Integrated Polymer Dissolution and Solution Blow Spinning Coupled with Solvent Recovery for Expanded Polystyrene Recycling

Abstract

With increasing buoyant plastic wastes entering into oceans and food chains, the disposal and recycling of waste expanded polystyrene (WPS) has become an imminent environmental problem. In this work, a recycling scheme for waste WPS is proposed that combines the polymer dissolution recycling approach with the solution blow spinning (SBS) technique that facilitates the high-volume bulk WPS transportation and the value-addition of WPS to nanofibers. Solvent selection is critical for an economical and environmentally favorable implementation of this recycling scheme at large scale. Here, the effect of three solvents with distinct volatility, viz. ethyl acetate, toluene, and N, N- dimethylformamide (DMF) have been studied on the fiber formation and the ease of the solvent recovery, in order to ascertain the practicability of using these solvents for the recycling process. The fiber formation is experimentally demonstrated for the WPS-solvent systems using the SBS process. It is found that the fiber morphology varies for the different WPS-solvent systems. A solvent recovery scheme to recover the solvent from the air-solvent mixture (leaving SBS) is evaluated using ASPEN Plus simulation. The % solvent recovery is determined as a function of the required energy input for different process parameters including compressor pressure and air to polymer solution feed ratio. The simulation studies show that a lower feed air to polymer solution ratio and higher compressor pressure are required to obtain > 70% solvent recovery for high volatility solvents (ethyl acetate and toluene) with lower energy input and optimal operating condenser temperature (~ 0 °C). Conversely, significant solvent losses occur in the SBS process with a lower volatility solvent (DMF), leading to a lower solvent recovery for the whole process. The % DMF recovery can be improved upon by using higher feed air to polymer solution ratio although at a higher energy penalty.