CA2243350A1 - Treatment of fabrics - Google Patents

Abstract

Fibrous cellulosic material is treated by applying an aqueous solution including a polycarboxylic acid crosslinking agent and a hydroxycarboxylic acid, particulalry an aromatic ortho-hydroxy carboxylic acid, especially salicylic acid or salt particularly alkali metal ammonium or alkaline earth metal salts, as an esterification catalyst, drying the fabric and heating it to promote crosslinking esterification of the polycarboxylic acid and the cellulose of the fibrous cellulosic material to give fabric with improved wrinkle and/or crease and/or shrink resistance and/or smooth drying properties. The method has the advantage that it does not use formaldehyde derivatives and thus the operation of the method and treated materials do not release formaldehyde during manufacture or use and the catalysts do not contain or use phosphorus containing compounds.

Description

CA 022433~0 l998-l0-07 CPW 50522 ' T, edl" ,e"l of Fabrics This invention relates to a method of il I Ipdl lil Ig wrinkle and/or crease and/or shrink, eSi ldnce and/or smooth drying p,upe, lies to fabrics made from cel' I~- c i~ fibres or yarns or blends containing 5 cellulosic fibres or yarns. More particularly it relates to such a method of lledtll,e,,l which does not involve the use of formaldehyde or rO"" ~ehyde derivatives or phosphorus containing compounds.

Many con""e,~.ial processes for imparting wrinkle, crease and/or shrink lesi:,ldnce and/or smooth drying properties to cellulosic fabrics, particularly cotton textiles, are known. The treated fabrics and 10 ga""erlts made from them retain their dil"ensions and smooth apped,dnce in use and also during machine wash and tumble dry prucesses.

Co" " "eruidlly, such properties can be i" ~pa~ led to cellulosic fabrics by a finishing t, edl" ,enl with resinous co""~osi~ions. The most con""only used resins for such finishing are based on 15 formaldehyde derivatives such as formaldehyde-urea or sl ~hstitl Ited urea addition products such as DMEU and DMDHEU. Such resins are believed to function by prull,uli"g crosslinking of the cellulose in the fabric thereby imparting the desired properties. In recent years, efforts have been made to develop crosslinking agents which do not include rullll ''shyde or its derivatives to remove the possible evolution of formaldehyde during manufacture, storage and/or use of cellulose, particularly 20 cotton fabrics, treated with ru"" '~ehyde addition products.

Non-rur", '' -. hyde clussli~ ~kirlg agents which have been suggest~d previously include polycarboxylic acids as ~ osed by Gaghiardi and Shipee, American Dyestuff Repol ler 52, 300 (1963). Ru/~land et al., Textile Resea,~l1 Joumal 37, 393 (1967), ~lisclosed the use of partially neutralized 25 polycarboxylic acids with base prior to the al-plic~liol1 to the fabric in a pad, dry and heat cure lled~",enl, elaborcled US Patent 3526048. Canadian Patent No 2097483 describes rapid es~eriri.;dtion and crosslinking of fibrous cellulose in textile form using boric acid or derivatives as crosslinking catalyst.

30 Welch et a/. in US Patents 4975209,4820307,4936865 and 5221285 disclose the use of alkali metal salts of phospl1orus containing acids, particularly sodium hypophosphite as crosslinking e~le, iri~,dlion catalysts in the tledtlnelll of cellulosic ",aler;als. The use of sodium hypophosphite has several disad\ dnldges: it is expensive, relatively high levels are needed in practice and it tends to cause shade ul~al1ges in fabrics dyed with sulphur dyes or certain reactive dyes. In addition, phosphorus 35 containing emuents can promote algal growth and/or eul,oph "~ n of dovvllal,ec", water bodies such as streams and lakes.

