A New Method for Preventing Catalytic Degradation of Cotton Cellulose by Ferrous or Ferric Ions During Bleaching with Hydrogen Peroxide

Abstract

Tendering of cotton cellulose caused by the presence of Fe2+ and/or Fe3+ ions during bleaching with H2O2 using the exhaustion method and the pad-steam method were studied. This was carried out by staining the cotton fabric samples with different concentrations of Fe2+ or Fe3+ ions then subjecting these samples to bleaching. Ceasing of cotton tendering resulting from Fe2+ and/or Fe3+ during bleaching with H2O2 by pretreatment of the fabric by oxalic acid were also studied under a variety of conditions. The onset of this pretreatment on the properties of the cotton fabric compared to the untreated fabric are discussed. The samples were monitored for degree of polymerization, Eisenhut's tendering factor, whiteness index, tensile strength and elongation at break. Results obtained show that the catalytic degradation of the cotton samples resulting from Fe2+ and Fe3+ ions are identical and the maximum tendering was observed when the fabric samples were contaminated with 0.3 mg/g fabric Fe2+ and/or Fe3+ ions. The catalytic degradation is much higher when the cotton samples were bleached with the pad-steam than with the exhaustion method. The ceasing of such catalytic tendering could be achieved by pretreatment of the cotton fabrics with a bath containing 1% oxalic acid at 40°C for 1 min. The pretreated fabrics have higher degree of polymerization, whiteness index, tensile strength and lower Eisenhut's tendering factor compared with the untreated fabrics. The state of the fabric (i. e., grey, desized, scoured) does not play any significant role in such pretreatment.