EMULSIONS, COATINGS AND ADHESIVES

Microemulsions [512, 513] are special types of emulsions that form spontaneously and have very small particles. Microemulsions are optically clear, thermodynamically stable dispersions of two immiscible liquids obtained by the use of carefully adjusted surface-active molecules (surfactants). Both liquids in a microemulsion will be present in regions of the same order of magnitude, with the dispersed phase on the order of 10-100 nm. Aggregates of surface-active molecules, or micelles, form into colloidal-sized clusters in such a way that hydrophilic groups are directed toward the water. These definitions [514] are general in nature, but they suffice for the current purpose the interested reader is directed to texts on this 

Adhesives are polymers in this general class of materials used in many applications, from the back of postage stamps to demanding military applications cementing metal joints in military aircraft with polymers such as epoxy resins. The interfaces of such materials must be characterized to determine the strength of the adhesive bonds and the relation of properties such as peel strength with morphology. Adhesion science has been described in the literature (e.g., [517, 519-523]. 

It is well known that the particle shape, size, and distribution of a latex or emulsion control the properties and end-use applications. Many types of latex are manufactured with a controlled and sometimes monodisperse distribution of particle sizes. These polymer liquids are wet and sticky, making specimen preparation for microscopy very difficult. Because particle size and shape are so important to properties, the preparation must focus on not changing the particles as found in the fluid state. Preparation includes simple methods (see Section 4.1) such as dropping a solution onto a specimen holder, staining/fixation (see Section 4.4), microtomy (see Section 4.3), and special cryo methods (see Section 4.9). All microscopy techniques can be used for these studies. This section is meant to provide a brief survey of the types of microscopy applications that have been found useful in the evaluation of emulsions, latexes, and their use as coatings and adhesives. 

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Uses Defoamer for industrial use, esp. resin emulsions, coatings, and adhesives defoamer in food-contact coatings, paper/paperboard food pkg. adhesives... 

Higher alkyl acrylates and alkyl-functional esters are important in copolymer products, in conventional emulsion appHcations for coatings and adhesives, and as reactants in radiation-cured coatings and inks. In general, they are produced in direct or transesterification batch processes (17,101,102) because of their relatively low volume. 

Itaconic acid is a specialty monomer that affords performance advantages to certain polymeric coatings (qv) (see Polyesters, unsaturated). Emulsion stabihty, flow properties of the formulated coating, and adhesion to substrates are improved by the acid. Acrylonitrile fibers with low levels of the acid comonomer exhibit improved dye receptivity which allows mote efficient dyeing to deeper shades (see Acrylonitrile polymers Fibers, acrylic) (10,11). Itaconic acid has also been incorporated in PAN precursors of carbon and graphite fibers (qv) and into ethylene ionomers (qv) (12). 

The stabilizing of aqueous latexes succeeded by using emulsifiers (anionic, nonionic) and/or their mixture, steric stabilizators (polyvinyl alcohol (PVOH), hydroxyethyl cellulose, polyethylene glycol, new protective colloids etc.), and polymerizable surfaces active agents, in general. Vinyl acetate (VAc) emulsion homopolymers and copolymers (latexes) are widely used as binders in water-based interior and exterior architectural paints, coatings, and adhesives, since they have higher mechanical and water resistance properties than the homopolymers of both monomers [2, 4, 7]. 

Polymers of vinyl acetate are produced commercially in large volumes. Emulsions of poly(vinyl acetate) are used as paint bases, coatings, and adhesives. Overall, the polymerization processes involving vinyl acetate are quite straightforward. 

Emulsion polymerization is the process of choice for the commercial production of many polymers used for coating and adhesive applications, especially for those products that can be used in latex form. Emulsion polymerization uses free-radical polymerization mechanisms with unsaturated monomers. The heterogeneous nature of the reaction mixture, however, has a significant influence on the chemical and physical reaction mechanisms and on the nature of the final product. 

Azelaic acid (AA), 1,9-nonanedioic acid or heptane-1,7-dicarboxylic acid, is used in manifold application areas. AA is offered in the pharmaceutical field for the treatment of acne and rosacea due to its antibacterial effect [1,2]. However, AA is much more widely applied as a monomer for the production of polymers such as alkyd resins, polyamides, and impact-proof polyesters or for the synthesis of plasticizers, lubricants, lithium complex greases, corrosion inhibitors, dielectric fluids, heat-transfer fluids, metal to glass fluxes, emulsion breakers, waxes, tobacco sheet plasticizers, hot-melt coatings and adhesives, water-soluble coating resins, hydraulic fluids, fungicides, insecticides, and so on [3-7]. 

Chem. Descrip. Organo-silicone emulsion Uses Defoamer for foods, pharmaceuticals, paper coatings and adhesives in contact with food, cosmetics, pulp/paper applies. 

Uses Defoamer for latex paints, coatings and adhesives based on B/S, acrylic, polyvinyl acetate emulsion systems and monomer stripping of PVAc, PVA, and acrylic latex Features Low-vise. 

Uses Antifoam for water-based coatings and adhesives, latex paints, acrylic emulsions, waterborne systems, esp. for formulations sensitive to silicone-caused surf, imperfections Features In-grind antifoam... 

Uses Used in mfg. of water-based coatings and adhesives as crosslinker in water-borne polymers, esp. polymers contg. reactive h roxyl groups offers controlled reactivity and extends pot life in latex emulsions Features Provides improved solv. and water resist. prods, will yel. on exposure to UV light... 

Chem. Descrip. 50% Methacrylamidoethylethyleneurea, 20% methacrylic acid, 30% water, 2000 ppm hydroquinone inhibitor Uses Monomer for emulsion polymerization of acrylic, vinyl-acrylic, and styrene-acrylic latex paints with improved wet adhesion, wet scrub resist., solv. resist. adhesion promoter in water- and solv.-based coatings and adhesives... 

Various copolymers of ethylene with vinyl acetate are prepared by free-radical mechanism in emulsion polymerizations. Both reactivity ratios are close to 1.0 [106]. The degree of branching in these copolymers is strongly temperature-dependent [107]. These materials find wide use in such areas as paper coatings and adhesives. In addition, some are hydrolyzed to form copolymers of ethylene with vinyl alcohol. Such resins are available commercially in various ratios of polyethylene to poly(vinyl alcohol), can range from 30% poly(vinyl alcohol) to as high as 70%. 

In the emulsion pol)anerization products, poly(vinyl acetate) emulsion homopol aner and vinyl acetate based emulsion copol)aners have a great importance in industrial aspect as well as scientific aspect. They account for 28% of the total waterborne synthetic latexes. Poly(vlnyl acetate) emulsion homopol)aner was the first synthetic polymer latex to be made on a commercial scale [6-9]. Its production is growing steadily in both actual quantities and different applications. The largest volume applications are in the area of coating and adhesive. It offers good durability, availability at low cost, compatibility with other materials, excellent adhesive characteristic, and ability to form continuous film upon drying... 

Emulsion polymers used in paints, coatings, and adhesives... 

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