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Title:
NON-FIBRILLATING FLAME RESISTANT CELLULOSIC FABRIC, ITS USE AND METHOD FOR PRODUCING THE SAME
Document Type and Number:
WIPO Patent Application WO/2014/100842
Kind Code:
A1
Abstract:
This invention relates to a flame resistant fabric made from or including FR lyocell produced by resin finishing the fabric characterized by a resin content on the FR lyocell fibres which is higher than obtainable by known resination methods.

Inventors:
BISJAK CLEMENS (AT)
TAYLOR JAMES MARTIN (GB)
CRNOJA-COSIC MARINA (AT)
BURROW THOMAS RICHARD (GB)
MALINOWSKY ROBERT (AT)
MATHES ULF (AT)
BAUMGARTINGER CHRISTIAN (AT)
Application Number:
PCT/AT2013/000193
Publication Date:
July 03, 2014
Filing Date:
November 19, 2013
Export Citation:
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Assignee:
CHEMIEFASER LENZING AG (AT)
International Classes:
A41D31/00; A47C31/00; C09K21/00; D06M15/423; D06N3/00
Domestic Patent References:
WO2011137470A12011-11-10
WO2002059416A22002-08-01
WO1995000697A11995-01-05
Foreign References:
GB2322142A1998-08-19
EP2278063A12011-01-26
US6491727B12002-12-10
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Claims:
Claims

1 . A flame resistant fabric made from or including FR lyocell fibres

produced by resin finishing the fabric characterized by a resin content on the FR lyoceil fibres of at least 1 .5 weight-% of resin based on the cellulose content.

2. A flame resistant fabric according to claim 1 where the fabric is a woven fabric.

3. A flame resistant fabric according to claim 1 where the fabric is a knitted fabric produced by any method including flat bed knits, circular knitting , warp knitting or any other method of knitting .

4. A flame resistant fabric according to claim 1 where the fabric is a

nonwoven fabric produced by any method including air laying , wet laying , spun laying , needling of a carded or air laid web,

hydroentanglement or any other method of producing a nonwoven fabric. 5. A flame resistant fabric according to claim 1 in which the FR lyocell fibres are blended with one or more other textile fibres chosen from the group containing meta-aramid , para aramid, modacrylic, PBI , cotton, wool, silk, linen , FR modal, FR viscose, non-FR lyocell , modal, viscose, nylon , acrylic and polyester,

6, A method for resin finishing a flame resistant fabric made from or

including FR lyocell fibres, characterized by rinsing the fabric with an acid bath prior to resin finishing .

7. A method according to claim 6 where the acid bath is 0.1 g/l to 2.0 g/l of acetic acid in water.

8. A method for resin finishing a flame resistant fabric made from or

including FR lyocell fibres, characterized by increasing the concentration of catalyst in the applied resin solution to 1 .2 to 5 times the normally used level recommended by the resin manufacturer.

9. A method according to claim 8 where the catalyst is magnesium chloride hexahydrate at a concentration of 1 5 to 50 g/l.

10, A method for resin finishing a flame resistant fabric made from or

including FR lyocell fibres, characterized by adding an acid buffering component to the resin bath applied to the fabric.

1 . A method according to claim 10 where the acid buffering component is citric acid and the pH of the resultant dried, uncured fabric is less than 6.2. Use of the fabric according to claim 1 to 1 1 for the manufacture of

articles which may be accidentally exposed to flame or other source of ignition such as garments worn where accidental exposure to flames or other sources of ignition is a possibility such as jackets, coats, trousers, boilersuits, coveralls, shirts, sweaters and jumpers, sweatshirts, T-shirts, children's nightwear. adults nig htwear, socks, aprons, gloves and gauntlets, hoods for head protection other headwear and any other garment that may be worn when accidental exposure to flame or other source of ig nition is a possibility as well as shoe and boot components, welding screens, fire curtains, tents, upholstery, home furnishings including curtains, sleeping bags, tarpaulins, filters, interlinings, coating substrates, wipes, cleaning cloths, disposable or short-life clothing, padd ing and barrier layers for upholstered furniture and any other similar articles made in whole or in part from fabric.

