High-temperature aging performance testing evaluates how plastic materials degrade under sustained thermal exposure, providing critical data on mechanical property retention, thermal endurance, and long-term service life. This technical guide covers test sample types, evaluation parameters, standard testing methods based on ISO, ASTM, IEC, UL, and GB standards, and typical industrial applications, supporting material selection, qualification, and quality control.
Technical Overview
High-temperature aging performance testing (also referred to as thermal aging or heat aging testing) is a laboratory procedure used to assess the ability of plastic materials to withstand prolonged exposure to elevated temperatures. When plastics are subjected to heat over extended periods, thermo-oxidative degradation mechanisms such as chain scission, crosslinking, oxidation of polymer backbones, depletion of antioxidants, post-crystallization, and volatilization or migration of plasticizers and additives cause progressive deterioration of physical, mechanical, and electrical properties.
The primary objectives of high-temperature aging testing include:
- Quantifying the retention rate of key properties (such as tensile strength and elongation at break) after defined thermal exposure periods
- Determining thermal endurance characteristics, including the Temperature Index (TI) per IEC 60216 or the Relative Thermal Index (RTI) per UL 746B
- Establishing time-temperature limits and extrapolating long-term service life using Arrhenius-based acceleration models
- Comparing candidate materials, validating formulations, and qualifying plastics for specific high-temperature applications
- Supporting compliance with industry specifications and regulatory requirements
Because real-time aging at service temperatures may take years, accelerated aging is performed in forced-ventilation air ovens at temperatures well above the intended service temperature. The resulting degradation data are then mathematically extrapolated to predict performance over the actual product lifespan.
Testing Samples
A wide range of plastic materials and product forms can be evaluated through high-temperature aging programs at accredited third-party laboratories. Samples are typically prepared as injection-molded or compression-molded test specimens in accordance with the relevant material standards.
General-Purpose Thermoplastics
Commodity resins such as polypropylene (PP), polyethylene (PE), polystyrene (PS), ABS, polyvinyl chloride (PVC), and polymethyl methacrylate (PMMA) are commonly tested, particularly for consumer goods, packaging, and appliance applications where moderate heat exposure occurs.
Engineering Thermoplastics
Materials including polyamide (PA6, PA66), polycarbonate (PC), polyoxymethylene (POM), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), modified polyphenylene ether (PPE/PPO), and thermoplastic polyurethane (TPU) are evaluated for structural and electrical applications involving sustained thermal loading.
High-Performance and Specialty Plastics
Polymers such as polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyetherimide (PEI), polyimide (PI), liquid crystal polymer (LCP), and polytetrafluoroethylene (PTFE) are tested for demanding environments in automotive under-hood, aerospace, and high-end electronics applications.
Thermosetting Materials
Epoxy resins (EP), unsaturated polyesters (UP), phenol-formaldehyde resins (PF), and melamine-formaldehyde resins (MF), including laminates and molding compounds, are assessed for thermal endurance in electrical insulation systems.
Finished and Semi-Finished Products
In addition to standardized specimens, testing can be performed on end products such as wire and cable insulation, electrical connectors and housings, automotive interior and under-hood components, plastic pipes and fittings, films, sheets, and injection-molded parts.
Testing Items
High-temperature aging programs evaluate multiple performance parameters before and after thermal exposure to calculate retention rates and identify degradation trends. Core testing items include:
- Tensile strength and elongation at break (ISO 527, ASTM D638, GB/T 1040)
- Flexural strength and flexural modulus (ISO 178, ASTM D790, GB/T 9341)
- Izod and Charpy impact strength (ISO 180, ISO 179, ASTM D256, GB/T 1043)
- Hardness (Shore hardness per ISO 868, ball indentation hardness per ISO 2039)
- Mass change and weight loss resulting from volatilization of additives
- Color change (Delta E) and yellowing index (ASTM E313, ISO 11664)
- Melt mass-flow rate change (ISO 1133, ASTM D1238, GB/T 3682)
- Heat deflection temperature (HDT) under load (ISO 75-1 and ISO 75-2, ASTM D648, GB/T 1634)
- Vicat softening temperature (ISO 306, ASTM D1525, GB/T 8802)
- Dimensional stability and warpage after heat exposure
- Electrical properties, including dielectric strength, volume resistivity, and surface resistivity (IEC 60243, IEC 62631, GB/T 1408, GB/T 1410)
- Oxidation induction time (OIT) by differential scanning calorimetry (ISO 11357-6)
- Thermal stability by thermogravimetric analysis (TGA) (ISO 11358, ASTM E1131)
The typical acceptance criterion is the retention of at least 50 percent of the initial value of a critical property, although specific product specifications may define alternative thresholds.
Testing Methods
Air Oven Thermal Aging
The most widely applied method is accelerated aging in a forced-ventilation air oven, performed in accordance with standards such as ISO 188, ASTM D3045 (Practice for Heat Aging of Plastics Without Load), ASTM D573, GB/T 7141, and GB/T 3512. Test specimens are exposed to controlled elevated temperatures, commonly ranging from 70 °C to 300 °C depending on the polymer type, with exposure durations from 168 hours up to several thousand hours. Specimens are removed at predetermined intervals, reconditioned per ISO 291 (23 °C / 50 percent relative humidity), and tested to construct property retention curves versus aging time.
