Polymer particle dispersion

In water-based paints, the dominant solvent is water. There may be a small amount of other solvents to carry out certain functions. There are two types of water-based paints—one with latexes (composed of fine polymer particles dispersed in the solvent) and the other with water-soluble polymers. Latex paints are very common in the architectural market with flat, semigloss, and gloss coatings. More and more industrial coating applications are switching to water-based paints for environmental reasons. 

Polymer latexes which consist of very small (0.05-5 fim in diameter) polymer particles dispersed in water as shown in Fig. 3.1 are usually produced by emulsion polymerization. 

The monomer consumption from the interfacial layer (cosurfactant effect, see Sec. II.B) modifies the film curvature energy. The formation of water-swollen spherical polymer particles dispersed in the oily phase corresponds to the minimum free energy of the system. 

Ang Angola, J., Fujita, Y., Sakai, T., Inoue, T. Compatibilizer-aided toughening in polymer blends consisting of brittle polymer particles dispersed in a ductile polymer matrix. J. Polym. Sci. Part B Polym. Phys. 26 (1988) 807-816. 

For local spalling where the cover is between 12 and 25-30 mm, polymer modified cementitious materials are more appropriate. The polymers are usually supplied as very fine polymer particles dispersed... 

Emulsion pol)m erization is a complex process in which the radical addition polymerization proceeds in a heterogeneous system. This process involves emulsification of the relatively hydrophobic monomer in water by an oil-in-water emulsifier, followed by the initiation reaction with either a water-soluble or an oil-soluble free radical initiator. At the end of the pol)nnerization, a milky fluid called "latex", "synthetic latex" or "pol)rmer dispersion" is obtained. Latex is defined as "colloidal dispersion of polymer particles in an aqueous medium". The pol)nner may be organic or inorganic. In general, latexes contain 40-60 % pol)nner solids and comprise a large population of polymer particles dispersed in the continuous aqueous phase (about lO particles per mL of latex). The particles are within the size range 10 nm to 1000 run in a diameter and are generally spherical. A typical of particle is composed of 1-10000 macromolecules, and each macromolecule contains about lOO-lO " monomer units [10-16]. 

Polymerisation in disperse media takes pride of place in production of polymer materials. This is because polymers can be obtained as dispersions of particles (latexes) and these are often used in industry. Terminology is adopted from the study of emulsions. A normal latex is a system composed of hydrophobic polymer particles dispersed in water. A reverse latex is a system in which water-soluble polymer particles are swollen with water and dispersed in an organic phase. 

Formulation is quite different for polymerisation in an oil-in-water microemulsion or an inverted microemulsion (water-in-oil). In the first case, hydrophobic monomers are liquids (e.g., styrene, methyl methacrylate) which can be dispersed in a microemulsion without addition of a solvent. Conversely, at the kind of temperatures generally used, water-soluble monomers are powders. They must first be dissolved in water (to a level of about 50%). For this reason, reverse (water-in-oil) microlatexes are formed from water-swollen polymer particles dispersed in an organic phase. 

The basic equation for swelling of a polymer particle with a monomer was given by Morton et al. who considered a system where a monomer in bulk swells polymer particles dispersed in water and where the presence of water in monomer and in polymer phase could be neglected. Denoting the monomer as compound Zp the Morton equation reads ... 

Acrylic latexes are high MW acrylic (co)polymer particles dispersed in water. Synthetic latexes are prepared by a radical polymerization mechanism using an emulsion polymerization technique. The emulsion polymerization is carried out in water using monomer(s), surfactant (emulsifier) and water-soluble initiator. In a typical manufacturing process, an initiator and a separate emulsion of monomer(s) in water are slowly added to a reaction vessel containing water and emulsifier, at a predetermined rate. Polymerization of monomers occurs within tiny pockets formed by aggregation of emulsifier molecules, called micelles, resulting in formation... 

The product obtained from (conventional) emulsion polymerization is a colloidal dispersion comprising a very large population of submicron hydrophobic polymer particles dispersed in the continuous aqueous phase. This colloidal system is not thermodynamically stable because of the incompatibility between polymer and water (i.e., the very low solubility of polymer in water) in nature. As a matter of fact, the fate of most common latex products is the coagulation of polymer particles in order to minimize the particle-water interfacial area. Moreover, the monomer-swollen particles may even lose their colloidal stability and flocculate with one another in the course of emulsion polymerization. This will inevitably make the particle nucleation and growth mechanisms more complicated. 

Many common coatings are latexes. A latex is a stable suspension of small, insoluble polymer particles dispersed in water. These materials have become increasingly popular because they do not contain large quantities of organic solvents that are emitted into the environment—that is, they have low volatile organic compound (VOC) emissions. 

Uses Lubricant improving load bearing of oil-based lubricants monomer/water emulsifier polymer particle dispersant emulsifier for caustic sol ns., aliphatic soivs., solv. cleaners, dry cleaning textile antistat detergent floor cleaners EP fluids corrosion inhibitor personal care formulations Properties Cl. liq. sol. 25% in ethanol, CCI4, perchloroethylene, xylene, heavy aromatic naphtha, kerosene, min. oil insol. in water sp.gr. 1.02 pour pt. IOC acid no. 105 (to pH 5.5) 185 (to pH 185) surf. tens. 32.3 dynes/cm pH 2.0 (3% aq.) 100% cone. 

Aqueous polymer dispersions are important raw materials used in a variety of industrial processes. They consist of very small polymer particles dispersed in water and appear as milky fluids. When finally processed and providing the function for which they were selected, they are barely visible. Polymer dispersions are used to protect metal, wood, and leather against water and microorganisms, and are used as binders for pigments, fillers, and fibers and to finish the surfaces of metal, wood or paper. Protecting, binding, and finishing are the essential effects achieved by use of polymer dispersions. 

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