Tensile Testing of Paper

ASTM D828, TAPPI T 220, TAPPI T 456, and TAPPI T 494 are testing standards used to measure the properties of paper and paperboard products. TAPPI T 494 and ASTM D828 are the most commonly used paper testing standards and measure tensile strength of dry paper products. TAPPI T 456 is used to test the tensile strength of water saturated paper (wet tensile strength), and TAPPI T 220 is used to test pulp sheets.

Manufacturers of paper goods need to evaluate the physical properties of their products to ensure they are able to function as intended. Small variations in fibers, fiber treatments, or manufacturing processes can impact the tensile strength of paper products. Certain papers are required to conform to a desired contour, such as paper towels or napkins, and require a certain tensile stiffness. Printing paper, which is usually produced in large sheets or rolls, must withstand forces experienced during its travel through processing equipment. Aside from paper manufacturers, the packaging industry also uses paper testing standards to ensure that bags, boxes, and other packaging materials do not fail during transport or shipment. 

System capacity will depend on the strength of the paper material. However, most tests to these standards will fall well below 5 kN, making this application perfect for a single column frame such as Instron's 68SC or 34SC with Bluehill Universal software. Bluehill Universal is easy to use and highly customizable with all calculations and statistics necessary for testing to any of these paper standards, including Tensile Energy Absorption (TEA).

Pneumatic side action grips and advanced screw side action grips are the most appropriate gripping solutions for testing paper. Pneumatic gripping pressure can be easily adjusted to avoid specimen damage and slippage, while making specimen insertion quick repeatable and safe. Advanced screw side action grips can also be carefully adjusted by hand to ensure appropriate gripping pressure.

Both types of grips feature quick-change jaw faces that can be easily changed to accommodate different materials. Paper testing standards typically recommend line contact jaw faces. However, if these are not appropriate, smooth faces are also a good option. Serrated faces will damage the paper and will likely lead to premature breaks.

• The Technical Association of the Pulp and Paper Industry (TAPPI) publishes much of the literature for the industry, as does the Pulp and Paper Association of Canada (PAPTAC).
• Specimen alignment is particularly important to ensure that an even load is applied across the materials fibers. The clamping lines must be parallel and coplanar, and the force applied to the specimen should be perfectly perpendicular.
• Jaw breaks may occasionally occur. This is common in rectangularly-shaped specimens with no reduced section, as stress is concentrated at the point of contact with the jaw faces. If the break forces are consistent regardless of break location, this is not a concern.
• The most common properties measured are as follows:
  • Tensile Energy Absorption (TEA) – Calculated as the area under the load-elongation curve and expressed as energy per unit area (test span x width).
  • Stretch – Also defined as maximum tensile strain and expressed as percent elongation.
  • Tensile Stiffness – Ratio of tensile force per unit width to tensile strain within the elastic (linear) region of the test.