Enzymatic Modification of the Interaction Between Lignin and Recycled Cellulose Fibers

Abstract: The pulp and paper industry have been a growing market during the last decades. Due to higher environmental concerns among people, the recycling of papers has become an even more important part of the industry. Recycled paper fibers however are of lower quality than virgin fibers. This report aims to analyze the possibility to use a laccase enzyme to modify the interaction between lignin and recycled pulp fibers in order to improve the recycled papers strength under humid conditions. Experiments were carried out in order to characterize the effect of the enzyme on lignin interaction with the paper fibers and pulp. Several experiments were made, e.g. drop tests to measure the absorptivity of the paper, burst and compression strength tests to measure how sturdy the paper was, and moisture content tests to measure how much water the paper absorbed from the surrounding air. Tests were also carried out where sugars were added to the process, to find out if the presence of carbohydrates would improve the integration of lignin. The results indicate that the lignin reacts fast in the presence of the enzyme, and also indicate that an interaction between the paper fibers and the lignin results from these reactions. The drop tests show that a treatment with enzymes and lignin increase the absorption time with around 20 seconds, and both the burst and compression strength tests show an increase in strength, normalized by the surface weight, by 0.5 MN/kg and 2 kNm/kg respectively. However, the significance of these improvements needs to be validated by further experiments. The addition of carbohydrates seems to only have a small effect on some of the different tests, but these effects are most likely not significant. More experiments to tests other types of lignin, carbohydrates and enzymes should be carried out on order to optimize the procedures and validate the results.