US2829943A - Tanning agent and process - Google Patents

Description

2,829,943 Patented Apr. 3, 1%58 2,829,943 TANNiNG AGENT AND PnocEss Edward M. Filachione and Edward H. Harris, in, Philadelphia, Pa., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Application January 24, 1956 Serial No. 561,163

9 Claims. (Cl. 8-94.33) (Granted under Title 35, U.-S. Code (1952), sec. 266) A non-exclusive, irrevocable, royalty-free license in the invention herein described for all governmental purposes, throughout the world, with power to grant sublicenses for such purposes is hereby granted to the Government of the United States of America.

This invention relates to the tanning of hides andskins and to the leather thus produced.

An object of this invention is to provide novel tanning materials and processes. Another object is to provide leather having new and improved properties; in particular, leather that retains leatherlike properties after being heated above its shrink temperature and that shrinks reversibly when so heated.

The shrink temperature of leather is intimately related to the type and degree of tannage used in its preparation. Untanned hides have a very low shrink temperature (about 60 C.) and, when heated at or above this temperature in the presence of water, shrink irreversibly to yield on drying a hard, horny, translucent product having no resemblance to leather. Conventional tannage yields leather of somewhat elevated shrink temperature. If heated above such temperature, however, itshrinks irreversibly and becomes hard and stiff, thus becoming useless for most purposes.

Accordin to the invention, a new t e of leather is made by applying a tanning composition, preferably 211- kaline, containing as the tanning agent a polyglycidyl ether of glycerol, preferably in aqueous suspension, to hides, skins, or pretanned leather until they are tanned. These tanning agents are conveniently made by condensing epichlorohydrin with glycerol according to well known procedures, such as those described in U. S. Patents 2,5 81,464 and 2,633,458. They are a mixture of glycidyl ethers having the general formula wherein R is a glyceryl residue, at is l to 2, y is 1 to 2, z is 1 to 2 and x+z=2 to 3. It is to be understood that since these materials are complex mixtures and are polymeric in nature, the above formula represents only their average composition.

Since glycerol is trifunctional, it can react with three moles of epichlorohydrin, thus thus giving rise to branched-chain or even crosslinked products. It is believed that this actually occurs to a certain extent, either in the preparation of the polyglycidyl ether or in the use of the latter as a tanning agent, or both, and that the unique tannage achieved in the practice of the invention is directly related to this ability of the polyglycidyl ether to form branched and/or cross-linked chains. This view is substantiated by the fact that, of the many monoand di-epoxides that have been used or suggested for use in tannage, none has been observed or reported to give the unique valuable properties achieved with the glycerol polyglycidyl ethers of this invention.

Hides, skins or pretanned leather, after being tanned with our polyglycidyl ethers of glycerol, not only show the usual valuable properties imparted by conventional tannages but in addition show several distinctive new and useful properties. The most startling new property is the behavior of the leather when exposed to steam or hot water. Ordinary vegetable tanned leather has a characteristic shrink temperature of about 80 C. and if heated above this point undergoes irreversible shrinkage such that after it is cooled and dried it is shrunken, warped and misshapen and is also hardened, stiffened and embrittled so that it no longer has leatherlike properties. In contrast, when leather tanned by the process of this invention is heated above its shrink temperature, although it shrinks somewhat, the shrinkage is reversible and the article recovers substantially its original shape and dimensions upon being cooled. Of equal importance, it retains substantially its original shape, feel, flexibility and other useful properties. Another highly valuable property of leather tanned by our process in. its ready wettability. in the commercial processing of hides, skins and leather occasions frequently arise where it is necessary to rewet them after they have been dried. Frequently such rewetting is a slow and tedious process and often the efiectiveness of the subsequent treatment is impaired by the rewetting having been uneven or incomplete. We have found that hides, skins and leather treated by our process rewet with great speed and uniformity. Frequently this case of rewetting is a valuable property in the finished leather product, as in chamois leather for instance. Where it is objectionable it is easily counteracted by conventional treatment of the leather with oils, waxes, or other hydrophobic agents. Another advantage of tanning by our proc ess is that a White leather is produced thus eliminating various steps in conventional white leather manufacture, such as bleaching and/or filling with white pigments. Furthermore the leather is white throughout its entire thickness in contrast to bleached and/ or pigmented white leathers. Also the leather produccdby our process is completely resistant to detannage by means of acids, alkalies and other agents and hence is more stable than conventional mineral and vegetable tanned leathers.

Our process of tanning can be carried over a wide range of conditions. The pH range can be varied widely, however, we prefer to carry out the process in alkaline solution preferably in the pH range of about 8 to 12. If desired inorganic salts may be used as in conventional tannery practice to control osmotic pressure but are not essential for tanning to be effected. Our process can be carried out in organic solvents such as the lower ketones and ether alcohols or mixtures of these with water. However, we prefer to use aqueous systems because of the greater cost and hazards of organic solvents. 'If desired surface active agents may be used in our process to increase the rate of tanning.

The practice of the invention is illustrated by the following examples.

