Plastic Aging Coefficient Determination Test: Methods, Standards, and Applications

The plastic aging coefficient determination test quantitatively evaluates how plastic materials retain their mechanical and physical properties after exposure to heat, light, oxygen, and other environmental stressors. By comparing key performance indicators before and after accelerated aging, this experiment provides essential data for material qualification, service life prediction, and formulation optimization. This article explains the test principle, applicable standards, sample requirements, calculation methods, and typical industrial applications.

Technical Overview

Plastic aging refers to the gradual deterioration of polymer properties caused by thermal energy, ultraviolet radiation, oxygen, humidity, and mechanical stress acting individually or in combination. During aging, polymer chains undergo oxidation, chain scission, crosslinking, and additive migration, resulting in reduced tensile strength, embrittlement, discoloration, and surface cracking. The aging coefficient is a dimensionless ratio that expresses the degree of property retention after a defined aging period relative to the unaged condition.

The aging coefficient K is typically calculated using the following formula: K = (property value after aging) / (property value before aging) × 100%. Common reference properties include tensile strength, elongation at break, impact strength, and flexural strength. A coefficient of 1.00 (or 100%) indicates complete property retention, while values below the specified acceptance threshold—for example, 0.80 or 0.50 depending on the product standard—indicate unacceptable degradation. This experiment is widely used in quality control, comparative material selection, stabilizer evaluation, and accelerated service life estimation based on Arrhenius extrapolation.

Testing Samples

Thermoplastic Resins and Compounds

Granules or molded specimens of polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), ABS, polyamide (PA), polycarbonate (PC), polyethylene terephthalate (PET), and polyoxymethylene (POM) are conditioned and molded into standardized test pieces before aging exposure.

Thermosetting Plastics

Epoxy resins, phenolic molding compounds, unsaturated polyester, and polyurethane systems can be evaluated to assess their thermal-oxidative stability and post-curing effects during long-term service at elevated temperatures.

Elastomers and Thermoplastic Elastomers

Rubber-modified plastics, TPE, TPV, and other elastomeric materials are tested to determine retention of elongation and tensile properties, which are highly sensitive to oxidative crosslinking and chain scission.

Finished Plastic Products

Films, sheets, pipes, profiles, injection-molded components, cable insulation and sheathing compounds, geomembranes, and greenhouse films can be sampled directly or cut into specimens representing the actual product configuration.

Testing Items

• Tensile strength aging coefficient (retention rate after aging)
• Elongation at break aging coefficient
• Flexural strength and flexural modulus retention
• Izod and Charpy impact strength retention
• Hardness change (Shore A/D, Ball indentation)
• Mass change rate and mass loss during thermal aging
• Color difference (ΔE) and yellowing index after light exposure
• Dielectric strength and volume resistivity retention for electrical materials
• Oxidation induction time (OIT) for thermal stability assessment
• Melt flow rate change before and after aging

Testing Methods

Thermal Aging in Air Oven

Specimens are exposed to circulating hot air at controlled temperatures, typically ranging from 70 °C to 150 °C depending on the polymer type, following GB/T 7141 and ASTM D3045. Test durations are selected as multiples of 24 h, 48 h, 72 h, 96 h, 168 h, or longer periods such as 1000 h or 3000 h. After exposure, specimens are conditioned at 23 °C and 50% relative humidity per ISO 291 before mechanical testing.

Accelerated Weathering with Laboratory Light Sources

Xenon arc lamp exposure is performed per ISO 4892-2, ASTM G155, and GB/T 16422.2, while fluorescent UV condensation exposure follows ISO 4892-3, ASTM G154, and GB/T 16422.3. These methods simulate the combined effects of UV radiation, temperature, and moisture, and are particularly relevant for outdoor-use materials such as profiles, films, and coatings.

Natural Weathering Exposure

Direct outdoor exposure is conducted per ISO 877, ASTM D1435, and GB/T 3681 to obtain reference data for correlating accelerated laboratory results with real-world aging behavior over months or years.

Property Measurement and Calculation

Tensile testing is carried out per ISO 527, ASTM D638, and GB/T 1040 using dumbbell-shaped specimens. Impact testing follows ISO 179 and ASTM D256. For cable materials, thermal endurance evaluation is performed per IEC 60811 and IEC 60216. The aging coefficient is calculated as the ratio of the mean post-aging property value to the mean initial value, expressed as a percentage. At least five valid specimens per condition are tested, and results are reported with the aging temperature, duration, light source, and radiation dose.

Applications

• Service life assessment of wire and cable insulation and sheathing materials
• Qualification of automotive interior and exterior plastic components
• Durability verification of PVC window profiles, pipes, and fittings
• Anti-aging performance evaluation of agricultural and packaging films
• Effectiveness comparison of UV stabilizers, antioxidants, and carbon black masterbatches
• Long-term performance prediction using Arrhenius-based thermal endurance curves
• Incoming material inspection and batch consistency control in manufacturing
• Failure analysis of degraded or prematurely aged plastic products

FAQ

What is the formula for the plastic aging coefficient?

The aging coefficient K equals the measured property value after aging divided by the measured property value before aging, multiplied by 100%. For example, if the tensile strength decreases from 40 MPa to 32 MPa after thermal aging, the aging coefficient is 0.80, or 80% retention.

How is the test duration and temperature selected?

Selection depends on the polymer type and the intended service environment. A common practice is to test at the maximum continuous use temperature of the material plus one or two elevated increments, using multiple exposure periods to construct a degradation curve. Product standards frequently specify fixed conditions, such as 135 °C for 168 h for certain cable compounds.

What is the difference between thermal aging and weathering tests?

Thermal aging evaluates oxidative degradation under dry heat in an air oven, whereas weathering tests combine UV radiation, temperature cycling, and moisture using xenon arc or fluorescent UV lamps to simulate outdoor exposure conditions.

How many specimens are required?

Typically, at least five specimens are needed for each aging condition and for the unaged control group, ensuring statistical validity of the calculated coefficient.

Can aging coefficients be used to predict product lifetime?

Yes. By measuring the aging coefficient at several elevated temperatures and plotting the degradation rate against reciprocal absolute temperature, an Arrhenius extrapolation can estimate the time to reach a critical property threshold at the actual service temperature, as described in IEC 60216 thermal endurance procedures.