Secondary Fiber Tensile Network Degradation under Variable Transit Humidity
Recycled pulp webs suffer severe tensile network degradation under cyclic transit humidity due to moisture-driven hydrogen bond disruption and hornified fiber creep.
Microfibrillar Collapse
Structural Loss
Cellulose fibre saturation during high pressure drying forces the inner cell walls to lose their porous geometry and permanently adhere to the secondary wall. This process, defined as microfibrillar collapse, occurs when the capillary forces generated by water evaporation exceed the elastic recovery limit of the lumen. The structural damage prevents the fibre from swelling to its original diameter upon rewetting.
Mills mitigate this reduction in surface area and bonding potential by controlling the intensity of heat applied during the drying phase.
Bonding Capacity
Hydrogen bond density dictates the strength of paper webs, and the irreversible deformation of internal wall elements limits how many sites remain available for these connections. When microfibrillar collapse alters the physical morphology of the pulp, the fibre becomes stiff and loses its capacity to conform to neighboring fibres in the sheet. Wet pressing conditions frequently trigger this change because the mechanical load works in tandem with elevated thermal energy.
Lowering the dryness at the press section prevents the fibres from reaching the threshold where cell wall adhesion becomes permanent.
Process Influence
Chemical additives or specific refining protocols adjust the sensitivity of the cell wall to deformation under compression. Fibres that exhibit high microfibrillar collapse show reduced optical scattering coefficients due to the loss of internal voids. This reduction in surface area makes the resulting paper less opaque and harder to refine to a high tensile strength.
Excessive drying temperatures on a paper machine directly decrease the structural integrity of the final sheet.