The Mechanism And Characterization Of Dye-free Coloration Silk Fabric Based On Tryptophan

Silk is a natural protein fiber. It is soft, elegant and with highly moisture permeability. So it is very popular with consumers. Currently, the dyeing of silk fabric mainly uses acid dyes or reactive dyes. Dye was combined to fiber through the interaction between dye and fiber. The fastness of these dyes is poor, and some of them are harmful to human and environmental during the process of production and use. Therefore, they can not meet people’s growing requirements of textile such as health, ecology and environmental protection. For this situation, this article had raised a new dyeing concept, dye-free coloration, which means colored fabric without dyes. Tryptophan of silk proteins was used to coloration with benzaldehyde derivatives in acidic conditions in the fiber itself. So the fiber became color body and the dye-free coloration achieved. Different benzaldehyde derivatives in the reaction can generate different color material in the silk fabric.In this paper, the dye-free coloration of tussah silk and mulberry silk were studied. For tussah silk, p-hydroxybenzaldehyde and dimethylaminobenzaldehyde were chosen to do the coloration in concentrated nitric acid condition. Through orthogonal experiments and single factor analysis, the optimum process of dye-free coloration was determined. For the dye-free coloration of mulberry silk, the optimum process was determined through single factor analysis under the condition of concentrated nitric acid with p-hydroxybenzaldehyde and dimethylaminobenzaldehyde. Meanwhile, tests of dye-free coloration silk fabrics which included chromaticity, saturation, color difference, color fastness, levelness, strength and surface morphology of fiber were taken.The results showed as follow.1. The optimum process of tussah silk dye-free coloration was:(1) the amount of p-hydroxybenzaldehyde5%(o.w.f), mass fraction of nitric acid2.5%, temperature90℃, time60min and bath ratio1:30.(2) mass fraction of dimethylaminobenzaldehyde2.5%, mass fraction of nitric acid1%, temperature90℃, time70min and bath ratio1:30. Meanwhile the test results showed that, the color of tussah silk fabric after dye-free coloration was bright, the levelness was good, the surface of the fiber was almost no damage, both rubbing fastness and washing fastness were reached4grade or above and no significant change were shown in breaking strength.2. The optimum process of mulberry silk dye-free coloration was:(1) mass fraction of p-hydroxybenzaldehyde2.5%, mass fraction of nitric acid1.5%, temperature80℃, time60min and bath ratio1:30.(2) mass fraction of dimethylaminobenzaldehyde2.5%, mass fraction of nitric acid1.5%, temperature90℃, time60min and bath ratio1:30. Meanwhile, the results of color fastness test and breaking strength test showed that, the levelness of dye-free coloration mulberry silk was good, both rubbing fastness and washing fastness were reached4grade or above and no significant change was shown in breaking strength.