Online monitoring of polymer nanoparticle growth as valuable tool in the development of adhesive dispersions
Presentation held at In-Adhesives Symposium, Munich, 15th of February 2017
The efficient implementation of synthesis concepts into robust and reproducible emulsion polymerization processes requires a reliable process control, ideally also with respect to an inline monitoring of polymer nanoparticle growth. If critical process parameters like e.g. emulsification of the monomers, particle formation, colloidal stability during processing, heat flux, and viscosity are monitored inline and continuously, an increased understanding of the polymerization process is achieved, resulting in safe and cost-optimal processes and feedback control strategies. For example, polyvinylacetate based dispersion adhesives (white glues) are usually modified with functionalized comonomers to control glue properties like viscosity, pH, film formation, hydrophobicity, and adhesive strength (via crosslinking). However, the modification will also influence process characteristics like particle nucleation and growth or polymerization rates. Technologies which provide information about these features might improve process control and hence product quality. To date only a limited number of process analytical technologies, suitable for high concentrations of nanoparticles, exist. The recently developed Photon Density Wave (PDW) spectroscopy allows for the precise and calibration-free characterization of the optical properties of particles and droplets during their processing. Its fundamental benefit - the quantitative separation of light absorption and light scattering - enables particle sizing also in highly concentrated polymer dispersions (> 40 vol%), in diameter ranges of approx. 50 nm 500 µm. The contribution will introduce PDW spectroscopy and discuss its benefits based on the monitoring of polymerization processes like the synthesis of highly concentrated functionalized polyvinylacetate adhesives.