Laccase treatment of recycled blue dyed paper: physical properties and fiber charge.

Recycled blue colored paper was treated with laccase under various combinations of physical and chemical parameters including enzyme concentration, temperature, oxygen, and reaction time. Laccase treatment of recycled dyed pulp increased acid group content, tear index, tensile index, and color removal in a dose-dependent manner. Lengthening the treatment time from 2 to 4 h was beneficial to acid group content (12% increase), dye removal, and tensile index but had a detrimental 8% decrease on the tear index. A higher reaction temperature (65 vs. 45 degrees C) had a beneficial effect on acid group content (+31%), and tensile index (+26%) and a slightly negative effect on tear index (-5%), but significantly reduced the ability of laccase to remove color. Comparison of reactions subjected to different levels of oxygen supplementation showed the greatest beneficial effect for laccase treatment with slow oxygen bubbling. The experimental results indicate that laccase treatment increases fiber carboxylic acid content and tensile strength, in addition to reducing the color of the enzyme treated paper.