ASTM D578 Test for Wetting Tension of Polyethylene and Polypropylene Films

Scope:

The interaction between the surface of a solid, the liquid, and the gas determines whether a drop of liquid will spread or bead up when it rests on the solid surface. Wetting tension is defined as the maximum surface tension of a liquid that can cause it to spread on a surface rather than bead up. ASTM D578 is used to determine the wetting tension of polyethylene and polypropylene films.

Test Procedure:

In ASTM D578, the surface of the polyethylene or polypropylene film is prepared and test liquids with gradually increasing surface tensions are applied to the surface until a mixture is found that just wets the film surface. The wetting tension of the film is then approximated by the surface tension of the test liquid that just wets the film surface.

Specimen Size:

The amount of film required for this test depends on the operator’s skill. The surface of the film sample should not be touched in the areas where the test is to be performed.

Data:

The average wetting tension value of each sample is reported to the nearest 0.5 dynes/cm. If the film surface is unevenly treated, it may not be possible to obtain a single value of wetting tension. In such cases, individual values may be reported whenever the largest value exceeds the smallest by more than 1 dyne/cm. The values are stated in SI units and are considered standard.

Conclusion:

ASTM D578 is a reliable test method for determining the wetting tension of polyethylene and polypropylene films. The test involves placing a drop of test liquid on the film surface and gradually increasing the force required to detach the drop from the film until it breaks away. The force required to detach the drop is then used to calculate the wetting tension of the film, which is a measure of its surface energy.