Enzyme catalyzed cross-linking of spruce galactoglucomannan improves its applicability in barrier films

• Novel method for cross-linking wood hemicelluloses was developed.
• Increased molecular weight improves the mechanical properties of barrier films made of spruce galactoglucomannan.
• Separation of pure hemicelluloses from those with bound aromatic moieties.
• The method takes advantage of lignin–carbohydrate complexes.
• Bound aromatic moieties in hemicelluloses can be used for cross-linking by employing laccase oxidation.

Hemicelluloses are one of the main constituents of plant cell walls and thereby one of the most abundant biopolymers on earth. They can be obtained as by-products from different wood based processes, most importantly from the mechanical pulping. Hemicelluloses have interesting properties in e.g. barrier film applications. However, their relatively low molecular weight after isolation and co-extraction with lignin has limited their use. In this work, we present a novel technique for increasing the molecular weight of different wood hemicelluloses from mechanical pulping process waters as well as from pre-hydrolysis extracts. This is achieved by enzyme-catalyzed cross-linking of aromatic moieties bound to the hemicelluloses. The cross-linking treatment resulted in significantly improved mechanical properties in barrier films made with spruce galactoglucomannan. To our knowledge, this is the first time that wood hemicelluloses have been cross-linked by utilizing the bound aromatic moieties and creates new possibilities for utilizing this raw material source.