Plastic Ozone Aging Test Determination: Standards, Methods, and Evaluation Criteria

Plastic ozone aging test determination is an accelerated weathering procedure used to evaluate the resistance of plastic and elastomeric materials to ozone-induced surface cracking and degradation. By exposing specimens to controlled ozone concentrations, elevated temperatures, and defined strain conditions in accordance with standards such as ISO 1431, ASTM D1149, and GB/T 7762, manufacturers can predict long-term service performance and validate material formulations. This article explains the testing principle, sample requirements, test parameters, procedures, and typical applications of ozone aging determination for plastics.

Technical Overview

Ozone (O3) is a highly reactive gaseous allotrope of oxygen that occurs naturally in the atmosphere at trace concentrations, often reaching higher levels in urban, indoor, and indoor-electrical environments. Even at concentrations as low as a few parts per hundred million (pphm), ozone aggressively attacks polymer chains containing unsaturated carbon-carbon double bonds. For plastic products that operate under tensile stress, this chemical attack manifests as characteristic surface cracks that can propagate rapidly and cause premature product failure. Ozone aging test determination therefore serves as a key accelerated durability test for qualifying plastic and elastomeric materials used outdoors or in ozone-generating environments.

Degradation Mechanism

Ozone reacts directly with double bonds on the polymer surface to form ozonide intermediates that undergo chain scission, producing a brittle, oxidized surface layer. When the material is stretched even slightly, microcracks initiate at surface defects and grow perpendicular to the direction of strain. Unlike thermal-oxidative aging, ozone cracking is essentially a surface phenomenon: the interior of the material remains largely unaffected until cracks penetrate deeply. This is why ozone aging is typically evaluated on strained specimens rather than unstrained ones.

Why Plastics Are Tested

Fully saturated polymers such as polyethylene (PE), polypropylene (PP), and polyamide (PA) are intrinsically resistant to ozone. However, many technically important plastic materials contain unsaturated or elastomeric phases and are therefore susceptible, including thermoplastic elastomers (TPE, TPV), styrenic block copolymers (SBS, SEBS), rubber-toughened plastics such as ABS and high-impact polystyrene, plasticized PVC compounds, and polymer blends modified with unsaturated rubbers. Ozone aging tests verify whether antiozonant packages and protective wax formulations in these materials provide adequate protection, and they support material selection, batch release, and product certification by accredited third-party laboratories.

Testing Samples

Standard Laboratory Specimens

The most common sample forms are dumbbell-shaped tensile specimens prepared according to ISO 37 or ASTM D412, which allow both ozone exposure and post-aging tensile testing on the same geometry. Rectangular strips, typically 10 mm to 25 mm wide and 2 mm thick, are also widely used; these are mounted on sample holders that impose a fixed elongation during exposure. Test pieces should be conditioned at 23 °C ± 2 °C and 50% ± 5% relative humidity for at least 16 hours prior to testing, and testing is normally performed no sooner than 16 hours and no later than 4 weeks after molding.

Material Forms and Compounds

• Thermoplastic elastomer compounds (TPE-S, TPO, TPV) in pellet, sheet, or molded plaque form
• Styrenic block copolymer formulations (SBS, SEBS, SIS) used in compounding and adhesives
• Rubber-modified plastics such as ABS and HIPS
• Plasticized PVC and PVC/elastomer blends for flexible applications
• Compression-molded or injection-molded sheets from raw compound

Finished Components

Complete parts may be tested directly, either in the as-received state or mounted in a fixture that applies strain representative of service conditions. Typical component samples include automotive weather strips and gaskets, wire and cable sheathing, hoses, bellows, sealing profiles, and footwear components. Triangular cross-section specimens wrapped around a mandrel, as described in ASTM D1171, are used for certain rubber-like compounds to concentrate stress and accelerate crack initiation.

Testing Items

Ozone aging determination is defined by a set of controlled exposure parameters and corresponding evaluation endpoints. The principal parameters are:

• Ozone concentration: commonly 50 ± 5 pphm (parts per hundred million, equivalent to approximately 0.5 ppm by volume); extended levels of 25, 100, 200, or 500 pphm may be specified for more severe testing
• Test temperature: typically 40 °C ± 2 °C, with 23 °C and 50 °C as alternative setpoints
• Relative humidity: usually 55% ± 10%, or dry air where specified
• Static strain: specimen elongation of 5%, 10%, 15%, or 20%, with 20% being the most common reference condition
• Dynamic strain: cyclic elongation at a frequency of approximately 0.5 Hz between specified strain limits
• Exposure duration: 24, 48, 72, 96, or 168 hours, or longer periods agreed between parties
• Air flow rate and chamber air exchange, which affect ozone uniformity and depletion around specimens

The evaluation items determined after exposure include time to first visible crack, crack density and crack length ratings, tensile strength retention, elongation at break retention, hardness change, and surface appearance changes such as discoloration, blooming, or tackiness.

