Composite Fibre

Abstract

A composite fibre comprising polyurethane and a particulate, wherein the particulate has mean particle diameter in the range 50 nm-100 μm. A web comprising this fibre, and the use of the web for non-slip applications or antimicrobial applications, together with a method for making the fibre.

Description

FIELD

The invention relates to a polyurethane fibre/web, in particular to composite fibres/webs of polyurethane and a particulate, together with uses and processes for manufacture.

BACKGROUND

With the advent of synthetic polymeric fibres, such as Nylon came the possibility to create a vast range of fibres, including copolymers, with different physical properties. Nonwoven fabrics made from these fibres soon became popular and are used in applications across numerous technical arenas.

The invention relates to the provision of non-slip products, for instance, but not limited to, for applications in which silicone bands are currently used. These include hosiery (hold-ups for instance), and intimate apparel (for instance brassieres and shapewear), where silicon bands are provided to prevent the garment shifting out of place during wear. For example, hold ups are only possible as a product because of the silicone band replacing the suspender belt which would otherwise retain the stocking on the leg. Further applications include sportswear (such as swimwear and strap tops) and medical clothing applications (for instance compression garments or supports, such as knee or ankle supports). However, there is a desire to improve upon the current technology as silicone bands can cause allergies in some wearers, can lack flexibility leading to discomfort, and are not easily coloured. In addition, the lack of breathability and concerns about silicone leaching can deter some consumers from wearing products including silicone bands. The invention is intended to overcome or ameliorate at least some aspects of this problem.

SUMMARY

Accordingly, in a first aspect of the invention there is provided a polyurethane and particulate composite fibre of mean particle diameter in the range 50 nm-50 μm. It has been found that adding particulates (particles) to a polyurethane fibre modifies the friction properties of the fibre, generally resulting in an increase in the frictional coefficient relative to prior art polyurethane fibres and, as a result, in a web which has good non-slip/gripping properties, even where moisture is present, such as water, perspiration or other aqueous solutions so that the skin is wet. Further the webs have excellent shape recovery properties, preventing sagging of the garment in use, and loss of fit over time. These webs are porous providing for improved comfort to the wearer because of the increased flexibility offered relative to the use of silicone bands, and the breathability. In addition, the product has been shown to be colour fast, where coloured, and there is no evidence of leaching, one reason why it is believed that the fibres cause fewer allergies than silicone technologies, and do not carry the stigma of the silicone bands in medical terms. An added advantage is that the fibres, and resulting webs, have been found to be antimicrobial, where an appropriate additive is present.

As noted above, the particulate modifies the friction co-efficient of the fibre, making it suitable for use in non-slip applications. As used herein the term “modify” is intended to mean that the friction co-efficient of the fibre is modified by at least ±1.8% relative to the value for any substrate when compared to present commercial polyurethane containing products (i.e. polyurethane without particulate matter). Typically, the friction co-efficient will be increased, for instance by at least ±1.8%, although often the modification will be far greater, for instance ±20%, or ±50% or even ±100%; often the modification will be an increase.

The particulate may be any particulate which modifies the friction coefficient of the fibre, typically to increase this. However, it can be desirable to use an antimicrobial particle, and so the particle may be selected from a metal, such as silver, copper, gold, titanium, zinc, iron, aluminium or combinations thereof. Silver will often be used to enhance the antimicrobial properties of the fibre. Alternatively, pigment particulates may be used, as these can colour the fibre in addition to modifying the friction properties thereof. Further, inorganic compounds such as silica (such as Celite), calcium phosphate (such as ivory black), ceramic or glass microparticles may be used as these are inexpensive, safe on the skin, non-toxic and have been shown to give high friction values. Polymeric particles may also be added, for instance polyethylene or cellulose acetate particles for the same reasons.

The use of silver particles in the size range 5-10 μm has been found to offer particularly high static friction coefficients, as has silver in the range 0.5-1 μm, this latter particle size being especially effective when used at low levels, such as in the range 1-3 wt % or around 2 wt %.

Often the fibre will comprise in the range 1-25 wt % particulate, often in the range 2-10 wt %. At these ranges the particulate has been found to increase the friction coefficient of the fibre and resulting web, without, it is believed, reducing overall fibre strength significantly. The range 2-10 wt % particles has been found to be particularly effective at providing a web which had good non-slip properties.