Description:
Non-fibrillating flame resistant cellulosic fabric, its use and method for

producing the same

This invention relates to a flame resistant fabric made from or including FR lyocell fibre produced by resin finishing the fabric characterized by a resin content on the FR lyocell fibres which is higher than obtainable by known resination methods.

Prior Art

Textile materials vary considerably in their ability to resist flame and hence protect underlying materials. Most fabrics made from natural fibres and from synthetic fibres will burn when exposed to flame. The rate of burn and ease of ignition are determined primarily by the chemical nature of the polymer from which the fibre is made and the construction of the fabric, Many polymers, such as cellulose, polyester and nylon will burn readily. The rate of burn is lower the heavier a fabric is. Wool is the most common natural fibre which has flame resistant properties to some degree - heavy weight wool fabrics will not burn readily and have long been used in firefighter's clothing.

Fabrics can be treated to make them flame resistant by applying an

appropriate chemical to the fabric. The first FR treated fabrics used inorganic salts such as aluminium hydroxide, antimony trioxide and borates to make cotton fabrics flame resistant, These were effective but were non-durable to washing.

Organic phosphorous containing compounds that are reacted onto the cotton either by grafting or network formation are more durable and are widely used . Two of the leading brand names are Proban® and Pyrovatex®. While these finishes are durable, they can be removed by harsh chemical treatments and the level of finish reduces with the number of washing cycles. The finish application has an adverse stiffening effect on the fabric. Flame retardant finished cotton fabrics are in use for a wide variety of applications where it is required that the fabric does not ignite. When exposed to flame, fabrics of this type will not burn , but char and become highly embrittled and may break open leaving the wearer's skin or other underlying materials exposed to the hazard.

The first flame resistant cellulosic man made fibres produced were made by the viscose process. A hig h viscosity liquid flame resistant additive was dispersed in the spinning solution prior to extrusion of the fibre. The liquid was trapped in the cellulose by physical means as very small bubbles. The result was effective as a flame resistant fibre, but the additive could be removed by repeated washing. The strength of the fibre was reduced in proportion to the amount of additive included , The additive was withdrawn from the market due to safety concerns and production of the fibre was discontinued.

An improved flame resistant viscose fibre can be produced by using a solid pigment flame retardant. Fibre of this type will be referred to as FR viscose. The pigment is finely ground and mixed with the spinning solution prior to extrusion of the fibre. The result is a d ispersion of the insoluble particulate additive in the fibre. The strength of the fibre is reduced in proportion to the amount of additive included . All of the cellulose in the fibre contains some of the add itive and the additive cannot be removed by washing or normal fabric dyeing or finishing processes. Hence the result of the process is an inherently flame resistant fibre, A well-known fibre of this kind is Visil®, which contains silica pigment flame retardant,

A further improvement can be achieved by incorporating the solid pigment flame retardant in the spinning solution used to produce modal fibre, The modal process is a modified viscose process designed to produce a fibre with a higher strength and higher wet modulus than normal viscose. The resultant fibre containing the flame retardant pigment is inherently flame resistant, It is stronger than fibre produced by the viscose process and gives fabrics with higher strength and better stability, Fibre of this type will be referred to as FR Modal but note that the properties of the fibre do not conform to the BISFA definition of modal fibre. Proven flame retardant pigments for this kind of fibres are organic phosphorous compounds and a preferred pigment is Exolit® (2'- oxybis[5,5-dimethyl-1 ,3,2-dioxaphosphorinan]2,2'disulphide). FR Modal is normally used in blend with other flame resistant fibres to produce fabrics which have a combination of the properties of the fibres in terms of strength and physical performance, aesthetics, comfort and physiological effects on the wearer. FR Modal is only rarely used in 100% form in a few applications in the field of apparel such as metallised fabrics or fabrics which are mixtures of two or more yarns. On its own its performance is inadequate in a number of respects compared to other products.

