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D5815-95 – Standard Test Method Technical Guide
ASTM D5815-95 (Reapproved 2001) defines a liquid chromatographic (LC) procedure designed for the separation and quantitation of phenolic antioxidants and erucamide slip additives in Linear Low-Density Polyethylene (LLDPE). The method relies on solvent extraction followed by reverse phase chromatography with UV detection, employing an internal standard for precise quantification.
🔬 Scope and Principle of the Test Method
This test method is applicable to LLDPE samples containing additives such as BHT, Irganox 1010, Irganox 1076, Isonox 1296, Tinuvin P, and Kemamide-E. The LLDPE is milled to a 20-mesh particle size to ensure efficient extraction. The ground sample is refluxed with a suitable solvent, either isobutanol or isopropanol, to isolate the additive package. The resulting extract is analyzed via a reverse phase liquid chromatography system, typically utilizing a C-18 column. Detection is achieved by measuring ultraviolet (UV) absorbance at 200 nm, and the concentration of each additive is determined against an internal standard.
🧪 Extraction Solvents and Analytical Conditions
The selection of the extraction solvent is critical for method accuracy and directly correlates with the density and crystallinity of the LLDPE matrix. Specifically, isopropanol is recommended for lower crystallinity grades with a density of 0.925 g/cm³ and below. For higher crystallinity LLDPE or samples containing Irganox 1010, isobutanol is the specified extraction solvent. The method does not require conversion of the extracted additives and provides a direct measure of additive concentration in the polymer.
| 🟦 Solvent | 📐 Recommended Application |
|---|---|
| Isopropanol | Lower crystallinity LLDPE (density ≤ 0.925 g/cm³) |
| Isobutanol | Higher crystallinity LLDPE / Presence of Irganox 1010 |
📌 Technical Note: Note 2 of the standard emphasizes the importance of matching the solvent to the polymer grade. Using isopropanol on high-crystallinity LLDPE or isobutanol on low-crystallinity material where Irganox 1010 is absent may lead to poor recoveries and erroneous quantitation. Always verify the density and additive package of the target material before selecting the extraction solvent.
📊 Key Additives and Detection Parameters
The standard specifically targets several classes of additives. The table below summarizes the compounds, their abbreviations, and chemical names as defined in Section 3 of the standard.
| 🟦 Abbreviation / Trade Name | 🔬 Chemical Name / Description |
|---|---|
| BHT | 2,6-di-t-butyl-cresol (Butylated Hydroxy Toluene) |
| BHEB | 2,6-di-t-butyl-4-ethyl-phenol (Butylated Hydroxyethyl Benzene) |
| Irganox 1010 | Tetrakis[methylene(3,5-di-t-butyl-4-hydroxy hydrocinnamate)]methane |
| Irganox 1076 | Octadecyl-3,5-di-t-butyl-4-hydroxy hydrocinnamate |
| Isonox 1296 | 2,28-ethylidene bis (4,6-di-t-butyl phenol) |
| Kemamide-E | Cis-13-docosenamide (Erucamide) |
| Tinuvin P | 2(28-hydroxy-58-methyl phenyl)benzotriazole |
⚡ Safety Note: The standard explicitly states that it does not address all safety concerns. Specific precautionary statements are detailed in Section 9. Users must establish appropriate safety, health, and environmental practices (e.g., fume hoods, PPE) before utilizing this test method.
❓ Frequently Asked Questions
🔍 What types of additives are covered by ASTM D5815?
The standard specifically covers the determination of phenolic antioxidants (e.g., BHT, BHEB, Irganox 1010, Irganox 1076, Isonox 1296) and the slip additive erucamide (Kemamide-E) in LLDPE.
💡 What is the required sample preparation for this test?
The LLDPE resin must be ground to a 20-mesh particle size. The additives are then extracted from the ground polymer by refluxing with a specific solvent (isobutanol or isopropanol) before LC analysis.
⚡ How is the quantitation of additives performed?
Quantitation is performed using the internal standard method. The extract is analyzed using reverse phase liquid chromatography (C-18 column) with UV detection set at 200 nm. The response of the target analytes is compared to the internal standard to calculate concentration.
📌 Why are there two recommended extraction solvents?
Note 2 of the standard specifies that isopropanol is best suited for lower crystallinity LLDPE (density ≤ 0.925), while isobutanol is recommended for higher crystallinity LLDPE or when Irganox 1010 is present. This ensures complete extraction and accurate results.