Applications of Polymer Latexes

The elaboration of particles of colloidal dimensions is desirable in many industrial domains. Some obvious cases where the colloidal state is required are, for instance, paints, inks and lacquers [24]. The reasons for using colloidal suspensions are varied. The most important benefits are a very large specific surface area, a great versatiHty in terms of particle size and surface properties, the ability to introduce functional groups and to selectively design the particles interior, and - finally - the possibihty of controlling the rheological properties of the suspension. 

The largest industrial uses of polymer latexes are latex paints and adhesives, but other major applications include paper coatings and textiles. Latex paints mostly involve acryhc polymers, while natural and synthetic styrene-butadiene rubbers (SBR) are the main binders of latex adhesives. The most common types of polymer latexes used in coating applications are listed in Table 4.1. 

Paints Vinyl acetate/dibutyl maleate copolymers, pure acrylics, styrene/acrylic copolymers, vinyl acetate/butyl acrylate copolymers, slyrene/acrylate copolymers 

Adhesives Natural mbber, styrene-butadiene rubber (SBR), vinyl acetate, acrylics, chloroprene and copolymers 

Paper coating Styrene, butadiene, acrylonitrile, acrylic esters, unsaturated carboxylic acid 

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The word latex has become a generic term that applies to all kinds of polymer colloidal dispersions, including those found in nature and those obtained by emulsion polymerization. Latex obtained from the sap of certain trees was used around 1600 BC by the Mayas in the ancient Mesoamerica for medicines, paints, manufacturing of rubber balls, waterproof cloths, and other mbber artifacts [1]. At present, there are a vast number of applications of polymer latexes, some of which are mentioned below. The growing variety of applications and environmental concerns has constituted the driving force for the development of this fleld. 

Background Knowledge of Heterophase Polymerization Processes 191 Table 4.1 Principal industrial applications of polymer latexes. 

In this part, it is intended to give some overlook of the various specialty applications of polymer latex particles. For illustration, Table 10.4 provides a non-exhaustive list of the numerous applications of these polymer coUoids showing that a broad range of domains is presently covered. 

For the development, production, and application of polymer latices the determination of the size distribution and the analysis of the chemical composition and heterogeneity of the latex particles are important. The size distribution can be determined rapidly by ultracentrifugation, electron microscopy or light scattering > but for the analysis of the... 

The presence of free surfactant is not preferred in some applications of polymer emulsions. It may, for instance, result in water sensitivity of dried latex coatings or... 

In Table II, common characteristics of a variety of polymer latexes are listed. Throughout the text, the more important requirements for each application were alluded to. Initial work on a specific problem should quickly establish the properties needed in both the polymer and its latex. The table is organiz to permit easy determination of the capability of different classes of latexes to satisfy property requirements. Latex producer s specific product literature should he consulted to determine which of the many products within a polymer class would be must likely to satisfy the desired application. Although this book is devoted to emulsion polymerization, natural rubber latex has been included in this chapter for two... 

Aqueous dispersions of poly(vinyl acetate) and vinyl acetate-ethylene copolymers, homo- and copolymers of acrylic monomers, and styrene-butadiene copolymers are the most important types of polymer latexes today. Applications include paints, coatings, adhesives, paper manufacturing, leather manufacturing, textiles and other industries. In addition to emulsion polymerization, other aqueous free-radical polymerizations are applied on a large scale. In suspension polymerization a water-irnrniscible olefinic monomer is also polymerized. However, by contrast to emulsion polymerization a monomer-soluble initiator is employed, and usually no surfactant is added. Polymerization occurs in the monomer droplets, with kinetics similar to bulk polymerization. The particles obtained are much larger (>15 pm) than in emulsion polymerization, and they do not form stable latexes but precipitate during polymerization (Scheme 7.2). 

The role of the surfactants is two-fold first, to provide a locus for the monomer to polymerise, and second, to stabilise the polymer particles as they are formed. In addition, surfactants aggregate to form micelles (above the cmc), and these can solubilise the monomers. In most cases a mixture of anionic and nonionic surfactant is used for the optimum preparation of polymer latexes. Cationic surfactants are seldom used, except for specific applications where a positive charge is required on the surface of the polymer particles. 

The methods that are most economical and capable of preserving the original properties of the Cl are diffusive saturation of the polymer matrix by inhibiting liquids, their introduction into the polymer solutions (latexes) or application of polymer layers (varnish, glue, etc.) onto the film base carrying the Cl. 

The method of casting solutions and polymer latexes, as well as application of polymer plastisols containing Cl on the forming substrate is used for the manufacture of both single-layer and multilayered inhibited films [3,4,23,25,41,43,53,84] as well as films with an adhesive layer [57,58]. 

DeFusco AJ, Sehgal KC, Bassett DR. Overview of uses of polymer latexes. In Asua JM, editor. Polymeric Dispersions Principles and Applications. NATO ASI Series. The Netherlands Kluwer Academic Publishers 1997. p 379. 

Figure 4.50i l indicates the adhesion of latex-modified mortars to ordinary cement mortar as a substrate, measured by four types of test methods. CJenerally, the adhesions in tension, flexure, and direct compressive shear of the latex-modified mortars to ordinary cement mortar increase with a rise in the polymer-cement ratio regardless of the type of polymer and test method. The adhesion in slant (indirect) compressive shear of the latex-modified mortars attains a maximum at a polymer-cement ratio of 5 or 10%, and is extremely large compared to the adhesions determined by other test methods irrespective of the polymer type and polymer-cement ratio. The reasons for diis may be due to the effects of the combined shear and compressive stresses and their relaxation by the polymer films formed on the bonding joints. Considering the above adhesion data, it is most important to select the best test methods to successfully reproduce service conditions in the applications of the latex-modifled mortars. 

Of various polymer-modified mortar and concrete, latex-modified mortar and concrete have superior properties, such as high tensile and flexural strengths, excellent adhesion, high waterproofhess, high abrasion resistance, and good chemical resistance, compared to ordinary cement mortar and concrete. Accordingly, they are widely used in many specialized applications in which the ordinary cement mortar and concrete have been employed to a lesser extent till now. In these applications, the latex-modified mortar is widely used rather than the latex-modified concrete from the viewpoint of a balance between their performance and cost Typical applications of the latex-modified mortar and concrete are listed in Table 9.1. 

Particle geometry and size distribution is of prime importance in nanotechnology ILBSs play an important role in controlling the growth of NPs, for example, those of polymer latex, gold, silica, and iron oxides. Other applications include their use as... 

Styrene-butadiene, acrylonitrile-butadiene, chloroprene, and vinyl chloride emulsion (co)polymers are mainly used in their dried form. Carboxylated SBR, VAc (co)polymers, acrylics, and styrene-acrylic copolymers are used, on the other hand, as binders of formulation for several industrial applications in their dispersed form. Figure 7 shows the share of each of these families and the major industrial applications of these latexes. ... 

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