Abstract
The potential of extracellular alkali stable and thermo tolerant xylanase produced by Bacilluspumilus SV-85S through solid state fermentation was investigated in pulp bleaching in association with conventional bleaching using chlorine and chlorine dioxide. The biobleaching of kraft pulp with xylanase was the most effective at an enzyme dose of 10 IU/g oven dried pulp, pH 9.0 and 120 min incubation at 55 °C. Under the optimized conditions, xylanase pretreatment reduced Kappa number by 1.6 points and increased brightness by 1.9 points. Subsequently, chlorine dioxide and alkaline bleaching sequences (CDE1D1D2) finally resulted in brightness gain of 2.7 points as compared with the control. The pretreatment of pulp with xylanase resulted in 29.16 % reduction in chlorine consumption by maintaining the same brightness as in control. An improvement in pulp strength properties was also observed after bleaching of xylanase pretreated pulp. Scanning electron microscopy revealed loosening and swelling of pulp fibers after enzyme treatment. These results clearly demonstrated that the B. pumilus SV-85S xylanase was effective as a pulp biobleaching agent. The decrease in chlorine consumption by pretreatment of pulp with xylanase apparently made the biobleaching process not only economical but also eco-friendly.
Highlights
The secondary cell walls of plants contain a wide range of additional compounds that modify their mechanical properties and permeability
Scanning electron microscopy revealed loosening and swelling of pulp fibers after enzyme treatment. These results clearly demonstrated that the B. pumilus SV-85S xylanase was effective as a pulp biobleaching agent
The hand sheets prepared from untreated and xylanasetreated pulps were evaluated for various physical properties following the Technical Association of Pulp and Paper Industry (TAPPI) protocols (TAPPI Test Methods, Atlanta, GA, TAPPI Press, 1996)
Summary
The secondary cell walls of plants contain a wide range of additional compounds that modify their mechanical properties and permeability. The wood is composed of cellulose (35–50 %), xylan (20–35 %), and lignin (10–25 %). Lignin is a complex phenolic polymer that penetrates the spaces in the cell wall between cellulose, hemicellulose, and pectin components, driving out water and strengthening the wall. Lignin is present in all woody plants and other agro-residues which are used as raw materials for paper manufacturing. The removal of lignin is essentially required during paper manufacturing. The brown color of the pulp is due to the presence of lignin which has to be removed during paper making process (Viikari et al 1986; Koponen 1991)
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