Highly-efficient defibrillation of bamboo-based lignin-coated cellulose nanofibrils via facile hydrothermal and ethanol solvothermal pretreatments

To develop a clean and facile method to prepare lignin-coated cellulose nanofibrils (LCNFs) derived from bamboo, this study aims to investigate the effects of hydrothermal and ethanol solvothermal pretreatments at various temperatures and durations on the efficiency and performance of mechanical defibrillation. The variations on contents and structures of chemical constituents, microscopic and crystal structures, and nano-mechanical properties of bamboo cell walls as well as the micro-morphology, water retention value (WRV), thermal stability, and dispersibility of resultant LCNFs were comparatively investigated. The results indicate that ethanol solvothermal pretreatment at lower temperatures yields superior defibrillation efficiency compared to hydrothermal pretreatment. The thermal stability of the resultant LCNFs is enhanced because of the retention of lignin components. The ultrafine LCNFs achieved the smallest diameter of 14.78 nm and the highest WRV value (789 %) when subjected to a 30 wt% ethanol solvothermal pretreatment for 60 min at 180 °C. More hemicelluloses were hydrolyzed, and more hydrogen bonds among the network of the three main chemical components were disrupted, while fewer β-O-4 structures in lignin were affected after ethanol solvothermal pretreatment. This promotes shear strength during the grinding process and provides a promising way for manufacturing bamboo-based LCNFs. • Defibrillation effects of hydrothermal and solvothermal pretreatments were compared. • Ultrafine bamboo-based LCNFs can be obtained by ethanol solvothermal pretreatment. • More hemicelluloses, hydrogen bond networks were disrupted by ethanol pretreatment. • Fewer β-O-4 structures in lignin were affected after ethanol pretreatment. • A green, facile, and promising way for preparing bamboo-based LCNFs were provided.