ASTM F88

What the test does

A strip is cut across a sealed area of a package so the seal runs through its middle. The two unsealed tails are clamped in opposing grips with the seal roughly midway between them, and the crosshead separates the grips at a constant rate until the seal pulls fully apart. Force against grip separation is recorded throughout, so the whole peel trace is captured, not just the peak.

What it measures, and why it matters

The method reports seal strength — the force needed to pull a defined width of seal apart — as maximum, average or the whole force curve, together with the failure mode observed. Maximum force is what medical device and pharmaceutical manufacturers use for lot release and for validating a sealing process window against a specification. Average force describes how a peelable seal opens in a clinician's hands, which is a usability question rather than a strength one. Failure mode is the diagnostic half of the result: the same peak force means something different if the film tore instead of the seal peeling.

Strip and sampling

Width

15 mm (1 in.)

Length

75 mm plus the seal widthSo both tails reach their grips.

Orientation

Cut across the seal, seal at the middle

Sampling

From the user's planSterile barrier work commonly takes specimens from every seal of a pouch and several positions along a long one, because seal strength varies with position under the jaws.

Cuts

Clean and parallelA nicked or tapered edge starts a tear and the result is discarded.

Conditioning

23 °C and 50 % RH, typically 24 hASTM E171, the flexible-barrier standard atmosphere, testing in the same.

Test speed and tail support

Rate

Constant, commonly 200 to 300 mm/minRead the rate from the edition and the specification in force.

Technique A

Unsupported tailsThe tails hang free. The commonest and the least constrained.

Technique B

Supported at 90°

Technique C

Supported at 180°

The technique changes the number

MateriallySupport changes the peel angle at the seal, so a specification that names a seal strength must also name the technique.

Calculations

How the test runs

1. 01Take specimens according to the sampling plan, from each seal and several positions along long seals.
2. 02Cut 15 mm strips across the seal, cleanly and parallel, seal roughly midway.
3. 03Condition to ASTM E171 and test in that atmosphere.
4. 04Choose the technique — A, B or C — from the specification, and record it.
5. 05Clamp the two tails in opposing grips.
6. 06Separate at the constant specified rate, recording force against separation.
7. 07Continue until the seal pulls fully apart.
8. 08Record maximum force, average force, or the whole curve as required.
9. 09Classify the failure mode — adhesive peel, cohesive, delamination, or material tear.
10. 10Discard anything that tore from a cut edge rather than failing at the seal.

The same peak force means something quite different if the film tore instead of the seal peeling. A tear can read higher than a clean peel while representing a package that will fail unpredictably, which is why the failure mode is not optional.

Grips and fixtures for this method

Standard 25 mm

Pneumatic Vice Action Grip

Constant air pressure across the full jaw face holds a thin film tail without cutting it — a seal test that fails at the grip has measured the grip.

Specifications

HJ-42

Light Duty Pneumatic Grip

Light duty closure for the lowest seal strengths, where a heavier grip would damage the web before the seal is loaded.

Specifications

What the report has to contain

• Reference to ASTM F88 and the TECHNIQUE used — A, B or C
• Material identification, both webs, and the sealing process parameters
• Sampling plan and where on the package each specimen came from
• Specimen width as measured
• Conditioning and test atmosphere
• Rate of grip separation
• Maximum force, average force, or the curve, as specified
• FAILURE MODE for every specimen
• Number of specimens, mean and standard deviation

What the machine must be capable of

Seal forces are light. Medical device seals commonly peak between about 4 and 9 N per 15 mm strip, pharmaceutical seals a little higher, and tough laminates or tray lidding run to a few tens of newtons, so a 50 N to 500 N load cell on a single-column frame is the normal fit rather than a general-purpose high-capacity frame. Force resolution at the bottom of the range matters more than headroom: a peel trace read on a 5 kN cell resolves nothing useful. The method does not itself set an accuracy class, so the applicable force-verification requirement comes from the laboratory's quality system.

Grip separation runs at 200 to 300 mm/min (8 to 12 in./min). Travel demand is short — full separation normally occurs within 50 mm of crosshead movement — but the initial grip separation is a required reporting item, so it has to be set and logged rather than assumed. No extensometer is involved; peel is a force-against-displacement measurement, not a strain one.

Fixturing is what the three techniques differ on. Technique A leaves the seal unsupported between the grips; Technique B supports it perpendicular to the tails at 90°; Technique C folds the more flexible tail 180° back over the seal with the stiffer member held flat, and the 2023 edition adds two Technique C approaches for flexible-to-rigid and semi-rigid trays using alignment plates. Opposing side-action grips, commonly pneumatic, hold the tails at constant clamping force. Mixing techniques within a series destroys comparability.

What goes wrong in practice

Bending force is the standard bias: in Technique A the tails flex as they load, and that parasitic bending adds to the reading, so unsupported results sit above supported ones on the same seal. Film tear instead of seal peel gives a high number that describes the substrate, not the seal. Delamination — laminate layers separating internally — reads as a low, ragged trace and is often logged as a weak seal when the seal never failed. Slipping tails give a false early peak.

What F88 does and does not tell you

A strong seal and an intact seal are different claims. F88 can pass a package that carries a narrow channel leak, because the surrounding seal still carries the load — which is why sterile barrier programmes run integrity testing alongside it rather than instead of it.

Questions we are asked about this test