Application of solid state 13C NMR in the study of lignin and carbohydrate contents in acid-treated sugarcane bagasse samples

Abstract

In a worldwide scenario of search for renewable fuels, the knowledge of the contents of cellulose, lignin and hemicellulose in different biomass materials is of great importance for their use in the biofuels industry. However, the current methods used for the determination of these contents are long, involve laborious procedures and make use of hazardous chemicals. In this context, solid-state 13C nuclear magnetic resonance (NMR) spectroscopy appears as one of the possible spectroscopic methods to be used for quantification of the lignin and carbohydrate contents in lignocellulosic materials. In this work, this method was used to monitor the evolution of the lignin and carbohydrate contents as function of treatment time for a sample of Brazilian sugarcane bagasse treated with hydrochloric acid. The recorded 13C NMR spectra allowed the observation of the fast removal of hemicellulose and of cellulose in structurally disordered regions, as well as the process of depolymerization of the lignin structure for long treatment times. Through the construction of calibration curves from commercial samples of lignin and cellulose, it was possible to estimate the lignin, holocellulose and crystalline cellulose contents in the studied samples. An increase in the lignin and crystalline cellulose contents was then observed for the samples with long treatment times. The analysis of the crystallinity index by X-ray diffraction corroborated the information obtained by solid-state NMR, whereas the images obtained by scanning electron microscopy allowed to observe general characteristics of the surface of the fibers of the natural and acid-treated sugarcane bagasse samples.