Specific molecular structure changes and radical evolution during biomass–polyethylene terephthalate co-pyrolysis detected by 13C and 1H solid-state NMR

• 13C NMR proved cross-linking reaction between biomass and PET during co-pyrolysis.
• Radical effect on faster thermal degradation PET was studied upon co-pyrolysis.
• 1H NMR revealed evolution of radical as a function of temperature and blend ratio.
• Co-pyrolysis samples showed higher radical density than single pyrolysis samples.

Co-pyrolysis of biomass with polyethylene terephthalate (PET) was studied as a function of blend ratio and co-pyrolysis temperature by 13C and 1H solid-state nuclear magnetic resonance (NMR). The 13C NMR spectra showed that upon heating to 400 °C in presence of the biomass, the formation of crystallites in PET was completely suppressed and that at higher temperatures there was increased formation and growth of the polycyclic aromatic hydrocarbons (PAHs). This change in the PET degradation behaviour was attributed to the presence of radicals formed in char from biomass. The measurement of the 1H–T1 relaxation enabled monitoring the changes in the concentrations of radicals formed, as a function of the blend ratios and the co-pyrolysis temperatures. It indicated that the increase in the radical concentrations correlated well with the increased degradation of the PET and growth of PAHs.