CA 022433~0 l998-l0-07 CPW 50522 ' The present invention is based on the discovery that certain hydroxycarboxylic acids and/or their salts, particularly alkali metal salts at lower concer,ttdlion show acc~lc,dti,lg effect on eslelircdlion and crosslinking of cellulose by polycarboxylic acids. The use of such catalysts can enable the provision of a treatment method that uses neither rur",~''ehyde derivatives or phosphorus 5 compounds, but can give adequ~t~ly rapid esl~rir~;dlion and crosslinking of cellulosic in fibres to provide effective wrinkle, crease or shrink ,t:sistance or smooth drying pro,tellies to "rdlerials made from such cellulosic fibres. Thus, in this invention fibrous cellulosic material is treated with a polycarboxylic acid in the pr~sence of a hydroxycarboxylic acid curing catalyst at elevated l~nlperd~ure. The process can be carried out by ill,~,r~yndli"g the material with a solution containing 10 the polycarboxylic acid and the curing catalyst followed by heat ll ~d~l "enl to produce eslerircdlion and crosslinking of the cellulose with the polycarboxylic acid.

The present invention accordingly provides, a method of treating fibrous cellulosic textile material which cor, IlJ, ises:
15 a apply;l ,9 to the cellulosic textile material an aqueous solution including at least one polycarboxylic acid as a crosslinking agent for the cellulose and a hydroxycarboxylic acids or a salt as an eslt:, ir.,dlion catalyst, b drying the textile material and heating it to promote crosslinking esl~:rir,cdlion of the polycarboxylic acid and the cellulose of the cellulosic textile material.

In re~er, i"g to the material as being "cellulosic", we mean that the major part of the fibre forming components of the material is cellulose. Thus, the term includes purely cellulosic ",dlerials such as cotton and cellulose-rich blends particularly cellulose-rich polyester blends, such as polycotton " ,alerials. Typically, the material contains from 30 to 100% of cellulosic fibres. Typical cellulosic 25 fibre ",dl~r;als which can be included in fabrics treated according to this inventions include cotton, flax, rayon, jute, hemp and ramie. It can also be a synthetic cellulosic fibre material such as rayon, particularly viscose rayon or solvent derived rayon co"""only called Iyocell fibre. The cellulosic material can be a blend of fibres of cellulosic mdlerial 5 with non-cellulosic Illdl~ ls and in particular includes blends of cellulosic fibres, particularly cotton, with polyester, particularly polyethylene 30 telephll,dldle polymer or related copolymers. The textile can be a woven (including knitted) or non-woven textile, but as crease lesislance is particularly illlpOIldlll in clothing, the textile will usually be a clothing textile material.

The terrn ,~,r",-''~hyde free" means that the process does not release formaldehyde during the 35 ll ~:dll"ent of the fabric with the resin or during s~lhsequent manufacture of yd""enl:, or their use including washing and wearing. The term "wrinkle or crease, t:si;,~dnce" means that a treated fabric is less likely to be wrinkled or creased after being worn or after a laundering operation than it would if it had not been so treated.

CA 022433~0 1998-10-07 CPW 50522 ' The invention uses polycarboxylic acids as cellulose c, ussli, Ihil lg agents to improve the wrinkle ~t:sisla"ce, sl" i"kage It:sistance and smooth drying properties of cellulosic fibre containing textile without the use of rur", ~ehyde or agents that release fur", ~ 'Ehyde. Some such polycarboxylic 5 acids are known from the literature. Suitable polycarboxylic acids for use in the method of this invention include aliphatic, including open chain and alicyclic, polycarboxylic acids, and alullldlic polycarboxylic acids. Desirably the polycarboxylic acid includes at least 3, particularly at least 4 and often more carboxylic acid groups per ",a'e :~'r~.

10 Particularly suitable aliphatic polycarboxylic acids include acids in which at least two carboxylic acid groups are sepa, dled by 2 or 3, more usually 2, carbon atoms and desirably where the poly-carboxylic acid includes a plurality of such arranged pairs of carboxylic acid groups. Where such an aliphatic acid includes an ethylenic double bond, it is very desil, ''e that it is positioned a,~- to a carboxylic acid group; such an aliphatic acid may include a hydroxyl group on a carbon atom also 15 carrying a carboxylic acid group; and further the aliphatic chain or ring may include one or more oxygen and/or sulphur atoms. Suitable dl unldlic acids include those where at least two carboxylic acid groups are attached to a~acenl aro" ,alic ring carbon atoms.

