Title of Invention

"A NOVEL OXIDATIVE PROCESS FOR THE UNHAIRING OF HIDES/SKINS"

Abstract

The present invention relates to a novel oxidative process for the unhairing of hides/skins. The process provides an eco-friendly as well as time saving option for unhairing of hide/skin. More particularly, the present invention relates to a non-enzymatic, sulfide-free process for unhairing of hides and skins using ozone for application in the beam house of the tanning industry. This process not only leads to a significant reduction in pollutional load in the beam house effluent but also ensures that the hair/wool, recovered as the by-product of the process may be used for making value added products. The advantages of the present invention are that it does not result in generation of toxic pollutants, uneven stains do not appear on the grain and is not adversely affect the physical or chemical characteristics of the unhaired stock.

Full Text

The present invention relates to a novel oxidative process for the unhairing of hides / skins. More particularly, the present invention relates to a non-enzymatic, sulfide-free process for unhairing of hides and skins using ozone for application in the beam house of the tanning industry. This process not only leads to a significant reduction in pollutional load in the beam house effluent but also ensures that the hair/wool, recovered as the by-product of the process may be used for making value added products. The keratinous matter, present in the animal hide/skin in the form of hair or wool, is conventionally removed during the pretanntng stage in leather processing industry, unless the tannage is intended to be of hair-on type. Traditionally, the hair saving unhairing process has been practised, as reported by Sarkar ( Theory and Practice of Leather Manufacture, page 121, 1997), by sweating method, in which the skins to be unhaired are hung in a chamber, maintained at 20-30°C temperature and 80-90% Relative Humidity, followed by the scrapping of the loosened hair/wool after a period of 2-7 days. The major limitation of this process is that the skins are prone to damage by the proteolytic organisms present in the sweating chamber as they are essentially subjected to the attack of the bacteria, already present therein. This process has therefore not gained much popularity among the present day tanners. The unhairing of hides and skins is conventionally carried out at a pH around 12 by treating with alkali in the presence of an unhairing agent. The soaked hides/skins are usually treated with calcium hydroxide and sodium sulfide either in pit, paddle or drum, whereby the hair is loosened and removed. In principle, the sulfide forms the sulphhydride ion that breaks the disulfide bond of keratin. This process thus essentialy follows the principle of reduction type of reaction while loosening the hairs. The major limitation associated with this method is that the loosened hair tend to form pulp, that cannot be reused for any other purpose. Moreover, the process results in the formation of products like soluble keratins, glyco-proteins and saponified fats, which create serious environmental concern. This limitation has been overcome by the painting process, in which a calcium hydroxide-sodium sulfide paste, prepared by mixing 1.5 to 2% w/w, sodium sulphide, 10% w/w, calcium hydroxide and 20% w/w, of water, based on the soaked weight, is applied on the flesh side of the hides/skins to be unhaired, followed by piling the same in grain to grain manner, covering well with wet gunny bag and leaving for a period of 12-16 hrs during which the hair gets loosened and are removed by scrapping. The major limitation of using sulfide in the paste is that the resulting leather often exhibits harsh grain and uneven colouration on the surface. Moreover, the use of sulphide leads to the liberation of hydrogen sulphide which is a serious hazard to the people working in the tannery and treatment plant. Further, the hydrogen sulphide may undergo oxidation by bacterial action and produce sulphuric acid that damages the concrete and iron works of the treatment plant. High concentration of dissolved sulphide, exceeding 250 ppm as sodium sulfide (Na2S), interferes with the bacterial oxidation process of the treatment itself. The use of sulphide and the practice of the hair pulping method of depilation are attributive to tremendous increase in Biological Oxygen Demand ( BOD). The contribution of BOD load by sulfide based unhairing is around 55% of the total BOD load. This proportion is imprudent and has drawn attention of the researchers. There has been a dramatic change in the priorities of the leather industry from time to time. Global Leather industry in general and the Indian scenario in particular has currently been under tremendous pressure arising out of various environmental issues. The substantial load of BOD in the effluent of the hitherto known calcium hydroxide -sulphide based system of unhairing has motivated the researchers to try for better alternative. As reported by Sarkar ( Theory and Practice of Leather Manufacture, p. 127,1997), the hair loosening power of calcium hydroxide is enhanced by adding organic or inorganic reducing agents. The use of different sharpening agents like sodium hydrosulfide, calcium hydrosulfide, arsenic sulfide, methyl amine, dimethyl amine, sodium bisulfite, mercaptan have already been reported. It has further been reported that the use of hypo, sodium sulfite or sodium bisulfite in unhairing paste accelerates unhairing. Our copending patent application No. 380DEL2000 has disclosed a method to replace sulfide by sulfite salt, whereby it has been possible to achieve hair loosening