Example I Pickled cowhide was depickled by a one day immersion in 5% aqueous solution of sodium bicarbonate. After being rinsed with water, 15 g. (dry weight) of the wet hide was rolled in a jar mill together with a suspension of 10 g. of a glycerol polyglycidyl ether in 200 ml. of water. The polyglycidyl other had an epoxide equivalent of about and its average composition corresponded to the structural formula above wherein x, y and z had values of about 1, l and l. After two days in the jar the pH ofthe liquid, originally 8.1, had dropped to 6.9. The hide was rinsed with water and its shrink tempera.

Example II A 20 g. (dry wt.) sample of the used in Example I was treated as in Example I with 10 g. of the same glycerol polyglycidyl ether in 100 ml. of water, the significant difference being that a wetting agent wet depickled hide polyglycidyl ether used in Example I and 100 ml. of water or 0.2 M aqueous buffer solution. The various treatments are shown in the table below at regular time intervals the pH of the liquor and the shrinkage temperature (Ts) was determined with the results shown in the table. As expected calfskin was tanned more rapidly than cowhide, a leather showing reversible shrinkage being obtained after 8 hours of tanning (Examples XII to XIV). Cowhide required one or more days, excepting when treated in the presence of lime, to give a leather showing reversible shrinkage (Examples VI to XI).

Shrinkage temp., 0., after Example Buffer Salt, percent pH 8 hrs. 24 hrs. 48 hrs. 72 hrs. 96 hrs.

Cowhide VI Na lactate. 0.2 M 6. 4-7. 8 65 71 75 77 77 VII None (H2O) None" 5. 8-7. 3 66 69 77 80 79 VIII NaHCOs. 0. M 8. 1-8.3 68 74 75 77 76 IX NarCOa, 0.1M 9.9 74 80 78 80 83 XI Ca(OH)z, Silt. Na2SO4, 10---- 10. 8-11. 1 79 78 86 86 Calfskin:

XII--." NazCOz, 0.2 M NfizSOi, 10---. 10.2 81 85 85 87 86 XIII MgO.1 a Na2S04,10- 10.2 78 85 85 85 XIV---" Oa(OH 2, Sat NazSO4, 10.--. 10.2-11.3 85 87 88 89 was used (1 g. of sodium lauryl sulfate). After 24 hours in the jar mill the sample was removed, rinsed and evaluated. Its shrink temperature was 80 C. After 1 minute in boiling water it was cooled, whereupon it regained its original dimensions and appeared identical to the product of Example I.

Example III A sample of pickled grain split steerhide was depickled, brought to its isoelectric point, and dehydrated by immersion in two changes of acetone. A g. sample of the dehydrated steerhide was then treated with a solution comprising 10 g. of the glycerol polyglycidyl ether used in Example I in 90 ml. of ,B-methoxyethanol diluted with 10 ml. of water which solution contained 0.5 g. of sodium carbonate. After 4 days the hide under treatment was removed, rinsed twice with acetone and washed in water. The shrinkage temperature of the leather was about 80 C. and the original dimensions were regained upon cooling the shrunken leather.

Example IV A sample of pickled calfskin was depickled and tanned with the same glycerol polyglycidyl ether and the same procedure as in Example I except that the aqueous suspension of tanning agent contained 10% of sodium chloride and was 0.2 molar with respect to sodium carbonate. The tanned leather had a shrinkage temperature of 80 C. even after a treatment for only 8 hours. The shrinkage caused by boiling in Water for 1 minute was fully recovered on cooling and all characteristic leather-like properties were retained after such treatment.

Example V A sample of the depickled cowhide used in Example I was relimed by soaking it for 24- hours in saturated lime water. The hide was then tanned as in Example I. After one day of treatment the pH of the liquid remained at about 9. The treated hide was Washed in water and found to have a shrinkage temperature of 80 C. The leather showed the same reversibility of shrinkage as that in Example I.

Examples VI-XI V A series of experiments was run to show the rate of tannage under various conditions.

Pickled calfskin and cowhide were depickled by immersion in 5% aqueous sodium bicarbonate solution, rinsed, brought to the isoelectric point (pI-I about 5) and then washed to remove salts. Samples of about 10 g. (on a dry basis) were placed in bottles with 5 g. of the glycerol In all of the treatments the maximum shrinkage temperature was reached in about three days or less. The fully tanned leathers were white, firm and flexible, and all showed the reversible shrinkage when heated in boiling water that is characteristic of the invention.

Example XV Grain split steerhide, split out of the lime, was obtained after the conventional liming, unhairing and splitting bearnhouse process. The split steerhide was delimed with an acetic acid-sodium acetate solution (pH about 5) and washed. The drained hide, 90 g. on a dry basis, was added to 875 ml. of an aqueous solution which was 0.2 molar with respect to sodium carbonate and contained 87 g. of sodium sulfate. Then 45 g. of the glycerol polyglycidyl ether used in Example I was added and the tanning carried out at room temperature by rolling the contents in a bottle placed on a jar mill. After one day of treatment the steerhide was removed and thoroughly washed in water. The shrinkage temperature of the leather was 85 C. and the shrinkage was reversible. The leather when air dried showed a gain in weight of 14%.

