Hot-Air/Hot-Steam Process for the Production of Laccase-Mediator-System Bound Wood Fiber Insulation Boards

Abstract

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...

Pre-pressing and Pre-heating via Hot-Air/Hot-Steam Process for the Production of Binderless Medium-Density Fiberboards

“…These results reveal the high potential of the hot-air/hot-steam process to pre-heat the wood fiber fleeces effectively. As in the previous study by Euring et al (2015), the sudden increase of the temperature from approximately 145 °C to over 160 °C at the moment the fiber fleece is heated with hot air and then with hot steam also occurs during MDF production.…”

“…It is known that high temperatures are required for MDF production, especially with natural binder systems such as LMS (Kües et al 2007;Euring et al 2015). MDF temperatures were measured during different pre-heating and pressing treatments lasting all together 12 s/mm (Fig.…”

“…In a previous study, Euring et al (2015) described a new hot-air/hot-steam process, which was originally developed as a soft-pressing unit for the production of insulation boards. The difference from the ContiTherm or CSS systems is the higher process temperature.…”

“…The difference from the ContiTherm or CSS systems is the higher process temperature. By applying hot air and afterwards hot steam, temperatures well over 100 °C are reached, which are required in the hardening of native wood fiber lignin (Euring and Kharazipour 2012;Euring et al 2015). Especially thermo-mechanical-pulping (TMP) wood fibers have the ability for self-bonding, also called auto-adhesion (Zavarin 1984;Back 1987;Suzuki et al 1998;Unbehaun et al 2000).…”

“…LMS application for the production of wood fiber composites offers many advantages. In addition to the independence from fossil oil resources, the use of LMS causes no extra emissions (either formaldehyde or volatile organic compounds, VOCs) out of the products (Müller et al 2009;Euring et al 2011Euring et al , 2013Euring et al , 2015Euring et al , 2016.…”