Painting Unhairing for Manufacture of Upper Leather

Mubark Yahia, A.E Musa, G.A. Gasmelseed, E.F. Faki , H.E Ibrahim, O.A Haythem, M.A Manal, S.B Haythem

The unhairing step is a heavy pollution operation in the leather industry. The conventional lime-sulfide process produces a large amount of sulfide, which is toxic to health and difficult to dispose. Moreover, conventional process leads to the destruction of the hair causing increased chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total suspended solids (TSS) loads in the effluent. Painting unhairing process is hair-save process in which the soaked skins are piled to drain off surplus water and then painted on the flesh side with a "paint" which may be made from hydrated lime, water and sodium sulfide (fused). The sodium sulfide and lime dissolves in the water and penetrate through the corium and dissolve the keratin cells which enclose the hair roots. In the present study, an attempt has been made to produce upper leather using two methods of unhairing : painting unhairing (Experimental)   and hair burning (Control). The strength characteristics of the experimental leathers are found to be comparable to those of control leathers. The organoleptic properties of the experimental leathers were shown to be similar or even better (especially softness) than the control leathers. The evaluation of softness shows that experimental leather has greater softness. The physical and chemical analysis indicates that the experimental leathers are comparable to control leathers in terms of all the properties. One of the main benefits of this work is the lower environmental impact. The spent tan liquor analysis shows significant reduction in sulfide loads compared to control.