Growing of 2D/3D graphene structures on natural substrates from aromatic plastic wastes by scalable thermal-based upcycling process with a comparative CO2 footprint analysis

Recycling aromatic plastics, such as polystyrene (PS) and polyethylene terephthalate (PET), is complex and strongly sensitive to the process design and conditions due to the presence of polycyclic aromatic hydrocarbons and interunit C–O and/or C–C linkages. Herein, the upcycling process becomes crucial to attain high-value-added products from aromatic plastics. With this study, graphene growth was achieved on the natural substrates of talc and organically modified montmorillonite (OMMT), from waste PS and PET sources via a sustainable, affordable, and environment-friendly upcycling technique. This promising method promotes the formation of 2D and 3D graphene structures from waste PS and PET. This provides dimension-controlled graphene growth by tailoring the substrate type and size, surface composition of the substrate, and the degree of aromaticity in the polymer. In addition, polymer processing techniques of twin-screw extrusion and thermokinetic mixing, were investigated in the development of graphene-grown hybrid additives to tailor the degree of crystallinity. Regarding structural characterization results, a high shear rate mixer led to the change in crystalline planes of talc, whereas conventional twin screw extrusion preserved the structure of talc indicating that high shear rate triggered the exfoliation of talc. Furthermore, a systematic life cycle assessment was conducted to evaluate the CO2 footprint of upcycled graphenes grown on talc and OMMT compared to graphene produced from graphite. Upcycled graphene structures obtained by direct carbonization and even catalyst impregnated natural substrate-based graphene growth process with PS or PET source have comparably lower CO2 emission than graphene received from graphite. Therefore, these newly developed and upcycled hybrid additives opens a way for the conversion of aromatic complex plastic wastes into value-added nanomaterials being candidate as reinforcing agent by adopting a circular economy model