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D3495-10 – Standard Test Method Technical Guide
🧪 Purpose, Scope, and Significance
This test method, formally designated as ASTM D3495 −10 (Reapproved 2023), establishes the standard procedure for the quantitative extraction of all types of leather using hexane. It is critically important to note that this method does not apply to wet blue leather. All values stated in SI units are to be regarded as standard.
The primary significance of this test is the measurement of hexane-soluble lubricant present within the leather structure. Adequate lubrication is essential for preventing the abrasion of leather fibers during flexing. This lubrication is predominantly imparted by the fat liquor added during the tannery process, with additional contribution from the natural grease inherent in the animal hide.
🔬 Apparatus, Reagent Specifications, and Sampling
The required apparatus includes an analytical balance, a standard Soxhlet extraction apparatus (boiling flask, extraction tube, and condenser), a forced circulating air oven, an electric hot plate, a steam bath, and fat-free extraction thimbles (cellulose, Alundum, or fritted) with fat-free absorbent cotton.
The sole reagent specified is Hexane, ACS Reagent Grade, which must meet the stringent purity requirements detailed in the standard. The hexane used is typically a mixture of isomers, predominantly n-hexane and methylcyclopentane.
| 🟦 Hexane Property | 📏 Specification | 🎯 Limit |
|---|---|---|
| Color (APHA) | 10 | max |
| Density at 25 °C (g/mL) | 0.687 | max |
| Boiling Range (1 mL to 95 mL) | 4.0 °C | max |
| Residue After Evaporation | 0.001 % | max |
| Acidity (as CH₃COOH) | 0.002 % | limit |
| Sulfur Compounds (as S) | 0.005 % | max |
| Thiophene | To pass test | |
Leather sampling must be conducted strictly in accordance with Practice D2813. Test specimens are obtained from a composite sample that is ground in a mill (such as a Wiley mill) fitted with a No. 5 (4 mm) sieve. The ground leather passing through this sieve is thoroughly mixed and used as the analytical sample.
⚠️ Critical Exclusion: This test method explicitly does not apply to wet blue leather. Ensure the sample has been fully processed through crust or finishing stages prior to analysis to avoid interferences and invalid results.
⚙️ Extraction Procedure and Key Parameters
The moisture content of the composite sample is first determined following Test Method D3790 (Volatile Matter of Leather by Oven Drying). The accurately weighed test specimen is placed into a fat-free extraction thimble, plugged with fat-free absorbent cotton, and subjected to exhaustive Soxhlet extraction using ACS Reagent Grade hexane. Upon completion of the extraction, the hexane is distilled off. The residual extract is dried to a constant weight in the forced circulating air oven, cooled, and weighed gravimetrically. The percentage of hexane-extractable material is calculated based on the moisture-free weight of the leather.
| ⚡ Key Procedure Element | 📐 Specification / Reference |
|---|---|
| Sampling Standard | ASTM D2813 |
| Specimen Particle Size | Through No. 5 (4 mm) Sieve |
| Moisture Determination | ASTM D3790 |