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D5097-90 – Standard Test Method Technical Guide
🧪 Scope and Significance
The ASTM D5097-90 (Reapproved 1996) standard provides a definitive gravimetric test method for quantifying the filter-retained solids (grit) content of polymeric latex vehicles. Specifically, this method measures the mass of material retained when a latex specimen is washed through a standard 200-mesh (75 µm) screen (Scope, Section 1.1).
Excessive grit can severely detract from the appearance of applied coatings and cause blockages in processing filters. Therefore, this test is invaluable as a quality control metric during latex manufacturing and for comprehensive product characterization (Significance and Use, Section 4). The standard emphasizes that values are stated in SI units, and users must establish appropriate safety protocols (Section 1.2, 1.3).
✅ Core Principle: The test directly measures the amount of oversized particulate matter. A lower ppm value indicates a cleaner, higher-quality latex with fewer coarse particles that could cause film defects or filtration issues.
⚙️ Apparatus and Procedure
Executing the D5097-90 method requires precision equipment adhering to strict ASTM specifications. The table below outlines the critical apparatus and test parameters derived from Section 5 and Section 6 of the standard.
| 🟦 Apparatus / Parameter | 📏 Specification / Value |
|---|---|
| Analytical Balance | Sensitivity of 0.1 mg (for weighing screens) |
| Top-Loading Balance | 500 g capacity, 0.1 g sensitivity (for latex) |
| Oven | Forced-Ventilation, Type II B (per E 145) |
| Pre-Filter Screen | 20-mesh (removes skins/large coagulum) |
| Test Screen | 200-mesh, 90 mm diameter (per E 11) |
| Latex Specimen Mass | ~50 g (weighed to nearest 0.1 g) |
| Wash Water | 500 g |
The procedural sequence is critical for accuracy. First, weigh the clean, dry 200-mesh screen to 0.1 mg (Weight A). Hand-stir the latex sample thoroughly for 15 seconds, avoiding air entrapment, and then pass approximately 150 g through the 20-mesh sieve. Next, weigh out ~50 g of the filtered latex by difference into an 800-mL beaker (Weight B, recorded to 0.1 g).
Wash the entire latex specimen through the preweighed 200-mesh screen using all 500 g of water from a wash bottle. After washing, carefully dry the screen and retained residue in the oven, cool it in a desiccator, and weigh the combination to 0.1 mg (Weight C). The filter-retained solids are calculated using the formula:
Filter-Retained Solids (ppm) = ((C – A) / B) × 1,000,000
⚠️ Key Technique Notes:
- Ensure the 200-mesh screen seats smoothly on the plastic ring of the filtration unit to prevent any latex bypass (Section 6.2, Note 2).
- Stir the latex gently to ensure homogeneity without beating in air, which could alter the measurement (Section 6.4).
❓ Frequently Asked Questions
🔍 Why is the latex pre-filtered through a 20-mesh screen?
The 20-mesh pre-filtration is a crucial preparatory step designed to remove large skins, films, and oversized agglomerates. These large pieces would not normally represent the “grit” that causes problems in fine filtration systems, and their removal prevents them from blinding the 200-mesh test screen, ensuring the test focuses on the relevant particle size range (Section 6.4).
💡 How are the filter-retained solids expressed?
The result is expressed as parts per million (ppm) by mass. This provides a highly sensitive measurement of the very small quantities of residue typically found in quality latexes. For example, a 1 mg residue on a 50 g sample equates to 20 ppm (Section 3.1).