Pretreatment-free inkjet printing of cotton fabric using a reactive dye ink with a thermo-responsive pH buffer system

A thermo-responsive pH buffer system enables pretreatment-free reactive dye inkjet printing. • HPMC suppresses ink penetration and NaAc/HAc provides alkaline fixation during steaming. • Ink stays weakly acidic for storage yet turns alkaline upon steaming for dye fixation. • The novel ink achieves color yield and fastness comparable to conventional pretreated processes. • This strategy simplifies processing, cuts energy and chemicals, and reduces environmental pollution. Conventional reactive dye inkjet printing relies on fabric pretreatment to suppress ink penetration and provide alkaline fixation conditions, which leads to long production cycles, high energy and chemical consumption, and environmental pollution. Herein, a novel pretreatment-free reactive dye ink with a temperature-sensitive pH buffer was developed for cotton fabric. The ink employs hydroxypropyl methyl cellulose (HPMC) to control ink spreading and sodium acetate/acetic acid (NaAc/HAc) as a thermo-responsive pH regulator. The ink remains weakly acidic at room temperature to ensure stable storage and jetting, and turns alkaline during steaming to satisfy the requirements of dye fixation. Four colored novel inks (cyan, magenta, yellow, black) were prepared and compared with commercial inks. Results show that NaAc barely affects the visible absorption, surface tension, viscosity, or droplet formation of the dye inks, ensuring excellent printability. With increasing NaAc content, the K/S values of all four colors are significantly enhanced without any hue shift. When applied to untreated cotton fabric, the novel ink achieves color performance, image clarity, and rubbing fastness (≥ grade 4) equivalent to those of commercial inks on pretreated fabric, while completely eliminating the pretreatment process. This work provides a green, efficient, and biocompatible strategy for cleaner textile inkjet printing with reduced cost and pollution.