Investigation of the use of enzyme preparations in leather manufacture
Keywords:hide, unhairing, enzyme, hydrogen peroxide
An important component in tanning is the removal of hair from the hide (unhairing), a process which generates considerable amounts of toxic effluent characterized by a high concentration of sulphur, rich mineral compounds, a high alkalinity, and a high organic load. Herewith, the cleaning of unhairing solutions, polluted with lime, sulphides and products of protein degradation remains, is very complicate and expensive. Special attention is paid to lime and sulphides, which are used for beamhouse processes, trying to decrease their amounts or replace them by systems of other materials. Developing new and less polluting technologies of leather processing, it is supposed that components of more environmentally friendly unhairing systems may be enzymatic preparations characterized by a wide spectrum of effects, and, also, oxidizing materials.
The presented research is aimed to develop an efficient unhairing system for hides, which contains the oxidation material and the enzyme. Hydrogen peroxide was chosen as a comparatively cheap and environmentally friendly material.
Since the action of hydrogen peroxide in the unhairing system depends on its decomposition duration, the decomposition of hydrogen peroxide has been investigated with a modelling medium in the presence of metal ions (Mn2+, Fe2+, Cu2+). The addition of 28–56 μmol/L of Mn2+ or Fe2+ leads to a complete decomposition of hydrogen peroxide during 5–6 hours.The investigation of the unhairing process has shown that the separate use of hydrogen peroxide or the enzyme preparation does not lead to a qualitative unhairing of the hide. An environment-friendly and effective unhairing system has been prepared using hydrogen peroxide 2–4 % on hide mass, the enzyme preparation Aquaderm A 0.2 % on hide mass, and divalent manganese or iron salt in the range of concentration from 28 to 56 μmol/L. A good unhairing effect has been achieved in the following case: a full degradation of the epidermis; an easy hair removal by a slight mechanical action; no damage of the hide surface. The use of the developed unhairing system allows avoiding wastewater pollution by dangerous sulphides and lime.