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D5775-95 – Standard Test Method Technical Guide
ASTM D5775-95 (Reapproved 2023) outlines a standard test method for determining bound styrene in styrene butadiene rubber (SBR) using refractive index measurement. This method is intended for solid uncompounded emulsion SBR with less than 55% bound styrene and is critical for monitoring monomer composition and product uniformity.
📐 Apparatus and Material Preparation
Essential apparatus for this test includes an Abbe-type refractometer with fourth decimal place accuracy, a vacuum oven capable of maintaining 100°C at 1.3 kPa (10 mm Hg), and a hydraulic press that can apply at least 2.2 kN (500 lbf) per specimen. Aluminum foil with a thickness between 0.025 mm and 0.08 mm is used for pressing samples into thin sheets. Optional pressing plates measuring 210 mm × 210 mm × 3 mm may also be utilized.
| 🟦 Apparatus | 📏 Specification |
|---|---|
| Refractometer | Abbe-type, fourth decimal accuracy, with Amici compensator |
| Vacuum Oven | 1.3 kPa (10 mm Hg), 100 °C |
| Aluminum Foil | 0.025 mm to 0.08 mm thick |
| Hydraulic Press | 2.2 kN per specimen or 100 kN for plates |
| Pressing Plates (optional) | 210 mm × 210 mm × 3 mm |
| Glass Test Piece | Standard for refractometer adjustment |
| Spiders | 13 mm squares with Nichrome wire legs |
💡 Tip: Ensure the polymer is thoroughly extracted with ETA and dried before pressing to avoid contamination and ensure accurate readings.
⚙️ Test Procedure and Measurement
The dried ETA‑extracted polymer is placed between aluminum foil sheets and pressed in a hydraulic press at 100 °C to form a sheet with a thickness not exceeding 0.50 mm. The refractive index is then measured at 25 °C using the Abbe refractometer. The bound styrene content is calculated from the refractive index using appropriate tables. For solution‑polymerized SBR, different refractive index tables must be used due to variations in butadiene vinyl content.
⚠️ Note: The sample thickness must not exceed 0.50 mm to ensure reliable refractive index measurement.
📊 Significance and Use
The bound styrene test provides a critical check on monomer charging accuracy and serves as a guide to product uniformity. Since the bound styrene content directly affects the physical properties of the rubber, this test method is essential for quality control in rubber manufacturing. References include Practices D1418 and D4483 for nomenclature and precision evaluation.
❓ Frequently Asked Questions
🔍 What is the scope of ASTM D5775-95?
This test method applies to solid uncompounded styrene‑butadiene copolymers (SBR) prepared by the emulsion process, with bound styrene content less than 55 %.
💡 What are the key apparatus requirements?
An Abbe‑type refractometer with fourth decimal accuracy, a vacuum oven at 1.3 kPa and 100 °C, aluminum foil 0.025–0.08 mm thick, and a hydraulic press providing at least 2.2 kN per specimen.
⚡ How is the sample prepared?
The dried ETA‑extracted polymer is pressed between aluminum foil to a thickness of not more than 0.50 mm, and the refractive index is measured at 25 °C.
📌 Why are different refractive index tables required for solution polymers?
Solution‑polymerized SBR has a different vinyl content in the butadiene portion compared to emulsion polymers, necessitating separate tables for accurate bound styrene calculation.