EXdlll, 'es of suitable aliphatic polycarboxylic acids include maleic acid, methylmaleic (~,itldcon e) 20 acid, citric acid, itaconic acid, 1,2,3-propanel, iCdl ~oxylic acid, 1,2,3,4-buld,let~:ll dCdl L,oxylic acid (co"""only known as BTCA), all cis-1,2,3,4-cyclopentanel~l,dcd,Loxylic acid, oxydisuccinic acid, Ih - ~isuccinic acid; oligo- and/or poly-maleic acid and/or anhydride (as ~lesc, i~ed in GB 2295404 A
and WO 96/26314 A and abbreviated "OMA") and suitable a~umdlic polycarboxylic acids include benzene hexaca, l oxylic acid and ll il l l e " 'ic acid .
The amount of crosslinking agent used will typically be from 1 to 10%, particularly from about 2 to about 7%, by weight based on the dry fabric weight. The particular concer,t~ dliOIl of crosslinking agent used in the treating solution will depend upon the degree of cross linking desired, the p,opo, lion of cellulosic fibres in fabric being treated and the solubility of the crosslinking agent.
30 Typically, the concen~,dtion is from about 1 to 20%, more usually 2 to 10% particularly from 0.5 to 7 and esp~ ~ 'Iy about 5%, by weight of the solution.

The curing catalyst used in this invention is one or more hydroxycarboxylic acid(s). The curing catalyst can be a'i, halic, a(c ",dlic. Suitable aliphatic compounds include mono-carboxylic 35 mono-hydroxyl acids, in particular of the formula (I): H-R1-CH(OH)-R2-COOH (I) where each of R1 and R2 is a direct bond or a C1 to C4 alkylene group, in particular where R1 is a direct bond, such CA 022433~0 1998-10-07 that the total number of carbon atoms in the acid ",G'e~l~'e is from 2 to 6 (??). Examples include hydroxyacetic acid (glycollic acid), glyoxalic acid (di-hydroxyacetic acid) and 4-hydroxybutyric acid.
Suitable a~ol"alic compounds include mono-carboxylic hydroxy acids in which at least one of the carboxyl and hydroxyl groups is directly ~ cl1ed to the alor"dlic ring. Desirably, the carboxyl group 5 and at least one hydroxyl group are directly attached to the arol"alic ring. The ring may also carry inert 5~hstituents such as one or more C1 to C4 alkyl group(s), but desirably, not more than two such groups are ~ldched to the a~c""~lic ring. Particular aro",~lic acids are of the formula (Il):

~ " j/--R --COOH (Il) where R3 is a CH2 group, or, and desirably, a direct bond;
n is from 1 to 3, particularly 1 or 2;
each R4 is independently a C1 to C4 alkyl group; and misO, 1 or2.
Among a(o",dlic acids, those where the carboxylic acid group and a hydroxyl group are directly dlldclled to the alUllldl.iC ring and are positioned substituted ortho- to each other on the ring are 20 particularly useful. Very desirable such 'o~tho-acids' are those of the formula (Ill):

( HO ) n ~ OH
~, ,, ,: COOH (Ill) 25 where m and R4 are independently as defined for formula (Il) and n' is O or 1.
Examples include 3-hydroxybenzoic acid, 4-hydroxy- benzoic acid and 2-hydroxyphenylacetic acid and examples of suitable ortho-acids include 2-hydroxybenzoic acid (salicylic acid), 2,4-dihydroxybenzoic acid (b-recorcylic acid), 2,4-dihydroxy- 5-methylbenzoic acid (orcinylic acid) 30 and the cresotic acids, especially 2-hydroxy-3-methyll,an~ ~ ~ acid, 2-hydroxy-4-methylbenzoic acid and 2-hydroxy-5-methylL en-c c acid.

