Prospects of physical, mechanical, and advanced recycling of end-of-life polystyrenes: Towards full recyclability

The high sensitivity of polystyrene (PS) to thermo-mechanical stress and its diverse applications, for example, bulky foams, rigid forms, have made the conventional mechanical recycling process of PS quite challenging. On the contrary, emerging recycling techniques such as the fast dissolution of PS in various industrial solvents at room temperature has opened new horizons towards its full recycling. Moreover, the development of counter-rotating twin-screw extruders with special designs along with the application of stabilizers to lessen degradation has opened the door for PS mechanical recycling. Advanced recycling of PS to styrene up to 80% has also made huge steps with the first commercial units being commissioned driven by the rapid increase in fundamental understanding of PS catalytic and non-catalytic pyrolysis and improved sorting. Yet, increasing the yield of the styrene monomer remains the main challenge. However, with more advanced reactor designs such as vortex and conical spouted bed reactors (CSBR), shorter residence times, and working at lower pressures, the styrene selectivity can be further increased by avoiding secondary reactions.