AbstractInteractions between biomass constituents (cellulose, hemicelluloses, and lignin) under pyrolytic conditions have received more and more attention in recent years. A synthesized sample was prepared through mixing of cellulose and lignin with a mass:mass ratio of 1:1. The cellulose-lignin mixture (C-L-M) was heated from 20 to 800 °C using a thermogravimetric analyzer coupled with a Fourier transform infrared spectrometer (TG-FTIR). The presence of the cellulose-lignin complex was theoretically confirmed by the suggestion of a hydrogen bond network between cellulose- and lignin-related oligomers through the density functional theory (DFT) method. To estimate the strength of the interaction between cellulose and lignin in different regions, correlation coefficients r were employed to nominate three regions: region I (20 to 305 °C), in which lignin and cellulose were pyrolyzed into oligomers without interacting with one another; region II (305 to 432 °C), which was deemed the intensive interaction region, with an r value of about 0.2; and region III (432 to 800 °C), in which the pyrolysis of cellulose ceased and only lignin was further degraded. A kinetic scheme was also proposed to model the co-pyrolysis of cellulose and lignin.