NZ626695B2

NZ626695B2 - A yarn comprising gel-forming filaments or fibres

Info

Publication number: NZ626695B2
Application number: NZ626695A
Authority: NZ
Inventors: Wayne Bonnefin; Amelia Prentice; Sarah Wroe
Original assignee: Convatec Technologies Inc
Priority date: 2011-12-01
Filing date: 2012-11-29
Publication date: 2017-01-05

Abstract

yarn comprising a blend of from 50% to 100% by weight gel-forming fibres and 0% to 50% by weight textile fibres. The individual fibres are carded to form a continuous web, the web is drawn to produce a sliver and the sliver is rotor-spun into yarn.

Description

A YARN COMPRISING RMING FILAMENTS OR FIBRES This invention relates to a yarn comprising gel-forming filaments or fibres and particularly one used to make a woven or knitted wound ng or other gelling fabric structure.

It is known to make wound dressings from gel forming fibres. Typically such fibres are derived from a polysaccharide such as cellulose or alginate which is chemically modified in order to enhance the absorbency and gelling properties of the fibre.

Gel-forming fibres tend to be fragile and because of this their use has been confined to simple fabric ures such as those made using non woven ques. For instance carding fibres into a non woven felt, layering the felts and needle punching to give a fabric with some integrity. This means that the variety of dressing types that can be made with staple gel forming fibres is restricted to those that can be made from non woven fabrics and thus their use is limited. For instance, it is difficult to prepare a wound dressing sing gel forming fibres in a format that is to be subjected to tension as its non woven character means that it is weak in tension. It is also difficult to make certain shapes, for instance tubes or socks.

It would therefore be desirable to be able to make a yarn comprising gel-forming filaments or fibres, the yarn having sufficient strength that it can be processed into fabrics by weaving or knitting.

The discussion of the background to the invention included herein including nce to documents, acts, materials, devices, articles and the like is included to n the context of the t invention. This is not to be taken as an admission or a tion that any of the material referred to was published, known or part of the common l knowledge in New Zealand or in any other country as at the priority date of any of the claims.

Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereto. - 1a - Accordingly the present invention provides a yarn comprising a blend of from 50% to 100% by weight gel-forming fibres and 0% to 50% by weight textile fibres. The individual fibres are carded to form a continuous web, the web drawn to produce a sliver and the sliver rotor-spun into a yarn.

Preferably the yarns comprise from 60% to 100% by weight of rming fibres with the balance of textile fibres.

By the term yarn is meant a thread or strand of continuous nt or staple fibres.

By gel forming filaments or fibres is meant hygroscopic filaments or fibres which upon the uptake of wound exudate become moist slippery or gelatinous and thus reduce the tendency for the nding fibres to adhere to the wound. The gel forming fibres can be of the type which retain their ural integrity on tion of exudate or can be of the type which lose their ﬁbrous form and become a structureless gel. The gel forming ﬁlaments or ﬁbres are preferably spun sodium carboxymethylcellulose ﬁbres or ts, chemically modiﬁed cellulosic ﬁbres or ﬁlaments, pectin ﬁbres or ﬁlaments, alginate ﬁbres or ﬁlaments, chitosan ﬁbres or ﬁlaments, hyaluronic acid ﬁbres or ﬁlaments, or other polysaccharide ﬁbres or ﬁbres or ﬁlaments derived from gums. The cellulosic ﬁbres preferably have a degree of substitution of at least 0.05 carboxymethyl groups per glucose unit. The gel forming ﬁbres or ﬁlaments preferably have an absorbency of at least 2 grams 0.9% saline solution per gram of ﬁbre (as measured by the free swell absorbency method BS EN 13726- 12002 Test methods for primary wound dressings — Part 1 : s of absorbency, Method 3.2 free swell absorptive capacity).

Preferably the gel forming ﬁbres or ﬁlaments have an ency of at least 10g/g as ed in the free swell absorbency method, more preferably between 15g/g and 25g/g- The ﬁbres present in the yarn preferably have a staple length of 30 to 60mm, more preferably 40 to 55mm and most preferably 45 to 55mm.

Preferably the textile ﬁbres or ﬁlaments have an absorbency of less than 10g/g as measured by the free swell method and more preferably less than 5 g/g. ably the textile or ﬁlaments ﬁbres are Tencel, cotton or viscose and may comprise lycra or other elastic ﬁbre.

The yarns of the present invention ably have a dry tensile strength of at least 10cN/tex, preferably from 10 to 40 cN/tex and most preferably from 16 to 35 cN/tex as measured by British Standard ISO 2062 2009.

A yarn made according to the processes of the present ion need not contain textile ﬁbres enabling structures to be ed which consist wholly of gel-forming ﬁbres.