after a period of 8hrs. Sehgal et al (Indian Patent application No.0026 DEL 1992), reported the development of an improved process for unhairing hides and skins by sulfide free methods using carbonates of heavy metals. The metal salts of nickel, mercury and silver, used for unhairing, pose occupational safety and health problems and are also not cost effective. While the mercury salts, because of their inherent toxic nature, pose threat to safety in material handling and use, the silver based system may not find commercial utility because of economic reasons. Moreover, as reported by Seghal et al (Journal of Society of Leather Technologists and Chemists, 5/6, p91-92,1996) the leather processed by nickel salt result in health problems while using. There have thus been attempts to replace the conventional chemical based system of dehairing with biological system by using enzymes of microbial, plant or animal sources. The system may either be enzyme assisted or enzymatic. While an enzymatic unhairing process involves the application of enzymes on the flesh side of the soaked stock to be unhaired followed by piling grain to grain and subsequent removal of hair by manual scrapping, the partial replacement of calcium hydroxide/sulfide is effected with enzyme in an enzyme assisted system. The major limitation of the enzyme based system is the pre-requisite of appropriate storage facility under stipulated conditions to ensure optimum activity during the shelf life period, thereby implying additional cost. Moreover, the period required for loosening of hair may extend upto not less than 12 hrs. The limitations of the hithertoknown processes have been prompting the researchers to explore possibilities of switching over to oxidative system for loosening of hair. As reported by Sarkar (Theory and Practice of Leather Manufacture, p. 138,1997), oxidative unhairing has been attempted using chlorine dioxide under acidic conditions. The major limitation associated with this process is that the process involves enormous health hazards due to the presence of toxic chlorine gas and hence is not feasible. Manner et al ( Journal of American Leather Chemists Association,98(9),351-358,2003) adopted oxidative approach employing caustic hydrogen peroxide to replace sodium sulfide. While the process has been reported to be faster, it has also been associated with grain damage, which has again been controlled by reducing the amount of sodium hydroxide and adding calcium hydroxide or KOCN (Potassium percyanide). Another rapid oxidative method of unhairing has been reported by Gehrig et al (Journal of American Leather Chemists Association,98(6),216-223,2003), who used alkaline calcium peroxide at a pH around 13 and temperature around 45°C to loosen the hair. The major limitation associated with these approaches is the generation of toxic chemicals that add to the hazards relating to health and environment.No prior art is available on the use of any other oxidising agent for the purpose of unhairing to explore possibilities of providing a system that enables loosening of hair without adding to effluent or health/environment hazards. Unhairing or hair removal is an important step in leather processing. The main objective of the present invention is to provide a novel oxidative process for the unhairing of hides / skins, which obviates the limitations as stated above. Another objective of the present invention is to provide a process to effect loosening of hair within a period as low as 30 minutes. Yet another objective of the present invention is to provide a process for unhairing having no adverse impact on the issues related to effluent or health/environment hazards Still another objective of the present invention is to provide a process that is capable of resulting in uniform unhairing without adversely affecting the physical/chemical characteristics of the resulting leathers. Yet another objective of the present invention is to provide a process which does not cause unevenness of colour on the leather surface. Still another objective of the present invention is to provide a process to unhair hides/skins without resulting in any harshness on the leather surface. Accordingly, the present invention provides a novel oxidative process for the unhairing of hides / skins, which comprises treating soaked hide/skin characterized in that with 0.234 to 0.240 %w/w, of ozone for a period of 30-35 minutes in the presence of 5-10%w/w, of oxide, hydroxide or carbonate salt of a mono or divalent metal in aqueous medium at a pH in the range of 10 to 12, followed by removing the hair by known method to get unhaired hide / skin. In an embodiment of the present invention, the salt used may be selected from calcium hydroxide, magnesium oxide, sodium carbonate either individually or in any combination. In another embodiment of the present invention, the known method for removing the hair may be such as manual, mechanical. The process of the present invention is described below in detail. Soaked hide/skin is exposed to not less than 0.234%w/w, of ozone for a period of not less than 30 minutes in the presence of alkaline medium of pH not less than 10, prepared with 5-10%w/W, of oxide, hydroxide or carbonate salt of a mono or divalent metal, based on the soaked weight of the hide/skin to be unhaired. The loosened hair is removed by known method to get unhaired hide /skin. The inventive step of the present invention lies in the use of ozone at alkaline condition to loosen the hair, thereby providing an eco-friendly option for unhairing of hide/skin ensuring simultaneously economy of time. The following examples are given by way of illustration only and therefore should not be construed to limit the scope of the present invention. Example 1 One piece of soaked goat skin weighing 550 gms was taken in a glass column. 