Foxing - a new approach to an old problem

An investigation was conducted to elucidate the nature of foxings. A connection has been found between foxing formation and paper production, duration of its exposing to light, level of its dusting and storage conditions. UV investigations revealed that foxings show heavy fluorescence at the initial stage of development; luminescence decreases as the colour intensity increases. ESR-spectroscopic technique has revealed the presence of peroxide radicals in the area of foxings. In the initial stage of formation, their amount in stains was the double of that in the surrounding areas. In some fox spots a little bit more iron and copper is found than out of them. Fe(III) exists usually as slightly soluble oxides in dust and impurities. Cellulose oxidation by air O2 is resulting in the formation of peroxide radicals that are able to reduce Fe(III) to Fe(II) in acid media. Fe2+ containing compounds are much more soluble, therefore they can diffuse from dust particles and impurities into the surrounding fibres. The oxidation process increases in the area of Fe(II) diffusion, as the ions of Fe2+ are the radical forming centers. The products of cellulose oxidation can undergo reactions of condensation with compounds that contain nitrogen, thus forming brown-coloured products.