Determination of Aging Resistance of Plastics: Test Methods, Standards, and Evaluation

Aging resistance testing determines how plastic materials withstand ultraviolet radiation, heat, oxygen, and moisture over their intended service life. By combining accelerated weathering technologies such as xenon arc and UV fluorescent exposure with standardized property measurements, manufacturers can predict long-term durability, optimize stabilization formulations, and qualify products against ISO, ASTM, IEC, GB, UL, and JIS requirements. This article explains the degradation mechanisms, sample requirements, test items, methods, and typical applications involved in the determination of plastic aging resistance.

Technical Overview

Plastic aging is the irreversible deterioration of polymer structure and performance caused by environmental factors such as ultraviolet (UV) radiation, temperature, oxygen, humidity, and chemical media. Degradation proceeds mainly through photo-oxidation and thermo-oxidation: incident UV photons break polymer chains to form free radicals, which react with oxygen to generate peroxy and hydroperoxide species that propagate further chain scission and crosslinking.

Macroscopically, aging manifests as surface chalking, discoloration, yellowing, gloss loss, micro-cracking, blistering, embrittlement, and a measurable decline in tensile strength, elongation, impact toughness, and electrical insulating performance. Because natural degradation may take years to develop, laboratory determination of aging resistance relies on accelerated methods that intensify the dominant degradation factors while preserving mechanistic similarity to real-world exposure. Results are expressed as property retention rates, visual rating grades, and colorimetric changes referenced to unexposed control specimens.

Why Aging Resistance Determination Matters

Systematic aging evaluation supports raw material qualification, formulation development of UV absorbers, hindered amine light stabilizers (HALS), and antioxidants, incoming quality control, regulatory compliance, warranty substantiation, and service-life prediction. Accredited third-party laboratories routinely perform these determinations to provide objective, standards-based evidence of long-term durability.

Testing Samples

Commodity Thermoplastics

Polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polystyrene (PS) materials are typically processed into standardized test pieces such as ISO 3167 multipurpose specimens or ASTM D638 Type I dumbbells, ensuring that mechanical testing before and after exposure is directly comparable.

Engineering and High-Performance Plastics

ABS, polycarbonate (PC), polyamide (PA6, PA66), polyoxymethylene (POM), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU), modified polyphenylene oxide, and fluoropolymers are tested in both unfilled and glass-fiber-reinforced, pigmented, or stabilized grades, since additives significantly influence aging behavior.

Fabricated Products and Components

Pipes and fittings, window and door profiles, films and sheets, geomembranes, cable insulation and sheaths, automotive trim parts, photovoltaic backsheets, and electrical enclosures can be exposed as finished items and subsequently assessed. Specimens should be conditioned at 23°C and 50% relative humidity per ISO 291 or ASTM D618 before baseline measurement, and a sufficient number of replicates, typically five or more per exposure interval, should be prepared together with dark controls.

Testing Items

The core of aging resistance determination is the comparison of key properties before and after exposure. Commonly measured parameters include:

• Mechanical property retention: tensile strength and elongation at break (ISO 527, ASTM D638), flexural strength (ISO 178, ASTM D790), and Charpy or Izod impact strength (ISO 179, ISO 180, ASTM D256)
• Appearance and surface quality: color difference (ASTM D2244, ISO 7724), yellowness index (ASTM E313), gloss retention (ASTM D523, ISO 2813), and visual ratings for cracking, blistering, and chalking per ISO 4628
• Microstructural and chemical changes: carbonyl index and hydroxyl index by FTIR spectroscopy, molecular weight distribution by gel permeation chromatography (GPC), oxidation induction time (OIT) by DSC (ISO 11357-6, ASTM D3895)
• Processing and rheological behavior: melt mass-flow rate change (ISO 1133, ASTM D1238)
• Thermal endurance: temperature index per IEC 60216 and relative temperature index per UL 746B for long-term heat ratings
• Physical and dimensional stability: mass change, dimensional change, and water absorption (ISO 62, ASTM D570)
• Electrical properties for insulating applications: dielectric strength and volume resistivity per IEC 60243 and IEC 60093

Property retention is calculated as the aged value divided by the initial value multiplied by 100 percent. Many specifications define failure as a retention below 50 percent for tensile strength or elongation at break, or as a defined color change limit.

Testing Methods

Xenon Arc Lamp Weathering

Governed by ISO 4892-2, ASTM G155, ASTM D2565, GB/T 16422.2, and JIS B 7753, xenon arc exposure with daylight or window-glass filters reproduces the full solar spectrum most faithfully. Typical conditions use an irradiance of 0.35 W/(m²·nm) at 340 nm, a black standard temperature of 63°C to 65°C, and a cycle such as 102 minutes of light followed by 18 minutes of light with water spray. Total exposure is quantified as radiant exposure in kJ/m² per ISO 9370, making xenon testing the preferred method for colorfastness and comprehensive durability evaluation.

