Experimental Evaluation of the Interfibre Joint Strength of Papermaking Fibres in Terms of Manufacturing Parameters and in Two Different Loading Directions

The strength properties of interfibre bonds play a vital role in the response of fibrous materials, such as paper and paperboard, under mechanical loading. To help tailor the properties of such materials by chemical or mechanical treatments of the fibre wall and fibre surfaces, improved understanding of the microscopic damage and failure mechanisms of interfibre joints is desirable. In this paper, a method for manufacturing and testing of interfibre joint specimens in two principally different modes of loading is presented. The method was applied to investigate the strength of Kraft pulp interfibre joints with different geometries and in two different modes of loading: the conventional shearing mode and also a peeling mode of loading. The method was also used to investigate the influence of drying pressure, defined as the nominal pressure between two Teflon surfaces or between a rubber surface and a Teflon one as well as a simple comparison of a pulp with two different degrees of refining. The results are presented in terms of rupture force and using different methods of normalization such as nominal overlap area, length, and width of the joint region, measured using a microscope. It was shown in this study that normalising the force at rupture by either geometric parameter reduced the scatter of the strength measurements slightly, but, neither were unambiguously more successful than the other. The results of tests done with the peeling type of loading were about 20 % of those done with the conventional shearing type of loading.