Recycled Containerboard Compression Loss under Constant Atmospheric Humidity
Recycled containerboard loses up to 45% compression strength under constant 85% RH; specify ISO 2233 derated SCT metrics to prevent static stack collapse.
Constant Humidity
Environmental Specification
Standardized laboratory testing relies on controlled air moisture levels to ensure the repeatability of physical measurements on cellulose sheets. Establishing a state of constant humidity prevents paper fibres from expanding or contracting during tensile and burst evaluation. The boundary for this requirement rests at standard temperature, since moisture capacity fluctuates with thermal shifts.
Moisture Equilibrium
Fiber networks exchange moisture with the surrounding atmosphere until they reach a stable weight. This hygroscopic behavior means that paper exhibits hysteresis, where the equilibrium moisture content depends on whether the material is drying out or absorbing water. To eliminate this variability, test sheets undergo pre-conditioning at low humidity before entering the final test environment.
This ensures that every sample approaches the final target from a dry state, providing uniform physical characteristics for measurement. Accurate control of this pre-conditioning phase removes the risk of structural variance in the sample.
Testing Standard
International protocols dictate the specific environment for physical paper testing, which is typically maintained at fifty percent relative humidity and twenty-three degrees Celsius. Operating within these tight tolerances prevents discrepancies between mills and converting plants. A deviation of even five percent relative humidity can alter the tear resistance and stiffness of paperboard enough to cause processing issues on automated packaging lines.