ASTM F88/F88M
Seal Strength Testing
ASTM F88/F88M provides a tensile test framework for measuring the force required to separate seals in flexible barrier materials. Seal strength testing is used with packaging materials in medical, pharmaceutical, food, and consumer applications where consistent seal performance is important.
CellScale evaluated ASTM F88/F88M-based seal strength testing using a UniVert S with a 2 N load cell and self-sealing sterilization pouch material. The study examined average peel force, maximum force, repeatability, load cell selection, and force-displacement behaviour during progressive seal separation.
At A Glance
- Standard: ASTM F88/F88M
- Property measured: Seal strength
- Typical material type: Flexible barrier materials
- General test method: Tensile seal separation
- CellScale system evaluated: UniVert S
- CellScale study: 12 sterilization pouch specimens
- Study standard revision: ASTM F88/F88M-15
What is ASTM F88/F88M?
ASTM F88/F88M is a seal strength test method for flexible barrier materials. The test measures the force required to separate a sealed specimen using tensile loading and can be used to evaluate average peel force, maximum force, and specimen failure behaviour.
Seal strength measurements can be useful when evaluating opening force, package performance, process validation, process control, and the consistency of a sealing process. Because the measured response can be affected by specimen geometry, material behaviour, and test configuration, these factors should remain consistent when results are being compared.
What Does ASTM F88 Seal Strength Testing Measure?​
Seal strength is not represented by a single feature of the force curve. Depending on the test objective, several parts of the seal-separation response can be useful.
Average Peel Force
Average peel force describes the representative force required to continue separating the seal over a selected region of the test. In the CellScale study, the average was calculated from the central 80% of the peel response.
Maximum Force
Maximum force is the highest tensile load recorded as the specimen is progressively separated.
Failure Behaviour
The force-displacement response can also show how separation develops through the specimen. Material bending, elongation, tearing, delamination, and seal geometry can all contribute to the measured response.
For this reason, ASTM F88 seal strength results should be interpreted together with the specimen configuration and test conditions rather than as an isolated force value.
ASTM F88 Test Techniques
ASTM F88/F88M-15 describes three tail-holding techniques for seal strength testing. The selected technique can affect the measured force, so the same approach should be maintained throughout a comparative test series.
Technique A: Unsupported
Technique A: Unsupported is when both specimen tails are secured in opposing grips while the seal remains unsupported.
Technique B: Supported 90°
Technique B: Supported 90° is when the seal is supported at approximately 90° to the specimen tails during separation.
Technique C: Supported 180°
Technique C: Supported 180° is when one specimen tail is supported against an alignment plate while the other is folded 180° over the seal.
Different tail-holding arrangements change how bending and other specimen effects contribute to the measured force. Results obtained using different techniques should therefore not be treated as directly interchangeable without considering the test configuration.
Equipment for ASTM F88 Seal Strength Testing
ASTM F88 seal strength testing requires a controlled tensile separation setup capable of recording tensile force and grip separation. For the ASTM F88/F88M-15 conditions evaluated in this study, the test system required adjustable constant-rate jaw separation, suitable grips, and force and displacement measurement.
Mechanical Test System
The test frame must provide controlled tensile motion over the required separation distance and speed. In our case, the UniVert.
Load Cell
The load cell should provide enough capacity for the expected maximum seal force while still giving useful measurement performance within the force range of interest.
Grips
The specimen must be held securely during separation. The gripping arrangement should minimize slippage and avoid unnecessary concentration of stress at the grip.
Force and Displacement Measurement
Both tensile force and grip separation are relevant measurements. The required accuracy should be confirmed against the specific revision of the standard being followed.
Selecting the highest-capacity sensor available is not necessarily the best approach for low-force seal strength testing. The measurement range should be matched to the forces generated by the specimen.
ASTM F88 Testing with the CellScale UniVert
CellScale evaluated whether the UniVert S could characterize the low-force peeling response of a commercially available self-sealing sterilization pouch using test conditions based on ASTM F88/F88M-15.
The study focused on five questions:
- Could average peel force be measured consistently?
- Could maximum force be identified across repeated specimens?
- How repeatable would the response be across 12 tests?
- Was a 2 N load cell appropriate for the low forces generated by the specimens?
- What would the force-displacement response look like during progressive seal separation?
