Swelling and dissolution mechanism of regenerated cellulosic fibers in aqueous alkaline solution containing ferric–tartaric acid complex—Part II: Modal fibers

Morphological changes of modal fibers swollen in FeTNa (Fe–tartaric acid–NaOH complex solution) were investigated by means of microscopy. FeTNa solutions had a constant molar ratio of 1:3.28 for Fe:tartaric acid. In FeTNa solutions, Fe and free NaOH concentration were in the range of 0.15–0.55 and 0.4–5 M, respectively. Fiber diameter measurements following 2 min of swelling and swelling rate of modal fiber up to 60 min were studied. Depending on Fe and free NaOH concentrations in FeTNa solutions and fiber swelling time; limited swelling, swelling, disintegration, dramatic swelling and dissolution of modal fibers were observed. Lyocell fibers showed the same morphological changes but mainly in different FeTNa solutions. In addition, uneven swelling was observed for lyocell fibers in selected FeTNa solutions. Morphological changes of viscose fibers were different than that of lyocell and modal fibers, which was attributed to its inhomogeneous (skin-core) fiber structure compared to homogeneous fiber structure of lyocell and modal fibers.