Latex application properties

Batch, semicontinuous, and continuous reactors that are designed intelligently can be utilized to manipulate almost any fundamental and/or application property. Suitable products for most applications can usually be manufactured in several different reactor systems. One may he required, however, to adjnst the latex recipe and reaction conditions to produce a satisfactoiy product in one reactor type if that produce has been developed in another reactor system. Thus, if a reactor system has been chosen for the commerdal unit one should plan on some, and in most cases considerable, product development work in a similar, small-scale system. 

Chem. Descrip. Sodium dinonyl sulfosuccinate CAS 63217-13-0 EINECS/ELINCS 221-820-7 Uses Rewetting agent for textile finishing, in applic. of resins, softeners, starches wetting agent, dispersant for latex paints Properties Liq. anionic 48% act. 

Copolymer composition has a direct effect on the Tg of the polymer, which determines the minimum film forming temperature (MFFT) of the latex and the application. Thus, a 95/5 wt/wt butyl acrylate/methyl methacrylate is an adhesive, whereas a 50/50 copolymer of the same monomers is a binder for paints. Copolymer composition affects properties such as resistance to hydrolysis [4] and weatherability. In situ formed blends of random copolymers of different compositions may be beneficial for application properties [5]. Conventional free-radical polymerization, which is the process used to manufacture almost all commercial emulsion polymers, does not allow the production of block and gradient copolymers (accessible by means of controlled radical polymerization [6], Section 3.3). Nevertheless, graft copolymers are frequently formed, and the extension of grafting largely determines the application properties. Thus, grafting determines the size of the rubber domains in ABS polymers, and the toughness of these polymers increases with rubber size. 

The application properties of many latexes are strongly affected by the chemistry of the surface of the polymer particles. Relatively small amounts (1-2 wt% based on monomers) of acidic monomers (e.g., acrylic acid, AA) are frequently used in the manufacture of latexes. Because this monomer is water-soluble, upon polymerization, most of the AA-rich polymer chains are located at the surface of the polymer particles. The presence of AA at the surface of the polymer particles is beneficial for both the stability of the latex [11] and the application properties (e.g., both the shear strength of the adhesives [ 12] and the pick strength of coated paper [9] increase with the AA content). In addition, the type and amount of surfactant affects application properties such as colloidal stability and water sensitivity of the film [13]. 

In most of the applications of the synthetic polymer dispersions (e.g., paints and coatings, adhesives and paper coatings), the commercial product is a complex formulation. Table 6.3 presents an example of a coating formulation. In these formulations, the latex is the key ingredient, but the application properties are also affected by the other components of the formulation. Product formulation is out of the scope of this booL... 

Particle size distribution. PSD strongly affects rheology [21,93], which in turn influences heat removal rate, mixing, mass transfer and stability of the latex. AU these aspects determine on many occasions the scale-up and the feasibility of the operation. In addition, PSD affects film formation and some application properties [22,94, 95]. 

Polychloroprene latex. Anionic or non-ionic latices can be used. The polymer determines the initial tack and open time, the bond-strength development and hot bond strength, the application properties and the adhesive viscosity. Anionic latices are stabilized with rosin soaps. Carboxylated polychloroprene latex is stabilized with polyvinyl alcohol and provides better freeze-thaw stability than the anionic types [78]. 

This article discusses in detail the use of ultra-fine latex in primers for building paints, considering in particular the market for primers, impressions and undercoats market requirements the benefits of ultrafine lattices improvement of application properties, and finally, film performance improvement. 

J. R. Grave and B. G. Bufkin, Survey of the Applications, Properties, and Technology of Crosslinked Emulsions. VI, J. Coatings Tech. 51(2), 34 (1979). Review of latex IPNs and related materials. 

RhGOlogy. Flow properties of latices are important during processing and in many latex applications such as dipped goods, paint, and fabric coatings. Rheology is used to characterize the stability of latices (45). For dilute, nonionic latices, the relative latex viscosity is a power-law expansion of the particle volume fraction. The terms in the expansion account for flow aroimd the particles and particle-particle interactions. For ionic latices, electrostatic contributions to the flow around the diffuse double layer and enhanced particle-particle interactions must be considered (46). A relative viscosity relationship for concentrated latices was first presented in 1972 (47). A review of empirical relative viscosity models is available (46). In practice, latex viscosity measurements are carried out with rotational viscometers (see Rheological Measurements). 

A third monomer may occasionally be used in a small quantity. For example a small quantity of styrene may be incorporated to improve the flow properties but this usually at the expense of the most desirable properties of the nitrile rubber. Incorporation of methacrylic acid produces very reactive polymers (carboxylated nitriles) which may be cross-linked by metal oxides. The use of such materials is largely confined to latex applications. 

The batch emulsion polymerization is commonly used in the laboratory to study the reaction mechanisms, to develop new latex products and to obtain kinetic data for the process development and the reactor scale-up. Most of the commercial latex products are manufactured by semibatch or continuous reaction systems due to the very exothermic nature of the free radical polymerization and the rather limited heat transfer capacity in large-scale reactors. One major difference among the above reported polymerization processes is the residence time distribution of the growing particles within the reactor. The broadness of the residence time distribution in decreasing order is continuous>semibatch>batch. As a consequence, the broadness of the resultant particle size distribution in decreasing order is continuous>semibatch>batch, and the rate of polymerization generally follows the trend batch>semibatch>continuous. Furthermore, the versatile semibatch and continuous emulsion polymerization processes offer the operational flexibility to produce latex products with controlled polymer composition and particle morphology. This may have an important influence on the application properties of latex products [270]. 

Surfactants and dispersants are used to disperse pigment, mineral and latex particles to promote suspension stability, to minimize the viscosity contribution of particle flocculation or agglomeration, and to enable higher solids content. Adjusting paint theology for optimal in-can stability and application properties normally requires the use of thickeners, thixotropes and rheology modifiers of various types. 

Since latex dispersion application properties are related to the surface properties of the latex particles, there is a need for surface characterization of the particles at large. Historically, these types of systems have been applied as model colloids (Hearn et al, 1981) and therefore required well-characterized surfaces but as the sophistication of new coatings increase, the latex particle surfaces become more important from an industrial perspective. In addition to these applications the utilization of latex particles in pharmaceutical and biomedical applications has also contributed to the development of new surface characterization methods. The surface engineering, that is, variations in size, surface charge and surface hydrophobicity, of latex particles as colloidal carriers has been demonstrated to provide opportunities for the site-specific delivery of drugs (Ilium Davis, 1982). Surface... 

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