High and Low Temperature Tensile Testing of Packaging Materials: Standards, Methods, and Application

High and low temperature tensile testing evaluates the tensile strength, elongation, seal strength, and peel resistance of packaging materials under extreme thermal conditions that simulate cold-chain distribution, frozen storage, retort sterilization, and high-temperature processing. This article explains the testing principle, applicable standards such as ASTM D882, ISO 527-3, and ASTM F88, typical sample types, test methods, industry applications, and frequently asked questions for packaging manufacturers and quality engineers.

Technical Overview

High and low temperature tensile testing is a mechanical evaluation performed on a universal testing machine equipped with an environmental chamber. Packaging specimens are clamped inside the chamber, stabilized at a target temperature above or below ambient conditions, and stretched to failure while force and extension are continuously recorded. The resulting stress-strain curves reveal how strength, stiffness, and ductility change across the thermal range the package will actually experience.

The test is essential because most packaging materials are polymeric, and polymers are viscoelastic: their mechanical behavior depends strongly on temperature. When the test temperature approaches or falls below the glass transition region, molecular chain mobility decreases and films become stiff and brittle; when the temperature approaches the softening or melting region, strength drops and elongation increases dramatically. A film that performs well at 23°C may shatter during cryogenic transport or lose seal integrity during retort sterilization. For example, polypropylene films become markedly brittle below approximately 0°C, while PET films soften noticeably above 70°C.

Packaging materials encounter thermal extremes throughout their life cycle, including:

• Cold-chain and frozen distribution at -18°C to -40°C, and ultra-cold biologic shipping at -70°C to -80°C
• Retort sterilization and autoclaving at 121°C to 135°C
• Hot filling, pasteurization, and shrink tunnel processing at 85°C to 180°C
• Global transport and outdoor storage extremes of -40°C to +60°C or beyond

Standard environmental chambers typically cover -70°C to +150°C with a temperature accuracy of approximately ±2°C. Extended ranges down to about -180°C (using liquid nitrogen cooling) and up to 300°C (using resistance heating) are available from accredited third-party laboratories for aerospace, cryogenic, and high-temperature process applications.

Testing Samples

Plastic Films and Sheets

Monolayer and coextruded films of PE, CPP, BOPP, PET, PA (nylon), EVOH, PVC, and PLA, typically 20 μm to 200 μm thick, are tested as longitudinal strips in both machine direction (MD) and transverse direction (TD) in accordance with ASTM D882, ISO 527-3, GB/T 1040.3, and JIS K 7127.

Multilayer Laminates and Foil Composites

High-barrier structures such as PET/AL/PE, PA/AL/PP, PA/EVOH/PE, and paper/foil/PE used for retort pouches, coffee bags, and pharmaceutical sachets are tested for overall tensile performance and interlayer cohesion at processing and storage temperatures.

Heat Seals and Seal Strips from Finished Packages

Fin seals, lap seals, and perimeter seals cut as 15 mm or 25.4 mm wide strips from pouches and bags are tested for seal strength per ASTM F88. Testing seals at -40°C, at 121°C to 135°C, or after thermal cycling reveals whether the sealing layer maintains integrity through freezing and sterilization.

Pressure-Sensitive Tapes and Label Adhesives

Packaging sealing tapes, carton tapes, and label adhesives are evaluated for 180° peel adhesion and holding performance at low and elevated temperatures per ASTM D3330, ensuring cartons stay sealed in refrigerated warehouses and hot shipping containers.

Strapping, Stretch Films, and Shrink Films

PP and PET strapping, LLDPE stretch wrap, and polyolefin shrink films are tested to verify load containment force after cold exposure or heat treatment, since strapping embrittlement in winter and stretch film stress relaxation in summer are common field failure modes.

Testing Items

Core mechanical parameters measured at each temperature point include:

• Tensile strength (MPa) and ultimate breaking force (N)
• Elongation at break and elongation at yield (%)
• Yield strength (MPa)
• Young's modulus / tensile modulus (MPa)
• Seal strength (N/15 mm or N/25.4 mm) per ASTM F88
• Peel force and delamination resistance, including T-peel per ASTM D1876 and ISO 11339
• Work (energy) to failure, derived from the force-extension curve
• Full stress-strain curves across the temperature spectrum for material database and simulation input

By comparing results at extreme temperatures against the 23°C baseline, engineers calculate a property retention ratio that supports material qualification, shelf-life estimation, and design margin analysis.

