Use of ball mill to prepare nanocellulose from eucalyptus biomass: Challenges and process optimization by combined method

A combination of mechanical methods was developed to obtain a suspension of nanocellulose (NC) from Eucalyptus sawdust. In this two-step process, the ball milling (1–4 h) was followed by a high-intensity ultrasound (10–30 min) irradiation. The prepared samples were characterized using Fourier-transform infrared spectroscopy, Raman, dynamic and static light scattering, Zeta potential, X-ray diffraction, X-ray photoelectron spectroscopy, Thermogravimetric analysis, Field-emission scanning electron microscopy, and Transmission electron microscopy. The crystallinity was calculated using different methods and compared. The mechanical grinding results in a random and irregular break of the fibers. In a combined method, the ultrasound waves generate more defibrillation and separation of the nanofibers and, consequently, the reduction of fiber diameters. The high-intensity ultrasound promoted an increase in the homogeneity, crystallinity, and electrostatic and thermal stability of the NC suspension. The samples milled for 2 h and 20 min ultrasound irradiation presented the high-efficiency in obtaining NC.