Kinetics of alkaline delignification of hemp and determination of lignin content by thermogravimetry

Abstract Raw hemp (Cannabis sativa L.) was subjected to alkaline delignification with the application of NaOH ranging from [0.125M] to [1M] for times from 5 to 480 min. Lignin contents of the original and delignified samples were determined. The samples were subjected to thermogravimetric analysis (TGA) under a N2 atmosphere with temperatures ramped from 25 to 600 °C at 10 °C min-1. Lignosulfonates samples of low, medium and high molecular weight were subjected to the same TGA and showed that lignin decomposed over the entire temperature range. The contributions of lignin to the mass loss during thermal decomposition of hemp and kinetics of lignin content and the most relevant TGA results were determined. Regression models estimating the lignin content of the fibers based on TGA results were formulated. These models allow for the prediction of mean lignin content within ± 0.1% (based on dry weight of pulp) in the central range of the experimental field.