Absorption Rate
Time dependent behavior of paper and board as they exchange water vapor with the surrounding air defines the speed of moisture uptake or release. Moisture sorption kinetics determine how quickly a stack of board reaches equilibrium in a new environment. This process is non-linear and typically slows down as the material approaches its saturation point.
Factors such as temperature and air velocity influence the observed rate.
Environmental Interaction
Hysteresis effects mean that the path to equilibrium differs depending on whether the board is drying out or getting wetter. Chemical additives on the fibre surface can significantly delay this transition.
Dimensional Stability
Production efficiency in printing plants relies on the board maintaining a flat profile, which is only possible if the moisture content is stable. If the moisture sorption kinetics are fast, the edges of a stack will expand or contract before the center, leading to wavy edges or tight centers. Controlling the relative humidity in the warehouse is the standard way to manage this risk.
High performance packaging for sea freight is engineered to have slow kinetics to survive long periods of high humidity. Testing these rates involves gravimetric analysis where the sample is weighed at regular intervals in a controlled chamber. Consistent performance ensures that high speed converting machinery does not jam due to sheet distortion.
