US3092436A - Tanning with lignin sulfonic acid-chromium reaction product and fatty acid salts - Google Patents

Description

3,092,436 Patented June 4, 1963 TANNING WITH LIGNIN SULFONIC ACID-CHRO- MIU Ihg REACTION PRODUCT AND FATTY ACID SAL Robert G. Banner and John H. Pierce, Painesville, and John T. Chain, Chardon, Ohio, assignors to Diamond Alkali Company, Cleveland, Ohio, a corporation of Delaware No Drawing. Filed Apr. 26, 1961, Ser. No. 105,563

16 Claims. (Cl. 8-94.26)

This invention relates toa new and improved process for the tanning of leather and more particularly relates to a new and improved leather tanning process which utilizes a chromium-containing tanning composition.

This application is a continuation-impart of our eopending applications Serial No. 650,825, filed April 5, 1957, now abandoned, and Serial No. 26,675, filed May 4, 1960, now US. Patent No. 2,995,415.

At the present time, two recognized types of tanning procedures have been accepted and widely-practiced in the leather industry. These are the so-called vegetable tanning wherein the conversion of the hide to leather is accomplished with aqueous tanning solutions extracted from materials of vegetable origin, such as, finely-ground oak or hemlock bark or the like, and the so-called chrome" tanning which utilizes various reducible salts of chromium, notably alkali metal bichromates, and especially sodium bichromate, to effect the conversion of the hides to leather.

Each of these tanning techniques has certain advan tages which has justified its continued use despite other somewhat serious disadvantages, which at the present time, have not been completely overcome. For example, vegetable tanning produces leather and particularly,

sole leather, of an excellent color, having wear properties and waterproofness which are generally quite satisfactory. However, vegetable tanning is an extremely slow process and hence despite the advantage of providing a so-called full leather of good color, the slowness of vegetable tanning has precluded its use in many applications where it otherwise would be highly desirable.

On the other hand, one of the outstanding advantages of chrome tanning is the speed with which the tanning can be efiected. Moreover, chrome tanned leather exhibits good wear and abrasion resistant properties. However, the principal disadvantages of conventionally chrome tanned leather, especially when used as sole leather, are that it is susceptible to distortion and at times is slippery on wet surfaces. Additionally, chrome tanned leather frequently has a poor color and generally does not cut well in that ragged edges are produced on cutting.

In an effort to overcome the recognized disadvantages of vegetable and chrome tanning, prior workers in the art have proposed several variations in tanning procedure.

For example, it has been suggested that leather first be tanned with a vegetable tanning material and then retanned with a cationic, chromium-containing tanning composition, i.e., the conventional type of chrome tanning composition. Advantages of such a procedure are that a higher shrinkage temperature is obtained, together with increased abrasion resistance, especially in sole leather so prepared. However, it has been found that leather thus produced frequently has a poor color. Moreover, since such a procedure involves additional treatment, inevitably there is an increase in the cost involved. In addition, the extremely slow vegetable tanning process, used as a first step, still is encountered.

Alternatively, prior workers in the art also have proposed first to chrome tan leather and then to use a vegetable tanning composition as a retan. However, this technique has not been found to be the complete answer to the problem either, because a heavy vegetable tan frequently is required to obtain a satisfactory leather color. Inasmuch as the desirable wear properties of the leather generally decrease with an increase in the amount of vegetable retanning effected, this procedure has resulted in leather, and particularly, sole leather, having poor Wear characteristics.

In addition to the above proposals for overcoming the disadvantages of chrome tanning and vegetable tanning, it has been proposed to tan the leather using a tanning composition containing a predominant amount of nonionic chromium as the tanning material. Such a tanning composition is prepared by reacting lignin sulphonic acid with sodium bichromate in the amount of at least 25% by weight of the lignin solids in the lignin sulphonic acid. This method is described in detail in our copending application Serial No. 650,825. Although by such a tanning process the principal disadvantage of chrome tanning and vegetable tanning is overcome and a leather having an abrasion resistance considerably greater than that of either chrome or vegetable tanned leather is generally obtained, the resistance to water absorption of this leather, although superior to that of conventionally chrome tanned leather, is not as good as that of vegetable tanned leather. Consequently, it is necessary to subject the leather to a waterproofing treatment, such as, impregnation with a silicone resin. Moreover, it has been found that the quality of the leather so produced often varies from one tanning run to the next. Thus, although the leatheer produced in one run may have good color and resistance to abrasion, that produced in succeeding runs may not.

