Low-Temperature Storage Testing of Plastic Materials: Standards, Methods, and Applications

Low-temperature storage testing evaluates how plastic materials and finished products withstand prolonged exposure to sub-ambient temperatures, identifying risks such as embrittlement, cracking, and loss of mechanical strength. Conducted in accordance with internationally recognized standards such as IEC 60068-2-1, GB/T 2423.1, and ASTM D746, the test provides essential data for material selection and product qualification in automotive, electronics, packaging, and cold-chain applications. This article explains the purpose, samples, test items, methods, and typical applications of low-temperature storage testing for plastic materials.

Technical Overview

Low-temperature storage testing is a controlled environmental test in which plastic materials, standard test specimens, or finished plastic products are exposed to a specified sub-ambient temperature for a defined period and then examined for changes in appearance, dimensions, and mechanical performance. The test simulates the conditions plastics experience during winter storage, cold-chain logistics, high-altitude transport, and service in arctic or subarctic climates, providing objective evidence of whether a material will remain safe, functional, and dimensionally stable after cold exposure.

Plastic materials are particularly sensitive to low temperatures because polymer chain mobility decreases sharply as the ambient temperature approaches or falls below the glass transition temperature of the polymer. Free volume contracts, molecular segments stiffen, and the material transitions from ductile to brittle behavior. Typical effects include embrittlement, surface cracking and crazing, loss of elongation, reduced impact strength, shrinkage, warpage, and seal or weld failures.

The most widely applied references include IEC 60068-2-1 (Environmental testing, Test A: Cold) and its Chinese counterpart GB/T 2423.1 for whole products and components, ISO 974 and ASTM D746 together with GB/T 5470 for determining the brittleness temperature of plastics by impact, and ISO 291 or ASTM D618 for specimen conditioning before and after exposure. Accredited third-party laboratories routinely perform these tests as part of material qualification, product certification, and design validation programs.

Testing Samples

Standard Molded Test Specimens

Injection-molded or compression-molded laboratory specimens are used when the objective is to characterize the base material. Typical specimens include:

• Tensile dumbbell bars prepared according to ISO 527-2 (specimen types 1A/1B) or ASTM D638 (Type I)
• Impact bars for Charpy and Izod testing per ISO 179-1, ISO 180, or ASTM D256
• Flexural specimens per ISO 178 or ASTM D790
• Plaques or discs for hardness, puncture impact, and thermal analysis

Finished Products and Components

Complete parts such as electronic enclosures, automotive trim, connectors, closures, appliance covers, and medical device components can be tested in their end-use configuration. Testing finished parts verifies that design features, including snap fits, ribs, bosses, living hinges, and welded or assembled joints, survive cold exposure, not just the raw material.

Films, Sheets, and Packaging Materials

Flexible films, laminates, and rigid sheets used for frozen-food packaging, pharmaceutical cold-chain packaging, and thermoformed containers are tested as strips, sealed pouches, or complete packages to evaluate seal strength, flexibility, and crack resistance after freezing and thawing.

Pipes, Fittings, and Profiles

Segments of pipes, fittings, and extruded profiles intended for outdoor installation in cold regions are exposed and subsequently evaluated for impact resistance, dimensional stability, and joint integrity.

Regardless of sample form, a statistically meaningful number of replicate specimens, commonly at least five per condition, should be tested together with an unexposed control group. All specimens should be conditioned to a standard atmosphere, typically 23°C ± 2°C and 50% ± 10% relative humidity for at least 24 hours, in accordance with ISO 291 or ASTM D618 before baseline measurements are taken.

Testing Items

Depending on the product specification and intended application, low-temperature storage testing may include the following evaluation items:

• Visual inspection for cracking, crazing, whitening, blistering, delamination, color change, gloss loss, warpage, and permanent deformation
• Dimensional measurement of length, width, thickness, and flatness, with calculation of dimensional change rate
• Mass change determination
• Tensile strength, yield strength, and elongation at break, expressed as percentage retention after exposure
• Flexural strength and flexural modulus
• Charpy, Izod, Gardner, or dart-drop impact strength, either measured at low temperature inside the chamber or after recovery at room temperature
• Hardness measurement by Shore durometer or ball indentation hardness
• Determination of brittleness temperature by impact per ISO 974, ASTM D746, or GB/T 5470
• Seal strength and seal integrity for flexible packaging
• Functional checks such as assembly fit, snap-fit engagement, thread torque, and, for electrical parts, dielectric withstand and insulation resistance

Testing Methods

Baseline Characterization

Before exposure, each specimen is inspected and measured, and baseline mechanical properties are recorded on representative samples. Careful documentation of the initial state is essential for calculating property retention values at the end of the test.

Exposure Conditions

Samples are placed in an environmental chamber equipped with forced-air circulation and mechanical or cryogenically assisted refrigeration, capable of maintaining temperature uniformity within approximately ±2 to ±3°C. Typical setpoints are −10°C, −20°C, −25°C, −40°C, −55°C, and −70°C, selected according to the application: −20°C to −30°C for freezer and cold-chain storage, −40°C for automotive and outdoor equipment, and −55°C or lower for aerospace and special applications. Exposure durations commonly range from 24, 48, 72, or 96 hours for qualification purposes to 500 or 1,000 hours for long-term storage simulation.

