METHOD FOR TANNING OF HIDES BY MEANS OF TANNING AGENTS

Abstract: The method for tanning of hides by means of tanning agents in a tanning bath is characterized by the fact that the bath besides the hides comprises an oxidoreductase, and as tanning agent an aromatic compound and possibly other compounds which are able to react with the hides and/or the aromatic compound, and that an oxidation agent is introduced into the equilibrated tanning bath. In this manner it is possible to increase the degree of fixation considerably in comparison to the prior art methods of this kind.

Description: METHOD FOR TANNING OF HIDES BY MEANS OF TANNING AGENTS The invention comprises a method for tanning of hides by means of tanning agents. The most used tanning agents are chrome based, but chrome based tanning agents are considered environmentally unfriendly, and thus, alternative tanning agents, which are environmentally friendly, are always welcome. In the tanning art it is intended to perform a fixation of tanning agents within the collagen matrix, both due to the fact that the quality of the leather will be better with increasing degree of fixation, and also because the pollution will be reduced with increasing degree of fixation and uptake of tanning agents. However, the prior art methods for tanning of hides by means of tanning agents are open to improvement in regard to degree of fixation. Thus, the purpose of the invention is the provision of a method for tanning of hides by means of tanning agents, in relation to which the degree of fixation and uptake of tanning agents is increased considerably in comparison to the prior art methods of this kind. Now, surprisingly it has been found according to the invention that it is possible to increase the degree of fixation considerably in comparison to the prior art methods of this kind, if the tanning is supported by an enzyme belonging to a specific enzyme category in the tanning bath, and if specific primary and secondary substrates for this enzyme are added sequentially. Thus, the method according to the invention for tanning of hides by means of tanning agents in a tanning bath is characterized by the fact that the bath besides the hides comprises an oxidoreductase, and as tanning agent an aromatic compound and possibly other compounds which are able to react with the hides and/or the aromatic compound, and that an oxidation agent is introduced into the equilibrated tanning bath. A further advantage related to the invention is the fact that the use of toxic coagents (like formaldehyde) used to crosslink organic tanning agents is avoided. Furthermore the invention is environmentally friendly, as cheap synthetic tanning agents can be used instead of the conventionally used tanning agents produced by extraction of wood from tropic forests. US 3,212,996 describes a process for enzymatic modification of organic tanning agents. This prior art process is concerned with the same enzymes and the 5 same organic tanning agents as in relation to the method according to the invention, but the modified tanning agents in the prior art method are produced separately from the leather, whereas the modified tanning agents in the method according to the invention are produced in situ on the leather. Due to this in situ process the degree fixation of the modified tanning agents is superior in the method according to the invention in comparison to the prior art method. Oxidoreductases which are defined and described in "Enzyme Nomenclature 1984, Academic press, Inc., New York, London" belong to a class of enzymes that catalyze transfer of electrons from one substance to another (oxidation-reduction). It includes dehydrogenases, reductases, oxidases, transhydrogenases, peroxidases, and oxygenases. Specific examples include horseradish peroxidase, ligninases and other peroxidases such as e.g. chloroperoxidase and lactoperoxidase, and such oxidases as laccase and tyrosinase. These enzymes are preferably of microbial origin. Examples of microorganism genera which may be used for production of suitable oxidoreductases are: Trametes, Rhizoctonia, Pseudomonas, Bacillus, Streptomyces, Hygrophorus, Coprinus, Polyporus, Candida, Curvularia, Cercospora. The invention, however, is not restricted to enzymes derived from the above mentioned taxa. All microorganisms producing oxidoreductases with the desired properties may be used in relation to this invention. The primary substrate for the oxidoreductase is the aromatic compound, preferably a phenol, which is a vegetable or synthetic tan or tanning agent. Examples of vegetable tans which usually are polyphenol compounds extracted from plant materials are. catechol tans (or so-called condensed tans) and pyrogallol tans (or hydrolysable tans) as described in Part 3, Tanning Processes, in Leather Technician's