Effect of pH on A1/Zr-Binding Sites Between Collagen Fibers in Tanning Process

Abstract

In this article, near infrared reflection (NIR) spectra were employed to investigate the pH influences on binding behaviors of collagen fiber (CF) towards conventional non-chromeinorganic salts (Al and Zr). Based on the analyses of NIR and corresponding 2D NIR spectra, the binding capacity of Al (or Zr) contributed by each type of functional groups on CF was successfully evaluated at different pH conditions by carried out the aluminum tanning (or zirconium tanning) to native CF deaminated collagen fiber (DACF) and decarboxylated collagen fiber (DCCF), respectively. Our experimental results indicated that, for aluminum tanning, both the carboxyl group and amino group of CF are the active sites responsible for Al-binding and the reactivity of carboxyl group to aluminum is higher than that of amino group. However, the amino binding sites are more influenced with different pH. As for zirconium tanning, amino group and carboxyl group are still the active binding sites while the reactivity of amino group is higher than that of carboxyl group in the pH range of 0.5~1.5 which increases with the increasing tanning pH. Furthermore, based on the analysis of Fourier transform infrared spectra of polycaproamides reacted with zirconium at different pH, it was found that the amide group in collagen is responsible for Zr-binding between collagen fibers and its reactivity with zirconium increases with the rise in pH.