Specimens are conditioned at 50 ± 3 °C for 24 hours, followed by cooling in a desiccator. This drives off moisture to test the material in its dry state.
ASTM D618-21 defines multiple procedures to ensure equilibrium:
Unlike a test method that dictates how to break or stretch a material, a "Standard Practice" outlines the steps required to prepare the material before testing begins. ASTM D618 defines the specific atmospheric conditions (temperature and relative humidity) and the duration for which plastics must be exposed to these environments before evaluation. Why Conditioning Matters for Plastics
To help apply this standard to your specific project, tell me: astm d618-21 pdf
Proper application of is critical for any laboratory conducting accurate plastic characterization.
The standard provides specific procedures (often categorized as Procedure A, B, C, etc.) to handle: High Humidity Environments: To simulate moist environments.
: This is the most common method. It uses an environmental chamber set to 23°C and 50% relative humidity. The conditioning time depends on thickness: 40 hours for specimens ≤7 mm and 88 hours for those >7 mm. This method is best for general testing and routine quality control. Specimens are conditioned at 50 ± 3 °C
Rachel immediately called a meeting with her team to discuss the issue. They pored over the production records and reviewed the testing procedures, but everything seemed to be in order. The team then decided to investigate further by reviewing the ASTM D618-21 standard, which covered the "Standard Practice for Conditioning Plastics for Testing."
When Lina found the sticky note under her keyboard — three letters, a dash, a number scrawled in hurried ink — she felt the tiny thrill that always came before a puzzle. ASTM D618-21 PDF, it read. For most people it would be a dry, technical reference: a standard for conditioning plastics for testing. For Lina, who had spent the last year rebuilding a family plastics lab from the ashes of an insurance claim, it was possibly the missing key to a certification that would keep the lab alive.
Specimens 7 mm or under in thickness are conditioned at 23 ± 2 °C and 50 ± 10% RH for a minimum of 40 hours. For thicker specimens, the time increases to 88 hours. : This is the most common method
Standardizing the pre-test environment to ensure the same test done today yields the same result next month.
The standard emphasizes that conditioning is not always about reaching absolute equilibrium, which can take weeks, but about achieving a reproducible state in a practical amount of time, sometimes lasting over 100 days for thick samples. When to Use ASTM D618-21 (PDF)
Waiting for up to 100 days for a sample to be ready is often impractical for routine manufacturing or quality control. Therefore, the standard makes a critical distinction: the conditioning procedures prescribed are designed to obtain in a reasonable timeframe, not necessarily to achieve complete equilibrium.
The most reliable source is to download the PDF directly from the ASTM website.
Unlike metals or ceramics, polymers are highly sensitive to their immediate environment due to their molecular structure. Two main factors dictate this sensitivity: