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D2403-96 – Standard Test Method Technical Guide
Phthalic anhydride is a versatile intermediate used extensively in the production of plasticizers, alkyd resins, and polyester resins. ASTM D2403 – 96 (Reapproved 2003), formally titled Standard Specification for Refined Phthalic Anhydride-1308, provides the definitive quality benchmark for this critical industrial chemical. By specifying rigorous limits for solidification point and color, the standard ensures a consistent and high-quality product suitable for demanding chemical syntheses. This specification is under the jurisdiction of ASTM Committee D16 on Aromatic Hydrocarbons and Related Chemicals.
📐 Scope and Conformance Requirements
The scope of this standard covers the specification limits for refined phthalic anhydride. A critical requirement is the application of Practice E 29 for rounding off test data. An observed or calculated value must be rounded “to the nearest unit” in the last right-hand digit of the specification limit. This ensures uniform interpretation of test results. Furthermore, all sampling procedures must adhere to Practice D 3438 for sampling and handling naphthalene, maleic anhydride, and phthalic anhydride. The standard explicitly requires compliance with current OSHA regulations, supplier’s Material Safety Data Sheets, and local regulations for all materials used.
Referenced Documents:
| 🟦 Standard | 📄 Title |
|---|---|
| D 1493 | Test Method for Solidification Point of Industrial Organic Chemicals |
| D 3366 | Test Method for Color of Maleic Anhydride and Phthalic Anhydride in the Molten State and After Heating (Platinum-Cobalt Scale) |
| D 3438 | Practice for Sampling and Handling Naphthalene, Maleic Anhydride, and Phthalic Anhydride |
| E 29 | Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications |
⚠️ Mandatory Safety Compliance: Section 1.3 of the standard mandates users to consult current OSHA regulations (29 CFR 1910.1000 and 1910.1200), the supplier’s Material Safety Data Sheets, and all applicable local regulations prior to handling phthalic anhydride.
⚙️ Required Test Methods and Property Specifications
The standard mandates two specific ASTM test methods for verifying the quality of the refined phthalic anhydride. Test Method D 1493 provides a precise procedure for determining the solidification point using a controlled cooling rate and a standardized thermometer. The solidification point is a classic purity assay; impurities almost invariably lower the freezing point. Test Method D 3366 measures color in the molten state and after a controlled heating period using the Platinum-Cobalt Scale. This provides insight into the material’s thermal stability and the presence of color bodies.
The following table summarizes the mandatory property limits and their corresponding test methods as defined in Section 3 of the standard.
| 📏 Property | 🎯 Specification Limit | 📐 Test Method |
|---|---|---|
| Solidification point, min, °C | 130.8 | D 1493 |
| Molten color, max | 30 | D 3366 |
| Molten color after heating, max | 100 | D 3366 |
📊 Conformance and Interpretation of Significant Digits
The precision of the specification limits requires careful application of rounding rules. For example, the solidification point has a minimum limit of 130.8 °C per D 1493. According to Practice E 29, this means only values rounded to the nearest tenth of a degree are considered. A reported value of 130.75 °C rounds to 130.8 °C and meets the minimum, while 130.74 °C rounds to 130.7 °C and does not. This strict adherence is critical for proper quality control and acceptance testing between producers and users.
💡 Technical Application Note: A measured solidification point significantly above the 130.8 °C minimum is not just acceptable but indicates a high level of refinement, provided the stringent color limits (30 max for molten, 100 max after heating) are also satisfied. These three criteria work together to define the