The grain split steerhide tanned as above with glycerol polyglycidyl ether was retanned with a blend composed of two thirds sulfited quebracho extract and one third chestnut extract in aqueous solution in the conventional manner. After 4 days the vegetable tannin had completely penetrated. The shrinkage temperature of the retanned leather was 91 C. and the gain in weight upon retanm'ng with the vegetable extract was about 50%.

Example XVI the initial value of 60 to 71 C.; after 8 hours it was 76 and after 32 hours it was Longer treatment caused no further change. The 4 and 8 hour samples showed excellent leatherlike properties and recovered almost their original dimensions after being boiled in waterfor 1 minute. The 32 hour sample was completely tanned and showed substantially full recovery from heat shrinkage without any apparent loss of its leatherlike properties.

While in the above examples the tanning agent used was :1 glycerol polyglycidyl ether having an average composition corresponding to the formula shown above in which x, y, and z had approximate values of 1, 1, and 1 respectively, equivalent results are obtained when similar glycerol polyglycidyl ethers in which x, y and 2 have values in the ranges 1-2, l-2 and l-2, respectively, are used, provided x+z is in the range 2-3.

Leather tanned according to the invention is suitable for use with any of the conventional finishing agents and processes. The process of the invention is applicable not only to the cowhide and calfskin used in the above examples but also to any hide or skin commonly used for tannage except the fur skins. The term hide, as used in the appended claims, includes all such hides and skins.

A combination tannage, in which the tannage with glycerol polyglycidyl ether either precedes or follows a conventional tannage, especially a vegetable tannage, is particularly advantageous when a highly tanned leather is desired.

We claim:

' l. A process of tanning hides comprising applying to the hides a tanning composition containing as the tanning agent a glycerol polyglycidyl ether corresponding to the formula [OOHPCETCIL O l 2Cl \o/ 1| wherein R is a glyceryl residue, x is 1 to 2, y is 1 to 2, z is l to 2, and x+z is 2 to 3 until the hides are tanned.

2. A process of tanning hides comprising applying to the hides an alkaline tanning composition .containing as the tanning agent a glycerol polyglycidyl ether corresponding to the formula CHzOl 0 I wherein R is a glyceryl residue, x is 1 to 2, y is 1 to 2, z is 1 to 2, and x+z is 2 to 3 until the hides are tanned.

3. A process of tanning hides comprising applying to the hides an alkaline tanning composition .containing as the tanning agent a glycerol polyglycidyl ether corresponding to the formla [ocHr-cH- om] R'/ 0 I OCH CH --00H OH-CH l-(g 2- 2] H201 0 wherein R is a glyceryl residue, x is 1 to 2, y is 1 to 2, z is 1 to 2, and x-I-z is 2 to 3 in aqueous suspension until the hides are tanned.

4. The process of claim 1 wherein x, y, and 2 each has a value of about 1.

5. The process of claim 2 wherein x, y, and z each has a value of about 1.

6. A process of tanning hides comprising tanning said v 6 hides with a vegetable tanning agent and thereafter applying to the resulting hides a tanning composition containing as the tanning agent a glycerol polyglycidyl ether corresponding to the formula \[(OCH2-(IJH )OGH2CCH2 O sOl 0 1 wherein R is a glyceryl residue, at is l to 2, y is l to 2, z is l to 2, and x+z is 2 to 3 until the hides are tanned.

7. A process of tanning hides comprising tanning said hides with a vegetable tanning agent and thereafter applying to the resulting hides an alkaline tanning composition containing as the tanning agent a glycerol polyglycidyl ether corresponding to the formula [0 CHFOE7CH2] O I 0 R\ OGHa-CH OCHz-OH-CH2 I l l C 2Cl y 0 wherein R is a glyceryl residue, x is 1 to 2, y is 1 to 2, z is 1 to 2, and x-l-z is 2 to 3 until the hides are tanned, and then retanning the resulting hides with a vegetable tanning agent.

9. A process of tanning hides .comprising applying to the hides an alkaline tanning composition containing as the tanning agent a glycerol polyglycidyl ether corresponding to the formula [0 Offs-(33701111 0 wherein R is a glyceryl residue, at is l to 2, y is l to 2, z is 1 to 2, and x-l-z is 2 to 3 in aqueous suspension until the hides are tanned, and then retanning the resulting hides with a vegetable tanning agent.

References Cited in the file of this patent UNITED STATES PATENTS Immendoerfer Aug. 31, 1937 OTHER REFERENCES Immendorfer, Das Leder 4, page 229 (1953).

Claims (1)

1. A PROCESS OF TANNING HIDES COMPRISING APPLYING TO THE HIDES A TANNING COMPOSITION CONTAINING AS THE TANNING AGENT A GLYCEROL POLYGLYCIDYL ETHER CORRESPONDING TO THE FORMULA