Manufacture of extruded articles

Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion

Patent

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Details

26421115, 26421118, 264233, B29C 4700, D01D 1006, D01F 202

Patent

active

060933550

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to methods for the manufacture of extruded lyocell articles such as fibres and films, wherein a solution of cellulose in an aqueous tertiary amine N-oxide solvent is extruded through a die into a coagulating bath. Lyocell is the generic name for cellulose produced by solvent extrusion or solvent-spinning processes of this kind. Tertiary amine N-oxides are hereinafter on occasion referred to for convenience as amine oxides.


BACKGROUND ART

The manufacture of shaped polymer articles by extrusion of a solution of cellulose in an aqueous tertiary amine N-oxide solvent (which solution may also be called a dope) into an aqueous coagulating bath is described for example in U.S. Pat. No. 4,246,221, the contents of which are incorporated herein by way of reference. Conventional dissolving-grade cellulose, for example in the form of woodpulp and cotton linters, is utilised as raw material in such processes.
EP-A-0,648,808 points out that the extrusion conditions for such solutions must be chosen to provide freedom from melt flow instability in the extrusion orifice, which can result in melt fracture and consequential production breakdown (loss of spinning stability). Melt flow instability can be countered without reducing extrusion productivity by reducing the viscosity of the solution, for example by reducing the concentration or degree of polymerisation (D.P.) of the cellulose in the solution. Such reduction also permits increases in the draft ratio which can be applied to extruded fibres and in the take-up velocity of such fibres. Nevertheless, such reduction is attended by disadvantages elsewhere in the process, notably by reductions in productivity and by increases in the load on the solvent recovery system. EP-A-0,648,808 describes a solution of cellulose in aqueous N-methylmorpholine N-oxide, wherein the cellulose comprises a mixture of (1) a first cellulose component having a degree of polymerisation (D.P.) in the range from 500 to 2000, and (2) a second cellulose component having a D.P. in the range from 350 to 900, with the proviso that the ratio of the D.P. of component (2) to the D.P. of component (1) is no greater than 0.9:1, the ratio by weight of component (1) to component (2) being in the range from 95:5 to 50:50. It is said that such solutions can be extruded at high velocity with process stability to yield lyocell fibres with mechanical properties similar to those produced by conventional lyocell processes.


DISCLOSURE OF THE INVENTION

According to the invention there is provided a method for the manufacture of an extruded lyocell article which comprises the steps of: form a solution; coagulating bath to form an extruded lyocell precursor; N-oxide; and lyocell article, defined in Test Method 2) to Jet Flow Index (as defined in Test Method 3) in the range from 0.85 to 6.0. Pipe Flow Index (PFI) is designed to assess the flow performance of a cellulose solution under low-shear conditions of the kind typically experienced in transfer pipework in a manufacturing plant. Jet Flow Index (JFI) is designed to assess the flow performance of a cellulose solution under high-shear conditions of the kind typically experienced in a spinnerette or other extrusion die. In both cases, higher Index values correspond to an increased flow rate at a given pressure or to a lower required pressure to induce a given flow rate.
The tertiary amine N-oxide is preferably N-methylmorpholine N-oxide (NMMO). The amount of cellulose in the solution is preferably in the range from 5 to 25, more preferably from 10 to 20, percent by weight. The amount of water in the solution is often in the range from 7 to 14 percent by weight, although it will be appreciated from the known behaviour of cellulose/NMMO/water compositions that the acceptable range of water concentration may vary with cellulose concentration.
The dissolution, extrusion, washing and drying steps may be performed in conventional manner.
The cellulose solution may conveniently be made by dispersing cellulose in a 60/40 mi

REFERENCES:
patent: 3758458 (1973-09-01), Dyer
patent: 4983730 (1991-01-01), Domeshek

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