Accordingly, it will be appreciated that up to the present time considerable effort has been expended in an attempt to improve the presently-available techniques for the tanning of leather, particularly leather destined for application as sole leather.

It is, therefore, the principal ob 'ect of the present invention to provide an improved leather, especially sole leather, characterized by a maximum of the desirable properties of vegetable tanned leather as well as those of chrome tanned leather, while minimizing the disadvantages of both prior tanning techniques.

Another object of this invention is to provide an improved leather tanning process wherein this improved leather will be consistently produced.

Another object of the present invention is to provide an improved leather, especially sole leather, which is characterized by a resistance to water absorption at least comparable to that of a vegetable tanned leather.

A further object of the present invention is to provide a new and improved tanning process by means of which this improved leather can be produced, which process is an improvement over the process set forth in applications Serial Nos. 650,825 and 26,675.

These and other objects of the present invention will become apparent to those skilled in the art from the description of the invention which follows.

The method of the present invention envisions a tanning process which utilizes a cationic compound selected from the group consisting of cationic salts of fatty amides, fatty amines, fatty amine esters and cyclic fatty amides in combination with a predominantly non-ionic, chromium-containing tanning composition, which composition is the product obtained by chemically reacting lignin sulphonic acid with at least sufiicient of a hexavalent chromium compound to produce a predominantly nonionic, chromium-containing material.

More specifically, in the practice of the present method,

where the cationic compound used is a cationic salt of a fatty amide, which is the preferred cationic compound, the fatty amide may be further defined as being the reaction product of a fat and an amine, which reaction product is then further reacted with an ionizable, saltforming compound to form the cationic substance. By a fat" is meant a solid or liquid oil consisting of the glyceryl esters of fatty acids and mixtures of fatty acids. The amines may be lower aliphatic amines, such as those containing up to about 7 carbon atoms in a straight or branched chain and may be primary, secondary or tertiary, mono-, dior tri-amines, or may be higher polyamines, such as triethylenetetramine or tetraethylenepentamine. The ionizable, salt-forming compounds are exemplified by aliphatic acids, acid salts, as Well as halides of both aliphatic and aromatic compounds, such as halogenated ethers and the like. It will, of course, be appreciated that in addition to reacting a fat and an amine to prepare the fatty amide, the amide may be prepared by the reaction of an amine and a fatty acid or by the reaction of a lower fatty acid ester, such as a methyl ester, with an amine or ammonia.

The non-ionic, chromium-containing tanning composition is prepared by reacting lignin solids, in the form of lignin sulphonic acid, with a hexavalent chromium compound, generally sodium bichromate, the sodium bichromate being in the amount of at least 25% by weight of the lignin solids and not in excess of about 50% by weight of the lignin solids. The preparation of this predominantly non-ionic, chromium-containing tanning composition is given in detail in our copending applications Serial Nos. 650,825 and 26,675. This chromium tanning composition, when used in conjunction with the cationic compound described hereinabove, in accordance with the practice of the present method, is found to yield consistently leather of improved properties, particularly with regard to resistance to water absorption and wear, thus providing a new and improved tanning process.

The expression lignin sulphonic acid as used throughout the specification and claims is intended to refer to lignin sulphonic acid obtained from neutralized sulphite waste liquors. In practice, these liquors, formed as a byproduct from the cooking of wood fibers in the paper industry, are generally neutralized with calcium or magnesium salts and the resulting liquors used as such or spray dried to obtain a crude water-soluble lignin sulphonate, generally calcium sulphonates, or as termed herein, lignin solids." One commercially-available product of this type is termed Goulac. The water-soluble lignin solids can be dissolved in water and acidified prior to use in the practice of this invention, or, if desired, may be formed in situ during the preparation of the composition embodying the present invention.