UV Fluorescent Lamp Weathering

Specified in ISO 4892-3, ASTM G154, ASTM D4329, and GB/T 16422.3, this method uses UVA-340 lamps that closely simulate the critical short-wavelength region of sunlight, or more aggressive UVB-313 lamps for rapid screening. A standard cycle consists of 8 hours of UV at 60°C black panel temperature followed by 4 hours of condensation at 50°C. The condensation phase realistically reproduces dew damage, and the method is economical, fast, and particularly effective at reproducing the physical degradation of polymers outdoors.

Carbon Arc Lamp Weathering

Covered by ISO 4892-4, ASTM G152, and GB/T 16422.4, enclosed and open-flame carbon arc devices remain referenced in certain legacy and JIS-based specifications, although their spectral mismatch with sunlight means xenon arc testing has largely replaced this technique.

Thermal Oxidative Aging (Air Oven Aging)

Per ASTM D3045, ISO 2578, GB/T 7141, and the IEC 60216 series, specimens are held in forced-ventilation ovens at several elevated temperatures for extended periods. Time-to-criterion data at each temperature are extrapolated using the Arrhenius relationship to determine the temperature index or relative temperature index, forming the basis of the long-term thermal ratings required under UL 746B for electrical applications.

Damp Heat and Hydrolytic Aging

Constant humidity exposure, for example 85°C and 85% relative humidity per IEC 60068-2-78 or the procedures of ASTM D2126, evaluates plasticization, hydrolytic chain scission, blistering, and dimensional change. This method is essential for hydrolysis-sensitive polymers such as PC, PET, PBT, and PA, as well as for fiber-reinforced composites and photovoltaic materials.

Ozone Aging

Although primarily applied to rubbers under ISO 1431, ozone exposure is relevant to plastics modified with unsaturated elastomers, such as impact-modified PP, TPO, and ABS, where ozone cracking under static or dynamic strain is assessed.

Natural Outdoor Weathering

Direct exposure, exposure behind glass, and concentrated sunlight tracking are specified in ISO 877, ASTM D1435, ASTM G7, and GB/T 3681. Specimens mounted at defined angles in representative climates such as humid subtropical, dry desert, or coastal environments serve as the benchmark for validating the correlation between accelerated laboratory results and real-world service life.

Interpretation and Correlation

Best practice combines accelerated testing with natural exposure: by comparing the radiant exposure or aging time required to reach the same degradation endpoint, a material-specific acceleration factor is derived, enabling service-life prediction with documented confidence.

Applications

• Automotive: exterior body cladding, bumpers, and interior trim require xenon weathering with window-glass filters and heat aging to demonstrate color and mechanical durability
• Building and construction: window profiles, roofing membranes, pipes, fittings, wood-plastic composites, and geomembranes are qualified against multi-year outdoor exposure requirements
• Agriculture: greenhouse and mulch films are evaluated for retained light transmission, tensile strength, and elongation after defined cultivation seasons
• Photovoltaics: backsheets, encapsulants, and junction boxes undergo damp heat, UV, and thermal cycling to verify a design life exceeding twenty years
• Wire and cable: insulation and sheath compounds are tested through thermal endurance programs per IEC 60216 and UL 746B to establish continuous operating temperature ratings
• Electronics and appliances: enclosures and connectors are assessed for yellowing, embrittlement, and retention of dielectric properties
• Consumer and outdoor goods: furniture, sporting equipment, and textiles verify UV stability and appearance retention under accelerated and natural weathering

FAQ

What is the difference between xenon arc and UV fluorescent weathering?

Xenon arc radiation matches the full solar spectrum including visible light, which is necessary for accurate colorfastness evaluation, while UV fluorescent lamps concentrate on the damaging ultraviolet band and use condensation to replicate dew, making them faster and more economical for screening physical degradation. The choice depends on the failure mode of interest and the governing product specification.

How long does an accelerated aging test take?

Screening exposures often run from several hundred to a few thousand hours, for example 500 to 2000 hours of xenon or UV exposure, while thermal endurance programs per IEC 60216 and UL 746B may require thousands to tens of thousands of hours to support extrapolated long-term ratings.

Can accelerated results predict outdoor service life?

Yes, when a correlation is established. By comparing the radiant exposure needed to reach the same degradation endpoint in the laboratory and at an outdoor benchmark site, a material-specific acceleration factor is calculated. Without such correlation, accelerated data should be treated as comparative rather than absolute lifetime predictions.

How many specimens are required?

Typically at least five replicate specimens are tested per exposure interval together with unexposed baseline specimens and dark controls. The total quantity depends on the number of exposure points and the properties to be measured, and accredited third-party laboratories can advise on the most efficient test plan.

Which standard should be selected for a specific product?

Selection follows the end-use environment and the applicable product specification: daylight-filtered xenon testing suits outdoor products, window-glass-filtered xenon suits automotive interiors, UV fluorescent testing suits screening and film products, and thermal endurance programs per IEC 60216, UL 746B, or GB standards apply to electrical and long-term heat-rated applications.