Anti-Microbial Fibres and Their Production

FIELD OF THE INVENTION

The present invention relates to anti-microbial lyocell fibres which can impart qualities of freshness and hygiene to fabrics made from the fibres. It also relates to a process for making such fibres.

BACKGROUND ART

There is an increasing interest in fabrics offering qualities of improved hygiene and freshness, for example for use as clothing, and also in fabrics having better protection from deterioration caused by microbes.

One way of achieving this is to apply anti-microbial agents to the fabric, for example as a finishing treatment. Another way, offering greater commercial flexibility, is to provide fibres that are already anti-microbial, by virtue of having an anti-microbial agent applied to or incorporated into the fibres.

Many organic anti-microbial agents have been used or proposed for use on fibres, including triclosan, biguanides, phenols and derivatives, isothiazolones, quaternary ammonium salts, tri-butyl tin oxide, haloamines and alcohols. The most widely used of these is triclosan, which has been used as a fibre finish and fabric finish for both natural and man-made fibres and has also been incorporated into man-made fibres such as regenerated cellulose fibres and acrylic fibres by inclusion in the spinning dope. Inorganic anti-microbial agents have also been used, and these are predominantly compounds in which a metal ion such as silver is supported on an inert matrix. An example of such an agent is silver zeolite.

Lyocell fibres are produced by extrusion of a solution of cellulose through a spinning jet into a coagulation bath by a process known as solvent spinning. They are therefore alternatively known as solvent-spun cellulose fibres. Such a process is described in U.S. Pat. No. 4,246,221 and uses as the solvent an aqueous tertiary amine N-oxide, particularly N-methylmorpholine N-oxide. Lyocell fibres are distinguished from regenerated cellulose fibres, such as viscose fibres, which are produced by forming the cellulose into a soluble chemical derivative and then extruding a solution of this derivative into a bath, which regenerates the extrudate as cellulose fibres.

Unfortunately, many of the anti-microbial agents that can be incorporated into other man-made fibres are incompatible with the amine oxide spinning system used to make lyocell fibres. For example, triclosan is too easily washed out of the fibres during processing. Also, some silver ion complexes are deactivated by amine oxide solvents and yield a brown or yellow colouration on the fibres that is not acceptable. A process using silver ion complexes in cellulose fibres, including viscose rayon fibres and organic solvent-spun cellulose fibres, is described in JP-A-6-235116. The process described has not become commercial possibly because of compatibility problems and colour problems with the spinning systems. Another process of this type is described in EP-A-0 905 289 and involves adding to a solution of cellulose in an amine oxide solvent a slurry of a silver-based anti-bacterial agent and a magnetised mineral ore powder. The selected silver-based anti-bacterial agents include silver zeolites, silver zirconium phosphates and silver calcium phosphates. These silver compounds produce unacceptable colour staining on the fibres.

Another concern with introducing silver compounds into the system for making lyocell fibres arises from the fact that, in addition to the amine oxide solvent itself, the spinning solution and its precursor components in practice also incorporate a stabiliser, particularly propyl gallate. The purpose of this stabiliser is to sequester free radicals, particularly metal ions, which can catalyse exothermic reactions in the system, leading to uncontrolled explosions. Use of such a stabiliser is, therefore, believed to be universal in practice. The concern with adding silver compounds is twofold: firstly, that the stabiliser will sequester the silver, deplete it as residual anti-microbial agent and cause staining, and, secondly, that the silver compound will use up the stabiliser and leave insufficient in the system to protect against exothermic reactions.

WO 03/018166 and WO 2004/022822 also relate to cellulosic materials which may contain silver.

Anti-microbial compositions disclosed and claimed in EP-A-0251783, the contents of which are hereby incorporated into this specification, comprise an anti-microbial silver compound deposited on a support comprising a physiologically inert oxidic synthetic material in particulate form and having an extended surface area. These compositions were developed by the proprietor of that patent, Johnson Matthey plc, for incorporation into coating or impregnating formulations for medical or other appliances or for topical application to bandages and dressings. The present invention is concerned with the use of anti-microbial compositions of this type.

