Emulsion polymerization equipment

In particular, if a latex is to be used for coatings, adhesives, or film applications, no silicone-base stopcock greases should be used on emulsion polymerization equipment. Although hydrocarbon greases are not completely satisfactory either, there are very few alternatives. Teflon tapes, sleeves, and stoppers may be useful, although expensive. 

In order to be economically viable, a continuous emulsion polymerization process must be able to produce a latex which satisfies application requirements at high rates without frequent disruptions. Since most latex products are developed in batch equipment, the problems associated with converting to continuous systems can be significant. Making such a change requires an understanding of the differences between batch and continuous reactors and how these differences influence product properties and reactor performance. 

Subsequently, we arranged to have him visit our laboratories in the Chemistry Department at McGill (how simple and unsophisticated were our methods and equipment then ). Suffice it to say that we had a stimulating session with him, discussing our research on emulsion polymerization and obtaining many valuable suggestions for future work. His special contribution then, as is the case even now, was that he was aware of the wide spectrum of polymer research which was being carried out in all parts of the world, and could immediately refer you to the literature or to people who could answer your questions. 

McCaffery etal. discuss the use of a low-resolution Raman spectrometer to directly monitor a batch mini-emulsion polymerization.41 While this kind of equipment is unlikely to be installed in an industrial facility, the article raises several important points. In order to compensate for laser-power fluctuations, a functional group present in both the reactants and the product, the phenyl ring in styrene, was used as an internal standard. Since internal standards cannot be added to industrial reactions, this approach can be quite helpful. However, scientists must be certain that the internal standard will remain unchanged by the reaction and that changes in its signal only reflect laser-power fluctuations. 

The emulsion polymerizations were carried out in vacuum sealed ampoules in a rotating wheel device positioned in the gamma field, providing agitation and assuring radiation uniformity by tumbling the ampoules end over end. The equipment used has been described previously (10). 

Figure 1. Sketch of equipment used for the continuous emulsion polymerization of styrene in a tubular reactor...

Emulsion polymerization reactors are made of stainless steel and are normally equipped with top-entry stirrers and ports for addition of reactants. Control of the reaction exotherm and particle size distribution of the polymer latex is achieved most readily by semibatch (also called semicontinuous) processes, in which some or all of the reactants are fed into the reactor during the course of the polymerization. Examples are given in Chapter 8. In vinyl acetate copolymerizations, a convenient monomer addition rate is such that keeps the vinyl acetate/water azeotrope retluxing. at about 70°C. 

Experiments using no emulsifier were conducted in tbe same stainless steel autoclave equipment described above (Machi et nf.. 1975). Stable latices were obtained, believed to be achieved by hydroxyl end groups and adsorbed hydroxyl ions. As with a number of the experiments with emulsifiers the polyethylene had a considerable cross-linked gel content. Finally, the same group of workers studied tbe radiation-induced emulsion polymerization of ethylene in a flow system (Kodama et al, 1974). Both potassium inyristate and ammonium perfluorooctanoate were used as emulsifiers. At longer residence times (above 0.2 hr) the rate of polymerization was essentially constant. As with the batch system it was assumed that the number of particles remained constant. In this region the rate was found to be proportional to tbe 0.3 power of the potassium myristate concentration and the 0.5 power of the dose rate, not too different from the batch systems. The kinetics was developed and estimates of tbe propagation rate constants obtained. Despite other similarities between the two systems, these were quite different, however, from those extracted from the batch experiment. 

Machi et at. (1974) first reported an investigation of the radiation-induced emulsion polymerization of tetrafluorocthylene, with ammonium perfluorooctanoate as the emulsifier. A 200-ml stainless steel autoclave, equipped with a magnetically driven propeller-type stirrer, was used. The standard recipe used was 28gm of monomer in 150 ml of water with 1% emulsifier (based on tbe water). n-Hexadecane (2.0 ml) was added to inhibit any gas-phase polymerization. The polymerizations were conducted at... 

