Case Study Emulsion Polymerization Process

As another case study a process synthesis of an emulsion polymerization process is given (Hurme and Heikkila, 1998). In emulsion polymerization unsaturated monomers or their solutions are dispersed in a continuous phase with the aid of an emulsifier and polymerized. The product is a dispersion of polymers and called a latex. The raw materials are highly flammable unsaturated hydrocarbons and the reaction is exothermic which both cause a risk. The main phases and systems in an emulsion polymerization plant are listed in Table 31. 

In the area of polymerization processes, case studies of batch process monitoring based on the Nomikos and MacGregor scheme were reported. In an emulsion batch polymerization, 46 batches were available each having 106 measurements taken during the batch run of 20... 

Continuous emulsion polymerization processes offer, in some cases, an economical method for commercial production of polymer colloids. Continuous reactors are destined to become more important as product volumes increase and as the marketplace becomes more competitive. The development of a continuous reactor system, however, is a path full of possible pitfalls which must be successfully handled. The present "state-of-the-art" is not adequate to permit a risk-free design of a continuous system from batch data. Hence studies in small-scale continuous systems are recommended for those who plan continuous processes. 

The control challenges in emulsion polymerization processes are similar to the ones discussed previously for suspension processes. Different from suspension processes, however, intense research activity has been conducted in the field, aiming to control emulsion polymerization reactions and the final latex properties. It is important to anphasize, though, that the lack of proper instrumentation for online measurement of latex properties has limited the development of control schemes basically to the control of latex composition. In these cases, control schemes depend heavily on the availability of complex process models for in-line evaluation of unmeasured properties, such as the MSD and the PSD. Comparatively, the online control of PSDs has received little attention, and few studies are devoted to this subject. 

Additionally, this approach offers, in the case of emulsion polymerization, a unified means of monitoring colloid/ polymer characteristics giving information about both the polymer and particle evolution, and thus allowing one to make correlations between key features of the two aspects of the emulsion polymerization process. Online monitoring of both particle and polymer characteristics should allow for studies of reaction kinetics, predictive and active reaction control, and also the ability to observe deviations and unexpected phenomena. 

The stirred-tank reactor and the tubular reactor are two basic reactors used for continuous processes, so much of the experimental and theoretical studies pubhshed to date on continuous emulsion polymerization have been conducted using these reactors. The most important elements in the theory of continuous emulsion polymerization in a stirred-tank reactor or in stirred-tank reactor trains were presented by Gershberg and Longfleld [330]. They started with the S-E theory for particle formation (Case B), employing the same assumptions as stated in Sect. 3.3, and proposed the balance equation describing the steady-state number of polymer particles produced as ... 

For both O/W and W/O systems, the amount of monomer is usually restricted to 5-10 wt% with respect to the overall mass, and that of surfactant(s) lies within the same range or even above. Nevertheless, there have been a few studies in which the formulation deviated from these conditions. For instance, surfactant concentrations of 2 wt V() were reported [56-58,69,124,125]. However, in this case the amount of monomer was also very low (< 2 wt%) so that the systems must be considered as micellar solutions rather than true microemulsions. Conversely, a 1994 study of Gan et al. [82] reported the polymerization of styrene up to 15 wt% using only about 1 wt V(> dodecyltrimethylammonium bromide surfactant (DTAB) in a Winsor I-like system. This system consists of a microemulsion (lower) phase topped off with pure styrene. The polymerization takes place in the microemulsion phase, while the styrene phase acts as a monomer reservoir. Such a polymerization process is novel, but it yields latices of large particle size ( 100 nm) that can be more easily obtained by conventional emulsion polymerization. 

It is well known that polymer miscibility is not only important in the case of simple mixture, but it also determines the physical nature of block and graft copolymers. Multi-layer structures have been studied in recent years as a means for improving physical and mechanical properties of the polymer composition. It is possible to obtain a number of functional properties by means of the multi-stage sequential emulsion polymerization. As concerns this multi -layer structure, we have already reported some interesting results in a study of the processing aid for polyvinyl-chloride, 5 which amazingly improved the processability for polyvinylchloride due to its multi-stage polymer composition produced by sequential emulsion polymerization. 

The soap titration technique is strictly only applicable for dispersions which contain one type of emulsifier. However, many polymer dispersions are stabilized by a combination of emulsifiers, often both ionic and non-ionic types. One approach in such cases is to perform the study with the emulsifier mixture, though there is the problem of exchange processes occurring on the particle surfaces if one of the emulsifiers is preferentially adsorbed. The results may also be affected by adsorbed amphiphilic oligomers generated during the emulsion polymerization. 

Studies on rubbery polymers have rarely been reported. It was reported that in the case of non-emulsion polymerization, clays exfoliated in a rubbery matrix performed better than in a glassy matrix. A new type of nanocomposite of clay with poly (butyl acrylate) (PBA) has been prepared successfully using intercalation-polymerization process. 

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