Laccase in pulp activation and functionalisation

The presence of surface lignin in pulp fibres offers possibilities to enhance the existing pulp properties or even to create completely new pulp properties by enzymatic means. Improving the properties of wood fibres is a constant interest of pulp, paper and board manufacturing industry. New methods for targeted modification of wood materials could also reveal completely new application areas for wood fibres. Oxidative enzymes such as laccases can be used to activate the surface lignin of lignin-rich pulps by radicalisation. The primary reaction of laccase catalysed oxidation is the formation of phenolic radicals to the substrate. Due to the high reactivity of these radicals (either with each other or with a secondary substrate), reactions such as polymerisation, depolymerisation, co-polymerisation and grafting can occur. The size of laccases limits the action of the enzyme on the fibre surface, which can be considered both as a limitation or an opportunity when applying laccases in fibre applications. Enzymatic activation of fibre surfaces can be exploited after further functionalisation of fibres with specific chemical components in tailoring fibre properties. In this work the laccase catalysed activation and functionalisation of lignin-rich pulps was studied. The radical formation in pulps during oxidation with different laccases was analysed by oxygen consumption measurement and EPR spectroscopy. Changes in the pulp lignin stucture by laccase activation were determined by NMR. The factors affecting the activation and further functionalisation of pulps were elucidated. A novel chemo-enzymatic functionalisation method developed for lignin-rich pulps and its potential in modification of fibre properties will be discussed in the presentation.