High and Low Temperature Aging Testing for Plastics and Rubber: Standards, Methods, and Applications

High and low temperature aging testing evaluates how plastic and rubber materials withstand prolonged thermal exposure, extreme cold, and repeated temperature cycling, providing critical data on property retention, durability, and long-term reliability. Performed in accordance with international standards such as ISO 188, ASTM D573, IEC 60068, and GB/T 3512, these tests are essential for material qualification, quality control, and service-life prediction across automotive, electronics, aerospace, and industrial sectors. This article explains the technical principles, sample types, test items, testing methods, and typical applications of thermal aging evaluation for polymeric materials.

Technical Overview

Plastics and rubbers are polymer-based materials whose mechanical, thermal, and electrical properties change significantly over time when exposed to heat, cold, and temperature fluctuations. At elevated temperatures, thermo-oxidative degradation mechanisms such as chain scission, additional crosslinking, oxidation, and the volatilization or migration of plasticizers and additives cause materials to harden, embrittle, crack, or lose strength. At low temperatures, polymers approach their glass transition point, resulting in stiffening, reduced elasticity, and increased susceptibility to brittle fracture under impact or flexing.

High and low temperature aging testing artificially accelerates these degradation processes under strictly controlled laboratory conditions. Test specimens are exposed to elevated temperatures in forced-air ovens, to sub-zero environments in low-temperature cabinets, or to programmable thermal cycling in environmental chambers. After exposure, the specimens are evaluated for changes in tensile strength, elongation at break, hardness, mass, dimensions, compression set, and low-temperature flexibility. The percentage change or retention of each property compared with unaged reference specimens forms the basis of the pass/fail judgment.

By applying the Arrhenius relationship between aging temperature and degradation rate, data obtained at several accelerated temperatures can be extrapolated to estimate the useful service life of a material at actual operating temperatures, a methodology widely used in long-term thermal endurance programs such as those described in IEC 60216 and UL 746B.

The principal standards governing this field of testing include:

• ISO 188 and ASTM D573 — accelerated heat aging of vulcanized and thermoplastic rubber in air ovens
• ISO 812, ASTM D2137, and GB/T 15256 — determination of low-temperature brittleness by impact
• ISO 2921 and ASTM D1329 — temperature retraction (TR) testing of rubber at low temperatures
• ISO 1432 and ASTM D1053 — Gehman torsional stiffness tests for low-temperature flexibility
• ASTM D3045 and GB/T 7141 — heat exposure of plastics without applied load
• GB/T 3512 — accelerated thermal aging of rubber by the hot-air oven method
• IEC 60068-2-1, IEC 60068-2-2, and IEC 60068-2-14 — cold, dry heat, and change-of-temperature tests for components (equivalent to GB/T 2423 series)
• IEC 60216 and UL 746B — thermal endurance characterization and relative temperature index (RTI) determination for insulating and polymeric materials

Testing Samples

Raw and Compounded Rubber Materials

Vulcanized rubber compounds submitted for aging evaluation include natural rubber (NR), styrene-butadiene rubber (SBR), nitrile butadiene rubber (NBR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), silicone rubber (VMQ), and fluoroelastomers (FKM). Standard tensile dumbbell specimens, hardness test blocks, and compression-set cylindrical pellets are prepared from cured sheets so that the aging behavior of the compound itself can be characterized independently of part geometry.

Thermoplastic and Engineering Plastic Materials

Common plastic materials tested include polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), acrylonitrile butadiene styrene (ABS), polycarbonate (PC), polyamide (PA/Nylon), polyoxymethylene (POM), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and high-performance engineering plastics such as PEEK. Specimens are typically injection-molded or machined into standard tensile bars (ASTM D638 or ISO 527), flexural bars, and plaques for property comparison before and after thermal exposure.

Finished and Semi-Finished Products

Finished components frequently submitted for high and low temperature aging evaluation include O-rings, oil seals, gaskets, diaphragms, rubber hoses, vibration isolators, cable jackets and insulation, connectors, battery components, electronic enclosures, automotive interior and underhood parts, and medical device components. Testing on actual products verifies that the combined influence of material, geometry, molding process, and post-cure treatment meets the durability requirements of the end-use environment.

Testing Items

Depending on the material specification and product standard, the following items are typically measured before and after thermal exposure to quantify aging resistance:

• Tensile strength and tensile strength retention rate (ISO 37, ASTM D412, ASTM D638, ISO 527)
• Elongation at break and percentage retention after aging
• Shore hardness (Shore A / Shore D) and hardness change (ISO 48, ASTM D2240)
• Percentage change in mass and dimensions after exposure
• Compression set under constant deflection after heat aging (ISO 815-1, ASTM D395)
• Low-temperature brittleness temperature by impact method (ISO 812, ASTM D2137, GB/T 15256)
• Temperature retraction values TR10, TR30, TR50, and TR70 (ISO 2921, ASTM D1329)
• Gehman torsional stiffness and apparent glass transition region (ISO 1432, ASTM D1053)
• Thermal cycling endurance and resistance to cracking or delamination under alternating high-low temperature exposure (IEC 60068-2-14)
• Visual assessment of surface cracking, blistering, warping, discoloration, and other aging defects

Testing Methods

High-Temperature Air Oven Aging

In the most widely used method, specimens are suspended in a forced-convection air-circulating oven with close temperature control, in accordance with ISO 188, ASTM D573, and GB/T 3512. The exposure temperature is selected based on the polymer type and intended service condition: for example, 70 °C to 100 °C for natural rubber and SBR, 100 °C to 150 °C for EPDM and NBR, and 200 °C to 300 °C for silicone and fluoroelastomer compounds. Typical exposure durations are 24 h, 48 h, 72 h, 96 h, 168 h, 336 h, or 1000 h. After conditioning to room temperature, tensile, hardness, and mass measurements are repeated, and the percentage change relative to unaged controls is calculated. For more severe acceleration, oxygen-pressure (bomb) aging per ASTM D572 may be applied.

