Traditional micromechanical theories for the tensile strength of paper do not account for the tensile stiffness of paper, even though in practice tensile strength is closely coupled with tensile
stiffness. Another problem is with the micromechanical input parameters, few of which have a precise meaning in real paper. Especially the interpretation of inter-fiber bonding is ambiguous.
None of the existing theories connects tensile strength with an independently measurable value of bonding degree or bond strength. As a result, the conventional interpretation of tensile strength data is unreliable.
In this paper we will present a “macromechanical” study that connects tensile strength with independently measured values of tensile stiffness and z-directional fracture energy (alternatively
Scott bond or z-directional tensile index). The model expression agrees well with many – but not all – of the experimental datasets that we had available. The disagreements demonstrate that z-directional measurements do not capture some aspects of inter-fiber bonding that contribute to in-plane tensile strength.