Precise characterization and modeling of particle morphology development in emulsion polymerization

Resumen

This PhD aimed at paving the way to process optimization and on-line control of particle morphology in emulsion polymerization process. The bottleneck in achieving this goal is the lack of proper device for on-line monitoring of particle morphology. Therefore, the alternative is using a mathematical model as a soft sensor in on-line monitoring. . In this regard, the model developed by Hamzehlou et al.1 is the most promising possibility. The model needs to be capable of describing the evolution of the particle morphology during the polymerization as well as being sensitive to detect the effect of process variables on morphology changes. To evaluate the capacity of mathematical model on prediction of particle morphology development, composite polymer-polymer particle latexes were synthesized in a two-step seeded semi-batch emulsion polymerization by polymerization of more hydrophilic co-monomers (styrene/n-butyl acrylate) in the second stage of polymerization using a more hydrophilic seed of poly (methyl methacrylate-co-n-butyl acrylate). According to thermodynamics, the equilibrium morphology for the studied cases was ¿inverted core-shell¿ while in all synthesized cases in this thesis; kinetically meta-stable morphologies were achieved due to determining effect of radical concentration profile on the development of the particle morphology. The presented model was modified to account for radical concentration profile and the effect of different reaction variables to alter the movement of synthesized clusters at the exterior zone of the particles toward to the equilibrium position in the center of the particles was studied. It was recognized that although the combination of different characterization techniques can provide reliable knowledge about the particle morphology development, it was difficult to reach the conclusion on the effect of process variables on the morphology changes in some cases. To overcome this limit, a method for the precise quantitative 3D characterization of polymer-polymer composite waterborne particles based on high angular dark field -scanning transmission electron microscopy (HAADF-STEM) coupled with image reconstruction is presented. The information about the morphology gathered by this technique revealed mechanistic features on the development of the particle morphology that could not be captured by the conventional TEM images and hence it allowed upgrading the mathematical model. All overall, the upgraded model provides a better prediction of the effect of process variables on the morphology of composite polymer particles and this opens the way to use the model in optimization and on-line control strategies. (1) Hamzehlou, S.; Leiza, J. R.; Asua, J. M. A New Approach for Mathematical Modeling of the Dynamic Development of Particle Morphology. Chem. Eng. J. 2016, 304, 655¿666.