| Summary: | A multilevel factorial design of 2<sup>3</sup> with 12 experiments was developed for the preparation of cellulose nanocrystals (CNC) from <i>Agave tequilana</i> Weber var. Azul bagasse, an agro-industrial waste from tequila production. The studied parameters were acid type (H<sub>2</sub>SO<sub>4</sub> and HCl), acid concentration (60 and 65 wt% for H<sub>2</sub>SO<sub>4</sub>, 2 and 8N for HCl) temperature (40 and 60 °C for H<sub>2</sub>SO<sub>4</sub>, 50 and 90 °C for HCl), and hydrolysis time (40, 55 and 70 min for H<sub>2</sub>SO<sub>4</sub>; 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<sub>2</sub>SO<sub>4</sub>, respectively, and the crystallinity values ranged from 88–91%. The size and morphology of <i>A. tequilana</i> CNC strongly depends on the acid type and hydrolysis time. The shortest CNC obtained with H<sub>2</sub>SO<sub>4</sub> (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<sub>2</sub>SO<sub>4</sub> were shorter and thinner than those obtained with HCl. The total sulfate group content of CNC obtained with H<sub>2</sub>SO<sub>4</sub> increased with time, temperature, and acid concentration, exhibiting an exponential behavior of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>C</mi><mrow><mi>S</mi><mi>G</mi></mrow></msub><mo>=</mo><mi>a</mi><msup><mi>e</mi><mrow><mi>b</mi><mi>t</mi></mrow></msup></mrow></semantics></math></inline-formula>.
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