Particle size distribution suspension polymerization

The polymeric PVC is insoluble in the monomer therefore, bulk polymerization of PVC is a heterogeneous process. Suspension PVC is synthesized by suspension polymerization. These are suspended droplets approximately 10 to 100 nm in diameter of vinyl chloride monomer in water. Suspension polymerizations allow control of particle size, shape, and size distribution by varying the dispersing agents and stirring rate. Emulsion polymerization results in much smaller particle sizes than suspension polymerized PVC, but soaps used in the emulsion polymerization process can affect the electrical and optical properties. 

The particle size distribution after polymerizing a 5% Si02 particle in monomer suspension in water is depicted in Figure 5.11. Particles range in the size of 100 nm and distributions are rather narrow. As can be seen in the transmission electron microscopy (TEM) picture, the silica nanopartides are encapsulated in PMMA. As the particle content of the suspension was low, some polymer particles remain nonfilled. 

Suspension Polymerization. At very low levels of stabilizer, eg, 0.1 wt %, the polymer does not form a creamy dispersion that stays indefinitely suspended in the aqueous phase but forms small beads that setde and may be easily separated by filtration (qv) (69). This suspension or pearl polymerization process has been used to prepare polymers for adhesive and coating appHcations and for conversion to poly(vinyl alcohol). Products in bead form are available from several commercial suppHers of PVAc resins. Suspension polymerizations are carried out with monomer-soluble initiators predominantly, with low levels of stabilizers. Suspension copolymerization processes for the production of vinyl acetate—ethylene bead products have been described and the properties of the copolymers determined (70). Continuous tubular polymerization of vinyl acetate in suspension (71,72) yields stable dispersions of beads with narrow particle size distributions at high yields. 

New templated polymer support materials have been developed for use as re versed-phase packing materials. Pore size and particle size have not usually been precisely controlled by conventional suspension polymerization. A templated polymerization is used to obtain controllable pore size and particle-size distribution. In this technique, hydrophilic monomers and divinylbenzene are formulated and filled into pores in templated silica material, at room temperature. After polymerization, the templated silica material is removed by base hydrolysis. The surface of the polymer may be modified in various ways to obtain the desired functionality. The particles are useful in chromatography, adsorption, and ion exchange and as polymeric supports of catalysts (39,40). 

Each of the PLgel individual pore sizes is produced hy suspension polymerization, which yields a fairly diverse range of particle sizes. For optimum performance in a chromatographic column the particle size distribution of the beads should be narrow this is achieved by air classification after the cross-linked beads have been washed and dried thoroughly. Similarly, for consistent column performance, the particle size distribution is critical and is another quality control aspect where both the median particle size and the width of the distribution are specified. The efficiency of the packed column is extremely sensitive to the median particle size, as predicted by the van Deemter equation (4), whereas the width of the particle size distribution can affect column operating pressure and packed bed stability. 

Suspension Polymerization. The suspension or pearl polymerization process has been used to prepare polymers for adhesive and coaling applications and for conversion to poly(vinyl alcohol). Suspension polymerization are carried out with monomer-soiubie initiators predominantly, with low levels of stabilizers Continuous tubular polymerization of vinyl acetate in suspension yields stable dispersions of beads with narrow particle size distributions at high yields. 

For example, the particle size distribution in emulsion, suspension, and precipitation polymerization can be a crucial product specification. One of the greatest difficulties in achieving quality control of the polymer product is that the actual customer specifications may be in terms of non-molecular parameters such as tensile strength, crack resistance, temperature stability, color or clarity, absorption capacity for plasticizer, etc. 

Batch suspension reactors are, theoretically, the kinetic equivalent of water-cooled mass reactors. The major new problems are stabilization of the viscous polymer drops, prediction of particle size distribution, etc. Particle size distribution was found to be determined early in the polymerization by Hopff et al. (28, 29,40). Church and Shinnar (12) applied turbulence theory to explain the stabilization of suspension polymers by the combined action of protective colloids and turbulent flow forces. Suspension polymerization in a CSTR without coalescence is a prime example of the segregated CSTR treated by Tadmor and Biesenberger (51) and is discussed below. In a series of papers, Goldsmith and Amundson (23) and Luss and Amundson (39) studied the unique control and stability problems which arise from the existence of the two-phase reaction system. 