It will generally be the case that the particulate comprises particles of mean particle size in the range 50 nm-50 μm, often in the range 0.5-25 μm, in the range 0.5-10 μm or in the range 0.7-1.5 μm. Particle size is important as it is believed that this offers one of the advantages over known technologies, in that particle sizes in this range offer a web with a very fine surface topography, such that the particles can settle in the grooves of the skin, providing intimate contact, without loss of comfort. This micro-scale contact is much more effective at preventing slipping of the web across the skin than the macro-scale friction based contact provided by silicone band technologies. Similarly, it will often be the case that the particles will be in the micro- or sub-micro scale rather than the nano-scale to ensure that toxicity is avoided.

To increase the number of skin types with which the web works effectively, and to improve the grip of the web still further by offering contact with a wider range of grooves in the skin, it can be beneficial to provide a fibre in which the particulates have a multimodal, in some cases bimodal, particle size distribution.

As used herein the term “diameter” is intended to refer to the width of the fibre or particle across the largest part of its cross-section. Typically the fibre will be of mean diameter in the range 0.05-20 μm, often in the range 0.2-15 μm, or 1.5-5 μm. The diameter of the fibre can be controlled through careful selection of the manufacturing method, for instance, melt blowing processes generally produce fibres of larger diameter than electrospinning techniques. Fibres of the diameters described above have been found to offer increased contact with the skin, because of the large surface area relative to fibres of larger diameters. The provision of fibres with diameters in this range also allows for more particulate to be present at the surface of the fibre, improving the friction properties of the fibre relative to fibres of larger diameters. An advantage of these techniques is that they inherently produce fibres with a range of diameters. This allows them to interact more effectively with the skin, as the range of fibre diameters is well suited to interacting with the range of groove sizes found in the skin.

It will often be the case that a ratio of particle size to mean fibre diameter is in the range 0.05:1-2:5 This is desirable because at such ratios the friction with the skin is excellent.

In a second aspect of the invention there is provided a web comprising a plurality of fibres according to the first aspect of the invention.

In a third aspect of the invention there is provided the use of a web according to the second aspect of the invention, this use may be for non-slip applications, applications where fabric breathability is important and/or antimicrobial applications among others. For instance, the web may be used in hosiery (hold-ups for instance), and intimate apparel (for instance brassieres and shapewear). Further applications include sportswear (such as swimwear and strap tops) and medical clothing applications (for instance compression garments or supports, such as knee or ankle supports). A particular advantage of the invention is that the fibres offer their friction modification properties regardless of whether the substrate, for instance skin, is wet or dry. This makes them particularly suitable for use in swimwear and sportswear applications.

In a fourth aspect of the invention there is provided a method of making a fibre according to the first aspect of the invention, the method comprising forming the polyurethane and particulate composite fibre using a technique selected from but not limited to electrospinning or melt blowing. Often electrospinning will be used, such that the webs produced will be electrospun. Electrospinning offers the advantage that the fibre diameters are smaller than other methods, including melt-blowing. It is often the case that the fibre is sufficiently thin to interact with the grooves of the skin, working with the particulate to modify the friction co-efficient of the web. Often the method will comprise:

• • providing a 7.5-12.5 wt %, often a 9-11 wt %, or 10 wt % solution of polyurethane;
  • combining the polyurethane solution and a particulate; and applying an electrospinning technique.

These concentrations of polyurethane have been found to provide the optimal balance between fibre diameter and consistency of fibre diameter. Higher concentrations of polyurethane in the solution may produce fibres of undesirably thick diameter, reducing the surface area, surface availability of the particles and weakening the strength of the fibre matrix. Lower concentrations of polyurethane can lead to webs with uncontrolled fibre diameters along fibre lengths reducing the uniformity of the web. Where melt-blowing is used, the method will often comprise:

• • combining polyurethane and a particulate; and
  • applying a melt-blowing technique.

There is therefore provided a polyurethane and particulate hybrid fibre of mean particle diameter in the range 50 nm-50 μm wherein the particulate modifies the friction coefficient of the fibre. In the fibre, the particulate comprises 1-25 wt % of the fibre, and may be a particle selected from a pigment particulate, an inorganic compound (optionally selected from silica, calcium phosphate, ceramic or glass microparticles), a metal (optionally selected from silver, copper, gold, titanium, zinc, iron, aluminium or combinations thereof), a polymer or combinations thereof. Generally, the particulate comprises particles of mean particle size in the range 50 nm-50 μm. Alternatively, the particulate comprises particles of multimodal, in some cases, bimodal particle size distribution. Generally, the fibre will be of mean diameter in the range 0.2-20 μm, and a ratio of particle size to mean fibre diameter is in the range 0.05:1-2:5.

