Overview
ISO 15028:2014 specifies a standardized laboratory method for the determination of hydrolysable chlorine in aromatic isocyanates used to produce polyurethanes - principally toluene-2,4-diisocyanate (TDI), toluene-2,6-diisocyanate and their mixtures. The method can also be applied to other isocyanates of suitable solubility, including crude or refined polymeric isocyanates. This test supports quality control, raw-material acceptance and process protection in polyurethane manufacture.
Key Topics
-
Principle: Hydrolysable chlorine compounds react with methanol to liberate hydrogen chloride (HCl). The resulting chloride is determined potentiometrically by titration with a standardized silver nitrate (AgNO3) solution using a silver/silver chloride electrode pair.
-
Sampling & safety: Isocyanates react with atmospheric moisture; samples must be handled under dry inert gas (e.g., nitrogen) and with appropriate personal protective equipment. Laboratory humidity should preferably be below 50% relative humidity to minimise reaction with moisture.
-
Reagents & apparatus: Reagent-grade methanol and concentrated nitric acid are specified; AgNO3 solution is standardized (0,01 M typical; 0,1 M for higher chloride levels). Typical apparatus includes an automatic or manual titrator with Ag/AgCl electrode, volumetric pipette, 400 ml beaker, magnetic stirrer and analytical balance.
-
Procedure highlights: A representative test portion is weighed (document specifies typical masses), reacted with methanol, diluted with water and boiled to complete hydrolysis. After cooling and acidification with nitric acid, the sample is titrated potentiometrically with AgNO3. Cooling to about 10 °C is recommended (20 °C acceptable if validated).
-
Expression of results: Hydrolysable chlorine is calculated as a percentage by mass using the titration volume (V), concentration of AgNO3 (c) and sample mass (m):
Hydrolysable chlorine = 3,55 × V × c / m
- Precision: Based on an interlaboratory round robin, repeatability and reproducibility limits are provided in the standard (duplicate differences >0,0005 % at 0,001–0,2 % are suspect; inter-lab differences >0,003 % are suspect).
Applications
- Quality control for TDI/TDI blends and other aromatic isocyanates
- Raw material acceptance and supplier qualification
- Protecting polyurethane processing catalysts from acidic contamination
- Troubleshooting production issues related to catalyst neutralization and processing variability
Related Standards
This summary highlights the practical value of ISO 15028:2014 for laboratories and manufacturers involved in polyurethane raw-material testing and process control. For full procedural detail, precision tables and official requirements, consult the published ISO 15028:2014 document.
Open preview (PDF)Plastics — Aromatic isocyanates for use in the production of polyurethanes — Determination of hydrolysable chlorine