Structural Irreversibility
Drying and rewetting cycles alter the internal porous structure of wood pulp fibres by causing permanent hydrogen bonding between adjacent cell wall microfibrils. The physical mechanism behind fibre hornification locks collapsed internal pores during water removal, preventing complete re-swelling when recycled pulp suspended in water undergoes repulping. This irreversible structural compaction reduces the flexible surface area available for inter-fibre bonding in secondary papermaking processes.
Swelling Limitation
Water retention values measured in recycled pulp slurries drop in direct proportion to the number of drying cycles experienced by the cellulosic stock. As fibre hornification progresses, the water-holding capacity of the cell wall decreases, yielding a free-draining pulp slurry that forms a less dense paper structure. Mechanical refining forced onto recycled fibres can partially restore bonding capability by peeling away stiff outer cell layers, but refining also shortens fibre length and increases fine generation.
Consequently, the diminished swelling capability forces converters to adjust target grammages or incorporate virgin fibres when manufacturing high-strength packaging papers.
Tensile Impact
Rupture resistance and z-direction tensile strength decrease noticeably when recycled fibres dominate the paper furnish. The structural rigidity resulting from fibre hornification limits fibre conformability during sheet pressing, producing fewer inter-fibre hydrogen bonds per unit volume.