Unless otherwise stated each of the integers described may be used in combination with any other integer as would be understood by the person skilled in the art. Further, although all aspects of the invention preferably “comprise” the features described in relation to that aspect, it is specifically envisaged that they may “consist” or “consist essentially” of those features outlined in the claims. In addition, all terms, unless specifically defined herein, are intended to be given their commonly understood meaning in the art.

Further, in the discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, is to be construed as an implied statement that each intermediate value of said parameter, lying between the smaller and greater of the alternatives, is itself also disclosed as a possible value for the parameter.

In addition, unless otherwise stated, all numerical values appearing in this application are to be understood as being modified by the term “about”.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more readily understood, it will be described further with reference to the figures and to the specific examples hereinafter.

FIG. 1 is an SEM image of an electrospun polyurethane web (4480× magnification, mean fibre diameter 1.8 μm);

FIG. 2 is an SEM image of an electrospun polyurethane web similar to that of FIG. 1, but with the incorporation of silver particles to form a hybrid fibre (4970× magnification, mean fibre diameter 1.8 μm, particle size range 0.5-1 μm);

FIG. 3 is a graph illustrating the static friction of a range of web compositions when tested against a plain cotton sample;

FIG. 4 is a graph illustrating the static friction of a range of web compositions when tested against a cotton muslin sample;

FIGS. 5a, 5b and 5c are graphs illustrating the static friction of a range of web compositions when tested against dry pig skin;

FIG. 6a is a graph illustrating the static friction of a range of web compositions when tested against wet pig skin, FIG. 6b is a graph comparing the static friction of a range of web compositions when tested with dry and with wet pig skin (left hand graph is dry, right hand graph is wet);

FIG. 7 is a graph illustrating the static friction of web compositions comprising silver particles in selected size ranges against a pig skin sample;

FIG. 8 shows the results of antimicrobial testing for an electrospun membrane, 10% polyurethane with 10% (0.5-1 μm) silver particles membrane tested against [A] S. aureus and [B] E. coli;

FIG. 9 is a schematic showing the dimensional stability template pattern in a wash fastness test; and

FIGS. 10a-10d are graphs showing the colour fastness results of polyurethane webs with a) 10% red pigment, b) 10% violet pigment, c) 10% blue pigment and d) 10% blue pigment with Celite.

EXAMPLES

Materials

Selectophore™ polyurethane, Tecoflex™ polyurethane, dimethylformamide (DMF), silver microparticles (5.0-8.0 μm) and (2.0-3.5 μm), Celite® 545 (particle distribution=0.02-0.10 mm, median size=36 μm) were purchased from Sigma Aldrich. Tetrahydrofuran (THF) was purchased from VWR. Silver micro particles (0.7-1.3 μm) and (4.0-7.0 μm) were purchased from Alfa Aesar. The various powdered pigments were all purchased online from L. Cornelissen & Son. Plain cotton optic white 150 cm, CD12 (100% cotton) was purchased from Whaleys Bradford Ltd. Pig skin from belly pork was obtained from a local butcher (Crawshaw butchers, Leeds). Melt blown polyurethane TPU Estane 58237 was purchased from velox.com.

Preparation of Polyurethane Solutions

Polyurethane (Selectophore™, at the desired wt %) was dissolved in DMF:THF (15 ml, 60:40 (v:v)) with stirring over 24 hours. The particulate was added as defined in Table 1 below, slowly with stirring and allowed to disperse over the period of an hour.

