Thermal, Morphological and Cytotoxicity Characterization of Hardwood Lignins Isolated by In-Situ Sodium Hydroxide-Sodium Bisulfate Method

Abstract

In the present work lignin is isolated from three different agro-industrial waste, sweet sorghum, rice straw and sugarcane bagasse using in-situ sodium hydroxide-sodium bisulfate methodology. Characterization was performed using fourier transform infrared analysis (FTIR), scan electron microscopy (SEM), thermo gravimetric analysis (TGA). The SEM micrographs showed sponge-like structure except for sugarcane bagasse lignin reveals rock-like structure. The FTIR indicates the presence of hydroxyl, carbonyl and methoxyl groups in the lignin structure. TGA thermograms were relatively same and sugarcane bagasse lignin was found the most thermally stable up to 201ºC as compared to both of soda and kraft sugarcane bagasse lignin and its maximal temperature degradation rate DTGmax was found at 494ºC while 450ºC, 464ºC in addition to thermal stabilities up to 173ºC and 180ºC for sweet sorghum and rice straw lignins respectively. All lignins exhibited low percentage of bio-char less than 10% remained unvalotilized at the end of the thermogravimetric analysis at 800ºC in nitrogen atmosphere reveals a high conversion yield into volatiles. Moreover, all lignin samples depicted higher cytotoxic potential towards lung cancer cell line (A549), IC50: 12-17 µg/ml. These findings suggest that the in-situ separated lignins would be good candidates for pyrolysis, polymer composites preparations and seem to be promising natural anti-cancer agents.