Copper inclusion in cellulose using sodium d-gluconate complexes

Copper containing cellulose material is of growing interest, e.g. offering alternative in the field of antimicrobials. Solutions of copper d-gluconate complexes (Cu2+–DGL) were used to introduce copper ions into a swollen cellulosic matrix. A ligand exchange mechanism forms the chemical basis of the sorption process. Copper sorption in cellulose was studied in the range between pH 6 and 13. An estimate for the complex stabilities of the Cu-cellulose system could be derived from the calculated species distribution of the different Cu2+–DGL complexes present. Spectrophotometry and cyclic voltammetry of Cu2+–DGL complex solution were used to confirm the presence of different species participating in the ligand exchange reaction. The pH dependent uptake of Cu2+ ions in the cellulose matrix can be explained on the basis of the relative stabilities of Cu2+–DGL complex vs. Cu2+–cellulose complexes. In comparison to pH 10, higher copper content was observed at pH 6 and 13. Copper content was limited by carboxyl content of cellulosic materials, thus in analogy to the structure of Cu2+–DGL complexes participation of the carboxyl group as complex forming site is proposed. At high Cu2+-concentration and longer time of immersion in the copper complex solutions formation of solid deposits was observed on the surface of the treated fibres.