Laccase-Initiated Modification Of Occ Pulp Using Phenolic Compound And Alkali Lignin

To date, the key limiting factor for using laccase in industrial applications is still the finding of a relatively inexpensive and non-toxic mediator. In this work, we report the effect of using laccase (L), syringaldehyde (SyA) and kraft lignin (Lig) isolated from the black liquor in alkali pulping mill to improve the strength properties of old corrugated container (OCC) pulp. Results showed that the burst index and tensile index of pulp handsheet increased with the increase of syringaldehyde dosage when the pulps were treated by L/SyA. The dry- and wet- tensile strengths were enhanced by further adding alkali lignin to pulp, but excessive lignin make tensile strength decrease. In L/SyA/Lig treatment system, the alkali lignin can partially replace and play the role of SyA in fiber modification. The optimal treatment method is that the pulp was treated by laccase and syringaldehyde for 1 h and followed by addition of alkali lignin to reaction system for another 1 h. Compared with untreated sample, the dry- and wet- tensile index can increase by 16.6% and 47.1% respectively when the dosage of SyA and alkali lignin was 0.2% under given reaction conditions. The alkali lignin showed a highest reactivity to laccase. The participation of SyA promotes the enzymatic modification of pulp. An intense agglutination between large-area fibers can be observed in handsheet from L/SyA/Lig treated pulp. The improvement mechanisms of paper strength can be related to the graft of SyA and cross-linking of SyA to alkali lignin. The resulting polymer encapsulates the fibers in the handsheet and prevents the swelling of fibers and also protects existing hydrogen bonds, which contributed to the improvement of paper strength.