Desirable retanning system for aldehyde-tanned leather to reduce the formaldehyde content and improve the physical-mechanical properties

The aim of the present work is to provide a new retanning system for aldehyde-tanned leather, which can improve the physical-mechanical property of resultant leather and reduce the formaldehyde content in the resultant leather. This new retanning system consists of polyacrylic acid and gemini polyurethane surfactant, which are not harmful to human. The physical-mechanical property of leathers treated with different retanning system was analyzed, and the fiber structure of leather treated with the new complex retanning system was observed; the effects of some factors on the physical-mechanical property and formaldehyde content of leathers were studied, which were the hydrophobic chain length of gemini polyurethane surfactant, the offer percentage of retanning agent and the pH condition of retanning process. The results showed that the complex retanning system had better retanning effect, and the physical-mechanical property and formaldehyde content of leathers would be affected by above factors. When the hydrophobic chain length was eight and the offer percentage was 6%, the retanning effect was the best, and the thickening rate was 8.5%, the elongation and tear strength increased by 14.5% and 18.4%, respectively. At the same time, the reduction rate of formaldehyde content was 30.0%. Notably, when the value of pH decreased to 2.7 in the retanning stage, the reduction rate of formaldehyde content could increase to 39.3%. This retanning system had better retanning effect, which indicated that it would be helpful to the clean production of leather and the development of environmental protection. In addition, the work provided a good alternative to solve the other formaldehyde problems in our life.