Plastic waste presents a significant problem for the environment as significant amounts of plastics are produced, of which the majority are still landfilled contaminating soils, waterways and aquifers. A particular challenge present thermoset plastic material, which are more difficult to recycle compared to thermoplastic materials. One of these thermoset materials are melamine resins, noted for their heat resistance and stable structure, but usually disposed in landfills after the end of their life cycle. Hydrothermal processes present a promising method to tackle the issue of reprocessing thermoset materials, as they utilize water at high temperature and pressure to convert plastic waste into useful materials.
Hydrothermal decomposition of melamine etherified resin (MER) fibres is studied in this work. The reaction occurs in a hydrothermal reactor with water at subcritical conditions. The aqueous phase extracted from the post reaction mixture was analysed using tube tests for the contents of formaldehyde, organic acid, total nitrogen, and ammonium. Environmental footprints are further analyzed based on the data obtained from experimental work, and compared regarding three different decomposition temperatures: 200, 300 and 350 °C. Footprint assessment is performed mainly using OpenLCA software and various databases. Environmental comparison of the processes is evaluated regarding to greenhouse gas (GHG), nitrogen, phosphorus, energy, and ecological footprints, and human toxicity potential. Results show that decomposition at 200 °C yielded the lowest environmental impacts. However, the highest amounts of secondary compounds were obtained when conducting the process at 300 °C.