Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D618-21 – Standard Test Method Technical Guide
ASTM D618-21 is a standard practice for conditioning plastics for testing, ensuring that physical and electrical property measurements are not influenced by uncontrolled environmental conditions. This practice defines standardized atmospheres and procedures to achieve reliable and comparable test results across different materials and laboratories.
🌡️ Standard Laboratory Atmosphere and Temperature
The standard laboratory atmosphere is defined as a temperature of 23°C (73.4°F) and a relative humidity of 50%, with tolerances specified in Sections 7 and 8 of the standard. This atmosphere is used for conditioning specimens to equilibrium before testing. The standard laboratory temperature is also 23°C, used when humidity is not a controlled factor. Room temperature is defined as a range from 20 to 30°C (68 to 86°F).
| 🟦 Condition | 🌡️ Temperature | 💧 Humidity |
|---|---|---|
| Standard Laboratory Atmosphere | 23°C (73.4°F) | 50% RH |
| Standard Laboratory Temperature | 23°C (73.4°F) | Not controlled |
| Room Temperature | 20 to 30°C (68 to 86°F) | Not specified |
💡 Tip: Always check material specifications, as they may override the general procedures in D618-21, especially for materials like those listed in ASTM D4000.
⚙️ Conditioning Procedures and Practices
Conditioning should be performed prior to testing to standardize the specimen’s state. The practice requires that specimens be conditioned in the standard laboratory atmosphere for a sufficient period, typically 40 hours or until equilibrium is reached. However, for some materials, material specifications may dictate different conditions or durations. This standard and ISO 291 address similar topics but differ in technical content; ISO 291 describes only two temperature and humidity conditions.
⚠️ Important: The user is responsible for establishing appropriate safety, health, and environmental practices. This standard does not address all safety concerns.
📊 Referenced Standards and Tolerances
D618-21 references several ASTM standards for maintaining constant humidity and classifying plastics, including ASTM E104 for aqueous solutions and ASTM D4000 for plastic classification. Tolerances for temperature and humidity are critical and are specified in Sections 7 and 8 of the standard. For accurate conditioning, use practices like ASTM D5032 for glycerin solutions.
| 📄 Standard | 📝 Role in Conditioning |
|---|---|
| ASTM E104 | Maintaining constant relative humidity |
| ASTM D4000 | Classifying plastic materials |
| ISO 291 | International counterpart for conditioning |
❓ Frequently Asked Questions
🔍 Why is conditioning important for plastic testing?
Conditioning minimizes the effects of temperature and humidity on test results, ensuring reliable comparisons between materials and laboratories.
💡 What is the difference between standard laboratory atmosphere and standard laboratory temperature?
The latter is solely about temperature (23°C), while the former includes both temperature and humidity (23°C, 50% RH).
⚡ How does D618-21 relate to ISO 291?
Both cover conditioning, but ISO 291 specifies only two atmospheres, while D618-21 provides more options. The choice depends on the material and test standards.
📌 What should I do if my material specification conflicts with D618-21?
The material specification takes precedence. Always refer to the specific material standard before using D618-21.