Abstract Co-pyrolysis of biomass and plastics gives rise to synergistic effects that can improve the properties of the resulting bio-oil. In this paper, the co-pyrolysis of lignocellulose (softwoods and hardwoods) and plastic (polyethylene and polystyrene) mixtures at different ratios was investigated by evolved gas analysis-mass spectrometry (EGA-MS). Through the extraction of specific sets of m/z values, we were able to build component-specific thermograms representative of each component of the mixtures. Such thermograms were used to evaluate the presence of synergistic effects by the comparison with the theoretical thermograms. The shift of the peak temperatures and the differences between the integrated area of the two thermograms showed that both biomass and plastic influence the pyrolytic behaviour of the other component. Finally, the KAS model-free isoconversional method was used on component-specific thermograms to determine apparent activation energies of the biomass and plastic fractions.