Changes in fiber characteristics and handsheet properties of Eucalyptus globulus kraft pulps

A series of thirty-three 9-year-old Eucalyptus globulus trees planted in southwest Australia were examined to investigate variations in pulp fibre and handsheet properties during recycling. Each pulp refined for 7,500 rev. in the PFI mill was subjected to recycling of a sequence of wetting, defibration, dewatering and drying up to five cycles. Restraint drying was performed at 80°C for 24 hours in a forced air circulation oven as handsheet for the recycling procedure. For the Eucalyptus globules trees, strength of handsheets, such as tensile index, decreased with recycling, particularly after the first recycle. However, the strength property variations during recycling were considerably high among trees. The decrease in handsheet tensile strength during recycling was closely related to the fiber morphological characteristics and the water retention value. A decrease in fiber wall thickness was observed as a result of shrinkage configuration of the fiber wall during recycling. Tensile index at extended recycling was calculated by nonlinear regression analysis for each pulp. The expected tensile index was adequately correlated with fiber wall thickness of refined pulp.