US3807952A

US3807952A - Method of crosslinking cellulosic fibres

Info

Publication number: US3807952A
Application number: US00187848A
Authority: US
Inventors: A Lauchenauer
Original assignee: Raduner and Co AG
Current assignee: Raduner and Co AG
Priority date: 1971-10-08
Filing date: 1971-10-08
Publication date: 1974-04-30
Anticipated expiration: 1991-04-30

Abstract

Crosslinking of cellulose fibres to obtain good finishing effects while retaining a high degree of abrasion resistance is accomplished by a process which comprises treating cellulose fibres with a solution containing (1) as crosslinking agent 0.5 1.5, preferably 0.6 - 1.0 mols per litre, of a mixture of an aldehyde having a molecular weight not higher than 60 and a nitrogeneous component having a molecular weight not higher than 250, which nitrogeneous compound has at least two N-CH2OH groups adjacent to carbonyl groups, the molar ratio between the aldehyde and the nitrogeneous compound ranging between 12:1 and 2:1, preferably between 6:1 and 0:1, (2) a catalytically effective amount of a mixture consisting of (a) a potentially acidic inorganic salt of magnesium or zinc, preferably magnesium chloride, and (b) a salt of fluorine-containing acid selected from the group consisting of alkali metal, alkaline earth metal and zinc fluoborates and silicofluorides, the molar ratio of the potentially acidic salt to the fluorine-containing salt ranging between 5:1 and 15:1, and the molar concentration of the crosslinking agent in the bath ranging from 1:4 to 1:15, and (3) as an abrasion resistance improving additive from 0:3 to 3 mols of a neutral alkali metal salt of an inorganic monobasic acid.

Description

United States Patent [1 1 Lauehenauer [451 Apr. 30, 1974 4] METHOD OF CROSSLINKING CELLULOSIC FIBRES 8/18, 8/l15.6, 8/115.7, 8/ll6.4, 8/129,

8/181, 8/182, 8/186, 8/187, 8/192, 8/194, 8/196, 8/DIG. 4, 8/9, 8/12, 8/17, 8/21, 38/144, 117/9331, 117/1394, 260/29.4 R. Int. C1.D06m 13/12, D06m 15/56, D06m 15/58 Field of Search 8/11613, 116.4, 116.2, 8/181, 182, 186, 187, 192; 38/144 [56] References Cited UNITED STATES PATENTS 2,541,457 2/1951 Beer 3/1164 2,602,018 7/1952 Beer 8/1 16.3

3,443,987 5/1969 Ferrante 8/1 16.4

2,826,514 3/1958 Schroeder 8/1 16.4 3,173,751 3/1965, Daul et a1. 8/1 16.4 3,181,927 5/1965 Roth et a]. 8/1 16.3 3,220,869 ll/l965 Ruemens et a1. 8/1 16.3 3,369,858 2/1968 Lourigan et a1. 8/1 1613 3,441,366 4/1969 Pierce et a1 8/1 16.3 3,617,199 ll/l97l Russell 8/1164 3,622,261 ll/l97l Cotton et al... 3/1 16.4 3,656,885 4/1972 Gagliardi 8/1 16.3 3,674,418 7/1972 Lyons et a1. 8/116.3 3,676,053 7/1972 Miyake et a1. 8/l l6.4

FOREIGN PATENTS OR APPLICATIONS 4/1965 Great Britain 8/1 16.3

1,120,965 7/1968 Great Britain 8/116.4

Primary ExaminerGeorge F. Lesmes Assistant Examiner 1. Cannon Attorney, Agent, or Firml-Iowson and Howson [57] ABSTRACT Crosslinking of cellulose fibres to obtain good finishing effects while retaining a high degree of abrasion resistance is accomplished by a process which comprises treating cellulose fibres with a solution containing (1) as crosslinking agent 0.5 1.5, preferably 0.6 1.0 mols per litre, of a mixture of an aldehyde having a molecular weight not higher than 60 and a nitrogeneous component having a molecular weight not .higher than 250, which nitrogeneous compound has at least two NCH OH groups adjacent to carbonyl groups, the molar ratio between the aldehyde and the nitrogeneous compound: ranging between 12:1 and 2:1, preferably between 6:1 and 0:1, (2) a catalytically effective amount of a mixture consisting of (a) a po-' I tentially acidic inorganic salt of magnesium or zinc,

preferably magnesium chloride, and (b) a salt of fluorine-containing acid selected from the group consisting of alkali metal, alkaline earth metal and zinc fluoborates and silicofluorides, the molar ratio of the potentially acidic salt to the fluorine-containing salt ranging between 5:1 and 15:1, and the molar concen tration of the crosslinking'agent in the bath ranging from 1:4 to 1:15, and (3) as an abrasion resistance improving additive from 0:3 to 3 mols of a neutral alkali metal salt of an inorganic monobasic acid.

