Modelling the morphology evolution of polymer materials undergoing phase separation Michal Vonka, Juraj Kosek ⇑ Department of Chemical Engineering, Institute of Chemical Technology Prague, Technická 5, 166 28 Prague 6, Czech Republic highlights " We model mechanisms of ‘salami’ morphology formation in high-impact polystyrene. " Graft-stabilized polystyrene particles are preserved through phase inversion. " Thermodynamically consistent reaction induced phase separation is presented. " The shear imposed by mixer forms the occlusions inside the PB domains. article info Article history: Available online xxxx Keywords: Cahn–Hilliard model Heterophase polymers Morphology evolution Phase inversion abstract This contribution models the morphology evolution of hetero-phase polymers that undergo phase sepa- ration and inversion during their formation. High impact polystyrene (HIPS) is a selected representative of hetero-phase polymers with double-emulsion (or ‘salami’) morphology, because it consists of the con- tinuous polystyrene (PS) phase with dispersed micron-sized polybutadiene (PB) particles containing sub- micron occlusions of the partially grafted copolymer (PB-g-PS). Our modelling effort builds on the work of Nauman and He (2001) [1], but addresses the weakest point of the Cahn–Hilliard model applied to HIPS evolution: the Ostwald ripening, which is in reality suppressed or reduced by grafting. Phase inversion is the most critical but so far least-modelled step in double-emulsion morphology evolution. Therefore we demonstrate the modelling of all three experimentally observed mechanisms of double-emulsion forma- tion: (i) encapsulation of PS particles into PB domains by shear forces, (ii) thermodynamically consistent reaction-induced phase separation, and (iii) preservation of graft-stabilized PS particles through the phase inversion. We stress out the requirement of proper setting of three-component (polystyrene–poly- butadiene–styrene) thermodynamics as the basis for the realistic description of the phenomena occurring during the evolution of hetero-phase morphology. We thus present the first phenomenological model capable to describe all principal steps in the HIPS double-emulsion morphology evolution and can thus conclude with the discussion of future efforts aimed at its quantitative refinement and modelling of industrial reactors. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Understanding the morphology evolution of hetero-phase poly- mers is a key point for developing of advanced materials. A prom- ising way in tailoring the materials with desired properties is the morphology modification of known materials with massive indus- trial production. High-impact polystyrene (HIPS) is an example of the hetero-phase polymer and its morphology evolution is the sub- ject of our modelling effort. HIPS is a polymer produced in large amounts, but it is not considered to be a commodity plastics due to a widely varying characteristics of HIPS grades produced by var- ious technologies. HIPS grades differ not only in their application properties (i.e., mechanical and optical properties, rheology and toughness), but also in the underlying morphology, extent of graft- ing, cross-linking of polybutadiene (PB) and average molecular weights of polymer species. There are several objectives in the innovation of HIPS products, e.g., the reduction of the content of the more expensive PB while preserving the toughness and volume fraction of PB domains by increasing the content of PS occlusions immersed in micron-sized PB domains [2]. Other objectives relate to the improvement of material gloss related to scattering on small PB particles and even achieving at least partial transparency of the normally white HIPS material. HIPS morphology develops by a sequence of several steps: (i) formation of the initial homogeneous blend, (ii) phase separation 1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.06.091 ⇑ Corresponding author. Tel.: +420 22044 3296; fax: +420 22044 4320. E-mail address: Juraj.Kosek@vscht.cz (J. Kosek). Chemical Engineering Journal xxx (2012) xxx–xxx Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Please cite this article in press as: M. Vonka, J. Kosek, Modelling the morphology evolution of polymer materials undergoing phase separation, Chem. Eng. J. (2012), http://dx.doi.org/10.1016/j.cej.2012.06.091