Role of lignin activation in laccase-catalysed functionalisation of lignin-containing materials

Lignocellulosic materials such as wood pulps and non-wood fibres can be modified by chemo-enzymatic functionalisation method [WO2005/061790]. This method enables the further development of native properties and even the creation of completely novel properties to lignin-containing materials. The method is based on the ability of oxidative enzymes, especially laccases, to catalyze the formation of phenoxy radicals which can thereafter be used as reactive site to further bonding of selected functional chemical groups to lignin-containing materials. Chemo-enzymatic modification is thus composed of two steps, activation and bonding. Understanding of the role of each step and the correlation between these steps is important regarding the result of modification by chemo-enzymatic functionalisation. The role of lignin activation in laccase-catalysed functionalisation of lignin-containing materials has been studied by EPR measurements and by bonding model compounds to differently activated lignin-containing wood pulps. The effect of enzyme type and its ability to bond to lignin substrate during activation step on subsequent bonding of functional chemical has been elucidated with the help of dynamic QCM-D measurements. The factors affecting the activation and functionalisation as well the correlation between the activation and bonding step will be discussed based on the results obtained.