Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Chemical treatment after start or completion of mechanical...
Patent
1996-02-15
2000-08-08
Alvo, Steven
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Chemical treatment after start or completion of mechanical...
162 72, 435278, D21H 2502
Patent
active
060996889
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process in accordance with the preamble of claim 1 for preparing mechanical pulp.
According to a process of this kind, the wood raw material is disintegrated into chips, which then are defibered to the desired drainability, the raw material being subjected to an enzymatic treatment during the production process.
The invention also relates to an enzyme preparation according to the preamble of claim 15, suitable for the treatment of mechanical pulp.
Chemical and mechanical pulps possess different chemical and fibre technical properties and thus their use in different paper grades can be chosen according to these properties. Many paper grades contain both types of pulps in different proportions according to the desired properties of the final paper products. Mechanical pulp is often used to improve or to increase the stiffness, bulkiness or optical properties of the product.
In paper manufacture the raw material has first to be defibered. Mechanical pulp is mainly manufactured by grinding and refining methods, in which the raw material is subjected to periodical pressure impulses. Due to the friction heat, the structure of the wood is softened and its structure loosened, leading finally to separation of the fibres.
However, only a small part of the energy spent in the process is used to separate the fibres, the major part being transformed to heat. Therefore, the total energy economy of these processes is very poor.
Several methods for improving the energy economy of mechanical pulping are suggested in the prior art. Some of these are based on pretreatment of chips by, e.g., water or acid (FI Patent Specifications Nos. 74493 and 87371). Also known are methods which comprise treating the raw material with enzymes to reduce the consumption of the refining energy. Thus, Finnish Patent Application No. 895676 describes an experiment in which once-refined pulp was treated with a xylanase enzyme preparation. It is stated in the application that this enzyme treatment would, to some extent, decrease the energy consumption. In said prior art publication the possibility of using cellulases is also mentioned, but no examples of these are given nor are their effects shown. As far as isolated, specified enzymes are concerned, in addition to hemicellulases, the interest has been focused on lignin modifying enzymes, such as laccase. A treatment using the laccase enzyme did not, however, lead to decreased energy consumption.
In addition to the afore-mentioned isolated enzymes, the application of growing white rot fungi in the manufacture of mechanical pulps has also been studied. Carried out before defiberization, such a treatment with a white rot fungus has been found to decrease the energy consumption and to improve the strength properties of these pulps. The drawbacks of these treatments are, however, the long treatment time needed (mostly weeks), the decreased yield (85 to 95%), the difficulty to control the process and the impaired optical properties.
The aim of this method of invention is to remove the drawbacks of the known techniques and to provide a completely new method for the production of mechanical pulp.
It is known that the amount and temperature of water bound to wood are of great importance for the energy consumption and quality of the pulp. The water bound to wood is known to decrease the softening temperature of hemicelluloses and lignin between the fibres and simultaneously to weaken the interfibre bonding, which improves the separation of fibres from each other. During refining the energy is absorbed (bound) mainly by the amorphous parts of the fibre material, i.e. the hemicellulose and lignin. Therefore, an increase of the portion of amorphous material in the raw material improves the energy economy of the refining processes.
The invention is based on the concept of increasing the amorphousness of the raw material during mechanical pulping by treating the raw material with a suitable enzyme preparation, which reacts with the crystalline, insoluble cellulose.
The enzymes
REFERENCES:
patent: 5116474 (1992-05-01), Fuentes et al.
patent: 5308449 (1994-05-01), Fuentes et al.
Pilon et al, Tappi, "Increasinf Water Retention of Mechanical Pulp by Biological Treatments"; vol. 65, No. 6, Jun. 1982; pp. 93-96.
Pere Jaakko
Siika-aho Matti
Viikari Liisa
Alvo Steven
Valtion teknillinen tutkimuskeskus
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