ASTM D618 Conditioning Procedures for Plastic Specimens
ASTM D 618 Standard Test Practice covers conditioning plastics for testing is crucial as their physical and electrical properties are significantly influenced by temperature and humidity. Standardizing these conditions ensures consistent and accurate results for reliable comparisons between different materials and laboratories.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM D618 describes the standard conditioning procedures for plastic materials prior to testing. Conditioning is used to achieve consistent results by stabilizing moisture and temperature.
Achieving full equilibrium may require a considerable amount of time, which can range from 20 to 100 days, depending on the material and its thickness. Conditioning is essential for general purchase specifications, product control tests, and material comparisons.
Scope, Applications, and Benefits
Scope
ASTM D618 applies to plastic materials prior to performing mechanical, physical, and electrical tests. It ensures that test specimens are properly conditioned in accordance with the relevant ASTM plastic test method to achieve consistent and reliable results.
Standardized Conditioning Procedures:
Procedure A: Standard laboratory atmosphere conditioning
Procedure B: Oven conditioning followed by desiccation
Procedure C: Water immersion conditioning
Procedure D: High humidity conditioning
The quantity and type of specimens must conform to the requirements specified in the applicable ASTM material test method.
Applications
- Quality control testing of plastics
- Preconditioning for mechanical property evaluation
- Electrical property testing
- Dimensional stability assessment
- Moisture absorption studies
- Research and development of polymer materials
- Comparative material performance evaluation
Benefits
- Ensures repeatable and standardized testing conditions
- Controls moisture and temperature effects on plastics
- Improves reliability of test data
- Supports accurate purchase specifications
- Reduces variability between laboratories
- Enhances consistency in product evaluation
- Provides uniform conditioning terminology
Test Process
Procedure A
Condition at 23°C, 50% RH for 40 h (≤7 mm) or 88 h (>7 mm).
1Procedures B & C
B: 50°C for 48 h, then desiccator cooling. C: Water immersion at 50°C for 48 h, cool to 23°C before testing.
2Procedure D
Condition at 23°C and 96% RH as specified.
3Compliance
Maintain humidity per ASTM E104 and use required specimen type and quantity.
4Technical Specifications
| Parameter | Details |
|---|---|
| Applicable Materials | Plastic materials |
| Standard Laboratory Atmosphere | 23°C ± 1°C, 50% ± specified RH |
| Oven Conditioning Temperature | 50 ± 2°C |
| Water Conditioning Temperature | 50 ± 1°C |
| High Humidity Condition | 96 ± 1% RH at 23 ± 1°C |
| Specimen Thickness Criteria | ≤7 mm or >7 mm determines conditioning duration |
| Condition Notation Format | Time/Temperature/Humidity or immersion medium |
| Output | Condition designation and pre-test conditioning record |
Instrumentation Used for Testing
- Environmental conditioning chamber
- Circulating-air oven
- Desiccator with anhydrous calcium chloride
- Distilled water bath
- Humidity control system
- Thermometer and hygrometer
- Specimen racks or mesh supports
Results and Deliverables
- Conditioning designation (e.g., 48/50/water, 96/23/50)
- Pre-test environmental conditioning record
- Documented temperature and humidity conditions
- Quality control documentation
Frequently Asked Questions
The conditioning process reduces the effects of the environment by equalizing the moisture content and temperature of the polymer. This ensures that the results of the tensile, flexural, and impact tests are accurate and representative of the true physical state of the material.
While applied in a similar manner, composites often need longer exposure times to achieve equilibrium because of their complex internal structures. Controlled cycles also prevent the absorption of moisture from artificially lowering the glass transition temperature (Tg) during testing.
The most generally specified conditioning environment is 23 ± 2°C and 50 ± 10% relative humidity. However, alternative temperature and humidity conditions may be required depending on the material type and applicable test method.
ASTM D618 is normally applicable to most thermoplastic and thermosetting plastics used in laboratory testing. However, specific product standards may override these requirements.
If the specimens are not conditioned properly, then the results of strength, stiffness, and dimensional stability could be affected by the variations in moisture content and temperature.
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