Deep coloration of chrome-tanned leather by glucose oxides

Abstract

Our laboratory has reported in many papers on the coloration of fiber materials with amino groups, such as wool, silk, and nylon, using the Maillard reaction, i.e., the reaction with sugars. In particular, by using oxides of reducing sugars oxidized by the Fenton reaction, we have succeeded in significantly shortening the coloration time compared to conventional reducing sugars. For example, in the case of d-glucose, it was revealed that its color concentration was increased by about 200 times. Therefore, in this work, leather with low heat resistance was colored using reactions with oxides of reducing sugar and the relationship between the color concentration and mechanical strength was investigated in detail. First, the coloration of chrome-tanned leather was studied using oxides of d-glucose. Similar to the coloration of wool previously studied, the reaction was highly reactive to leather, and the leather could be colored to a dark, almost dark brown color even under the low temperature condition of 40 °C. In addition, the mechanical strength of leather is reduced by hydrochloric acid, a byproduct during the formation of glucose oxide. The concentration of glucose oxide, temperature of the reaction solution, and pH of the reaction solution were investigated in detail in order to darken the leather and control the reduction of its mechanical strength. As a result, not only was it possible to achieve a darker, almost black coloration, but the reaction in an aqueous solution containing a strongly basic glucose oxide produced interesting results in that the mechanical strength of the leather increased compared to that of the leather before treatment.