The yarn of the invention can be made in various ways. The ﬁrst is to spin gel-forming ﬁbres to produce a spun gelling yarn. For example gel forming ﬁbres which are for instance modiﬁed cellulose, or carboxymethyl cellulose or alginate can be spun into yarns comprising various blends of gel-forming staple ﬁbres and textile ﬁbres. The spinning may be done by ﬁrst carding the ﬁbres in the blend and ng a yarn from the carded blend. The second is to chemically convert a cellulosic yarn to a gelling yarn either by starting with a spun cellulosic yarn or a ﬁlament cellulosic yarn.

We have found that particularly suitable yarns can be formed by rotor spinning or open end spinning. In such a process, staple gel-forming ﬁbres are blended with textile ﬁbres and carded to e a continuous web. The web is condensed to produce a card sliver and then rotor spun. In rotor spinning, a high speed centrifuge is used to collect and twist individual ﬁbres into a yarn. The yarns produced from this technique have the characteristics of a sufﬁcient tensile th to enable them to be further processed using ng or weaving machinery.

A r embodiment of the invention provides a process for making a yarn sing gel-forming ﬁbres sing the steps of: blending staple rming 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.

The ﬁbres present in the spun yarn preferably have a staple length of 30 to 60mm, more preferably 40 to 55mm and most preferably 45 to 55mm.

A yarn made according to this process need not contain textile ﬁbres ng structures to be produced which consist of gel-forming ﬁbres.

Alternatively a gelling yarn can be produced using a spun yarn consisting of natural cellulose ﬁbres or solvent spun cellulose staple ﬁbres or a blend of cellulose ﬁbres and other textile ﬁbres or by using a t yarn of solvent spun cellulose which is then converted to chemically modify the yarns to produce gelling properties. For example, Lyocell yarns can be used as a starting material and converted in a kier process to impart gel- forming behaviour to the yarn.

A preferred method of converting the yarns or fabrics is described in W0 00/01425.

For example the yarns or fabrics can be carboxymethylated by pumping a reaction ﬂuid through the reaction vessel and therefore the cellulosic materials at 65°C for 90 minutes. The reaction ﬂuid is a solution of an alkali (typically sodium hydroxide) and sodium monochloroacetate in industrial denatured alcohol. After the reaction time, the reaction is lised with acid and washed before being dried in a laboratory oven for 1 hour at 40°C.

The invention is illustrated in the following drawings in which: Figure 1 shows a graph giving yarn tensile strength data for a number ofyarns of the invention; Figure 2 shows Table 1 of Example 3 giving ﬂuid handling data for a number of yarns of the invention; Figure 3.1 shows a graph of ﬂuid management against yarn ﬁbre t for a number of yarns; Figure 3.2 shows a graph ofﬂuid retention against yarn ﬁbre content for a number of yarns; Figure 3.3 shows a graph of tensile strength against yarn ﬁbre content for a number of yarns; Figure 4 shows Table 2 of Example 3 giving tensile strength data for a number of yarns of the ion; and Figure 5 shows Table 3 which gives the helix angle and images of both dry and hydrated 2O yarns for a number of yarns of the invention.

The invention will now be illustrated by the following examples.

Example 1 - Spinning Yarn from staple gel-forming ﬁbres 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. 3O e 2 — Converting a textile yarn to a gel-forming yarn Yarns were converted in the laboratory using a mini kier. In both , staple and ﬁlament lyocell yarns were converted. The yarns used for the conversion were staple 33 Tex Tencel®; HF—2011/090; and 20 Tex t lyocell batches 1/051 (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.

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 g ﬁbres is avoided, thus reducing the number of processing steps required and damage to the ﬁbres.

Trial 1 — Yarn Wrapped Around Kier Core 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 es for speed.

This meant that the yarn was wrapped tightly around the core under tension.

The yarn Was converted by a s as described in WO 00/01425 in which carboxymethylation was carried out by g ﬂuid through the kier and therefore the cellulosic materials at 650 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.

The conversion was successful and both staple and ﬁlament gelling yarns were produced; 1/103 and HF-2011/105 respectively. Due to the tight and uneven wrapping of the staple yarn around the core, it had to be d using a scalpel which left multiple short lengths (approximately 14cm) of the converted yarn.

Trial 2 — Small Yarn Hanks The aim of the second trial was to produce longer lengths of converted yarns for testing hence a small hank was made ofeach the staple and ﬁlament lyocell yarns by hand and these were placed between layers of fabric for the conversion. 3o The yarn was ted by placing the hanks in a kier and converting to form a gel- forming ﬁbre yarn as described above for Trial 1.

The conversion was successful and both staple and ﬁlament gelling yarns were V produced; HF-2011/146 and 1/147 respectively.

