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.
Recycled Fiber Shortening
Morphological Change
The physical reduction in the length of wood fibers happens each time they are processed through the repulping and refining stages of a paper mill. This recycled fiber shortening limits the number of times a single fiber can be reused before it is too small to contribute to the strength of the sheet. It is a natural consequence of the mechanical shearing and cleaning needed to recover the pulp.
Strength Impact
Longer fibers provide the network structure that gives paper its tensile and tear resistance. As recycled fiber shortening occurs, the resulting paper or board becomes weaker and more brittle unless it is blended with virgin pulp.
Process Adjustment
Mills compensate for shorter fibers by increasing the amount of refining or adding dry strength chemicals to the wet end of the machine. Despite these efforts, recycled fiber shortening eventually leads to a decrease in the bulk and stiffness of the final product. Monitoring the fiber length distribution allows the mill to maintain a consistent quality of board for the packaging market.
This property is a key variable in the sustainability of the global fiber supply. Higher percentages of virgin fiber are required for packaging that demands extreme durability.