Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D3235-23 – Standard Test Method Technical Guide
📐 Test Overview and Scope
The ASTM D3235-23 standard specifies a precise gravimetric method for determining the solvent extractables in petroleum waxes. This parameter, often referred to as “oil content,” is a critical quality indicator. As outlined in Section 5 of the standard, the level of extractables fundamentally influences a wax’s physical properties, including its strength, hardness, flexibility, scuff resistance, coefficient of friction, and melting point. Whether these effects are beneficial or detrimental strictly depends on the wax’s intended application. The stated values in SI units are regarded as the standard.
🛡️ Safety Alert: This procedure mandates the use of flammable and toxic solvents
(Methyl Ethyl Ketone and Toluene). Users must establish appropriate safety, health, and
environmental practices per their local regulatory limitations before performing this test.
⚙️ Test Procedure and Key Apparatus
The method relies on a straightforward phase separation process driven by temperature and solvent selectivity.
- Dissolution: The wax sample is dissolved in a solvent mixture composed of 50% methyl ethyl ketone (MEK) and 50% toluene by volume.
- Precipitation: The solution is cooled to a tightly controlled temperature of -32 °C (-25 °F) using a calibrated cooling bath. This forces the wax to precipitate out of the solution.
- Filtration: The cold mixture is filtered under pressure using a specialized Filter Stick and Assembly to separate the solid wax from the liquid containing the extractables.
- Quantification: The solvent is carefully evaporated from the collected filtrate, leaving behind a residue of extracted material. The mass of this residue is then determined.
💡 Technical Tip: The cooling bath must be capable of maintaining a stable
temperature. Suitable media include kerosine, with cooling achieved via a circulating refrigerant
or solid carbon dioxide. Precise temperature control at -32 °C is critical for reproducible
precipitation of the wax.
📊 Critical Equipment Specifications
The reproducibility of this test method strictly depends on adherence to the exact apparatus dimensions and tolerances defined in Section 6 of the standard.
| 🎯 Parameter | ⚡ Glass Filter Stick | 🔧 Stainless Steel Filter Stick |
|---|---|---|
| Filter Diameter | 10 mm | 12.7 mm (0.50 in.) disk |
| Max Pore Diameter | 10 µm to 15 µm | 10 nm to 15 nm |
| Test Tube Size | 25 mm by 170 mm | 25 mm by 150 mm |
| Pore Size Test Method | Per Appendix X1 | Per Test Method E128 |
| 📏 Feature | 🟦 Tolerance |
|---|---|
| Test Tube Hole Diameter | 30 mm ± 5 mm (1.2 in. ± 0.2 in.) |
| Cooling Medium | Kerosine (or suitable alternative) |
| Cooling Method | Circulating refrigerant or solid CO₂ |
❓ Frequently Asked Questions
🔍 What constitutes “solvent extractables”?
These are primarily low-molecular-weight hydrocarbons (oils) and other non-wax components that
are soluble in the MEK/Toluene solvent mixture at the specified low temperature of -32 °C.
💡 Why is a specific solvent ratio of 50/50 MEK/Toluene used?
This ratio provides the ideal polarity and solvency power to fully dissolve the wax at room
temperature while allowing for sharp precipitation of the wax crystals at the low test temperature,
leaving the extractable oils in solution.
⚡ What is the significance of the pore size difference between the glass and metallic filters?
The metallic filter stick features a much finer pore size (nanometer vs. micrometer scale).
The standard ensures both are validated to provide a functionally equivalent separation of the
precipitated wax from the solvent.
📌 How does the “solvent extractables” result affect end-use wax properties?
Higher extractable content generally leads to softer wax with lower melting points, higher
coefficient of friction, and greater staining tendencies. Lower extractables yield harder, more
brittle waxes with higher melting points.