ASTM F88 Test Configuration Used in the CellScale Study
The same UniVert configuration and test protocol were used throughout the 12-specimen test series.
| Parameter | Test Configuration |
|---|---|
| Mechanical test system | CellScale UniVert S |
| Test mode | Tension |
| Load cell | 2 N |
| Load cell accuracy | ±0.2% of rated capacity |
| Tail-holding technique | Technique A, unsupported |
| Grip separation rate | 4.5 mm/s, equivalent to 270 mm/min |
| Initial grip separation | 25 mm |
| Motion accuracy | ±0.05% of desired distance |
| Position accuracy | ±0.02 mm |
| Data acquisition rate | 50 Hz |
| Number of specimens | 12 |
The 2 N load cell has an accuracy of ±0.2% of rated capacity, corresponding to ±0.004 N. The UniVert actuator motion accuracy is within ±0.05% of the desired distance, with positional accuracy specified as ±0.02 mm. The white paper notes that ASTM F88/F88M-15 requires both tensile-force and grip-separation measurement systems to be accurate within ±2%.
The 270 mm/min grip separation rate used in the study falls within the 200 to 300 mm/min range described for ASTM F88/F88M-15.
ASTM F88 Specimen Preparation and Test Method
Self-sealing sterilization pouches were selected as the flexible barrier material for the study. Twelve specimens were prepared, each consisting of a plastic-film tail and a waxed-paper tail joined by the pouch seal.
| Parameter | Value |
|---|---|
| Material | Self-sealing sterilization pouch |
| Specimen width | 15 mm |
| Specimen length | 110 mm |
| Conditioning time | 72 h |
| Temperature | Approximately 23°C |
| Relative humidity | 45% |
| Upper grip material | Plastic film |
| Lower grip material | Waxed paper |
| Initial grip separation | 25 mm |
Each specimen was mounted using the unsupported Technique A configuration. The plastic-film tail was secured in the upper grip and the paper tail in the lower grip. The moving grip then separated the specimen at 4.5 mm/s, equivalent to 270 mm/min.
Application-Specific Specimen Orientation
The specimen orientation used in the CellScale study is an important distinction from the conventional ASTM F88/F88M-15 configuration.
ASTM F88/F88M-15 specifies that the seal line should normally be perpendicular to the direction of pull. In this study, the sterilization-pouch specimens were intentionally tested parallel to the seal.
Why was the orientation changed?
The pouch contained multiple sealed regions. When specimens were pulled across the seal, those regions produced several distinct force responses. Testing parallel to the seal produced a more continuous peeling response and better represented the opening behaviour being investigated.
This orientation was therefore treated as an application-specific modification rather than presented as the conventional ASTM F88 specimen configuration.
That distinction matters when interpreting the results and when comparing them with tests performed using the standard orientation.
ASTM F88 Force-Displacement Analysis
Each specimen produced a force-displacement curve showing how much force was required as the pouch seal progressively separated.
Average Peel Force
Average peel force was calculated from the central 80% of the peel response.
Maximum Force
The highest tensile load recorded during each test was reported as maximum force.
Data Acquisition
Force and displacement were collected at 50 Hz, producing a detailed force-displacement record throughout the peeling process.
The initial rise from zero force and the final portion of the curve were excluded because these regions do not represent the steady seal-separation response. The expanded study notes that ASTM F88/F88M-15 also describes excluding the initial loading region and the return toward zero from the average seal-strength calculation.
ASTM F88 Seal Strength Test Results
Twelve specimens were tested using the same UniVert configuration and test protocol.
0.705 N Mean Average Peel Force
1.186 N Mean Maximum Force
| Result | Average Peel Force | Maximum Force |
|---|---|---|
| Mean | 0.705 N | 1.186 N |
| Range | 0.608 to 0.801 N | 0.980 to 1.346 N |
| Standard Deviation | 0.0537 N | 0.106 N |
Across the test series, the coefficient of variation was approximately 7.6% for average peel force and 8.9% for maximum force. The mean maximum force normalized by the 15 mm specimen width was 79.1 N/m.
The results showed a relatively narrow distribution across the 12 specimens while still preserving measurable specimen-to-specimen variation.
Load Cell Selection for Low-Force Seal Strength Testing
Load cell selection had a noticeable effect on the quality of the measured force response.
Initial trials used a higher-capacity 10 N load cell. At the low forces produced by the sterilization-pouch specimens, the recorded response showed greater apparent signal noise. Repeating the test with the 2 N load cell produced a cleaner signal and more clearly resolved the seal-peeling behaviour.
The practical lesson is straightforward: load cell capacity should be high enough to accommodate the expected maximum load, but capacity alone is not the only consideration. For low-force seal strength testing, the sensor should also provide useful measurement performance in the actual force range being studied.
Factors That Influence Seal Strength Measurements
Measured seal strength can be influenced by more than the seal itself.
