Development of Ecobinders Using Technical Lignins Modified by Laccases
G. Sena-Martins and J. Cardoso-Duarte
ecobinders, industrial lignins, laccases, MDF boards/cork panels production
Prevention, reduction and elimination of environmental contamination stand out as major issues on the agenda for the 21st century. Worldwide it is occurring intensive R&D aiming cleaner industrial practices, more eco-friendly products, higher industrial usage of renewable raw materials and, finally, the technological improvement of by-products up-grading which will contribute to waste minimization. Technical lignins are by-products from the pulp and paper industry, as well as from other biomass-based industries. But there is still a very small market for these lignins: only about 2% of the lignins available from the pulp and paper industry are commercialised, being the rest of it burned to generate energy and to recover chemicals. Technical lignins present highly reactive locations that can be surprisingly modified through a selection of chemical, physical and/or enzymatic reactions, which gives them a great potential for their exploitation as industrial raw materials. Enzymes bring undoubting advantages to industrial processes, justifying the intensive research done in this field for the last three decades. For those technical processes requiring modifications on the lignin structure, research has focused on the oxidative enzymes produced by ligninolytic fungi. The yielding of free radical species as a result of peroxidases and laccases activity is of utmost importance from the industrial point of view: these radicals greatly increase the reactivity of the lignin molecules, leading to further polymerisations in a random non-enzymatic way to form 3-dimensional polymers of higher Mw and with a variety of new linkages. As a result, a wide variety of new materials with distinct properties can be obtained. In this study we performed laccase pre-treatments of industrial lignins to develop new ecofriendly binders for replacing the synthetic adhesives commonly used in the MDF boards processing, and also to agglomerate cork particles in the cork transformation industry. For the enzymatic activation of lignins different combinations of lignins, laccases and treatment conditions were done. The new formulations were further tested to make lab-scale MDF boards and for cork panels production. Adjustments of some process parameters were necessary to do, mostly relatively to reaction temperature, pressing and curing conditions, processing time, etc. An evaluation the most important properties was done concerning uniquely the new ecobinders that originated the most promising results.
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