The most recently introduced manmade cellulosic fibre is lyocell. It is produced by a solvent spinning process. The solvent is an amine oxide, which is non-toxic. A slurry of cellulose in a mixture of amine oxide and water is prepared . Water is removed from the slurry by evaporation and as the water content decreases, the cellulose dissolves in the amine oxide producing a solution which is a viscous liquid above 80°C. The solution is extruded through spinneret holes into a water bath . The solvent is diluted by the water and the cellulose precipitates to form a fibre. In the remainder of the process, the fibre is washed to remove any amine oxide solvent, cut into staple fibre, finished with a lubricant and antistatic agent and then dried .

The amine oxide solvent is recycled in a closed loop in the factory. Recovery rates of greater than 99.5% are achieved. Recycling of the additive means that the effect of the process on the environment is very low. It is also essential for the economics of the process.

Lyocell is much stronger than viscose and is stronger than cotton in both the wet and the dry state. It is used in apparel, home furnishings, workwear and nonwovens. Over 90% of the world's lyocell production is produced by Lenzing AG and branded TENCEL®.

The superior properties of lyocell make it possible to produce a version which contains an incorporated flame retardant and which will have superior properties compared to FR viscose and FR Modal. This version will be named FR lyocell for the purposes of this invention. FR lyocell will be capable of producing blend fabrics with superior properties to current fabrics and will also be capable of producing 100% FR lyocell fabrics with enhanced comfort and physiological effects compared to existing fabrics, FR lyocell is the subject of patent application WO 2012/083318.

FR lyocell fibres as described in WO 2012/083318 are made using a flame retardant which is a solid condensate prepared from the reactants used in the Proban process. The condensate is finely ground to particles of about 1 micrometer and then mixed into the viscous liquid solution used to produce the lyocell fibre during its preparation. In the dried finished fibre, each particle of the flame retardant is completely surrounded by cellulose. Under normal textile processing and use, it cannot be removed from the fibre because it is insoluble and entrapped within the fibre.

It is well known to those in the textile business who have produced fabrics from lyocell that it is necessary to take action during its processing to prevent or control fibrillation of the fibre at the surface of the fabric. Fibrillation is a phenomenon where the individual fibres at the surface of a fabric split to form fibrils which are parallel to the axis of the fibre and usually attached to the fibre at one end . Fibrillation is usually caused by wet abrasion of the surface of the fabric and of fibres protruding from the surface of the fabric during textile processing or in laundering of the fabric. Fibrillation at the surface of the fabric is due to abrasion of fibres at the most exposed points on the fabric. This creates a break in the cellulose crystallites in the fibre at or just below the surface. Further abrasion peels fibrils of cellulose away from the body of the fibre which remain attached to the fibre at one of the fibril's ends. Fibrillation of fibre protruding from the surface of the fabric is caused by mechanical action and abrasion causing the free end of the fibre to split into fibrils. Typically a lyocell fibre has a diameter of 1 2 micrometers. Fibrils which are created by the process described are typically 1 micrometers diameter. Due to the large increase in surface area when fibrillation occurs, there is an increase in the amount of spectral reflection from the surface of the fabric wherever fibrillation is present. The fabric appears whiter; colours are muted . Often the fabric surface has a variable appearance depending on the degree of mechanical action each region has received. Where the fabric is creased during processing the amount of fibrillation will be enhanced giving white lines on the surface of the fabric.

Fibrillation can be a desirable effect in apparel textiles provided it is done under controlled conditions and is stabilised before the fabric is used. It can be used to create a peach touch on the fabric. I n this case the fibres protruding from the surface of the fabric are removed either before fibrillation occurs or during the process. There are several methods by which these protruding surface fibres may be removed including singeing of the fabric, enzyme treatment of the fabric using a cellulase enzyme and embrittlement of the surface fibres by chemical treatment followed by mechanical action.

