Here we demonstrate di-carboxylic acid hydrolysis for the integrated production of lignin containing cellulose nanocrystals (LCNC) and nanofibrils (LCNF) using two unbleached mixed hardwood chemical pulps of lignin contents of 3.9 and 17.2%. Acid hydrolysis experiments used maleic acid solution of 60wt% concentration at 120°C for 120min under ambient pressure. Yields of LCNC were low of less than 6% under this set of conditions. The higher lignin content sample produced LCNC with greater height (diameter) of 25nm but similar length of approximately 230nm to that from the lower lignin content fibers (height of 20nm). Interestingly, the higher lignin content sample resulted in LCNF with smaller height (diameter) of 7nm but longer length of >1μm, or greater aspect ratio than the LCNF from the lower lignin fibers of height 10nm and length <1μm. Lignin protected cellulose from esterification which resulted in LCNC and LCNF that was less carboxylated compared to those lignin-free CNC and CNF and therefore had lower charges. However, lignin is more hydrophobic and thermally stable than carbohydrates therefore LCNC and LCNF are favorable for composite applications.
Keywords: Carboxylation; Di-carboxylic acid hydrolysis; Hydrophobicity; Lignin containing cellulose nanomaterials; Lignocellulosic crystals (LCNC); Lignocellulosic nanofibrils (LCNF); Mechanical fibrillation; Thermal stability.
Published by Elsevier Ltd.