MEASURE OF THE INTERNAL BOND STRENGTH OF PAPER BOARD

Three methods are used to measure the internal bond strength of papers made from TMP, CTMP, and kraft pulps. These are the z-directional ten sile test, the delamination test, and the Scott bond test. The compari sons between these methods using the same unit of measure (J/m(2)) sho w that even though the results are highly correlated, these tests do n or measure the same thing. In addition to the fiber-to-fiber bond brea kage energy, the delamination energy includes the energy dissipated in the fibrous network of thick papers, while the z-directional tensile energy includes the energy of intrafiber bond failure especially for p apers made from flexible chemical pulp fibers. On the other hand, the Scott bond energy is affected by basis weight and by the dynamic natur e of the test which tends to over evaluate this parameter. This analys is further shows that the z-directional tensile strength is the best s uited measure to determine the internal bond strength especially for h igh basis weight papers.