Waste to valuable products: an innovative route to chemical recycling of elastomeric polyurethane waste through aminolysis

In today’s world, we have been witnessing the massive amounts of plastic wastes. The world is changing and so are our needs and demands. With the overwhelming consumption rate of plastic material by humans in different forms, an immense amount of waste is left untreated. One of the major plastic wastes is polyurethane, specifically polyurethane foams (PUFs). PUFs are widely utilized in every day’s life, from cushions, mattresses, shoe insoles, car seats, insulation panels and much more. PUFs constitute a major part of the human life. Post consumption, piles of PUFs waste are left untreated and require further disposal. Many disposal techniques are present and exploited, such as landfilling, incineration, and recycling in its two forms; chemical and mechanical recycling. Our work focuses on the chemical recycling of PU wastes. Aminolysis, a chemical recycling method is adopted to recycle our waste (shoe insoles). The waste is dissolved in a solution of a short chain polyol, polyethylene glycol (PEG), and dibutyl amine (DBA) as a chemical reagent under a relatively high temperature of 160 ˚ C. The reaction that occurs is a depolymerization reaction, breaking the urethane bond into polyol, MDA and some other products as well. The resulting product is a liquid like polyol, with a high hydroxyl value and strong odor. Nonetheless, a further step is implemented and it is called deamination. The deamination step requires reacting the liquid product with and epoxy resin to decrease the amounts of aromatic amines (MDA) in our product as per safety regulations (<1000ppm). Multiple aminolysis tests were carried out at a set temperature of 160 ˚ C, fixed reaction time, but varying weight composition of reagents. The weight percentage of DBA varied between 20%, 15%, and 10%. Once the final product characterization test results were compared, it was proved that a 10 % by weight of DBA is the optimum amount to be used upon recycling shoes insoles PU waste. Later the final recycled product was used to produce elastomeric foams, with an aim to possess similar mechanical and chemical properties as the original foam. Foams produced were tested for flexibility and compressive recovery to deem them suitable for market usage. In brief, a new and innovative method of chemically recycling elastomeric PU waste is proved to actually accommodate and treat such type of waste with future endeavors to enhance such a method.