Alkali induced changes in spatial distribution of functional groups in carboxymethylated cellulose

The aim of the work was to investigate treatment parameters that exert most influence on performance of cellulose fibers carboxymethylated from aqueous solutions. Viscose fibers were carboxymethylated in alkaline solutions of sodium monochloroacetate at two temperatures (30 °C, 50 °C) and with different levels of alkali (0.5 mol/L and 4 mol/L NaOH). The degree of carboxymethylation was assessed with both back titration and conductometric titration methods, and the performance of carboxymethylated fibers was assessed from their propensity for sorption of the cationic dye methylene blue, a putative wastewater contaminant. Higher degrees of carboxymethylation were generally observed for fibers carboxymethylated in 4 mol/L NaOH, but in dye sorption propensities, the fibers carboxymethylated in 0.5 mol/L NaOH performed better. A combination of observations from dye sorption, color measurement and conductometric titration suggested that dye permeation was greater through fibers carboxymethylated in 0.5 mol/L NaOH as compared to 4 mol/L NaOH. As permeability differences were evinced in cases also where the degrees of carboxymethylation were very similar, it appears that the reaction conditions (i.e., alkali content during carboxymethylation), in addition to degree of carboxymethylation, affected fiber performance. The effect of alkali may stem from their influence on the topographical distribution of the substituted carboxymethyl functional groups.