Handbook, J.H. Sharphouse (Ed), Leather Producers Assoc, Kings Park Road, Moulton Park Northhampton, NN31 JD, 1989. Examples of synthetic tans include, but are not limited to, mono- or oligomeric aromatic or aliphatic compounds, optionally substituted with one or more of the following functional groups: -halogen, -OH, -SO3H " , -COOH, -NH 2 , -OCH3, or aryl, alkyl, alkene each of which may also be substituted as above. Further compounds, which may be used as tanning agents include heterocyclic and aliphatic compounds with the same functional groups as above indicated. Specific examples of aromatic compounds which may serve as primary substrates for the oxidoreductase in the present invention include: catechol, aniline, tyrosine, catechin, aromatic amino acids and derivatives thereof, pyrogallol, gallic acid, ferulic acid, 2-methyl-1 napthol, 2,6-disubstituted monophenols, guaiacol, coniferyl alcohol, protocatechuic acid, resorcinol, hydroquinone, caffeic acid, m-cresol, p-coumaric acid, anisidine, syringuldazine and syringaldehyde. The oxidizing agent which is the secondary substrate for the oxidoreductase can be hydrogen peroxide, methyl peroxide, or ethyl peroxide if the oxidoreductase is a peroxidase, and oxygen, if the oxidoreductase is an oxidase. In the last mentioned case the hides and the tanning bath are kept under oxygen free conditions in order to prevent uncontrolled polymerization prior to a sufficient penetration of the oxidase and the tanning agent into the hide matrix. In the equilibrated tanning bath the oxidase and tanning agent has penetrated into the hide matrix to such degree that an equilibrium condition is obtained. In the leather art enzymes have previously been used in relation to several hide treating steps, as appears from the below indicated table. However, to the best of applicant's knowledge, the introduction of an enzymatic treatment during tanning does not belong to the prior art and thus represents a pioneer achievement. It belongs to the prior art, however, that peroxidases and oxidases can effect oxidative polymerization of a wide variety of phenolic compounds (vide e.g. US patents 4,900,671 and 4,647,952), and furthermore that the reaction products from these reactions are highly dependent on reaction conditions and the type of enzyme used. Also, it belongs to the prior art that oxidase and peroxidase catalyzed polymerization reactions, which involve the intermediacy of phenolic radicals, can be effected in both aqueous and solvent based systems, whereby the organic solvent can be water miscible or water immiscible. The method according to the invention is performed by first applying the tanning agent(s) and the oxidoreductase to the hide either as separate solutions or as a mixture. Having obtained a uniform distribution of enzyme and tanning agent(s) within the collagen matrix, secondly polymerization is initiated by addition of the oxidation agent. When using an oxidase substrate, enzyme and possibly solvent are brought in contact with the hide under oxygen free conditions in order to prevent uncontrolled polymerization prior to having achieved a sufficient penetration of the oxidoreductase/tanning agent mix into the hide matrix. Depending on the types of substrate and oxidoreductase used and on the desired characteristics of the hide, the polymerization process is carried out in a pure aqueous system or in solvent systems, the solvents) being water miscible or water immiscible. When using a water containing system the pH may be controlled by employing conventional buffers (e.g. phosphate, carbonate/bicarbonate, tartrate, carbonate, or acetate buffers). The polymerization process may be further controlled by metering the addition of peroxide or oxygen. The enzymatic reaction may be. terminated by chemical or thermal inactivation of the enzyme, by carefully metering the oxidizing agent or e.g. by addition of catalase in the case where a peroxidase is used. The enzymatic reaction may be carried out at room temperature, but temperatures between 0 and 95°C can also be used, although most enzymes will not work sufficiently well above about 60 - 70°C. The pH range of the process would be 2-11 depending on the enzyme employed. Process conditions may be additionally optimized by varying the relative concentrations of the organic and inorganic substrates, polarity and concentration of solvent, enzyme concentration etc. Peroxidases and oxidases are known to exhibit broad substrate specificity, and the present invention thus makes possible a "tailormade" process for tanning by allowing the use of new and improved tanning agents. Thus, new and/or additional functionalities (e.g. positively or negatively charged substituents) may be added to hitherto known or unknown tanning agents in order to improve hide characteristics such as: water retention, shrinking