Process for the manufacture of lyocell fibre

Details Process for the manufacture of lyocell fibre Process for the manufacture of lyocell fibre

1996-12-04

1998-03-10

Tentoni, Leo B.

Plastic and nonmetallic article shaping or treating: processes

Forming continuous or indefinite length work

Shaping by extrusion

26421115, 264233, D01D 1006, D01F 202

Patent

active

057258210

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a process for manufacturing lyocell fibre with an increased tendency to fibrillation.
It is known that cellulose fibre can be made by extrusion of a solution of cellulose in a suitable solvent into a coagulating bath. This process is referred to as "solvent-spinning", and the cellulose fibre produced thereby is referred to as "solvent-spun" cellulose fibre or as lyocell fibre. Lyocell fibre is to be distinguished from cellulose fibre made by other known processes, which rely on the formation of a soluble chemical derivative of cellulose and its subsequent decomposition to regenerate the cellulose, for example the viscose process. One example of a solvent-spinning process is described in U.S. Pat. No. 4,246,221, the contents of which are incorporated herein by way of reference. Cellulose is dissolved in a solvent such as an aqueous tertiary amine N-oxide, for example N-methylmorpholine N-oxide, generally containing a small proportion of water. The resulting solution is then extruded through a suitable die into an aqueous bath by way of an air gap to produce an assembly of filaments which is washed with water to remove the solvent and is subsequently dried. Lyocell fibres are known for their impressive textile-physical properties, such as tenacity, in comparison with fibres such as viscose rayon fibres.
Fibre may exhibit a tendency to fibrillate, particularly when subjected to mechanical stress in the wet state. Fibrillation occurs when fibre structure breaks down in the longitudinal direction so that fine fibrils become partially detached from the fibre, giving a hairy appearance to the fibre and to fabric containing it, for example woven or knitted fabric. Such fibrillation is believed to be caused by mechanical abrasion of the fibre during treatment in a wet and swollen state. Higher temperatures and longer times of treatment generally tend to produce greater degrees of fibrillation. Lyocell fibre appears to be particularly sensitive to such abrasion and is consequently often found to be more susceptible to fibrillation than other types of cellulose fibre. Intensive efforts have been made to reduce the fibrillation of lyocell fibres.
The presence of fibrillated fibres is advantageous in certain end-uses. For example, filter materials containing fibrillated fibres generally have high efficiency. Fibrillation is induced in paper-making processes by beating the fibres, which is generally known to increase the strength and transparency of the paper. Fibrillation may also be utilised in the manufacture of non-woven fabrics, for example hydroentangled fabrics, to provide improved cohesion, cover and strength. Although the fibrillation tendency of lyocell fibres is higher than that of other cellulose fibres, it is not always as great as may be desired for some end-uses. It is an object of the present invention to provide lyocell fibre with an increased fibrillation tendency.


BACKGROUND ART

In a paper in Fibre Chemistry, Vol.25 (1993), No.5, pages 368-371, V. V. Romanov and O. B. Lunina describe solutions of cellulose in N-methylmorpholine-N-oxide containing 10 to 30 percent by weight cellulose. The degree of polymerisation (D.P.) of the cellulose was 600. The solutions were extruded through an air gap into an aqueous coagulation bath to form lyocell fibres. Flow instability in the air gap was observed with solutions containing more than 15 percent cellulose.


DISCLOSURE OF INVENTION

The present invention provides a process for the manufacture of lyocell fibre with an increased tendency to fibrillation, including the steps of solution, fibre, and more than about 450 and the concentration of cellulose in the solution is at least 16 per cent by weight.
The solvent preferably comprises N-methylmorpholine N-oxide (NMMO), and it generally additionally comprises a small proportion of water. The filaments are generally washed in step (3) with an aqueous liquor to remove the solvent from the filaments.
The degree of polymerisation (D.P.) of cellulose is conveniently

REFERENCES:
patent: 4246221 (1981-01-01), McCorsley, III
patent: 5403530 (1995-04-01), Taylor
Rudi Breier, "Die Verendlung Von Lyocellfasern-Ein Erfahrungsbericht", provided!.
H. Firgo et al., "Kritische Fragen Zur Zukunft Der NMMO-Technolgie", provided!.
V.V. Romanov and O.B. Lunina, "Preparation of Hydrocellulose Fibres from Highly Concentrated Solutions of Cellulose in N-Methylmorphine-N-Oxide", Fibre Chemistry,vol. 25, No. 5, pp. 368-371 (1993).

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