Testing Methods

Specimen Preparation and Conditioning

Specimens are die-cut to the geometry required by the applicable standard. For thin films per ASTM D882 and ISO 527-3, rectangular strips with a preferred width of 15 mm or 25.4 mm and a gauge length of at least 50 mm (commonly 100 mm to 250 mm) are used; for thicker sheets and molded coupons, dumbbell specimens per ASTM D638, ISO 527-2, and GB/T 1040.2 apply. Specimens are first conditioned at 23°C and 50% relative humidity per ISO 291, ASTM D618, or GB/T 2918. They are then placed in the test chamber and thermally soaked, typically 10 to 30 minutes depending on thickness, with a thermocouple positioned near the specimen to confirm equilibrium before loading begins.

Test Procedure

• Set the chamber to the target temperature and allow the chamber, grips, and load cell region to stabilize
• Mount the specimen in pneumatic or mechanical grips with serrated, rubber-faced, or line-contact faces that prevent slippage without initiating premature failure
• Complete the thermal soak and verify specimen temperature with a calibrated thermocouple
• Select the crosshead speed according to the standard and expected elongation, typically 5 mm/min to 500 mm/min for films
• Run the test to specimen break while recording force and extension; use a video extensometer through the chamber window when accurate strain measurement is required
• Test a minimum of five valid replicates per direction, per temperature, and per structure; specimens that fail in the grips are discarded and replaced

For sub-ambient testing, cooling is achieved with liquid nitrogen or liquid CO2 injection, and a dry gas purge prevents frost formation on specimens and fixtures. For elevated testing, forced-air resistance heating maintains uniform temperature throughout the working volume.

Data Processing and Reporting

Engineering stress is calculated from the measured width and thickness of each specimen at the gauge region. The test report documents the temperature and humidity conditions, specimen geometry and orientation, crosshead speed, individual and mean values with standard deviations for each parameter, the failure mode and location, and the referenced standard. Results are frequently presented as property-versus-temperature curves covering, for example, -40°C, 23°C, and 121°C, providing a clear picture of performance across the full distribution and processing envelope.

Applications

• Food and beverage packaging: qualification of retort pouch laminates at 121°C to 135°C, frozen food films at -18°C to -40°C, and hot-fill and pasteurized packaging structures
• Pharmaceutical and medical packaging: verification of sterile barrier systems per ISO 11607, cold-chain biologic shipping components at -70°C to -80°C, and autoclave-resistant seals
• Cold-chain logistics and e-commerce: confirmation that tapes, films, and seals survive refrigerated warehouses and winter distribution without embrittlement or loss of adhesion
• Industrial and chemical packaging: evaluation of heavy-duty liners, strapping, and flexible intermediate bulk container fabrics at temperature extremes
• Electronics and lithium battery packaging: assessment of barrier pouches, ESD films, and transport packaging subjected to thermal cycling
• Aerospace and defense packaging: qualification of materials for extreme low-temperature and high-temperature environments
• Research and development: material selection, adhesive and resin formulation optimization, heat-seal process window studies, and generation of input data for finite element simulation

Manufacturers without in-house environmental chambers routinely outsource this testing to accredited third-party laboratories, which provide traceable calibration, standard-compliant procedures, and independent test reports for customer submissions and regulatory files.

FAQ

What temperature range can be tested?

Standard chambers cover -70°C to +150°C. With liquid nitrogen cooling and high-temperature heating elements, accredited third-party laboratories can extend the range to approximately -180°C to +300°C for special applications.

Why do packaging films become brittle at low temperatures?

As temperature drops toward the polymer's glass transition region, molecular chain segments lose mobility, so the material can no longer deform ductilely. Elongation at break falls sharply and failure becomes brittle fracture, which is why seal and film integrity must be verified at the lowest temperature the package will encounter.

How long should specimens be conditioned at the test temperature?

A thermal soak of 10 to 30 minutes is typical for thin films, scaled with thickness and thermal mass. A thermocouple placed next to the specimen should confirm that the target temperature has been reached and stabilized before the tensile load is applied.

Which standards are most commonly applied?

Thin plastic films are tested per ASTM D882, ISO 527-3, GB/T 1040.3, and JIS K 7127; thicker plastic sheets per ASTM D638, ISO 527-2, and GB/T 1040.2; heat seal strength per ASTM F88; tape peel adhesion per ASTM D3330; and laminate T-peel per ASTM D1876 and ISO 11339. Complementary whole-package methods include burst and internal pressurization per ASTM F1140 and ASTM F2054.

Can finished packages be tested instead of flat film?

Yes. Seal strips cut directly from finished pouches are tested per ASTM F88 at the temperature of interest, and whole-package burst or creep tests per ASTM F1140 and ASTM F2054 can be combined with tensile data to give a complete picture of package robustness.

Is humidity controlled during the test?

Humidity control is meaningful only at or above ambient temperature; sub-ambient tests use a dry purge gas to prevent condensation and frost. When moisture sensitivity matters, such as for nylon films, conditioning history should be standardized and documented in the report.