Information on the most widely used ASTM standards within the materials testing industry
ISO 291 Plastics - Standard atmospheres for conditioning and testing
ISO 291 is not a material property test itself. It is a fundamental conditioning and testing environment standard for plastics. It specifies the atmospheric conditions under which plastic samples must be prepared (conditioned) and tested to ensure data reproducibility and comparability.
Test Purpose & Importance
Purpose: To standardize the temperature, humidity, and atmospheric pressure under which plastic specimens are conditioned and tested .
Why is it important? Plastics are highly sensitive to environmental conditions, particularly temperature and moisture. Without strict environmental controls, test results (like mechanical strength or dimensions) will vary wildly between labs. ISO 291 provides the "neutral ground" (e.g., 23°C and 50% RH) ensuring that a test conducted in Japan yields the same comparable result as a test conducted in Germany.
The standard defines two primary constant atmospheres. The choice depends on the geographical climate of the testing laboratory:
Atmosphere 23/50: Air temperature of 23°C and Relative Humidity (RH) of 50%. (Recommended for non-tropical countries) .
Atmosphere 27/65: Air temperature of 27°C and Relative Humidity (RH) of 65%. (Recommended for tropical countries) .
Ambient Temperature: If humidity does not affect the property being tested, only the temperature needs to be controlled (e.g., 23°C or 27°C). If neither affects the test, the "ambient temperature" (18°C to 28°C) can be used.
Equipment
Conditioning/Cabinets/Chambers/Rooms: The equipment must be capable of maintaining the specified constant atmospheric conditions (temperature and humidity) .
Monitoring Requirements:
Air circulation velocity must be ≤ 1 m/s .
Atmospheric pressure should be between 86 kPa and 106 kPa .
The environment must be free from significant external radiation influences or chemical contaminants .
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