Enzyme-lignin bonded

The production of enzyme-lignin-bonded particleboard is much less hazardous than the production of isocyanate-bonded particleboard, for example. 

The plant cell wall contains different types of polysaccharides, proteins (structural glycoproteins and enzymes), lignin and water, as well as some inorganic components (1, 14-16). The plant cell suspensions, however, grow as a population of cells with a primary cell wall(17). The main components of these walls are cellulose-free polysaccharides and pectic polysaccharides in particular, which constitute 1/3 of their dry weight. (18). Some fragments, e g. methanol, acetic, ferulic and p-cumaric acids, are connected with the pectic polysaccharides by ester bonds with the carboxylic and hydroxylic groups. 

The use of enzymatic systems for surface activation of wood particles to form binderless composites has been the subject of study for over 20 years. Enzyme-catalysed bonding of wood can be achieved either by activation of lignin, which is mixed with wood particles, or by surface activation of the wood particles directly (Grdnqvist etal., 2003). 

During enzymatic hydrolysis, nonproductive cellulose-lignin bonding limits the conversion via the enzyme. Should an enzyme adsorb onto lignin, it is irreversibly... 

The pulping of wood is at present based on either mechanical or chemical methods or combinations thereof, as previously described in this chapter. The interfiber lignin bond is broken down by the mechanical and chemical treatments to free the cellulose fibers for papermaking. In the forest, white rot fungi perform a similar task on wood left behind. The enzymes of the fungi do the work of lignin degradation. 

Kharazipour etal. (1998) used a peroxidase enzyme in combination with H2O2 to activate the surface of TMP fibres for self-bonding. Fibres were activated in a wet system, then dewatered and fluffed out before pressing at 190 °C for 5 minutes. The best IBS recorded for boards of 5 mm thickness made from the activated fibres was 0.55 MPa. The IBS was found to be dependent upon the pH of the treatment solution, the time of treatment and the board density. The authors noted that phenoloxidase gave comparable results to laccase, which was unexpected, since it was thought that the phenoloxidase would lead only to depolymerization of the lignin. 

No matter what its state is in the cell W all vivo, when the lignin molecule is released from its attachment to the cellulose matrix, either by breaking its tendril-like bonds (e.g. by pulping) or destruction of the cellulose matrix (c.g. by hydrolysis with acids or enzymes), it rolls up to a globular entangled mass something like tumbleweeds. 

Mechanisms which involve the cation radical intermediate were also proposed for the cleavage of Ca-C0 and 0-0-4 bonds of 0-0-4 lignin substructure models by the enzyme (26,27). Thus, mechanisms for most of the... 

Thus, for the degradation of polymeric lignin by the enzyme, two major questions were left (i) Can lignin peroxidase, by itself, depolymerize polymeric lignin without repolymerization or not (ii) Can lignin peroxidase cleave aromatic rings and /J-0-4 bonds of polymeric lignin, or not ... 

Milled wood lignin was mixed with the crude enzyme solution of Tram-ties versicolor extracellular phenoloxidases produced on spent sulfite liquor in a ratio of approximately 2 1. This comprised the main part of the two-component bio-adhesive. Industrial particles were bonded with 15% bioadhesive under conventional pressing conditions to have 19 mm particle boards (40 x 50 cm) of the properties described in Table IV. The bonding reaction (crosslinking) took place in aqueous solution at room temperature. If conventional pressing technology is applied, the temperature should be elevated in order to maintain water evaporation within a reasonable press time. 

In order to eluddate the mechanism of the further transformations of the primary lignin decomposition products including the cleavage reactions, we synthesized some of the important primary products labelled with Cu and introduced these into the cultures of fungi or enzymes. Thus, it could be shown, for example, that the breakdown of the side chain of ferulic acid occurs at the double bond vanillic acid is found. During polymerization in the presence of phenoloxidases, in the case of carboxyl-labelled ferulic acid, about 60% of the activity is split off as Cli02. The polymers labelled in the 2 and 3 position in the side chain or in the methoxyl group contain the whole applied activity. 

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