Yarn comprising gel-forming filaments or fibres

Abstract

A yarn comprising gel forming filaments or fibers particularly one used to make a woven or knitted wound dressing or other gelling fabric structure. The invention provides a yarn comprising a blend of from 30% to 100% by weight of gel-forming fibers and 0% to 70% by weight of textile fibers. Process for making the yarns are also described including those using rotor spinning.

Claims

1. A yarn comprising a blend of from 30% to 100% by weight gel-forming fibres and 0% to 70% by weight textile fibres, wherein the fibres are rotor spun to produce the yarn, and the yarn has a dry tensile breaking strength of at least about 400 cN, the yarn capable of being converted into a fabric by knitting.

2. A yarn as claimed in claim 1 wherein the staple fibre length is from 30 to 60 mm.

3. A yarn as claimed in claim 1 having a dry tensile strength of at least 10cN/tex.

4. A yarn as claimed in claim 1 wherein the yarn comprises a blend of from 50% to 100% by weight of gel forming fibres with from 0% to 50% of textile fibres.

5. A process for making a yarn comprising gel-forming fibres comprising the steps of: blending staple gel-forming fibres optionally with textile fibres; carding to form a continuous web; drawing the web to produce a sliver and rotor spinning to produce a yarn; wherein the yarn has a dry tensile breaking strength of at least about 400 cN.

6. A process for making a yarn comprising gel forming fibres or filaments, comprising the steps of (i) obtaining a yarn of cellulosic filaments or fibres; (ii) chemically modifying the yarn to give the yarn gel forming properties, wherein the chemically modified yarn has a dry tensile strength of at least about 400 cN, the yarn capable of being converted into a fabric by knitting.

7. A process as claimed in claim 6 wherein the chemical modification is carboxymethylation using a reaction fluid comprising a solution of an alkali and monochloroacetate in an organic solvent.

8. A process for making a yarn as claimed in claim 5 wherein the tensile strength of the yarn is at least 10cN/tex.

9. A yarn as claimed in claim 1 wherein the gel forming fibres are polysaccharide fibres, chemically modified cellulosic fibres, pectin fibres, alginate fibres, chitosan fibres, hyaluronic acid fibres or fibres derived from gums.

10. A yarn as claimed in claim 1 wherein the gel forming fibres are modified cellulose fibres.

11. A process for making a yarn as claimed in claim 5 wherein the gel forming fibres are polysaccharide fibres, chemically modified cellulosic fibres, pectin fibres, alginate fibres, chitosan fibres, hyaluronic acid fibres or fibres derived from gums.

12. A process for making a yarn as claimed in claim 5 wherein the gel forming fibres are modified gel forming fibres.

13. A process for making a yarn as claimed in claim 6 wherein the tensile strength of the yarn is at least 10 cN/tex.

14. A process for making a yarn as claimed in claim 6, wherein the gel forming fibres are polysaccharide fibres, chemically modified cellulosic fibres, pectin fibres, alginate fibres, chitosan fibres, hyaluronic acid fibres or fibres derived from gums.

15. A process for making a yarn as claimed in claim 6 wherein the gel forming fibres are modified gel forming fibres.

16. A process for making a yarn as claimed in claim 5, wherein the gel forming fibres are modified cellulose fibres.

17. A process for making a yarn as claimed in claim 6, wherein the gel forming fibres are modified cellulose fibres.

Description

(1) The invention is illustrated in the following drawings in which:

(2) FIG. 1 shows a graph giving yarn tensile strength data for a number of yarns of the invention;

(3) FIG. 2 shows Table 1 of Example 3 giving fluid handling data for a number of yarns of the invention;

(4) FIG. 3.1 shows a graph of fluid management against yarn fibre content for a number of yarns;

(5) FIG. 3.2 shows a graph of fluid retention against yarn fibre content for a number of yarns;

(6) FIG. 3.3 shows a graph of tensile strength against yarn fibre content for a number of yarns;

(7) FIG. 4 shows Table 2 of Example 3 giving tensile strength data for a number of yarns of the invention; and

(8) FIG. 5 shows Table 3 which gives the helix angle and images of both dry and hydrated yarns for a number of yarns of the invention.

(9) The invention will now be illustrated by the following examples.

EXAMPLE 1

Spinning Yarn from Staple Gel-Forming Fibres

(10) Lyocell fibres and carboxymethyl cellulose staple fibres in blends of 50:50, 60:40 and 70:30 CMC:Lyocell were made by carding on a Trutzschler cotton card and spinning the resulting sliver at a twist of 650 turns/meter.

