US3294479A - Clo2 depilation and kerating removal from hides and skins - Google Patents

Clo2 depilation and kerating removal from hides and skins Download PDF

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Publication number
US3294479A
US3294479A US429898A US42989865A US3294479A US 3294479 A US3294479 A US 3294479A US 429898 A US429898 A US 429898A US 42989865 A US42989865 A US 42989865A US 3294479 A US3294479 A US 3294479A
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hides
unhairing
chlorine dioxide
pelts
bath
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US429898A
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Rosenbusch Kurt
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Hoechst AG
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Hoechst AG
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    • C—CHEMISTRY; METALLURGY
    • C14—SKINS; HIDES; PELTS; LEATHER
    • C14C—CHEMICAL TREATMENT OF HIDES, SKINS OR LEATHER, e.g. TANNING, IMPREGNATING, FINISHING; APPARATUS THEREFOR; COMPOSITIONS FOR TANNING
    • C14C1/00—Chemical treatment prior to tanning
    • C14C1/06—Facilitating unhairing, e.g. by painting, by liming

Definitions

  • the present invention provides a new process for removing the keratin-containing parts of animal hides and pelts and the keratin-containing parts adhering to such hides and pelts, for example hairs or scales.
  • unhairing there is understood in the tanning industry an operation in which the hair of hides and pelts is loosened to such an extent that it can easily be mechanically removed from the dermis together with the keratin-containing parts of the hides such as the dermis, hairs, and scales.
  • Bacterial or enzymatic unhairing processes have the disadvantage that the short undercoat of the hair and the roots are often not affected; these spotted, incompletely dehaired pelts thus obtained must be subjected to a second chemical unhairing process.
  • the chemical liming process has the disadvantage that the hides are considerably swelled by the alkalies used, and this af fccts the sensitive grain. Because of this swelling, the finished leather shows protruding fat-wrinkles, and looseness of the grain of the finished leather caused by the movement imparted to the swollen hides during dressing is often observed.
  • the keratin-containing parts of animal hides and pelts and the keratin-containing parts adhering to such hides and pelts can be easily removed in a particularly advantageous manner when the hides and pelts are exposed to the action of chlorine dioxide.
  • This chlorine dioxide can be contacted with wet, preferably soaked hides and pelts in the form of a gas, suitably with exclusion of oxygen to prevent the risk of an explosion, and conveniently in admixture with an inert gas such as carbon dioxide or nitrogen.
  • the chlorine dioxide gas may be introduced into an aqueous medium containing the hides to be treated.
  • the chlorine dioxide gas can be easily produced in a suitable apparatus by, for example, acidification of an alkali metal chlorite solution, by reduction of chloric acid or its salts by means of a reducing agent such as sulfurous acid or oxalic acid, or .by the action of concentrated sulfuric acid on an alkali metal chlorate.
  • a suitable apparatus by, for example, acidification of an alkali metal chlorite solution, by reduction of chloric acid or its salts by means of a reducing agent such as sulfurous acid or oxalic acid, or .by the action of concentrated sulfuric acid on an alkali metal chlorate.
  • the production of chlorine dioxide gas from chloric acid and oxalic acid is very advantageous because carbon dioxide is formed as an oxidation product of oxalic acid and dilutes the explosive gaseous chlorine dioxide so that it can be handled without risk.
  • the chlorine dioxide gas stream is introduced into the unhairing bath through a distributing tube, if desired together with an inert gas, for example nitrogen or carbon dioxide, as a diluent.
  • the unhairing bath should have a pH-value below about 7.8, and preferably should not be alkaline, to prevent salt formation, for example the formation of alkali metal chlorites and chlorates.
  • aqueous solutions of substances which give off chlorine dioxide instead of gaseous chlorine dioxide, for unhairing in an aqueous'medium.
  • the watersoluble salts of chlorous acid, especially the alkali metal chlorites are especially suitable. For reasons of economy, sodium or potassium chlorite is preferred.
  • Aqueous solutions of these substances give off chlorine dioxide upon acidification, for example at pH-values below 7.8, preferably below pH 7. Therefore, if it is not intended to use chlorine dioxide 'gas in the unhairing process according to the present invention, aqueous acidic solutions of substances that give off chlorine dioxide are generally used at pH-values below pH 7.8.