In the practice of the present method, the hides which are to be tanned are subjected to the conventional pretanning treatments of soaking or washing, liming, fleshing, dehairing, bating and pickling. Thereafter, the hides are subjected to the cationic composition in combination with an aqueous solution of the non-ionic, chromium-containing tanning composition obtained by chemically reacting lignin sulphonic acid with a hexavalent chromium compound. Although there is no one critical point in the present process at which the hides must be contacted with the cationic compound and the non-ionic, chromium-containing tanning composition, it has been found to be essential that at the time the hides are contacted with the cationic compound and the non-ionic, chromium-containing tanning composition, a reaction between these materials can take place. Thus, for example, the cationic compound can be added to the sodium chloride solution with which the hides are wetted and in which they are fioated prior to the addition of the non-ionic, chromiumcontaining tanning agent. Alternatively, the cationic compound and the non-ionic, chromium-containing tanning composition can be added simultaneously to the hides,

or, as a further alternative, the cationic compound can be added to the hides immediately after tanning with the non-ionic, chromium-containing agent has been completed. However, it has been found that when the hides are contacted with the cationic composition after the non-ionic, chromium-containing tanning material has been removed therefrom or at the time of some subsequent treatment, such as, during retanning or fat liquoring, at which time no appreciable reaction between the cationic compound and the non-ionic, chromium-containing tanning agent takes place, the leather thus produced may be of a poorer quality, particularly with regard to color, fullness, and resistance to water absorption.

While it is not known for certain why a leather having superior characteristics can be consistently produced only when the cationic composition and the non-ionic, chromium-containing tanning agent are brought into contact with the hides at a time when a reaction between the materials can take place, it is known that the cationic composition and non-ionic, chromium-containing tanning agent do react to give a product, which, when dry is only very slightly soluble in water and the common organic solvents, and only slowly soluble in acids or alkalies. It is believed that the formation of this product in the hides which are tanned is responsible for the production of the leather having the above-described superior characteristics. It is for this reason that it is essential in the process of the present invention that the hides are contacted with the cationic material and the non-ionic, chromium-containing tanning agent at a time in the process wherein a reaction between these materials can take place. It has further been found that from the standpoint of penetration of the hides and completeness of reaction, it is preferable to add the cationic composition to the sodium chloride wetting or float solution prior to the addition of non-ionic, chromium-containing tanning agent.

It has further been found, in the practice of the present method, that the addition of a small amount of a buffering material such as sodium formate or to similar organic acid salts, the non-ionic, chromium-containing tanning material, e.g., in the amount of about 2%% by weight of the fleshed hides, results in faster penetration of the tanning composition into the hides, thus speeding up the rate of tanning. Moreover, when sodium formate is added to the tanning solution, it is no longer necessary to raise the pH of the tannage by the addition of alkali, such as, sodium bicarbonate, in order to obtain a good degree of tanning. Thus, where previously it has been necessary to raise the tannage pH to within the range of about 4.5 to 5.0, by adding sodium formate to the tanning composition, leather having characterisitcs at least as good as that previously produced and in most instances even better, can be produced using a pH of about 3.0 to 4.0. It is apparent that by this use of sodium formate the tanning of the hides is accomplished in a shorter time.

The leather thus-produced may be used without further tanning treatments or, as desired, it may be retanned with a conventional vegetable tanning material or any of the conventional chrome tanning materials. Additionally, the leather may be fat liqwored prior to usage, either with or without the additional retannjng. It is, of course, appreciated that retannage of the leather produced in accordance with the present method will be determined by the characteristics that are necessary according to the end use of the leather. Inasmuch as the characteristics imparted to leather by use of the conventional vegetable and/or chromium retanning are well known to those skilled in the art, it is not deemed to be necessary to give a detailed explanation as to when the various retannages are desirably used. Similarly, the various processes for fat liquoring leather and the characteristics imparted to leather which has been so treated, are also deemed to be well known to those skilled in the art, so that no further explanation of these processes is seen to be necessary.

In the practice of the preferred method of the present invention, the hides to be tanned, after the conventional preliminary treatments of washing, liming, fleshing, dehairing, baring and pickling, are floated in an aqueous solution containing about to by weight of sodium chloride. The weight of the aqueous solution used is approximately equal to the weight of the hides to be tanned. In addition to the sodium chloride, the aqueous float solution also contains up to about 3% by weight of the hides, preferably about 0.3% to 1.2% of the cationic compound, which compound is preferably in the form of an oil emulsion so as to be dispersed more easily in the aqueous float solution. The hides are run in the aqueous float solution for a period up to about one hour whereupon to by weight of the predetermined nonionic, chromium-containing tanning material and up to about 2 /2 by Weight of sodium formate is added thereto. Taming of the hides is carried out at a temperature of about 100 F. for a period of time sufiicient to eifect complete penetration of the hides, generally about 4 to 8 hours. Thereafter, the hides are removed from the aqueous solution and held for a period of about 8 hours, whereafter they may be subjected to further treatment, such as, retanning, with a vegetable tan, retanning with a conventional chrome tanning liquor, fat liquoring, or they may be washed and dried and used wtihout further treatment. The leather thus produced is found to have a good color as well as exceptional resistance to abrasion and water absorption. It is to be understood that all of the weights given above are based on the weight of the fleshed hides.