14 Claims, N0 Drawings METHOD OF CROSSLINKING CELLULOSIC FIBRES.

Cellulosic fibres are known to retain creases when subjected to treatments such as actual wear or laundering, which cause fibres in the form of textile sheet material to be flexed, folded or creased. Thisdeficiency may be overcome by increasing the intermolecular cohesion of cellulosic fibres, i.e., by forming additional bonds between adjacent cellulose chains. Such additional intermolecular bonds have to be introduced in such a number that the crosslinked fibre is no longer soluble in cellulose solvents such as cuprammonium. By crosslinking, effects commonly known as dimensional stability, crease-proofing, wash and wear and durable press properties may be achieved on textile sheet material at least partly consisting of cellulose fibres, in particular of cotton. A large number of chemically different crosslinking agents, crosslinking catalysts and crosslinking procedures have been proposed over the last 40 years and many of these formulations are or have been widely used. Irrespective of their chemical nature, these crosslinking formulations are known to produce undesirable side-effects, in particular a reduction of tensile, tear and abrasion strengths of the cellulosic material. These strength losses unfortunately grow with desirable effects such as creaserecovery angles and wash-and-wear ratings. Even small deviations from optimum processing conditions may lead not only to erratic and unpredictable results, but also to an increase of undesirable side-effects.

To obtain good effects, high concentrations of relatively expensive crosslinking agents have to be used.

High bath concentrations may cause the formation of surface deposits due to migration of these agents from the interior of fibres to the surface during drying. Since such surface deposits may seriously affect desirable properties and the handle of the textile material treated, they have to be removed by afterwashing followed by drying, which further increases the cost of such processes. To vary finishing effects with conventional crosslinking formulations to meet requirements differing as to the degree of crosslinking, the ratio between dry and wet crease recovery, chlorine retention or costs, one had in many cases to apply chemically different agents. The actual crosslinking treatment, practically always carried out by subjecting the textile material containing the crosslinking agent and the crosslinking catalyst to a heat treatment (curing) after drying, required a carefully selected balance between curing time and curing temperature if excessive tendering of the cellulosic fibres was to be avoided, the duration of the heat treatment having to be increased when the curing temperature was lowered and vice versa. There was, however, an upper limit of about 180C. to the curing temperature due to the adverse effect such high temperatures might have on dye-stuffs, fluorescent brighteners and other finishing agents present. Even at this upper limitof the'temp'erature range, curing times would not be much below about 30 seconds. There was also a lower limit to the curing temperature, i.e., a threshold temperature below which crosslinking would take place insufficiently or not at all even if curing times were increasedto for instance 5 minutes. or more. This lower threshold temperature for most know crosslinking formulations was in the range of 130 to 150C. depending on the chemical nature of the agents involved. It thus was impossible to adjust within a wide range a given conventional crosslinking formulation to curing conditions or curing equipment available or desirable, and even for an adjustment within the relatively narrow range where such adjustments were feasible, one had to carefully determine by preliminary tests for each crosslinking formulation the proper balance between curing time and curing temperature. Curing at low temperatures such as for instance to C. with curing times below 2 minutes was impossible.

This invention relates to improvements in crosslinking formulations which produce better mechanical properties of the crosslinked cellulose fibres at the same or even higher levels of crease recovery or wash and wear performance.

According to the present invention there is provided a method of introducing crosslinks to a cellulosic fibre or material, which process comprises treating the material with a solution containing 1. a crosslinking agent comprising a mixture of an aldehyde having a molecular weight not greater than 60 and a nitrogeneous compound having a molecular weight of not greater than 250, said nitrogeneous compound having at least two groups, said groups being adjacent a carbonyl group,

the molar ratio of aldehyde to nitrogeneous compound being from about 12:1 and about 2:1;

2. a catalytically effective amount of a mixture of (a) i a potentially acidic inorganic salt of zinc or magnesium, and (b) a salt of fluorine-containing acid selected from the group consisting of alkali metal, al-

fluorides, and

3. an abrasion resistance improving additive comprising from about 0.03 to about 3.0 mols of a neutral alkali metal salt of an inorganic monobasic acid.