  • a weakly acid medium having -a pH-value in the range of pH 3 and pH 6. to ensure a slow and uniform evolution of chlorine dioxide and a long lasting action of the chlorine dioxide on the hides and pelts to be treated.
  • the use of pH-values below pH 3 involves the risk that the evolution of chlorine dioxide may proceed too violently so that the chlorine dioxide escapes too rapidly and is partly unused.
  • any mineral or organic acids which are inert towards chlorine dioxide may be used.
  • weakly dissociated acids for example formic acid, acetic acid, lactic acid, glycollic acid or oxalic acid
  • medium strength acids or even mixtures of various acids.
  • acid salts such as primary sodium phosphate or .primary sodium sulfate, or even buffer mixtures such as a mixture of a mineral acid with sodium acetate, can also be used to adjust pH.
  • the unhairing bath When unhairing is carried out in an aqueous medium, the unhairing bath is generally used in a quantity of about 10-500% (referred to the weight of the soaked hides).
  • the optimum quantity of unhairing bath depends above all on the manner in which unhairing is carried out. If unhairing is carried out in a pit, relatively large quantities of water are generally used, since the material to be unhaired must completely be covered by the unhairing solution.
  • the quantity of bath depends in this case essentially on the size and form of the pit in relation to the amount of hides. If unhairing is carried out in a closed drum, which in practice is the most widely used method, a relatively small quantity of bath, namely about l-100%, preferably 30-70%, referred to the weight of the soaked hides, is sufficient.
  • chloride dioxide is caused to act for several hours on hides or pelts, preferably at room temperature or at a slightly elevated temperature, either with or without movement of the hides.
  • the temperature maintained during unhairing has an influence on the time necessary for complete unhairing.
  • At very low temperatures for example, at temperatures below about 8 C., the oxidation proceeds so slowly that the process is no longer economical.
  • Operation at too elevated temperatures for example, at temperatures above about 50 C., involves the risk that the collagen of the skin may be damaged, so that it is not recommended to use temperatures exceeding about 50 C. Therefore, in practice, the process is carried out at temperatures between about 10 C. and about 45 C.
  • the period of time of hlorine dioxide action on the hides or pelts necessary to effect unhairing furthermore depends on the concentration of the chlorine dioxide in the aqueous ba-th. If the concentration of chlorine dioxide is high, unhairing will be completed in a shorter period of time than with a low concentration.
  • the operational conditions i.e. temperature, quantity of water, quantity of chlorine dioxide and number of revolutions of the drum, will generally be so adjusted that the treating period is within an economically acceptable range of 20 hours. In general, a minimum period of treatment of at least about 7 hours is necessary to achieve complete unhairing.
  • the necessary quantity of chlorine dioxide furthermore depends on the goods to liquor ratio and the manner in which unhairing is carried out.
  • the minimum quantity of chlorine dioxide is in the range of about l-2 kg. of chlorine dioxide per kg. of hair to be removed, i.e. for hides and pelts having hair in a quantity of, for example 1% by weight, about 1-2 kg. of chlorine dioxide are used per kg. of hides and pelts.
  • the unhairing according to the process of the present invention is carried out in aqueous solutions containing substances which yield chlorine dioxide, it will generally be sufficient to use these substances in quantities of about 1-10%, referred to the weight of the crude hides or pelts. This indication of the quantity, however, should not be considered as a limitation. It is quite possible to use larger quantities, but for reasons of economy the quantity of substance giving off chlorine dioxide will be kept at a minimum.
  • the loosened hairs or scales are scraped off the treated skins or hides in the usual manner either manually or mechanically by means of an unhairing or scraping machine.
  • the motion imparted to the skins is itself sufiicient to remove the hair.
  • the oxidative unhairing process of the present invention does not cause swelling of the skin substance, apparently since it is carried out in the acid pH-range.
  • a further advantage of the process of the invention over the known unhairing methods is that completely clean, pure white pelts are obtained even when spotted hides are unhaired, because the chlorine dioxide simultaneously has a bleaching action and destroys the hair pigment contained in the s In.
  • the chlorine set free by reduction of chlorine dioxide is bound irreversibly by the collagen and thereby apparently causes chlorine pre-tanning of the external portions of the hides.