Testing Methods

Static Ozone Exposure Method

The static method is specified in ISO 1431-1, ASTM D1149, and GB/T 7762. Specimens are clamped onto wooden, stainless steel, or aluminum holders at the chosen elongation and placed in an ozone test chamber. Ozone is generated on demand by a silent electrical discharge or ultraviolet ozone generator fed with purified air, and the chamber concentration is continuously monitored using an ultraviolet photometric ozone analyzer. After the chamber stabilizes at the target concentration and temperature, timed exposure begins. At each inspection interval, specimens are briefly removed and examined under 2x to 7x magnification in a well-lit area, and any cracks are recorded. A frequent automotive acceptance criterion is no visible cracking at 2x magnification after 72 hours at 50 pphm, 40 °C, and 20% elongation.

Dynamic Ozone Exposure Method

The dynamic method, covered by ISO 1431-2 and GB/T 13642, subjects specimens to cyclic tensile strain during ozone exposure, simulating flexing or reciprocating service. Specimens are gripped in a motorized fixture that alternates between a low strain and a specified maximum strain at approximately 0.5 Hz. Dynamic exposure is more severe than static exposure because the repeated strain refreshes the crack tip and accelerates crack initiation and growth, making it suitable for components such as flexible boots, bellows, and movable seals.

Typical Test Procedure

• Prepare and condition specimens; verify dimensions and record initial tensile properties where required
• Mount specimens on holders at the specified elongation without contaminating the test surface
• Stabilize the chamber at the set temperature, humidity, and ozone concentration
• Expose specimens for the defined duration, performing interim visual inspections without removing surface oxide by wiping
• Conduct final visual grading under magnification, followed by tensile testing of selected specimens
• Calculate property retention values and report results against the acceptance criteria

Evaluation Criteria

Visual results are typically graded on a scale from zero (no cracks) to severe (numerous large cracks), based on crack number and size observed at defined magnification. Quantitative results are expressed as retention percentages, calculated as the measured value after aging divided by the initial value multiplied by 100. A material is commonly considered acceptable when no cracks are observed under the specified magnification after the specified exposure, and tensile strength and elongation at break retention remain above the agreed threshold, for example 80%.

Applications

Ozone aging test determination is applied across industries where plastic and elastomeric components face atmospheric ozone, flexing, or both. Typical application areas include:

• Automotive engineering: qualification of weather strips, door and window seals, gaskets, underhood components, and air ducts against OEM material specifications
• Wire and cable: evaluation of insulation and sheathing compounds for outdoor, mining, and transit cable systems
• Construction: durability assessment of window and door profiles, expansion joints, and waterproofing membranes
• Footwear and consumer goods: validation of TPE soles, straps, and flexible plastic parts
• Research and development: screening of antiozonant chemistries, protective waxes, and polymer blend formulations
• Quality control: batch acceptance testing and periodic verification of incoming compound consistency

Test reports issued by accredited third-party laboratories are routinely used to support product certifications, supplier approvals, and regulatory submissions in these sectors.

FAQ

What ozone concentration is used in standard testing?

The most widely used reference concentration is 50 ± 5 pphm, approximately 0.5 ppm by volume, which accelerates natural exposure while remaining representative of polluted atmospheres. Severer screening tests may use 100, 200, or 500 pphm, while 25 pphm is sometimes specified for sensitive applications.

How long does a standard ozone aging test take?

Typical durations range from 72 to 168 hours for static exposure, though specifications may call for 24-hour screening tests or extended exposures up to several hundred hours. Dynamic tests are generally shorter because cyclic strain accelerates crack initiation.

What is the difference between static and dynamic ozone testing?

Static testing holds specimens at a fixed elongation, such as 20%, throughout exposure and is best suited to materials that experience constant deformation. Dynamic testing applies cyclic strain at roughly 0.5 Hz during exposure, better simulating flexing parts such as bellows and movable seals, and produces faster and more aggressive crack growth.

Are all plastics affected by ozone?

No. Saturated polymers such as PE, PP, and PA are intrinsically ozone resistant. Susceptible materials are those containing unsaturated double bonds or elastomeric rubber phases, including TPE, TPV, SBS, SEBS, ABS, and rubber-modified blends, which is why ozone aging determination focuses on these material classes.

How should ozone aging test results be reported?

A complete report should state the test standard, specimen type and dimensions, ozone concentration with analyzer verification, temperature, humidity, strain condition, exposure duration, inspection magnification, crack grading, and any tensile property retention values, together with a clear statement of pass or fail against the acceptance criteria.