Determination of Time-Temperature Limits
ISO 2578 and GB/T 7142 describe procedures for determining time-temperature limits after prolonged exposure to heat. Specimens are aged at a minimum of three or four temperatures, the time to reach the failure criterion is recorded at each temperature, and an Arrhenius plot is constructed to extrapolate the maximum temperature at which the material retains acceptable performance over the required service life.
Thermal Endurance Evaluation for Electrical Insulation
The IEC 60216 series and the corresponding GB/T 11026 standards specify methods for evaluating the thermal endurance of electrical insulating materials. Aging is conducted at multiple elevated temperatures, end-point criteria are defined for relevant properties, and the results yield the Temperature Index (TI) and the temperature corresponding to a half-life of a specified property in hours.
Relative Thermal Index Evaluation
UL 746B defines the long-term thermal aging program used to assign the Relative Thermal Index (RTI) to polymeric materials. Testing involves long-term oven aging, typically 5,000 hours or more, at multiple temperatures, with mechanical and electrical properties monitored until the 50 percent retention criterion is reached.
Short-Term Thermal Characterization
In support of aging studies, short-term techniques such as DSC (ISO 11357) for glass transition, melting behavior, and oxidation induction time, TGA for decomposition onset, and HDT/Vicat softening measurements are used to characterize baseline thermal performance and assist in selecting appropriate aging temperatures.
General Test Procedure
- Specimen preparation and marking in accordance with the applicable material or product standard
- Initial conditioning and baseline testing of all measured properties
- Oven exposure at the selected aging temperature with controlled air exchange rate
- Periodic specimen withdrawal at defined checkpoints (for example, 168 h, 336 h, 500 h, 1000 h, 2000 h, 3000 h)
- Reconditioning and post-aging testing of mechanical, physical, appearance, and electrical properties
- Calculation of property retention rates and generation of aging curves
- Arrhenius analysis and reporting of thermal endurance indices or predicted service life where required
Applications
High-temperature aging test data are essential across numerous industries in which plastics experience sustained or cyclic thermal stress:
- Automotive: under-hood components, connectors, sensors, air ducts, lighting housings, battery module components, and interior trim exposed to solar and cabin heat
- Electrical and electronics: wire and cable insulation, plugs and sockets, relays, transformer bobbins, PCB laminates, connector housings, and enclosures requiring long-term electrical insulation reliability
- Home appliances and consumer goods: housings, internal supports, kettle and coffee machine components, and cookware handles in contact with heat sources
- Building and construction: hot-water pipes (PP-R, PE-RT), cable conduits, wall coverings, and window profiles subjected to elevated ambient temperatures
- Aerospace and rail: cabin interior materials, ducting, structural composite matrices, and insulation components requiring verified thermal endurance
- Medical devices: components that must withstand repeated steam sterilization or elevated-temperature service conditions
- Material research and development: formulation screening, stabilizer package optimization, and comparative benchmarking of competitive resin grades
FAQ
What aging temperatures and durations are typically used?
The aging temperature is selected based on the polymer type and the intended service conditions, generally 10 °C to 40 °C above the maximum continuous use temperature, with common test points between 70 °C and 300 °C. Screening tests may run 168 to 1000 hours, while full thermal endurance programs such as those following IEC 60216 or UL 746B may require 5,000 hours or longer per temperature point.
What is the difference between heat deflection temperature and high-temperature aging testing?
Heat deflection temperature (HDT per ISO 75 or ASTM D648) is a short-term measurement of deformation resistance under load and does not reflect long-term chemical degradation. High-temperature aging testing evaluates progressive property deterioration over extended exposure and is the appropriate method for assessing long-term thermal endurance and service life.
How is long-term service life predicted from accelerated aging data?
By aging specimens at several elevated temperatures and recording the time to reach a defined failure criterion, an Arrhenius relationship between the logarithm of aging time and the reciprocal of absolute temperature is established. This model allows extrapolation of the expected lifetime at the actual service temperature, subject to the assumptions of a consistent degradation mechanism across the temperature range.
Which standards govern plastic high-temperature aging testing?
Key standards include ISO 188, ISO 2578, ISO 11357, ASTM D3045, ASTM D573, ASTM D638, IEC 60216, UL 746B, GB/T 7141, GB/T 3512, GB/T 11026, and GB/T 1040, along with material-specific and product-specific specifications.
What sample quantities are required for a testing program?
Requirements vary with the number of aging temperatures, checkpoints, and properties measured. As a general guideline, each temperature and time point requires a statistically valid set of specimens for every property evaluated, plus baseline specimens; accredited third-party laboratories can provide detailed specimen matrices during test plan development.
Why does elongation at break often decrease faster than tensile strength during aging?
Elongation at break is highly sensitive to embrittlement caused by chain scission, oxidation, and changes in crystallinity, and it typically serves as one of the most sensitive indicators of thermal degradation. For this reason, elongation retention is frequently selected as the failure criterion in thermal endurance evaluations.