This invention provides a new crosslinking system for fibrous material at least partly consisting of cellulosic fibres, particularly fibrous material present in the form of textile sheet material such as woven or knitted fabrics.

In some of its embodiments, this invention provides a crosslinking system which is inexpensive, simple to carry out and which requires application of a relatively small amount of solid material to the fibres.

which can be modified in a simple way by means of additives to give predeterrninable variations of finishing effects and mechanical properties, i.e., which can be adapted to requirements simply by varying the concentration of additives or finishing effects required and/or losses of mechanical strength to be tolerated.

which enables crosslinking to be effected at much higher speeds and yet at lower temperatures than have been necessary for conventional crosslinking systems.

which involves a low solids content formulation (where migration during drying is much less of a hazard) where most reaction components used in the formulation are low price chemicals; due to the low solids content it is in many cases unnecessary to afterwash the textile material after crosslinking.

kaline earth metal and zinc fiuoborates and silicowhich enables the obtaining of exceptionally good finishing effects at exceptionally low losses of abrasion resistance.

The process of this invention may be carried out on textile material consisting of or containing cellulose fibres such as cotton, linen, rayon, polynosic, high modulus rayon, and high wet strength rayon. The fibres may be in the form of textile sheet material such as woven or knitted fabrics.

In the present process, the aldehyde constituent of the crosslinking agent mixture may comprise such compounds as formaldehyde, glyoxal and acrolein, or compounds capable of producing these aldehydes, such as acetals.

The nitrogeneous compound of the crosslinking agent mixture may have at least two 1 groups, adjacent with each group a carboxyl group. The molar ratio of aldehyde to nitrogeneous compound of the crosslinking agent may be between about 12:1 and 2:1, preferably between about 6:1 and 2:1.

The nitrogeneous compound preferably is a dior polymethylol derivative of a cyclic urea, carbamate, uron or triazone. The nitrogen atom of the N-methylol groups preferably does not contain'a hydrogen atom, but is substituted with an alkyl, alkoxy, methylol, aceto or a halogenated alkyl group. The nitrogeneous compound is preferably dimethylol ethylene urea.

The potentially acidic inorganic salt of the crosslinking catalyst may be an inorganic salt of magnesium or zinc. The preferred salt of this type is magnesium chloride. The salts of fluorine-containing acids are selected from silicoborates and fluoborates. The preferred salts are the alkali metal, alkaline earth metal and zinc salts. The ratio of the molar concentration of the potentially acidic salt of the fluorine-containing salt of the crosslinking catalyst may be within the range of from about :1 to about :1.

The ratio of the molar concentration of the catalyst mixture to the molar concentration of the crosslinking agent may be from about 1:4 to about 1:15.

The abrasion improving additive may be a neutral salt selected from chlorides, bromides, thiocyanates and nitrates of the alkali metals sodium, potassium and lithium. Preferred modifiers are lithium chloride, lithium thiocyanate and sodium thiocyanate.

The treating solution may also include a cure retardant which may be a nitrogeneous compound having at least one amino group. The compound preferably has the formula in which R, R" and R are alkyl such as methyl or ethyl, acyl, oxyalkyl or alkoxy alkyl groups. The nitrogeneous cure retarding agent ordinarily will be present in the treating solution at a concentration not exceeding about 0.1 mol per litre.

The cure retardant may also comprise an alkali metal thiocyanate. Where the agent which improves abrasion resistance is an alkali metal thiocyanate, such compounds also serves as a cure-retarding agent. Where the cure-retarding agent is a thiocyanate, it will ordinarily be present in the treating solution at a concentration of less than about one mol per litre.

Other agents such as softeners, hydrophobing or flame-retarding agents, white or colored pigments, or dyestuffs may also be present in the bath.

The solvent for the treating solution may be aqueous or non-aqueous. Typical non-aqueous solvents are chlorinated hydrocarbons. Prior to heating the treated fibres to effect crosslinking, the solvent is removed, at least partially, by evaporation.

Crosslinking may be effected by heating in a dry state or if desired in presence of residual moisture (a dry cure being the preferred method), or by applying energy by irradiation. This crosslinking treatment may be carried out in one or in several steps involving if desired different reaction conditions as to the degree of swelling of the fibre, the temperature/duration of the cure or to reaction catalysts. The final curing step may be carried out after the textile material has been subjected to conventional textile processing (fibres spun into yarns, processing yarns into fabrics, fabrics into garments).'

