Bond strength of oxygen-delignified kraft pulps

Interfiber bond strength of northern hardwood kraft was measured using the delamination procedure of Skowronski and Bichard (16) on sample withdrawn following each stage of a commercial OD(EOP)DD bleach sequence. Bond strength measurements were also conducted on brown-stock pulp following medium-consistency oxygen delignification in which the temperature (90-110 degrees C), time (0-60 min), and alkali charge (1.5-3.5%) were varied in the oxygen stage. The results show that interfiber bond strength for both the laboratory and commercial samples increased across the oxygen state, provided that high amounts of alkali are not added, making the reaction conditions harsh. The increased bond strength is thought to result from increased hydrogen bonding, which compensates for the loss of wet zero-span tensile strength of the pulp following exposure to oxygen.