  • This chlorine pro-tanning produced simultaneously in the unhairing process of the present invention, additionally strengthens the grain.
  • a further advantage of the present invention is that, in unhairing with chlorine dioxide, a decomposition of transversely cross-linked collagen fibers is also caused. This in turn results in a desirable loosening of the structure of the fibers. Furthermore, the free chlorine liberated in the unhairing process of the present invention causes chlorination and saponification of triglyceridic fats. Assisted by the keratin-sulfonic acids contained in the unhairing bath, the chlorinated fats emulsify in the bath and are thus removed to a large extent from the hide. Hence, when operating by the unhairing process of the invention, it is possible to omit the step of degrading the skin by means of a saturated calcium hydroxide solution, usually carried out after dehairing, and of degrading by bating enzymes.
  • Oxidative unhairing according to the present invention permits the saving of labor and a, paratus and, moreover, it permits automation of the individual process steps in the manufacture of leather, starting from soaking up to tanning, without it being necessary to touch the skins after they have been introduced into the drum.
  • the process of the present invention can be applied to all animal hides and pelts. It is not limited to the unhairing of hides and pelts of any particular kind, and can be used for dehairing the hides or pelts of haired animals such as cattle. goats, stags, buffaloes, antelope, or sheep. It is also suitable for removing other keratincontaining parts of animal hides, for example, for removing scales from reptile skins.
  • Example I A black and white spotted bovine hide having a soaked weight of 26 kg. was treated, after soaking in a pit, for 20 hours with a solution of 1.25 kg. of sodium chlorite and 0.5 kg. of glycollic acid in 100 l. of water and adjusted to pH 3.3-3.5 by means of about 0.5 kg. of 57% aqueous glycollic acid.
  • the pelt dehaired with sodium chlorite could be directly chrometanned without pickling and gave, after dyeing and stuffing, a leather having a uniform coloration and closely fixed grain.
  • One-half of a calf hide having a soaked weight of 2.3 kg. was drummed for 15 hours at 35 C. with a bath containing 3 l. of water and 0.3 kg. of a 30% aqueous sodium chlorite solution.
  • the bath had been adjusted to pH. 3.2-3.5 by the addition of 0.1 kg. of a 57% aqueous glycollic acid solution;
  • the second half of the calf hide was drummed with a conventional limesulfide solution.
  • Example 3 The separated neck of a heavy bulls hide was placed into a pit charged with 350% of water (referred to the weight of the skin) having a temperature of 25 C. The bath was adjusted to pH 7.5. Then, gaseous chlorine dioxide was introduced into the bath through a distributor tube for 25 hours. The chlorine dioxide was produced from a sodium chlorite solution by the addition of acid and transferred by means of a continuous stream of gaseous nitrogen serving as an inert diluent. In the same manner, a streain of a gaseous mixture of chlorine dioxide and carbon dioxide, produced by the action of oxalic acid on sodium chlorate, could be used. The bleaching action of the chlorine dioxide was already evident after a period of action of 3 hours.
  • the sulfonated hair can be dissolved by adding a 10% sodium carbonate solution. A well degreased pelt was obtained, the hair pigments of which were completely dccolorcd, and which showed no protruding fat-wrinkles.
  • the soaking solution was then discharged and 50 l. of water at 15 C. and 10 kg. of 30% aqueous sodium chlorite were added.
  • the hides were then drummed for 2 minutes with this solution.
  • -1 kg. of lactic acid was added slowly through the tubular axle of the drum and the pH-value of the unhairing bath was adjusted to a value in the range of 3 and 3.5 by the addition of a 30% sulfuric acid.
  • the pickle pelt thus obtained was free of neck and fat-wrinkles which this type of hide usually shows.
  • chromic oxide 50 l. of water and 5% of chromic oxide (referred to the weight of the crude hides), in the form of the commercially available powdered chromium tanning salt, were then introduced into the drum and the hides wcrc drummed for 5 hours.
  • the tanning agent was then neutralized during drumming in the course of 5-6 hours b the slow addition of about 1-1.5 kg. of sodium bicarbonate.
  • the bovine hides in the above-described method of operation are dcpickled. al'tcr unhairing and discharge of the uuhairiag bath. by the addition of 1.5 kg. of powdered sodium thiosulfate and drumming for 30 minutes without addition of water. and then rinsed for 15 minutes v. ith water.
