recovery yields of up to 93% recorded for some used surfaces. It was also discovered that the extent of wax remaining on a surface affects the efficiency of separation, with high remaining wax content resulting in poor sand recovery. The quality and purity of the isolated sand was evaluated using analytical techniques including SEM, EDX and IR spectroscopy, showing that the recovered sand has a particle size distribution similar to that of the supplier sand. Results discussed in chapter 4 also revealed how fibres can also be separated from surfaces by utilizing size-separation techniques; however, the fibres recovered from used surfaces appear heavily contaminated with sand and other solid materials. The quality of the fibres was briefly evaluated via SEM-EDX analysis and tensile strength tests, both of which highlighted a reduction in quality and purity following surface usage. Further testing is necessary to evaluate the reusability of the fibres, however, since this material is already recycled it may not be economically viable to pursue further recycling. In this way, further research to provide an end-of-life solution for the used surface fibres should be conducted. We concluded that, equestrian surface recycling is not a trivial process, and that wax removal from surfaces is a complex, costly, and unnecessary step that can be avoided due to loss of the coating during surface usage. The small-scale separation techniques developed in this report provide a tool that can be used by Equestrian Surfaces LTD to determine the EOL state of their surfaces. Surfaces which meet the set requirements detailed in chapter 5 can be deemed as fully EOL and subsequently subject to direct mechanical separation without the need for wax removal. This has been recognised as the most suitable recycling strategy for use in industry due to the simplicity of separation and the high yields of sand recovery attainable. The sand recovered from this process can then be incorporated into newly manufactured surfaces, with further testing needed to establish the quality of the surfaces made from reused non-dewaxed sand. Further research is also required to improve the circularity of the proposed process, with the ability to reuse both the large fibres and microplastics isolated from surfaces being key examples.