Effects of alkaline treatment and kinetic analysis of agroindustrial residues from grape stalks and yerba mate fibers

This work aims to evaluate the alkaline treatment using NaOH of the agroindustrial residues of grape stalks (GS) and yerba mate (YM) in order to improve their adhesion in applications in the area of polymer composites. The samples were evaluated according to the chemical analysis, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and kinetic study. It was observed that after the alkaline treatment, there was a change in the morphology of the samples due to the partial removal of lignin and hemicellulose, which is consistent with the chemical analysis and FTIR. The activation energy (E_a) found was of 252.79 ± 21.07 kJ mol⁻¹, 218.99 ± 3.28 kJ mol⁻¹, 236.05 ± 9.50 kJ mol⁻¹ and 216.25 ± 14.87 kJ mol⁻¹ for GS, GSNaOH, YM and YMNaOH samples, respectively, confirming the fibers that present a larger amount of lignin require higher activation energy for the degradation. Thus, this material has the potential to be used as a reinforcing filler in composite materials because of the modifications caused by the alkaline treatment, which improves the matrix/fiber interface.