In order that those skilled in the art may better understand the method of the present invention and the manner in which it may be practiced, the following specific examples are given.

EXAMPLE 1 Preparation of Cationic Compounds 50 parts by weight of prime lard oil and 25 parts by weight of dipropylene triamine are heated together for a period of 3 hours at a temperature in the range of 220- 240 F. Thereafter the reaction mixture is cooled to a temperature of 170 F. and 25 parts by weight dichloroethyl ether is added thereto while maintaining the tempcrature below 300 F. After the addition of the dichloroethyl ether, the temperature of the reaction mixture is maintained within the range of 290-3l0 F. for a period of 2 hours. The resulting cationic compound is found to have the following structural formula:

Using the procedure of Example 1, the following cationic compounds are formed:

Examples Components J Amounts Prime Lard Oil 50 parts by wgt.

Dipropylene Thiamine .l 25 parts by wgt. Acetic Acid 25 parts by Wgt. 3 Prime Lard Oil..

50 parts by wgt. 25 parts by wgt. 25 parts by wgt.

These compounds are found to have the following structures:

group represents the a-cryl radicals of the fatty acids present in the lard oil, consisting substantially wholly of stearic, palmitic, oleic and linoleic acids, R being approximately C H EXAMPLE 5 To illustrate the oil-emulsion composition of the cationic compound, the following composition is formed:

Percent by wgt.

Product of Example 1 30.0 Mineral oil (solvent refined petroleum oil having a Saybolt viscosity of 200 seconds at 100 F.) 39.7 Fleshing oil (animal oil pressed from fleshing grease) 24.0 Polyethylene glycol mono-oleate 6.0 Diamyl phenol 0.3

This composition is easily dispersed in water and is thus found to provide an excellent way of bringing the cationic compound into thorough Contact with the hides to be tanned.

EXAMPLE 6 Preparation of the Non-Ionic Chromium Tanning Composition One hundred lbs. of lignin solids is dissolved in 250 lbs. (30 gallons) of Water and 35 lbs. of by weight sulphuric acid is added thereto and the resulting mass is agitated for 1 hour, during which time S0 fumes are evolved. Twenty-five lbs. of Na Cr O ll-i o as a 50% by weight solution is then added slowly with continuous and vigorous agitation to avoid formation of any chromelignin gel lumps. After all the bicromate solution is added, the mass is agitated for 2 hours after which time 5.5 lbs. of sodium hydroxide is added, as a 25 solution, with continuing vigorous agitation. The resultant mixture is allowed to stand overnight, after which time another 5.5 lbs of sodium hydroxide, as a 25% solution, is added with vigorous agitation and sufficient water is then added to make a total volume of 50 gallons. The pH of the resultant liquid tanning solution is 4.0. Chemical analysis of the liquid tan so prepared is as follows:

Percent by wgt.

Solids 28.6 Cr O Anionic chromium 23.9 Non-ionic chromium 70.7 Cationic chromium 5.4

This material can be employed either as a liquid or spray dried, advantageously with the desiccating chamber of the dryer adjusted so as to provide an inlet air temperature of about 400 F. and an outlet air temperature of about 2l0230 F. during the drying operation.

EXAMPLE 7 lbs.) and 1.6% by weight of the stock of the composition of Example 5 (5.0 lbs). The tanning drum is run for a period of about 1 hour while the temperature of the float solution is maintained at about 70 F. Thereafter, the non-ionic, chromium-tanning composition of Example 6, as a 30% solution, is added to the drum in the amount of about 40% by Weight of the stock (126 lbs.). Additionally, 2% by weight of the stock of sodium formate (6.25 lbs.) is also added to the tanning drum. Thereafter, the drum is run for a period of about 4 hours at a temperature of about 95 F., at the end of which time the pH of the tanning solution is about 3.4. The stock is allowed to remain in the drum in the tanning solution overnight. The liquids are then drained from the tanning drum and the tanned hides are washed. The leather thus-produced, which has a shrink temperature of about 195 F., is found to have excellent color as well as excellent resistance to abrasion and water.

