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D5318-97 – Standard Test Method Technical Guide
📐 Scope and Significance
ASTM D5318-97 provides a standard test method for determining hydrolyzable chloride content in peroxy esters and peroxy dicarbonates. These compounds are widely used as initiators and chemical intermediates in the production and modification of polymers such as PVC, polyethylene, and polypropylene. The level of hydrolyzable chloride can significantly affect the performance of the peroxide in these applications. As defined in the standard, hydrolyzable chloride is the sum of the inorganic chloride content and the chloride content generated upon alkaline hydrolysis of the sample.
⚙️ Apparatus and Reagents
The method requires an automatic potentiometric titrimeter with a sensitivity of 62 mV and a buret graduated in 0.001 mL divisions. A combined silver electrode is used for potentiometric endpoint detection. Table 1 lists the key apparatus specifications, including a typical system that has been used successfully.
| 🟦 Component | 📏 Specification |
|---|---|
| Potentiometric Titrimeter | Sensitivity: 62 mV; Buret: 0.001 mL |
| Recommended System | Metrohm AG Model 682 Titroprocessor with Model 664 Control Unit and Model 665 Dosimat |
| Combined Silver Electrode | Metrohm AG 6.0404.100 or equivalent |
Table 2 lists the reagent requirements as specified in the standard.
| 🧪 Reagent | 📋 Requirement |
|---|---|
| Reagent Water | ASTM D1193 Type IV or better |
| Silver Nitrate Solution | Prepared and standardized per ASTM E200 |
| Other Chemicals | Reagent-grade per ACS specifications |
⚠️ Safety Warning: Peroxy compounds are reactive and may present explosion or fire hazards. Refer to Section 8 of the standard for specific hazard statements. Always handle with appropriate personal protective equipment in a fume hood.
📊 Test Procedure and Key Measurements
The test method involves the alkaline hydrolysis of a peroxy ester or peroxy dicarbonate sample. After hydrolysis, the liberated chloride is titrated volumetrically with silver nitrate solution using the automatic potentiometric titrimeter. The endpoint is detected potentiometrically based on the change in potential. The hydrolyzable chloride content is then calculated from the volume of titrant used.
This method provides a comprehensive measurement of both inorganic chloride and chloride released from the peroxy compound, ensuring accurate assessment of total hydrolyzable chloride.
💡 Technical Tip: Ensure the combined silver electrode is properly conditioned and maintained for consistent potentiometric readings. The sensitivity of 62 mV is critical for accurately detecting the titration endpoint.
❓ Frequently Asked Questions
🔍 What is the purpose of ASTM D5318-97? It provides a standardized procedure for measuring hydrolyzable chloride in peroxy esters and peroxy dicarbonates, which is important for their performance in polymer applications.
💡 How is the test performed? The sample undergoes alkaline hydrolysis, followed by potentiometric titration with silver nitrate to determine chloride content.
⚡ What equipment is essential for this test? An automatic potentiometric titrimeter with 62 mV sensitivity and a 0.001 mL buret, along with a combined silver electrode.
📌 What does hydrolyzable chloride include? It includes both free inorganic chloride and chloride generated from the breakdown of peroxy compounds during alkaline hydrolysis.