The curing conditions used to effect crosslinking according to the present invention are such that the abrasion improving additives have per se virtually no catalytic effect, i.e., they will not produce any appreciable and durable increase of dry crease recovery if applied to cellulose fibres together with the crosslinking agents in absence of the catalyst mixture mentioned above and subjected to curing conditions which in presence of the catalyst mixture will produce a high degree of crosslinking, nor will their presence appreciably affect the degree of dry crease recovery angles obtained. Their main effect thus is on mechanical properties, in particular on the abrasion resistance as determined for instance according to AATCC 934966, a standardized method for determining the abrasion resistance, developed by the American Association of Textile Chemists and Colorists. The term abrasion improving additive thus essentially means an agent which when added to the crosslinking formulation will produce very substantially better wear resistance for a given level of crease recovery. The amount and kind of reaction modifier added to the formulation is determined by requirements as to the maximum loss of abrasion strength which can be tolerated at a given level of crosslinking. The addition of such agents will of course increase costs to a small degree, and they thus will be added only to the degree necessary to obtain beneficial effects on mechanical properties. Some of these additives, in particular lithium salts, will improve wash and wear ratings by raising wet creasing angles virtually without affecting dry crease recovery.

The cure-retarding agents may be used to adjust curing conditions to requirements as regards curing temperatures and curing time. In most cases the mildest cure (low temperature, short reaction times) will be the most economical and also the most desirable cure with regard to the prevention of heat induced discoloration and to hydrolytic damage to the cellulose present. In some cases it is, however, desirable to use a system which requires a hard cure, for instance if the processing sequence commonly called post-cure, Permanent Press or Durable Press is to be used, i.e., where curing is effected only after making-up operations, or in cases where fabrics are to be embossed or subjected to other treatments involving mechanical deto change the ratio between other components of the system or to use different agents.

The treatingsolution of this invention may be applied to textile material in the form of single fibres, yarns or woven, knitted or non-woven fabrics. The preferred application, however, is to apply to the textile material the components and agents from a bath, to remove the 120C, these temperatures being increased by 10C.

for 5 g/litre, 20 for 10 g/l and 30 for 20 g/l of the triazone or'35C. if 0.5 to 1 mol ofNaCNS was present). The aim of most trials was to compare mechanical properties (tensile strength loss, abrasion resistance) at the same level of dry crease recovery and/or wash and solvent, i.e., to dry at least partly and to effect .crosslinking of the cellulose by subjecting toa heattreatment (curing). Drying and curing maybe effected in one or in separate steps. Between drying (which may be only partial at that state and may be completed subsequently) and curing one may subject the textile material to treatments involving mechanical deformation such as to embossing or pressing in a dry state or in presence of residual solvent, or to known textile processing operations such as spinning fibres into threads or yarns, producing textile sheet material from yarns, or to making-up operations on fabrics. The textile material may consistof cellulose fibres alone, or of blends of cellulosic with non-cellulosic fibres such as for instance synthetic thermoplastic fibres spun from polyamides, polyesters, acrylic or vinylic polymers, polyurethanes, polycarbamates, polyefins, from copolymers, from mixtures of polymers of from thermoplastic material such as cellulose esters. The cellulose component may be native cellulose such as cotton and linen, or regenerated cellulose fibres such as rayon,. polynosic, high modulus, high wet strength rayon fibres or chemically modified regenerated cellulose fibres.

Following is a description by way. of example .only of methods of carrying the invention into effect.

In the following examples, asatisfactory level for noiron, Durable Press or Permanent Press performance. on an all cotton shirting broadcloth, is considered to be a wash and wear rating of 4.5 or higher of AATCC 88-1961 T Standard, dry creasing angles of around 300 (sum of warp and filling) according to AATCC 66-1968 a maximum tensile strength loss of around 50 percent and as an acceptable Accelerator abrasion resistance (determined according to AATCC 93- l969),a weight loss of less than percent.

These values are widely acceptedas borderlines for Durable Press or No-Ironall-cotton fabrics all over the world. In the case of blends, these accelerator abrasion and tensile strength loss values do not apply.

