A process for the provision of a plant extract containing condensed tannins, with astringent characteristics, modified by copolymerization, for use in tanning and retanning of skins, a plant extract with astringent characteristics, modified by copolymerization, and use of a modified plant extract containing tannins

摘要

The present invention refers to a process for obtaining a plant extract containing condensed tannins, with astringent characteristics, modified by copolymerization, to be used for tanning and retanning of skins; it also refers to the plant extract thus obtained; and it also refers to the use thereof for treating hides.;The process according to the present invention comprises the following steps:(a) adding water to a reactor at a ratio between 2.0 and 5.8%, by weight, to the total desired weight of the load;(b) adding to the reactor an amount between 1.2 and 2.5%, by weight, of a copolymerization agent, selected from acrylic acid, metacrylic acid, mixtures of acrylic acid and metacrylic acid or esters thereof; all the while stirring the mixture;(c) adding thioglycolic acid at a ratio between 0.1 and 1.7%, by weight, while cooling the mixture, allowing the same to react whereupon there occurs the exothermal reaction and the temperature reaches 95° C, and after the said reaction the product obtained from the reaction being left to cool;(d) adjusting the pH to values in the range between 3.5 and 7.0, by adding an alkali to the mixture;(e) mixing a powdered extract of a plant with water at a ratio of about 0.5 to 2.0 kg per liter of water; or   alternatively, mixing a solution of tannin in liquid form in a concentration of 25% to 60%;(f) raising the temperature of the mixture to a range between 67 and 98° C, to carry out the reaction, for a period of 2 to 7 hours, preferably for 5 hours;(g) adding the sodium bisulphite at a ratio of 0.5 to 4.0%, by weight, over the amount of tannin;(h) raising the temperature of the mixture, keeping the reaction system heated at a temperature between 45 and 127° C, the pressure being comprised between 0.2 and 7 kgf/cm²; and(i) allowing a reaction time of about 4 hours.