Laccase mediated phenol/chitosan treatment to improve the hydrophobicity of Kraft pulp

Herein, a great potential approach initiated by laccase is applied to graft the biopolymers (chitosan and phenols) onto the unbleached Kraft pulp fibers to enhance the hydrophobicity and strength. The results showed that the chitosan and laccase/phenols exhibited a synergistic action on the significant improvement of the hydrophobicity of the KP pulp fibers. Compared with the base paper, a high sizing degree value (227.08 s) was achieved when the fibers were treated by the laccase/4-hexyloxyphenol/chitosan (Lac/HP/CTS) system. The water retention value of the corresponding KP fibers reduced from 176.8 to 171.3%, and the Kappa number of treated fibers increased from 26.8 to 29.3, confirming the successful graft of HP onto the fibers. The effect of the reaction parameters, including the temperature, pH, HP and chitosan dosage, reaction time and pulp suspension consistency on the strength and hydrophobicity was investigated. pH value was found as the most remarkable factor influencing the sizing degree and gave a highest sizing value (506.2 s) at pH 5.5. The strength performance presented an opposite trend against the hydrophobicity, since the number of formed hydrogen bonds is the least when the hydrophobicity is the best. This work is extremely significant for providing valuable reference on improving the hydrophobicity and strength performance of papers through a green and biological way. Graphic abstract