ASTM F88/F88M-23 Standard Overview for Seal Strength Testing

F88 applies to seals between two flexible materials, and between a flexible material and a rigid or semi-rigid one. The seals can come from any source, either made in the laboratory or cut from commercial packages.

The method does not cover peeling an entire lid off a rigid or semi-rigid round container. That case belongs to ASTM F2824. Strips cut from a lid that is sealed to a tray are still prepared and tested under F88.

ASTM positions seal strength as a quantitative measure for process validation, process capability and process control. F88 does not set pass or fail limits. The user sets them, with lower limits giving assurance of closure and upper limits mostly used for seals that the end user peels open.

The 2023 edition gives three widths for the specimen cutter, which are 25 mm, 15 mm and 25.4 mm (0.984 in, 0.591 in and 1.00 in). The cutter must meet section 6.5 of ASTM D882, and the recommended cutter tolerance is ±0.5%. Any deviation from the width or tolerance needs a documented rationale or supporting data.

SI and inch-pound values in F88/F88M are each a standard in their own right. They are not exact equivalents, and combining the two systems may result in non-conformance. Choose one system for a test series and record it.

Seals for the specimens are usually made on a laboratory heat sealer before they reach the tensile tester. Our laboratory heat sealers prepare those seals, and the strips are then pulled on a tensile tester to F88.

For specimen width, conditioning and test speed in practice, see our guide to ASTM F88 specimen preparation.

Questions about a model or a test? Email Amy Zhao, Export Manager, at [email protected].

The specimen is pulled at a constant rate of grip separation between 200 and 300 mm/min (8 to 12 in/min). F88 includes an appendix on how a change in grip separation rate affects results, so keep one rate for the whole series. The initial distance between the grips is also set and recorded for each series.

Part of the measured force can come from bending rather than from the seal itself. F88 therefore describes three ways to hold the specimen tails.

• Technique A, unsupported. Each tail is clamped in an opposing grip and the seal is left unsupported.
• Technique B, supported 90° by hand. The seal is held loosely at a right angle to the tails.
• Technique C, supported 180°. The less flexible tail lies on a rigid alignment plate and the other folds back.

ASTM recommends staying with one technique for a test series, because each technique affects results differently. Tail movement or flipping during the pull should be reported with the results.

If you need seal curves across several temperatures, our 5-point gradient heat seal tester seals five specimens at five temperatures in one run. Seal strength is then measured separately on the tensile tester per ASTM F88.

F88/F88M-23 points to ASTM E171 when conditioning before the test is desired and appropriate. E171 sets the standard temperature and humidity for conditioning and testing flexible barrier packaging at nominally ambient conditions.

F88 does not fix a minimum conditioning time. Heat seal conditioning periods may be set by experiment, long enough for seal strength to stabilize, and conditioning can be adjusted for specific test objectives. E171 suggests conditioning when comparing results between labs, when temperature or humidity is expected to matter, or when other variation must be kept low.

F88 defines maximum and average seal strength as force per unit width of the seal. Maximum force is reported for every specimen, preferably in N/m or lbf/in of original specimen width, to three significant figures. Average peel force is worth reporting only when the strip peels apart in the seal area, not when the material mostly breaks, tears or stretches.

The table lists key report fields from section 10.1. It is not the complete list, which also covers items such as seal width and the sampling method.

We sell direct from our factory, so you work directly with our factory team. Questions about a model or a test? Email Amy Zhao, Export Manager, at [email protected].