However, in many applications a clean fabric surface is highly desirable. This can be achieved in a lyocell fabric by cross-linking the cellulose in the fibre. Cross-linking increases the bonding between cellulose molecules in the fibre and prevents fibrils from forming by the peeling effect described above even if the surface of the fibre has been damaged by wet abrasion. Cross-linking can be done during fibre manufacture or may be done by resin finishing of the fabric. Some reactive dyestuffs have multiple functionality and can therefore cross-link the cellulose molecules and hence prevent fibrillation when they are used to dye the fabric. Examples of lyocell fibres which are cross-linked during manufacture are

Tencel A1 00® and Tencel LF® both produced by Lenzing AG. An example of a cross-linking resin designed for use on fabric is dimethylol

dihydroxyethyleneurea which is sold as, for example, Fixapret CPL produced by BASF AG. A cross-linking resin is applied to a fabric as a precondensate mixed with a catalyst and softeners. In one well known process, the dry cure process, the fabric is dried and then heated to about 1 80°C and the precondensate reacts with the cellulose molecules in the fibre. Each molecule of the precondensate combines with more than one reaction site on the cellulose molecules and as a result forms a bridge between adjacent cellulose molecules. The reaction is initiated and accelerated by the presence of the acid catalyst. Curing times are typically 30 to 60 seconds.

The fibres in a correctly cross-linked fabric will not fibrillate. The surface of the fibres and the fabric will remain free from fibrils. The fabric will not display any whitening of the surface or muting of colours. It will have a smooth clean, touch with none of the peach touch described above. Fabrics used for protective clothing and similar applications normally are expected to have these characteristics.

There are many different methods of reacting a cross-linking resin onto a cellulosic fabric which vary in the temperature and times required, the amount of resin applied to the fabric, the type and quantity of catalyst used and the softeners used . I n one process, the moist cure process, after application of the precondensate mixture to the fabric, the fabric is not dried and is allowed to cure at ambient temperature for 24 hours or more. Attempts to cross-link an FR lyocell fabric by using the conventional methods of application and curing of a resin, in order to prevent fibrillation during processing and laundering , failed. The surface of the fabric became pilled and whitened. White lines were present on the surface. Microscopic examination showed that the fabric surface had extensive fibrillation which varied from region to region. The fibrillation increased when the fabric was laundered .

Problem

If FR lyocell fibre is to be used in protective clothing and similar applications where fabric made from the fibre is used to make garments that are laundered then it is essential to identify a route that will make it possible to prevent or control the formation of fibrillation at the surface of the fabric.

Description It is an object of the present invention to provide a non-fibrillating FR lyocell fibre suitable for use in fabrics for protective clothing and similar applications and which are washable in industrial laundries with excellent resistance to highly aggressive laundry conditions and a process for producing it. This flame resistant fabric made from or including FR lyocell produced by resin finishing the fabric is characterized by a resin content on the FR Lyocell fibres of at least 1 .5 weight-% of resin based on the cellulose content. Fabrics of this type will have wider utility in areas such as upholstery, home furnishings, child rens nightwear and any other area where protection of the user of the fabric or of property from exposure to flame is required .

For the purposes of this invention the term "fibre" always includes staple fibres as well as - wherever applicable - continuous filaments.

In a preferred embodiment the fabric can be a woven fabric. I n another preferred embodiment the fabric can be a knitted fabric produced by any method including flat bed knits, circular knitting , warp knitting or any other method of knitting . In yet another preferred embodiment the fabric can be a nonwoven fabric produced out of fibres by any available method including air laying , wet laying , spun laying, needling of a carded or air laid web, hydroentanglement or any other method of producing a nonwoven fabric. Spun or continuous filament yarns made in whole or in part from FR lyocell or any other fibre type may be included in such a nonwoven or may form a sig nificant part of it.

