Variation of the milling conditions in the obtaining of nanocellulose from the paper sludge

Abstract

This work aimed to evaluate three different milling conditions, seeking the optimization of CNS isolation
process. The paper sludge was chemically treated with detergent and H2O2, by two steps, to remove the noncellulosic
contents (hemicellulose and lignin). After these treatments, the sample was milled with the variation
of a liquid medium. The three liquids milling medium were: i) dry medium (CNS-D); ii) moist with water
and (CNS-W) iii) moist with ethanol (CNS-E). The CNSs were characterized by Fourier transform infrared
spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), zeta potential
and dynamic light scattering (DLS). The milled samples presented different behavior, depending on
the medium applied. The CNS-W presented low efficiency due to the formation of agglomerates around the
ceramic ball, resulting in larger fiber sizes (microsizes). Although, the samples CNS-D and CNS-E presented
similar behavior of sizes distribution, with average size 340 nm and 373 nm, respectively, determined by
DLS. The CNS-E sample presented higher yield and electrostatic stability in solution, besides not presenting
loss of crystallinity, as occurred with CNS-D, observed by FTIR analysis. Thus, the isolation with ethanol
showed more efficient process among the three processes studied. This work achieved the isolation of CNS;
besides, it proposed an environmentally friendly isolation method, and this may add value in the paper sludge.
Keywords: industrial residue, cellulose nanostructures, ball mill, cellulose characterization.