Title of Invention

AN IMPROVED PROCESS FOR THE UNHAIRING OF HIDES/SKINS

Abstract

The present invention relates to an improved process for the unhairing of hides/skins. More particularly, the present invention relates to a non-enzymatic, sulfide free hair-save process of unhairing hides and skins for application in the beam house of the tanning industry. The process results in 100% uniform unhairing. Moreover, it not only leads to a significant reduction in pollution load in the beam house effluent but also ensures that the hair/wool recovered as a by-product of the process may be used for some beneficial purposes.

Full Text

The present invention relates to an improved process for the unhairing of hides/skins. More particularly, the present invention relates to a non-enzymatic, sulfide-free, hair-save process of unhairing hides and skins for application in the beam house of the tanning industry. This hair-save 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 some beneficial pupose. It has been the age old practice in the leather tanning industry to remove the keratinous matter, present in the animal hide/skin in the form of hair or wool, during the pretanning operations, unless the hide/skin is intended to be processed for hair-on tannage. Conventionally, the unhairing of hides and skins is carried out at a pH around 12 by treating with alkali in the presence of an unhairing agent, which ensures complete unhairing avoiding any immunisation of keratin. The soaked hides/skins are usually treated with lime and sodium sulfide either in pit, paddle or drum, whereby the hair is disintegrated and removed. The main limitation of this method is that the removed hair cannot be reused for any other purpose. In addition, in these processes the hair gets pulped resulting in the formation of products like soluble keratins, glyco-proteins and saponified fats, which create serious environmental concern. It is necessary at times to recover the keratinous matter in undamaged condition in order to explore the possibilities for its industrial application. For example, wool is considered to be more important for various end-uses, it has, therefore, been the practice to separate out the wool from the animal skin before further processing to ensure that the same could be used for different industrial purposes. This is known as hair saving unhairing process. Traditionally, the hair saving unhairing process has been practised 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 be damaged by the proteolytic organisms in the sweating chamber as they are essentially subjected to the attack of the bacteria, already present. This drawback has been overcome by the painting process, in which a lime-sodium sulfide paste, which is prepared by mixing 1.5 to 2% w/w, sodium sulphide, 10% w/w, lime 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 a gunny bag and leaving for a period of 12-16 hrs during which the hairs get loosened removed by scrapping. The major limitation of using sulfide in the paste is that the resulting leather often has uneven colouration on the surface and harsh grain. Morever, 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 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 had drawn the attention of the researchers. There has been a dramatic change in the priorities of the leather industry from time to time. Leather industry world wide in general and India in particular is currently under the pressure of environmental issues. It is the environmental health which is given the top priority at present. The industry has been taking necessary steps needed to wipe out the stigma of polluting image. The substantial load of BOD in the effluent of the hitherto known sulphide based system of unhairing has motivated the researchers to try for better alternative. The need for development of sulfide free unhairing method has thus been widely recognised and has been investigated by number of researches. One of the important alternatives is enzymatic unhairing, whereby an enzymatic paste, prepared by using microbial enzymes,extracted from fungi / bacteria such as Aspergillus, Proteus vulgaris , is applied on the flesh side of the soaked stock to be unhaired followed by piling grain to grain for 12 hrs and subsequent removal of hair by manual scrapping. According to Sivaparvathi (Leather Science, 21, 183, 1974), enzyme present in the hide/skin could unhair autolytically, which basically depends upon the enzymatic loosening of hair by the action of bacteria, already present in the hide or skin. This method does not result in uniform hair loosening over the entire surface area of the hide or skin. Moreover, the process is difficult to control and often results in loss of hide substance and putrefaction of hides and skins due to uncontrolled action of autolytic bacteria present in the hides/skins. Elsingeretal (Das Leder, 38, 143, 1987) have explored the possibilities of use of enzymes for unhairing and have observed that the enzymatic process was not suitable for hides. It was however observed that only 40 to 50% of sodium sulfide could be replaced by enzymes for unhairing hides, with an obvious inference that the sulfide free enzymatic unhairing for hides was yet to be a reality. As reported by John ( Possible defects in Leather Production, p-40,1996), preliminary alkaline soaking or preliminary treatments and/or addition of activating salts such as sodium hydrogen carbonate, sodium bisulphite or sodium sulphite promote loosening of the hair in case of enzymatic unhairing. As reported by Sarkar ( Theory and Practice of Leather Manufacture, p. 127,1997 Edition), the hair loosening power of lime 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. 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. Sivakumar (M. Tech thesis, Anna University, 1996), Jagannathan & Deepa (B. Tech thesis, Anna University, 1997), used carbonates for unhairing of goat skins in which 100% unhairing efficiency was not achieved. There has been no report of the use of carbonates for unhairing hides. The main objective of the present invention is to provide an improved process for the unhairing of hides / skins, which obviates the drawbacks stated above. Another objective of the present invention is to provide a process, which is applicable to both hides and skins. Yet another objective of the present invention is to provide a process, capable of resulting in 100% uniform unhairing without adversely affecting the physical/chemical characteristics of the resulting leathers. Still another objective of the present invention is to provide a process which does not cause unevenness of colour on the surface of leather. Yet another objective of the present invention is to provide a process which does not produce harshness on the