| Summary: | Nearly 40 metric tonnes of expanded polystyrene (XPS) waste is collected through Kingston’s curbside recycling program annually before being outsourced to companies with the means to recycle it. However, transporting XPS foam products is not economically viable. Therefore, a significant challenge is finding an efficient way to reduce the volume of the XPS foam prior to transportation since it has a very low density, consisting of up to 98% air. Currently, XPS products are compacted physically which requires the use of expensive compactors and energy-intensive compression processes. In 2011, Jessop et al. demonstrated that N,N-dimethylcyclohexylamine (DMCHA), a solvent with relatively low toxicity and volatility, can be used to recycle XPS using a greener approach. DMCHA is relatively hydrophobic under neutral conditions (e.g., in water), but becomes more hydrophilic when exposed to carbonated water (CO2 dissolves in water, forming carbonic acid which protonates the DMCHA). I have worked on optimizing this process via the following steps. Firstly, the XPS is dissolved in a small volume of DMCHA in its hydrophobic, neutral form. Then, the PS-DMCHA mixture is added to carbonated water causing the DMCHA to become hydrophilic and to dissolve in the aqueous solution, resulting in a layer of PS on the surface. The PS can then be easily collected and air-dried. By adding a 30 wt.% PS/DMCHA solution to carbonated water at 60oC, I have been able to achieve a typical purity of 95 wt.% of the final XPS (i.e., 5 wt% of DMCHA remains in the XPS), determined by 1H NMR.
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