Environmental Fluctuation
Atmospheric conditions that alternate between high and low moisture levels create a dynamic stress environment for cellulose based materials. Exposure to cyclic relative humidity accelerates the rate of creep in corrugated board significantly faster than constant exposure to a single high moisture level. This phenomenon occurs because the fibers expand and contract as they absorb and release water vapor, which breaks internal hydrogen bonds and allows the structure to shift.
Structural Impact
Stacked containers often fail during transport or storage because the cyclic relative humidity causes the board to lose its stiffness through mechanical fatigue. The repeated swelling and shrinking of the liners against the rigid glue lines creates internal shear stress that weakens the fluting. Testing in a humidity chamber reveals that a box might survive for months at eighty percent humidity but collapse in days if the air cycles between fifty and ninety percent.
Conversion Factor
Designing for these conditions requires a higher safety margin during the grade selection process for paperboard. Engineers use a multiplier to reduce the expected compression strength of the box to account for the damage caused by cyclic relative humidity during international shipping. This adjustment ensures the secondary packaging remains intact despite passing through different climate zones.
