Batch emulsion polymerization : a chemical engineering approach Citation for published version (APA): Kemmere, M. F. (1999). Batch emulsion polymerization : a chemical engineering approach. Technische Universiteit Eindhoven. https://doi.org/10.6100/IR525404 DOI: 10.6100/IR525404 Document status and date: Published: 01/01/1999 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. 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Kemrnere Omslagontwerp: Ben Mobach, TUE Druk: Universiteitsdrukkerij TUE Batch emulsion polymerization A chemica! engineering approach PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de Rector Magnificus, prof. dr. M. Rem, voor een commissie aangewezen door het College voor Promoties in het openbaar te verdedigen op woensdag 29 september om 16.00 uur door Maria Francisca Kemmere geboren te Loon op Zand Dit proefschrift is goedgekeurd door de promotoren: prof. dr. ir. A.A.H. Drinkenburg en prof. dr. ir. A.L. German Copromotor: dr. J. Meuldijk Het in dit proefschrift beschreven onderzoek werd financieel gesteund door de Stichting Emulsie Polymerisatie (SEP) SUMMARY Emulsion polymerization is an important industrial process for the production of latex paints, rubbers, coatings and adhesives. Although the process has been used for a long time, relatively little attention has been paid to the engineering aspects of the polymerization. In the work described in this thesis batch emulsion' polymerization has been investigated from an engineering point of view with the objective to imprave the operation of current processes and to allow for improvements in the development of navel emulsion polymerization processes. For this purpose, different issues have shown to he important, for which this work has been focused on four topics: emulsification, colloidal stability, rheology and flow in high sohds polymerization and heat transfer. These topics have been studied using the polymerization of styrene and vinyl acetate as two representative model systems. In the first stage of the polymerization, emulsification of the monoroers is important, because insufficient emulsification influences the product properties. This is due to the fact that once poor emulsification has affected the polymerization in terrus of a broad partiele size distribution, the consequences of insuftleient emulsification work out through the further course of the reaction. From visuahzation experiments and polymerizations in combination with reaction calorimetrie studies, a critica! impeller speed, N*, can accurately be determined for a particular reactor setup and a given recipe. Impeller speeds equal or above N* guarantee intrinsic polymerization rates. Then the monoroer dropiets are small enough to eosure a sufficiently high mass transfer coefficient, thus making the reaction the rate limiting step. For the emulsion systems investigated, it has nat been possible to properly measure monoroer droplet sizes. Nevertheless, an indirect method, the visual criterion for suftleient dispersion based on N* has proven to be a reliable tooi to study emulsification in emulsion polymerization systems rather than monoroer droplet size measurements. The results show that styrene/water mixtures are more difficult to emulsify than vinyl acetate/water mixtures. This is a result of the difference in physico-chemical properties, in which the density of the dispersed monoroer phase plays a major role. For the samereactor configuration, more power input for suftleient emulsification is required for styrene/water mixtures than for vinyl acetate/water mixtures. Small and large turbine and pitched blade impeliers have been tested for emulsification purposes. In genera!, a large turbine impeller appears to be more effective in emulsifying monoroer/water dispersions than a pitched blade impeller. For studying the colloidal stability of polystyrene and polyvinyl acetate latex systems, emulsion polymerizations as well as coagulation experiments without polymerization have been performed. In order to study coagulation properly, sufficient emulsification is required. The experimental results clearly show that Brownian coagulation is the predominant mechanism in emulsion polymerization. This condusion is supported by the fact that the model developed at the ETH Zürich by Melis and Morbidelli, which considers Brownian coagulation based on the DLVO-theory, agrees well with our experimental data. Shear effects are negligible, since the polymer particles are smaller than the Kolmogorov microscale of turbulence. In order to provide sufficient colloidal stability, proper stabilization by emulsifier and a low ionic strength are required. This implies that the recipe dominates the coagulation behavior rather than the process conditions. The rheological properties and flow have been stuclied for the high solids emulsion polymerization of styrene. The increasing volume fraction of monoroer swollen polymer particles causes an increase in viscosity. At the same time the rheology changes from Newtonian into pseudo-plastic behavior, which results from the orientation of the polymer particles in the flow. Due to the shear rate distribution in the reactor, the pseudo-plastic behavior results in intensive mixing in the vicinity of the impeller, while relatively low mixing rates occur in the almost stagnant zones far from the impeller. The partiele size distribution has a significant influence on the rheology and flow. Latices with a bimodal partiele size distribution show Newtonian rheology and have a lower viscosity at the same solids content as compared to latices with a narrow and unimorlal partiele size distribution. This implies that generation of a bimodal partiele size distribution by secondary nucleation can avoid stagnant zones and thus can improve the mass and heat transfer in high solids emulsion polymerization. Reaction calorimetry has been applied to determine the partial heat transfer coefficient at the reaction side in batch emulsion polymerization of styrene and vinyl acetate. It has been shown that system properties such as solids content and monoroer type have a strong influence on the ra te of heat transfer. A large turbine impeller provides the highest heat transfer coefficient under the same conditions as compared to pitched blade impellers. insufficient emulsification I aeration I surface heat transfer ccc overall electrolyte concentration i CE.ecrit N* N** · ____... impeller speed Schematic representation of the operaring window of a particu/ar batch emulsion polymerization system andreactor configuration. Some implications of this work for industrial emulsion polymerization processes have been addressed. The most critica! parameters for batch emulsion polymerization process design are the recipe in terms of emulsifier and electrolyte concentrations, the energy dissipated into the reaction mixture, the heat transfer and the rheology of the reaction mixture. The limits between which a batch emulsion polymerization process can be operated are schematically summarized in the operating window, as shown in the accompanying figure. SAMENVATTING Emulsiepolymerisatie is een belangrijk proces voor de productie van o.a. verf, rubbers, coatings en lijmen. Hoewel het proces reeds lang op technische schaal wordt uitgevoerd,