Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Extrusion molding
Patent
1997-05-02
1998-08-04
Tentoni, Leo B.
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Extrusion molding
264101, 264187, 264485, B29B 1308, D01F 202
Patent
active
057889392
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with a process for the production of a cellulose moulded body, particularly cellulose fibers.
BACKGROUND OF THE INVENTION
As an alternative to the viscose process, in recent years there has been described a number of processes wherein cellulose, without forming a derivative, is dissolved in an organic solvent, a combination of an organic solvent and an inorganic salt, or in aqueous saline solutions. Cellulose fibers made from such solutions have received by BISFA (The International Bureau for the Standardisation of man made Fibers) the generic name Lyocell. As Lyocell, BISFA defines a cellulose fibre obtained by a spinning process from an organic solvent. By "organic solvent", BISFA understands a mixture of an organic chemical and water.
So far, however, only one process for the production of a cellulose fibre of the Lyocell type, i.e. the amine-oxide process, has achieved industrial-scale realization. In this process preferably N-methylmorpholine-N-oxide (NMMO) is used as a solvent. For the purposes of the present specification, the abbreviation "NMMO" is used in place of the term "tertiary amine-oxides", NMMO referring additionally to N-methylmorpholine-N-oxide, today preferably used.
Tertiary amine-oxides have been known for a long time as alternative solvents for cellulose. It is known for instance U.S. Pat. No. 2,179,181 that tertiary amine-oxides are capable of dissolving high-grade chemical pulp without derivatisation and that from these solutions cellulose moulded bodies, such as fibers, may be produced by precipitation. In U.S. Pat. Nos. 3,447,939, 3,447,956 and 3,508,941, further processes for the production of cellulose solutions, wherein cyclic amine-oxides are preferably used as solvents, are described. In all of these processes, cellulose is dissolved physically at elevated temperature.
When the solution is prepared using a double screw extruder or a stirring vessel, the pulp has to be subjected to preactivation to carry out the dissolution process at a sufficiently high rate (see "Das Papier", volume 12, pages 784-788). As pre-activation, production and regeneration of alkaline cellulose or a hydrothermal pulp treatment are proposed.
Also according to DD-A - 226 573, cellulose is pre-activated before preparation of the solution, which is also carried out in an extruder. The DD-A cited starts from an NMMO-containing cellulose supension which is first homogenized in a stirring vessel. Afterwards, its consistency is increased to 12,5% by mass by centrifugating or squeezing and it is dried to a water content of 10-15% by mass (based on NMMO) and converted into a clear solution in an extruder exhibiting a degassing zone at temperatures of from 75.degree. to 120.degree. C.
In EP-A - 0 356 419 of the applicant, a process carried out using preferably a thin-film treatment apparatus is described, in which thin-film treatment apparatus a suspension of shredded pulp in an aqueous tertiary amine-oxide is spread as a thin layer and transported across a heating surface, said surface of this thin layer being exposed to reduced pressure. When transporting the suspension across the heating surface, water evaporates and the cellulose may be brought into solution, so that a spinnable cellulose solution may be delivered from the thin-film treatment apparatus.
All of the processes described above use high-grade chemical pulp produced e.g. from beech or pine wood as starting materials. In the state of the art, little is known about the use of other cellulose-containing materials.
Processing lignocellulose materials using the NMMO process is known from WO 86/05526. For processing, relatively aggressive conditions are suggested. Thus for instance poplar wood is first subjected to a specific hydrolysis process, and the solid product obtained is mixed at room temperature with NMMO having a water content of 13,5%. The NMMO used is the monohydrate of NMMO (melting point>70.degree. C.), which at room temperature is present in a solid state. The solid mixture is homogenized, heate
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Mulleder Eduard
Schild Gabriele
Schrempf Christoph
Lenzing Aktiengesellschaft
Tentoni Leo B.
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