In order to obtain-comparable results in the following I examples, all crosslinking treatments were carried out by the pad-drycure method, i.e., by paddingthe formulation on to the'fab'ric (pick-up 70 to 75 percent),

drying to less than 2 percent humidity at temperatures not exceeding.120, followed bycuring at the proper,

temperature DMEU andcarbamate with MgCl at catalyst: 3 minutes at 150C., with MgCl lfluoborate: 1 minute at 130C., DMEU with MgCl as catalyst 3 min-.

utes at 145C with MgCl plus fluoborate 1 minute at wear performance.

All concentrations listed in Tables I to IV are in grams per litre.

Abrasion resistance is in percent weight loss after the standard abrasion test described in AATCC 93l969.

w Table I, belowfdemonstrates that mixtures of an al- A comparison of Examples 1 and 2 shows that while formaldehyde by itself is a strong and cheap crosslinking agent when used with the fluoborate/mag'nesium chloride catalyst, a concentration of 27 g/l solid formaldehyde is too low for obtaining a wash and wear rating of 4.5 even though the tensile strength loss already is reaching 55 percent and abrasion strength is no longer acceptable for practically all end uses. An increase of theformaldehyde concentration to 36 g solid formaldehyde per litre (100 g 36 percent solution) as in Example-2, does give a wash and wear-rating of 4.5, but tensile strength losses and abrasion strength are totally unacceptable.

In the case of DMEU or carbamate used above, (Examples 3 and 4), the situation is similar. To obtain good wash and wear ratings, one has to apply high concentrations, which give excessive tensile and particularly cent). These effects are. shown only by the mixtures forming the subject of the present invention, irrespective of the nitrogeneous compound used together with formaldehyde, (DMEU responding best) as is shown in the following tables. Examples 6 and 7 also show that these formulations are cheap and have a very low solids concentration, thus affecting the hand to much lesser degree and showing a much lower tendency for the formation of surface resin due to migration during drying.

- Formaldehyde (36% sol.) DMEU (50% sol.) Q

TABLE I' Fabric: Cotton poplin, bleached and mercerized '100 g 7's g g g 80 g TABLE I Fabric: Cotton poplin, bleached and mercerizcd DMPU (50% sol.) Carbamate (N-ethyl.) (50% sol.) 180 g 180 g MgCl o aq. g 20 g 20 g 40 g 40 g 20 g 20 g NaBF 2g 2g 2g 2g 2g 2g 2g LiCl 40 g 40 g NaCNS 80 g Softener 30 g 30 g 30 g 30 g 30 g 30 g 30 g Tensile Strength loss"(lill) 55% 75% 37% 61% 58% 43% 47% Abrasion 24.5% 34.4% 12% 24% 21% 6.5% 7.5% Wash & Wear Rating" 4 4.5 2.75 4.5 4.5 4.75 4.5 Dry Crcasing Angle" 300 310 275 310 290 310 305 (1) Determined according to ASTM 1) 1682-64. (2) Determined according to AATCC 93-1969. (3) Determined according to AATCC 88-1961 T. (4) Determined according to AATCC 66-1968.

Table II, below, demonstrates that mixtures of forlating 4.5 4.5 4.0

ry creasing maldehyde with DMEU in different ratios within the angles,

ranges defined in the specification gives an excellent balance of properties.

Table II also shows that there is an optimum concentration for the lithium chloride (Examples 11, 12 and 13).

TABLE ll Fabric: Cotton poplin, bleached and mercerized Formaldehyde (36% sol.) 75 g 50 g 50 g 50 g 50 g 50 g DMEU (50% sol.) 80g 80g 100g 100g 100g 100g MgCI -(a aq. 20 g 20g 20 g 20 g 20 g 20 g NaBF. 2g 2g 2g 2g 2g 2g LiCl 40 g 40 g 40 g 20 g 40 g 60 g Softener g 30 g 30 g 30 g 30 g 30 g Tensile strength (loss fill.) 43% 40% 36% 38% 43% Abrasion(2) 6.5% 7.5% 7.1% 5.2% 4% 4.2% Wash and Wear Rating(3) 4.75 4.5 4.5 Dry Creasing Angles(4) 300 290 290 290 290 295 Table lll, below, shows that various widely used rii trogeneous cross-linking compounds when used in mixture with formaldehyde give an excellent balance of properties. Example 16 shows that an acetal (a polyethylene glycol acetal in this case) can be substituted for formaldehyde in the aldehyde/nitrogeneous compound mixture to obtain similar results.

