ASTM F88/F88M

ASTM F88 test method covers the measurement of the strength of seals in flexible barrier materials. Seal strength is the tensile strength of the seal at ambient temperature. It is the maximum force required to separate the two layers of a seal under particular conditions. A series of seals at different sealing temperatures are made, using a machine employing hot-bar jaws. Each tail of the sealed specimen is secured in the opposing grips of a universal test bench. The maximum tensile force required to separate the two ends of the seal is recorded. While the test is being conducted the seal may be unsupported (technique A), at an angle 90º to the pull direction (technique B) or at an angle of 180ºC to the pulling direction (technique C) . A rectangular specimen is used; the specimen width may be either 25 mm, 15 mm or 1.00 inch. A curve can be plotted showing the effect of the sealing conditions (mainly temperature) on the seal force. This curve is called the seal curve. At a certain temperature a seal force level is reached which is related to the maximum tensile force of the film.

ASTM F88 seal strength is not only relevant to opening force and package integrity but to measuring the processes ability to produce consistent seals. Seal strength is a necessary package requirement and it is often desirable to limit the strength to facilitate opening the package. Properties of interest are the maximum seal force and the average force to open the seal. The average force is calculated over an 80% zone situated between the data markers of 10% - 90% of the peeling distance.

Before conducting ASTM F88, it is important to read the entire specification. Standards can be obtained from appropriate standard authorities.

Standards

Featured or equivalent test standards for Mecmesin solutions in this section

Term Video

Test summary

Specimens are cut to a specified width. The seal is then peeled apart by holding the two “legs” of the barrier material in the jaws of a force testing stand set to separate at a constant speed between 200 - 300 mm/min. while the force and displacement are continuously measured. The peak force required to separate the seal is reported, this can also be expressed as peak force per width of the seal material in N/m. Depending upon the characteristics of the specimen, it may also be informative to report the average peeling force over the width of the seal as it separates, discarding the first 10% and the last 10% of the force Vs displacement curve.

Test apparatus

Tensile tester with grips and suitable range loadcell. This may be a vertical testing stand, or alternatively a horizontally oriented instrument

Preparation

Cut a sufficient quantity of strips from a representative sample to a width of 15 mm, 25 mm or 25.4 mm perpendicular to the seal, and 75mm plus the width of the seal in length. If required, condition the specimens in accordance with ASTM E 171

Test method

1. If required, condition the samples as per ASTM E 171.

2. Cut strips from the sample to the dimensions defined in the standard.

3. Clamp the ends of the sample strip into the jaws of the tensile tester with the seal perpendicular to the direction of movement, and equidistant between the fixed and moving jaws.

4. If required, support the tail of the test specimen (see the standard for an explanation).

5. Set the tensile tester in motion at a speed between 200 and 300 mm/min.

6. Record the tensile force and displacement as the seal is peeled apart.

Report

Record all details necessary to identify the sample including width and machine direction in relation to the direction of pull.

Report the speed of separation used by the tensile tester, and the method used to support the tail of the sample if appropriate.

Report the maximum tensile force in newtons encountered as the specimen is stressed to failure. This can also be expressed as force per unit width of the seal in newtons per metre.

Note the method of failure of the seal.

Depending upon the characteristics of the force Vs displacement curve, it may be informative to calculate the average force as the seal is separated, discarding the first and final 10% of the force Vs displacement curve.