Coloration of Wool Fibers by Reducing Sugars

We have experienced in our daily living well that foods including both reducing sugar, such as xylose and glucose, and amino compound, such as amino acid and protein, become yellow or brown after the heating process or long storage such as the fermentation process. These coloration reactions are called the Maillard reaction, melanoidin reaction or browning reaction. It was clarified in our previous works that not only protein fibers such as wool, silk, and leather, but also polyamide fibers such as nylon 6 were also colored yellow or brown by the reducing sugars. However, it was also clear that these coloration reactions were very slow compared with usual dyeing. In this paper, the effects of pretreatment using polyallylamines were investigated on the Maillard reactions between wool fiber and D-xylose, where the polyallylamines were expected to increase the amino groups on the fiber surface. As a result, their pretreatment using lower-molecular-weight polyallylamine could afford their deeper colorations. For example, the wool fibers pretreated by polyallylamine PAA-01 (M.W. 1600) became dark brown after the reaction with D-xylose. Furthermore, their detailed pretreatment conditions, such as pretreatment time, its temperature, polyallylamine concentration, and the type of reducing sugars, were also examined here to enhance their color density.