The subject of this invention is the method for obtaining adhesive from protein waste, especially leather waste from tanning, meat and fish processing industries, designed for bonding of paper, cardboard and wood. This method allows for environment friendly management of tanning waste of „wet blue" type.

Waste generated in tanning industry requires special management, is subjected to various utilization processes e.g. to composting. However, most frequently it is burned in specialized plants. Storage of such waste is dangerous for sanitary reasons.

During„wet blue" recycling, consisting of alkaline protein hydrolysis and separation of chrome hydroxide sediment, water solutions of hydrolyzed proteins are created which are not effectively managed and constitute troublesome waste.

From the Polish patent No. PL175363, the method for preparation of chrome-tanned leather waste for utilization, especially for leaching of gelatin and leather glue. The method consists of the following: crushed leather waste is subjected to de-tanning with alkaline substance such as lime, sodium carbonate, ammonia, magnesium hydroxide, magnesium oxide, favourably magnesium oxide, used in the minimum quantity of 4% by weight in relation to the waste matter. Next, the waste is rinsed and subjected to de-chroming with mineral acid, applied in the quantity up to 10% by weight in relation to the waste matter, in the presence of sodium chloride solution. After separation After separation of the chromium salts, waste is subjected to hydrolysis with the help of sodium hydroxide and further the alkaline pulp is subjected to neutralization first by sodium hydrocarbon applied in the minimum quantity of 12,5% by weight in relation to the waste matter, and after centrifugation, by ammonium chloride applied in the quantity of up to l 5% by weight in relation to the waste matter, after which the obtained pulp rinsed with water and centrifuged. This process does not provide guarantee of removal of the entire quantity of chromium from waste.

In the method known from another patent description number PL184763 liquid or solid waste is led to solutions with pH = 12-13, after which Cr(lll) is extracted with quaternary ammonium salts, favourably with methyltrioctylammonium chloride or dimethylbenzyldodecyloammonium bromide, which is earlier dissolved in hydrocarbon organic solvent such as: n- heptane, kerosene or benzene with addition of higher-level aliphatic alcohol, favourably n-decanol.

In turn, in the Polish patent application No. P. 315360 the method for de- chroming leather and/or leather waste which were tanned with chromium components, especially collagen derived waste, consists of contacting such waste with salt solutions with addition of acids and/or acid anhydrides which are the original acids of those salts and/or at least medium strong mineral acids. This method leads to recovery of non-tanned collagen of leather with the possibility to preserve its fibrous structure and having high purity. Besides, chromium compounds solutions are obtained which can be returned to technological process of obtaining chrome-tanned leather directly or after relevant treatment. This method does not guarantee removal of the entire quantity of chromium contained in waste.

Patent US1712077 presents the method for production of water resistant adhesive of animal origin through addition of formaldehyde, and then of acid, favourably oxalic acid, tartaric acid, citric acid, benzoic acid, acetic acid or phosphoric acid to preserve adhesive liquidity.

Patent US5210982 presents the method for obtaining adhesive from a partly condensed urea and formaldehyde, used for crosslinking of collagen or polysaccharides and improvement of rheological properties of adhesive. In accordance with the invention the method for obtaining adhesive from protein waste, especially leather waste from tanning, meat and fish processing industries, consists of the following: hydrolyzed proteins are subjected initially to alkaline or acidic or enzymatic or thermal hydrolysis, and then polycondensation reaction is carried out with the use of aldehydes and aliphatic or aromatic amines and mixed with modifying and biocidal additions. To water solution of hydrolyzed protein, favourably collagen, gradually aldehyde is introduced, favourably formaldehyde in the quantity from 2:1 to 5:1 in relation to dry matter of hydrolyzate. Condensation reaction is carried out, favourably in alkaline environment, dosing urea gradually to the solution in the quantity from 1:1 to 3:1 in relation to dry matter of hydrolyzate for the period of 1 hour to 5 hours in temperature from 450C to 750C, favourably 70EIC. Simultaneously, salt content is mixed and supplemented from 1 % to 3 % by weight of dry matter of hydrolyzate. Next, the reaction mixture is evaporated, after which, modifying and biocidal additions are introduced to the concentrated solution, and after mixing a homogeneous solution of protein adhesive is obtained.

