Swelling and dissolution mechanism of lyocell fiber in aqueous alkaline solution containing ferric tartaric acid complex

Swelling properties of lyocell fibers in FeTNa (ferric tartaric acid complex) solutions were studied. Concentrations of Fe and free NaOH in FeTNa were varied, while the ratio between FeCl(3).6H(2)O: tartaric acid was kept constant as 1:3.28. The concentration of Fe ion varied from 0.15 to 0.55 M. The free NaOH concentration in FeTNa solutions was chosen as 0.4; 0.8; 1.25; 2.5 and 5 M. Fiber diameter measurements following 2 min of swelling and swelling rate of lyocell fiber up to 60 min were studied. Depending on concentration of Fe and free NaOH in FeTNa solutions and fiber swelling time; swelling, dissolution, disintegration or dramatic swelling were observed. 0.4 and 5 M free NaOH containing FeTNa solutions could only swell the fiber but could not dissolve it. 2.5 M free NaOH containing FeTNa solutions dissolved the fiber in a few minutes. FeTNa solutions containing free NaOH concentration from 0.8 to 1.25 M resulted in either dissolution or limited swelling depending on Fe concentration.