Peel tests on terminally sterilized medical packaging - ISO 11607

To guarantee the sterility of the objects they contain, medical packaging must meet a number of mechanical requirements. One of these requirements is the quality of the weld that seals the packaging.

Various methods exist for testing the quality of welds, one of the main ones being the peel (or separation) test of the two materials making up the package. In simple terms, this involves measuring the force required to separate the two materials, which corresponds to the opening force of the pouch or package.

In the field of medical packaging, these tests are required by standard ISO 11607 (Packaging for terminally sterilized medical devices). This standard is the main guide for validating sterilized medical packaging and is required to obtain CE marking. It is also recognized by the FDA in the USA. A package that complies with this standard guarantees that the object it contains is sterilized and protected until it is used. The main requirements of this standard are tests of stability, strength, integrity and dynamic performance.

One part of the standard concerns the resistance of the packaging weld. In particular, a peel test of the weld is required. According to the standard, two test methods are acceptable:

• In Europe : EN868-5 (annex D) - Packaging materials and systems for terminally sterilized medical devices - Part 5: heat-sealable pouches and tubs consisting of one side porous material and one side plastic film - Requirements and test methods

• In the USA: ASTM F88 - Standard Test Method for Seal Strength of Flexible Barrier Materials

These two measurement methods are relatively similar, but there are differences in terms of testing, presentation of results and acceptability criteria.

EN868-5 - Annex D

This involves cutting a 15mm-wide strip on the packaging and using a pulling machine to separate the two materials. The cut strip must be perpendicular to the weld. A sample of each package seam should be taken from the center of each seam for testing.

For example, if the shape of the bag is as follows :

Tensile tests are then carried out at a tensile speed of 200mm/min and the force recorded. The maximum stress recorded must be at least equal to 1.5N / 15mm of weld. If this force is lower on one of the welds, the packaging is considered non-compliant.

The test report must also contain at least the following information:

• The date

• Identification of the product tested

• Maximum strength for 15mm width

• The measuring device used

• Instrument acquisition frequency

• The end of the sample was held or not

• The test standard used

• Measured force evolution curve

ASTM F88

This standard has the advantage of applying to more cases than its predecessor (e.g. adhesion of flexible and rigid materials), and covers relevant technical points not covered in its predecessor (average force, different test techniques, etc.). However, it does not specify the minimum force required to hold the weld in place.

The different techniques on offer:

Several sample widths are also available:

• 25 mm (0.984 in)

• 15 mm (0.591 in) - identical to EN868-5 standard

• 25.4 mm (1 in)

And several pulling speeds are also available: 200 to 300 mm/min (8 to 12 in/min)

The way in which the sample is held is described in greater detail:

• A length of 76 mm (3in), excluding weld, for each sample leg is recommended (can be shortened depending on the type of jaws used).

• The original distance between grips is recommended (10mm for highly elastic materials and 25mm for others).

• The sample must be centered in the middle of the jaws and no pre-tension must be applied. The weld must be perpendicular to the tensile axis.

The results to be recorded in the report :

• Maximum force in N/m or lb/in

• Sample failure mode (weld, material at weld, delamination, material failure, elongation, weld elongation)

• Average effort (optional) between 10% and 90% of the test

• The effort curve

• Sample identification

• The test machine used

• Test conditions

• Test speed

• Sample width

• Tongue retainer type

• Number of samples tested

Comparison of the 2 standards:

These two standards are different in terms of the samples used and the speeds, but it turns out in practice that similar results can be found in both standards. Particularly with regard to maximum effort, when related to the width of the sample, the results cannot be discriminated according to the speed or width of the initial sample.

Examples of equipment used for this type of test :

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