Polymer particle size distribution

Research on the modelling, optimization and control of emulsion polymerization (latex) reactors and processes has been expanding rapidly as the chemistry and physics of these systems become better understood, and as the demand for new and improved latex products increases. The objectives are usually to optimize production rates and/or to control product quality variables such as polymer particle size distribution (PSD), particle morphology, copolymer composition, molecular weights (MW s), long chain branching (LCB), crosslinking frequency and gel content. 

M.-T. Cells, A. Forgiarini, M.-l. Briceno, L.H. Garcia-Rubio, Spectroscopy measurements for determination of polymer particle size distribution. Colloids Surf. A 331(1-2), 91-96 (2008). doi 10.1016/j.colsurfa.2008.07.024... 

Molecular weight distributions are predicted to be of the Flory type with a dispersion index equal to 2.0. The numerical results show that the dispersion index has a value of 4/3 at the beginning of the reaction, very quickly approaching a value of 2.0. These results are in complete agreement with the predictions of Saidel and Katz (5). They are the same whether or not the polymer particle size distribution has been considered. 

On-command polymer properties Product quality and product yield are much more complex issues in polymerization than in more conventional small molecule reactions. The key polymer properties are dependent on the polymer particle size distribution (PSD) and molecular weight distribution (MWD). These properties are sensitive to the process and kinetic history. The ACOMP platform, by directly monitoring these properties, will enable the production of polymers with desired properties on-command. ... 

The rate of polymer dissolution is an important property that impacts high-molecular-weight polyacrylamide availability and performance commercially. Polymer particle size distribution in dry powder polymers and the polymer solids content and level of activating surfactant in inverse emulsion polymers are factors that impact polymer dissolution. The rate of polymer dissolution is typically determined by following the rate at which the viscosity in a polymer solution builds during dissolution. 

In suspension polymerization where controlled agglomeration is not used, the monomer droplet size distribution is the final polymer particle size distribution (PSD), except for some volume shrinkage. There is little mass transfer between particles. The PSD depends on the type and amount of steric stabilizer as well as agitation and vessel design. Controlled agitation and various types of steric stabilizers both inorganic and organic are used to maintain stable suspension and to obtain desired size, bulk density, and porosity of the particles. 

Only one additional stipulation needs to be made before adapting the results that follow from Eq. (5.24) to addition polymers. The mode of termination must be specified to occur by disproportionation to use the results of Sec. 5.4 in this chapter, since termination by combination obviously changes the particle size distribution. We shall return to the case of termination by combination presently. 

Suspension Polymers. Methacrylate suspension polymers are characterized by thek composition and particle-size distribution. Screen analysis is the most common method for determining particle size. Melt-flow characteristics under various conditions of heat and pressure are important for polymers intended for extmsion or injection molding appHcations. Suspension polymers prepared as ion-exchange resins are characterized by thek ion-exchange capacity, density (apparent and wet), solvent sweUing, moisture holding capacity, porosity, and salt-spHtting characteristics (105). 

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. 

Testing. Various test methods are provided by ASTM (16). These iaclude pigment tests of importance such as chemical analysis, presence of oversize particles, oil absorption, particle size distribution, degree of dispersion, presence of soluble components, etc. Numerous tests are also given by ASTM for the properties of filled and unfilled polymers. These iaclude, for example, such properties as impact resistance, stiffness, viscosity, tear resistance, hardness, color, and electrical resistivity. 

It is found that the viscosity of a paste made from a fixed polymer/plasticiser ratio depends to a great extent on the particle size and size distribution. In essence, in order to obtain a low-viscosity paste, the less the amount of plasticiser required to fill the voids between particles the better. Any additional plasticiser present is then available to act as a lubricant for the particles, facilitating their general mobility in suspension. Thus in general a paste polymer in which the pastes have a wide particle size distribution (but within the limit set by problems of plasticiser absorption and settling out, so that particles pack efficiently, will... 

Figure 12.12. PVC pasle polymer particles with distribution of size-efficient packing...

Where the polyurethane comprises <30% of the blend, the polyurethane remains in discrete droplets within the polyacetal matrix. In this range the particle size and particle size distribution of the elastomer particles are of importance. Where the elastomer component is in excess of 30%, interpenetrating polymer networks exist in the sense that there are two interpenetrating continuous phases (as opposed to two cross-linked interpenetrating polymer systems). 

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). 

However, the chief purpose of introduction of fillers into PCM is to make possible the modification of polymers and thereby create materials with a prescribed set of physico-mechanical properties, and, obviously, the properties of filled materials may be controlled by, for example, varying the type of the base polymer (the matrix ) and filler, its particle size distribution and shape. It may not require a large quantity of filler [7]. Thanks to considerable advances in PCM research, their use in a broad range of industries — machine building, construction, aerospace technology, etc. — has become extensive [8 — 11]. 

The final polymer particles have a narrow particle size distribution. Figure 2 (] ), and the mean particle size is a strong function of the agitation in the prepolymerizer. 

FIGURE 38.9 Particle size distribution of ambient ground acrylonitrile butadiene rubber (NBR) waste powder. (Reprinted from Anandhan, S., De, P.P., Bhowmick, A.K., Bandyopadhyay, S., and De, S.K., J. Appl. Polym. Sci., 90, 2348, 2003. With permission from Wiley InterScience.)... 

By performing in situ the polymerization of acrylamide in water/AOT/toluene microemulsions, clear and stable inverse latexes of water-swollen polyacrylamide particles stabilized by AOT and dispersed in toluene have been found [192-194], It was shown that the final dispersions consist of two species of particles in equilibrium, surfactant-coated polymer particles (size about 400 A) with narrow size distribution and small AOT micelles (size about 30 A). 

In [53], segregated catalyst and polymer particles act as micro reactors where the polymerization process takes place. Each particle is an individual reactor with its own energy and material balance. During polymerization, the catalyst particles undergo a change in volume by a factor of 10 -10, thereby generating the corresponding polymer particles. The particle size distributions of catalyst and polymer are the same. 

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

Modified amino acids such as N-acyl-dehydroalanine polymers and copolymers with N-vinyl-N-methyl acetamide seem to be particularly effective [396]. The crystallization kinetics in the presence of polyvinylpyrrolidone and tyrosine have been tested by time-resolved experiments [981]. An influence is evident on the particle size distribution of the hydrate [1433]. 

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