Functionalization of Cotton Fabrics by TEMPO-Mediated Oxidation

Abstract

A cotton fabric was oxidized using either TEMPO/NaBr/NaClO or TEMPO/Na₂SO₄/NaClO system in water at pH 10 under various conditions. Carboxylate contents increased from 0.06 to 0.30-0.44 mmol/g through the TEMPO-mediated oxidation, while viscosity-average degrees of polymerization (DP_v) decreased from 2200 to 1000-1220; remarkable depolymerization was inevitable during the oxidation. Because degrees of whiteness reduction of TEMPO-oxidized cotton fabrics after heating treatment were clearly decreased by post-NaBH₄ treatment, small amounts of C2/C3 ketone groups are likely to be present in the TEMPO-oxidized cotton fabrics, which may have caused the whiteness reduction after heating treatment. When the TEMPO/Na₂SO₄/NaClO system was used, carboxylate contents of the TEMPO-oxidized cotton fabrics were a little lower than those prepared using the conventional TEMPO/NaBr/NaClO system. However, the TEMPO/Na₂SO₄/NaClO-oxidized cotton fabrics had still sufficient amounts of carboxylate groups, and higher DP_v values and lower degrees of whiteness reduction after heating treatment than those of the TEMPO/NaBr/NaClO-oxidized cotton fabrics; the TEMPO/Na₂SO₄/NaClO oxidation system has some advantageous points in terms of suitable functionalization of cotton fabrics as clothing materials. The different whiteness reduction behavior between the TEMPO/NaBr/NaClO- and TEMPO/Na₂SO₄/NaClO-oxidized cotton fabrics was explained in terms of different distribution of carboxylate groups in fiber cross-section of TEMPO-oxidized cotton fabrics prepared using the two different oxidation systems; the cotton fibers in the TEMPO/Na₂SO₄/NaClO-oxidized cotton fabrics had more homogeneous distribution of carboxylate groups in the fiber cross section. The TEMPO-oxidized fabrics with 0.31-0.32 mmol/g carboxylate contents had sufficient burst strength and stiffness values for clothing materials, and clear deodorant efficiencies to ammonia and acetic acid gases even after 100 repetitions of laundry treatment. Thus, TEMPO-oxidized cotton fabrics have potential application as functional clothing materials.