Fibre Peeling
Partial detachment of the outermost layers of a wood pulp fibre represents a critical initial stage in the development of inter-fibre bonding during stock preparation. A fibrillated primary wall occurs when mechanical shear in a refiner peels back the primary wall to expose the underlying secondary wall. This exposure increases the swelling capacity of the fibre and allows it to absorb water more readily.
The loose fibrillar material on the surface acts as an adhesive during paper sheet consolidation.
Bond Formation
Exposing the hydrophilic cellulose of the secondary wall allows for more hydrogen bonding sites during sheet drying. The presence of a fibrillated primary wall prevents the fibre from resisting deformation, making the individual fibres more flexible and conformable. Highly conformable fibres create a denser, smoother paper sheet with superior printing properties.
Slurry Behavior
Altering the pulp drainage characteristics affects the vacuum demand and drying speed on the paper machine. When the fibrillated primary wall is generated, the drainage resistance of the stock slurry increases, which can slow down production on the wire section. Mill operators monitor this change using tests like the Schopper-Riegler or Canadian Standard Freeness measurements.
A higher degree of fibrillation improves the strength properties of the finished paper but requires a careful balance to avoid excessive drying energy. This mechanical modification is tailored to the final product, with packaging boards requiring less fibrillation than fine writing papers.
