Enzymatic hydrolysis of sugarcane and oil palm residues after hydrothermal pretreatment: the attainment of cellulose nanofibers

In the present work, the use of enzymatic hydrolysis to obtain cellulose nanofibers composed of purified cellulose from sugarcane bagasse (SCB) and oil palm empty fruit bunches (OPEFBs) was addressed. First, the cellulose was purified by applying hydrothermal treatments conducted at various temperatures (180 and 200 °C) and times (10, 20 and 30 min) and then 2% (m/v) sodium chlorite treatment. Then, enzymatic hydrolysis was conducted for 24, 48 or 72 h using cellulase from Trichoderma reesei at 50 °C and pH = 5.0 to isolate the cellulose nanofibers. The composition, morphology, crystallinity, thermal stability and zeta potential characteristics were evaluated for each cellulosic material. The crystallinity index increased significantly after hydrothermal pretreatment and bleaching from 42.6% to 87.3% and from 42.5% to 86.1% for SCB and OPEFB, respectively. In addition, the obtained pulps showed better thermal stability than residues when used as feedstock. Enzymatic hydrolysis was effective at extracting cellulose nanofibers, as long as the reaction time was controlled to less than 48 h, to avoid compromising the crystallinity and thermal stability of the isolated nanostructures. The enzymatic pathway is a promising alternative to the use of acid catalysts.