ASTM D5155 Standard Test Methods for Polyurethane Raw Materials Determination of the Isocyanate Content of Aromatic Isocyanates

Get Certified ASTM D5155 Testing for Reliable Polyurethane Raw Material Quality 

Manufacturers use certified ASTM D5155 testing because the amount of isocyanate in a raw material directly influences the stoichiometry of a polyurethane formulation. Setting an isocyanate value results in under- or over-reacted polyurethane systems, which create processing issues and result in inconsistent properties of the final product. Certified testing confirms that a batch of aromatic isocyanate meets its intended specification before it is used in production. 

The scope of ASTM D5155 includes: 

• Material type: Aromatic isocyanates, including toluene diisocyanate, methylene-bis-(4-phenylisocyanate), and polymethylene polyphenylisocyanate.
• Purpose: Determination of isocyanate content for polyurethane raw material research and quality control. 
• Properties measured: Isocyanate content and amine equivalent of the raw material. 
• Method: The method of testing is reaction with dibutylamine and back-titration with standardized acid (Test Methods A, B, or C). 
• Result: Content of isocyanate and amine equivalent in SI units. 
• Test Limitations: Method selection is dependent on the type of isocyanate (refined, crude, modified) and on the reactivity and solubility of the isocyanate. 
• Environmental conditions: Test Method A is unheated; Test Method B is heated; Test Method C uses a solvent system of trichlorobenzene-toluene. 
• Applications: Quality control of polyurethane raw materials, formulation research, verification of specifications. 

What are the Uses of ASTM D5155 Testing?

ASTM D5155 testing provides a consistent method for laboratories to characterize the isocyanate content of aromatic isocyanates, while formulators utilize the data for formulating and research of polyurethane production. This standard-

• Determines the isocyanate content and amine equivalent of aromatic isocyanates, refined, crude, and modified aromatic isocyanates.
• Performs incoming isocyanate raw material quality control checks.
• Helps assay isomer mixtures of toluene diisocyanate and methylene-bis-(phenylisocyanate).
• Helps the formulations to keep the correct stoichiometric ratio in the polyurethane mixing systems.
• Assists in formulation development and research of new formulations containing isocyanates.
• Helps to confirm the specification for raw material purchases. 

What Materials Can Be Tested Under ASTM D5155? 

ASTM D5155 is primarily for aromatic isocyanates, which are utilized as raw materials in the manufacture of polyurethane. Typical substrates for ASTM D5155 testing include refined toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and crude or modified isocyanates from these two compounds, or polymethylene polyphenylisocyanate. Test Method A also extends to other isocyanates of suitable reactivity and solubility, broadening its use beyond the isocyanate types listed directly in the scope.

Why is ASTM D5155 Important? 

ASTM D5155 testing is significant as it helps manufacturers ensure the consistency of their raw materials before formulation, which helps to avoid production problems and ensure the final polyurethane product performs as intended. The amount of isocyanate is a key factor in the reaction ratio between isocyanate and polyol in the formulation of polyurethanes. The difference in isocyanate content may lead to processing issues like incomplete curing, over-curing, or a lack of uniformity in mechanical characteristics of the polyurethane product. 

ASTM D5155 Testing Process and Data Collection

The process starts with an analyst weighing a representative sample of the isocyanate and selecting the applicable test method, depending on the type of isocyanate. The technician then dissolves the sample in the prescribed solvent and reacts it with excess dibutylamine (heat is added during the reaction if Test Method B is used). The operator back-titrates the excess amine with the standardized acid during titration. Finally, analysts determine the amount of isocyanate and amine equivalents and compare with the specifications of raw materials. 

Common Challenges and Troubleshooting

Accurate ASTM D5155 results require careful handling of moisture-sensitive isocyanate samples, careful weighing, and an accurate, standardized titration reagent. Common causes of inaccurate isocyanate values include moisture contamination, incomplete dissolution, and titration endpoint errors. Technicians reduce these errors by minimizing sample exposure to atmospheric moisture and verifying reagent standardization before testing. Laboratories also obtain more consistent results when they test samples from a single isocyanate batch under the same test conditions. 

• The laboratory report indicates the content of isocyanate in percent by the amount of acid needed to acidify the sample.
• The technician documents the amine equivalent with the isocyanate content of the sample tested.
• The analyst records the test method used (A, B, or C) depending on the quality of the isocyanate used: either refined, crude, or modified.
• When interpreting the results, the chemist considers the type of solvent used, how the solution was heated, and how accurately the titration was performed.
• The manufacturer uses the measured isocyanate content value to accept and control polyurethane raw material specifications.

Link to ASTM D5155