Action of Xylanase Prebleaching on Wheat Straw and Oxygen Delignified Wheat Straw Soda Pulps - Probable Mechanisms

Xylanase pretreatment is known to reduce consumption of bleach chemicals, AOX and improve biodegradability of effluents. Very limited information is available on mechanistic aspects of xylanase prebleaching especially on agro residue pulps that are important in Indian context. In the present study certain experiments were conducted to understand the mechanism of xylanase aided bleaching on wheat straw and oxygen delignified wheat straw pulps. The experiments were conducted to understand the significance of xylanase action on surface xylan, on fiber swelling and on mechanical & optical properties of the pulp. Studies on fractionation and mechanical peeling suggest that surface xylan may not be the sole target substrate for xylanase aided bleaching though it appears that xylanase tend to hydrolyze surface xylan more due to its higher accessibility. The xylan present in the fiber wall is not easily accessible and participates less in enzymatic action. Oxygen delignified pulp respond better to xylanase prebleaching. The decrease in absorption coefficient after enzyme pretreatment gives an evidence of xylanase attack on chromophoric groups. No change in light scattering coefficient and tensile index in xylanase-pretreated pulps suggest that enzyme does not cause a change in fiber bonding. The water retention value, a measure of fiber swelling decreases slightly on xylanase pretreatment suggesting that the enzyme has little effect on fiber swelling. Results indicate that xylanase increase the bleachability of the pulp by more than one mechanism.