Diffusion of reactive dyes through cationized cellophane films

Abstract Cellophane films were cationized using 3–chloro–2–hydroxypropyltrimethyl ammonium chloride (CHPTAC) via a cold pad-batch method at four treatment levels (25, 50, 75, and 100 g/L). These modified films were used to investigate the diffusion behavior of five structurally diverse reactive dyes—C.I. Reactive (Blue 19, Violet 5, Red 198, Red 11, and Blue 109)—differing in molecular structure and sulfonate group content, under isothermal conditions at 60 °C. Time-lag diffusion plots were generated, and diffusion coefficients were calculated for all dyes and treatment levels.Cationization was found to significantly enhance dye diffusion through films compared to untreated samples. A typical increase of 2 × to 10 × in diffusion coefficient is observed due to CHPTAC treatment, depending on the dye structure and treatment level. Ionic interactions between the cationized cellulose and anionic dyes increased the driving force for diffusion. Diffusion coefficients generally decreased with the number of sulfonate groups, attributed to increased water solubility and steric hindrance.To better understand structure–property relationships, the equilibrium molecular geometries of the most stable conformers of selected dyes were calculated using density functional theory (DFT).Analysis of the optimized molecular geometries revealed a strong correlation between molecular coplanarity and dye mobility, and consequently, dye diffusion. Dyes with more coplanar geometries, such as C.I. Reactive Blue 109 and C.I. Reactive Violet 5, exhibited faster diffusion, likely due to reduced steric hindrance and more favorable molecular packing. In contrast, dyes with twisted or non-coplanar conformations, such as C.I. Reactive Red 198, displayed increased time-lags and lower diffusion rates, suggesting that geometric distortion can impede molecular transport properties.High resolution LC–MS analysis was also performed to characterize the structure and the ratio of vinyl sulfone versus sulfatoethylsulfone forms of C.I. Reactive Violet 5 and C.I. Reactive Blue 19 dyes, with approximately 47–53% de-esterification observed for these dyes. This provides additional insight into their diffusion behavior. These findings highlight the critical role of both substrate modification and molecular geometry in governing dye diffusion kinetics. This refined understanding can inform the design of more effective dyeing strategies for cationized cellulose in textiles and sustainable packaging applications.