Dynamic moisture sorption behavior of cotton fibers with natural brown pigments

The moisture sorption behavior of white and naturally colored cotton fibers is studied by dynamic vapor sorption. Dark brown and brown fibers show a higher sorption capacity compared to beige and white fibers. The differences in sorption capacity are found to be related to the maturity and crystallinity index of the fibers. All fibers exhibited sorption hysteresis to varying degrees throughout the full relative humidity range. The variations in hysteresis behavior are mainly attributed to the differences in crystallinity index of the fibers. In addition the monolayer and polylayer moisture content is analyzed using the Hailwood Horrobin model. Monolayer sorption is most closely related to the crystallinity index and, to a lower extent, maturity of the fibers. For beige and white fibers monolayer sorption remains almost constant, whereas for darker fibers it shows a substantial increase with increasing color difference. In contrast, polylayer sorption shows a general increasing trend over the whole studied color spectrum. Also a noticeable relationship was found between the total hysteresis and the monolayer sorption. Yet such relation was less evident for polylayer sorption. This study contributes to the better understanding of the dynamic moisture sorption behavior of white and naturally colored cotton fibers. This improved understanding is important for optimal application of naturally colored cotton fibers in novel materials.