Compression of paper in the z-direction - the effects of fibre morphology,wet pressing and refining

The z-direction compression properties of paper have been shown to be depen dent upon the morphological properties of pulp fibres. In particular, the c ross-section dimensions of fibres greatly influence collapse behaviour of t he fibres when dried, and hence greatly affect the final z-direction compre ssive properties of the sheet. Juvenile 6-year-old Eucalyptus regnans fibre s were measured to have an average cell wall thickness approximately half t hat of 20-year-old E. globulus. Further, the percentage of collapsed fibres for unrefined E. regnans fibres measured in the dry state was significantl y higher than for E. globulus. Confocal microscopy imaging of the sheet structure prior to, and after, loa ding some of the prepared samples allow qualitative observations of the eff ect of refining, wet pressing and z-direction compressive loads on the shee t structure. The images are consistent with observed compressive strain beh aviour of the sheets.