The cell walls of woody plants are compounded materials made by in situ polymerization of a polyphenolic matrix (lignin) into a web of fibers (cellulose), a process that is catalysed by ...polyphenoloxidases (laccases) or peroxidases. The first attempt to transform the basic strategy of this natural process for use in human craftsmanship was the ancient lacquer method. The sap of the lacquer tree (Rhus verniciflua) contains large amounts of a phenol (urushiol), a polysaccharide and the enzyme laccase. This oil-in-water emulsion solidifies in the presence of oxygen. The Chinese began using this phenomenon for the production of highly creative art-work more than 6,000 years ago. It was the first example of an isolated enzyme being used as a catalyst to create an artificial plastic compound. In order to apply this process to the production of products on an industrial scale, an inexpensive phenol must be used, which is transferred by an enzyme to active radicals that react with different components to form a compounded material. At present, the following approaches have been studied: (1) In situ polymerization of lignin for the production of particle boards. Adhesive cure is based on the oxidative polymerization of lignin using phenoloxidases (laccase) as radical donors. This lignin-based bio-adhesive can be applied under conventional pressing conditions. The resulting particle boards meet German performance standards. By this process, 80% of the petrochemical binders in the wood-composite industry can be replaced by materials from renewable resources. (2) Enzymatic copolymerization of lignin and alkenes. In the presence of organic hydroperoxides, laccase catalyses the reaction between lignin and olefins. Detailed studies on the reaction between lignin and acrylate monomers showed that chemo-enzymatic copolymerization offers the possibility to produce defined lignin-acrylate copolymers. The system allows control of the molecular weights of the products in a way that has not been possible with chemical catalysts. This is a novel attempt to enzymatically induce grafting of polymeric side chains onto the lignin backbone, and it enables the utilization of lignin as part of new engineering materials. (3) Enzymatic activation of the middle-lamella lignin of wood fibers for the production of wood composites. The incubation of wood fibers with a phenol oxidizing enzyme results in oxidative activation of the lignin crust on the fiber surface. When such fibers are pressed together, boards are obtained which meet the German standards for medium-density fiber boards (MDF). The fibers are bound together in a way that comes close to that by which wood fibers are bound together in naturally grown wood. This process will, for the first time, yield wood composites that are produced solely from naturally grown products without any addition of resins.
The incubation of wood fibres with a phenoloxidase (laccase) results in the oxidation of the lignin crust on the fibre surface which finally is released from the fibre surface into the incubation ...medium. During this reaction, the lignin is highly oxidized, as can be seen from its high
carboxyl content. When fibres treated with the enzyme are pressed together under conditions usually employed during the process of making fibre boards, boards are obtained which meet the required standards for German medium density fibre board (MDF). The enzymatically activated fibres in the
wood composites made by this process are bound together in a way which is closer to the situation in the naturally grown wood than any other process used today in the present production of wood composites.
Abstraet-When commercially produced wood fibres were treated with the enzyme peroxidase and H
2
O
2
for a certain time and then pressed together under conditions usually employed during the process ...of making fibre boards, boards were obtained which came close to the
required standards for German medium density fibre (MDF) boards. Thus, surprisingly, peroxidase in this system gives the same results as laccase, for which this reaction has been described previously. Successful implementation of this process will yield wood composites which can be produced
without any addition of resins, solely from naturally grown products.
Polyphenoles for compounded materials Kharazipour, Alireza; Mai, Carsten; Hüttermann, Aloys
Polymer degradation and stability,
01/1998, Volume:
59, Issue:
1
Journal Article, Conference Proceeding
Peer reviewed
The cell walls of woody plants are compounded materials made by an
in-situ polymerisation of a polyphenolic matrix (lignin) into a web of fibres (cellulose) catalysed by polyphenoloxidases (laccases) ...or peroxidases. The transfer of this construction strategy to the actual production of compounded materials required the adaptation of a process that takes weeks in nature to technical conditions in which reaction times of only a few minutes are allowed. Several strategies have been developed to find conditions under which lignin becomes so active that the reaction may be feasible for technical purposes. Thus, the following industrial processes for the production of compounded materials are now available: (1) wood composites either by the addition of adhesives composed of lignin and phenoloxidases or activation of the wood fibres by these enzymes; (2) compound materials made from lignin and carbohydrates; (3) duroplasts from lignin and other monomers. The main advantage of all these substances is that they are totally compatible with the terrestrial carbon cycle.
Biotechnological production of wood composites Kharazipour, A; Huttermann, A. (Forschung und Entwicklung, Pfleiderer Industire GmbH and Co. KG, Westring 19-21, D-59759 Arnsberg (Germany))
1998
Book
Polyphenoles for compounded materials Huttermann, A; Kharazipour, A; Mai, C
Polymer degradation and stability,
06/1997, Volume:
59, Issue:
1-3
Journal Article
Peer reviewed
The cell walls of woody plants are compounded materials made by an in situ polymerisation of a polyphenolic matrix (lignin) into a web of fibers (cellulose) catallysed by polyphenoloxidases ...(laccases) or peroxidases. The transfer of this construction strategy to the actual production of compounded materials required the adaptation of a process that takes weeks in nature to technical conditions in which reaction times of only a few minutes are allowed. Several strategies have been developed to find conditions under which lignin becomes so active that the reaction may be feasible for techical purposes. Thus, the following industrial processes for the production of compounded materials are now available: (1) wood composites either by the addition of adhesives composed of lignin and phenoloxidases or activation of the wood fibers by these enzymes; (2) compound materials made from lignin and carbohydrates; (3) duroplasts from lignin and other monomers. The main advantage of all these substances is that they are totally compatible with the terrestial carbon cycle.
