Cellulose co-crystallization and related phenomena occurring in hydrothermal treatment of sugarcane bagasse

Lateral dimensions of cellulose crystallites have been widely reported to increase as plant biomasses are submitted to a variety of high-temperature chemical treatments. Cellulose co-crystallization is often indicated to be the phenomenon underlying crystallite dimensional change, but precise mechanisms and relationships with concurrent phenomena are not well understood. This work investigates cellulose structural evolution in sugarcane bagasse submitted to wide range (160-190 degrees C, up to approximate to 50 % solubilization) of hydrothermal treatments, performed in pressurized liquid hot water. Cellulose structural characterization combines fiber and powder X-ray diffraction with analysis of two-dimensional diffraction patterns employing the Cellulose Rietveld Analysis for Fine Structure (CRAFS) model. We observe that increases in lateral dimensions of cellulose crystallites closely follow changes in bagasse chemical composition. For a given composition, treatment temperature per se seems to be secondary for changes in crystallites. Partial cellulose de-crystallization and decreasing distortion of crystallite unit cell are found to co-occur with increasing crystallite lateral dimensions. Our interpretation of results emphasizes the importance of removing hemicelluloses acting as intercrystallite spacers, which seems to be the limiting factor for cellulose co-crystallization.