surface of the leather. Accordingly, the present invention provides an improved process for the unhairing of hides/skins characterized in that a novel alkaline paste comprising of 5 to 10 % w/w of lime, 1 to 4% w/w of alkali metal/alkaline earth metal sulfite with pH in the range of 9 to 13 is applied to the flesh side of the soaked hides and skins to be unhaired followed by piling the pasted hides and skins grain to grain for at least 8 hours, subsequently removing the hair by known methods to obtain unhaired hides/skins. In an embodiment of the present invention, the alkali used to make paste may be such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bi carbonate. In another embodiment of the present invention, the alkali metal sulfite used to make paste may be such as sodium sulfite, potassium sulfite and alkaline earth metal used may be such as calcium sulfide. In yet another embodiment of the present invention, the concentration of the paste may be in the range of 18-24 Be1 ( Baume). In still another embodiment of the present invention, the amount of paste used may be in the range of 250-450 gms/ kg of the hide/skin. In yet another embodiment of the present invention, the known method for removing the hair may be such as manual, mechanical. An alkaline paste is prepared by mixing 1-4%w/w, of a metal sulfite, 5-10%w/w, of lime on soaked hide/skin in water and adjusting the concentration of the resulting paste in the range of 18-24 Be1. pH of the paste is adjusted in the range of 9-13.The paste, thus prepared, amounting to 250-45*0 gms/ kg of the hide/skin is applied on the flesh side of the soaked hides/skins to be unhaired and the resulting hides/skins are piled grain to grain. After a period of at least 8 hrs, the hides/skins are unhaired by known method to get unhaired hides/skins. The novelty and non-obviousness of the present invention lies in the use of the "metal sulfite and not only in providing an option of using the paste, unlike the hitherto known chemical painting processes, even at a pH of 9, thereby avoiding the risk of grain getting harsh, but also in producing the unhaired hides/skins within a period of 8 hrs, which is much lesser than those in the conventional systems,thereby providing a cost-effective and eco-friendly method of unhairing, ensuring wider applicability, unlike the conventional systems, of the process to any stock, irrespective of whether it is hide or skin. The invention is described in detail with reference to the examples given below which should not however be construed to limit the scope of the present invention. Example -1 Ten pieces of soaked goat skins were taken for unhairing and the weight was noted to be 10 kgs. The following ingredients were then mixed with stirring to form a paste. Sodium sulfite 100 gms Lime 500 gms, Sodium hydroxide 50 gms Water 1850 gms pH - 10 Be1 - 24 The paste, thus prepared, was applied manually on the flesh side of each of the skins with the help of a brush. The pasted skins were piled grain to grain and then covered completely with a wet gunny bag. After a period of 8 hours, hairs on the skins were found to be loose, which were scrapped off manually to produce the unhaired skins. Example - 2 Ten pieces of soaked cow hides were taken for unhairing and the weight was noted to be 120 kgs. The following ingredients were then mixed with stirring to form a paste. Calcium sulfite 2.4 kgs Lime 12.0 kgs, Sodium carbonate 1.2 kgs Water 30.0 kgs pH - 12 Be1-18 The paste, thus prepared, was applied manually on the flesh side of each of the hides with the help of a brush. The pasted hides were piled grain to grain and then covered completely with a wet gunny bag. After a period of 10 hours, hairs on the hides were found to be loose, which were scrapped off manually to produce the unhaired hides. Example - 3 Ten pieces of soaked sheep skins were taken for unhairing and the weight was noted to be 12 kgs. The following ingredients were then mixed with stirring to form a paste. Potassium sulfite 360 gms Lime 500 gms, Sodium hydroxide 50 gms Water 2200 gms pH -9 Be1 - 22 The paste, thus prepared, was applied manually on the flesh side of each of the skins with the help of a brush. The pasted skins were piled grain to grain and then covered completely with a wet gunny bag. After a period of 8 hours, hairs on the skins were found to be loose, which were scrapped off manually to produce the unhaired skins. Example - 4 Ten pieces of soaked buffalo hides were taken for unhairing and the weight was noted to be 200 kgs. The following ingredients were then mixed with stirring to form a paste. Sodium sulfite 8.0 kgs Lime 10.0 kgs, Potassium hydroxide 2.0 kgs Water 70.0 kgs pH - 13 Be1-18 The paste, thus prepared, was applied manually on the flesh side of each of the hides with the help of a brush. The pasted hides were piled grain to grain and then covered completely with a wet gunny bag. After a period of 12 hours, hairs on the hides were found to be loose, which were scrapped off manually to produce the unhaired hides. 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. 3. It ensures that uneven stains do not appear on the grain. 4. The process does not result in harsh grain. 5. It does not adversely affect the physical or chemical characteristics of the unhaired stock. 6. The process is cost effective and environmentally friendly. We Claim: 1. An improved process for the unhairing of hides/skins characterized in that a novel alkaline paste comprising of 5 to 10 % w/w of lime, 1 to 4% w/w of alkali metal/alkaline earth metal sulfite with pH in the range of 9 to 13 is applied to the flesh side of the soaked hides and skins to be unhaired-followed by piling the pasted hides and skins grain to grain for at least 8 hours, subsequently Removing the hair by known methods to obtain unhaired hides/skins. 2. A process as claimed in claim 1, wherein the alkali metal used is selected from sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate. 3. A process as claimed in claim 1, wherein the alkali metal sulfite used is selected from sodium sulfite, potassium sulfite and alkaline earth metal is preferably calcium sulfite. 4. A process as claimed in claim 1, wherein the concentration of the alkaline paste is in the range of 18 to 24 Be. 5. A process as claimed in claim 1, wherein the amount of said alkaline paste used is in the range of 250 to 450 g/kg of the hides/skins. 6. An improved process for the unhairing of hides/skins substantially as herein described with reference to the foregoing examples.

Documents:

380-del-2000-abstract.pdf

380-del-2000-claims.pdf

380-del-2000-correspondence-others.pdf

380-del-2000-correspondence-po.pdf

380-del-2000-description (complete).pdf

380-del-2000-form-1.pdf

380-del-2000-form-19.pdf

380-del-2000-form-2.pdf