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D6405-99 – Standard Test Method Technical Guide
ASTM D6405 – 99 (Reapproved 2020) establishes the standard practice for extracting tannins from raw and spent plant materials. This water extraction procedure is the critical first step in determining the tannin content of materials such as woods, barks, leaves, nuts, and industrial by-products. The resulting water extract is analyzed to calculate total solids, soluble solids, and soluble non-tannins, providing the information necessary to determine the extractable tannin content.
📜 Scope and Key Terminology
This practice covers the extraction of tannins from a wide variety of plant products and by-products. The values stated in SI units are regarded as the standard. Key definitions per the standard are essential for consistent application:
| 🟦 Term | 📐 Definition |
|---|---|
| Raw Material | Various parts of plants used as a source of vegetable tannins (e.g., woods, barks, leaves, nuts, fruits, roots). |
| Spent Material | Plant tissue by-products from industrial processes which may contain significant quantities of vegetable tannins. |
| Vegetable Tannins | Mixtures of natural substances obtained from plant tissues by water extraction that possess the properties necessary to convert animal hides into leather. |
Note on Units: The values stated in SI units are to be regarded as the standard. Inch-pound units given in parentheses are for information only (Section 1.2). It is the responsibility of the user to establish appropriate safety, health, and environmental practices (Section 1.3).
⚙️ Practice Summary and Sample Preparation
The sample is first brought to moisture equilibrium with the laboratory atmosphere. For wet materials, such as spent materials from industrial processes, this requires drying under ambient laboratory conditions. The material is then ground sufficiently to pass through a specified sieve. The prepared, ground sample is extracted with water using a steam-jacketed extractor (Section 4).
This standard practice provides a uniform method for obtaining the water-soluble materials (including tannins) from any vegetable source. This test method has been adapted from and is a replacement for Method A5 of the Official Methods of the American Leather Chemists Association (ALCA).
📊 Referenced Analytical Framework
The extraction practice depends on several other ASTM standards for the comprehensive analysis of the water extract. The table below lists the key methods referenced in Section 2 of the standard.
| ⚡ Standard | 🎯 Focus of Analysis |
|---|---|
| D4903 | Total Solids and Water in Vegetable Tanning Material Extracts |
| D6401 | Non-Tannins and Tannin in Extracts of Vegetable Tanning Materials |
| D6402 | Soluble Solids and Insolubles in Extracts of Vegetable Tanning Materials |
| D6403 | Moisture in Raw and Spent Materials |
| D6404 | Sampling Vegetable Materials Containing Tannin |
Technical Tip: The calculation of extractable tannin content relies on subtracting the soluble non-tannins (via D6401) from the total soluble solids (via D4903 and D6402) found in the water extract prepared per this practice.
❓ Frequently Asked Questions
🔍 What is the specific purpose of ASTM D6405?
The purpose is to provide a standard practice for extracting water-soluble materials, specifically tannins, from raw and spent plant materials. This water extract is then used in subsequent analyses to calculate the total tannin content of the original material (Section 1.1).
💡 What types of materials are analyzed using this practice?
This practice is intended for products of plants such as woods, barks, leaves, nuts, fruits, and roots, as well as any wide variety of by-products (spent materials) from industrial processes that utilize these plant products (Section 1.1).
⚡ What is the definition of “spent material” in this standard?
According to Section 3.1.3, a spent material is defined as plant tissue by-products from industrial processes which may contain significant quantities of vegetable tannins. These materials are often wet and must be dried under ambient conditions before grinding.
📌 Which standard is used for determining Non-Tannins and Tannin in the extract?
The test method specifically for determining Non-Tannins and Tannin in extracts is ASTM D6401. This method is applied to the water extract produced using the D6405 practice to differentiate the true tanning agents from other soluble solids (Section 2.1, D6401).