Study of the water-softening properties of nitrated silk fibroin

Abstract

In this study, natural silk fibroin fibres were modified by nitration and their water-softening properties were investigated. Fibroin fibres were nitrated in a 30% nitric acid solution and subsequently neutralised using a sodium hydrogen carbonate (NaHCO₃) solution. The nitrated fibroin fibres were washed, bleached, and immersed in water with a hardness of 8.4 mg-eq/L for 24 hours. Water hardness was determined by complexometric titration with Trilon B. A decrease in hardness from 8.4 to 7.9 mgeq/L was observed. The obtained results demonstrated that nitrated fibroin fibres exhibit sorption activity towards Ca²⁺ and Mg²⁺ ions.