Optimization of sulfuric acid hydrolysis conditions for preparation of nanocrystalline cellulose from enzymatically pretreated fibers

Preparation of nanocrystalline cellulose (NCC) by 62 and 65 % wt. sulfuric acid hydrolysis of cellulase-pretreated fibers was optimized to obtain the highest yield by applying two statistical plans. At optimal conditions (10 U/g odp cellulase, 25 min hydrolysis, 47 °C, 62 wt.% H₂SO₄), high yields (≥80 %) were obtained, including an increase of ~9 points due to the enzyme. Optimal conditions produced nanosized particles of around ~200 nm with reduced surface charge and sulfur content. The optimization allowed reduction of hydrolysis time by 44 % and increase of yield by more than 10 points compared with results in previous work. The effects of cellulase pretreatment were noticeable even under aggressive hydrolysis conditions, emphasizing its possibilities. Zeta potential and polydispersity index indicated that all studied conditions led to good-quality final products, with values around −50 mV and 0.2, respectively. Transmission electron microscopy (TEM) analysis confirmed the presence of NCC. Fourier-transform infrared (FTIR) spectroscopic analysis provided evidence that cellulase treatment increased the crystallinity of both cellulose fibers and NCC, as well as fiber accessibility, supporting the other analyses of NCC.