Standard Test Method for Seal Strength of Flexible Barrier Materials - PDF

ASTM F88 outlines the standard method for measuring the seal strength of flexible barrier materials, typically used in packaging applications like medical device pouches, food packaging, and sterile product containers.
This test is critical for verifying the integrity of heat seals to ensure that the package protects its contents until intended use.

This article explains the scope of ASTM F88, required equipment, testing procedures, and other related ASTM standards commonly referenced alongside F88.

Purpose of ASTM F88

The purpose of ASTM F88 is to quantify the strength of a sealed joint between flexible materials.
This ensures that the seal:

• Provides adequate protection against contaminants.

• Withstands expected handling stresses.

• Opens predictably (easy-peel or tear-resistant, depending on the application).

Seal strength is an important performance indicator, but ASTM F88 is not intended to evaluate package leakage, barrier properties, or shelf life.

Equipment Required

Performing ASTM F88 testing typically requires:

• Universal Testing Machine (UTM):

  • With low-force load cells (typically 50 N to 500 N range).

  • Capable of maintaining a constant crosshead speed, usually around 200–300 mm/min.

• Grips or Fixtures:

  • Pneumatic grips or mechanical grips with appropriate jaw faces to firmly hold flexible materials without slippage or damage.

  • Jaw surfaces may be smooth, rubber-coated, or serrated depending on material type.

• Cutting Dies or Guides:

  • To cut uniform test specimens, typically 1 inch (25.4 mm) wide, although other widths are permitted.

• Conditioning Chambers (optional):

  • For conditioning specimens at specified temperatures and humidity prior to testing, if required by specifications.

Test Specimens

Test specimens are rectangular strips cut from the sealed area of the flexible package.
Typically:

• Width: 1 inch (25.4 mm) or as otherwise specified.

• Length: Long enough to allow proper gripping without jaw interference during the test.

• The seal must be centered between the grips during testing.

Specimens can be tested in different peel configurations depending on the type of seal and package design.

Test Procedures for ASTM F88

There are three primary techniques for conducting the ASTM F88 test:

1. Technique A – Unsupported:

   • Each side of the seal is gripped and pulled apart without supporting the rest of the material.

   • Commonly used for evaluating "peel-open" seals where the user tears the package open.

2. Technique B – Supported at the Seal Interface:

   • The unsealed material is supported up to the edge of the seal.

   • Simulates the forces acting only on the seal itself, isolating the seal from the packaging.

3. Technique C – Supported Entirely:

   • Both sides of the specimen are fully supported, preventing stretching of the flexible material.

   • Ensures that only the seal strength is measured, independent of the material strength.

Test Procedure Summary:

• Mount the specimen in the grips with careful alignment.

• Set the crosshead speed, typically 200 to 300 mm/min unless otherwise specified.

• Apply tension until the seal separates or the material tears.

• Record the peak force (seal strength) in pounds-force (lbf), newtons (N), or pounds-force per inch width (lbf/in).

Results and Reporting

The final ASTM F88 report should include:

• Average, maximum, and minimum seal strength values.

• Type of failure (e.g., peel, adhesive failure, cohesive failure, material tear).

• Width of the specimen.

• Test technique used (A, B, or C).

• Crosshead speed and environmental conditions if relevant.

• Description of grips and jaw surfaces.

Some applications require minimum acceptable seal strength values, while others require consistency (low variation across samples) as the primary measure.

Related ASTM Standards

Several other ASTM standards are closely related to ASTM F88 and may be referenced for complete flexible packaging validation:

• ASTM F1140 – Standard Test Methods for Internal Pressurization Failure Resistance of Unrestrained Packages:
  Evaluates package integrity by applying internal air pressure to sealed packages.

• ASTM F2054 – Standard Test Method for Burst Testing of Flexible Package Seals Using Internal Air Pressurization:
  Measures the maximum pressure a sealed package can withstand before bursting.

• ASTM F1886 – Standard Test Method for Determining Integrity of Seals for Flexible Packaging by Visual Inspection:
  A simple but important visual inspection method to detect seal defects like wrinkles or incomplete seals.

• ASTM F2096 – Standard Test Method for Detecting Gross Leaks in Packaging by Internal Pressurization (Bubble Test):
  A low-cost method to detect gross leaks in flexible packages by visual observation of bubbles.

• ASTM D882 – Standard Test Method for Tensile Properties of Thin Plastic Sheeting:
  Provides tensile properties of the film materials themselves, not just the seals.

Applications of ASTM F88 Testing

Packages evaluated using ASTM F88 standards are commonly found in:

• Medical device packaging (surgical tools, catheters, implants)

• Pharmaceutical packaging

• Food packaging (vacuum pouches, retort pouches)

• Industrial and electronics packaging

Proper seal strength testing ensures that packages maintain sterility, freshness, or functionality during transport, storage, and use.

Conclusion

ASTM F88 provides a critical method for quantifying the seal strength of flexible barrier materials.
The test ensures that packages will perform reliably under real-world conditions without premature failure.
Depending on the material type and packaging design, complementary standards such as ASTM F1140, ASTM F1886, and ASTM D882 may be used alongside ASTM F88 to validate the overall performance and safety of flexible packaging systems.