Abstract:

Objective The application of natural dyes in textile printing and dyeing has attracted extensive attention because of their non-toxic and harmless characteristics. In order to improve the color yield and color fastness of plant dye dyeing products, mordant dyeing treatment is often needed in the dyeing process, but this will lead to long dyeing process and a large number of metal ions in wastewater. Metal ions were introduced into natural dye molecules in advance through complexation reaction to prepare metal complexed plant dyes, and their dyeing properties and influencing factors on textiles were studied in detail. These studies were deemed necessary for developing short dyeing process with natural dyes and achieving energy saving and emission reduction.

Method In this paper, catechin-iron ion complex dye C-Fe was prepared by hydrothermal method through the coordination reaction between catechin and metal ion Fe²⁺. Fourier transform infrared spectroscopy (FT-IR), ultraviolet visible spectrophotometer (UV-VIS), scanning electron microscope energy spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) were adopted to characterize and analyze the structure of the complex dyes. The dyeing of a silk fabric with iron ion complexed catechin was studied by grinding dispersion method. The influences of technological parameters such as pH value, dyeing temperature and dye dosage on the K/S value of textiles were analyzed, and the technological conditions were optimized.

Results Energy spectrum analysis of plant complex dyes showed that the C-Fe molecules contained not only C and O elements, but also Fe elements(Fig.2, Tab.1). Based on the energy spectrum scanning component element content analysis and the structure analysis of the complex dye, the complex ratio of C-Fe molecule was calculated as 1:2. UV-VIS spectrum analysis showed that the maximum absorption wavelength of catechin was red shifted after complexation with metal ions, which was consistent with the law that the UV-VIS spectrum of dye molecules moved to the long wavelength direction caused by the attraction of metal ions to electrons (Fig.3). IR spectrum analysis showed that the complex dye C-Fe produced a new absorption peak at 556 cm^-1, indicating that it was the stretching vibration peak of Fe—O bond formed after coordination (Fig.4). X-ray photoelectron analysis showed that the peak position of Fe element was found at 706.7 eV for the complex dye C-Fe (Fig.5). The coordination of metal ions had different effects on the whole molecular chemical environment. The complex dye occurred on the adjacent hydroxyl groups or the adjacent hydroxyl groups and carbonyl groups of the benzene ring (Fig.6, Fig.7, Tab.2 and Tab.3).

A complex dye suspension with an average particle size of 405.47 nm was obtained by grinding and dispersion (Fig.8). The test showed that the optimal process parameters for dyeing silk fabrics with complex dye C-Fe were pH value of 4, dyeing temperature of 90 ℃, and temperature maintaining and continuous dyeing for 60 min (Fig.9, Fig.10 and Fig.11). The color fastness to sunlight and rubbing of silk fabrics dyed with complex dye C-Fe reached grade 3, and the color fastness to perspiration and soaping were all above grade 4 (Tab.4). The UPF value of silk fabrics dyed with complex dye was 72, reflecting excellent ultraviolet protection performance (Tab.5).

Conclusion In this paper, plant complex dyes were prepared by the coordination reaction between plant dyes and metal ions, and then the silk fabric was dyed with good dyeing effect, and the fabric demonstrated good color fastness and UV resistance. The experimental results show that the preparation of plant complex dyes from plant dyes as raw materials is feasible for textile dyeing. It is expected to be developed as a short process technology for plant dye dyeing, which provides a theoretical basis for the development of metal complex natural dyes and their application in textile dyeing.

Key words: catechin, iron ion, complex plant dye, natural dye, silk, dyeing