  • Tanning with vegetable or synthetic tanning agents can then directly be carried out. There is no risk of over-tanning. in which the tanning agent precipitates too rapidly on the surface of the pelt and thus forms 'a diffusion-inhibiting layer which prevents the tanning agent from further penetration into the pelt.
  • the amotnt of water required in the above-described method of operation. i.c. from soaking to tanning, or of waste water obtained in this operation, is in the range of only 4-5 m. per 1000 kg. of hides. in addition, the
  • the waste water is biologically harmless, as is evidenced by the fact that when it is added, for example, to a fishpond in a quantity of 150 g./l., it does not harm the fish or affect the plants therein.
  • the amount of waste water in the hitherto used limesodium sulfide unhairing process for the same quantity of hides is in the range of at least about 40-50 m5.
  • the removal of the waste water of the limesulfide process involves the ditficulties described in the introductory part of this specification.
  • Example 5 100 kg. of sheep skins were soaked in the usual manner and sheared on a wet--ncaring machine to a length of hair of a out 0.3 cm. 'lhe wool obtained could be sold as not chemically treated sheared wool.
  • the shorn hides ⁇ tere drummed in a drum containing 100 l. of water, kg. of a 30% aqueous sodium chlorite solution and 2 kg. of 60% aqueous acetic acid.
  • the pH-value of the unhairing liquor was from 3.3 to 3.5.
  • the hides were unhaired and. simultaneously, the chlorine set free caused chlorination and saponification of the natural fat which was thus easily emulsified and separated from the pelt.
  • Example 6 10 kg. of dried snake hides (python) were soaked in the usual manner and then drtnnmed for 25 hours in a drutn containing 20 l. of water of 20 C., 1.5 kg. of a aqueous sodium ehlorite solution and 0.25 kg. of phosphoric acid.
  • the pH-value of the liquor was 3.0- 3.3. Head parts and tail parts were tied together in order to avoid entanglement.
  • the keratin-containing scales of the hides were removed completely from the collagen fiber structure.
  • about of the design of the hides was bleached off.
  • the hides were drummed for 8 hours at 20 C. with a soltttion of 0.1 kg. of potassium permanganate in 20 l. of water, then after treated in the drttm for 1 hour with a solution of 0.15 kg. of sodium bisulfite in 20 l. of water in orderto remove the manganese dioxide formed, and subsequently rinsed with water.
  • the pelt obtained in this manner was of a pure white and could be treated directly with tawing agents.
  • Example 7 A calfs hide soaked in the usual manner was hung in a wet state in a chamber which could be closed hermetically and which was provided with a gas inlet and outlet tube. The chamber was closed and the air contained in this chamber was displaced by the introduction of nitrogen. Then. a uniform stream of a mixture of gases, consisting of nitrogen and chlorine dioxide in equal parts by volume, was passed through for 2:) hours at 20 C. After a period of action of 1 hour, a strong bleaching effect could be observed. After 20 hours, the gas mixture in the chamber was displaced by the introduction of pure nitrogen. The discolored hair of the calfs hide could then be easily removed from the hide manually or by means of an unhairing machine. The pelt thus obtained could be treated directly with vegetable tanning agents or, after pickling. with chrome tanning agents.
  • a method for removing the keratin-containing parts 01' animal hides and pelts and the keratin-containing parts adhering to such hides and pelts which comprises contacting said hides and pelts with chlorine dioxide in an aqueous bath for a time sutficient to loosen said keratincontaining parts, said aqueous bath having a pH up to pH 6 and comprising from about 1 to 10 percent. by weight of the hides and pelt treated, of an alkali metal chlorite. said chlorine dioxide being generated in situ in said aqueous bath from said alkali metal chlorite.
  • a method for removing the keratin-containing parts of animal hides and pelts and the keratin-containing parts adhering to such hides and pelts which comprises contacting said hides and pelts with chlorine dioxide in an aqueous bath for a time sufiicient to loosen said keratincontaining parts.
  • said aqueous bath having a pH up to pH 6 and said chlorine dioxide being introduced as a gas into said aqueous bath from a source outside said bath in an amount of at least 1-2 kilograms per kilogram of keratin-containing parts to be removed.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Treatment And Processing Of Natural Fur Or Leather (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
US429898A 1963-08-17 1965-02-02 Clo2 depilation and kerating removal from hides and skins Expired - Lifetime US3294479A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DEF40522A DE1230517B (de) 1963-08-17 1963-08-17 Verfahren zum Enthaaren und Auflockern von Haeuten und Fellen

