Stock material or miscellaneous articles – Composite – Of carbohydrate
Reexamination Certificate
1999-11-09
2001-09-11
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of carbohydrate
C527S400000, C527S403000, C530S500000, C524S073000, C524S074000
Reexamination Certificate
active
06287708
ABSTRACT:
This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/FI98/00024 which has an International filing date of Jan. 14, 1998, which designated the United States of America.
The present invention relates to the manufacture of fiber boards, in particular of medium density fiber boards, which comprise fibrous lignocellulosic particles mixed with and bonded together with an adhesive binder. In particular, the present invention concerns novel adhesives binders and a preparation process thereof as well as fiber boards manufactured using the adhesive.
The rapid increase in the production of particle boards, flake boards and fiber boards, in particular medium density fiber boards and especially MDF board production during the last decades demands an adhesive that is cheap, available in large quantities, and independent of crude oil. Lignin meets well these demands, and it does not contain formaldehyde, which traditionally has been considered a serious problem with ureaformaldehyde (UF) adhesives. As a major wood component, native lignin is neither hygroscopic nor soluble in water. However, during pulping, lignin becomes soluble in water, due to degradation and chemical changes.
According to 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 (lignosulpbonate or kraft lignin) have been shown to have serious limitations due to their low reactivity (kraft lignin) or due to their high hygroscopicity (lignosulphonates).
The use of spent sulphite liquor (SSL) as an adhesive for paper, wood and other lignocellulosic 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 Pat. 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. For this reason it cannot really compete with other natural or synthetic adhesives.
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 fiber boards 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 causes 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). 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 oxidized phenolic polysaccharides. These xylans occur only in annual plants, not in softwood or hardwood materials. They are not industrially available.
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 carbohydrate/lignin-based adhesive for the preparation of fiber boards and similar wood-based products. It is another object of the present invention to provide new fiber boards and similar wood-based products. It is a third object to provide a method for manufacturing the adhesive.
These and other objects, together with the advantages thereof over known lignin-based adhesives and processes for the preparation thereof, 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 mechanical refining of chips, a part of the compounds of the fibrous raw material is dissolved (about 1% of the fiber weight). This fraction, which primarily contains the same chemical components as the fibers (carbohydrates, extractives and lignin) decontaminates the circulation waters and effluents of paper mills and increase the volumes of waste waters that have to be treated. Different filtration and concentration methods are being employed to separate the dissolved compounds from the process waters. As a result, a concentrated waste fraction without any practical use today is being obtained.
In our copending application is has been shown that this soluble lignin/carbohydrate fraction is particularly useful as an additive or adjuvant for gluing of particles boards, fiber boards and other similar wood-based composite products. Particularly good gluing is achieved if this fraction is polymerized with laccase (or similar oxidase) enzyme(s). The results are on the same level as those obtainable with conventional phenol or urea formaldehyde resins.
In the context of the present invention, we have found that a similar fraction of soluble carbohydrates, extractives and lignin compounds can be obtained by hydrolyzation and peeling of lignocellulosic fibres by using enzymes capable of removing carbohydrate layers from the fibre surfaces. These enzymes comprise hydrolases, i.e. enzymes typically hydrolyzing cellulose, hemicellulose or pectin from the fibres. In addition to carbohydrates, these enzymes also remove lignin-carbohydrate fractions present in the woody materials.
This method thus produces an increased amount of a water-soluble fraction containing carbohydrates, extractives and lignin useful as an adhesive binder. The method can be used also for any other type of raw material derived from plants, and used for limited or extensive hydrolysis.
The invention also concerns a process for preparing an adhesive binder composition, which comprises the steps of
treating fibrous lignocellulosic raw material with a hydrolytic enzyme in an aqueous medium,
recovering the solubilized material of the enzymatic treatment,
forming an aqueous suspension containing said material and an oxidase, and
oxidizing said material in the presence of said oxidase by introducing oxygen-containing gas into the suspension.
The above process can be carried out by mixing lignocellulosic particles, fibers and flakes of vegetable origin with the solubilized material and the oxidase to form a hardenable composition which can be shaped into particle boards, fiber boards, flake boards or similar wood-based products by oxidizing, and by polymerizing the solubilized material in the presence of said oxidase and oxygen.
The enzymatically obtained fraction can be combined or used together with a (non-enzymatically produced) soluble fraction of mechanical or chemimechanical refining of lignocellulosic raw material.
The invention will now be explained in more detail with the aid of the following detailed description and with reference to a number of working examples.
Within the context of the present invention the terms “adhesive”, “adhesive binder” and “resin” designate a chemical composition which, in the wet stages of the manufacture of, e.g.
Gädda Lars
Hase Anneli
Kataja Kirsi
Qvintus-Leino Pia
Tuominen Simo
Acquah Samuel A.
Birch & Stewart Kolasch & Birch, LLP
Neste Chemicals Oy
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