The hydroxycarboxylic acid catalyst can be used as the free acid or as a salt, particularly an alkali metal, a"""on ~m or alkaline earth metal salt, or a mixture of the free acid and a salt or salt(s). The 35 salt forming cations are particularly of potassium, sodium, a" " "on Im""ayl lesium, calcium or a mixture of these cations. It is not clear whether the free acid form or the salt form of the curing catalyst is the more active component of the catalyst. The form present will depend on the acidity of the solution used for the 1, a~l" ,enl of the textile and the effect of the drying and heating steps. We CA 022433~0 1998-10-07 CPW 50522 ' have found that the textile is advanl,.geously treated using a ",ode,dlaly acidic solution, typically having a pH of from 2 to 6, usually not more than 4.5, more usually from 2.5 to 4 and especially about 3. Under such conditions, the curing catalyst may be present as the neutral free acid, as acid anions or a mixture depending on the acidity of the catalyst. Aromatic 2-hydroxy- carboxylic acids 5 (ortho-acids) typically have acidities in aqueous solution such that both the neutral free acid and the acid anions are present at significant conce"l,d~ions (relative to he overall concer,l,dlion of the catalyst) at pH values of about 3.

In making up ll~d~l"enl solutions, it will often be convenient to start by di~solvi"g a readily water 10 soluble metal or all ""on - ~m salt and sl Ihsequently adjusting the pH of the solution rather than to try to dissolve what may be a Spdl i, Iyly soluble free acid at the use pH directly.
The amount of hydroxy alullldlic acid catalyst used will typically be from 1 to 100%, more usually 1 to 50%, desirably 2 to 30% and especially 5 to 20%, by weight of the polycarboxylic acid cr. s s" ~king 15 agent. Expressed as a per.;en~dge based on (the dry weight ofl the material being treated, the amount will typically be from 0.1 to 10%, more usually from 0.2 to 3%, particularly 0.5 to 2% by weight. The concehl,dlion used in the treatment solution is typically from 0.1 to 10%, more usually from 0.2 to 5%, particularly from 0.3 to 2%, by weight of the solution.

20 The action of the hydroxy a,on,dlic acid catalysts used in this invention seems to go beyond the effect that might be ex~e~;tad of a simple catalyst. We do not know why this may be, but suspect that bec~llse the hydroxy alcJrlldlic acid catalysts have at least two potentially reactive sites, they may be acting to form further cross links by reacting with the cellulose and/or with the polycarboxylic acids used as cellulose crosslinking agents. The precise ",ecl1an;;.lll by which the effect arises is not 25 critical to the invention.

The catalysts used in this invention can be used alone or in co" ,~. ,alion with other catalytic ",dlal ;als. In particular they can be used in combination with organic or inorganic sulphonic or sulfinic acids or salts. In such cor, IL . ,ations, suitable organic or inorganic sulphonic or sulfinic acids 30 or their salts include illûlyal1 C sulphonic acids i.e. compounds including the group SO3H (or SO2OH), particularly halosulphonic and amidosulphonic acids, particularly those of the general formula: XSO2OH where X is Cl, F or NH2, respectively chlorosulphonic and fluorosulphonic acids and amidosulphonic acid (taurine); and organic sulphonic acids which typically have the general formula: RSO2OH where R is an organic group, particularly an alkyl or cycloalkyl group, an unsaturated straight or b,dnched chain h~lucdllJyl, particularly alkenyl group, or an unsaturated cyclic or arene group. especially suitable organic catalysts inlcude the alkane sulphonic acids and CA 022433~0 1998-10-07 their alkali metal salts e.g. methane, ethane, propane, butane, pentane and hexane sulphonic acids, ca"")hor sulphonic acid, isell, ~n ~ acid (2-hydroxyethane sulphonic acid), methane- di-sulphonic acid and trifluolo",t:~l ,anesulphonic acid. Other useful curing catalysts include arene and alkyl arene sulphonic acids such as benzene, p-hydroxybenzene, p-toluene and dodecylbanzene sulphonic 5 acids, naphll,-'-ne-1- and napthalene-2-sulphonic acids and 1,3-benzene and 2,6-naphtl,-'~ne disulphonic acids and benzene sulphinic acid.

