Medical device packaging peel force testing quantifies the seal strength of sterile barrier systems, verifying that terminally sterilized devices remain protected against microbial ingress while still allowing clean, aseptic opening at the point of use. Guided by ISO 11607 and the ASTM F88 test method, this article reviews the principles, sample types, test procedures, acceptance criteria, and practical applications of peel force determination in medical device packaging validation and quality control.
Technical Overview
Peel force testing, also referred to as seal strength testing, measures the mechanical force required to separate two sealed flexible materials in a medical device package. For terminally sterilized medical devices, the sterile barrier system (SBS) is the minimum package that prevents the ingress of microorganisms and permits aseptic presentation of the product. If the seal is too weak, sterility may be compromised during handling, distribution, or storage; if the seal is too strong, clinicians may struggle to open the package aseptically, and tearing or particulate generation may occur. Peel force determination therefore evaluates the balance between protective strength and openability.
ISO 11607-1 requires that seal strength and seal integrity be demonstrated for any sterile barrier system, while ASTM F88/F88M provides the internationally recognized laboratory method for measuring the seal strength of flexible barrier materials. In China, GB/T 19633 adopts the requirements of ISO 11607, and the EN 868 series specifies materials for sterilization packaging. Testing is typically performed on a universal tensile testing machine equipped with appropriate grips and fixtures, and results are expressed as force per unit seal width, such as N/15 mm or N/25 mm.
Key technical objectives of peel force determination include:
- Quantifying peak and average peel force of finished seals
- Verifying consistency of seal strength along the entire seal perimeter
- Classifying failure modes (adhesive, cohesive, substrate tear, delamination)
- Confirming clean-peel behavior without fiber tear or shredding
- Supporting validation of sealing processes, shelf-life studies, and regulatory submissions
Testing Samples
Preformed Peel Pouches
Flat and three-dimensional pouches made from combinations of medical-grade paper, Tyvek-type porous materials, and multilayer plastic films are the most common samples. Specimens are cut from the finished seal zones, typically with the seal running perpendicular to the direction of pulling so that the entire seal width is peeled simultaneously.
Thermoformed Rigid Trays with Lidding Films
Rigid trays formed from PETG, PVC, or PP and sealed with Tyvek or film lidding are tested by cutting strips across the perimeter flange seal. The specimen geometry must account for the stiffness of the tray material, and bending fixtures or slip plates are often used to maintain a controlled peel angle.
Roll Stock and Web Materials
Unconverted roll materials, such as laminated films and coated porous webs, are sealed in the laboratory using defined combinations of temperature, pressure, and dwell time (for example, in accordance with ASTM F2029) to establish process windows before production sealing equipment is validated.
Header Bags and Sterilization Wraps
Reusable and single-use sterilization containers, header bags with film windows, and nonwoven wraps may also undergo peel or seal strength evaluation where a heat-sealed or adhesive seam forms part of the sterile barrier.
Testing Items
Depending on the validation protocol, the following quantitative and qualitative items are assessed during peel force determination:
- Peak peel force: the maximum force recorded during separation of the seal, normalized to specimen width (N/15 mm or N/25 mm)
- Average peel force: the mean force sustained over the peeled distance, indicating consistency of the seal
- Minimum peel force: the lowest local force observed, useful for detecting weak spots or channels
- Peel force distribution: force values recorded at multiple locations along the seal perimeter (corners, sides, chevron apex)
- Failure mode classification: adhesive failure at the interface, cohesive failure within the adhesive layer, substrate tear, film delamination, or fiber tear of porous materials
- Clean-peel characteristics: visual assessment of whether the seal opens without shredding, tearing, or particulate generation
- Statistical parameters: mean, standard deviation, and process capability indices for validated sealing processes
Testing Methods
Specimen Preparation and Conditioning
Representative specimens are cut to the width specified by ASTM F88, commonly 25.4 mm (or 15 mm in many medical device protocols), with the seal centered along the specimen and excess tails long enough for gripping. Specimens must be free of wrinkles, creases, or damage within the test region. Immediately after heat sealing, samples should be allowed to equilibrate, and all specimens are conditioned at 23 °C ± 2 °C and 50 % ± 5 % relative humidity for a minimum of 24 hours in accordance with ISO 291 or ASTM D618 before testing.
