Laccase modified lignosulfonates as novel binder in pigment based paper coating formulations

The exploitation of renewable and cheaper paper coating formulations especially for graphic paper products is gaining increasing importance due to concerns regarding the use of fossil based raw materials. For this reason, a novel process for enzymatic modification of lignosulfonates to substitute fossil based styrene-butadiene (SB) latex as binders in conventional paper coating formulations was developed. Laccase polymerization of ultrafiltrated lignosulfonates (LS) resulted in an increase of the molecular weight from an average of 26 kDa to 170 kDa as compared to non-ultrafiltrated LS which increased from 5.7 kDa to 76 kDa. When used in coating formulations, laccase polymerized LS resulted in coated paper with improved printing properties (reduced picking compared to non polymerized LS) provided that the LS was ultrafiltrated before polymerization. Abo Akademi gravimetric water retention properties of the paper coatings were comparable (395 g m^{− 2}) to those obtained with reference latex (350 g m^{− 2}). Similarly, cross sectional fluorescence microscopy images showed that ultrafiltration prior to laccase polymerization reduced penetration of the polymerized lignosulfonates into the base paper to 33% and additionally reduced polymerization time from 6 h to 2 h. These results demonstrate the possibility of substituting fossil based styrene-butadiene (SB) latex binders with on-site produced lignosulfonates which have traditionally been considered so far mainly as a by-product used for energy production in the pulp and paper industry.