Sulphonic or sulfinic acid catalysts can be used as the free acids or as salts, particularly an alkali metal, a"""on Im or alkaline earth metal salts, or a mixture of free acid and salt(s). The salt forming 10 cations are particularly of potassium, sodium, a~ on ~m, magnesium, calcium or a mixture of these cations. It is not clear whether the free acid form or the salt form of this type of catalyst is the more active form. The form present will depend on the acidity of the solution used for the l,~dl",enl of the textile and the effect of the drying and heating steps. At the ",oder.~t~,ly acid con "'ians typically used in this invention, it is likely that any sulphonic or sulfinic acid catalysts used will be present mainly as 15 the (electrically) neutral free acid.

When the catalyst system includes a sulphonic or sulfinic acid catalyst, the amount of this additional catalyst used will typically be from 10 to 200%, more usually 25 to 150%, desi,dbly 50 to 120%, by weight of the polycarboxylic acid clussli~hi~g agent. Ex~,,essed as a percen~dge based on the (dry 20 weight of the) textile being treated, the amount will typically be from 1 to 30%, more usually from 2 to 20%, particularly 2.5 to 10% by weight. The conce"l,dlion used in the l,eal",ent solution is typically from 0.1 to 20%, more usually from 0.2 to 10%, particularly from 0.5 to 7%, by weight of the solution.

The use of sulphonic or sulfinic acids as a reaction catalyst in the preparation of fibrous cellulosic 25 textile ",alerials having improved crease and wrinkle résislance is the subject of a co-pending arr. ~ on claiming priority from Indian Patent App' ~, ~icn No 1361/CAU97 and GB Patent App' -2~ion No 9802031.6 and filed as ~pp' - 'icn No (Applicant's reference CPW 50525).

The l~ed~",enl is typically carried out by first i",prey"dli"g the cellulosic or cellulosic containing textile 30 Illdlel ials with an aqueous treating solution containing the crosslinking agent and the curing catalyst, and removing excess liquid e.g. using w, i"ger~, with these steps being repeated, if necessd(~, to obtain the desired liquid pick up. The material is then dried to remove the solvent and then cured, e.g. in an oven, typically at about 150 to 240~C, usually from 160 to 200~C for a time of from 5 seconds to 30 minutes, usually 1 to 5 minutes to promote the esle,iri~;dlion and crosslinking of the 35 cellulose by the polycarboxylic acid. Typically the pick up of ll~d~ lll solution is from 30 to 120%, more usually from 50 to 100%, particularly about 80% of the dry weight of the ~" ,t\ ~dled textile.

CA 022433~0 l998-l0-07 CPW 50522 ' We have corlri, l l led the presence of cellulose ester carbonyl groups in cellulosic textile material treated according to the invention by FT-IR (Fourier lldnsfollll infra red) spe~A,us~py. The absol ~,tion band of the carbonyls of cellulose esters in infra red spectra has been reported and in the range of 1720 to 1750 cm~1 (Zhbankov, P.G., "Infrared spectra of cellulose and its derivatives", Consultant Bureau, New York, 1968, pp 315-316). Our observations show an absol~,lion peak at about 1720 to 1735 cm .

The ll~dllllenl solution containing the crosslinking agent and the curing catalyst forms part of the 10 invention which accordingly specifically includes an aqueous solution of at least in one polycarboxylic acid cellulose crosslinking agent, particularly at a concel Ill dlion of from 1 to 20% by weight of the solution, and at least one hydroxycarboxylic acid esleriricalion catalyst, particularly at a conce,ll,dlion of from 0.2 to 10% by weight of the solution. The invention further includes an aqueous solution of at least in one polycarboxylic acid ce'lulcse crosslinking agent, particularly at a concerll'dlion of from 1 15 to 20% by weight of the solution, at least one hydroxycarboxylic acid esteriricdlion catalyst, particularly at a concer,l, dlion of from 0.2 to 10% by weight of the solution and at least one organic or illo~an ~ sulphonic or sulfinic acids or a salt esleliricalion catalyst, particularly at a concel'l'dlion of from 0.2 to 10% by weight of the solution.

