Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles
Reexamination Certificate
1999-10-13
2001-06-12
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
C210S632000
Reexamination Certificate
active
06245269
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the manufacture of fiber boards and similar wood-based products comprising finely divided lignocellulosic particles and fibers mixed with and bonded together with an adhesive binder. In particular the present invention concerns a novel process for the production of fiber boards.
BACKGROUND OF THE INVENTION
The rapid increase in the production of particle boards, flake boards and fiber boards, especially medium density fiber boards (in the following also abbreviated MDF boards), during the last decades has created a demand for adhesives that are inexpensive, available in large quantities, and independent of crude oil. Lignin meets well these requirements, and it does not contain any formaldehyde, which traditionally has been considered a serious problem with conventional urea-formaldehyde (UF) adhesives. As a major wood component, native lignin is neither hygroscopic nor soluble in water. Because of its structure as a polyphenol, lignin as an adhesive should be similar to phenol-formaldehyde (PF) resins. This is true for native lignin in wood, while technical lignins (lignosulphonate or kraft lignin) have been shown to have serious limitations due to their low reactivity (kraft lignin) or due to their high hygroscopicity. Furthermore, during technical pulping lignin becomes soluble in water, due to degradation and chemical changes.
The use of spent sulphite liquor (SSL) as an adhesive for paper, wood and other ligno-cellulosic materials is well-known in the art, and a large number of patent applications has been filed during the last three decades for the use of lignin products as adhesives for particle board, plywood and fiber board instead of conventional PF or UF adhesives. Reference is made to DE Patents Nos. 3 037 992, 3 621 218, 3 933 279, 4 020 969, 4 204 793 and 4 306 439 and PCT Applications published under Nos. WO 93/25622, WO 94/01488, WO 95/23232 and WO 96/03546.
The main drawback of using SSL as an adhesive for fiber board manufacture is its hygroscopicity.
It has been shown that laccase enzymes and other peroxidases can be used as polymerization or curing catalysts of lignin (DE Patent No. 3 037 992, WO 96/03546). However, the enzymes for creating radical reactions have shown limited success so far. Fibers and wood chips used in the production of the fiber board contain 5-20% water and the laccases used need some water to effectively catalyze the polymerization reaction needed for extensive bonding of the fiberboard. Kraft lignin like native lignin to its major part is, however, insoluble in water and thus two solid phases are formed on the production line. An uneven distribution of the solids cause spotting and major failure in the strength properties of the board formed in the pressing stage.
A further problem relating to the use of isolated lignin is the high price of kraft lignin, which is near the limit for economical production of particle boards.
For the above mentioned reasons, lignin-based board production processes have not, so far, led to any major practical applications.
Instead of lignin-based adhesives, it has been suggested to activate the lignin of wood fibers with laccase and to use these fibers as such without any additional binders for manufacturing wood fiber boards (cf. EP Patent Application No. 0 565 109). The main problem relating to said technology is the long incubation time required (up to seven days or even more).
Components derived from annual plant materials, such as feruloylarabinoxylans, can also be used as additives for adhesives in particle boards. Thus, according to Feldman et al. (WO 96/03546) wood fibers and chips can be bonded together using an oxidized phenolic polysaccharide. These xylans occur only in annual plants, not in softwood or hardwood materials. They are not industrially available.
SUMMARY OF THE INVENTION
The present invention aims at eliminating the problems relating to the prior art. In particular it is an object of the present invention to provide a novel process for manufacturing fiber boards.
These and other objects, together with the advantages thereof over known lignin-based adhesives, which shall become apparent from the specification which follows, are accomplished by the invention as hereinafter described and claimed.
It is known in the art that during the preparation of MDF fibers, there is formed a water-soluble fraction during refining which contains components of wood. This fraction is separated from the fibers before the fibers are dried. The fraction contains about 1 to 2 wt-% of the original dry substance of the fibers. In conventional processes this fraction adds to the BOD and COD loading of the effluents and it increases the need for biological purification.
The present invention is based on the idea of recirculating said fraction to the process, wherein it forms at least a part of the adhesive binder used for binding of the fibers. In order to improve the adhesive properties of the fraction its components are polymerized with an oxidative enzyme.
The gluing results of the novel process are comparable to those obtained with commercially available glues (synthetic resins).
In short, according to the present invention, it has been found out that the adhesive, usually externally produced, such as phenolformaldehyde or ureaformaldehyde, can be replaced by natural, wood-derived fractions, separated from refining of the wood raw material of the process. The process for manufacturing fiber boards comprises the steps of
refining lignocellulosic raw material having a moisture content of at least 10 wt-% to provide a defibered pulp containing lignocellulosic fibers and an aqueous effluent containing solubilized wood material,
separating the refined lignocellulosic fibers from the aqueous effluent,
concentrating the aqueous effluent to increase the concentration of the solubilized wood material thereof,
treating the solubilized wood material with enzymes in the presence of oxygen in order to oxidize the solubilized wood material,
mixing the oxidized wood material with the fibers,
forming the fiber mixture into a board, and
hardening the boards to form a fiber board.
The additional benefit of this method is that the volumes of waste waters requiring external purification are diminished. Furthermore, MDF boards with excellent strength properties can be obtained.
The invention will now be explained in more detail with the aid of the following detailed description and with reference to the attached drawing and further referring to a number of working examples.
REFERENCES:
patent: 4432921 (1984-02-01), Haars et al.
patent: 4765901 (1988-08-01), Field
patent: 3037992A1 (1982-08-01), None
patent: 3621218A1 (1988-01-01), None
patent: 3933279C1 (1990-07-01), None
patent: 4020969C1 (1991-07-01), None
patent: 4204793C1 (1993-04-01), None
patent: 4306439C1 (1994-08-01), None
patent: 565109A1 (1993-10-01), None
patent: WO9325622 (1993-12-01), None
patent: WO9401488 (1994-01-01), None
patent: WO95/07604 (1995-03-01), None
patent: WO9523232 (1995-08-01), None
patent: WO9603546 (1996-02-01), None
Abstract of EPO 565,109 (Oct. 13, 1993).
Gädda Lars
Niku-Paavola Marja-Leena
Qvintus-Leino Pia
Tuominen Simo
Viikari Liisa
Birch & Stewart Kolasch & Birch, LLP
Neste Chemicals Oy
Tentoni Leo B.
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