Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
26421115, 264233, D01F 400
FIELD OF THE INVENTION
This invention relates to a process for manufacturing lyocell fibre with an increased tendency to fibrillation and to lyocell fibre having 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. Lyccell 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. Lyocell fibres are known for their impressive textile physical properties, such as tenacity, in comparison with fibres such as viscose rayon fibres. 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. The resulting solution is then extruded through a suitable die into an aqueous bath to produce an assembly of filaments which is washed with water to remove the solvent and is subsequently dried.
Fibres 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 fibres 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.
DISCLOSURE OF THE INVENTION
The present invention provides a process for the manufacture of lyocell fibre with an increased tendency to fibrillation, including the steps of: and fibre; and the characterising step of Degree of Polymerisation of the cellulose by at least about 200 units.
The solvent preferably comprises a tertiary amine N-oxide, more preferably N-methylmorpholine N-oxide (NMMO), and it generally contains a small proportion of water. When a water-miscible solvent such as NMMO is used, the filaments are generally washed in step (3) with an aqueous liquor to remove the solvent from the filaments.
Lyocell fibre at the end of step (3) is in never-dried form and generally requires to be dried. In one embodiment of the invention, the degradation step (4) is performed on never-dried fibre which is subsequently dried. In another embodiment of the invention, the fibre is dried between steps (3) and (4). Use of the degradation step (4) according to the invention on previously-dried fibre may be convenient if batchwise processing or longer treatment times are desired. Previously-dried fibr
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Gannon James Martin
Johnson Pamela Ann
Woodings Calvin Roger
Acordis Fibres (Holdings ) Limited
Wortman Donna C.
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