TABLE 1
	Polyurethane	Additive 1 -	Additive 2 -
Sample label	wt %	weight/name	weight/name
Polyurethane only	10	n/a	n/a
2% Ag 0.5-1.0 μm	10	0.3 g/Ag	n/a
		0.5-1.0 μm
10% Ag 0.5-1.0 μm	10	1.5 g/Ag	n/a
		0.5-1.0 μm
10% Ag 0.7-1.3 μm	10	1.5 g/Ag	n/a
		0.7-1.3 μm
10% Ag 2.0-3.5 μm	10	1.5 g/Ag	n/a
		2.0-3.5 μm
10% Ag 5.0-8.0 μm	10	1.5 g/Ag	n/a
		5.0-8 μm
10% Ag 4.0-7.0 μm	10	1.5 g/Ag	n/a
		4.0-7.0 μm
5% Celite 0.02-	10	0.75 g/Celite 545	n/a
0.1 mm
10% Celite 0.02-	10	1.5 g/Celite 545	n/a
0.1 mm
10% Charcoal	10	1.5 g/Charcoal -	n/a
		100 mesh
10% Ivory Black	10	1.5 g/Ivory black	n/a
10% Violet only	10	1.5 g/Ultramarine	n/a
		violet
10% Blue only	10	1.5 g/Cobalt blue	n/a
10% Blue + 10%	10	1.5 g/Cobalt blue	1.5 g/
Celite 0.02-0.1 mm			Celite 545
10% Red only	10	1.5 g/Cadmium red	n/a
10% Red + 10% Ag	10	1.5 g/Cadmium red	1.5 g/
5-8 μm			Ag 5-8 μm
10% Red + 10%	10	1.5 g/Cadmium red	1.5 g/
Celite 0.02-0.1 mm			Celite 545
10% Yellow + 10%	10	1.5 g/Cadmium	1.5 g/
Celite 0.02-0.1 mm		yellow middle	Celite 545

Electrospinning General Procedure (Nanospider)

A 10 wt % solution of Selectophore™ polyurethane was prepared using a 60:40 DMF:THF solvent ratio. Selectophore™ polyurethane (1.5 g) was added to 15 ml of the solvent mixture with stirring and left to dissolve overnight. Once dissolved particle/pigment additive was then added to the solution with continuous stirring for 10 minutes (according to Table 1), the solution was then added to the 10 ml syringe and electrospun for approximately 4 hours. The aluminium foil collection plate was periodically rotated 90 degrees resulting in more uniform fibre coverage. The syringe and needles were wiped clean using tissue and then washed using acetone, followed by distilled water.

Melt-Blowing General Procedure

500 g batches of hybrid polyurethane pellets were prepared by adding 25 g (5 wt %) and 50 g (10 wt %) of silver or 50 g (10 wt %) and 100 g (20 wt %) of Celite respectively. Melt-blowing experiments were carried out using a pilot scale melt blowing machine. A 43 hole 250 μm diameter spinneret was used throughout the testing. Polyurethane webs of 75 g m⁻² (fibre diameter range 11.25-18.50 μm mean=14.69 μm) and 94 g m⁻² (fibre diameter range 6.69-14.88 μm mean=11.11 μm) were produced.

Methodology

Friction Test:

The friction coefficient was determined in accordance with European Standard EN ISO 8295:2004. Applied force (F_p) of 1.96N via an 80 g sled, and a 120 g weight for a total weight of 200 g. The speed was 100 mm/min. Sample size was 90×755 mm. The coefficient of static friction can be defined by the equation:

$\mathrm{Coefficient}\mathrm{of}\mathrm{static}\mathrm{friction}{\mu }_S=\frac{F_s}{F_p}$

Where F_p=1.96N (the normal force which comes from 200 g of weight applied to the top of the sample). F_s represents the static friction force (N) measured by the machine and is always proportional to the static friction coefficient. The static friction force arises from the interlocking of surface irregularities between the polyurethane sample and the test surface. As a force is applied horizontally to the test sample this interlocking force will increase to prevent any relative movement of the sled. This force increases until a threshold force is reached where motion of the sled begins. It is this threshold point of motion which defines the static force.

Hydration, lipid films as well as surface structure of the skin will all affect frictional behaviour when in contact with textiles. For example, moist skin has an elevated frictional coefficient and dry skin has lower frictional coefficient. Age has been seen to have little effect on the frictional coefficient of human skin, while the anatomical region the skin is located has a large influence. Regarding gender; skin viscoelasticity was found to be comparable however, the friction of female skin shows significantly higher moisture sensitivity than that of men. It should be noted that as pig skin is a natural product, test results will vary from batch to batch. Therefore, each set of comparative tests were carried out on a single sample of pig skin to ensure the validity of the test. However, absolute values of static friction would be expected to (and have been observed to) vary slightly with each pig skin sample.

