CHANGES IN NEWSPRINT PAPER DURING ACCELERATED AGEING

Degradation of cellulose is an important factor influencing its physical, mechanical, optical and chemical properties, as well as paper longevity in electrical industry and in stored paper and books. Accelerated ageing of newsprint paper has been performed at 98 degrees C, for 0, 1, 2, 3, 5, 7, 10, 15, 20, 30 and 60 days. Degradation has been studied by viscometry, gel permeation chromatography (GPC), and determination of tensile strength, brittleness index, folding endurance, surface pH, cold extract pH, colour of paper surface and amount of saccharides. In the first stages of accelerated ageing, cellulose depolymerization takes place homogeneously (as mainly due to hydrolysis), after which other reactions (such as oxidation, crosslinking) occur. The amount of saccharides in paper decreases, the hemicelluloses being degraded faster. Tensile strength and folding endurance decrease. The colour of the surface changes rapidly from light to dark, while lightness decreases and the chromaticity parameters increase. The pH values decrease, while surface pH decreases less than the cold extract pH.