135 degree peel

The 135° peel test is a method for measuring the seal strength of semi-rigid packaging, typically where a flexible lid is sealed onto a rigid or vacuum-formed container. In this test, the bonded materials are pulled apart at a fixed angle of 135°, providing a controlled way to evaluate how a seal will perform during opening.

This method is especially relevant for medical device and pharmaceutical packaging, where sterile barrier integrity is critical, and for consumer goods where packaging must be both reliable and easy to open. The 135° angle is chosen because it reflects how lids are usually peeled back in real-world use, making it more representative than 90° or 180° methods in many cases.

Seal strength testing plays a vital role in packaging quality control. For medical packaging, compliance with ISO 11607-1 requires that packaging for terminally sterilised devices maintains a sterile barrier until the point of use. A peel test provides evidence that seals are strong enough to protect sterility but not so strong that they are difficult to open in clinical environments.

In consumer applications, such as food and household goods, seal strength testing ensures that trays and vacuum-formed containers remain intact during transit yet open smoothly for the end user. The 135° test provides a balance between simulating real-world opening conditions and producing reliable, repeatable laboratory data.

Specimen preparation

Test specimens are usually strips cut from the sealed edge of a tray or container. A typical strip width is 25 mm, although this may vary depending on packaging design. Samples are conditioned to standard laboratory conditions before testing to ensure consistency.

Test setup

The container or tray is held securely in a vacuum fixture that positions the flexible lid at 135°. The lid is gripped by a clamp attached to the moving crosshead of the testing machine. As the crosshead moves upwards at a constant speed, the lid is peeled back from the container at the fixed angle.

Peel rate and measurement

Test speed is commonly set between 200 and 300 mm/min, in line with industry standards such as ASTM F88. The test records the force required to separate the seal, usually expressed as force per unit width, for example N/15 mm or N/25 mm. Both average and peak force values can be reported.

A 90° peel test is often used for flexible packaging films.

A 180° peel test is typical for adhesives and laminates.

The 135° method is preferred for semi-rigid packaging, where it more closely simulates how users peel lids from trays and thermoformed containers.

Mecmesin offers a range of test systems designed for peel testing applications.

• FPT-H1 Automated Friction, Peel and Tear Tester: a dedicated system for peel and seal strength testing, controlled by Mecmesin’s VectorPro software for precise control of speed, angle, and data capture.
• OmniTest and MultiTest-dV universal testers: versatile testing machines that can be configured with variable-angle peel fixtures, allowing accurate positioning at 135° or other required test angles.
• Custom fixtures: Mecmesin engineers design vacuum and clamping fixtures for semi-rigid trays, cups, and containers with complex geometries, ensuring repeatable and secure testing.

Case studies include testing of medical device packaging where sterile barrier seals must meet both regulatory requirements and practical usability needs. Mecmesin’s expertise in fixture design and software control ensures results are both accurate and relevant to real-world use.

Several recognised standards define methods for peel strength testing of semi-rigid and flexible packaging.

• ASTM F2824-10: Standard test method for mechanical seal strength of round cups, bowls, trays, and lidded thermoform containers.
• ISO 11607-1: Packaging for terminally sterilised medical devices - requirements for materials, sterile barrier systems, and packaging systems.
• ASTM F88: Standard test method for seal strength of flexible barrier materials, often used as a reference for peel speed and reporting units.
• ASTM D6862: Standard test method for 180° peel resistance of adhesives, included here for context when comparing peel angles.

Mecmesin’s VectorPro software enables data to be captured, stored, and analysed in compliance with these standards. Test reports can be customised to provide traceability for quality assurance and regulatory audits.

Mecmesin’s technical specialists can advise on selecting the right fixtures, test methods, and equipment for 135° peel testing. Whether you are testing medical packaging to ISO 11607-1, verifying the integrity of vacuum-formed trays, or developing new consumer packaging, the team can help configure a solution tailored to your needs. Contact Mecmesin to discuss your application or arrange a demonstration.

What specimens can be tested using a 135° peel method?

Semi-rigid trays, vacuum-formed containers, medical device packs, and other rigid-lid packaging formats can be tested.

How does a 135° peel test differ from 90° and 180° tests?

The 135° test is designed for semi-rigid packaging and better represents the way lids are peeled in practice, while 90° and 180° tests are more suited to flexible laminates and adhesives.

Which standards specify 135° peel testing?

ASTM F2824-10 specifically defines 135° testing for round containers. ISO 11607-1 requires seal strength testing for sterile barrier systems and is commonly demonstrated with a 135° method.

Can Mecmesin design custom fixtures for unusual packaging shapes?

Yes, Mecmesin regularly develops custom vacuum and clamping fixtures to handle challenging packaging designs.

What industries typically use 135° peel testing?

Medical device, pharmaceutical, and consumer goods industries use this method to validate packaging performance and seal integrity.