DISCLOSURE OF THE INVENTION

The present invention provides anti-microbial lyocell fibres incorporating an anti-microbial composition which includes a silver compound held on a support material, characterized in that the anti-microbial composition comprises a silver compound deposited on a support material in the form of porous particles having an extended surface area and comprising an oxidic material which is essentially insoluble in water and incapable of forming hydrates.

The support material, in the form of the porous particles, is oxidic and may comprise an oxide or a hydroxide or a complex oxy-anion species such as phosphate or sulphate. It is essentially insoluble in water and also stable in water, in the sense of being incapable of forming a hydrate but being able to adsorb water to form an associated aqueous species.

Oxidic materials which may be used for the support material, used in the form of porous particles, include oxides of titanium, magnesium, aluminium, silicon, cerium, zirconium, hafnium, niobium and tantalum, calcium hydroxyapatite (a phosphate), and barium sulphate, all to the extent of being insoluble and stable in water as specified. Titanium dioxide is a preferred oxidic support material and is stable to water in its anatase, rutfle and brookite crystalline forms; hydrated or hydratable oxides of titanium are not suitable for use in this invention.

The particle size of the porous particles which comprise the oxidic support material is preferably as small as possible commensurate with achieving the desired anti-microbial effect Preferably, the average particle diameter is less than about 25 microns and more preferably it is in the range 0.5 to 10 microns. The particles may have a highly open structure, for example generally spherical clusters of crystallites having a large physical voidage. The surface area of the particles may extend from about 1 or 2 square metres per gram up to about 240 square metres per gram or more, but it is preferably in the range 5 to 100 square metres per gram.

The silver compound deposited on the porous particles which comprise the oxidic support material is preferably one which has a low solubility in water and aqueous media, for example a solubility below 0.01 gram per litre of water at 20° C., and in which the silver is present as an ionic species. It may be present at a level of about 1 to about 75 percent by weight of the oxidic support material, preferably 10 to 60 percent by weight. A preferred silver compound is silver chloride. Silver phosphate is also suitable.

A preferred anti-microbial composition comprises silver chloride deposited on titanium dioxide particles, with appropriate concentrations of the silver chloride being, for example, about 15 to about 25 percent, such as about 15 percent, about 20 percent or about 25 percent, by weight based on the weight of the titanium dioxide particles.

The silver compound may be deposited on the porous support particles by controlled nucleation and growth so that the silver compound is largely contained within the pores of the particles and the particle size distribution is maintained by avoiding any coalescence.

The anti-microbial composition may be used in relatively low concentrations in the lyocell fibres of the invention and still produce effective anti-microbial properties. For example, with a composition comprising about 20 percent by weight of silver chloride deposited on titanium dioxide particles, we have found that effective and durable anti-microbial properties are obtainable with concentrations of the anti-microbial composition in the fibres below about 1 per cent by weight owc (on weight of cellulose). In that circumstance, there is no benefit in using higher concentrations as this would merely increase the cost and, depending on the level used, diminish the physical properties of the fibres. Indeed, much lower concentrations of that particular anti-microbial composition have been used satisfactorily, and it is preferred to use a level of concentration below about 0.1 percent by weight owc. For example, good results have been achieved using a concentration of 0.0125 percent by weight owc, which is a remarkably low concentration.

The fibres can, in addition to the silver-containing anti-microbial composition, contain a matting agent, for example Ti 0₂, to produce fibres which are dull or matt. Matting agent concentrations of from 0.5 to 2.5 percent by weight Ti 0₂ or equivalent can be used. Such agents are especially useful for non-woven products.

The silver-containing fibres of the invention may be used in textiles for hospital use (e.g. bedding, towels, gowns, uniforms), socks and underwear, military textiles (combat suits), sportswear, interlinings for garments and home textiles (mattresses and upholstery), fibre fill for duvets pillows outdoor jackets and ski suits, blankets towels and towelling, carpets and mats, and conveyor belts for frozen food, and for non-wovens such as wound dressings (cosmetic pads, filters, wet wipes, wipes, baby wipes, medical devices, incontinence products, water filters, plaster cast linings, interlinings, roller towels, shoe linings, dry wipes and floor tiles.