20 The invention further includes cloth treated by the method of the invention and in particular, a cellulosic textile material, which may be woven (including knitted) or non-woven, which carries residues of at least in one polycarboxylic acid cellulose crosslinking agent esleriried to hydroxylic sites in the cellulose and residues of at least one hydroxycarboxylic acid e~ rir~,dlion catalyst. In this aspect, the invention also includes a cellulosic textile material, which may be woven (including 25 knitted) or non-woven, which carries residues of at least in one polycarboxylic acid cellulose crosslinking agent eslerirled to hydroxylic sites in the cellulose, residues of at least one hydroxycarboxylic acid eslel iricdlion catalyst (which may be bound chemically to the textile or to residues of at least in one polycarboxylic acid cellulose crosslinking agent), and at least one hydroxycarboxylic acid estel iricdliol1 catalyst, particularly at a con~l ~ll dlion of from 0.2 to 10% by 30 weight of the solution In these aspects of the invention particularly desil ' 'e features are as described for the method of the invention.

CA 022433~0 l998-l0-07 The following Examples illustrate the invention. All parts and pe,cenlage are by weight unless otherwise stated.

5 BTCA 1 2 3 4-butanelt:l, dCdl l,oxylic acid OMA oligo-maleic acid Surf Cor"",er( ;dl pr~,prield,y do",eslic d~l~,yenl ex Hindustan Lever Test M_lhods 10 Wrinkle recovery angles (WRA) were determined by ATCC Test Method 66-1990 Wrinkle recovery of fabrics: Recovery angle method. The wrinkle resistance of woven textiles is, ~prt:senl~d by the wrinkle recovery angles; the greater the WRA the greater the wrinkle resislance of the fabric.
Results are repo, led in degrees.

Example 1 This Example illustrates the use of salicylic acid (introduced as sodium salicylate) as a curing catalyst for the durable press finishing of cotton fabric using BTCA.

20 Cotton cloth test pieces (10 inches square; ca. 25X25 cm;) were thoroughly wetted by i"""er:jion in a treatment bath containing an aqueous solution (80 ml) of BTCA (5 9) and sodium salicylate (0.5 9) as curing catalyst at a pH adjusted to 3. The wetted cloth was passed between the rolls of a wringer and the process l~pealed twice to give an overall pick up 80% by weight of the l,edl",enl solution based on the dry weight of the untreated cloth. The test pieces were stretched on a rack and dried in 25 an air forced draft oven at 85~C for 5 minutes. The dried test pieces were then treated in an air draft oven at 180~C for 2 minutes.

The measured WRA was 278~. Treated test pieces had a WRA of 256~ after i" " "e, aion for 5 minutes with 1% Surf solution followed by rinsing with water and air drying.
FY~rnple 1C
Example 1 was repeated but substituting sodium benzoate (5 9) for the sodium s- Jldl~ used in Example 1 and gave a WRA (before washing) of 261~.

Example 2 35 Example 1 was repeated but substituting ~c 9- " - c acid (OMA) for the BTCA used in Example 1 and gave a WRA (before washing) of 255~.

CA 022433~0 l998-l0-07 CPW 50522 ' _ g _ F~:~rr ple 3 Example 1 was repeated, but suhstituting sodium 3-hydroxy~nzo~L~ (1 9) for the sodium salicylate used in Example 1 and gave a WRA (before washing) of 276~.
Example 4 Example 1 was repeated, but substituting sodium 4-hydroxy~enzodle (1 9) for the sodium salicylate used in Example 1 and gave a WRA (before washing) of 276~.