Webs:

The tested webs were electrospun polyurethane with added particulates.

Antimicrobial Tests:

These followed AATCC 100. 3 mm diameter samples of the web were tested against E. Coli, (MacConkey agar plates) and S. Aureus (blood agar plates) by 24 hour incubation at 37° C. The plates were inoculated with 30 μl of 0.5 McFarland standard E. coli or S. aureus diluted in 3 ml of PBS or saline solution. Anaerobic testing used the above methods, however C. difficile was the model bacteria selected (CCEYL plates) and the incubation period was 48 hours at 37° C. in an anaerobic incubator. All tests were repeated three times.

Scanning Electron Microscopy:

The structure and morphology of the electrospun fibre mats produced were examined by scanning electron microscopy (SEM; Carl Zeiss EVO) at the Leeds Electron Microscopy and Spectroscopy (LEMAS) centre. SEM images were taken at different magnifications for all electrospun fibres for comparison.

Fibre Analysis:

Media Cybernetics Image Pro Analyser Plus was used to analyse images captured via SEM. The software was used to measure fibre diameters of samples; a minimum of 75 fibre diameters were recorded for each sample and digitised in order to obtain values for the mean, maximum and minimum fibre diameters for each sample.

Colour Fastness:

These measurements were carried out on a datacolor Spectraflash SF600 Plus-CT using a medium aperture measuring between 360 nm-700 nm, where the front face of each sample was tested a minimum of four times in different positions over the membrane to create a fair mean of the measurements across the material. K/S is a measure of the colour strength of a particular sample and can be calculated by measuring the reflection values of a material and applying these to the equation:

K/S=((1−R)²/2R)

Where R is the reflectance value at a specific wavelength, K is absorbance coefficient and S is the scattering coefficient.

Wash Fastness:

These tests were carried out on a Roaches washtec machine following the international standard—ISO 105-006:2010. A section of SDC multifibre was secured adjacent to each polyurethane sample, the multifibre used contained sections of cotton, wool, polyester, acetate, nylon and acrylic to compare the colour transfer to various fabric types. In addition simultaneous dimensional stability measurements were carried out on the samples, to establish the shrinkage potential of these electrospun membranes. Dimensional stability was used to establish a level of shrinkage occurring in the samples after washing. This was done using a template pattern to set out fixed measurement points on the unwashed piece of material (FIG. 8), then after washing these distances were remeasured and finally compared to the original.

Breathability:

Breathability tests were carried out following the BS 7209:1990 standard for 20 hours in a climate controlled laboratory (temperature 20±2° C. and relative humidity 65±5%). Test samples were placed over a weighed amount of distilled water and the water allowed to evaporate slowly (through the fabric) prior to reweighing after a set time. This calculation of water loss can be applied to the following equation which allows the relative breathability of the fabric to be assessed.

$\mathrm{WVP}=\frac{24\Delta m}{\mathrm{At}}$

WVP is the water vapour permeability (g/m²/day), Δm is the change in mass of water in grams, A is the area of the test material in m² and t equals the time in hours for the experiment.

Following this calculation for the polyurethane membranes and the polyester reference fabric the below equation is then applied to give the WVP index for each sample. The WVP index is a breathability ratio which compares the test samples to the reference fabric.

$I=\frac{{\mathrm{WVP}}_S}{{\mathrm{WVP}}_R}\times 100$

I is the water vapour permeability index of the material, WVP_s is water vapour permeability of a particular test sample whilst WVP_R is the water vapour permeability value calculated for the polyester reference fabric. The experiments were conducted over 20 hours using test dishes with a diameter of 76 mm which gives a material test area of 0.004537 m².

Example 1: Friction Test with Cotton

The friction test was applied to a medium weight cotton weave fabric (100% plain cotton optic white 150 cm CD12) as a skin substitute. It is known that for a fabric to adhere to the skin, a static force (N) of at least 2.0 and a friction coefficient (μS) of at least 1.1 be observed. The test results are shown in Table 2 below and summarised in FIG. 3.