Low-Temperature Exposure and Brittleness Testing

Low-temperature performance is evaluated by conditioning specimens in alcohol or silicone-oil baths, or in mechanically refrigerated chambers, at temperatures commonly ranging from -10 °C down to -70 °C. In the brittleness test per ISO 812, ASTM D2137, and GB/T 15256, conditioned strip specimens are struck by a traveling impact head at the specified temperature; the lowest temperature at which no specimen exhibits cracking is reported as the brittleness point. Alternatively, the temperature retraction (TR) test stretches a specimen, freezes it in the elongated state, and records the temperatures at which it retracts by 10 %, 30 %, 50 %, and 70 %, while the Gehman torsion test measures the modulus increase of a specimen as the temperature is lowered to identify the stiffening region.

High-Low Temperature Alternating (Thermal Cycling) Tests

Thermal cycling tests subject specimens or complete products to repeated transitions between temperature extremes, for example -40 °C to +85 °C or -40 °C to +125 °C, in a programmable environmental chamber per IEC 60068-2-14 and GB/T 2423.22. Each cycle typically includes a dwell period at each extreme and a controlled rate of temperature change, with test programs commonly specifying 5, 10, 50, 100, or 500 cycles depending on the product specification. This method reveals failure modes that single-temperature exposure cannot detect, such as fatigue cracking from differential thermal expansion, delamination of bonded interfaces, and loss of sealing force in gaskets and seals.

Evaluation and Lifetime Prediction

Test results are normally expressed as percentage retention or percentage change of each property after aging. Acceptance criteria are defined by the applicable material or product standard; a common requirement for rubber compounds, for example, is a tensile strength and elongation retention of at least 75 % to 80 %, with a hardness change within ±10 Shore A degrees. For lifetime prediction, aging is conducted at three or more elevated temperatures, the logarithm of the time to reach a defined failure criterion is plotted against reciprocal absolute temperature (Arrhenius plot), and the resulting linear relationship is extrapolated to the intended service temperature to estimate thermal endurance indices such as the Temperature Index (TI) per IEC 60216 or the Relative Temperature Index (RTI) per UL 746B.

Applications

High and low temperature aging testing supports material selection, design validation, batch quality control, and regulatory compliance in virtually every industry that relies on polymeric components:

• Automotive — underhood hoses, seals, mounts, belts, and interior parts must withstand continuous heat aging and winter cold without hardening or cracking
• Electronics and electrical engineering — potting compounds, connector seals, cable insulation, and encapsulants are qualified through thermal endurance and thermal cycling tests
• Wire and cable — jacket and insulation materials are assigned long-term thermal ratings through accelerated aging programs
• Aerospace — seals, gaskets, and composite matrix polymers are verified for performance across extreme altitude and temperature ranges
• Construction — window and door sealing profiles, waterproofing membranes, and expansion joints are evaluated for years of outdoor thermal exposure
• Medical devices — tubing, stoppers, and polymer housings are validated for stability after sterilization-level heat exposure and cold-chain storage
• Energy and battery systems — gaskets, insulators, and encapsulation materials for lithium-ion batteries and photovoltaic modules are tested for both high-temperature endurance and low-temperature flexibility

Manufacturers, design engineers, and supply-chain quality teams routinely submit materials to accredited third-party laboratories for these evaluations to demonstrate conformance with international standards and customer specifications.

FAQ

What temperature range is typically used for aging tests?

High-temperature aging of rubber is commonly performed between 70 °C and 300 °C depending on the polymer family, while plastic heat exposure typically ranges from 60 °C to 150 °C or higher for engineering grades. Low-temperature tests are usually carried out at -10 °C, -25 °C, -40 °C, -55 °C, or -70 °C, selected according to the intended service environment and product specification.

How long does a high or low temperature aging test take?

Standard exposure durations range from 24 hours to 1000 hours depending on the specification, with 72 h, 96 h, and 168 h being the most common durations for rubber oven aging. Full thermal endurance or lifetime prediction programs, which require multiple temperatures and long exposure periods, may take several weeks or months to complete.

How are test results judged as pass or fail?

Results are judged by comparing properties measured after aging with those of unaged reference specimens. Typical criteria include tensile strength and elongation retention of at least 75 % to 80 %, hardness change within ±10 Shore degrees, and a mass or dimensional change within the limit defined by the applicable material or product standard. For brittleness testing, the specimen must not crack when impacted at the specified low temperature.

Can aging tests predict real service life?

Yes. By aging specimens at several elevated temperatures and applying the Arrhenius extrapolation method described in IEC 60216 and UL 746B, the degradation rate at the actual operating temperature can be estimated, allowing prediction of the time required for a critical property to fall below its failure criterion. This approach underpins long-term thermal ratings such as the Temperature Index and Relative Temperature Index.

What specimens and quantities should be submitted?

For material characterization, standard tensile dumbbells, hardness blocks, and compression-set pellets are required, typically with a minimum of three to five specimens per condition plus unaged reference specimens. For finished products, complete parts in their final manufacturing state should be submitted, and the test laboratory can advise on the exact quantities needed to cover all exposure conditions and evaluation points.