Metrohm’s inline monitoring of free isocyanate (%NCO) content in polyurethane
18 Feb 2020
Polyurethanes (PU) are a class of synthetic polymers used to create solid or foam structures; such as mattresses, shoe soles, safety helmets, insulation, packing material, surfboards, wind turbine blades and much more.
The vast variety of densities, hardness, and durability found in PU products is due to the sheer amount of additives and recipes available. PU are formed by reacting liquid di/polyisocyanates and polyols with a catalyst and various additives. The step additions of these chemicals occur in a reactor before the final mixture is spread on rollers or injected into moulds to be further processed to customer specifications.
The reaction between polyisocyanates and polyols is quick and exothermic, beginning with the addition of a catalyst into the reactor. The process reaches an initial equilibrium, after which three stepwise chemical additions are made in the reactor to modify the PU properties. The final reagent quenches NCO functional groups from unreacted isocyanates; therefore knowing the precise concentration is crucial here.
Determining the %NCO in the PU manufacturing process is a critical parameter to help determine the proper mixing ratio between the different reagents for optimized production of various PU characteristics. This is generally performed in the lab by titration methods. Spot samples are taken from the reactor at various points in the mixing process and %NCO is determined.
Laboratory titration is slow and uses chemicals which need proper disposal. During transportation to the laboratory, sample properties have already changed as it is exposed to ambient conditions not representative of the reactor. A safer way to increase PU production, decrease waste, save time and money is monitoring %NCO inline in real-time.
Reagent free near infrared (NIR) spectroscopic analysers enable comparison of real-time spectral data from the process to the primary method (titration) to create a simple, yet indispensable model for your process needs. Gain more control over your production with a Metrohm Process Analytics NIR XDS system, capable of monitoring up to nine process points with the multiplexer option.