Water Absorption
Liquid resistance testing over extended thirty-minute durations quantifies absorption capacity in heavy corrugated linerboard and solid containerboard. Standard cobb 1800 absorbency measures the mass of water absorbed by one square meter of paperboard surface during eighteen hundred seconds of direct contact. High values indicate low internal or surface sizing, permitting liquid penetration that softens paperboard structures.
Testing applies primarily to outdoor storage containers and agricultural packaging subjected to prolonged moisture exposure. The test boundary stops at total saturation or sample leakage, where mass measurements no longer reflect controlled liquid uptake rates.
Testing Protocol
A metal cylinder with an internal cross-sectional area of one hundred square centimeters clamps securely over a pre-weighed paperboard specimen. One hundred milliliters of distilled water fills the column, starting the eighteen-hundred-second timer. At seventeen hundred and forty seconds, the technician pours off the liquid, unclamps the sample and places it between blotting papers.
A heavy steel roller passes over the blotter assembly twice to remove unabsorbed surface water droplets. Immediate weighing reveals net water absorption expressed in grams per square meter.
Sizing Control
Internal chemical sizing agents like alkyl ketene dimer reduce fiber wetting rates. Hydrophobic additives slow capillary action through porous fiber networks.