EXAMPLE 2

Converting a Textile Yarn to a Gel-Forming Yarn

(11) Yarns were converted in the laboratory using a mini trier. In both trials, staple and filament lyocell yarns were converted. The yarns used for the conversion were staple .sub.33 Tex Tencel; HF-2011/090; and 20 Tex filament lyocell batches HF-2011/051 (trial 1) and HF-2011/125 (trial 2). Tencel is a Lenzing owned, trademarked brand of lyocell and the Tencel yarn used was a spun staple yarn. The filament lyocell was supplied by Acelon chemicals and Fiber Corporation (Taiwan) via Offtree Ltd.

(12) The advantages of converting a yarn are that complete cones of yarn could potentially be converted in one relatively simple process, and the processing of gelling fibres is avoided, thus reducing the number of processing steps required and damage to the fibres.

(13) Trial 1Yarn Wrapped Around Kier Core

(14) In this trial, Tencel yarn was tightly wrapped around the perforated core of the kier using an electric drill to rotate the core and pull the yarn from the packages for speed. This meant that the yarn was wrapped tightly around the core under tension.

(15) The yarn was converted by a process as described in WO 00/01425 in which carboxymethylation was carried out by pumping fluid through the kier and therefore the cellulosic materials at 65 C for 90 minutes. The reaction fluid was a solution of an alkali (typically sodium hydroxide) and sodium monochloroacetate in industrial denatured alcohol. After the reaction time, the reaction was neutralised with acid and washed before being dried in a laboratory oven for 1 hour at 40 C.

(16) The conversion was successful and both staple and filament gelling yarns were produced; HF-2011/103 and HF-2011/105 respectively. Due to the tight and uneven wrapping of the staple yarn around the core, it had to be removed using a scalpel which left multiple short lengths (approximately 14 cm) of the converted yarn.

(17) Trial 2Small Yarn Hanks

(18) The aim of the second trial was to produce longer lengths of converted yarns for testing hence a small hank was made of each the staple and filament lyocell yarns by hand and these were placed between layers of fabric for the conversion.

(19) The yarn was converted by placing the hanks in a kier and converting to form a gel-forming fibre yarn as described above for Trial 1.

(20) The conversion was successful and both staple and filament gelling yarns were produced; HF-2011/146 and HF-2011/147 respectively.

(21) Yarn Summary

(22) TABLE-US-00001 Sample HF# Gelling Yarns 50:50 Spun staple gelling yarn HF-2011/001 60:40 Spun staple gelling yarn HF-2011/088 70:30 Spun staple gelling yarn HF-2011/108 Converted staple yarn (trial 1) HF-2011/103 Converted filament yarn (trial 1) HF-2011/105 Converted staple yarn (trial 2) HF-2011/146 Converted filament yarn (trial 2) HF-2011/147 Non-Gelling Yarns Staple Tencel HF-2011/090 Filament lyocell (sample) HF-2011/051 Filament lyocell (bulk) HF-2011/125

(23) Results from Examples 1 and 2

(24) With the exception of HF-2011/051, all of the yarns were tested for wet and dry tensile strength. Adaptations were made to the standard method BS EN ISO 2062:2009; TextilesYarns from packages: Determination of single-end breaking force and elongation at break using constant rate of extension (CRE) tester. A Zwick tensile testing machine was used with a gauge length of 100 mm. The test uses a 100 N or 20 N liad cell to exert a constant rate of extension on the yarn until the breaking point is reached. Wet tensile testing was measured by wetting the samples with 0.2 ml of solution A in the central 3 to 4 cm of each yarn and leaving for 1 minute. The wetted sample was then placed in the jaws of the Zwick and clamped shut. Tensile strength was tested as the yarns produced need to be strong enough to withstand the tensions and forces applied during knitting, weaving and embroidery.

(25) Tensile Strength

(26) The results are shown in FIG. 1. All of the yarns were stronger when they were dry than when they were wet, with HF-2011/108, the 70:30 gelling yarn, showing the largest proportional strength decrease.

(27) Of the yarns tested, HF-2011/108 was the weakest yarn both when wet and dry with tensile strengths of 12.4 and 3.4cN/Tex respectively, despite containing 30% lyocell fibres. Although this was the weakest yarn, it was successfully weft knitted; HF-2011/120 and woven; HF-2011/169 into fabrics, it is believed that all of the other yarns would also be strong enough to be converted into fabrics.

