Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With chemical or physical modification of liberated fiber
Reexamination Certificate
1997-06-13
2001-03-27
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With chemical or physical modification of liberated fiber
C162S024000, C162S072000, C435S278000
Reexamination Certificate
active
06207009
ABSTRACT:
TECHNICAL FIELD
This invention relates to a process for production of paper or paperboard of increased strength from mechanical pulp.
BACKGROUND ART
Mechanical pulp, such as ground wood pulp, refined mechanical pulp, thermomechanical pulp, etc. is generally produced by grinding logs or chips in a grinder or refiner where the temperature increases to near or above boiling. The three main constituents of the pulp are cellulose, hemicellulose and lignin.
From these types of pulp, paper or paperboard is generally manufactured as follows:
The pulp is treated in a screening process, is mixed with paper or paperboard making additives in the stock preparation section in order to prepare the paper or paperboard furnish. A paper or paperboard is then made from the furnish on a paper machine.
The mechanical pulps have an advantage of providing high yield but on the other hand they have inferior strength properties compared to chemical pulps.
High paper strength is generally desirable. Conventional methods for increasing the paper strength include the use of wet strength additives and binders.
EP,A1,0 433 258 discloses a process for the production of mechanical pulp from a fibrous product wherein the fibrous product is subjected to an enzymatic treatment in which a binding agent is linked with the lignin in the fibrous product. The binding agent may be a hydrophilic substance, particularly a protein or a carbohydrate, e.g., oxidized, medium cationic starch. The enzymatic treatment may be done with a laccase.
U.S. Pat. No. 4,687,745 discloses a process for enhancing the strength properties of mechanical pulps. The process uses ligninolytic enzymes present in the extracellular growth medium of a fermentation of
Phanerochaete chrysosporium.
STATEMENT OF THE INVENTION
We have found that, surprisingly, the strength of the paper of paperboard can be increased by treating the pulp with a phenol-oxidizing enzyme system (e.g. laccase and oxygen) after the mechanical refining. It is believed that this strengthening is due to polymerization or cross-linking of the lignin present at the surface of the fibers.
Accordingly, the invention provides a process for increasing the strength of a mechanical pulp for paper or paperboard production, comprising treating the pulp with a phenol-oxidizing enzyme system, selected from the group consisting of:
a) a peroxidase together with hydrogen peroxide, and
b) a laccase or a catechol oxidase together with oxygen, provided that no grinding or refining occurs during this treatment, and that no binding agent is present during this treatment.
EP 429,422 discloses reduction of energy consumption in the refining stages by use of laccase during pulp preparation between the first and second refining stage; the document indicates that some increase of paper strength is also obtained. However, the enzyme treatment is done at 20° C., so this prior-art process requires an extra cooling stage after the first refining step. The process of this invention would obviously defeat the object of EP 429,422 as the enzyme treatment occurs after the last refining stage and therefore has no effect on energy consumption during refining.
DETAILED DESCRIPTION OF THE INVENTION
Phenol Oxidizing Enzyme System
The enzyme system used in the invention consists of a suitable oxidase together with O
2
or a suitable peroxidase together with H
2
O
2
. Suitable enzymes are those which oxidize and polymerize aromatic compounds such as phenols and lignin.
Examples of suitable enzymes are catechol oxidase (EC 1.10.3.1), laccase (EC 1.10.3.2) and peroxidase (EC 1.11.1.7). Some preferred enzymes are peroxidase derived from a strain of Coprinus, e.g.
C. cinerius
or
C. macrorhizus,
peroxidase from Bacillus, e.g.
B. pumilus
and laccase from Trametes, e.g.
T. versicolor
(previously called Polyporus). It may be preferable to use two different phenol oxidizing enzymes together.
The amount of peroxidase should generally be in the range 10-10,000 PODU per g of dry substance (PODU unit of peroxidase activity defined below). The amount of laccase should generally be in the range 10-10,000 units per g of dry substance (unit of laccase activity defined below).
Molecular oxygen from the atmosphere will usually be present in sufficient quantity. A suitable amount of H
2
O
2
will usually be in the range 0.01-10 mM, particularly 1-10 mM.
Process Conditions
The enzyme treatment can be done at conventional consistency, e.g. 0.5-10% dry substance, at temperatures of 20-90° C.
Determination of Peroxidase Activity (PODU)
Peroxidase activity is determined from the oxidation of 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) by hydrogen peroxide. The greenish-blue colour produced is photometered at 418 nm. The analytical conditions are 0.88 mM hydrogen peroxide, 1.67 mM ABTS, 0.1 M phosphate buffer, pH 7.0, 30° C., 3 minutes reaction.
1 peroxidase unit (PODU) is the amount of enzyme that catalyses the conversion of 1 &mgr;mol hydrogen peroxide per minute at these conditions.
Determination of Laccase Activity
Laccase activity was determined by a similar method without addition of hydrogen peroxide. 1 unit of laccase activity was defined as the amount of enzyme that catalyses the oxidation of 1 &mgr;mol ABTS per minute.
REFERENCES:
patent: 4687745 (1987-08-01), Farrell
patent: 5273896 (1993-12-01), Pedersen et al.
patent: 5505772 (1996-04-01), Kharazipour et al.
patent: 0 345 715 (1989-06-01), None
patent: 0 433 258 A1 (1990-12-01), None
patent: 0 429 422 (1991-05-01), None
patent: WO 92/20857 (1992-11-01), None
Trotter, “Biothechnology in the pulp and paper industry: a review, Part 2”; Tappi J., pp. 201-205, May 1990.*
Haars, “Room-Temperature Curing Adhesives Band on Lignin and Phenoloxidases”, Inst. of Forest Butany, 1989; p. 126-134.
Hansen Tomas Tage
Nielsen Peder Holk
Alvo Steve
Green, Esq. Reza
Gregg, Esq. Valeta
Novo Nordisk Biochem North America, Inc.
Zelson Esq. Steve
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