A Chrome-Free and Chrome-Less Tanning System Based on the Hyperbranched Polymer

This paper discusses the terminal carboxyl groups of the hyperbranched polymer (HPAE-C) complexing Al3+ in aluminum sulfate to synthesis a new chrome-free tanning agent (HPC-Al). The molecular structure of HPC-Al was characterized and analyzed by IR, UV, and XRD. In the tanning process, the results indicate the following: (1) The shrinkage temperature of HPC-Al tanning leather is 79.5 °C. (2) The shrinkage temperature is greater than 95 °C after chrome retanning and about 87 °C after zirconium retanning. (3) It has greatly improved the fullness, softness, and physical-mechanical properties of the leather. Meanwhile, the environmental impact assessment after tanning was evaluated. The results show that biochemical oxygen demand, total dissolved solids, and total suspended solids are reduced. This indicates that the use of HPC-Al as a tanning agent, with chrome-free or chrome-less tanning, can be achieved.