(28) Both approaches successfully produced gelling yarns.

(29) For converted yarns, the spun and filament yarns behaved equivalently showing no advantage or disadvantage to having a twisted material in terms of fluid handling and strength of an 100% CMC yarn.

EXAMPLE 3

(30) Yarns have been produced using open end spinning technology utilising 50 mm staple length CMC fibre. CMC has been blended with Tencel fibres in order to help the spinning process.

(31) HF-2011/08860%CMC 40% Tencel

(32) HF-2011/10870% CMC 30% Tencel

(33) HF-2012/08080% CMC 20% Tencel

(34) Fluid Handling

(35) The yarns were tested for their fluid handling capabilities using a modified version of TD-0187 Liquid handling of dressings using direct immersion technique. 3 m of yarn was used for each repeat and wrapped around a cylinder of 7.5 cm to give a constant number of twists. Samples were immersed in 10 ml of solution A for 30 minutes before being drained for 30 seconds and their hydrated weight measured. The amount of fluid retained was assessed by applying a vacuum to the sample for 1 minute and the final sample weight measured.

(36) Tensile Strength

(37) Tensile strength of the yarn was measured using the Zwick Universal Testing Machine (UTM). Samples were tested using a 20N load cell with a test speed of 100 mm/min and gauge of 100 mm. For wet strength, yarns were hydrated with 0.1 ml of solution A, prior to testing using the same machine settings.

(38) Microscopy

(39) Yarns were visually assessed using an optical microscope in a wet and dry state. The helix angle was also measured.

(40) Results

(41) Fluid Handling

(42) An increased amount of CMC content caused an increase in the retention of the yarns, as shown in Table 1 (FIG. 2) and FIG. 3.1 and 3.2. There was a slight drop in absorbency when increasing the CMC content from 60% to 70% however the retention was improved.

(43) In order to produce a fabric that has a comparative absorbency to Aquacel of 0.18 g/cm.sup.2(2), theoretically a fabric of 256gsm should be formed from the 80% CMC yarn. In comparison Aquacel has a weight per unit area of 119gsm.sup.(2).

(44) Tensile Strength

(45) Increased CMC content within the yarn also caused a decrease in the tensile strength shown in FIG. 3.3. However a satisfactory wet strength was still able to be achieved at 80% CMC content, with individual yarns providing more than double the strength of Aquacel dressing per cm width in the machine direction (0.61N/strand of yarn in comparison to 0.21N/cm Aquacel.sup.(2)), and almost equalling the dressing strength per cm width in the transverse direction (0.61N/strand of yarn in comparison to 0.66N/cm Aquacel.sup.(2)). HF-2012/088 and HF-20122/108 have both been knitted successfully, and therefore the breaking strengths of these yarns are high enough to withstand tensions within the knitting process. HF-2012/108 was also woven using a leno structure; although some problems occurred suggesting a higher breaking strength is required for weaving. FIGS. 3.3 and 4 (Table 2) show the tensile strength data.

(46) Microscopy

(47) Visually the yarns gelled and swelled when hydrated. As the fibres swelled the helix angle of the twist increased, shown in Table 3 (FIG. 5), this is due to the increased yarn thickness. Some non gelling fibres are visible at this magnification.

(48) Twist Factor

(49) The twist factor of a yarn determines the yarn characteristics, and is dependent on the linear density of the yarn and the twist level. Since the twist angle, and properties resulting from this will vary depending upon the twist level and the yarn thickness the twist factor normalises yarns of different linear densities so that their twist properties can be compared. Table 4 outlines the twist factors used for cotton yarns for a number of end processes.

(50) TABLE-US-00002 TABLE 4 Twist Factors most commonly used in cotton yarns.sup.(3) Yarn Application Tex Count Twist Factor (K.sub.t) Soft Knitwear 2400-2900 Weft Yarn 2900-3400 Warp Yarn 3900-4300 Warp/Extra Strong Yarn 5300-6300 Crisp 6800-8700

(51) HF-2012/080 has a twist level of 580 turns/meter (given by the manufacturer). From this the twist factor can be calculated using the equation 7.
K.sub.t=textpm (equation 7)

(52) Where

(53) K.sub.t is the twist factor (using tex count)

(54) Tex is the linear density of the yarn in tex

(55) tpm is the twist level in turns per meter.

(56) HF-2012/080K.sub.t=50580=4101.

(57) This shows that the yarn is at its optimum twist for its strength.