The lyocell fibres may be carboxymethylated, partially or even completely.

The lyocell fibres of the invention possess excellent anti-microbial properties, and these properties are durable to conventional scouring, washing and dyeing procedures for lyocell fibres and fabrics. The fibres retain their usual good mechanical properties and are not spoiled by colour staining or by permanent yellowing or greying. To the extent that there is a slight fall in whiteness of the fibres, this is only temporary and is removed by the normal washing and scouring processes to which the fibres are subjected in manufacture.

Considering the previous experience with trying to use silver-based anti-microbial compositions in lyocell fibre manufacture, the properties of the lyocell fibres of the invention are both excellent and unpredicted.

The invention includes a process for making anti-microbial lyocell fibres in which cellulose is dissolved in a solvent of aqueous amine oxide to form a spinning solution which is extruded through a spinning jet into a coagulation bath to produce lyocell fibres, and an anti-microbial composition is incorporated into the fibres, characterized in that the anti-microbial composition is added to the fibre spinning solution or to a precursor or ingredient of that solution and comprises a silver compound deposited on a support material in the form of porous particles having an extended surface area and comprising an oxidic material which is essentially insoluble in water and incapable of forming hydrates.

The anti-microbial composition may be added to the spinning solution or to an ingredient of that solution, for example the amine oxide solvent. However, it is preferably added to a precursor of the cellulose solution comprising a pasty pre-mix of the cellulose pulp and the amine oxide solvent. One method of forming the solution of cellulose in an amine oxide solvent such as tertiary amine N-oxide, for example N-methylmorpholine N-oxide, is to form a pre-mix of cellulose and aqueous amine oxide solvent incorporating an excess of water over the optimum required for solution to take place. The pre-mix, which is a paste or dough, is then subjected to an evaporation process, for example in a thin-film evaporator, to remove the excess water and form a solution of the cellulose. The anti-microbial composition, which has been added to the pre-mix, is effectively dispersed throughout this resulting cellulose solution.

In this preferred solution process, the anti-microbial composition may be added to the pre-mix itself or to an ingredient of the pre-mix, preferably the former.

The anti-microbial composition may be added in the form of a dispersion in a liquid, for example in water, or in dry powder form. It may be added to the vessel in which the pre-mix is made but, preferably, is added to the pre-mix in the hopper feeding the pre-mix to the thin film evaporator which forms the spinning solution. Addition may be made using injection equipment such as is used to add matting agents such as titanium dioxide. In fact, the anti-microbial composition and the matting grade of titanium dioxide may be added together.

The process of the invention may be carried out without any significant processing problems. The sequestering stabiliser, which is preferably propyl gallate, appears to remove insignificant amounts of the silver compound from the anti-microbial composition. The oxidic support material appears to stabilise the silver compound against the activity of the propyl gallate during the manufacturing process. The corollary of this is that the propyl gallate does not become excessively used up by reacting with the silver compound and instead remains in the system to scavenge radicals which could otherwise trigger explosive exothermic reactions. Propyl gallate does not leave the spinning system with the fibres and so cannot affect the anti-microbial composition once it is incorporated into the fibres.

There may be a slight fall in whiteness of the spun fibres compared with standard lyocell fibres, but this is only temporary. Normal standards of whiteness are restored by the usual washing and scouring steps to which the spun lyocell fibres are subjected. It is thought that any colour present is a complex formed between a chromophore of degraded amine oxide together with the propyl gallate and the silver compound. This complex does not appear to become bound to the cellulose of the lyocell fibres.

The invention is illustrated by the following Examples:

EXAMPLES 1 & 2

The anti-microbial composition used for the purposes of both of these Examples was a product, JMAC-PG, supplied by AddMaster (UK) Ltd. and comprised a dry powder of porous titanium dioxide particles on which 20 percent by weight of silver chloride had been deposited. The particle diameters were in the range 0.5 to 2 microns, with the majority of particles being sub-micron in diameter.

