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D3971-89 – Standard Test Method Technical Guide
📖 Scope, Summary, and Significance of the Test
ASTM D3971-89 (Reapproved 2019) defines a standard test method for measuring dichloromethane-soluble matter in cellulose, applicable to dissolving-type cellulose pulps prepared from cotton or wood. The extracted substances—commonly waxes, fats, resins, and oils—are collectively referred to as extractives.
The presence of these organic materials, which originate in the raw wood or cotton, serves as an indicator of the efficiency of the pulping and bleaching processes. High levels of extractives can inhibit the downstream processing of cellulose into derivatives, making this test critical for quality control in the dissolving pulp industry.
⚠️ Safety Notice: Dichloromethane is a hazardous chemical. Standard safety practices, including adequate ventilation, proper personal protective equipment (PPE), and adherence to regulatory limitations, must be strictly followed when performing this test. Always consult the Safety Data Sheet (SDS).
⚙️ Apparatus and Reagent Specifications
The test requires specific glassware and reagents to ensure accurate and reproducible results. Standard taper 45/50 joints are required for the extraction system to maintain a sealed environment during the hot extraction.
| 🟦 Component | 📏 Specification |
|---|---|
| Soxhlet Apparatus | Extractor tube (45/50 top joint), 250 mL flask, Allihn or Friedrichs condenser (45/50) |
| Extraction Thimbles | Paper (43×123 mm), Aluminum Oxide (34×100 mm), or Glass (45×130 mm, coarse frit) |
| Dish & Desiccator | Disposable light aluminum dish (63 mm x 17.5 mm deep), desiccator with efficient desiccant |
| Support Equipment | Heating mantle / steam bath, Oven (105 ± 3°C) |
The specified reagent is Dichloromethane (ACS grade, ≥99% CH₂Cl₂) with a maximum non-volatile residue after evaporation of 0.002%. This high purity prevents the introduction of contaminants into the extracted sample residue.
📊 Detailed Test Procedure and Parameters
Sample preparation varies based on the physical form of the cellulose. For loose pulp, an 8 to 12 g sample is weighed into a pre-extracted thimble. For sheet pulp, the sample is cut into strips approximately 10 mm wide and 70 mm long, and a ~20 g sample is used. A separate portion must be weighed for moisture determination in accordance with Test Methods D1348.
| 📐 Parameter | 🎯 Specification / Value |
|---|---|
| Sample Mass (Loose Pulp) | 8 – 12 g (nearest 0.01 g) |
| Sample Mass (Sheet Pulp) | ~20 g (cut into 10 mm x 70 mm strips) |
| Solvent Volume | 250 mL |
| Extraction Duration | 5 hours |
| Siphoning Rate | 6 – 8 cycles per hour |
The extraction thimble is placed in the extractor, and 250 mL of dichloromethane is poured into the body of the extractor. The assembled system is connected to the condenser with cooling water running. The heating rate is adjusted to cause siphoning 6 to 8 times per hour, and the extraction proceeds for exactly 5 hours. After extraction, the solvent is evaporated, and the residue is dried in an oven at 105 ± 3°C, cooled in a desiccator, and weighed.
💡 Technical Tip: The thimble must be previously extracted with dichloromethane to remove any inherent extractives that could skew the results. Adjusting the heating rate to achieve the specified siphoning rate of 6 to 8 times per hour is critical for the kinetics of the extraction. Ensure the heating device is stable to maintain this rate over the full 5-hour extraction period.
❓ Frequently Asked Questions
🔍 What materials are measured as dichloromethane-soluble matter?
This method measures the combined content of waxes, fats, resins, and oils present in the cellulose pulp. These materials are organic extractives that originated in the original wood or cotton feedstock.
⚡ What purity is required for the dichloromethane reagent?
ACS grade dichloromethane (≥99% CH₂Cl₂) must be used, with a specified maximum residue after evaporation of less than 0.002%. This ensures that the solvent itself does not add a significant amount of non-volatile residue to the measurement.
💡 What are the critical extraction parameters?
The extraction must run for 5 hours. The heating rate must be carefully adjusted to maintain a siphoning cycle of 6 to 8 times per hour. The oven for drying must be maintained at 105 ± 3°C.
📌 What types of extraction thimbles are acceptable?
Three thimble types are specified: standard paper (43 x 123 mm), aluminum oxide (34 x 100 mm, medium porosity), and glass (45 x 130 mm, coarse-porosity fritted disk). All thimbles must be pre-extracted with dichloromethane before use.