FIBRES

Abstract

Fibres suitable for use in the production of wound dressings comprise carboxymethyl cellulose and alginate in a total amount of at least 90% by weight of the fibre, the carboxymethyl cellulose and alginate are homogeneously distributed throughout the fibre and are present in amounts such that: (a) the amount of carboxymethyl cellulose present in the fibre is at least 50% by weight of the total weight of the carboxymethyl cellulose and alginate; (b) the alginate has a Guluronate-content of 50-90% by weight, and (c) the value of z given by the expression (1): z=(2x/40)/(2x/40)+(y/23) where x and y are the percentages by weight of calcium and sodium respectively in the fibres is at least 80. The fibres may be produced by spinning a solution comprising dissolved CMC and alginate in appropriate proportions into a coagulation bath containing calcium ions.

Claims

1. Fibres comprising carboxymethyl cellulose and alginate in a total amount of at least 90% by weight of the fibre, the carboxymethyl cellulose and alginate being homogeneously distributed throughout the fibre, wherein: (a) the amount of carboxymethyl cellulose present in the fibre is at least 50% by weight of the total weight of the carboxymethyl cellulose and alginate; (b) the alginate has a Guluronate-content of 50-90% by weight, and (c) the value of z given by the expression $\begin{array}{cc}z=\frac{\left(2.Math.x/40\right)}{\left(2.Math.x/40\right)+\left(y/23\right)}& \left(1\right)\end{array}$ where x and y are the percentages by weight of calcium and sodium respectively in the fibres is at least 80.

2. Fibres as claimed in claim 1 wherein the total amount of carboxymethyl cellulose and alginate present in the fibre is at least 95% by weight of the fibre.

3. Fibres as claimed in claim 1 comprising at least 55% by weight of the carboxymethyl cellulose and at most 45% by weight of the alginate based on the total weight of the alginate and carboxymethyl cellulose.

4. Fibres as claimed in claim 1 wherein the carboxymethyl cellulose has a degree of carboxymethylation of at least 0.65.

5. Fibres as claimed in claim 1 wherein the alginate has a Guluronate-content of 50-80% by weight and an M-content of 20-50% by weight.

6. Fibres as claimed in claim 1 wherein the value of z is at least 85.

7. Fibres as claimed in claim 6 wherein the value of z is at least 90.

8. Fibres as claimed in claim 1 produced by co-spinning an aqueous dope comprising dissolved carboxymethyl cellulose and dissolved alginate into a coagulation bath.

9. Fibres as claimed in claim 1 in staple form.

10. A non-woven material which comprises entangled fibres as claimed in claim 1.

11. A non-woven material as claimed in claim 10 in the form of a non-woven needled felt.

12. A non-woven material as claimed in claim 11 in combination with a substrate into which the fibres of the material are needled.

13. A woven material comprising fibres as claimed in claim 1.

14. A knitted material comprising fibres as claimed in claim 1.

15. A wound dressing comprising a non-woven material, woven material or knitted material wherein the non-woven material, woven material or knitted material comprises the fibres as claimed in claim 1.

16. A wound dressing as claimed in claim 15 wherein said material forms one layer of a multi-layer dressing.

17. A method of producing fibres comprising spinning a dope which is an aqueous solution containing dissolved carboxymethyl cellulose and dissolved alginate into a coagulation bath containing dissolved calcium ions that cause cross-linking of the alginate and precipitation of fibres comprised of the alginate and polysaccharide wherein: (a) the amount of carboxymethyl cellulose in the dope is at least 50% by weight of the total weight of the carboxymethyl cellulose and alginate, (b) the sodium alginate has a Guluronate-content of 50-90% by weight, (c) the concentration of calcium ions in the coagulation bath provides fibres in which the value of z in the expression $\begin{array}{cc}z=\frac{\left(2.Math.x/40\right)}{\left(2.Math.x/40\right)+\left(y/23\right)}& \left(1\right)\end{array}$ where x and y are the percentages by weight of calcium and sodium respectively in the fibres is at least 80, and (d) the fibres produced contain carboxymethyl cellulose and alginate in a total amount of at least 90% by weight of the fibre.

18. A method as claimed in claim 17 wherein the amount of carboxymethyl cellulose in the dope is at least 55% by weight of the total weight of the carboxymethyl cellulose and alginate.

19. A method as claimed in claim 18 wherein the amount of carboxymethyl cellulose in the dope is at least 60% by weight of the total weight of the carboxymethyl cellulose and alginate.

Description

[0054] FIG. 1 illustrates wetted samples of felts produced from (a) fibres in accordance with the invention, and (b) comparative fibres, the felts being shown against a background of random text to demonstrate their relative translucency.

EXAMPLE

[0055] This Example describes preparation of fibres in accordance with the invention and utilises a procedure as described more fully above.

[0056] 55 kg of sodium carboxymethyl cellulose powder was dissolved in 1718 litres of pure water using a mixing system in which the CMC powder was added by vacuum into a recirculating stream of water via a homogenizer. Once the CMC had been fully dissolved, 44 kg of a High G sodium alginate powder (G content 65-70%) was added and dissolved (using the same mixing system) to produce a homogenous solution (dope).

[0057] The dope was allowed to degas for 30 hours.

[0058] The dope was pumped through spinnerets producing a total of 80,000 filaments, into a coagulation bath containing dissolved calcium chloride dihydrate maintained in an amount of 2-3% w.w (expressed as CaCl.sub.2.2H.sub.2O).

[0059] The fibres produced in the coagulation bath were collected to form a tow which was subjected to a stretching operation in water at a temperature of 50-60 C., the stretch ratio being 150-160%.

[0060] After stretching, the fibres were passed through a series of cold water baths to remove residual salt. The washed fibres were then passed successively through acetone baths containing increasing concentrations of acetone (35% to 95%).

[0061] Excess liquid was then mechanically removed from the fibres by passage through the nip between a pair of rollers. The tow was then passed through an oven to reduce residual moisture content to 5-15% by weight.

[0062] A spin finish of Polysorbate 20 was then applied to the fibres at a level of 0.5-2.0%, prior to the fibres being crimped and then cut into 50 mm staple lengths.

[0063] A non-woven felt having a weight of about 220 g m.sup.2 was produced from the staple fibres.

[0064] For the purposes of comparison, the above spinning procedure was repeated but to produce fibres comprising 15% by weight of the CMC and 85% by weight of the alginate. Again using the procedure outlined above, these fibres were used to produce a felt having a weight of about 220 g m.sup.2.

[0065] Analysis of both fibre types demonstrated that (prior to application of the spin finish) the fibres had a value of z as determined by equation (1) in excess of 90.

[0066] Samples of the two felts (area=120 cm.sup.2) were saturated with Solution A (8.298 g of sodium chloride and 0.368 g of calcium chloride made up to 1 litre with purified water) and allowed to drain.

[0067] The felt produced from the fibres comprising 55% CMC and 45% alginate had a higher absorption than the felt produced from the fibres comprising 85% alginate and 15% CMC. Additionally, the fibres in the felt produced from the fibres comprising 55% CMC and 45% alginate were gelled and the wetted felt had a translucent appearance. In contrast, the fibres comprising 85% alginate and 15% CMC did not gel and the felt produced therefrom remained generally opaque.

[0068] The test results as summarised in the previous paragraph are shown in FIG. 1 of the accompanying drawings in which the wetted felts are shown against a background of random text. The translucent nature of the felt produced form the fibres comprising 55% CMC and 45% alginate can clearly be seen.