temperature or degree of fixation within the collagen matrix. A preferred embodiment of the method according to the invention is characterized by the fact that the oxidoreductase is a peroxidase, and the tanning agent is a synthetic or vegetable, aromatic tanning agent. In this manner a high quality leather can be produced, especially a leather with high shrinking temperature. A preferred embodiment of the method according to the invention is characterized by the fact that the oxidoreductase is an oxidase, and the tanning agent is a synthetic or vegetable, aromatic tanning agent. In this manner a high quality leather can be produced, especially a leather with high shrinking temperature. A preferred embodiment of the method according to the invention is characterized by the fact that the oxidoreductase is producible by means of Polyporus pinsitus {Trametes villosa). In this manner use can be made of commercially available and cheap oxidoreductases. A preferred embodiment of the method according to the invention is characterized by the fact that the oxidoreductase is a laccase producible by means of Polyporus. In this manner use can be made of commercially available and cheap oxidoreductases. A preferred embodiment of the method according to the invention is characterized by the fact that the oxidoreductase is producible by means of Coprinus cinereus. In this manner use can be made of commercially available and cheap oxidoreductases. A preferred embodiment of the method according to the invention is characterized by the fact that the oxidoreductase is a peroxidase producible by means of Polyporus pinsitus {Trametes villosa). In this manner use can be made of commercially available and cheap oxidoreductases. A preferred embodiment of the method according to the invention is characterized by the fact that the tanning bath is aqueous. In this manner the 5 tanning can be performed in an environmentally friendly manner. A preferred embodiment of the method according to the invention is characterized by the fact that the tanning bath is organic. In this manner an improved polymerization and thus an improved degree of fixation can be obtained. A preferred embodiment of the method according to the invention is characterized by the fact that the pH of the tanning bath is 2 - 11 , preferably 2 - 8. Inside these pH intervals the enzymes exhibit satisfactory activity, and thus, a satisfactory degree of fixation can be obtained. The invention will be illustrated by the following examples. EXAMPLE 1 10 strips of leather, each extracted from the official test area IUC/2 or IUP/2, and each with a dimension of 1 cm x 6 cm, were introduced into a mixture of 100 ml of a solution of 2 mM catechol in 0.1 M universal buffer at pH 5.5. This mixture was stirred for 2 hours at room temperature. Subsequently 100 ml of laccase (235 PODU/ml) was added. The laccase was produced by means of Polyporus pinsitus, reference being made to the product sheet SP 504, B610-GB50, available on request from Novo Nordisk A/S, Novo Alle, DK-2880 Bagsvaerd, Denmark. The PODU is the laccase activity unit, defined in AF 279/2-GB, except for the fact that no hydrogen peroxide was added, and that the buffer is 0.1 N sodium acetate with pH 5 (instead of 0.1 M phosphate buffer with pH 7). The mixture was stirred on a magnetic stirrer at room temperature for about 2.5 days whereafter the shrinking temperature was measured according to the method indicated in Messung der Schrumpfungstemperatύr, Bibliothek des Leders, Vol. 10, page 157-154, Joachim Lange, 1982, Umschau Verlag. The oxidation agent during the stirring was atmospheric oxygen. In a control experiment the ten strips of leather were introduced into a mixture of 100 ml of a solution of 2 mM catechol in 0.1 M universal buffer of pH 5.5 and 100 ml of 0.1 M universal buffer. The mixture was stirred on a magnetic stirrer for about 2.5 days before the shrinking temperature was measured. 5 The shrinking temperatures were: 58°C in the control experiment, and 66°C in the experiment with enzyme. It is to be noted that a higher degree of fixation will result in a higher shrinking temperature. 