As a modifying addition plasticizers are introduced such as glycerine, polyglycerine, glycols and polyethylene esters, in the quantity from 0,5 % to 5,0 % by weight of dry matter of hydrolyzate.

As an organic biocidal addition is introduced phenol or cresol or sodium benzoate in the quantity from 0,1 to 1,0 % by weight of dry matter of hydrolyzate or as a inorganic biocidal addition is introduced copper sulphate in the quantity from 0,1 % to 0,5 % by weight of dry matter of hydrolyzate. As a result of the process, a homogeneous liquid solution of protein adhesive is obtained for bonding paper, cardboard and wood.

Use of the method according to the invention is particularly beneficial for the environment friendly waste management. It allows for the use of protein waste generated in tanning, meat and fish processing industries. The obtained water-based adhesive is environment friendly, and the process of its obtaining is simple, effective and cheap. Besides, adhesive, due to good adhesion parameters, has wide possibility of application, especially for production of corrugated paper packages. The invention is presented in three examples of execution. Example 1

To reactor with the capacity of 3 m ³ with a mixer and heating jacket, dry tanned leather waste was introduced in the quantity of 250 kg, which was flooded with water in the quantity of 1200 dm ³ . Next, 16 kg sodium hydroxide was introduced and while continuously mixed, it was heated until boiling. In this condition leather was maintained until digested for the period of 3 hours. The obtained hydroiyzate solution was filtered in order to remove any contaminants present in leather, precipitated chromium hydroxide Cr(OH) ₃ and the remnants of non-hydrolyzed leather fragments. A clear protein hydroiyzate solutions was obtained with light yellow color. To that solution 19 kg of concentrated sulphuric acid was introduced in order to neutralize sodium hydroxide. Next, to the hydroiyzate solution with pH=9 125 kg of urea and 500 kg 37% of formaldehyde were added. The content in the reactor was mixed. After four hours, to the reactor 15 kg of 20% hydrogen peroxide was added and heated for 3,5 hours. Finally, 5 kg of starch in water suspension 1:1, 4 kg of vegetable glycerin and 5 kg of phenol were introduced. After dissolution of starch, reactor was cooled down and 2030 kg of adhesive was obtained in the form of a homogeneous liquid.

Example 2

300 kg of dry„wet-blue" waste was introduced to the same reactor as in Example 1, and flooded with 1200 kg of water supply water. Next, gradually 22,5 kg of solid KOH was introduced to that reactor, while mixing until dissolved and after heating up to temperature 95°C it was maintained in that temperature for 3 hours under ordinary pressure. After that period, the solution was filtered removing the insoluble contaminants and obtaining clear hydrolyzed protein solution with light brown color. 50 kg of 35% sulphuric acid water solution was added to the obtained solution, obtaining pH=9, next was mixed for the period of 3 hours. The obtained mixture was boiled and 250 kg of water was evaporated. 12 kg of acetylated starch in suspension in 15 kg of cold water, 6 kg phenol, 4 kg PEG-400 were added to the concentrated solution. Besides, the salt content in the solution was supplemented by adding 15 kg of sodium sulphate. After mixing, a homogeneous solution of protein adhesive was obtained.

Example 3

176 kg of fragments of raw bovine leather with humidity of 50%, generated during cutting were introduced to tank reactor with the capacity of 750 dm ^3, equipped with the heating jacket and a propeller mixer and were flooded with 220 kg of tap-water and 18 kg of solid NaOH was introduced. After mixing and closing of the reactor, the reactor was heated with steam with the pressure of 6 atm. After heating to temperature ca. 100 ^e C the reactor content was maintained in that temperature for the period of 3,5 hours. The reactor content was filtered obtaining a light yellow hydrolyzate solution. The filtrate was re-introduced to the cleaned reactor, into which next 70 kg of 30% sulphuric acid solution was added obtaining pH 9,2. After mixing, 85 kg of urea and 235 kg of 37% formaldehyde solution were added consecutively. All was mixed maintaining temperature on the level not higher than 55°C for the period of 3 hours. After that time, 3 kg of sodium benzoate and 4 kg of diglycerine were added. Besides, the salt content in the solution was supplemented by adding 11 kg of trisodium phosphate. A homogeneous adhesive was obtained with the dry matter content at the level of 45%.