Ammonified modification and dyeing of ramie fabric in liquid ammonia

In this study, ammonified ramie fabric was prepared via chemical modification and subjected to a series of analyses. Ammonified ramie fabric was synthesized by Mannich reaction using methanal and ammonia gas as the reactants; the obtained material was then characterized by elemental analysis, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). The results indicated that NH2 groups were successfully grafted on the surface of the ramie fiber. Next, raw and ammonified ramie fabrics were respectively dyed in liquid ammonia with reactive dyes (C.I. Reactive Red 195) and direct dyes (C.I. Direct Blue 71), then tested for color fastness to washing and rubbing; the color strength (K/S) of the fabric samples were also measured. The time taken to attain equilibrium on Red 195 was 50 s and was 100 s for raw and ammonified ramie fabrics, respectively. The exhaustion time for raw and ammonified ramie fabrics dyed with Blue 71 presented an increasing trend with no obvious plateau. The experimental data for dyeing ramie fabric with reactive dyes fitted the Langmuir model, while the kinetics of ramie fabric dyed with direct dyes fitted the Freundlich isotherm. Ammonified treatment also increased the dye exhaustion and fixation, improved the wash fastness and the rubbing staining degree, and strengthened the color strength (K/S) of ramie fabric.