Modification of properties of old newspaper pulp with biological method

Modification of properties of old newspaper (ONP) deinked pulp with laccase and histidine was investigated. It was found that the optimum conditions for laccase–histidine treatment were: the concentration of laccase 0.9 U/g dry pulp, the concentration of histidine 1% relative to the dry pulp, room temperature, reaction time 1.5 h, pH 7, the pulp consistency 5% and O2 atmosphere. The results also showed that, in the optimum conditions, compared to the control pulp, the wet tensile strength, the carboxyl group content and water retention value of ONP treated with laccase and histidine were increased by 55.1%, 39.1% and 45.7%, respectively. Moreover, environmental scanning microscope images showed that more collapse and more fibrillation were observed on the laccase–histidine-treated fiber surface than the control samples, which led to form better bonding between fibers in handsheets resulting in the increase of the paper strength of laccase–histidine-treated ONP pulp.