Some basic information about wet and dry tensile tests for paper and cardboard materials.

In the paper and board industry, the mechanical properties of materials are critical for determining their suitability for various applications. Among these properties, wet and dry tensile strength are key indicators of the durability and performance of materials under stress. The ISO 3781:2011 and TAPPI T 456 standards define the methodologies for conducting these tests. This article provides a detailed explanation of these tests’ methodologies, significance, and application areas.

What is a Wet Tensile Test?

A wet tensile test measures the strength of paper or board materials after exposure to water. This test is particularly important for evaluating materials used in moisture-prone environments, such as packaging, food-grade applications, and construction.

Testing Procedure

Sample Preparation:

• Samples are cut to standard dimensions (typically 15 mm wide).

• Before testing, samples are stabilized at 23°C and 50% relative humidity.

Immersion:

• Full Immersion Method: The sample is fully immersed in distilled water for a specified period (e.g., 30 seconds).

• Finch Method: Only one end of the sample is immersed, making it suitable for more delicate materials.

Tensile Testing:

• The wet sample is placed in a tensile testing machine operating at a constant elongation rate.

• Testing continues until the sample breaks, and the maximum force is recorded.

Results:

• Wet Tensile Strength (kN/m): The maximum force the sample can withstand.

• Wet Strength Retention (%): The ratio of wet tensile strength to dry tensile strength is calculated as:

  Wet Strength Retention (%) = (Wet Tensile Strength / Dry Tensile Strength) x 100

What is a Dry Tensile Test?

A dry tensile test evaluates the strength of paper or board materials in their dry state. It serves as a baseline to understand the overall mechanical durability of the material.

Testing Procedure

Sample Preparation:

• Samples are cut to standard dimensions (e.g., 15 mm wide, 200 mm long).

• Samples are stabilized in a controlled environment before testing.

Tensile Testing:

• The sample is placed in a tensile testing machine.

• A constant elongation rate is applied until the sample breaks, and the maximum force and elongation at break are recorded.

Results:

• Dry Tensile Strength (kN/m): The maximum force the sample can withstand.

• Maximum Elongation (%): The extent to which the sample stretches before breaking.

Comparison of Wet and Dry Tensile Tests

Conclusion

Wet and dry tensile tests are crucial for understanding the durability of paper and board materials and evaluating their suitability for various applications. The ISO 3781:2011 and TAPPI T 456 standards provide comprehensive guidelines for conducting these tests consistently and reliably. The data obtained from these tests are invaluable for improving product quality and optimizing the material properties for specific applications.