Surface charge and isoelectric point of leather: A novel determination method and its application in leather making

Surface charge and isoelectric point (pi) of leather play an important role in leather making processes. However, a proper method for the determination of surface charge and pi of leather is unavailable nowadays due to the complexity of leather structure and property, especially for the burgeoning chrome- free tanned leathers. Therefore, it is necessary to develop a quantitative determination method. In this study, a novel method for determining zeta potential (to characterize the surface charge of leather) of solid-state leather was established using a zeta potential analyzer based on the principle of streaming potential. Test conditions including suspension concentration, sample grain size, temperature and conductivity were optimized. Then the pi (the pH value at the zero point of zeta potential) of a variety of chrome-free tanned leathers, such as mineral, vegetable, organic and combination tanned leather, were obtained by this zeta potential method. Moreover, we managed to monitor the pi and surface charge state of zirconium tanned leather during post-tanning processes using this method. As a result, application of this precise and rapid determination method enables us to reasonably regulate the pi and surface charge of chrome-free leather so as to effectively improve tanning and post-tanning performances.