What kind of stretch properties can I expect from my TPE?

Tensile Properties

Tensile properties are measurements used to describe how an elastomer performs when stretched. Several tests are commonly used to give an indication of how a TPE will perform in end-use environments.

Tensile at Break

This measurement is also called Ultimate Tensile. In this test, a piece of elastomer is stretched until it breaks. The amount of force needed to break the material is measured. Units are typically given in pounds per square inch (psi) or megaPascals (MPa). Elastomers with high ultimate tensile properties will be more difficult to break by stretching than an elastomer with lower values on this test.

Tear Strength

This value describes how well the elastomer resists tearing. The tear strength test essentially the same as the tensile at break test except the test bar is notched on one side to provide a propagation point. The material is stretched and the amount of force at which the test bar tears completely is recorded. Units are typically given in psi or kiloNewtons per meter (kN/m).

Tensile Modulus

In the tensile modulus test, the elastomer is stretched and resistance to the stretching is measured over a range of elongation points. This is often reported as tensile at various percentages of the original length of elastomer, such as 50, 100 and 300 percent. An elastomer might have a strong resistance to stretching initially but become weaker as it elongates (called "necking").

Elongation at Break

Elongation does not measure how hard or easy the material is to stretch, but simply how far it will stretch before it breaks. This is reported in percentage of original length. Some soft elastomers will stretch to greater than 1000 percent of their original length before breaking. A soft elastomeric TPE will typically have a much higher value than a hard rigid material.

Factors Affecting Values

The method in which test plaques are molded and the direction of flow affect the tensile property values. For this reason, many elastomers are measured for tensile properties in both direction of flow and transverse to direction of flow.

Direction of Flow

Like many other elastomer properties, tensile properties are affected by the orientation of the polymer molecules upon molding. Thus tensile properties can vary widely depending on whether the stretching was done in the direction of the polymer flow during molding, or in the transverse direction.

Test Plaques (Extrusion vs. Injection Molded)

Some tests are performed on injection molded plaques, while others are performed on extruded plaques. It is important to compare values only on similar test plaque types since there can be a significant difference in values.

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