Increasing prices of petrochemical resins and possible harmful formaldehyde emissions from conventionally produced wood composites have resulted in increased interest in enzymatic binder systems as environmentally friendly alternatives for gluing lignocellulosic products. In this study, laccase mediator systems (LMSs) were used to activate lignin on wood fiber surfaces in the pilot-scale production of medium-density fiberboard (MDF) using a dry process. Three different mediators were applied: 4-hydroxybenzoic acid (HBA), 1-hydroxybenzotriazole (HBT), and acetosyringone (AS) of which HBA performed best. The mechanical properties of the manufactured boards produced with thermomechanical pulp (TMP) fibers, laccase, and HBA fulfilled all required European standards for wood-based panels. Oxygen consumption rates of the different LMSs and (13)C NMR spectroscopy results for treated TMP fibers were obtained for qualitative and quantitative analysis of lignin activation. The results show that reactions were most effective within the first 30 min of incubation. Oxygen consumption was fastest and highest for the LMS using HBA. (13)C NMR spectroscopy indicated the highest decrease of aromatic groups in the wood fiber lignin with this LMS. The data correlated well with the quality of the MDF. The required enzymatic reaction times allowed direct integration of the LMS into standard MDF production techniques. The results indicate that application of LMSs has a high potential for environmentally friendly MDF production.

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In this study, a new technical process for hardening wood fiber insulation boards is introduced. During the dry-process, the fibers are usually glued with polymeric-diphenylmethane-diisocyanate (pMDI) and hardened to wood fiber insulation boards using a steam-air mixture. However, the maximum temperature reached in the steam-air process was 100 °C, and it was impossible to use an alternative binding agent for the gluing of the wood fiber insulation boards other than pMDI. When incubated with laccase-mediator-system (LMS) as a naturally based bonding system, temperatures of over 120 °C are required because of the chemical wood composition, especially the lignin. In this case, the hot-air/hot-steam process offers new technical opportunities for realizing temperatures above 100 °C. In this study, wood fiber insulation boards were glued with LMS, vs. reference boards with inactivated LMS, laccase alone, and 4% pMDI. Then, the boards were hardened using one of three processes: with steam-air mixture, with hot-air, and with hot-air/hot-steam. Through the hot-air/hot-steam process, temperatures of well over 120 °C were attainable. All the insulation boards hardened using the hot-air/hot-steam process showed better physical and technical properties than those hardened with steam-air mixture or hot-air alone. The reason for this is a sudden increase of temperature after the adding of steam because high temperatures insure that the LMS activated wood fiber surface lignins are completely plasticized. As a result the physical-technological properties such as internal bond strength, compression strength, and short term water absorption of insulation boards treated with LMS were comparable to those boards treated with 4% pMDI.Keywords: Wood insulation boards; pMDI Contact information: Faculty of Forest Science and Forest Ecology, Department of Molecular Wood Biotechnology and Technical Mycology, Büsgenweg 2, Goettingen 37077, Germany; *Corresponding author: meuring@gwdg.de INTRODUCTIONIn the production of wood based panels, large quantities of petrochemical binding agents, such as urea formaldehyde or phenol formaldehyde resins, are required (González-Garciá et al. 2011). Besides the dependency on crude oil, harmful formaldehyde is released during the production process as well as out of the products, and this adversely affects ecosystem quality (Imam et al. 1999; US. EPA 2002). Possible solutions are seen in the reduction of those binder systems as well as the replacement by more environmentallyfriendly, natural binders (González-Garciá et al. 2011). Equally, the recycling process of naturally bonded wood products is more efficient (Euring 2008). PEER-REVIEWED ARTICLEbioresources.com Euring et al. (2015). "Hot wood binding with laccase," BioResources 10(2), 3541-3552. 3542In the market of insulation materials, there has been a recent increase in the use of renewable raw materials as insulation in house walls, ceilings, flooring, and roofs due to the Energy Saving Ordinance 2012 in Europe (Brandhorst 2012). In German...

<p class="1Body">Medium density fiberboards (MDF) are produced mainly by urea-formaldehyde resins (UF) as binding agent, which are synthesized from finite fossil resources. Those boards may emit critical amounts of formaldehyde, which can influence the health of humans and animals. In recent times the wood panel board industry is looking for alternative glues which contain less or no formaldehyde. In order to avoid potential formaldehyde emissions altogether it would be preferable not to use binders which are formaldehyde based at all. One possibility is to use natural binders or to activate the wood fibers’ own binding forces by applying Laccase-Mediator-Systems (LMS). As a support of the LMS interactions with wood fibers technical lignin can be added. In this study it was found out that the addition of technical lignin intensified the fiber to fiber bindings. Two Lignin-Laccase-Mediator-Systems (LLMS) were analysed by Gel-Permeation-Chromatography and Cyclic voltammetry. Later the LLMSs were tested in the pilot scale production of MDF. The determination of the physical technological properties revealed that the LLMS treated MDF have higher dimension stabilities than only LMS treated MDF and approximately the same thickness swelling after 24 h. The results indicate that the application of LLMSs have a high potential for natural bonded MDF.</p>

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Residues of Bagasse (Saccharum officinarum L.), canola (Brassica napus L.) and hemp (Cannabis sativa L.) as well as industrial wood chips in various proportions from 0-100% were used as raw materials for the main component of the middle layer in urea formaldehyde bonded particle boards.The results reveal that most of the investigated mechanical-technological properties of the boards achieved the requirements of EN 312-2 (2003). Only increasing the percentage of canola chips usage in the middle layer to more than 30% negatively affect the internal bond (IB) properties. Comparing the water absorption (WA) and thickness swelling (TS) values, the boards containing up to 50% bagasse and hemp reach similar values to the ones of the reference boards, while increasing the amount of canola leads to more and more disadvantageous WA and TS.In summary, the results reveal that agri-fibers can be used for making composite panels conforming to the standards (EN 312-2 2003). One possible application for these panels could be the production of furniture. Einsatz von Ernterückständen von Bagasse, Rapsstroh und Hanfschäben bei der Herstellung von dreischichtigen SpanplattenThis article is dedicated to Gerd Wegener on the occasion of his retirement as professor at the Technische Universität München.

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In this work, the results of the enzymatic oxidation of TMP-fibers (thermomechanical pulp) and a well-structured lignin model compound, the dehydropolymer (DHP), were investigated by different 14 C and 13 C methods, caused by a Laccase-Mediator-System (LMS). These methods are the nuclear magnetic resonance spectroscopy ( 13 C-NMR) with DHP (unmarked) and the determination of the 14 CO 2 release of 14 C-marked DHP and TMP-fibers. The 13 C-NMR measurements were chosen to analyze the structural changes of the LMS-treated DHP model compounds and TMP-fibers qualitatively and quantitatively. The data of 14 CO 2 release give an explanation of the demethylation of DHP and TMP-fibers. The effect of the LMS is shown by comparing the results in respect of DHP and TMP-fibers, which were only treated with laccase and of an inactivated LMS as the control. Comparing the results of the 13 C-NMR method, in particular the use of the Mediator during the enzymatical treatment, showed significant changes in the structure of the DHP. Also, the TMP-fibers were materially influenced by the LMS. The analysis of the 14 CO 2 release data of the 14 C-marked DHP and TMP-fibers revealed that the rate of 14 CO 2 increases in the 14 C-2 atom as well as in the O 14 CH 3 group within the first hour of Laccase-Mediator incubation. Therefore, the 14 CO 2 release from the DHP was higher than from the TMP-fibers.