Title
Elemental chlorine-free bleaching of soda rapeseed pulp
Authors
FRANTISEK POTUCEK and MARTINA RIHOVA

Received Dedicated to the memory of the founder of the Cellulose Chemistry and Technology Journal, Acad. Professor Cristofor I. Simionescu
Published Volume 51 Issue 9-10 September-December
Keywords soda rapeseed pulp, elemental chlorine-free bleaching, brightness, zero-span breaking length, degree of polymerisation

Abstract
Soda rapeseed pulps delignified to kappa numbers of 21.4 and 16.4 underwent elemental chlorine-free bleaching using chlorine dioxide, hydrogen peroxide, and peracetic acid as bleaching agents under laboratory conditions. Three four stage bleaching sequences, DEPPPaa, D0EPD1P and D0EPD1D2, were applied to investigate the properties of bleached soda pulps, namely their brightness, zero-span breaking length and degree of polymerisation. For comparison, an oxygen-predelignified kraft softwood pulp with an initial kappa number of 10.5 was bleached under the same conditions. Soda pulps subjected to bleaching processes comprising two or three D stages were found to have a final brightness of 83.1 to 83.8% ISO, which was lower than that of 87.6 to 87.9% ISO obtained for kraft softwood pulp. The decrease in fibre strength was of only 7-9% for soda pulps, slightly greater than that of kraft softwood pulp. In contrast to fibre strength, the loss in the degree of polymerisation was considerable, roughly of 35% for soda pulps and 40 to 47% for kraft softwood pulp, depending on the bleaching sequence.