The ASTM F88/F88M discussion in the expanded study identifies factors including:
- Material bending
- Material elongation
- Tearing and delamination
- Specimen geometry and orientation
- Tail-holding technique
Grip configuration, separation rate, and the analysis method can also affect comparisons between tests.
For comparative seal strength testing, these conditions should therefore be kept consistent across the test series wherever possible.
This is also why results obtained using different ASTM F88 techniques or different specimen orientations should be interpreted with care.
What the CellScale ASTM F88 Study Demonstrated
The UniVert S equipped with a 2 N load cell successfully characterized the low-force peel response of the self-sealing sterilization pouch material using test conditions based on ASTM F88/F88M-15.
The study demonstrated:
- Measurement of average peel force and maximum force across 12 specimens
- Operation at a grip separation rate of 270 mm/min
- Use of a 2 N load cell appropriate to the low force range generated by the specimens
- Force and actuator-position performance within the measurement criterion discussed for ASTM F88/F88M-15
- Average peel-force analysis using the central 80% of the recorded response
- The influence of specimen geometry and orientation on the measured seal response
Across the 12 specimens, mean average peel force was 0.705 N and mean maximum force was 1.186 N. ASTM F88 White Paper (Expanded)
ASTM F88 Standards Statement
This study demonstrates seal strength testing using a UniVert configuration and test conditions based on ASTM F88/F88M-15. An application-specific specimen orientation was used. The study should therefore not be interpreted as a demonstration of full procedural conformance to ASTM F88/F88M-15.
A mechanical testing system meeting relevant force, displacement, or motion requirements does not by itself establish full procedural conformance. Specimen preparation, orientation, conditioning, fixture configuration, test parameters, analysis, reporting, and the specific revision of the standard may all affect conformance.
Users performing formal ASTM F88 testing should consult the current official standard and confirm the requirements that apply to their material, laboratory, product, or regulatory context.
ASTM F88 Seal Strength Testing Resources
For a shorter overview or a more detailed review of the CellScale study, both versions are available.
ASTM F88 FAQs
What is ASTM F88?
ASTM F88/F88M is a test method used to measure seal strength in flexible barrier materials. The method uses tensile loading to separate a sealed specimen while force is recorded.
What does ASTM F88 measure?
ASTM F88 seal strength testing can be used to evaluate the force required to separate a seal, including average seal or peel force, maximum force, and the behaviour of the specimen during separation.
What materials are tested using ASTM F88?
ASTM F88 applies to flexible barrier materials. In the CellScale study, the test specimens were prepared from commercially available self-sealing sterilization pouches with plastic-film and waxed-paper layers joined by a seal.
What are ASTM F88 Techniques A, B, and C?
Technique A leaves the seal unsupported while the specimen tails are held in opposing grips. Technique B supports the seal at approximately 90°. Technique C supports one tail against an alignment plate while the other is folded 180° over the seal. The selected technique can influence the measured force.
What test speed is used for ASTM F88?
For ASTM F88/F88M-15, the CellScale study references a jaw-separation range of approximately 200 to 300 mm/min. The UniVert test was performed at 270 mm/min, or 4.5 mm/s.
What equipment is needed for ASTM F88 seal strength testing?
The test requires a controlled tensile separation system capable of measuring tensile force and grip separation, together with suitable grips for the flexible specimen. The appropriate load cell depends on the force range expected from the seal.
How is average seal strength calculated in the CellScale ASTM F88 study?
Average peel force was calculated from the central 80% of the force-displacement response. The initial loading region and final return toward zero were excluded from the calculation.
Can the CellScale UniVert perform ASTM F88 seal strength testing?
The CellScale study demonstrated ASTM F88/F88M-15-based seal strength testing using a UniVert S with a 2 N load cell, an unsupported Technique A configuration, and a separation rate of 270 mm/min. Because an application-specific specimen orientation was used, the study is not presented as a demonstration of full procedural conformance.
Is seal strength the same as package integrity?
Seal strength describes the force required to separate a seal and is one useful measure when evaluating packaging performance. It does not by itself describe every aspect of package integrity. Other package or barrier characteristics may need to be evaluated separately depending on the application.
Need to Perform Seal Strength Testing?
If you are evaluating flexible barrier materials, packaging seals, or another low-force peel application, CellScale can help assess the expected force range, specimen geometry, grips, and test configuration.
The UniVert supports interchangeable load cells and fixtures for tensile, peel, and other mechanical testing applications involving flexible packaging, films, adhesives, biomaterials, and other low-force specimens.
