WASTE/CONTAMINATED POLYSTYRENE RECYCLING THROUGH REVERSE POLYMERIZATION

Polystyrene (PS) is the most employed aromatic thermoplastic polymer. PS finds a wide range of application from food contact packaging to thermal insulator in buildings. Its disposal is an environmental and social problem which is ceaselessly addressed from academic and industrial researchers. Among several recycling processes exploited the most used is direct remanufacturing through milling, washing, drying, and moulding but this is possible only for un-contaminated waste. Safeguarding of energy and material content of waste PS is a mandatory key to save oil stocks and contaminated PS may be disposed through conservation and valorisation of the phenyl moiety. Pyrolysis meets these requirements: it may convert waste PS into single ring aromatic compounds, together with low amount of char and gas, if appropriate pyrolysis conditions are employed. Thermal pyrolysis is already active at 350 °C, where the main product is a dark viscous liquid rich in single ring aromatic compounds (benzene, toluene, ethylbenzene, and styrene). Char formation increases when pyrolysis temperature rises. Anyway different pyrolysis behaviour is observed for different classes of PS (virgin, expanded, and compacted from containers), especially for what concerning the composition and distribution of aromatics in the liquid fraction. In the last few years microwave (MW) heating has encountered a sound and reliable application in polymeric waste treatment. Microwave assisted pyrolysis (MAP) encloses a number of advantages than classical methods. One of these is the direct and extremely fast heating in the presence of a MW absorber. MAP of PS has been investigated in the presence of a microwave absorber such as carbon, iron mesh, or aluminium, as coil or mesh.