In a flame resistant fabric according to the invention the FR lyocell may be blended with one or more other textile fibres chosen from the group containing other FR fibres such as meta-aramid , para aramid, modacrylic, PBI , FR modal, FR viscose and any other FR fibre and/or with other non-FR fibres including cotton , wool, silk, linen, non-FR Lyocell, modal, viscose, nylon, acrylic and polyester. Of course each blend must be tested to ensure that it is capable of producing a fabric with the required flammability performance for the intended application , The product of this invention therefore is a fabric made entirely of FR Iyoceli or containing a proportion of FR lyocell which can be processed to its finished state without fibrillation of the surface occurring and which can be used to make garments which are washable without fibrillation occurring . A fibre, filament, yarn, fabric or garment which has been made using the solution to the fibrillation problem described above is encompassed by the invention of this patent.

The FR additive used to produce FR lyocell as described in WO 2012/08331 8 is an oxidised condensate of a tetrakis hydroxyalkyl phosphonium salt with ammonia and/or a nitrogenous compound which contains one or several amine groups. Surprisingly it was found that by reducing or neutralising the alkalinity of the FR additive the cross-linking of the FR Lyocell fibre or filament can be significantly improved up to the level needed for the purposes described above. There are several specific embodiments of this invention which have been found:

1 ) Rinse the fabric in an acid bath prior to applying the cross-linking resin ; therefore a preferred embodiment of the invention includes a method for resin finishing a flame resistant fabric made from or including FR Lyocell which is characterized by rinsing the fabric with an acid bath prior to resin finishing . I n a specifically preferred embodiment the acid bath contains 0.1 g/l to 2.0 g/l of acetic acid in water.

2) Increase the quantity of catalyst in the solution applied to the fabric to a level where the catalyst is active despite some combining with the FR additive; therefore another preferred embodiment of the invention includes a method for resin finishing a flame resistant fabric made from or including FR Lyocell which is characterized by increasing the concentration of catalyst in the applied resin solution to 1 .2 to 5 times the normally used level

recommended by the resin manufacturer. In a specifically preferred embodiment the catalyst is magnesium chloride hexahydrate at a

concentration of 1 5 to 50 g/l.

3) I nclude a buffering agent in the solution which is applied to the fabric;

therefore another preferred embodiment of the invention includes a method for resin finishing a flame resistant fabric made from or including FR Lyocell which is characterized by adding an acid buffering component to the resin bath applied to the fabric. I n a specifically preferred embodiment the acid buffering component is citric acid and the pH of the resultant dried , uncured fabric is less than 6. It will be clear to anyone skilled in chemistry and textiles that any method of reducing or neutralising the alkalinity of the FR additive will achieve the same result as the three methods listed . All methods of achieving this result are intended to be covered by this patent.

Treatment with an acid bath , which may also be referred to as a sour rinse, can conveniently be carried out in a jigger dyeing machine. The same machine can be used to scour and desize the fabric before rinsing the fabric with the acid rinse. The standard treatment used was to rinse with a 1 g/l solution of 60% acetic acid for 1 0 minutes at 40°C. The effect of this treatment on a 1 00% Tencel lyocell fabric was to reduce the pH of the fabric from 8.1 for a desized and scoured only fabric to 5,63 after the acid rinse. The effect of this treatment on a 1 00% Tencel FR lyocell fabric was to reduce the pH of the fabric from 8, 1 for a desized and scoured only fabric to 4,78 after the acid rinse.

Normally when a fabric is given an acid rinse as described it is then washed with water to remove any excess acid from the fabric before it is dried. With FR lyocell it has been found that drying the fabric without performing a water rinse gives a better result in preventing the inactivation of the acid catalyst during resin finishing . This is because removing the acid from the fabric allows the FR additive to return to Its alkaline state and it would subsequently, during the resin finishing process, inactivate the acid catalyst. Increasing the amount of catalyst in the resin finishing recipe can also be used as a way of overcoming the acid inactivation caused by the FR additive.

