ASTM F88/F88M-23

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F88/F88M − 23
Standard Test Method for
Seal Strength of Flexible Barrier Materials
This standard is issued under the fixed designation F88/F88M; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the measurement of the strength
D882 Test Method for Tensile Properties of Thin Plastic
of seals in flexible barrier materials.
Sheeting
1.2 The test may be conducted on seals between a flexible
D883 Terminology Relating to Plastics
material and another flexible material, a rigid material, or a
E171 Practice for Conditioning and Testing Flexible Barrier
semi-rigid material.
Packaging
E177 Practice for Use of the Terms Precision and Bias in
1.3 Seals tested in accordance with this test method may be
ASTM Test Methods
from any source, laboratory or commercial.
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
1.4 This test method measures the force required to separate
F17 Terminology Relating to Primary Barrier Packaging
a test strip of material containing the seal. It also identifies the
F2824 Test Method for Mechanical Seal Strength Testing for
mode of specimen failure.
Round Cups and Bowl Containers with Flexible Peelable
1.5 This test method differs from Test Method F2824. Test
Lids
Method F2824 measures mechanical seal strength while sepa-
F3263 Guide for Packaging Test Method Validation
rating an entire lid (cover/membrane) from a rigid or semi-rigid
3. Terminology
round container.
3.1 Definitions:
1.6 The values stated in either SI units or inch-pound units
3.1.1 average seal strength, n—average force per unit width
are to be regarded separately as standard. The values stated in
of seal required to fully separate a flexible material from a rigid
each system may not be exact equivalents; therefore, each
material, semi-rigid material, or another flexible material,
system shall be used independently of the other. Combining
under the conditions of the test.
values from the two systems may result in non-conformance
3.1.1.1 Discussion—The average force normally is calcu-
with the standard.
lated by the testing machine from the digitized plot of force
versus grip travel. The plot starts from zero force after slack
1.7 This standard does not purport to address all of the
has been removed from the test strip. The initial ramp-up from
safety concerns, if any, associated with its use. It is the
zero to the force level required to peel the seal is not indicative
responsibility of the user of this standard to establish appro-
of seal strength, and data from that part of the curve should not
priate safety, health, and environmental practices and deter-
be included in the calculation of average strength, nor should
mine the applicability of regulatory limitations prior to use.
the return to zero following complete failure of the specimen.
1.8 This international standard was developed in accor-
The amount of data actually discarded on each end of the
dance with internationally recognized principles on standard-
measured seal-profile curve must be the same for all tests
ization established in the Decision on Principles for the
within any set of comparisons of average seal strength (see
Development of International Standards, Guides and Recom-
6.1.1 and 9.9.1).
mendations issued by the World Trade Organization Technical
3.1.2 maximum seal strength, n—maximum force per unit
Barriers to Trade (TBT) Committee.
width of seal required to fully separate a flexible material from
a rigid or semi-rigid material, or another flexible material,
under the conditions of the test.
This test method is under the jurisdiction of ASTM Committee F02 on Primary
Barrier Packaging and is the direct responsibility of Subcommittee F02.20 on
Physical Properties. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2023. Published August 2023. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1968. Last previous edition approved in 2021 as F88/F88M – 21. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/F0088_F0088M-23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F88/F88M − 23
flipping of the tail throughout the course of the test; this has potential to
3.1.3 flange, n—any geometric feature of a rigid or semi-
impact the measured strength and should be reported with results.
rigid component, which provides a counterpart surface to
NOTE 6—Test method validation should account for use of fixtures or
which a flexible component can form a seal.
alignment plates, as well as determination of which material is placed into
3.1.4 interferences, n—conditions that may lead to increased which grip as these factors are known to impact results, and feasibility of
each approach may vary depending on design features. Examples of
variation or challenges in obtaining consistent measurement of
optional fixtures and equipment with built in fixturing are included in
test samples.
