1. Objective
The purpose of this test is to evaluate the seal strength of flexible barrier materials used in packaging. The test measures the force required to separate a sealed area to ensure packaging integrity, product protection, and compliance with industry standards.
2. Scope
This test applies to flexible packages, medical pouches, food packaging, and other sealed materials where seal strength is critical for product safety, sterility, and durability. The test determines:
- The maximum force required to separate the seal.
- The mode of seal failure (e.g., adhesive failure, cohesive failure, delamination).
3. Test Specimen & Preparation
- Select at least five representative samples of sealed flexible packaging in their final production form.
- Cut rectangular test strips from the package with a uniform width (typically 1 inch or 25 mm), ensuring the seal is centered in the strip.
- Condition the specimens per ASTM D4332 (Standard for Conditioning Packaging for Testing) before testing.
4. Test Equipment & Setup
- Universal Testing Machine (UTM): A tensile testing machine capable of measuring seal strength in Newtons (N) or pounds-force (lbf).
- Grips/Fixtures: Pneumatic or mechanical grips to hold the test strips securely.
- Test Speed Controller: To apply force at a controlled rate as per the standard.
5. Testing Procedure (Based on ASTM F88 Index)
5.1 Selection of Test Technique
The test can be conducted using one of the three techniques:
- Technique A (Unsupported Tail) – One side of the sample is gripped, and the other side is free, simulating real-world peeling forces.
- Technique B (Supported Tail – Same Side Grip) – Both sides of the seal are gripped at the same end, which reduces sample slippage.
- Technique C (Supported Tail – Opposite Side Grip) – The sample is fully supported, improving repeatability and alignment.
✅ Decision Required: Which technique is most appropriate based on the packaging type?
5.2 Seal Strength Testing Parameters
- Grip the Sample Properly: Ensure the seal remains centered between the grips.
- Test Speed: Apply a tensile force at a constant speed of 200–300 mm/min (8–12 in/min).
- Measure Peak Force: Record the maximum force required to separate the seal.
5.3 Failure Mode Analysis
After testing, classify the failure mode:
- Adhesive Failure – The seal separates at the bond line (weak adhesion).
- Cohesive Failure – The material tears within itself, indicating strong bonding.
- Delamination – The layers of the material separate without breaking the seal.
- Peel Opening – The seal peels without significant resistance.
✅ Decision Required: What failure mode criteria define a pass or fail for the package?
5.4 Data Collection & Observations
- Seal Strength Measurement: Report peak force values in Newtons (N) or pounds-force (lbf).
- Mode of Failure: Record and classify failure types.
- Comparison to Acceptance Criteria: Determine whether the seal meets required strength thresholds.
✅ Decision Required: What is the minimum acceptable seal strength for the package?
6. Reporting & Recommendations
- Test Results Summary: Tabulate seal strength values and failure modes.
- Graphical Data (Optional): Include force-displacement curves for seal performance visualization.
- Photographic Evidence: Capture images of test samples before and after failure.
- Recommendations for Improvement: If failure occurs, suggest seal redesigns, material changes, or process optimizations.
7. Safety Considerations
- Ensure grips are securely tightened to prevent sample slippage.
- Avoid sharp edges on torn samples that may cause injury.
- Calibrate testing equipment before use to maintain accuracy.
8. Undecided Factors in the Test Plan
1. Selection of Testing Technique (A, B, or C)
- The test allows three different grip techniques, each suited to different package types.
- Decision Required: Which technique is most representative of real-world package opening forces?
2. Acceptance Criteria for Seal Strength
- The required seal strength depends on industry standards (e.g., medical, food, industrial).
- Decision Required: What is the minimum acceptable seal strength for this product?
3. Failure Mode Classification
- Certain failure modes (e.g., adhesive failure vs. cohesive failure) may be acceptable or unacceptable.
- Decision Required: Which failure modes are considered a failure, and which are acceptable?
4. Environmental Conditioning
- Testing under different humidity or temperature conditions may be required.
- Decision Required: Should the test be performed in controlled environmental conditions?
Next Steps
To finalize the test plan, the above undecided factors need to be clarified based on:
✅ Packaging type and intended use case
✅ Industry-specific seal strength requirements
✅ Environmental conditions relevant to the package lifecycle
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