10 Values of parameters which are not indicated in Examples 2 - 4, are identical to the values indicated in Example 1. EXAMPLE 2 10 strips of leather, each with a dimension of 1 cm x 6 cm, were introduced into a mixture of 100 ml of a solution of 100 ml 2 mM phenol in 0.1 M 15 universal buffer of pH 5.5. This mixture was stirred for 2 hours at room temperature. Subsequently 100 ml of laccase (235 PODU/ml) was added. The mixture was stirred overnight at room temperature on a magnetic stirrer, whereafter the shrinking temperature was measured. In a control experiment the ten strips of leather were added to a mixture 20 of 100 ml of a solution of 2 mM phenol in 0.1 M universal buffer of pH 5.5 and 100 ml of 0.1 M universal buffer of pH 5.5. The mixture was stirred on a magnetic stirrer for about 2 hours before the shrinking temperature was measured. The shrinking temperatures were: 58°C in the control experiment, and 25 62°C in the experiment with enzyme. EXAMPLE 3 A stock solution of Indulin AT 8 Kraft lignin (from Westwaco) was made as follows. A suspension of the Kraft lignin in 0.1 M universal buffer of pH 5.5 was heated to 80°C for 15 minutes followed by centrifugation and filtration, so that only the soluble part of the Kraft lignin was used. The solubility at pH 5.5 is 5.5 mg/ml. 10 strips of leather, each with a dimension of 1 cm x 6 cm, were introduced into 100 ml of the stock solution. The mixture was stirred at room temperature for 2 hours. Subsequently 100 ml of laccase (235 PODU/ml) was added. The mixture was now stirred overnight at room temperature, whereafter the shrinking temperature was measured. In a control experiment the ten strips of leather were introduced into a mixture of a solution of 100 ml of stock solution and 100 mi of 0.1 M universal buffer of pH 5.5. The mixture was stirred on a magnetic stirrer for about 20 hours before the shrinking temperature was measured. The shrinking temperatures were: 64°C in the control experiment, and 70°C in the experiment with enzyme. EXAMPLE 4 10 strips of feather, each with a dimension of 1 cm x 6 cm, were placed in a mixture of 100 ml of a solution of 100 ml Lignosite 431 sodium lignosulfonate (Georgia Pacific Corp.) in 0.1 M universal buffer of pH 5.5 (100 mg/ml). This mixture was stirred for 2 hours at room temperature. Subsequently 100 ml of laccase (235 PODU/ml) was added. The mixture was stirred at room temperature for 20 hours before the shrinking temperature was measured. In a control experiment the ten strips of leather were introduced into a mixture of a solution of 100 ml sodium lignosulfonate in 0.1 M universal buffer of pH 5.5 and 100 ml 0.1 M universal buffer pH 5.5. The mixture was stirred on a magnetic stirrer for about 20 horus before the shrinking temperature was measured. The shrinking temperatures were: 59°C in the control experiment, and 65°C in the experiment with enzyme. Similar experiments were carried out with Coprinus peroxidase, reference being made to product sheet SP 502, available on request from Novo Nordisk A/S, Novo Alle, DK-2880 Bagsvaerd, Denmark. In this case the oxidation agent was hydrogen peroxide, a universal buffer of pH 7.0 was used, the reaction was conducted with a magnetic stirrer at room temperature overnight, an enzyme dosage of 4000 PODU/ml was used, and the concentration of hydrogen peroxide was 10 mM. Also, a surplus amount of hydrogen peroxide was added every 15 minutes during the first 5 hours of the reaction. The results in regard to shrinking temperature of the leather strips pertaining to the experiments with Coprinus peroxidase were similar to the results indicated in Examples 1 - 4.

Claims: CLAIMS 1. Method for tanning of hides by means of tanning agents in a tanning bath, characterized by the fact that the bath besides the hides comprises an oxidoreductase, and as tanning agent an aromatic compound and possibly other compounds which are able to react with the hides and/or the aromatic compound, and that an oxidation agent is introduced into the equilibrated tanning bath. 2. Method according to Claim 1, characterized by the fact that the oxidoreductase is a peroxidase, and the tanning agent is a synthetic or vegetable, aromatic tanning agent. 3. Method according to Claim 1, characterized by the fact that the oxidoreductase is an oxidase, and the tanning agent is a synthetic or vegetable, aromatic tanning agent. 4. Method according to Claim 1, characterized by the fact that the oxidoreductase is producible by means of Polyporus pinsitus {Trametes villosa). 5. Method according to Claim 1, characterized by the fact that the oxidoreductase is a laccase producible by means of Polyporus. 6. Method" according to Claim 1, characterized by the fact that the oxidoreductase is producible by means of Coprinus cinereus. 7. Method according to Claim 1, characterized by the fact that the oxidoreductase Is a peroxidase producible by means of Polyporus pinsitus {Trametes villosa). 8. Method according to Claims 1 - 7, characterized by the fact that the tanning bath is aqueous. 9. Method according to Claims 1 - 7, characterized by the fact that the tanning bath is organic. 10. Method according to Claims 1 - 9, characterized by the fact that the pH of the tanning bath is 2 - 11, preferably 2 - 8.

Inventors: INGVORSEN KJELD, MOELLGAARD ANNETTE, SOERENSEN NIELS HENRIK, INGVORSEN, KJELD, MOELLGAARD, ANNETTE, SOERENSEN, NIELS, HENRIK
Applicants: NOVONORDISK AS, NOVO NORDISK A/S
Application year: 1992
Main classification: C14C3
IPC codes: C14C3, C14C9