The fibre-making process was based on a commercial process for making lyocell fibres of 1.4 dtex by spinning a solution of cellulose in a solvent of aqueous N-methylmorpholine N-oxide through a spinning jet into an aqueous coagulating bath to form fibres.

The spinning solution was made by a process in which cellulose pulp and the solvent of aqueous N-methylmorpholine N-oxide were fed into a mixing vessel and mixed to form a paste or dough, known as the pre-mix. The solvent contained excess water over the optimum required for the cellulose to go into solution, in order to promote efficient wetting and mixing of the cellulose with the solvent. This excess water was then evaporated from the pasty pre-mix by passing the pre-mix through a type of thin-film evaporator called a Filmtruder (trademark of BUSS AG) to form the spinning solution.

The JMAC powder was dispersed in water and added as a dispersion to the pre-mix at the hopper feeding the pre-mix into the Filmtruder. Two different concentrations of JMAC were used in two different production runs. The first (Example 1) was a concentration of 125 ppm (parts per million) by weight owc, which is 0.0125 percent by weight owc. The second (Example 2) was a concentration of 250 ppm by weight owc, which is 0.0250 percent by weight owc.

The JMAC anti-microbial composition was evenly distributed in the spinning solution formed by the Filmtruder and so was evenly distributed in the spun lyocell fibres. The JMAC composition did not adversely affect the process of making the spinning solution or of spinning the fibres, and it was not itself adversely affected by these processes.

The fibres were tested for physical properties and found to have properties generally in line with a Control fibre, which was a standard Tencel lyocell fibre of 1.4 dtex. (Tencel is a registered trademark of Lenzing Fibers Limited.)

The results of the physical property measurements are shown below in Table 1:

TABLE 1

Example 1

Example 2

Control

(125 ppm

(250 ppm

Sample

Fibre

JMAC)

JMAC)

Dry breaking tenacity (cN/tex)

33.1

34.0

36.3

Dry breaking extension (%)

11.3

11.8

11.8

Dry initial modulus

1250

1272

1440

Knot breaking tenacity (cN/tex)

22.4

20.2

21.1

Knot extension at peak (%)

14.9

10.3

11.8

Loop breaking tenacity (halved)

13.9

13.9

12.1

(cN/tex)

Loop extension at peak (%)

2.8

2.6

1.8

Samples of spun yarns of count 20 Tex were made from the respective fibres of Examples 1 and 2 and of the Control, the fibres having been cut to 38 mm staple length. These yarns were used to weave respective greige fabrics in an interlock construction, each of basis weight 200 gms per square metre.

A portion of each of the fabrics made from the respective fibres of the Examples and of the Control was given a scour in an aqueous scour bath containing 2 g/l (gms per litre) of soda ash and 2 g/l Zetex HPLFN for 30 minutes at a temperature of 70° C.

The scoured fabrics produced from the fibres of Examples 1 & 2 were tested for colour whiteness against the scoured Control fabric produced from the standard lyocell Control fibres. Testing was carried out using a Minolta Spectrophotometer CM-3300d and produced a CIE (Commission Internationale d'Eclairage) whiteness index of 70.7 for the fabric of Example 1 and a CIE whiteness index of 67.1 for the fabric of Example 2, as against a CIE whiteness index of 73.7 for the Control fabric. This shows that the anti-microbial composition JMAC has no significant effect on fibre colour, particularly at the lower concentration of 125 ppm used in Example 1.

The fabrics were re-tested after controlled exposure to a xenon lamp, which mimicked 4 weeks' outdoor natural light exposure, and, again, there was little difference in colour between the fabrics.

