Vessel picking in Eucalyptus globulus bleached kraft pulp sheets: Effect of mechanical and enzymatic treatment

Vessel picking is a phenomenon that hampers printing quality, consisting of white spots due to plucked vessel elements in the paper surface. This study aims to understand the mechanism behind vessel to fibre bonding and its relation to picking. Eucalyptus globulus bleached kraft pulp beating aided by enzymatic treatment was used to achieve that purpose. Beating by itself reduced vessel picking over 90 %. Concentrated vessels prepared at lab scale were mixed with refined fibres. When these vessels were subject to enzymatic treatments (xylanase and a cellulase plus laccase cocktail), a reduction up to 94 % was obtained. Bulk enzymatic treatments followed by beating on the original pulp decreased its vessel picking up to 96 %. Water contact angle and surface energy showed vessels to be more hydrophobic than fibres. Enzymatic treatments improved vessels hydrophilic character aiding its adhesion to fibres, leveraged by its higher flexibility and better retention with beating.