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 highintensity 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 highefficiency in obtaining NC.