Analysis of thermal degradation kinetics and carbon structure changes of co-pyrolysis between macadamia nut shell and PET using thermogravimetric analysis and 13C solid state nuclear magnetic resonance

Thermal degradation kinetics of co-pyrolysis of polyethylene terephthalate (PET) blended with macadamia nut shell were investigated using a large-scale customised thermogravimetric analysis (TGA) and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. Blending ratios ranging 20–80 wt.% of PET with macadamia nut shell were analysed at heating rates of 3, 5 and 8 °C/min up to 1273 K in the presence of N2 atmosphere with a flow rate of 1 L/min. The differential thermogravimetric analysis (DTG) data was analysed by the Freeman–Carroll method to yield kinetic parameters which were correlated with chemical analysis by 13C solid-state NMR. The results indicated that two synergistic effects occurred between PET and macadamia nut shell during co-pyrolysis, which were characterised by an enhanced carbon yield of the co-pyrolysis products. The secondary reaction occurring between primary products of macadamia nut shell and PET was identified as the cause of the synergistic effect and this effect varied with weight fraction of macadamia nut shell in the blend and the heating rate. The measured changes in activation energy and reaction order indicated that the thermal degradation mechanism of co-pyrolysis is different to that of the individual components. The NMR results indicated that macadamia nut shell catalysed the degradation behaviour of PET leading to growth of polycyclic aromatic hydrocarbons (PAHs) through cross-linking reaction and enhancing the carbon yield from the PET.