Ultimate Seal Strength of Thermoplastics ASTM F88

Seal strength is the tensile strength of the seal at ambient temperature. It is the maximum force required to separate the two layers of a seal under particular conditions.

A series of seals at different sealing temperatures are made, using a machine employing hot-bar jaws. Each tail of the sealed specimen is secured in the opposing grips of a universal test bench. The maximum tensile force required to separate the two ends of the seal is recorded. While the test is being conducted the seal may be unsupported (technique A), at an angle 90º to the pull direction (technique B) or at an angle of 180ºC to the pulling direction (technique C)

Specimen size:
A rectangular specimen is used; the specimen width may be either 25 mm, 15 mm or 1.00 inch.

A curve can be plotted showing the effect of the sealing conditions (mainly temperature) on the seal force. This curve is called the seal curve. At a certain temperatures a seal force level is reached which is related to the maximum tensile force of the film. 

**Please note that this test description is intentionally generic in nature and aimed at providing a descriptive summary to enhance test understanding. Standards can be obtained from appropriate standard authorities.
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