Wash and Wear different blends including polynosic and polyester fibre blends. Examples 17 and 18 demonstrate that improved abrasion resistance can be obtained on blends. The frosting effect observed on crossdyedcotton polyester blends, which is due to preferential fibrillation and removal of crosslinked cotton fibres, was found to be 4 for the fabric treated according to Example 17 (with LiCl), while it was 3 for the same fabric given a conventional treatment, the untreated material having a rating of 4.5, i.e., only slightly better than the sample treated according to Example 17 (5 is the best rating). Example 19 demonstrates that sodium silicofluoride may be used in place of the fluorborate without affecting effects.

Dry creasing angles(4) What is claimed is:

1. A process for crosslinking cellulose fibres which comprises treating cellulose fibres with a solution containing l a crosslinking agent comprising a mixture of an aldehyde having a molecular weight not greater than 60 and a nitrogeneous compound having a molecular weight not greater than 250, said nitrogeneous compound having at least two groups, and each such group being adjacent a carbonyl group, the molar ratio of aldehyde to nitrogeneous compound being from about 12:1 to 2:1; (2) a catalytically effective amount of a mixture of (a) magnesium chloride, and (b) a salt of a fluorine-containing acid selected from the group consisting of alkali metal, alkaline earth metal, and zinc fluoborates and silicofluorides, the molar ratio of magnesium chloride to that of the salt of, a fluorine-containing acid being in the range between about :1 and 15:1, and the molar concentration of the catalytic mixture to the molar concentration of the crosslinking agent mixture in said solution being in the range of from about 1:4 to about 1:15, and (3) as an abrasion improving additive from about 0.3 to about 3 mols per litre of a neutral lithium halide or alkali metal thiocyanate, and heating said fibres to cause said crosslinking agent to react with said fibres.

2. The process of claim 1 wherein the molar ratio of aldehyde to nitrogeneous compound of the crosslinking agent is between about 6:1 and about 2:1.

3. The process of claim 1 wherein said nitrogeneous compound is selected from the group consisting of diand poly-methylol derivatives of cyclic ureas, carbamates, and triazones.

4. The process according to claim 1 wherein said aldehyde is formaldehyde.

5. The process of claim 3 wherein the nitrogeneous compound is dimethylol-ethylene urea.

6. The process of claim 1 wherein the abrasion improving additive is lithium chloride.

7. The process of claim 1 wherein the salt of a fluorine-containing acid is sodium fluoborate.

8. The process of claim 1 wherein the catalyst comprises a mixture of magnesium chloride and sodium fluoborate.

9. The process of claim 1 wherein the solution for treating the cellulose fibres is an aqueous solution.

10. The process of claim 1 wherein said treating solution contains from about 0.5 to about 1.5 mols per litre of said crosslinking agent mixture.

1 l. The process of claim 10 wherein said treating solution contains from about 0.6 to about 1.0 mols per litre of said crosslinking agent mixture.

12. The process of claim 1 wherein said treating solution contains as a cure-retarding agent a nitrogeneous compound having formula 14. Cellulosic fibres which have been treated according to the process of claim 1.

Claims

2. The process of claim 1 wherein the molar ratio of aldehyde to nitrogeneous compound of the crosslinking agent is between about 6:1 and about 2:1.
3. The process of claim 1 wherein said nitrogeneous compound is selected from the group consisting of di- and poly-methylol derivatives of cyclic ureas, carbamates, and triazones.
4. The process according to claim 1 wherein said aldehyde is formaldehyde.
5. The process of claim 3 wherein the nitrogeneous compound is dimethylol-ethylene urea.
6. The process of claim 1 wherein the abrasion improving additive is lithium chloride.
7. The process of claim 1 wherein the salt of a fluorine-containing acid is sodium fluoborate.
8. The process of claim 1 wherein the catalyst comprises a mixture of magnesium chloride and sodium fluoborate.
9. The process of claim 1 wherein the solution for treating the cellulose fibres is an aqueous solution.
10. The process of claim 1 wherein said treating solution contains from about 0.5 to about 1.5 mols per litre of said crosslinking agent mixture.
11. The process of claim 10 wherein said treating solution contains from about 0.6 to about 1.0 mols per litre of said crosslinking agent mixture.
12. The process of claim 1 wherein said treating solution contains as a cure-retarding agent a nitrogeneous compound having formula
13. The process of claim 12 wherein the cure-retarding agent is sodium thiocyanate.
14. Cellulosic fibres which have been treated according to the process of claim 1.