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Keywords:

  • Bacillus pumilus;
  • bleaching;
  • Cyathus stercoreus;
  • laccase;
  • soda pulp;
  • waste pulp;
  • xylanase

Abstract

Aims:  Investigation of waste pulps and soda pulp bleaching with xylanase (X) and laccase mediator system (LMS) alone and in conjunction (one after the other) (XLMS).

Methods and Results:  Soda and different grades of waste pulp fibres [used for making three-layered duplex sheets – top layer (TL), protective layer (PL) and bottom layer (BL)] when pretreated with either xylanase (40·0 IU g−1) or LMS (up to 200·0 U g−1) alone and in combination (one after the other) (XLMS) exhibited an increase in release of reducing sugars [up to 881·0% soda pulp; up to 736·6% (TL), up to 215·7% (PL) and up to 198·0% (BL) waste pulp], reduction in kappa number [up to 17·6% soda pulp; up to 14·0% (TL), up to 25·3% (PL) and up to 10·9% (BL), waste pulp], improvement in brightness [up to 20·4% soda pulp; up to 23·6% (TL), up to 8·6% (PL) and up to 5·0% (BL), waste pulp] when compared with the respective controls. The usage of XLMS along with 15% reduced level of hypochlorite at CEHHXLMS/EHHXLMS bleaching stage reduced kappa number [5·5% soda pulp; 11·4% (TL), 7·9% (PL), waste pulp] and improved brightness [1·0% soda pulp; 0·9% (TL), 1·4% (PL) waste pulp] when compared with the controls. Scanning electron microscopic studies revealed development of cracks, flakes, pores and peeling off the fibres in the enzyme-treated pulp samples. These modifications of the fibre surface during enzymatic bleaching in turn indicated the removal of lignin and derived compounds from the fibre cell wall.

Conclusions:  The work describes synergistic action of xylanase with LMS for bleaching of waste and nonwood pulps for eco-friendly production of paper and thus reveals a new unexploited arena for enzyme-based pulp bleaching.

Significance and Impact of the Study:  The drastic improvement in pulp properties obtained after xylanase and LMS treatment would improve the competitiveness of enzyme–based, environmentally benign processes over chemicals both economically and environmentally.