The influence of non-aqueous solvents on lime and pickle swelling of goat skin

Swelling during leather manufacture is of great importance in controlling the quality of final leather. A more intensive fibre separation produces finished leather that is softer and more flexible, but also shows a decrease in hide substance and mechanical strength, whilst at the same time exhibiting an increased looseness. The amount of collagen degradation is dependent on the degree of swelling and occurs in a number of stages in the manufacture of leather. Conventionally, references to swelling are usually restricted to liming and pickling. Suggested mechanisms of swelling are charge effects, osmotic swelling and lyotropic swelling. In the case of the liming process, swelling is suppressed to a lesser degree by additives whereas in pickling, salt is added to suppress the swelling. The swelling of skin in non-aqueous solvents and aqueous co-solvent system was investigated. Goat skin samples were limed and pickled in a series of alcohol (methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol and diacetone alcohol), acetone, dimethyl sulfoxide, urea and 1,4-dioxane to produce aqueous co-solvent systems of varying dielectric constants. The results confirmed that the degree of swelling in skins was suppressed, in both cases, as the concentration of the non-aqueous solvent increased. The solvent uptake of skin decreased from 500% (w/w) to 100% (w/w) in an ‘acidic’ non-aqueous solvent system, and was reduced from 400% (w/w) to 50% (w/w) in an ‘alkaline’ environment.