Influence of retanning on the adsorption capacity of water on cattlehide collagen fibers

There are plenty of hydrophilic groups in the collagen fibers in leathers. Because the affinity between these hydrophilic groups and water molecules varies with environmental changes in temperature and relative humidity, leathers will adsorb or de-adsorb water in the environment if the environmental factors change. The strength, permeability, and thermal stability of leathers may be greatly affected by the water within them. Retanning is a key operation in leather making. The main purpose of retanning is to get leathers with some special performances. The water content in leathers is around 20wt%, an amount that cannot be neglected. However, no reports are found on the interactions between collagen and water, particularly the influence of retanning on the interaction between water and collagen fibers. The state that water molecules exist in collagen fibers, the mechanism for collagen fibers to adsorb water, the de-adsorption kinetics for water molecules to escape from collagen fibers, and the influence of retanning on the adsorption of water on collagen fibers should be made clear to improve the leathermaking technology by controlling the structure and behaviors of leathers. In the present paper, after being chrome tanned, collagen fibers were retanned with chrome, glutaraldehyde, TGR retanning agent (proprietary acrylic based), and wattle extract, respectively, to get different retanned samples. The water adsorption isotherms of the samples were obtained by the use of the gravimetric method, by which the influence of retanning on the equilibrium water adsorption capacity and the influencing mechanism were discussed. On the base of adsorption characterization and equilibrium adsorption capacity for the samples to adsorb water, different mathematics models were used to describe the adsorption process and the adsorption mechanism. Six models were chosen to fit the experimental data, and it was found that the Bradley model is the best to describe the adsorption.