Appendix X4 for reference. Refer to Guide F3263 for guidance on test
method validation.
4. Significance and Use
4.1 Seal strength is a quantitative measure for use in process
5. Interferences
validation, capability, and control. Seal strength is not only
5.1 The value obtained for seal strength can be affected by
relevant to opening force and package integrity, but to mea-
properties of the specimen other than seal strength. Some
suring the packaging processes’ ability to produce consistent
flexible barrier materials have properties, such as shape and
seals. Seal strength at some minimum level is a necessary
dimension, that may vary or change and need to be taken into
package requirement, and at times it is also desirable to have an
consideration when testing for seal strength. Examples include
upper limit to the strength of the seal to facilitate opening.
materials that may stretch (elongation), flexing around the
NOTE 1—Seal strength values are a measurement of the output of the
perimeter of a seal flange, or the shape/design of the rigid or
seal separation and may also involve mechanical properties of the
semi-rigid material flanges (for example, in a tray), or variation
materials that form the seal, given the potential for deformation or
in material properties such as caliper. These interferences are
elongation over the course of the test. This separation is indicative of the
area of the package being sampled and does not take into account discussed in Annex A1.
simulation of a user interfacing with an entire package during the opening
process.
6. Apparatus
NOTE 2—Lower seal strength specifications are typically utilized to
provide assurance of package closure, which can contribute to seal
6.1 Tensile Testing Machine—A testing machine of the
integrity.
constant rate-of-jaw-separation type. The machine shall be
NOTE 3—Upper seal strength specifications are typically utilized to
equipped with a device for recording the tensile load and the
limit the amount of force required to open a package, ensuring that a user
amount of separation of the grips; both of these measuring
is able to open the design. Upper seal strength specifications are typically
limited to seals that are intended to be peeled by the end user.
systems shall be accurate to 62 %. The rate of separation of
the jaws shall be uniform and capable of adjustment from
4.1.1 The maximum seal force is important information, but
approximately 8 in. to 12 in. [200 mm to 300 mm] ⁄min. The
for some applications, average force to separate the seal may
gripping system shall be capable of minimizing specimen
be useful, and in those cases also should be reported.
slippage and applying an even stress distribution to the
4.2 A portion of the force measured when testing materials
specimen.
may be a bending component and not seal strength alone. A
number of fixtures and techniques have been devised to hold NOTE 7—If the tensile testing machine utilizes a spring and hook-based
apparatus to extend the sample, it is expected to impart more variation in
samples at various angles to the pull direction to control this
results as it travels, as compared to modern equipment. When utilizing
bending force. Because the effect of each of these on test
spring and hook-based apparatus, it is recommended to take this factor
results is varied, consistent use of one technique (Technique A,
into consideration and limit the variation imparted by the weighing system
Technique B, or Technique C) throughout a test series is
movement to a maximum distance of 2 % of the specimen extension
recommended. Examples of techniques are illustrated in Fig. 1. within the range being measured.
NOTE 8—Impact of jaw-separation rate is discussed in Appendix X3.
4.2.1 Technique A: Unsupported—Each tail of the specimen
is secured in opposing grips and the seal remains unsupported
6.1.1 If calculation of average seal strength is required, the
while the test is being conducted.
testing machine system shall have the capability to calculate its
4.2.2 Technique B: Supported 90° (By Hand)—Each tail of
value over a specified range of grip travel programmable by the
the specimen is secured in opposing grips and the seal remains
operator. Preferably, the machine shall have the capability also
hand-supported at a 90° perpendicular angle to the tails while
to plot the curve of force versus grip travel.
the test is being conducted.
6.2 Specimen Cutter, conforming to the requirements of 6.5
NOTE 4—Excessive lateral forces applied via hand may impact results.
of Test Method D882, sized to cut specimens to a width of
Actual gripping of samples is not intended and will influence results;
0.984 in. [25 mm], 0.591 in. [15 mm], or 1.00 in. [25.4 mm].
contact is intended to be loose, only preventing tail movement up or down.