TABLE 2
Electrospun Fibre
Composition	Static Force (N)	Friction Coefficient (μS)
Polyurethane	2.01	1.03
2 wt % silver particles of	1.97	1.01
size range 0.5-1 μm
10 wt % silver particles of	2.70	1.38
size range 0.5-1 μm
10 wt % ivory black	2.29	1.17
particles

The friction test was also applied to a cotton gauze (CX202 cotton gauze L/State 96 cm, CC28). The gauze is a lighter weight muslin style fabric in which the fibre surfaces are sized so that they are smoother. It would be expected that a lower friction be observed in these tests. The results are shown in Table 3 and FIG. 4.

TABLE 3
Electrospun Fibre
Composition	Static Force (N)	Friction Coefficient (μS)
Polyurethane	2.04	1.04
2 wt % silver particles of	2.01	1.03
size range 0.5-1 μm
10 wt % silver particles of	1.98	1.01
size range 0.5-1 μm
10 wt % silver particles of	2.04	1.04
size range 0.7-1.3 μm
10 wt % ivory black	1.99	1.02
particles

The inventive samples have good friction properties indicating utility in non-slip apparel applications.

Example 2: Friction Tests with Pig Skin

Porcine (pig) skin models are a useful tool to predict human interactions with compounds because both human and porcine skin have a spare hair coat, a thick well differentiated epidermis, a dermis that has a well-differentiated papillary body and a large content of elastic tissue, alongside similar size, distribution and communication of the dermal blood vessels. There are also immunohistochemical and biochemical similarities between to two organisms. The porcine and human skin differ in the type of sweat glands present in majority (apocrine vs. eccrine). In humans, apocrine glands are located mainly in the armpits, genital area and around the nipples, the prevalence of apocrine glands in porcine skin samples makes porcine skin an excellent model for human skin in these areas. The results of these tests are shown in Tables 4-6 and FIGS. 5a-c below:

TABLE 4
(data for graph of FIG. 5a)
Electrospun Fibre
Composition	Static Force (N)	Static Coefficient (μS)
Polyurethane	3.17	1.62
2 wt % silver particles of	3.82	1.95
size range 0.5-1 μm
10 wt % silver particles of	1.82	0.93
size range 0.5-1 μm
10 wt % silver particles of	2.18	1.11
size range 0.7-1.3 μm
10 wt % silver particles of	4.49	2.29
size range 5-8 μm
10% Celite 0.02-0.1 mm	2.88	1.47
Silicone	2.28	1.16

TABLE 5
(data for graph of FIG. 5b)
Electrospun Fibre
Composition	Static force (N)	Static coefficient (μS)
polyurethane only	4.74	2.42
10% Ag 4.0-7.0 μm	5.06	2.58
2% Celite 0.02-0.1 mm	2.25	1.15
5% Celite 0.02-0.1 mm	2.54	1.30
10% Celite 0.02-0.1 mm	2.75	1.40
10% Charcoal	2.27	1.16
10% Blue only	5.29	2.70
10% Blue + 10% Celite	3.22	1.64
0.02-0.1 mm
10% Red only	6.51	3.32
10% Red + 10% Ag 5.0-8.0 μm	5.70	2.91
10% Red + 10% Celite	3.11	1.59
0.02-0.1 mm
10% Yellow + 10% Celite	4.65	2.37
0.02-0.1 mm
Silicone	2.68	1.37

TABLE 6
(data for graph of FIG. 5c)
Electrospun Fibre
Composition	Static Force (N)	Static Coefficient (μS)
Polyurethane (Tecoflex)	4.27	2.18
Vermillion Red 1.5% wt	3.73	1.91
Ultramarine Pink 7.5% wt	4.15	2.12
Teratop Pink crude 1.5% wt	4.33	2.21
Woven PU Fibre	2.07	1.06
Silicone	3.14	1.60

In some cases, the static friction observed is significantly higher than the minimum values for skin adherence, for instance 10% silver at 5-8 μm provides an excellent static friction coefficient. Further, the FIG. 5c clearly shows that the fibres of the invention outperform both conventional silicone systems and (specifically a woven elastane, Nylon and polyurethane system in which the polyurethane is present in the warp only). polyurethane systems. This series of tests also showed that pigment particles can successfully form composite fibres, and that the pigment particles are sufficient, when used alone with polyurethane, to increase the friction properties of the web.

