Effect of Fibre Shape and Fibre Distortions on Creep Properties of Kraft Paper in Constant and Cyclic Humidity

The purpose of this investigation was to study the effect of fibre shape and fibre distortions on the creep properties in constant and cyclic humidity and compare these data to other standard paper properties. The fibre shape and magnitude of fibre distortions were varied by low consistency beating and high consistency treatment of the pulp. The term virgin were used for these pulps. Furthermore the effect of drying history was investigated where papers from straight fibres were dried under restrained- and freely-dried followed by reslushing. The term re-dried were used for these pulps. Fibre shape and fibre distortions of the virgin pulps had different effects on the creep stiffness. Straight fibres with few distortions had the highest stiffness values. By making the fibres curlier, the creep stiffness decreased significantly. The presence of fibre distortions in the straight fibres had no effect on the creep stiffness. The creep stiffness of papers from re-dried pulps depended on the drying method that produced the fibres. Without beating, fibres of the freely-dried paper gave a lower stiffness than fibres of the restrained-dried paper. The fibres had a memory of the distortions that were introduced by the free drying. After beating, the difference due to the drying method disappeared.