Cellulose enzymatic hydrolyzability and fermentability of sugarcane bagasse was well improved to produce bioethanol by H2SO4-catalyzed atmospheric acetic acid (AA) pretreatment, which was mainly ascribed to delignification and modification of lignin structure. Crude bagasse milled lignin (CBML) was further used to investigate the structural changes of lignin macromolecule. Results showed that lignincarbohydrate complex (LCC) underwent significant cleavage by acid hydrolysis as revealed by the reduction of polysaccharide content after AA treatment. The cleavage of beta-O-4' aryl ether bond was the predominant reaction responsible for lignin depolymerization. After AA treatment the negative effects of CBML were greatly weakened mainly due to the acylation of hydroxyl groups. The phenolic hydroxyl group mediated non-productive adsorption of cellulases was primarily attributed to hydrogen bonding interaction for endoglucanase and cellobiohydrolase, but both hydrogen bonding and electrostatic attraction played important roles for the adsorption of beta-glucosidase on lignin. (C) 2018 Elsevier Ltd. All rights reserved.