Catalysts used in resin finishing are commonly Lewis Acids. One such catalyst is magnesium chloride. When it is heated to the temperatures used to cure a resin during resin finishing it decomposes to yield hydrochloric acid which is the chemical which catalyses the cross-linking reaction. The amount of hydrochloric acid produced is proportional to the amount of magnesium chloride on the fabric. By increasing the amount of magnesium chloride added to the resin finishing recipe, the amount of hydrochloric acid produced will also be increased. At the right level there will be sufficient hydrochloric acid produced so that when some of it is inactivated by the FR additive there is still enough available to effectively catalyse the cross-linking reaction. It should be noted that too great an excess of magnesium chloride can result in deg radation of the cellulose in the fibres and hence should be avoided . The third method of overcoming the inactivation of the resin finishing catalyst by the FR additive is to add a buffering system to the solution applied to the fabric. A buffering system will maintain the pH of the solution at a desired level across a range of additions of acid or alkali. If an acidic buffering agent such as citric acid or acetic acid is added to the solution applied and the fabric is dried, it will maintain an acidic pH until the fabric is heated during curing of the resin. The acid thus produced by the catalyst will not be inactivated by the FR additive, but will be available to catalyse the cross-linking reaction .

The choice of the method for preventing the inactivation of the catalyst is made taking into account the economics, the design of the equipment being used to apply and cure the resin finish, the availability of the chemicals and the effects on the aesthetics and physical properties of the fabric produced . A skilled textile finisher will test the approach selected on a small scale to ensure that the desired result will be obtained.

The three methods described are all aimed at achieving the objective of this patent which is to prevent inactivation of the catalyst by the FR additive so that the fabric can be cross-linked during resin finishing . Any other method which achieves the same objective is also within this patent. The process for producing the product of the invention includes the step of cross-linking the cellulose in the FR lyocell fibre to prevent fibrillation during use and laundering . The whole process of converting FR lyocell fibre into a finished useable fabric may include many other steps before and after resin finishing. Any combination of normal textile processes which includes a treatment to prevent inactivation of the acid catalyst used in resin finishing is also the subject of this patent. The cross-linking of the cellulose is preferably done on fabric but may also be done on fibre, yarn or filament yarn before the fabric is produced. Garments made from the fabric are also products of the invention. The product of the invention may be used for the production of all types of garments worn where accidental exposure to flames is a possibility. It can be used for jackets, coats, trousers, boilersuits, coveralls, shirts, sweaters and jumpers, sweatshirts, T-shirts, children's nightwear, adults nightwear, socks, aprons, gloves and gauntlets, hoods for head protection other headwear and any other garment that may be worn when accidental exposure to flame or other source of ignition is a possibility.

Other articles made from the fabric are also products of the invention. They include articles which may be accidentally exposed to flame or other source of ignition such as shoe and boot components, welding screens, fire curtains, tents, sleeping bags, tarpaulins, filters, interlinings, coating substrates, wipes, cleaning cloths, disposable or short-life clothing, padding and barrier layers for upholstered furniture and any other similar articles made in whole or in part from fabric. Therefore the invention encompasses the use of the fabric described above for the manufacture of articles which may be accidentally exposed to flame or other source of ignition. Such articles can be garments worn where accidental exposure to flames or other sources of ignition is a possibility such as jackets, coats, trousers, boilersuits, coveralls, shirts, sweaters and jumpers,

sweatshirts, T-shirts, children's nightwear, adults nightwear, socks, aprons, gloves and gauntlets, hoods for head protection other headwear and any other garment that may be worn when accidental exposure to flame or other source of ignition is a possibility as well as shoe and boot components, welding screens, fire curtains, tents, upholstery, home furnishings including curtains, sleeping bags, tarpaulins, filters, interlinings, coating substrates, wipes, cleaning cloths, disposable or short-life clothing , padding and barrier layers for upholstered furniture and any other similar articles made in whole or in part from fabric.