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US (1) US3294479A (da)
BE (1) BE651921A (da)
CH (1) CH446597A (da)
DE (1) DE1230517B (da)
DK (1) DK109679C (da)
GB (1) GB1049706A (da)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3445178A (en) * 1965-04-08 1969-05-20 Degussa Depilation with a chlorite and hydrogen peroxide or a perborate
US3482924A (en) * 1966-06-08 1969-12-09 Ugine Kuhlmann Depilation using dichromate and strong acid
US3508857A (en) * 1966-02-25 1970-04-28 Hoechst Ag Process for removing keratin-containing parts from animal hides and pelts and the keratin-containing parts adhering to such hides and pelts
US4224029A (en) * 1978-11-27 1980-09-23 Heinz George G Exotic leather, method of processing same, and method of processing domestic fowl

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT118721B (de) * 1927-06-30 1930-08-11 Fr Cinechromatique Procedes R Einrichtung für die Photographie und Kinematographie in natürlichen Farben.
DE935991C (de) * 1952-03-30 1955-12-01 Waldhof Zellstoff Fab Verfahren zum Bleichen und Reinigen von Leder
GB749769A (en) * 1953-06-01 1956-05-30 British Leather Manufacturers Improvements in or relating to preserving hides and skins from bacterial damage
US3097049A (en) * 1959-03-26 1963-07-09 Meybeck Jean Process for bleaching and shrinkproofing wool

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT118721B (de) * 1927-06-30 1930-08-11 Fr Cinechromatique Procedes R Einrichtung für die Photographie und Kinematographie in natürlichen Farben.
DE935991C (de) * 1952-03-30 1955-12-01 Waldhof Zellstoff Fab Verfahren zum Bleichen und Reinigen von Leder
GB749769A (en) * 1953-06-01 1956-05-30 British Leather Manufacturers Improvements in or relating to preserving hides and skins from bacterial damage
US3097049A (en) * 1959-03-26 1963-07-09 Meybeck Jean Process for bleaching and shrinkproofing wool

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3445178A (en) * 1965-04-08 1969-05-20 Degussa Depilation with a chlorite and hydrogen peroxide or a perborate
US3508857A (en) * 1966-02-25 1970-04-28 Hoechst Ag Process for removing keratin-containing parts from animal hides and pelts and the keratin-containing parts adhering to such hides and pelts
US3482924A (en) * 1966-06-08 1969-12-09 Ugine Kuhlmann Depilation using dichromate and strong acid
US4224029A (en) * 1978-11-27 1980-09-23 Heinz George G Exotic leather, method of processing same, and method of processing domestic fowl

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Publication number Publication date
DK109679C (da) 1968-06-04
BE651921A (da) 1965-02-17
GB1049706A (en) 1966-11-30
CH446597A (de) 1967-11-15
DE1230517B (de) 1966-12-15

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