Under IEC 60068-2-1 and GB/T 2423.1, several test variants are available, such as testing with abrupt temperature change, gradual temperature change, or extended duration with full temperature stabilization, allowing the test to reproduce either rapid transfer into a cold environment or slow seasonal cooling.

Recovery and Post-Exposure Evaluation

After the exposure period, specimens intended for room-temperature evaluation are recovered at standard laboratory conditions, typically 23°C and 50% relative humidity, for a defined period, commonly one to four hours or until thermal equilibrium is reached, before final measurements. Where true low-temperature properties are required, mechanical testing is performed inside the chamber at the exposure temperature so that the specimen never warms before loading. Both approaches are valid but answer different questions: in-situ testing characterizes behavior while cold, whereas post-recovery testing characterizes permanent damage caused by cold storage.

Data Analysis and Acceptance Criteria

Post-exposure results are compared with baseline values, and property retention is calculated as the ratio of the final value to the initial value, expressed as a percentage. Typical acceptance criteria specify no visible cracking or deleterious deformation, dimensional change below a defined limit such as ±0.5% to ±1%, and retention of tensile and impact properties above a defined threshold, commonly 70% to 90% depending on the product specification. The test report should state the material designation, specimen geometry, conditioning, exposure temperature and duration, recovery conditions, measured properties, and any observed failures.

Applications

Low-temperature storage testing supports material selection, product qualification, and regulatory compliance across a wide range of industries:

• Automotive: exterior trim, bumpers, mirror housings, under-hood connectors, and electric vehicle battery enclosures must withstand −40°C winter service and cold transport conditions
• Electronics and electrical engineering: enclosures, cable insulation and jackets, connectors, and switch components are qualified using IEC 60068-2-1 or GB/T 2423.1 as part of product safety and reliability programs
• Packaging and cold-chain logistics: frozen-food trays, pouches, and pharmaceutical packaging must survive freezer storage at −20°C to −40°C without cracking or seal failure
• Aerospace: cabin interior parts and on-board equipment are verified for the low-temperature exposure encountered during ground soak at high altitudes and high latitudes
• Construction and infrastructure: pipes, fittings, seals, and geomembranes intended for arctic and alpine installations are validated for cold-weather impact resistance and flexibility
• Consumer and outdoor goods: sporting equipment, garden tools, and camping products sold in cold-climate markets are screened for embrittlement risk
• Medical and laboratory products: device components and laboratory consumables subjected to refrigerated or frozen storage are confirmed to remain functional after thawing

FAQ

What is low-temperature storage testing of plastic materials?

It is a laboratory test in which plastic specimens or finished products are held at a specified low temperature for a defined duration and then evaluated for appearance, dimensional, and mechanical changes. The test determines whether a material can be stored or used in cold environments without cracking, embrittlement, or loss of performance.

Which temperatures and durations are typically used?

Common setpoints are −10°C, −25°C, −40°C, −55°C, and −70°C, with −40°C being the most frequent requirement for automotive and outdoor applications. Durations typically range from 24 to 96 hours for standard qualification and may extend to 500 or 1,000 hours when long-term cold storage must be simulated.

What standards govern the test?

IEC 60068-2-1 and GB/T 2423.1 define cold-exposure test methods for products and components; ISO 974, ASTM D746, and GB/T 5470 cover the determination of brittleness temperature by impact; and ISO 291 and ASTM D618 specify conditioning atmospheres. Industry bodies such as UL also reference low-temperature conditioning within polymeric material qualification programs.

Should properties be measured at low temperature or after recovery at room temperature?

Both approaches exist and serve different purposes. In-situ measurements at the exposure temperature show how the part behaves while cold, whereas measurements after recovery at 23°C reveal permanent damage, such as micro-cracking, caused by the cold exposure. The choice depends on the product specification and the real-world failure mode being addressed.

How are test results assessed?

Results are typically expressed as percentage retention of the pre-exposure property values, combined with visual and dimensional inspection against defined acceptance limits. A common criterion is the absence of visible cracks combined with at least 70% to 90% retention of tensile and impact properties, although exact limits are set by the customer specification.

Why do plastics become brittle at low temperatures?

As temperature drops, polymer chain segments lose mobility, especially near and below the glass transition temperature. The material stiffens, elongation decreases, and the failure mode shifts from ductile yielding to brittle fracture. The temperature at which half of the specimens fail in a brittle manner under impact is reported as the brittleness temperature.

Can finished products be tested, or only raw material specimens?

Both can be tested. Standard molded specimens characterize the material itself, while finished products are tested to verify that geometry, processing, weld lines, and assembly details also survive cold exposure. Accredited third-party laboratories routinely handle both categories of samples within the same test program.