Selective dissolution and supercritical recovery of barrier layers from multilayer plastic packaging.

Plastic multilayer food packaging structures are indispensable in modern society. However, traditional sink/float or air stream sortation methods are not applicable them due to the presence of “tie” layers in the structures. Thus, many multilayer structures are notoriously difficult to recycle and are ineligible for most municipal recycling programs. Even in the multilayer structures that are recycled, the more expensive barrier layer is lost to commodity recycling streams. Solvent-based processes have been proposed to reclaim individual materials from multilayer polymer waste. However, these processes can be slow, require extra/additional antisolvents and commensurate solvent recovery systems, or rely on solvent evaporation to recover the polymer. Here, we report a process to selectively dissolve and recover high-value materials such as ethylene vinyl alcohol and polyamides, from polyolefin/oxygen barrier multilayer structures without first dissolving the outer polyolefin layers. The impact of solvent choice and dissolution conditions on the dissolution rate and efficiency and the effects of supercritical antisolvent recovery pressure and temperature on the dissolved polymer recovery efficiency are described. The impacts of the dissolution and recovery process on the recovered polymer are also quantified. Finally, mechanical analysis of the undissolved polyolefin layers suggests these materials are suitable for placement in the corresponding polyolefin recycling stream.