Abstract:

The purpose of this work was to determine the optimal duration of free swelling for refined unbleached kraft pine pulp. Free swelling is the effect of water sorption by cellulose fibres without their simultaneous mechanical treatment (e.g. refining). The second purpose was to determine the possibility of improving the mechanical properties of paper by testing various combinations of refining and free swelling processes. The pulp SR value and water retention value (WRV) of the fibres were tested. As regards paper properties, the tensile index and tear index were tested. Based on the results obtained, it was found that for the pulp tested, refined to 35 °SR, the optimal time of free swelling was 70 min. It was also proved that the free swelling had a significant impact on both the WRV of fibres and the mechanical parameters of paper tested. For the scheme in which refining was followed by free swelling, a 7% increase in the tear index was obtained. However, an 11% increase in the tear index was attained for the scheme with three refining stages, followed by free swelling after each refining.