In-situ enzymatic generation of hydrogen peroxide for bleaching purposes

Abstract

Bleaching detergent formulations contain environmentally unfriendly bleaching agents (perborates and percarbonates), which cause aquatic eutrophication, although without these compounds detergents are much less efficient for the washing processes. In an effort to replace these compounds, in this study, hydrogen peroxide was generated as a bleaching compound by means of enzymatic reactions. Three different pathways were investigated. The first one was the H2O2 production from glucose by glucose oxidase. The second one was the production of H2O2 from carboxymethylcellulose (CMC) by the action of both cellulase, which promotes the hydrolysis of the polymeric chain, and glucose oxidase, which oxidizes the smaller fractions to produce H2O2. Finally, H2O2 was also obtained from ethanol, which is present in liquid detergents, by the action of the enzyme alcohol oxidase. In the search for maximal peroxide production, substrate concentration and enzymatic activities were optimized. The effect of H2O2 produced in the washing process was simulated by means of a process of cotton bleaching. Although enzymatic-reaction oxidations produced higher levels of hydrogen peroxide (up to 1 g/L after 8 h), higher improvement of cotton whiteness was achieved from CMC and from ethanol. The milder conditions of temperature and pH, biodegradability and less consumption of water and energy are advantageous for enzymes as good substitutes for H2O2 precursors and make them appropriate to be considered in detergent formulations. These enzymes could be combined with other oxidative enzymes, such as peroxidases, in order to lower the required temperature and use a pH close to the neutral value during the bleaching processes.