Environmental Stress
The repetitive exposure of paper or paperboard substrates to alternating high and low ambient moisture levels represents a critical test for packaging performance during storage and maritime transport. Within the packaging testing domain, relative humidity cycles simulate the physical expansion and contraction that occurs as environmental moisture fluctuates. These cycles lead to progressive loss of stacking strength and can cause severe package deformation.
Laboratory tests use these simulated cycles to evaluate the durability of corrugated boxes under extreme real-world conditions.
Creep Behavior
Corrugated cartons stored in unventilated warehouses can fail under loads that are well below their initial static compression strength. When subjected to relative humidity cycles, paper fibers undergo accelerated moisture creep, which is a process where the fiber-to-fiber bonds weaken under stress. The paperboard experiences cumulative damage during each transition from dry to humid air.
This cyclic swelling and shrinking breaks the hydrogen bonds in the sheet, causing the walls of the box to bulge and eventually collapse under the weight of the stacked pallets.
Material Formulation
Developing boxes with high resistance to climate variation requires using specialized sizing agents and wet-strength resins. The application of relative humidity cycles in the laboratory allows chemical suppliers to test the durability of these protective coatings. These barrier formulas slow down moisture absorption and help maintain box structural integrity during long transit times.
