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D3900-17 – Standard Test Method Technical Guide
🧪 Overview of Test Methods for Ethylene Determination
ASTM D3900-17 (Reapproved 2021) provides standardized infrared spectrometric procedures for determining the ethylene content in Ethylene-Propylene Copolymers (EPM) and Ethylene-Propylene-Diene Terpolymers (EPDM). The standard covers a range from 35 to 85 mass percent ethylene. Four distinct test methods are defined to accommodate various polymer compositions and additives that can interfere with specific infrared peaks.
| 🟦 Method | 📏 Film Type | 🎯 Ethylene Range (mass %) | 🔬 Key IR Wavelengths | ⚠️ Exclusions |
|---|---|---|---|---|
| A | Pressed Film | 35 – 70 | 8.65 / 13.85 µm (1156 / 722 cm⁻¹) | None specified for this range |
| B | Pressed Film | 60 – 85 | 7.25 / 13.85 µm (1379 / 722 cm⁻¹) | E/P/1,4-Hexadiene terpolymers |
| C | Pressed Film (Near IR) | 35 – 85 | 8.65 / 2.35 µm (1156 / 4255 cm⁻¹) | None |
| D | Cast Film | 35 – 85 | Standard IR Analysis | E/P/1,4-Hexadiene terpolymers |
⚠️ Important Limitation: These test methods are not applicable to oil-extended EPDM unless the oil is first removed in accordance with Test Method D. All values stated in the standard are in SI units.
⚙️ Procedure and Technical Basis
Methods A, B, and C utilize pressed films for analysis. The mass percent of ethylene is determined by measuring infrared absorbance ratios at specific wavelengths and comparing them against a calibration curve derived from standard polymers. Method D uses a cast film technique for broader applicability. The choice of method depends on the expected ethylene content and the presence of specific diene monomers.
For example, Method B relies on the absorbance ratio at or near 7.25/13.85 µm (1379/722 cm⁻¹), while Method A uses the 8.65/13.85 µm (1156/722 cm⁻¹) ratio. Method C employs near-infrared technology using the 8.65/2.35 µm (1156/4255 cm⁻¹) ratio, offering full range coverage from 35 to 85 mass % ethylene. General techniques for quantitative infrared analysis are referenced in Practices E168.
📊 Calibration and Key Measured Properties
All test methods rely on calibrations obtained from standard polymers with known ethylene content. The precision of the measurement is highly dependent on the quality of the film preparation and the absence of interfering compounds.
| 🔬 Peak Location | ⚡ Associated Method | 📌 Functional Group / Purpose |
|---|---|---|
| 13.85 µm (722 cm⁻¹) | A, B | Methylene rocking (Ethylene backbone) |
| 8.65 µm (1156 cm⁻¹) | A, C | Propylene methyl group |
| 7.25 µm (1379 cm⁻¹) | B | C-H bending (Methyl group) |
| 2.35 µm (4255 cm⁻¹) | C | C-H combination band (Near IR) |
💡 Technical Tip: The standard notes that the peak typically appears at the specified wavelength, but the peak position may shift slightly depending on the specific polymer and instrument. Analysts should identify the exact peak maximum for their specific analysis.
❓ Frequently Asked Questions
🔍 What is the scope of ASTM D3900?
This standard covers the determination of ethylene units in EPM and EPDM polymers over a range of 35 to 85 mass percent ethylene using infrared spectrometry. It does not directly apply to oil-extended compounds unless the oil is extracted per Method D.
💡 What is the difference between EPM and EPDM in this context?
EPM refers to Ethylene-Propylene Copolymers (no diene), while EPDM refers to Ethylene-Propylene-Diene Terpolymers. Certain test methods (B and D) are not suitable for specific diene types like 1,4-hexadiene.
⚡ Which test method should I use for the widest range of ethylene content?
Test Methods C (Pressed Film, Near IR) and D (Cast Film) both cover the full range of 35 to 85 mass % ethylene, making them the most versatile for unknown samples where interferences are managed.
📌 Is this standard applicable to oil-extended EPDM?
No. The standard explicitly states it is not applicable to oil-extended EPDM unless the oil is first removed in accordance with Test Method D. This procedure ensures that the extender oil does not interfere with the infrared measurement.