ASTM D1922 — Tear Propagation Resistance of Plastic Films (Elmendorf)

1. Principles and Scope of the Standard

ASTM D1922 is a test method designed to determine the average force required to propagate tearing through a specified length of plastic film or nonrigid sheeting, using an Elmendorf-type tearing tester. It applies to films with a nominal thickness not exceeding 0.25 mm (0.010 in.).

The principle relies on a calibrated pendulum operating under gravity. The specimen, held by two clamps — one fixed and the other attached to the pendulum — is pre-slit over 20 mm by a knife built into the apparatus. The pendulum is then released and swings in an arc, propagating the tear through the remaining 43 mm. The energy consumed during propagation is measured by the loss of kinetic energy of the pendulum.

It is important to note that this method exclusively measures tear propagation, not initiation. The tear is already initiated by the mechanical slit before measurement begins. The standard therefore does not predict film behaviour under puncture or impact, but characterises its resistance to the progression of an existing defect.

1.1 Measuring Propagation Tear Resistance

The test provides a tear force value expressed in millinewtons (mN) or grams-force (gf), along with the specimen thickness. The tearing speed, which varies according to the material's resistance, typically ranges from 7.6 to 46 m/min (300 to 1,800 in./min), significantly higher than standard tensile test speeds.

Two specimen types are defined by the standard: a rectangular specimen and a constant-radius specimen. The latter is the referee specimen, as it ensures a constant tear length regardless of the propagation path, reducing result variability.

1.2 Distinction from Related Test Methods

Confusion between the various tear standards is common. The fundamental difference lies in the property measured and the test kinematics:

Results from these different methods are not interchangeable due to differences in specimen geometry, loading speed and the property being measured.

2. Role in Packaging Film Evaluation

2.1 Ranking Tear Performance

ASTM D1922 is widely used as a benchmark index for ranking the tear resistance of plastic films in packaging applications. For films of comparable thickness, it enables objective ranking of materials: low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polyester (PET), polyamide (PA), and their multilayer complexes.

Results are systematically reported in the two principal film directions: machine direction (MD) and transverse direction (TD). The MD/TD ratio is a key indicator of material anisotropy, directly linked to extrusion and orientation conditions.

2.2 Production Quality Control

On the production line, the Elmendorf tear test serves as a statistical control to detect process drift (extrusion temperature variation, draw ratio changes, raw material contamination). A sudden drop in transverse direction tear resistance may signal excessive orientation or poor melt homogeneity.

2.3 Interpretation Limitations

The method has recognised limitations, particularly on highly extensible films. The main pitfalls to avoid:

• On highly extensible films (certain LDPE, stretch films), variable elongation and oblique tearing reduce result reproducibility and prevent their use as a precise production-control tool.
• Comparing results obtained on different thicknesses without normalisation (tear force depends directly on thickness).
• Using D1922 results to predict puncture or impact resistance (measured by ASTM D1709 or ASTM F1306).

Important: ASTM D1922 should only be used for specification acceptance testing after it has been demonstrated that data for the particular material are acceptably reproducible.

3. Test Procedure

3.1 Specimen Preparation

Specimens are conditioned in accordance with ASTM D618 (typically 23 ± 2 °C, 50 ± 10% RH, for at least 40 hours). A minimum of 10 specimens are cut in the machine direction (MD) and 10 specimens in the transverse direction (TD). The thickness of each specimen is measured with a micrometer, to the nearest micrometre. The referee specimen is the constant-radius type, with a width of 63 mm and a tear length of 43 mm.

3.2 Test Apparatus and Procedure

The test is performed using an Elmendorf-type tearing tester. The apparatus consists of a calibrated pendulum, two clamps (one fixed, the other attached to the pendulum) and a slitting knife. The procedure involves four steps:

• The specimen is positioned and clamped between the two jaws, perfectly aligned.
• The built-in knife makes a 20 mm slit, creating a tear initiation that stops 43 mm from the opposite edge.
• The pendulum is released from its raised position. As it swings through its arc, it moves the movable clamp away from the fixed clamp, propagating the tear through the specimen.
• The energy absorbed by the tear is read from the apparatus scale or recorded digitally, and converted to average tear force.

Pendulum calibration is verified regularly. The pendulum capacity must be chosen so that the measured value falls between 20 and 80% of the scale, the range where precision is optimal.

3.3 Data Collection and Analysis

Data are recorded for each specimen and analysed statistically. The key parameters reported are:

Any oblique tear or tear exhibiting excessive elongation must be reported in the test report, as it may invalidate the measurement or significantly reduce its reproducibility.

4. Regulatory Framework and Industrial Applications

4.1 Standards and Regulatory References

ASTM D1922 is part of a broader standards ecosystem. The main cross-references:

• 49 CFR § 171.7 (DOT, United States): the standard is incorporated into US federal law relating to the transportation of hazardous materials.
• ISO 6383-2: internationally equivalent method for determining pendulum tear resistance, facilitating trade.
• ASTM D882: often performed as a complement for tensile properties (strength, elongation, modulus) of the same film.
• ASTM D1709: dart impact test, complementary for evaluating impact resistance rather than tear resistance.

The current version in force is D1922-15(2020), developed by ASTM International Subcommittee D20.19.

4.2 Industry Applications

Food Packaging

Tear resistance is a critical criterion for food films: too low, and the film tears accidentally during packing or transport; too high, and consumer opening becomes difficult. ASTM D1922 enables optimisation of this balance, particularly for LDPE films and multilayer complexes used in flow-wrap, pouches and lidding.

Industrial and Agricultural Films

Stretch wrap, agricultural sheeting and protective films are subjected to repeated mechanical stress. Measuring tear resistance in both directions (MD and TD) ensures the film resists propagation of defects caused by surface roughness, sharp edges or accidental perforations.

Medical and Pharmaceutical Films

Barrier films used for sterile packaging (blisters, peelable pouches) must meet precise tear thresholds: sufficiently strong to guarantee package integrity, while allowing controlled opening by healthcare personnel.

5. Best Practices for Reliable Testing

5.1 Choosing a Laboratory

Result reliability depends directly on laboratory competence. Selection criteria:

• ISO/IEC 17025 accreditation, guaranteeing technical competence and metrological traceability.
• Calibrated equipment: Elmendorf tester with appropriately sized pendulums, maintained slitting knife (a blunt knife alters the initiation and distorts results).
• Demonstrated experience with the relevant film types, with knowledge of specific behaviours (oblique tearing, excessive elongation).
• Conditioning control: results are sensitive to temperature and humidity conditions; rigorous control of the test environment is essential.

5.2 Practical Recommendations

To maximise the value of D1922 testing:

• Always test in both directions (MD and TD) to characterise film anisotropy.
• Choose pendulum capacity so that readings fall between 20 and 80% of the scale, to ensure precision.
• Systematically check the tear type obtained: an oblique tear or excessive elongation must be reported and may require a change of method.
• Normalise results by thickness when comparing films of different grades, reporting tear force in mN/μm.
• For extensible films (LDPE, stretch films), consider ASTM D1938 (trouser tear test) as a complement or alternative, offering better reproducibility on these materials.

Food packaging, industrial and agricultural films, medical and pharmaceutical packaging, and technical films (optical, electronic) are the main user sectors. Any sector where film integrity is critical benefits from this standard for material selection and production control.