Effect of sequential acid-alkaline treatment on physical and chemical characteristics of lignin and cellulose from pine (Pinus spp.) residual sawdust

Abstract Timber industry generates large amounts of residues such as sawdust. Softwoods have a significant economic value for timber production and the Pinus genus is widely utilized. Thus, the aim of this work was to study the hemicellulose extraction and lignin recovery from pine (Pinus spp.) residual sawdust (PRS) by sequential acid-alkaline treatment, generating a cellulose-rich solid fraction. The hemicellulose removed was 87.11 % (wt·wt-1) after dilute acid treatment at 130 °C, 4.5 % (wt·wt-1) of H2SO4 for 20 minutes at 120 rpm. Three temperatures were evaluated for recovering the lignin and the highest yield, 93.97 % (wt·wt-1), was achieved at 170 °C, 10 % (wt·wt-1) of NaOH for 90 minutes at 120 rpm. Lignin was characterized by Fourier-transform infrared spectroscopy, nuclear magnetic resonance and thermogravimetry. The resulting cellulose-rich fraction exhibited polymorphic transformation. The results demonstrated that PRS is a promising lignocellulosic residue whose lignin and carbohydrates can be readily obtained.