The invention will now be illustrated by examples. These examples are not limiting the scope of the invention in any way.

Examples

Example 1 (comparative sample)

A 1 /30s Ne yarn was made from FR lyocell fibres manufactured as described in patent application WO 201 2/08331 8, The yarns were woven to give a fabric with a 2x1 twill construction of 200gsm weight. The yarns had previously been dyed using vat dyestuffs.

The fabric was then padded at 75% pick up in: 40g/l Knittex FEL (modified DMDHEU resin from Huntsman). 12g/l Magnesium Chloride hexahydrate, 30g/l Perisoft GS (silicone micro emulsion from Dr Petry), 2g/l Kieralon JET (wetting agent from BASF). The fabric was then stenter dried at 120°C and the resin was then cured on the stenter for 45 seconds at 170°C. The fabric was then washed 5 times in a domestic washing machine at 60C using the machine manufacturers recommendations. The washed fabric was tumble dried in a domestic tumble drier.

The fabric was then inspected for its surface appearance. The surface of the fabric showed clear signs of frosting or whitening irreg ularly over the surface. Frosting of this type is a clear indication of fibrillation of the fibres at the surface of the fabric. A fabric which shows uncontrolled fibrillation is unlikely to be of commercial use. Example 2

A 2x1 twill fabric of 200gsm weight which was identical to the starting fabric used in example 1 was woven from yarns which had previously been vat dyed.

The fabric produced was treated on a jigger as follows: Treat the fabric with 1 g/l Acetic Acid (60%) at 40°C for 10 minutes or a minimum of two ends or cycles of operation of the dyeing machine. The fabric was not rinsed and was dried on a stenter drier. The fabric was then padded at 75% pick up in : 40g/l Knittex FEL (modified DMDH EU resin from Huntsman) , 12g/l Magnesium Chloride hexahydrate, 30g/l Perisoft GS (silicone micro emulsion from Dr Petry), 2g/l Kieralon JET (wetting agent from BASF). The fabric was then stenter dried at 120°C and the resin was then cured on the stenter for 45 seconds at 70°C. The fabric was then washed 25 times in a domestic washing machine at 60C using the machine manufacturers recommendations. The fabric was inspected after each 5 cycles of washing . The washed fabric was tumble dried in a domestic tumble drier,

The fabric was then inspected for its surface appearance. The surface of the fabric showed clear signs of frosting or whitening irregularly over the surface. Frosting of this type is a clear indication of fibrillation of the fibres at the surface of the fabric. A fabric which shows uncontrolled fibrillation is unlikely to be of commercial use.

At each inspection during the washing process the fabric had a bright clear appearance with no indication of frosting or whitening. This showed that the fibre in the fabric had not fibrillated during the 25 washing cycles and had the washing performance which would be required for commercial use.

Example 3

The fabric produced in example 1 above was finished by a wet cross linking technique as detailed below: The fabric was padded at 80% wet pick up in: 250g/l Fixapret CPN (DMDHEU resin from BASF), 50ml/l Sulphuric acid (98%) to give a pH of less than 1 . The wet fabric was rolled , placed on an A frame and covered in polythene, sealed and slowly rotated for 22 hours at room temperature. The fabric was then removed and washed using the following series of wash liquors: Cold water, 0g/i Soda Ash at 50°C, 2g/l Soda Ash, 2g/l detergent at 50°C, Hot water at 60°C, Cold water. The fabric was finally dried on the stenter. The fabric was washed 25 times as described in example 2. It was inspected after every 5 washes, The washed fabric was tumble dried. At each inspection during the washing process the fabric had a bright clear appearance with no indication of frosting or whitening. This showed that the fibre in the fabric had not fibrillated during the 25 washing cycles and had the washing performance which would be required for commercial use.