F~rnple 5 10 Example 1 was repeated, but sllhstitlltirlg sodium 2-hydroxyphenylact7l~le (1 9) for the sodium salicylate used in Example 1 and gave a WRA (before washing) of 274~.

Claims (16)

1 A method of treating fibrous cellulosic textile material which comprises:
a applying to the cellulosic textile material an aqueous solution including at least one polycarboxylic acid as a crosslinking agent for the cellulose and a hydroxycarboxylic acids or a salt as an esterification catalyst, b drying the textile material and heating it to promote crosslinking esterification of the polycarboxylic acid and the cellulose of the cellulosic textile material.

2 A method as claimed in claim 1 wherein the esterification catalyst is a mono-carboxylic hydroxy acid of the formula (II):

where R3 is a CH2 group, or, and desirably, a direct bond;
n is from 1 to 3, particularly 1 or 2;
each R4 is independently a C1 to C4 alkyl group; and m is 0, 1 or 2, and/or a salt thereof.

3 A method as claimed in claim 2 wherein the catalyst is an aromatic hydroxycarboxylic acid of the formula (III):

where m and R4 are independently as defined for formula (II) in claim 2 and n' is 0 or 1 and/or a salt thereof.

4 A method as claimed in either claim 2 or claim 3 wherein the catalyst is one or more of 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, 2-hydroxyphenylacetic acid 2-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 2,4-dihydroxy5-methylbenzoic acid 2-hydroxy-3-methyl-benzoic acid, 2-hydroxy-4-methylbenzoic acid and 2-hydroxy-5-methylbenzoic acid and/or asalt thereof.

5 A method as claimed in any one of claims 1 to 4 wherein the polycarboxylic acid crosslinking agent includes at least two carboxylic acid groups are separated by 2 or 3 carbon atoms.

6 A method as claimed in any one of claims 1 to 5 wherein the polycarboxylic acid is one or more of maleic acid, methylmaleic acid, citric acid, itaconic acid, 1,2,3-propanetricarboxylic acid, 1,2,3,4-butanetetracarboxylic acid, all cis-1,2,3,4-cyclo-pentanetetracarboxylic acid, oxydisuccinic acid, thiodisuccinic acid, oligo- and/or poly-maleic acid and/or anhydride, benzene hexacarboxylic acid and trimellitic acid.

7 A method as claimed in claim 1 wherein the polycarboxylic acid is 1,2,3,4-butane tetracarboxylic acid and/or oligo- and/or poly-maleic acid and the catalyst is 2-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid (.beta.-recorcylic acid), 2,4-dihydroxy- 5-methylbenzoic acid 2-hydroxy-3-methylbenzoic acid, 2-hydroxy-4-methylbenzoic acid, 2-hydroxy-5-methyl-benzoic acid or a mixture or a salt thereof.

8 A method as claimed in any one of claims 1 to 7 wherein the amount of polycarboxylic acid crosslinking agent used is from 1 to 10% by weight based on the dry fabric weight.

9 A method as claimed in claim 8 wherein the amount of polycarboxylic acid used is from about 2 to about 7% by weight based on the dry fabric weight.

10 A method as claimed in any one of claims 1 to 9 wherein the amount of hydroxycarboxylic acid catalyst used is from 1 to 100% by weight of the polycarboxylic acid crosslinking agent.

11 A method as claimed in claim 10 wherein the amount of hydroxycarboxylic acid used is from 2 to 30% by weight of the polycarboxylic acid crosslinking agent.

12 A method as claimed in claim 11 wherein the amount of hydroxycarboxylic acid used is from 5 to 20% by weight of the polycarboxylic acid crosslinking agent.

13 A method as claimed in any one of claims 1 to 12 wherein the heating step is carried out at a temperature of from 150 to 240°C.

14 A method as claimed in claim 13 wherein the temperature is from 160 to 200°C.

15 A method as claimed in any one of claims 1 to 14 wherein the heating step is carried out for a time of from 5 seconds to 30 minutes.

16 A method as claimed in claim 15 wherein the time is from 1 to 5 minutes.