Example 3: Friction Tests with Wet Pig Skin

To determine the potential for the use of webs formed from the composite fibres in swim wear or other sports gear where high levels of sweat or moisture are possible, further tests were completed using wet porcine samples. The friction test method was identical to previous tests with the only modification being 1 ml of distilled water (skin area=184 cm², 0.005 ml cm⁻¹) sprayed onto skin surface before each sample run. After each sample was measured a folded tissue was laid onto the skin to remove the excess water and the method was repeated between each sample. The results are shown in Table 7 and FIG. 6a below. This data was generated from the same pig skin sample as the data for Table 4 and FIG. 5a

TABLE 7
(data for graph of FIG. 6a)
Electrospun Fibre
Composition	Static force (N)	Static coefficient (μS)
polyurethane only	4.19	2.14
2% Ag 0.5-1.0 μm	4.56	2.33
10% Ag 4.0-7.0 μm	5.60	2.86
10% Ag 5.0-8.0 μm	4.48	2.29
10% Charcoal	4.16	2.12
2% Celite 0.02-0.1 mm	4.81	2.45
5% Celite 0.02-0.1 mm	4.95	2.52
10% Celite 0.02-0.1 mm	3.75	1.92
10% Blue only	4.90	2.50
10% Blue + 10% Celite	5.09	2.60
0.02-0.1 mm
10% Red only	4.85	2.48
10% Red + 10% Ag 5.0-8.0 μm	5.17	2.64
10% Red + 10% Celite	5.11	2.61
0.02-0.1 mm
10% Yellow + 10% Celite	6.71	3.42
0.02-0.1 mm
Silicone	2.26	1.15

FIG. 6a and the table above shows that the samples in this test performed well, compared to the silicone product of the prior art (“silicone”) indicating that this material can provide higher friction in wet conditions. The main contributing factor to the good frictional resistance in wet conditions is believed to be the porous nature of the electrospun material. The water present on the skin surface is able to leach into the membrane (between the fibres) effectively removing some surface water and allowing the membrane to interact with the skin surface.

FIG. 6b shows that for the same pig skin sample, that performance in the wet is superior to that in the dry. The static friction values between all these samples are less variable than the dry tests. This supports the argument that it is the porosity of the material and not the added particles that leads predominantly to the high friction values in wet conditions. The results are shown in Table 8 below:

TABLE 8
Electrospun Fibre
Composition	Static force (N)	Static coefficient (μS)
DRY
10% Ag 5-8 μm	3.74	1.91
10% Celite	2.75	1.40
10% Blue + 10% Celite	3.22	1.64
Silicone	2.68	1.37
Woven Nylon and elastane	1.42	0.73
Retail product
WET
10% Ag 5-8 μm	4.48	2.29
10% Celite	3.75	1.91
10% Blue + 10% Celite	5.09	2.59
Silicone	2.26	1.15
Woven Nylon and elastane	1.02	0.52
Retail product

Example 4: Friction Tests with Dry Pig Skin with Multimodal Particles

To determine the effect of including multimodal particles in the webs, further tests were completed. The friction test method was identical to previous tests with the only modification being the particles selected. The samples were as shown below:

	Weight %
Sample	particle	Composition
Ag 0.7-1.3 μm	10 wt %	7 g of Ag 0.7-1.3 μm powder in 70 ml
		of PU solution
Ag 5-8 μm	10 wt %	7 g of Ag 5-8 μm powder in 70 ml of
		PU solution
Ag 635 mesh (up	10 wt %	7 g of Ag -635 mesh powder in 70 ml
to 20 μm)		of PU solution
Combination of	10 wt %	7 g total (2.33 g of Ag 0.7-1.3 μm +
above three		2.33 g of Ag 5-8 μm + 2.33 g Ag -635
particle sizes		mesh) in 70 ml of PU solution. One
		third of each particle size.

An average result was taken from three identical samples. The results of the test runs, are shown in Table 9 and FIG. 7 below.

TABLE 9
Sample                     Static Force (N)
Ag 0.7-1.3 μm              1.93
Ag 5-8 μm                  2.69
Ag 635 mesh (up to 20 μm)  2.91
Combination of three sizes 3.02

The data clearly shows that the presence of multimodal particle sizes offers a static friction at least comparable to single particle sizes, and that this can be higher compared to when a single particle size is used; although it is known that the nature of the skin sample can have a significant effect on the overall frictional value.

Example 5: Antimicrobial Properties

As shown in FIG. 8, the web has an antimicrobial effect on contact with the bacteria. There is no zone of inhibition around the web, indicating that there is no leaching of the particles from the web.

