ISO 23706:2020

Overview

ISO 23706:2020 specifies a laboratory test method for determining the apparent activation energy (Ea) of photochemical degradation reactions in plastics subjected to accelerated weathering. Using the Arrhenius model, the standard defines how to quantify the temperature dependence of specific property changes (for example, yellowing or surface cracking) by comparing exposures at two or more controlled temperatures while keeping all other test parameters constant.

Key topics and requirements

• Arrhenius principle - Apply the Arrhenius concept (Annex A) to relate temperature to degradation rate; Ea is derived from measured exposure times to reach the same property change.
• Minimum data - Perform weathering tests at two or more different specimen surface temperatures (or reference panel temperatures) under otherwise identical conditions.
• Controlled variables - Maintain identical spectral irradiance, relative humidity, cycles and other exposure parameters across tests; vary only the specimen surface temperature (or BST/BPT/WST/WPT as proxy).
• Temperature measurement - Measure and, where possible, control surface temperature; use black/white standard panel temperatures if direct measurement is not feasible.
• Radiation-source considerations - Distinguish between sources that emit IR (e.g., xenon-arc) - which can cause through-thickness temperature gradients and are best used with thin samples or surface-related properties - and sources that produce homogeneous temperatures in a climatic chamber (allowing bulk-property testing).
• Test procedure elements - Specifies specimen preparation, mounting, exposure conditions, measurement of radiant/effective irradiance, determination of property changes, and calculation methods for Ea (two-temperature and multi-temperature approaches).
• Uncertainty and limitations - Notes that Ea is material- and pathway-specific, may differ for different property changes, and that the Arrhenius model is a simplifying approach with assumptions and limitations (Annex D discusses uncertainty contributors).

Practical applications and users

ISO 23706:2020 improves the quantitative assessment of temperature effects in accelerated weathering, making artificial weathering tests more predictive and comparable. Typical users:

• Test laboratories performing accelerated weathering and correlation studies
• R&D teams developing UV-stable polymers, coatings and additives
• Quality assurance groups seeking temperature-corrected lifetime estimates
• Standards developers and researchers studying degradation mechanisms

Benefits include better correlation between different weathering regimes, improved predictive value for material lifetime, and more robust comparison of accelerated tests.

Related standards

• ISO 4892-1 / ISO 4892-2 / ISO 4892-3 (laboratory light-source exposure methods)
• ISO 4582 (colour and property change determination)
• ISO 10640 (photoageing assessment by spectroscopy)
• ISO 11358-2 and ISO 2578 (thermal degradation / activation energy methods)

Keywords: ISO 23706:2020, activation energy, photochemical degradation, Arrhenius model, accelerated weathering, plastics testing, surface temperature, xenon-arc, UVA, BST, effective irradiance.