Anti-microbial testing of the fibres of Examples 1 & 2 was carried out using two different tests:

Qualitative Agar Plate Test (Swiss SNV 195-920)

This is a quick test to determine the anti-microbial activity of leaching anti-microbial agents on a sample of fibre. Evaluation is based upon the presence or absence of bacterial growth beneath and surrounding the sample (inhibition zone). Non-leaching anti-microbial agents show no zones of inhibition and weak bacterial growth beneath the samples.

This test was carried out using a Staphylococcus aureus bacterium.

The results showed that each of the fibre samples of Examples 1 & 2 produced no zones of inhibition and weak bacterial growth beneath the samples, which confirmed the anti-microbial composition JMAC as being of the non-leaching type. This is the preferred type of agent for anti-microbial fibres because one is looking for a prolonged effect in which the agent acts at the fibre boundary but does not leach beyond it, for example onto skin adjacent to clothing.

Quantitative Dynamic Shake Flask Test (ASTM E2149-01)

This is a test of the American Society for Testing and Materials, which measure the anti-microbial activity of both leaching and non-leaching anti-microbial materials under dynamic contact conditions.

Evaluation is based upon the calculated percentage reduction in bacteria from counts taken at various times and expressed as calculated percentage reduction and also as log reduction versus a no-sample control.

The fibres of each of Examples 1 & 2 were tested alongside Control fibres, and also against a control in which no fibres were used, i.e. a no-sample control. Three different bacteria were tested: the Staphylococcus aureus bacterium; the Klebsiella pneumoniae bacterium; and the methicillin-resistant Staphylococcus aureus bacterium (MRSA).

Samples of the respective fibres were also tested after being given one or more of the following treatments:

• • 1. A scour in an aqueous scour bath containing 2 g/l of soda ash and 2 g/l Zetex HPLFN for 30 minutes at a temperature of 70° C.
  • 2. Dyeing in an aqueous dyebath for 60 minutes at a temperature of 80° C., the dyebath containing Procion Marine Blue H-EXL, a reactive dye, at 2 percent by weight on weight of fabric and soda ash at 20 g/l, followed by soaping off the dyed fabric.
  • 3. A detergent wash in a washing machine for 120 minutes at a water temperature of 60° C. using Persil Original Non-Biological Automatic washing powder and Comfort fabric conditioner, followed by tumble drying. (Persil and Comfort are trademarks of Lever Faberge Limited).

The results for the dynamic shake flask tests on these fibres after 24 hours are shown in the following Table 2.

TABLE 2

Staphylococcus

Klebsiella

aureus

pneumoniae

MRSA

Log

Log

Log

%

Reduc-

%

Reduc-

%

Reduc-

Sample

Kill

tion

Kill

tion

Kill

tion

Control

68.4

0.50

98.4

1.80

99.94

3.24

(scoured

lyocell fibres)

Example 1

99.94

3.24

99.99

4.25

99.999

5.15

Example 2

99.94

3.24

99.99

4.25

99.999

5.15

Example 1

99.93

3.20

99.99

4.20

99.999

5.15

(scoured)

Example 2

99.93

3.20

99.99

4.20

99.999

5.15

(scoured)

Example 1

99.94

3.24

99.47

2.27

99.999

5.15

(scoured &

dyed)

Example 2

99.94

3.24

99.99

4.25

99.999

5.15

(scoured &

dyed)

Example 1

99.94

3.24

99.99

4.25

99.994

4.22

(scoured,

dyed &

washed)

Example 2

99.94

3.24

99.98

3.75

99.999

5.15

(scoured,

dyed &

washed)

The results shown in Table 2 confirm strong anti-microbial activity against all three species of bacterium for the fibres of both Examples 1 and 2. Furthermore, as shown, this strong activity is sustained after the scouring, dyeing and detergent washing treatments given and is considered durable. The anti-microbial results obtained for the fibres of Example 2 are, generally, no better than those obtained for the fibres of Example 1. Therefore, considerations of the better whiteness obtained with the fibres of Example 1 and the lower cost of using half the concentration of the JMAC anti-microbial composition, compared with the fibres of Example 2, indicate that a concentration of 125 ppm by weight owc of the JMAC composition is to be preferred to higher amounts.