A new insight into the shrinkage phenomenon of hides and skins

Although the art of leather making has been known to exist for ages, the physical and physicochemical events accompanying the shrinkage phenomenon in leather and its parent substance collagen are largely unknown. In this study, to elucidate the shrinkage phenomenon in hide and leather, a model has been proposed for the total volume of the skin matrix consisting of three components: solid, liquid and air, which are expected to exhibit interfaces among them. On heating, it has been observed that the fibre structure does not collapse monotonically with the loss of moisture beyond a critical amount. Using dilatometry technique, it has been shown that amount of volume expansion on heating is 0.07 ml for 1g of hide. The phase transition leading to shrinkage in the hydrothermal shrinkage phenomenon is shown to be associated with drastic changes in volume composition and absorption of heat. About 30% change in volume has been observed due to the hydrothermal shrinkage. The effect of heat on the pore morphology of the matrix has been studied through scanning electron microscopy, which reveals changes in the macro porous structure of the matrix depending upon the moisture content.