The Role of Neutral Salt for the Hydrolysis and Hierarchical Structure of Hide Fiber in Pickling

Abstract

Pickling process carried out for adjusting the skin to the desired pH for tanning, in which neutral salts were added to avoid skin fiber from the acid swelling. This research study aimed at investigating the contribution of neutral salt to the hydrolysis and the fibrous structure of collagen fiber in acid solutions. Collagen fiber and bovine hide in sulfuric acid solutions with sodium chloride or sodium sulfate were investigated. The total protein concentration in the solutions was determined. The hierarchical structures of bovine hide in different acid and neutral salt systems were investigated by optical microscope, TEM and SEM. This study suggested the importance of neutral salt for the hydrolysis and the dispersion of collagen fiber in pickling. It implied that the osmotic swelling by acid could not reach the inner scale of fibril. The decrease in mechanical properties for the leather tanned with salt free pickling may have been caused by osmotic swelling destroyed the interactions among the fibril and fiber bundles.