4.2.3 Technique C: Supported 180°—For flexible to flexible NOTE 9—Alternate specimen cutting methods and tools may be utilized
if deemed appropriate for the application.
applications, the least flexible tail is typically supported flat
NOTE 10—Any deviation from sample tolerance or width shall be
against a rigid alignment plate held in one grip. The more
supported through documented rationale and/or supportive data. Recom-
flexible tail is typically folded 180° over the seal and is held in
mended tolerance for sample cutting tool is 60.5 %. Sample cutting
the opposing grip while the test is being conducted.
method and associated variation that may support to establish alternate
Alternatively, in rigid and semi-rigid applications, the package tolerances may be assessed in validation of the test method; refer to Guide
F3263 for test method validation guidance.
structure may be maintained for the least flexible side; with this
NOTE 11—Seal strength is proportional to sample width under the same
structure gripped or fixtured.
test conditions. Impact of variation in sample width is discussed in
NOTE 5—Properties of some flexible materials may cause movement or Appendix X3.
F88/F88M − 23
Diagram Key
APPLICATION LINE DESCRIPTION
Flexible to Flexible, Rigid, or Semi-Rigid Seal \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ Flexible Film or Substrate #1
Flexible to Flexible Seal Flexible Film or Substrate #2
Flexible to Rigid or Semi-Rigid Seal - - - - - - - - - - - - - - - - - - - Rigid or Semi-Rigid Film or Substrate
FIG. 1 Tail Holding Methods
F88/F88M − 23
7. Sampling 9. Procedure
7.1 The number of test specimens shall be chosen to permit 9.1 Calibrate the tensile machine in accordance with the
an adequate determination of representative performance. manufacturer’s recommendations.
7.2 Testing of samples with visual defects or other devia- 9.2 Prepare sealed test specimens for testing by cutting to
tions from normality may or may not be appropriate depending the dimensions shown in Fig. 2. Edges shall be clean-cut and
on the purpose of the investigation. Indiscriminate elimination perpendicular to the direction of seal. Specimen legs may be
of defects can bias results. shorter than shown, depending on the grip dimensions of the
testing machine, recommended distance between grips, or the
8. Aging and Conditioning
size of the package under test. Multiple locations around the
perimeter of the package may be tested.
8.1 If conditioning before testing is desired and appropriate,
then see Practice E171.
NOTE 12—In some applications, sample webs may be indistinguishable
from each other, but have differences relevant to test results. In these
8.2 Heat seal conditioning periods may be determined by
situations, it is recommended to properly label the tail of each web to
experimentation as sufficient to achieve seal strength stability.
enable consistency in gripping and material direction and support report-
ing considerations in 10.1.8 and 10.1.11.
8.3 Modification of conditioning practices may be necessary
to meet specific test objectives, such as the measurement of 9.3 When preparing test specimens of flexible material
seal strength at specified storage or handling temperature.
(such as a lid) sealed to a rigid material (such as a tray), and
NOTE 1—X is the seal dimension to be tested and this dimension varies with sealer configuration.
NOTE 2—Images above represent typical designs and preparation approaches; other designs compliant with this standard may warrant alternate
approaches.
NOTE 3—Sample width dimensions are referenced as examples only; reference 6.2 for options.
FIG. 2 Recommended Specimen Dimensions
F88/F88M − 23
where the flange thickness and seal geometry allow, cutting test report should indicate the details of any technique used to
through the flexible material (such as a lid), while leaving the control tail orientation.
rigid material intact is acceptable. Alternatively, cutting com-
9.7 The seal shall be tested at a rate of grip separation of
pletely through the flange is another acceptable approach, as
8 in. ⁄min to 12 in. ⁄min [200 mm ⁄min to 300 mm ⁄min].
long as all subsequent seal strength data for comparison is
NOTE 13—Impact of variation in grip separation rate is discus
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