Polymers (Partner Lead: Covestro)

Monitoring Particle Formation of Polyurethane
dispersions and Polyacrylate emulsions.

In this case study, process analytical techniques are applied to follow and control the (nano-)particle formation in the production of polymer dispersions and emulsions. Two types of polymers are of interest: polyurethanes and polyacrylates. Both types of polymers, and their particles, are used in the various resins and (latex) coating solutions of Covestro Resins and Functional Materials. Particle size (distribution) determines the quality of a coating both during, and after application. Therefore, the monitoring and control of the particle size during the process is of paramount importance for the polymer dispersion industry.

Various partners collaborate to prepare and execute the key activity of this case study: the inline characterization of particle and particle size distribution, as well as concentration, in a Covestro pilot process. The scale of the pilot will lie between 10 and 200 liters. The type of process will be batch radical emulsion polymerization. Initially, scientists at the Universidad del País Vasco (UPV) will implement photon wave density spectroscopy (PDWA; PDW Analytics GmbH) and turbidity spectrometry (TUS; IRIS) technologies in their downscaled process, a one liter batch reactor. These experiments should result in a correlation between the PAT outputs (size, shape and concentration) and process parameters (pH, temperature, solids content, monomer feeding strategies). Together with product, process and data specifications, enabling the installation of the PAT in the pilot reactor; the correlations from the one liter experiments will form the ground work for eventual real time control in the pilot scale reaction process, with respect to (nano-) particle size (80-350 nm) and distribution.


Key challenges to be addressed by PAT’s, such as PDW and TUS, include the characterization of a latex with a bimodal particle size distribution. Another key challenge is related to hybrid acrylic-polyurethane dispersions. They are created in a two-step process, each step being performed in its dedicated reactor vessel. An additional challenge is to work with complex reaction media, including those that are heterogenous or turbid.

PAT’s addressing some or all of this challenges, will allow convenient, inline monitoring over time, thus eliminating the need for additional batch time to allow for incumbent off-line monitoring techniques such as dynamic light scattering (DLS), specialized chromatography techniques, or electron microscopy methods. These techniques require additional sample preparation, dilution, time and/or costs. With PAT, we expect the overall batch times to be reduced, which includes costs-saving in terms of heating costs, manufacturing, and the like. These will sum up to substantial savings with an increased batch-to-batch control and coating quality.

Figure 1: Typical examples of water-borne polymer emulsions