27.5 gms of calcium hydroxide was taken in a beaker and 275 gms of water was added to it. pH of the resulting calcium hydroxide solution was noted to be 11.5 and the solution was poured in the glass column in such a way that the soaked skin was completely submerged. The glass column was connected to an ozone generator. Ozone containing oxygen was bubbled at the rate of 10L/min through the column. After a period of 60 minutes the hairs were found to be loosened. The skin was dehaired using knife to produce dehaired skin. Example 2 One piece of soaked sheep skin weighing 1 kg was taken in a glass column. 50gms of calcium hydroxide was taken in a beaker and 2 I its of water was added to it. pH of the resulting calcium hydroxide solution was noted to be 11 and the solution was poured in the glass column in such a way that the soaked skin was completely submerged. The glass column was connected to an ozone generator. The ozone containing oxygen was passed through the calcium hydroxide liquor using venturi. After a period of 4 minutes, bubbling of ozone was stopped and the skin was shifted to an experimental drum along with the calcium hydroxide liquor. The skin was drummed while passing ozone containing oxygen at the rate of 5L/min for 30 minutes . Total amount of ozone used was 2.3408gms. The skin was finally unloaded from the drum and dewooled manually by a blunt knife. Example 3 One piece of soaked cow side weighing 5 kgs was taken in a glass column. A mixture of 125gms of calcium hydroxide and 62.5 gms of sodium carbonate was suspended in 10 litres of water and the pH was found to be 10. This liquor was poured in the glass column in such a way that the soaked side was completely submerged. The glass column was connected to an ozone generator. Ozone containing oxygen was bubbled at the rate of 75L/min through the column. After a period of 45 minutes the hair was found to be loosened. Total amount of ozone used was 51.3gms. The side was dehaired using blunt knife. Example 4 One piece of soaked goat skin weighing 500 gms was taken in a glass column. 50gms of sodium carbonate was dissolved in 1 litre of water and the pH was found to be 12. The solution was poured in the glass column in such a way that the soaked skin was completely submerged. The glass column was connected to an ozone generator. Ozone containing oxygen was bubbled at the rate of 10L/min through the column. After a period of 30 minutes the hair were found to be loosened. Total amount of ozone used was 4.56 gms. The skin was dehaired using blunt knife. Example 5 One piece of soaked goat skin weighing 750 gms was taken in a glass column. 75gms of Magnesium oxide was dissolved in 1.5 litre of water and the pH was found to be 10. The solution was poured in the glass column in such a way that the soaked skin was completely submerged. The glass column was connected to an ozone generator. Ozone containing oxygen was bubbled at the rate of 10L/min through the column. After a period of 45 minutes the hair were found to be loosened. Total amount of ozone used was 6.84 gms. The skin was dehaired using blunt knife. EXAMPLE 6 One piece of soaked goat skin weighing 500 gms was taken in a glass column. 25gms of Magnesium oxide was mixed with 12.5 gms of calcium hydroxide taken in a beaker and the mixture was dissolved in 1 litre of water. pH was found to be 10. The solution was poured in the glass column in such a way that the soaked skin was completely submerged. The glass column was connected to an ozone generator. Ozone containing oxygen was bubbled at the rate of 10L/min through the column. After a period of 30 minutes the hair were found to be loosened. Total amount of ozone used was 4.56 gms. The skin was dehaired using blunt knife. The advantages of the present invention are the following 1. It is a versatile process, which is applicable to both hides and skins 2. Complete loosening of hair is effected by this process within a period as low as 30 minutes. 3. The process does not result in generation of toxic pollutants, thereby ensuring eco-friendly approach towards unhairing of hides/skins. 4. It ensures that uneven stains do not appear on the grain. 5. The process does not result in harsh grain. 6. It does not adversely affect the physical or chemical characteristics of the unhaired stock. We claim: 1. A novel oxidative process for the unhairing of hides / skins, which comprises treating soaked hide/skin characterized in that with 0.234 to 0.240 %w/w, of ozone for a period of 30-35 minutes in the presence of 5-10%w/w, of oxide, hydroxide or carbonate salt of a mono or divalent metal in aqueous medium at a pH in the range of 10 to 12, followed by removing the hair by known method to get unhaired hide / skin. 2. A novel oxidative process as claimed in claim 1, wherein the salt used is selected from calcium hydroxide, magnesium oxide, sodium carbonate either individually or in any combination. 3. A novel oxidative process for the unhairing of hides / skins, substantially as herein explained with reference to the examples.

Documents:

315-DEL-2004-Abstract-(30-07-2010).pdf

315-del-2004-abstract.pdf

315-DEL-2004-Claims-(30-07-2010).pdf

315-del-2004-claims.pdf

315-DEL-2004-Correspondence-Others-(30-07-2010).pdf

315-del-2004-correspondnece-others.pdf

315-del-2004-correspondnece-po.pdf

315-DEL-2004-Description (Complete)-(30-07-2010).pdf

315-del-2004-description (complete).pdf

315-del-2004-form-1.pdf

315-del-2004-form-18.pdf

315-del-2004-form-2.pdf

315-DEL-2004-Form-3-(30-07-2010).pdf

315-del-2004-form-3.pdf

315-del-2004-form-5.pdf