Cellular Displacement
Intramolecular movement describes the shifting of crystalline cellulose chains against one another under mechanical stress. This microfibrillar slip happens when hydrogen bonds between adjacent chains break and fail to recover during load application. The phenomenon dictates the plasticity of wood pulp fibres.
Fibre segments that undergo this internal reconfiguration exhibit reduced elastic recovery and lower tensile strength.
Mechanical Consequence
High levels of internal movement lead to permanent deformation in the paper web during the drying process. Tension applied across the paper machine causes individual fibres to stretch beyond their elastic limit. Converting lines encounter issues when this material property remains unchecked because uneven stretching affects registry in high-speed print runs.
Rolls with elevated internal displacement show non-uniform caliper profiles and variations in structural integrity.
Processing Limit
Controlling the rate of slippage requires precise management of moisture content and refining energy during initial pulp preparation. Moisture acts as a plasticizer, lowering the energy barrier required for chains to move past one another. Reducing the total energy input at the refiner minimizes the initial population of broken bonds that facilitate movement under later tension.
Manufacturers calculate optimal load limits by measuring the strain at break for specific paper grades to prevent excessive movement before the substrate exits the press nip. The degree of internal displacement limits the total dimensional stability achievable in high-density sheets.
