Aging testing of chemical raw materials is a critical durability evaluation process that uses accelerated thermal, photo-oxidative, ozone, and humidity exposure to predict how polymers, rubbers, resins, and additives will perform over their intended service life. By compressing years of environmental degradation into weeks or months of laboratory exposure, manufacturers can verify formulation stability, screen stabilizer packages, and qualify material suppliers in accordance with ISO, IEC, ASTM, EN, GB, UL, and JIS standards. This article explains the technical principles, testing samples, testing items, testing methods, and typical applications of chemical raw material aging testing.
Technical Overview
Aging testing refers to the systematic exposure of chemical raw materials to intensified environmental conditions—heat, ultraviolet radiation, oxygen, ozone, and moisture—in order to induce and measure the irreversible degradation processes that occur during real-world storage and service. Polymer-based raw materials such as resins, elastomers, adhesives, and compounded intermediates deteriorate through molecular-level mechanisms including chain scission, oxidative crosslinking, hydrolysis, and additive migration. The macroscopic consequences of these mechanisms include discoloration, surface cracking, embrittlement, loss of tensile strength, reduced elongation, and declining electrical insulation performance.
Accelerated aging reproduces degradation that may require several years of outdoor or in-service exposure within a compressed laboratory timeframe, typically ranging from 72 hours to several thousand hours. Test results are expressed as retention rates—the ratio of a property measured after exposure to the same property measured on unaged control specimens—and are used for formulation benchmarking, incoming quality control, and service life estimation. Accredited third-party laboratories and in-house quality departments routinely perform these evaluations under ISO/IEC 17025 quality management conditions.
The principal degradation mechanisms targeted by aging tests include:
- Thermo-oxidative degradation: autocatalytic oxidation of polymer chains at elevated temperature, softened by antioxidant additives.
- Photo-oxidation: UV-initiated radical reactions producing carbonyl groups, yellowing, and chalking.
- Hydrolysis: chain cleavage of ester, amide, or urethane linkages under combined heat and humidity, particularly relevant for polyesters, polyamides, and polyurethanes.
- Ozone cracking: attack of ozone on unsaturated polymer double bonds under tensile strain, critical for natural rubber and other diene elastomers.
- Additive depletion: volatilization, migration, or extraction of plasticizers, stabilizers, and light absorbers.
Testing Samples
Polymer Resins and Plastic Granules
Thermoplastic raw materials such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), polyamide (PA), polycarbonate (PC), polyethylene terephthalate (PET), polyoxymethylene (POM), and thermoplastic polyurethane (TPU) are typically converted into compression- or injection-molded plaques, standard dumbbell specimens, or thin films before exposure. Film samples of 0.5 mm to 1 mm thickness are preferred for light-exposure tests because UV penetration is limited.
Rubbers and Elastomeric Compounds
Vulcanized compounds based on natural rubber (NR), styrene-butadiene rubber (SBR), nitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM), chloroprene rubber (CR), silicone rubber (VMQ), and fluoroelastomers (FKM) are prepared as cured sheets from which tensile dumbbells and ozone test strips are die-cut. Unvulcanized masterbatch may also be evaluated for scorch safety and storage stability.
Adhesives, Sealants, and Coating Raw Materials
Epoxy resins, polyurethane prepolymers, acrylic emulsions, alkyd binders, and silicone sealant bases are cast into free films or applied to standard substrates and cured before aging, so that bond strength retention, color stability, and elongation can be measured after exposure.
Additives, Masterbatches, and Intermediate Materials
Antioxidants, hindered amine light stabilizers (HALS), UV absorbers, pigments, plasticizers, and filler concentrates are usually evaluated within a defined carrier-resin letdown or a model formulation, so that the effectiveness of the stabilization package can be quantified under identical exposure conditions.
All specimens are conditioned at 23 °C and 50% relative humidity in accordance with ISO 291 before baseline measurement, and parallel control specimens are stored in darkness at ambient conditions for comparison after each exposure interval.
Testing Items
The core of any aging evaluation is the comparison of selected properties before and after exposure. Commonly measured testing items include:
- Tensile strength and elongation at break retention, per ISO 527 and ASTM D638 for plastics and ISO 37 and ASTM D412 for rubbers.
- Flexural strength and impact strength retention for rigid engineering materials.
- Color difference (Delta E), yellowness index, and gloss retention, per ASTM E313 and ISO 4582.
- Hardness change, expressed in Shore A, Shore D, or IRHD units.
- Mass change and dimensional change, indicating plasticizer loss or moisture uptake.
- Melt flow rate shift, per ISO 1133 and ASTM D1238, revealing molecular degradation or crosslinking during processing-related aging.
- Oxidation induction time (OIT), per ISO 11357-6, ASTM D3895, and ASTM D6186, quantifying remaining oxidative stability.
- Carbonyl index by FTIR spectroscopy and molecular weight distribution by gel permeation chromatography (GPC) for mechanistic analysis.
- Dielectric strength and volume or surface resistivity, per IEC 60243 and IEC 62631, for insulation-grade raw materials.
