Tensile Protocol
Standardised laboratory procedures define the determination of the wet tensile strength of paper and paperboard after immersion in water for a specified period. Standard test protocol ISO 3781 specifies the conditioning, wetting parameters, and tensile testing geometry needed to evaluate paper integrity under saturated conditions. Test strips measuring fifteen millimetres in width undergo full immersion in distilled or deionised water within a temperature-controlled bath maintained at twenty-three degrees Celsius.
The immersion duration varies according to paper grade requirements, ranging from seconds for absorbent tissue papers to several hours for dense barrier boards. Following immersion, excess surface water is blotted using standardised filter paper under uniform pressure to avoid dry tensile testing of partially saturated cores. Clamping jaws positioned at an initial separation distance of one hundred or one hundred and eighty millimetres pull the specimen at a constant rate of elongation until fracture occurs.
Instrument Settings
Calibration of load cells ensures accurate registration of breaking forces that are often less than twenty percent of dry tensile values. Constant rate of elongation devices operate at standardized speeds, typically twenty millimetres per minute, to prevent rate-dependent viscoelastic reinforcement. Alignment of the test strip perpendicular to the clamping jaws eliminates edge tear stress concentrations that distort tensile readings.
Pneumatic clamps provide uniform gripping pressure across the specimen width, preventing slippage caused by water lubrication on metal surfaces.
Packaging Compliance
Corrugated container components and moisture-resistant packaging grades depend on this standard to prove wet performance compliance. Linerboard intended for cold chain transport or tropical produce packaging must retain specified wet tensile levels to resist stacking collapse in humid atmospheres. Sizing treatments, wet-strength resins, and hydrophobic coatings alter water uptake rates, shifting wet tensile outcomes during the prescribed soaking intervals.
Discrepancies in immersion times produce non-comparable values, mandating precise reporting of liquid exposure durations in test certificates. Compliance documentation in commercial supply contracts references this protocol to adjudicate acceptance thresholds for water-resistant industrial sacks and outdoor labelling papers.
