Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – By calendering
Patent
1995-09-12
1997-07-22
Tentoni, Leo B.
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
By calendering
10616401, 10620501, 162 90, 162 97, 162218, 264211, 26421111, 2643281, B29C 4324, B29C 4500, B29C 4700
Patent
active
056501110
DESCRIPTION:
BRIEF SUMMARY
The invention concerns dispersion of the cellulose based fibres in straw with alkali during strong mechanical action and at solid content up to 85%. This action leads to a moulding composition, which is suitable for plastic forming of cellulose containing fibre products.
The most valuable part of straw is cellulose fibre. This may be used for paper production, but it makes up only a bit more than 1/3 of the solid in straw. Almost half the solid is extractable with alkali. By such extraction carbohydrates with chains shorter than cellulose are made soluble, and in the paper industry that is called hemicellulose. It is mainly composed of pentosanes and it acts as a hydrocolloid.
Before straw can be used for paper production it is pulped in water after addition of alkali. The highest concentrations which are used in the beginning of the pulping process is 40% dry straw plus 8% alkali. At the end of the pulping the concentration is much lower, because the heating is done by direct supply of steam. The alkali usually is caustic soda, lime or mixtures thereof.
The pulping solubilizes most of the alkali extractable material. That softens the straw, so that the non-extractable cellulose fibres can be liberated by a succeeding milling operation. The concentration used for this dispersion of the fibres is typically a few percent and in special cases up to 8%.
One of the advantages of the invention is that it solves the problem of the low concentration by a new process for dispersion of the cellulose based fibres in straw with alkali in water. The new process is characterised in that the liberation of the fibres from each other is carded out under strong mechanical action at solid content up to 85%. In so doing, the suspension is transformed into a homogeneous paste.
Even though the inventor does not want to be committed to any particular theory to explain the mechanism which is behind the invention, it is supposed that the plasticity is given by the dissolved pentosane. It acts as a hydrocolloid. When the amount of water is low, the pentosane binds the water, and the mixture gets a high viscosity as a paste. In this way a self increasing effect is obtained, because the high viscosity conveys the movement of the agitator out into the paste to the individual straws and further into the individual fibres to tear them apart, by which mean still more pentosane is being dissolved. There is a great chemical affinity between the hydroxyl groups on the fibres and on the pentosane. This causes the pentosane to coat the fibres and prevents them from reassociation when the movement of the agitator stops.
If faster formation of paste is wished, than possible by the natural content of the pentosane in straw, extra hydrocolloid may be added, f. inst. starch, so that the agitator gets into attack with the fibres earlier.
The treatment of the straw may be performed in a particularly strong mixer, preferably in a kneading machine which can be heated.
The invention may be used as a introductory production step for traditional paper making, in such a way that the paste resulting from the liberation of the fibres is diluted with great amounts of water, and the obtained suspension is then dewatered on a water permeable wire, so that the fibres are retained on the wire. However, the large amount of pentosanes makes straw unsuited for traditional paper production. The pentosane causes three problems: after the milling. In so doing the greatest part of the extractable material and the surplus of alkali is lost. This amounts to about half of the solids, and is a great economical burden. water is a great environmental problem. cellulose or ground wood, which is normally being used for production of paper, and this reduces the speed at which the paper can be formed by dewatering on the water permeable wire.
The high content of pentosane in straw is responsible for the fact that it has not yet been possible to find a commercial viable usage of this great by-product from agriculture. Therefore straw is usually burnt.
It is another advantage of t
REFERENCES:
patent: 1718011 (1929-06-01), Vogt
patent: 3892586 (1975-07-01), Vladar et al.
patent: 4377440 (1983-03-01), Gasland
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