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D3594-93 – Standard Test Method Technical Guide
📋 Scope and Applications
This test method, designated D3594‑93, is specifically designed for the quantitative determination of copolymerized ethyl acrylate in ethylene‑ethyl acrylate copolymers containing from 1 % to 25 % ethyl acrylate. The method is essential for quality control in manufacturing films, moldings, and wire coatings, where ethyl acrylate significantly improves physical properties such as flexibility, stress crack resistance, and clarity. The procedure uses infrared spectroscopy to provide a rapid and accurate analysis.
⚙️ Test Procedure and Methodology
The analysis is based on the infrared absorption band at 11.60 µm, which is directly responsive to comonomer content and free from monomer interference. To ensure optimal absorption, film thickness is carefully selected based on the expected ethyl acrylate concentration:
| 🟦 Ethyl Acrylate Content (Weight %) | 📏 Recommended Film Thickness (mm) |
|---|---|
| Less than 5 % | 0.5 |
| 5 to 15 % | 0.25 |
| 15 to 25 % | 0.18 |
For unknown samples, press a film of approximately 0.25 mm and scan it to assess absorption intensity. The scanning range is from 10.50 to 12.50 µm, using the base‑line method for absorbance measurement. This technique minimizes errors from film thickness variations and ensures reliable results.
💡 Precision Note: Accurate measurement of film thickness is critical for high precision. The base‑line method, as outlined in Practices E168, helps compensate for baseline drifts during scanning.
📊 Calibration and Measurement
Calibration involves plotting absorbance per millimeter versus weight percent ethyl acrylate using reference copolymers with known compositions, established by fast neutron activation analysis of oxygen content. The calibration curve is then used to determine the ethyl acrylate content of unknown samples by matching their absorbance per millimeter values. This approach ensures consistency and accuracy across different analyses.
⚠️ Important: Ensure that the infrared absorption does not exceed 80 % at the analytical wavelength. Thicker films or higher comonomer content may require adjusting film thickness to maintain linearity.
❓ Frequently Asked Questions
🔍 How does the infrared method work for ethyl acrylate?
The method utilizes the absorption band at 11.60 µm, which is specific to the copolymerized ethyl acrylate. The intensity of this band increases with comonomer content, allowing precise quantification.
💡 What is the recommended film thickness for unknown samples?
If the ethyl acrylate content is unknown, start with a film thickness of approximately 0.25 mm. After scanning, adjust based on absorption intensity to fall within the optimal range.
⚡ How is the calibration curve validated?
The curve is validated using copolymers with known ethyl acrylate content, determined by independent methods like neutron activation analysis. Regular checks with standards ensure ongoing accuracy.
📌 Are there any interferences in this test method?
No significant interferences have been identified at 11.60 µm. The monomer itself does not absorb at this wavelength, making the method specific to the copolymer.