Applicability of Gravity Separation to Recycling Biodegradable Plastics

Biodegradable plastics should be appropriately managed independently of general plastics during and after use. To establish an effective recycling process for biodegradable plastics, the present study investigates and evaluates the applicability of gravity separation. Experimental results indicate that a laboratory specific-gravity separator achieves a recovery ratio of >98% at a purity of >99.9% for light-density plastics as a float product. We performed simulations by the discrete element method coupled with computational fluid dynamics to investigate the effect of the particle size and the feed quantity on the separation efficiency. A systematic series of simulations reveal that light-density particles such as polypropylene and heavy-density particles such as biodegradable plastics are well-separated. However, the separation efficiency is substantially reduced when the particle size decreases to 2 mm, and some light-density particles are in the sink product. Nevertheless, these results suggest that a laboratory-specific gravity separator is sufficient for separating and recycling biodegradable plastics. Consequently, the present study newly demonstrates the applicability of gravity separation of biodegradable plastics and will contribute to the recycling of various biodegradable plastics.