The Effect of Refining on Wet Fiber Flexibility and its Relationship to Sheet Properties

Abstract

The wet fiber flexibilities of several softwood and hardwood species were measured by Steadman’s method (5). Softwoods showed a broader range of wet fiber flexibilities than hardwoods. Refining* decreased the spread as measured by the IQR and increased the median values. The wet fiber flexibility and its distribution was sensitive to the type of refiner, beating load and refiner consistency. Refining at high intensity by increasing the refiner load in a Valley Beater, resulted in the production of pulps with inferior strength properties. When the pulps were at constant WFF, those prepared under low intensity exhibited superior tensile strength. The main effect on the fibers beaten at high consistency was to sharply reduce their fiber length. Changing loads in the PFI mill had less of an impact on the WFF and paper properties . Refining with the low load resulted in maximizing fiber flexibility. However, the tensile strength was inferior. The tensile-density relationship did not change as a function of refining load in the PFI mill, indicating that the quality of refining did not change. The WRV was useful in understanding the relationship between fiber and sheet properties.