Determination of load-bearing element length in paper using zero/short span tensile testing

This study presents an equation developed to estimate, from zero and short-span tensile tests, the average length of load-bearing elements (the distance between serious defects along a fiber length) within a sheet of paper. The equation was used to examine the effect of drying treatment on the average loadbearing element length in paper made from five furnishes: two radiata pine kraft pulps, a Eucalyptus globulus kraft pulp, a eucalypt neutral sulfite semichemical (NSSC) pulp, and a recycled pulp. Of the three sets of handsheets for each pulp, the first used never-dried pulps, the second used reslushed handsheets that had been air-dried under restraint, and the third set was made from reslushed handsheets that had been oven dried. For all five furnishes, the average length of load-bearing element was approximately equal to the optically measured arithmetic average fiber length and did not decrease after the fibers were dried. The results suggest that the reduction in the strength of paper made from previously dried fibers, compared to neverdried fibers, is not due to the introduction of serious defects during drying. Application: This study helps explain the loss of sheet strength that occurs after paper is made from recycled fibers.