Fig 10 - uploaded by Ursula Kües
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Polycondensation reactions of phenol-formaldehyde resins – resol is formed when OH -is used as catalysator (top), novalak with H + as catalysator (bottom)
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The contribution contains results of bonded joints strength tests. The tests were carried out according to the modified standard CSN EN 1465 (66 8510):2009. The spruce three-ply wood of 4 mm thickness was used for bonding according to CSN EN 636 (49 2419):2013. The test samples of 100 × 25 mm size were cut out from a semi-product of 2,440 × 1,220 m...
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... Due to their broad substrate range, laccases are attractive for many biotechnological applications. This includes processes involving lignin, for instance, to break down the unwanted lignin in "biobleaching" in the paper and textile industries, to optimize unhindered access and the transformation of all polymers in lignified cell walls in biorefinery, to functionalize lignin by grafting, and to modify lignified cell walls for fiber auto-adhesion in fiberboard production for better green bonding (Hüttermann et al., 2001;Mayer and Staples, 2002;Mai et al., 2004;Kloeser et al., 2007;Munk et al., 2017a;Kunamneni et al., 2008;Widsten and Kandelbauer, 2008;Kües, 2015;Zerva et al., 2019). ...
... There is considerable interest to replace conventional adhesives in MDF production by sustainable green alternatives, including enzymatic solutions Kirsch et al., 2016;Perna et al., 2019;Ostendorf et al., 2020). TMP fibers have a plasticized glassy lignin layer on the surface, due to heating above the glass transition point of lignin during the TMP process (Mai et al., 2004;Kloeser et al., 2007;Kües et al., 2007;Widsten and Kandelbauer, 2008). This lignin on the fiber surfaces can become activated through oxidation processes and radicalization of phenolic lignin groups with laccases (Felby et al., 1997;Kharazipour et al., 1997;Unbehaun et al., 2000;Felby et al., 2002;Widsten and Kandelbauer, 2008a;Euring et al., 2011). ...
Laccase-mediator-oxidized lignin offers replacement for conventional chemical binders to produce fiberboards. Compared to the previously reported laccase–mediator system (LMS), a lignin-laccase-mediator-system (LLMS) has an advantage in that it requires much shorter fiber-enzyme incubation time due to significantly increased redox reactions. However, the cost of regularly applying laccase on an industrial scale is currently too high. We have employed CcLcc5 from cultures of the basidiomycete Coprinopsis cinerea as a novel basi-laccase (a CAZy subfamily AA1_1 laccase) in medium-density fiberboard (MDF) production, in comparison to the commercial formulation Novozym 51003 with recombinantly produced asco-laccase MtL (a CAZy subfamily AA1_3 laccase-like multicopper oxidase from the ascomycete Myceliophthora thermophila). With the best-performing natural mediator 2,6-dimethoxyphenol (DMP), unpurified CcLcc5 was almost as good as formulated Novozym 51003 in increasing the molecular weight (MW) of the technical lignins tested, the hydrophilic high-MW Ca-lignosulfonate and the hydrophobic low-MW kraft lignin (Indulin AT). Oxygen consumption rates of the two distantly related, poorly conserved enzymes (31% sequence identity) with different mediators and lignosulfonate were also comparable, but Indulin AT significantly reduced the oxidative activity of Novozym 51003 unlike CcLcc5, regardless of the mediator used, either DMP or guaiacol. Oxygen uptake by both laccases was much faster with both technical lignins with DMP than with guaiacol. In case of lignosulfonate and DMP, 20–30 min of incubation was sufficient for full oxygen consumption, which fits in well in time with the usual binder application steps in industrial MDF production processes. LLMS-bonded MDF was thus produced on a pilot-plant scale with either crude CcLcc5 or Novozym 51003 at reduced enzyme levels of 5 kU/kg absolutely dry wood fiber with lignosulfonate and mediator DMP. Boards produced with CcLcc5 were comparably good as those made with Novozym 51003. Boards reached nearly standard specifications in internal bond strength (IB) and modulus of rupture (MOR), while thickness swelling (TS) was less good based on the hydrophilic character of lignosulfonate. LLMS-bonded MDF with Indulin AT and DMP performed better in TS but showed reduced IB and MOR values.
... Particleboard is one kind of wood composite that is manufactured on the basis of mechanically chopped, milled, and ground wood particles and bonded by adhesives, usually by a procedure at high temperature and pressure (Maloney 1993, Youngquist et al. 1997, Kharazipour 2004. The particleboard was introduced in Germany about 70 years ago to use wood residues from secondary milling operations, but it succeeded so well that some producers are using wood from trees and primary milling operations in addition to other sources (Kloeser et al. 2007). More than 60 percent of panel board production in Europe and also in Germany is particleboards (European Panel Federation 2005, Marutzky 2006). ...
This article deals with the feasibility of the use of wheat protein glue to produce general purpose particleboards from bagasse, canola, and hemp chips and of decreasing the formaldehyde emission by using a bioproduct adhesive. Three series of panels were produced using wood chips in the surface layers and a mixture of annual plants with industrial wood in the middle layers. Particleboards were manufactured using various annual plants. Wheat protein was used in combination with urea-formaldehyde resin (UF) in the surface layers. Pure UF was only used in the middle layer. Panels were tested for some physical and mechanical properties. In addition, the formaldehyde emission according to the perforator method and the bottle method was determined. The data were compared with the respective properties specified by the EN 312–2 standard for commercial wood-based particleboard. The results showed that all mechanical properties greatly exceeded the standard requirements for wood particleboards. An increase of more than 50 percent canola particles in the core negatively affected the
internal bond (IB) strength. All of the particleboards produced from hemp and bagasse had modulus of rupture and IB strength higher than required. With those containing up to 50 percent annual plant particles in the middle layer, thickness swelling values met the standard requirement. It was found that applying wheat protein as a bonding agent reduced the formaldehyde emission in comparison to when pure UF resin was applied. This study demonstrated that consistent, highperformance agricultural fiber composite panels with desirable environmental attributes can be successfully developed.
The tannin extract of Cissus dinklagei was used in the preparation of a 3 % paraformaldehyde resin for the manufacture of particleboard. This tannin is of the procyanidin type associated with furan residues. The modulus of elasticity of the resin obtained after the thermomechanical analysis is 3825 MPa. The TGA performed on the panels obtained shows three degradation zones with a thermal stability zone between 74 and 210 °C. These panels have good thermomechanical properties. The values of the best density, internal bond, modulus of elasticity in flexion (MOE) and resistance to flexion (MOR) are respectively 658 kg/m3; 0.52 MPa; 2035.4 MPa; 16.3 MPa. These results classify this panel for generalinterior construction and furniture uses according to the NF EN 312 standard.