Yarn Summary 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—2o11/108 Converted staple yarn (trial 1) HF—2011/1o3 Converted ﬁlament yarn (trial 1) 1/105 Converted staple yarn (trial 2) HF-2011/146 Converted ﬁlament yarn (trial 2) HF—2011/147 Non-Gelling Yarns Staple Tencel® HF—2o11/090 Filament lyocell (sample) HF—2011/051 Filament lyocell (bulk) HF—2011/125 Results from Examples 1 and 2 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; “Textiles — Yarns from packages: Determination of single-end breaking force and 2O elongation at break using constant rate of extension (CRE) tester”. A Zwick tensile testing machine was used with a gauge length of 100mm. The test uses a 100N or 2oN‘ liad cell to exert a constant rate of extension on the yarn until the ng point is reached. Wet tensile g was measured by wetting the samples with 0.2ml of solution A in the central 3 to 4cm of each yarn and leaving for 1 minute. The wetted sample was then placed in thejaws of the Zwick and clamped shut. Tensile th was tested as the yarns produced need to be strong enough to withstand the tensions and forces applied during ng, weaving and embroidery.

Tensile Strength 3o The results are sh0wn in Figure 1. All of the yarns were er when they were dry than when they were wet, with 1/108 the 70:3o gelling yarn, showing the largest proportional strength decrease.’ Of the yarns tested, HF—2011/108 was the weakest yarn both when wetand dry with tensile strengthsof 12.4 and 3.4cN/Tex tively, despite containing 30% lyocell ﬁbres. Although this was the weakest yarn, it was successfully weft knitted; HF- and woven; HF—2o11/169 into s, it is ed that all of the other yarns would also be strong enough to be converted into fabrics.

Both approaches successfully produced gelling yarns.

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

HF-2011/088 — 60%CMC 40% Tencel HF—2011/108 — 70% CMC 30% Tencel HF-2012/080 — 80% CMC 20% Tencel Fluid ng The yarns were tested for their ﬂuid handling capabilities using a modiﬁed version of TD-0187 ‘Liquid handling of dressings using direct immersion technique’. 3m ofyarn was used for each repeat and wrapped around a cylinder of 7.5cm to give a constant number of twists. s were immersed in 10ml of on A for 30 minutes before being drained for 30 seconds and their hydrated weight measured. The amount ofﬂuid retained was assessed by applying a vacuum to the sample for 1 minute and the ﬁnal sample weight measured.

Tensile Strength 3o Tensile strength of the yarn was measured using the Zwick Universal Testing Machine (UTM). s were tested using a 20N load cell with a test speed of 100mm/min and gauge of 100mm. For wet strength, yarns were hydrated with 0.1m] of solution A, prior to testing using the same machine settings.

Microscopy Yarns were visually ed using an optical microscope in a wet and dry state. The helix angle was also measured.

Fluid Handling An increased amount ofCMC content caused an increase in the retention of the yarns, as shown in Table 1 e 2) and Figure 3.1 and 3.2. There was a slight drop in absorbency when increasing the CMC content frdm 60% to 70% however the ion was improved; In order to produce a fabric that has a ative absorbency to ,Aquacel® of 0.1Bg/cm2 (2), theoretically a fabric of 256gsm should be formed from the 80% CMC yarn. In comparison Aquacel® has a weight per unit area of 119gsmm.

Tensile Strength Increased CMC content within the yarn also caused a decrease in the tensile th shown in Figure 3.3. However a satisfactory wet th 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 ofyarn in comparison to 0.21N/cm Aquacel®(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 l®(2)). HF—2012/088 and HF-20122/108 have both been d 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 ure; although some problems occurred suggesting a higher breaking strength is required for weaving.» Figures 3.3 and 4 (Table 2) show the tensile strength data.

Microscopy .

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

Twist Factor .35 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 -9... 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.

Table 4: Twist Factors most commonly usedin cotton 3) HF-2012/080 has a twist level of 580 turns/metre (given by the manufacturer). From this the twist factor can be calculated using the on 7.

= Jtex x tpm (equation 7) Where K is the twist factor (using tex count) Tex is the linear density of the yarn in tex tpm is the twist level in turns per metre.

HF—2012/080 - IQ =_'\/50 x 580 = 4101.

This 'shows that the yarn is at its optimum twist for its strength.

Claims

The claims defining the invention are as follows:

1. A yarn comprising a blend of from 50% to 100% by weight gel-forming fibres and 0% to 50% by weight textile , wherein the individual fibres are carded to form a 5 continuous web, the web drawn to produce a sliver and the sliver rotor-spun into yarn.

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

3. A yarn as d in claim 1 or claim 2 having a dry tensile strength of at least 10cN/tex. 10

4. A yarn as claimed in any one of the preceding claims 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.

5. A yarn as claimed in any one of the preceding claims wherein the gel forming fibres are modified cellulose fibres.