Example 6: Wash Fastness

The template pattern of FIG. 9 was used to determine dimensional stability. The results are shown in Table 10.

TABLE 10
Electrospun Fibre	% of shrinkage
Composition	MD	MD1	CD	% change in K/S
Polyurethane only	6.3	7	2.5	6.3
10% Ag 5.0-8.0 μm	5	5	0	4.0
10% Blue + Celite	5.7	6	2.5	10.4
10% Celite 0.02-0.1	1.4	2	0	1.5
mm only
10% Blue only	9.3	10	7.5	9.3
10% Violet only	21.4	22	20	21.4
10% Red only	20	21	20	20.0

These tests have revealed that no transfer of pigments to the SDC multifibre is observed for any of the samples examined. This suggests that the incorporated pigments within the electrospun membrane are stable and do not transfer readily in standard wash conditions.

Dimensional stability measurements have revealed that shrinkage occurs in all the samples tested after the first wash.

Electrospun fibrous polyurethane webs can be produced whilst simultaneously incorporating colour into the product in a single step, which provides a significant economic advantage in production relative to known multi-step methods.

It can be seen from Table 10 and FIGS. 10a-10d that the colour strength (K/S) values of five of the seven samples are seen to increase after washing and drying. Wash fastness testing of dyed products usually reveals a loss in colour from the material compared to the original sample, due to not all the dye or pigment staying fixed within the polymer matrix. Firstly this suggests that no loss of pigment is occurring from within the electrospun membranes and successfully demonstrates the one step method of spinning and colouring together. The one step manufacturing process of these coloured membranes mean that pigments can mix within the polymer solution before it has solidified. Upon solidifying into fibres the pigment molecules become “locked in” and stable, making removal only possible by melting or dissolving the polyurethane membrane. Secondly the observed increase in colour strength cannot be explained by the samples obtaining more pigment, this must arise from shrinkage.

Example 7: Water Vapour Permeability

Table 11 shows the results of the WVP testing:

	TABLE 11
	WVP (g/m2/day)	WVP Index (I)
Polyester reference material	907.76	100.00
10% Electrospun	969.57	106.81
polyurethane only
10% Electrospun PU with Ag	874.76	96.36
5.0-8.0 μm
10% Electrospun PU with	941.28	103.69
Celite 0.02-0.1 mm only
Melt blown polyurethane	992.36	109.32
only (75 g/m2)
Melt blown polyurethane	974.81	107.39
only (94 g/m2)
Melt blown 1% Ag	944.95	104.10
5.0-8.0 μm

It can be seen that the samples are at least as breathable, and generally more so, than the polyester reference sample.

It should be appreciated that the processes and apparatus of the invention are capable of being implemented in a variety of ways, only a few of which have been illustrated and described above.

Claims

1. A composite fibre comprising polyurethane and a particulate, wherein the particulate has mean particle diameter in the range 50 nm-50 μm.

2. A fibre according to claim 1, wherein the particulate modifies the friction co-efficient of the fibre.

3. A fibre according to claim 1, wherein the particulate comprises a particle selected from a pigment particulate, an inorganic compound, a metal, a polymer or combinations thereof.

4. A fibre according to claim 3, wherein the metal is selected from silver, copper, gold, titanium, zinc, iron, aluminium or combinations thereof.

5. A fibre according to claim 1, comprising in the range 0.1-25 wt % particulate.

6. A fibre according to claim 1, wherein the particulate comprises particles of mean particle size in the range 0.05-10 μm.

7. A fibre according to claim 1, wherein the particulate comprises particles of multimodal particle size distribution.

8. A fibre according to claim 1, of mean diameter in the range 0.1-20 μm.

9. A fibre according to claim 1, wherein a ratio of particle size to mean fibre diameter is in the range 0.05:1-2:5.

10. A web comprising a plurality of fibres according to claim 1.

11. A web according to claim 10, wherein the particulate is a pigment particulate.

12. A method, comprising:

using a web according to claim 10, for non-slip applications.

13. A method, comprising:

using a web according to claim 12 for non-slip applications in the presence of water.

14. A method, comprising:

using a web according to claim 4, for antimicrobial applications.

15. A method of making a fibre according to claim 1, comprising forming the polyurethane and particulate composite fibre using a technique selected from electrospinning or melt blowing.