Figure J. Equipment for discontinuous measuring of y-induced emulsion polymerizations...

The movement of the pharmaceutical industry away from volatile solvents for coating applications coupled with advancements in coating equipment design led to an increase in the popularity of latex and pseudolatex coating systems. Latexes and pseudolatexes are both colloidal dispersions of polymer droplets in a continuous aqueous phase, the difference between them being that latex systems are formed by emulsion polymerization... 

In a novel process, FIPI was also applied to the emulsiflcation of polymer melts in water, thus providing an alternative method to emulsion polymerization for the production of latexes. " " In fact, some thermoplastic melts (such as polyethylene) cannot be obtained through the emulsion polymerization route hence, the present technique is an example of PI providing a novel product form. To achieve the emulsiflcation of thermoplastics, it is necessary to operate near or above 100°C and at elevated pressures, which necessitates the use of polymer processing equipment fitted with a MFCS mixer at the outlet. It was found that molecular surfactants could not be used to obtain the initial (water-in-polymer melt) emulsion. Instead, hydrophobically modified water-soluble polymers were used as the surface active material. After the phase inversion in the MFCS mixer, the resulting emulsion was diluted to the level required. This also freezes the molten latexes. The important attributes of FIPI emulsification include a low level of surfactant use, low temperature processing, production of submicrometer particles with a narrow size distribution, and production of novel products. 

Emulsion Polymerization. The temperature of the polymerization can vary depending on the characteristics of the initiator used, but it is typically between 30°C and 125°C. The pressure of the polymerization is typically between 1380 and 8275 kPa, but it can be higher if the equipment permits operation at higher pressure. 

It can be noted that latexes of low-density polyethylene (LDPE) are prepared via free-radical emulsion polymerization as a specialty product [56]. However, fhe low variability wifh respect to fhe polymer microstructure is disadvantageous for tailoring latex properties (e.g. film-forming properties), resulting in a narrow property profile. In addition, working at pressures in excess of 1000 bar in fhe presence of water is challenging for the equipment used. 

Free-radical polymerizations are carried out by a variety of processes that require different design considerations with respect to recipe of polymerization and physical conditions for the process and process equipment. Generally free-radical polymerizations are carried out by four different processes (a) bulk or mass polymerization, (b) solution polymerization, (c) suspension polymerization, and (d) emulsion polymerization. 

Homopolymer DADMAC-Emulsion Polymerization. The equipment setup outlined in the solution polymerization was used to prepare the emulsion polymer. To the resin pot 321.5 g benzene, 138.5 g of 72.2% aqueous DADMAC monomer, and 40 g of 20% aqueous sodium octyl phenoxyethoxy-2-ethanol sulfate were added. The mixture was stirred at 170-180 rpm with a paddle stirrer and heated to 50° 1°C. The suspension was purged with nitrogen gas for 1 hr. Then, 7 ppm Fe+2 (added as Fe(NH4)2(S04)3 6H20) were added, followed by 2 X 10"3 mol f-butylperoxypivalate/mol monomer. The reaction mixture was stirred for 20 hr at 50° 1°C under a nitrogen blanket. The polymer conversion after 20 hr was 90 2%. The product was isolated by adding the benzene emulsion to acetone, filtering the product, and drying. 

The use of existing industrial scale equipment is also possible for the recently developed ab initio emulsion polymerization process, publication No. WO 2007025086 (International Application No. PCT/US06/33152). 

In large-scale industrial applications, emulsion polymerization is carried out in kettles that have adequate means of agitation and are equipped with reflux condensers. If one of the monomers is a gas or a low-boiling liquid, the polymerization is performed in a closed system capable of sustaining the pressure developed as a consequence of the increased temperature. An interesting method to control the temperature is to start with only a part of the batch in the kettle after the reaction has started and the liberated heat of the reaction has caused an increase of the temperature of the kettle content, additional cold monomer emulsion or water is gradually added to keep the temperature at the desired level. 

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