Dissolving pulp production from sugar cane bagasse

• The contents of cellulose, hemicelluloses and lignin in the sugar cane bagasse fractions varied significantly.
• The pre-hydrolysis soda process improves the xylan removal but decreases pulp yield.
• The pre-hydrolysis soda pulping followed by ECF bleaching is adequate for producing dissolving pulp from depithed bagasse.

The main goal of this study was characterizing the sugar cane bagasse two main fractions: pith and depithed bagasse, and evaluating the potential of the depithed for production of dissolving grade pulps. The depithed bagasse was chemically characterized and converted into brown pulp of two different extents of delignification degrees (kappa 16.9 and 9.2) by the pre-hydrolysis soda process, which consists of bagasse treatment with hot water (15 min at 180 °C) followed by conventional soda pulping. The resulting pulps were fully bleached by the O-D-(EP)-D-P sequence and evaluated for their main dissolving pulp characteristics. The contents of cellulose, hemicelluloses and lignin in the pith and depithed bagasse varied significantly. For example, the lignin S:G:H of the pith and depithed bagasse were 1.0:1.6:1.8 and 1.0:2.1:2.0, respectively. The pre-hydrolysis pretreatment terminated at pH 3.4 and removed 29% of the depithed bagasse weight. The pre-hydrolysis soda process improves the xylan removal but decreases pulp yield. The bleached pulps showed similar glucans (∼95%), xylans (∼5.0%), ash (∼0.4%), silica (∼0.15%) and α-cellulose content (∼92%) regardless of kappa number. The low viscosity values and the high ash and silica contents limit the uses of the bagasse pulps for certain dissolving grades applications, but it is useful for production of viscose rayon and CMC derivatives after some demineralization. The elucidation of the pith lignin S:G:H ratio and the production of high yield (35.1%) dissolving pulp from depithed bagasse fraction without bleaching cost penalties are the main novelties of this paper.