New colourimetric method for determination of hydroxyl radicals during ageing of cellulose

It is believed that oxidative degradation involving free radicals leads to the deterioration of alkaline paper during ageing. However, due to the high detection limit of conventional methods, e.g. ESR, the presence of radical species during ageing of pure cellulose at close to ambient conditions has not yet been established. In the present work, N,N´-(5-nitro,1,3-phenylene)bisglutaramide is used as a colour indicator of hydroxyl radical production in cellulosic materials. Quantitative determinations of its hydroxylated products can be performed using colourimetry. The measurements are rapid, non-destructive and demand a small amount of sample, which makes the new method attractive for use in industrial laboratories for a variety of materials. Several sources of systematic errors are identified and evaluated. Hydroxyl radicals are shown to be important intermediates in the oxidative processes during ageing of alkaline cellulose (pH>7). Furthermore, the importance of alkalinity on oxidative degradation of bleached chemical pulps is demonstrated.