Atmospheric formic acid pulping and TCF bleaching of dhaincha ( Sesbania aculeata), kash ( Saccharum spontaneum) and banana stem ( Musa Cavendish)

Abstract

Fractionation of dhaincha ( Sesbania aculeata), kash ( Saccharum spontaneum) and banana stem ( Musa Cavendish) was investigated by atmospheric formic acid pulping. Pulping of dhaincha, banana stem and kash was not satisfactorily delignified when the formic acid concentration was limited to 70%; even longer cooking time (120 min) at this concentration did not produce pulp of lower lignin content. The marked effect of delignification was observed in case of 90% formic acid concentration. Peroxyformic acid effectively reduced the residual lignin of the formic acid pulp. In alkaline peroxide bleaching, formic acid pulp was bleached to 75–83% brightness depending on the nonwood. The strength properties were almost comparable to conventional pulp. The dhaincha pulp was stronger than the banana stem and kash pulp. The bleaching improved the strength properties of the pulp. Isolated lignin from formic acid spent liquor had higher syringyl unit than guaiacyl unit. Its β- O-4 bond was cleaved during formic acid pulping, which increased phenolic hydroxyl group. The lignin was formylated during pulping. The major devolatilization of formic acid lignin was occurred between 200 and 550 °C as shown by TG graph. The xylose was the main sugar in water-soluble fractions of formic acid spent liquor that represented 50–60% of the content in original raw materials.