Making leather go further with lower temperatures
Animal skin constitutes three layers, which from the outside to the inside are the epidermis, the corium and the flesh. The middle layer, the corium, is the part that will become hide and eventually produced into leather. However to do this successfully, the process must protect the collagen fibres that make up the corium. Once an animal is dead, the skin starts to lose moisture so the epidermis (and hair) is loosened in order to separate it from the corium. The next stage is the tanning process, which is conducted in a moist and temperature controlled environment, and it is this process that penetrates the collagen and enables leather to be manufactured. Building upon this tried and tested process, a rheological model has been developed to underpin a new process, and define the environmental conditions for the manufacture of leather. Based upon a thermo-mechanical procedure that studied better temperatures and heating regimes, this model is concerned with the key viscoelastic parameters of storage modulus and tangent loss of the corium. The area gain this model obtains has been derived from the variations temperature profiles of tangent loss have upon the optimum temperature transitions for any given leather. For above the optimum temperature, the stress relaxation profiles change and this leads to significant gains in set and area gain. Because the stress relaxation profiles can be modelled with Maxwell elements, they show a marked reduction of the relaxation times of some elements during the transitional period. Further, the rheological model predicts an upper limit of the treatment temperature, which is 15 degrees Celsius below the classical shrinkage temperature for uncoiling the collagen molecules. Hence modelled temperature reductions increase area yields of leather.