EXAMPLE 8 Leather produced in accordance with the procedure of Example 7 is retanned with a commercial chromium-tanning composition indicated by the manufacturer, Diamond Alkali Company, as Tanolin KXD. The analysis of this material is as follows:

Percent by wgt.

S (hydrolyzable) 21.1

Na SO Basicity (basicity is defined as the percent of total chromium which is present which is linked to hydroxyl groups) 46-48 The leather is floated in the tanning drum in 34 gallons (283 lbs.) of water at a temperature of about 100 F. This amount of water is about 90% by weight of the leather in the drum. Four percent by weight of the leather in the drum, of Tanolin KXD" (12.5 lbs.) dissolved in 2 gallons of water is then added to the drum. The drum is run for about 2 hours at a temperature of about 100 F. at the end of which time the pH of the tanning solution is about 2.5. 0.5%, by weight of the leather in the drum, sodium bicarbonate (1.57 lbs.) is then added to the drum and the drum is run for an additional 30 minutes. The pH of the tanning solution is about 3.3. The leather is then removed from the drum and rinsed. The thus-produced leather is found to have excellent color and excellent resistance to abrasion and water absorption.

EXAMPLE 9 The leather tanned in accordance with the procedures set forth in Examples 7 and 8 is retanned using a vegetable tan. The leather is floated in a tanning drum in 314 lbs. of water at about 70 F. This amount of water is equal to about 100% of the weight of the leather. 23.5 lbs. quebracho, containing about 60% by weight tannin, is then added to the drum. This amount of quebracho is equal to about 4 /z%, by weight of the leather in the drum, of tannin. The drum is then run for about 2 hours after which time the leather is rinsed until the rinse water from the leather is clear. The thus-produced leather is found to have excellent color as well as excellent resistance to abrasion and water absorption.

EXAMPLE 10 Leather produced in accordance with the preceding three examples, Examples 7, 8 and 9, is loaded in an oil wheel using a conventional load consisting of sugar, mineral oil, sulfonated cod oil and fillers, for a period of about 45 minutes. At the end of this time, substantially complete penetration of the load into the leather has been accomplished.

EXAMPLE 11 A number of tanning runs are made using the procedure set forth in Example 7 with the exception that the amount of the composition of Example used is varied in each of the runs. The leather obtained from these runs is then subjected to a Water absorption test to determine the effect that variations in the amount of the composition of Example 5 has upon the leather produced. In the water absorption test, a leather sample is weighed before and after being immersed in distilled water for a period of /2 hour and a period of 2 hours. The water absorption is then expressed as the percent of weight increase of the sample after immersion. The exact test procedure used is Method 13-30 as set forth in the December 31, 1957, edition of the Official Technical Methods of the American Leather Chemists Association. Using this procedure, the results obtained are as follows:

Water Absorption in percent wgt. increase of the ample 5 in percent by \vgt. of the stock After )4 hour After 2 hours From these results it is seen that there is a decrease in the water absorption of the leather when the amount of the composition of Example 5 used is increased from 01% and 4% by weight of the stock being tanned. However, when the amount of the composition of Example 5 used is increased to about 12% by weight of the stock to be tanned, there is an increase in the water absorption of the leather produced.

While there have been described various embodiments of the invention, the methods described are not intended to be understood as limiting the scope of the invention as it is realized that changes therewithin are possible and it is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be uilized.

What is claimed is:

1. In the tanning of leather, the method which comprises subjecting the material to be tanned to a cationic compound selected from the group consisting of cationic salts of fatty amides, fatty amines, fatty amine esters and cyclic fatty amides in combination with an aqueous solution of a predominantly non-ionic, chromium-containing reaction product obtained by chemically reacting lignin sulphonic acid with a hexavalent chromium compound.

2. In the tanning of leather, the method which comprises the step of subjecting the material to be tanned to a cationic compound selected from the group consisting of cationic salts of fatty amides, fatty amines, fatty amine esters and cyclic fatty amides in combination with an aqueous solution of a predominantly non-ionic, chromiumcontaining reaction product obtained by chemically reacting lignin sulphonic acid with a hexavalent chromi um compound, in an amount within the range of 25% to about 50% by weight of the lignin sulphonic acid, expressed as lignin solids.

