The complexation of Fe(III)-ions in cellulose fibres: a fundamental property

In alkaline aqueous solution cellulose fibres, e.g. cotton, viscose, modal and lyocell fibres, show a distinct tendency to complex Fe(III)-ions by ligand-exchange reactions with iron(III)–d-gluconate (DGL), iron(III)–hepta-d-gluconate (HDGL) complexes. Two regions of high-binding capacity are identified at pH 8 and 13, respectively. Using a solution containing 0.001 mol l−1 of the Fe(III)-complex, accumulation of Fe(III)-ions is observed in the fibre; depending on the type of cellulose fibre 0.7–3.6×10−3 mol Fe(III) per kg of fibre are complexed at pH 8, which corresponds to 40–200 mg kg−1 Fe(III). At pH 13, higher amounts of Fe(III)-ions up to 2.1×10−2 mol kg−1 (1150 mg Fe(III) kg−1) are analysed in the fibre. The equilibrium of the ligand-exchange reaction between fibre and complex in solution is dependent on the type of ligand used (DGL, HDGL) and the fibre type (cotton, viscose, modal, lyocell). The amount of iron complexed remains below the carboxylic number of the cellulose. This finding points to an involvement of the carboxylic groups in the complex formation, which is in agreement with structures of soluble iron–carbohydrate complexes. sults permit identification and quantification of structural sites able to complex Fe(III)-ions and lead to a more detailed understanding of the mechanism of catalytic damage of cellulose fibres during peroxide bleach.