Salt-free dyeing of ramie fabric with an amino-terminated hyperbranched polymer

A new amino-terminated hyperbranched polymer (at-HBP) was synthesized, and its salt-free dyeing property on ramie fabric was studied. The structure and molecular weight of at-HBP were established by Fourier transform infrared spectrometer, H nuclear magnetic resonance and gel permeation chromatography. The untreated ramie fabric and modified ramie fabrics were characterized by an X-ray diffraction (XRD) and field emission scanning electron micrograph (FE-SEM). XRD results showed a transformation of the crystalline structure from ramie cellulose I to cellulose II allomorph during mercerization and epichlorohydrin modification, and the crystalline structure of cellulose II was maintained with an obvious crystallinity index increase after at-HBP modification. FE-SEM results confirmed that at-HBP was successfully grafted onto the fabric surface. Dyed with reactive dye C.I. reactive Blue 4, the color strength of the at-HBP-modified fabric was enhanced, even when dyeing was carried out without the electrolyte. The washing and rubbing fastness of the salt-free dyeing of fabrics was also good compared with those obtained by conventional dyeing. The adsorption isotherm of C.I. reactive Blue 4 on modified fabric was examined and found to follow a Langmuir-type adsorption model. The at-HBP modification mechanism of ramie fabric and dyeing mechanism with reactive dye were suggested.