Characterisation of Kraft lignin separated by gradient acid precipitation

Lignin is considered the second most abundant organic natural compound in the world. Lignin represents a promising source of new materials based on renewable resources. Currently the lignin is used in low value-added applications and for energy production and chemical recycling for industrial process itself in production of pulp and paper. Only a small amount is being used for other applications. The aim of this study was to analyze the effects of precipitation on the composition of lignin extracted from black liquor produced in industry CMPC Celulose Riograndense. For this, lignins were precipitated at different pH conditions, with various acids. Obtained lignin samples were characterized by various analytical techniques such as FTIR, GPC, HPLC and XRD. Furthermore, the quantity of carboxyl groups was also analyzed. The antioxidant activity of the analyzed lignins was evaluated by the radical ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) assay. Total phenolic contain was evaluated by Folin-Ciocalteu method while the antioxidant potential of lignins was measured by DPPH. The lignins showed a variable composition according to the acid used for its precipitation; the lignin precipitated with sulphuric acid presented Na2SO4 salts while with hydrochloric acid, NaCl was found. In addition, a change in lignin composition was observed at different pH.