A Solid-State Pathway towards the Tunable Carboxylation of Cellulosic Fabrics: Controlling the Surface's Acidity

We report on a tunable solid-state approach to modify the acidity of cotton substrates using citric, oxalic, and fumaric acids. The first stage of the method involves soaking the cotton swatches in an ethanolic saturated solution of the corresponding acid. After drying, the carboxylation reaction proceeds at high temperature (T > 100 °C) and in solid state. We quantified the effect of temperature and reaction time on the solid-state carboxylation reaction, which allowed us to tune the carboxylation degree and the acidity of the surface. We characterized the modified cotton by performing adsorption isotherms and by determining the kinetics of adsorption of a cationic dye: methylene blue (MB). We found that the MB uptake kinetics varied as a function of the acidic strength of the surface, which is closely related to the strength of the acid used for surface modification. The proposed solid-state cotton carboxylation procedure allows us to achieve sustainable cotton modification, which constitutes a starting point for several applications using cotton as the substrate.