Experimental study of capillary impregnation and wettability effects in porous cotton fiber structures

The study of capillary flows in cellulose fibers is important for various applications, including biomass pyrolysis and drying processes. This work investigates the behavior of cotton fibers during capillary impregnation using a dynamic approach. The analysis utilizes the Washburn equation and tensiometric methods to investigate geometric factors, apparent advancing contact angles, surface free energy of cotton fiber, and capillary pressure. The research is carried out in two phases. The first phase focuses on the theoretical application of the Washburn equation in porous cotton fibers, specifically examining capillary wicking behavior within a cylindrical holder. The second phase involves experimental analysis, using three different liquids: n-heptane, water, and glycerol. The surface tension of the liquids was measured, and the capillary impregnation process was characterized through the determination of geometric factors, apparent advancing contact angles, and surface free energy. The geometrical factors of cotton fibers within the sample holder were found to be 10 . 39 ± 1 . 28 mm 5 . The apparent advancing contact angles for water and glycerol were 74 . 93 ° ± 2 . 20 ° and 69 . 55 ° ± 1 . 83 ° , respectively. The surface free energy of cotton fibers was calculated to be 27.82 mN/m. The capillary pressures for n-heptane, water, and glycerol were 2 . 65 ± 0 . 33 , 2 . 50 ± 0 . 31 , and 2 . 91 ± 0 . 36 kPa for ɛ =0.483, respectively. The results highlight the relationship between the geometric properties of cotton fibers and the physicochemical characteristics of the liquids during the capillary impregnation process.