Effects of residual lignin on mechanical defibrillation process of cellulosic fiber for producing lignocellulose nanofibrils

Abstract High (14.9%), medium (2.4%) and low (0.1%) lignin-containing cellulosic fibers were processed through a micro-grinding method to mechanically produce lignocellulose nanofibrils (LCNFs). Effects of residual lignin on the mechanical defibrillation process were investigated in terms of the nanofibrils yields, the diameters of resultant LCNFs and the micro-grinding energy consumption. The results showed that the residual lignin delayed the initial defibrillation of cellulosic fibers due to its physical barrier. However, the residual lignin eventually facilitated the defibrillation and improved the maximum nanofibrils yields by 17.9–30.8%, and greatly reduced the diameters of the resultant LCNFs from 32.9 ± 7.7 to 9.2 ± 3.3 nm. The effects of lignin on counteracting the recombination reactions between the highly reactive cellulose radicals and hindering the aggregation of defibrillated fibrils through reducing the inter-fibrillar hydrogen bonding presumably resulted in the better eventual defibrillation of cellulosic fibrils. Graphical abstract