Thermal and kinetic analysis-guided selection of initial pyrolysis temperature for carbon nanotube synthesis from post-consumer recycled polypropylene

Abstract

The rapid escalation of post-consumer recycled polypropylene (PCR-PP) waste has raised environmental concerns and continues to exhaust municipal landfill capacity. Converting this plastic waste into high-value functional carbon materials is therefore necessary. This study investigates the thermal degradation behaviour of FeCp2-catalysed PCR-PP using TGA and analyses its kinetics using the Coats-Redfern method. The thermal and kinetic data were used to identify the decomposition window and guide the selection of the initial pyrolysis temperature. CNTs were synthesised using a single-zone horizontal tube furnace with a sequential two-step heating protocol, comprising initial pyrolysis at the selected temperature followed by CNT growth at 900 °C. The products were characterised using SEM, XRD and Raman spectroscopy. The thermal decomposition of FeCp2-catalysed PCR-PP was best described by an apparent first-order kinetic model with an activation energy (Ea) of 160.17 kJ/mol. Initial pyrolysis at a representative temperature of 400 C generated carbon precursors to yield bundles of aligned, graphitic CNTs. The integrated Raman ID/IG ratio of 0.69 indicated relative structural ordering. The gross solid-product yield was 1.84 wt%, showing the need for further optimisation of carbon deposition and product recovery. Practically, the identified decomposition window and apparent activation energy provide baseline thermal and kinetic data for optimising initial heating conditions and hydrocarbon precursor generation in the single-zone PCR-PP to CNT process. This study integrates thermal analysis and kinetic evaluation into a workflow for CNT synthesis from PCR-PP.