ASTM F88 Tensile Peel Test Procedure
The specimen is mounted in a universal testing machine fitted with pneumatic or manual grips, frequently lined with rubber or gritted faces to prevent slippage. ASTM F88 defines three gripping techniques: unsupported peeling with tails bent by hand (Technique A), 90° peeling supported by a fixture or slip plate that bends one tail (Technique B), and unsupported 180° peeling with one tail folded back (Technique C). The crosshead speed is typically set at 200 to 300 mm/min as permitted by the standard, and the force-displacement curve is recorded until the seal is fully separated or the specimen fails outside the seal region. The test is repeated on multiple specimens, commonly 10 to 30 per condition, to characterize variability.
Alternative Peel Configurations
For flexible-to-flexible laminates and material qualification studies, T-type peel testing in accordance with ASTM D1876 may be applied, in which both tails of the specimen are gripped and peeled symmetrically in opposite directions. Whole-package methods, such as internal pressurization burst and creep testing per ASTM F1140 or ASTM F2054, and constrained film tests per ASTM F2824 for finite pouch seals, are frequently used as complementary techniques to strip peel testing, particularly for quality control on finished packages.
Data Analysis and Acceptance Criteria
Peak force, average force, and failure mode are reported for each specimen together with specimen width, test speed, gripping technique, and conditioning history. Neither ISO 11607 nor ASTM F88 prescribes a universal numerical limit; acceptable peel force ranges must be established by the manufacturer based on a risk assessment covering distribution hazards, microbial barrier performance, and aseptic presentation requirements. In practice, clean-peel seals for porous film pouches are frequently targeted in the region of 1.5 to 5 N per 15 mm of width, with defined minimum individual values and statistical acceptance criteria documented in the validation protocol.
Applications
Peel force determination supports the entire lifecycle of medical device packaging, from material selection to post-market monitoring:
- Sealing process validation: establishing process windows during installation, operational, and performance qualification (IQ/OQ/PQ) of heat-sealing equipment, supported by ASTM F2029 seal-making studies
- Routine quality control: periodic destructive testing of production seals to monitor process stability through statistical process control
- Material and supplier qualification: comparing films, coatings, and porous webs during design transfer and incoming inspection
- Shelf-life verification: retesting seal strength after accelerated aging per ASTM F1980 and real-time aging, as well as after transport and distribution simulation per ASTM D4169
- Change control: demonstrating equivalence after changes in materials, sealing equipment, or packaging design
- Regulatory submissions: providing technical evidence for market approvals and conformity with ISO 11607 requirements, often generated by accredited third-party laboratories
- Failure investigation: analyzing field complaints, sterile barrier breaches, or opening difficulties reported by clinical users
FAQ
What is the difference between peel strength and seal integrity?
Peel strength measures the mechanical force required to open a seal, while seal integrity confirms the absence of channels or leaks that could allow microbial ingress. ISO 11607-1 requires both attributes to be demonstrated, so peel force testing is typically combined with visual inspection per ASTM F1886, dye penetration per ASTM F1929, or whole-package leak testing per ASTM F2096.
Is there a universal acceptable value for peel force?
No. Standards organizations define test methods and general requirements but not fixed limits. Each manufacturer must justify acceptance criteria based on intended use, distribution risk, and aseptic presentation needs. A commonly referenced engineering target for clean-peel porous-film seals is 1.5 to 5 N per 15 mm, but this must not be adopted without documented justification.
Which standards govern medical device packaging peel force testing?
The primary references are ISO 11607-1 and ISO 11607-2 for packaging requirements and validation, ASTM F88/F88M for seal strength measurement, ASTM F2029 and ASTM F2824 for seal preparation and finite seal testing, EN 868 for packaging materials, and GB/T 19633 as the Chinese adoption of ISO 11607.
How many specimens should be tested?
The number depends on the purpose of the study. Process validation typically requires statistically justified sample sizes across multiple seal locations and process settings, while routine quality control may use smaller sampling plans. Testing 10 to 30 specimens per condition is common practice for characterizing seal strength distributions.
Why do results sometimes show fiber tear or substrate tearing?
Fiber tear of porous materials or tearing of films indicates that the seal or substrate is stronger than the cohesive strength of the material, which is acceptable only when justified and consistent. It may reflect excessive sealing temperature or dwell time, or an incompatible material pairing, and it can compromise clean, particulate-free opening in clinical use.
Can peel force testing be performed on porous materials such as Tyvek-type webs?
Yes. Porous materials are routinely tested using ASTM F88 with appropriate gripping techniques and slip plates to control the peel angle. Care is required to distinguish true seal failure from fiber tear, and specimen conditioning is important because humidity can influence the mechanical behavior of porous substrates.