Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D2876-00 – Standard Test Method Technical Guide
The ASTM D2876-00 (Reapproved 2024) standard defines a specific laboratory procedure for determining the percentage of water-soluble matter present in vegetable-tanned leathers. This analysis is essential for evaluating the completeness of the tanning process and understanding the chemical residues left in the leather after manufacturing.
🔬 Test Method Scope and Principles
This standard applies exclusively to vegetable-tanned leathers and explicitly excludes wet blue (chrome-tanned leather). The water-soluble matter quantified by this test includes non-tanning components from the vegetable tanning materials, residual sugars, and various inorganic compounds such as Epsom salts (MgSO₄), Glauber’s salts (Na₂SO₄), and borax (Na₂B₄O₇) that are frequently added during curing and processing.
Before the water extraction can proceed, the leather sample must first be stripped of fats and oils. The specimen is prepared according to Test Method D3495 (Hexane Extraction of Leather). This crucial preparatory step ensures that the mass lost during water extraction is entirely attributable to water-soluble components, not greases or waxes.
⚙️ Apparatus and Specimen Specifications
The standard mandates very specific laboratory equipment to ensure reproducibility. The following table summarizes the critical dimensions and tolerances for the required apparatus:
| 🟦 Component | 📏 Specification | 🎯 Tolerance |
|---|---|---|
| Crystallizing Dish | Borosilicate glass, 50 mm tall, 70 mm outside diameter | Weight: 30 g to 39 g |
| Extraction Tube | Reed-Churchill Type | Internal Diameter: 45 mm ± 2 mm Length: 233 mm ± 10 mm |
| Water Bath | Temperature-controlled bath | 35 °C ± 0.5 °C |
| Circulating Air Oven | Drying oven for residue | 99 °C ± 1 °C |
⚡ Critical Weighing Requirement: The crystallizing dish is a specific component in the analysis. The standard requires the empty dish to weigh between 30 g and 39 g. Using a dish outside this weight range can negatively affect the sensitivity of the gravimetric analysis for the extracted residue.
The test specimen itself must be a 5 g leather sample that has already undergone the hexane extraction process outlined in Test Method D3495. Any deviation from this sample size must be explicitly reported with the analytical results.
📊 Extraction Procedure and Parameters
The core of the test involves a precise water leaching protocol. The parameters for this extraction are strictly defined to ensure that the results are consistent across different laboratories and operators.
| ⚡ Parameter | 📐 Requirement |
|---|---|
| Specimen Mass | 5 g (pre-extracted with hexane per D3495) |
| Extraction Medium | Distilled or deionized water |
| Extraction Temperature | 35 °C ± 0.5 °C |
| Extraction Duration & Volume | 1 L of water collected over exactly 3 hours |
| Extract Preparation | Cooled to 23 °C, adjusted to volume, and mixed thoroughly |
💡 Flow Rate Control: The extraction column flow must be adjusted so that precisely 1 liter of extract is collected in 3 hours. This rate ensures sufficient contact time between the water and the leather specimen to achieve equilibrium extraction of soluble components without channeling.
The procedure begins by inserting a plug of cotton or glass wool into the bottom of the Reed-Churchill extraction tube. The hexane-extracted specimen is then placed into the tube. The heated water (35 °C) is allowed to percolate through the leather sample at the specified rate for 3 hours. The resulting extract is then processed and evaporated in the tared crystallizing dish to determine the mass of water-soluble matter.
❓ Frequently Asked Questions
🔍 What is the specific scope of ASTM D2876-00?
This test method is specifically designed for determining the water-soluble materials in vegetable-tanned leathers. It explicitly does not apply to wet blue (chrome-tanned) leather due to differing chemical properties.
💡 Why is hexane extraction required before this test?
Hexane extraction, performed according to ASTM D3495, removes oils, fats, and greases from the leather. If these hexane-soluble materials were not removed first, they would be carried over into the water extract, causing an overestimation of the true water-soluble matter content.
⚡ What are the exact temperature tolerances for the water bath?
The standard mandates a highly stable water bath capable of maintaining a temperature of 35 °C ± 0.5 °C for the entire duration of the 3-hour extraction.
📌 How is the result calculated from the extract?
An aliquot of the combined 1 L extract is evaporated to dryness in the tared crystallizing dish. The dish is then dried in an oven at 99 °C ± 1 °C to a constant weight. The increase in mass represents the water-soluble matter extracted from the sample.