- Visual defect rating of cracking, crazing, blistering, chalking, and warpage on exposed surfaces.
Acceptance criteria are usually defined as a minimum retention percentage; many industry specifications require tensile strength and elongation retention of at least 50% to 80% after the specified exposure period.
Testing Methods
Thermal Air Aging (Hot Air Oven)
Specimens are held in a forced-ventilation oven at constant temperatures, commonly between 70 °C and 150 °C, for periods from 72 hours to 3000 hours or longer. Principal standards include ISO 188, ASTM D573, ASTM D3045, GB/T 3512, GB/T 7141, and JIS K 6257. Multi-temperature programs form the basis for temperature index determination and long-term thermal endurance assessment.
Xenon Arc Lamp Weathering
Xenon arc chambers equipped with daylight filters provide the closest laboratory reproduction of full-spectrum solar radiation and are used with cyclic light, dark, humidity, and water-spray phases. Governing standards include ISO 4892-2, ASTM G155, ASTM D2565, GB/T 16422.2, and the general guidance of ASTM G151 and ISO 4892-1. Xenon testing is the preferred method when color and appearance stability must be evaluated.
Fluorescent UV Lamp Weathering
Fluorescent UVA-340 or UVB-313 lamps combined with condensation cycles offer an economical screening method focused on the UV portion of the spectrum and on moisture-driven degradation, per ISO 4892-3, ASTM G154, and GB/T 16422.3.
Ozone Aging
Elastomer specimens are stretched to defined static or dynamic strain levels and exposed to controlled ozone concentrations, typically 50 pphm, at 40 °C. Cracking is rated visually or by time-to-first-crack. Standards include ISO 1431, ASTM D1149, GB/T 7762, and GB/T 13642.
Damp Heat (Humidity) Aging
Combined temperature and humidity exposure, for example 85 °C and 85% relative humidity or 40 °C and 95% relative humidity, evaluates hydrolytic stability and moisture sensitivity in accordance with ISO 4611, GB/T 12000, and related EN test procedures for construction products.
Natural Weathering
Direct outdoor exposure at benchmark climates, or exposure behind glass for interior environments, provides reference data for correlating accelerated results. Relevant standards include ISO 4607, ISO 877, ASTM D1435, ASTM G7, GB/T 3681, and GB/T 3511.
Lifetime Prediction and Thermal Endurance Rating
By applying the Arrhenius relationship to multi-temperature aging data, laboratories derive temperature indices, relative thermal endurance ratings under UL 746B, and extrapolated half-life values for electrical insulating materials under the IEC 60216 series and for plastics under ISO 2578.
Applications
Aging test data for chemical raw materials directly support product reliability and regulatory compliance across a wide range of industries:
- Automotive: qualification of interior and exterior polymer compounds, sealing profiles, hoses, and gaskets against heat and light exposure requirements.
- Wire and cable: verification of insulation and jacketing compound thermal classes for long-term rated operation.
- Construction: durability assessment of PVC profiles, pipes, waterproofing membranes, sealants, and coatings against outdoor weathering.
- Packaging: film stability, migration resistance, and mechanical integrity over extended storage periods.
- Electronics: evaluation of potting compounds, encapsulants, and laminate materials under damp heat and thermal cycling conditions.
- Coatings and paints: binder chalk resistance, gloss retention, and color fastness qualification.
- Research and supply chain management: comparative screening of stabilizer systems, benchmarking of competing suppliers, incoming raw material inspection, and change validation during reformulation.
FAQ
How long does an aging test take?
Accelerated thermal aging typically runs from 72 hours to 3000 hours depending on the material class and specification, xenon arc weathering commonly covers 500 to 3000 hours, ozone aging is often completed within 72 to 168 hours, and natural weathering benchmarks generally require one to three years of exposure. Test duration is selected according to the referenced standard and the intended service environment of the raw material.
Should xenon arc or fluorescent UV weathering be chosen?
Xenon arc testing is recommended when full-spectrum fidelity and color or appearance stability are decisive, while fluorescent UV testing with condensation is better suited for screening UV sensitivity and moisture-driven degradation at lower cost. Many specifications require correlation with natural weathering regardless of the chosen laboratory light source.
How is property retention calculated?
Retention is calculated as the measured property value after aging divided by the corresponding value before aging, multiplied by 100%. For example, a compound retaining 85% of its original elongation at break after 1000 hours of thermal aging at 100 °C is reported as 85% elongation retention.
What specimens are required for testing?
Most standards require at least five dumbbell or plaque specimens per exposure interval plus unaged control specimens, prepared from the same batch under identical molding conditions. Specific dimensions follow the tensile or impact standard referenced by the applicable aging method, and thin films are generally required for light-exposure testing.
Can accelerated aging predict real service life?
Accelerated aging provides reliable comparative rankings and, when combined with multi-temperature Arrhenius analysis under frameworks such as IEC 60216 and ISO 2578, supports quantitative lifetime extrapolation. However, predicted service life should always be validated against natural exposure data and the specific geometry, stress, and environment of the final application.