3. In a tanning of leather in accordance with claim 1, the further step which comprises retanning the thus-treated material with a vegetable tan.

4. In the tanning of leather in accordance with claim 1, the further step which comprises retanm'ng the thustreated material with a chrome tan.

5. In the tanning of leather in accordance with claim 3, the further step which comprises fat liquoring the thus-treated material.

6. In the tanning of leather in accordance with claim 4, the further step which comprises fat liquoring the thus-treated material.

7. A tanned animal skin having incorporated therein a substantially water-insoluble product formed by the reaction of a cationic compound selected from the group consisting of cationic salts of fatty amides, fatty amines, fatty amine esters and cyclic fatty amides and a predominantly non-ionic, chromium-containing composition formed by chemically reacting lignin sulphonic acid with a hexavalent chromium compound.

8. A tanned animal skin having incorporated therein a substantially water-insoluble product formed by the reaction of a cationic compound selected from the group consisting of cationic salts of fatty amides, fatty amines, fatty amine esters and cyclic fatty amides and a predominantly non-ionic, chromium-containing composition obtained by chemically reacting lignin sulphonic acid with a hexavalent chromium compound in an amount within the range of 25% to about 50% by weight of the lignin sulphonic acid, expressed as lignin solids.

9. A process of tanning leather which comprises subjecting a pickled hide to a cationic compound selected from the group consisting of cationic salts of fatty amides, fatty amines, fatty amine esters and cyclic fatty amides in combination with an aqueous solution of the reaction product obtained by chemically reacting a solution of lignin sulphonic acid with a solution of sodium bichromate in an amount of at least 25% and not more than 50% by weight of the lignin solids content of the lignin sulphonic acid, retaining said hides in said solution at an elevated temperature until the desired tanning is effected and thereafter washing the thus-tanned leather.

1 0. The process as claimed in claim '9 wherein the aqueous solution of the reaction product of lignin sulphonic acid and sodium bichromate also contain up to about 2.5% by weight of a buffering material.

11. The process as claimed in claim wherein the buffering material is an organic acid salt.

12. The process as claimed in claim 11 wherein the organic acid salt is sodium formate.

13. A method of tanning which comprises floating a pickel-d hide in an alkali metal chloride solution, which solution also contains up to about 3% by weight of the hides of a cationic compound selected from the group consisting of cationic salts of fatty amides, fatty amines, fatty amine esters and cyclic fatty amides, adding thereto a liquid tanning composition comprising the reaction product of lignin sulphonic acid and a hexavalent chromium compound in an amount Within the range of 25% to about by weight of the lignin sulphonic acid expressed as lignin solids, said liquid tanning composition also containing up to about 2.5% by weight of sodium formate, retaining said hides in said solution at a temperature between about to F. for a period of time sufficient to obtain a high leather shrink temperature and thereafter Washing the thus-treated leather.

14. The process according to claim 13 wherein the thus-treated leather is retanned.

15. The process as claimed in claim 13 wherein the cationic compound is present in an amount within the range of about 0.3% to 1.2% by weight of the pickled hides.

16. The method as claimed in claim 15 wherein the sodium formate is present in an amount of about 2.5% by weight of the aqueous tanning solution.

References Cited in the file of this patent UNITED STATES PATENTS 2,201,041 Katz May 14, 1940 2,328,901 Grimm et al Sept. 7, 1943 2,729,534 Ehrensperger Jan. 3, 1956 2,809,088 Meister et al. Oct. 8, 1957 2,938,892 Sheehan May 31, 1960 2,989,362 Heyden et al. June 20, 1961 2,995,415 Banner et a1. Aug. 8, 1961

Claims (1)

1. IN THE TANNING OF LEATHER, THE METHOD WHICH COMPRISES SUBJECTING THE MATERIAL TO BE TANNED TO A CATIONIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF CATIONIC SALTS OF FATTY AMIDES, FATTY AMINES, FATTY AMINE ESTERS AND CYCLIC FATTY AMIDES IN COMBINATION WITH AN AQUEOUS SOLUTION OF A PREDOMINANTLY NON-IONIC, CHROMINUM-CONTAINING REACTION PRODUCT OBTAINED BY CHEMICALLY REACTING LIGNIN SULPHONIC ACID WITH A HEXAVALENT CHROMIUM COMPOUND.