Treatment of wood fbres with laccases: improved hardboard properties through phenolic oligomerization

International audienceLaccase-treated wood fibres were tested for small-scale wet-process manufacture of hardboards. Two laccases of distinctredox potentials, one from Pycnoporus cinnabarinus and one from Myceliophthora thermophila, were compared in terms oftheir effect on the physical–chemical properties of the treated fibres and hardboards. Wood fibres were produced from Norway spruce (Picea abies) by thermomechanical pulping. The thermomechanical pulp was treated with each laccase in parallel, in the presence or absence of the synthetic laccase mediator 1-hydroxybenzotriazole (HBT). High-performance size-exclusion chromatography revealed that the ethanolic extractable phenolic compounds in the fibres underwent oligomerization upon enzymatic treatment, and that the extent of oligomerization was dependent on the enzyme source and concentration and on the presence or absence of mediator. Lower lignin oligomerization levels led to higher (up to two-fold) fibre internal bonding, whereas higher lignin oligomerization levels led to higher fibre hydrophobisation. X-ray photoelectron spectroscopy revealed a significant change in surface lignin content. These results demonstrate pre-treatment of spruce fibres with laccase–mediator systems prior to hot processing can improve the mechanical resistance of hardboards while using lower amounts of enzyme