Optimization of the Obtaining of Cellulose Nanocrystals from Agave tequilana Weber Var. Azul Bagasse by Acid Hydrolysis

A multilevel factorial design of 2(3) with 12 experiments was developed for the preparation of cellulose nanocrystals (CNC) from Agave tequilana Weber var. Azul bagasse, an agro-industrial waste from tequila production. The studied parameters were acid type (H(2)SO(4) and HCl), acid concentration (60 and 65 wt% for H(2)SO(4), 2 and 8N for HCl) temperature (40 and 60 °C for H(2)SO(4), 50 and 90 °C for HCl), and hydrolysis time (40, 55 and 70 min for H(2)SO(4); and 30, 115 and 200 min for HCl). The obtained CNC were physical and chemically characterized using dynamic light scattering (DLS), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XDR) techniques. The maximum CNC yield was 90 and 96% for HCL and H(2)SO(4), respectively, and the crystallinity values ranged from 88–91%. The size and morphology of A. tequilana CNC strongly depends on the acid type and hydrolysis time. The shortest CNC obtained with H(2)SO(4) (65 wt%, 40 °C, and 70 min) had a length of 137 ± 68 nm, width 33 ± 7 nm, and height 9.1 nm, whereas the shortest CNC obtained with HCl (2 N, 50 °C and 30 min) had a length of 216 ± 73 nm, width 69 ± 17 nm, and height 8.9 nm. In general, the obtained CNC had an ellipsoidal shape, whereas CNC prepared from H(2)SO(4) were shorter and thinner than those obtained with HCl. The total sulfate group content of CNC obtained with H(2)SO(4) increased with time, temperature, and acid concentration, exhibiting an exponential behavior of [Formula: see text].