| Abstract: | CONCLUSION. A new colourimetric method for quantitative de¬termination of HO● in alkaline paper is presented. NPG is introduced into alkaline cellulose samples and a formation of coloured hydroxylated derivatives with absorption maximum at 450-460 nm is observed during accelerated ageing. Neither the substrate nor the derivates are volatile or degrade at temperatures of interest, therefore, NPG is a suitable indicator of hydroxyl radical production. The colouration of cellulose samples was shown to correlate with the concentration of derivates, determined chromato-graphically. Their concentration in the samples is easily determined colourimetrically at 460 nm by measuring diffuse reflectance with the unaged con¬trol sample as the reference. Since their absorption properties are pH-dependant, but stable at pH > 7, the method may only be recommended for alkaline samples. Several sources of systematic errors are identified and evaluated. Colourimetry is a non-destructive technique and simple to use, and the new method could easily be extended for use with other materials. The results, combined with viscometric determinations of degree of polymerisation, may provide new insight into the oxidative degradation processes, especially in rapid comparative evaluations of new antioxidant systems. While it has been presumed that hydroxyl radicals are important intermediates in the autoxidation of solid alkaline cellulose, their existence has not been proven yet. The new method offers the possibility for their quantitative determination and is thus a valuable con¬tribution to material degradation studies. |
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