In Chapter 12 of this book, the mechanical properties of ceramic suspensions, pastes, and diy ceramic powders are discussed. Ceramic suspension rheology is dependent on the viscosity of the solvent with polymeric additives, particle volume fraction, particle size distribution, particle morphology, and interparticle interaction energy. The interparticle forces play a veiy important role in determining the colloidal stability of the suspension. If a suspension... 

Polystyrene can be easily prepared by emulsion or suspension techniques. Harkins (1 ), Smith and Ewart(2) and Garden ( ) have described the mechanisms of emulsTon polymerization in batch reactors, and the results have been extended to a series of continuous stirred tank reactors (CSTR)( o Much information on continuous emulsion reactors Ts documented in the patent literature, with such innovations as use of a seed latex (5), use of pulsatile flow to reduce plugging of the tube ( ), and turbulent flow to reduce plugging (7 ). Feldon (8) discusses the tubular polymerization of SBR rubber wTth laminar flow (at Reynolds numbers of 660). There have been recent studies on continuous stirred tank reactors utilizing Smith-Ewart kinetics in a single CSTR ( ) as well as predictions of particle size distribution (10). Continuous tubular reactors have been examined for non-polymeric reactions (1 1 ) and polymeric reactions (12.1 31 The objective of this study was to develop a model for the continuous emulsion polymerization of styrene in a tubular reactor, and to verify the model with experimental data. 

Masato, T., Hideyo, T., Isao, K., Natsakaze, S., Kazuhiko, H., Effect of stepwise and continuous reduction in impeller speed on particle size distributions in suspension polymerization of styrene, J. Chem. Eng. (Jpn.) 21 (1995) 118. 

Vivaldo-Lima, E., Wood, P. E. Hamielec, A. E., Penlides, A., Calculation of the particle size distribution in suspension polymerization using a compartmentmixing model, Can. J. Chem. Eng., 76 495. 

Emulsion polymerizations normally produce polymer particles with diameters ofO.I-l pm(l pm= I micron= 10 cm), although much larger particles can be made by special techniques mentioned in Chapter 8. Tlie polymer particles made by suspension reactions have diameters in the range of 50-500 pm. Recall that free-radical initiation in suspension reactions is in the monomer phase, whereas the aqueous phase is the initiation site in emulsion polymerizations. The two processes often dilTer also in the types of stabilizers that are used. Microsuspension polymerization is an alternative technique which can yield particles in the same size range as emulsion processes. This method uses a monomer-soluble initiator and anionic emulsifiers similar in nature and concentration to those used in emulsion polymerizations. A microdispersion of the mixture of the reaction ingredients is first produced mechanically and is then polymerized to provide polymer with essentially the initial fine particle size distribution. 

Hukkanen, E.J. Braatz, R.D. Measurement of particle size distribution in suspension polymerization using in situ laser backscattering. Sensors Actuators B 2003, 96 (1-2), 451-459. 

Sauakas, V., Kotoulas, C., Meimaroglou, D. Kiparissides, C. 2008 Dynamic evolution of the particle size distribution in suspension polymerization reactors a comparative study on Monte Carlo and sectional grid methods. Canadian Journal of Chemical Engineering 86, 924-936. 

PVC is insoluble in VCM. The precipitated polymer tends to coagulate in the conversion range of 1-8%. As the conversion continues, the precipitated polymer absorbs more and more monomer, and at a 15-20% conversion, the reactor contains solid polymer swollen with monomer in a monomer atmosphere. The horizontal autoclave prevents the formation of large polymer blocks by breaking them up. Advantages claimed for this process are the higher bulk density, improved particle size distribution, and more rapid plasticizer absorption. Talamini and coworkers (J ) have demonstrated that the bulk polymerization process is kinetically equivalent to suspension polymerization. 

Imamura et al. [28] describe a concentric cylinder reactor in which one cylinder is rotated. The axial flow rale and rotational speed are such to generate flows with Taylcn vortices which save to narrow the residence time and particle size distributions. The reactor is also claimed to be useful for continuous suspension polymerization. 

Kiparissides et al. [65] developed a comprehensive mathematical model for the quantitative prediction of the evolution of primary particle-size distribution during the free-radical polymerization of VCM. The population balance equation, describing the evolution of the primary particles in bulk or suspension polymerization, has the following general form ... 

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