Waterborne dispersed polymers

Waterborne dispersed polymers include both synthetic polymer dispersions and natural rubber. Synthetic polymer dispersions are produced by emulsion polymerization. A substantial part of the synthetic polymer dispersions is commercialized as dry products these include SBR for tires, nitrile rubbers, about 10% of the total PVC production, 75% of the total ABS and redispersable powders for construction materials. Carboxylated styrene-butadiene copolymers, acrylic and styrene-acrylic latexes and vinyl acetate homopolymer and copolymers are the main polymer classes commercialized as dispersions. The main markets for these dispersions are paints and coatings, paper coating, adhesives and carpet backing. 

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There are two main ways to reduce the VOC content in waterborne dispersed polymers post-polymerization and devolatilization. Post-polymerization can only be applied to emulsion polymers. Water-soluble redox initiators yielding hydrophobic radicals have been found to be advantageous for monomer removal by postpolymerization. In suspension polymers the devolatilization is limited by both the diffusion through the particle (because of the usually high Tg of the polymer) and the mass transfer from the particle surface to the aqueous phase (because of the large particle size that results in a relatively small interfadal area). Therefore, the temperature and the polymer particle size play an important role in the devolatilization efficiency. 

Emulsion paints consist of polymer dispersions as binders, pigments, extenders, and small amounts of auxiliaries (in some cases < 1 %). Waterborne polymer dispersions are produced by emulsion polymerization monomer droplets are polymerized in water-containing surfactants and protective colloids. The size and size distribution of the dispersed polymer particles can be controlled by adjusting the stirring rate in the polymerization reactor and by selecting appropriate protective colloids. 

Waterborne dispersions Carboxylated styrene-butadiene polymers Vi nyI acetate polymers Acrylic and styrene acrylic polymers... 

Colloid Polymer Science 278, No. 11, Nov.2000, p. 1103-8 PREPARATION OF WATERBORNE DISPERSIONS OF EPOXY RESIN BY THE PHASE-INVERSION EMULSIFICATION TECHNIQUE. II. THEORETICAL CONSIDERATION OF THE PHASE-INVERSION PROCESS... 

For waterborne dispersions the ability to deliver polymer particles to the hair near the critical 60-80% solids level will minimize the effects of water plasticization of the hair. As can be seen in Figure 34, however, waterborne dispersions rapidly gain viscosity as their solids level increases. In this regard, the more water evaporation that occurs during... 

Waterborne dispersions form films through a fascinating process. In order for crosslinking to occur and a coherent film to be built, the solid particles in dispersion must spread out as the water evaporates. They will do so because coalescence is thermodynamically favored over individual polymer spheres the minimization of total surface allows for a decrease in free energy [5]. 

Other polymerization processes in dispersed media. Some examples of these polymer materials are (i) dispersed polymers with well-defined microstructure obtained by controlled radical polymerization [53-56], (ii) waterborne linear polyethylene produced by catalytic polymerization [57-59],... 

Goikoetxea M, Minari RJ, Beristain I, Paulis M, Barandiaran MJ, Asua JM. A new strategy to improve alkyd/acrylic compatibUization in waterborne hybrid dispersions. Polymer 2010 51 5313-5317. 

Half of the polymer latexes synthesized by emulsion polymerization are commerdalized as waterborne dispersions and the rest as dry polymer. The main polymer families produced are based on (1) styrene-butadiene, (2) acrylonitrile-butadiene, (3) chloroprene, (4) vinyl chloride, (5) VAc and its copolymers, and (6) acrylic (co)polymers. ... 

The efforts to synthesize waterborne hybrid polymer-polymer nanopartide dispersions are due to the expected synergetic behavior of the positive properties of each polymer phase. Hybrid latexes made of alkyd resins, " polyurethanes, polydimethylsiloxane (PDMS), polyester,"" ... 

There are two types of polymers used in waterborne coatings and varieties that fall between these types. The polymers can be soluble or dispersed. The soluble polymers are either traly in solution in water (or a combination of water and a cosolvent) or their particle size is small enough so that light is not scattered. The solutions are clear rather than milky. The dispersed polymers are particles that are stabilized by internal or external surfactants. 

The chain extension step may then take place in the water phase. Hydrazine and ethylene diamine are commonly used chain extenders for waterborne urethane dispersions. The isocyanates react with the diamine chain extenders much faster than with the water, thus forming polyurea linkages and building a high molecular weight polymer. More detailed information regarding the synthesis and process of making waterborne polyurethane dispersions is found in Dieterich s review article [58]. 

Acrylic resins are generally well characterized by Py-GC/MS without the need for any derivatization reaction. However, in waterborne polymer dispersions it is common to have minor amounts of acrylic and/or methacrylic acid monomers added in the copolymerization to help the stability of the final latex. These monomers can also appear in the pyrolysis products, and it has been shown that with on-line derivatization they can be more efficiently revealed [85]. 

The most recent developments are water-based dispersions of PEEVE,81 some of them cross-linkable with waterborne isocyanates.82 Another FEVE-based polymer, developed and commercialized recently by Asahi Glass Co. Ltd., has trade name LUMISEAL and is used for high-performance sealants, similar to silicone sealants with the advantage of eliminating the staining problem associated with the latter.83... 

Chemical modification of the epoxy resin includes either attaching hydrophilic groups to the epoxy resin or attaching the epoxy resin to hydrophilic polymers. This is most often done by grafting. For example, one of the largest volume uses for waterborne epoxy is the coating of metal cans. In this application the epoxy resin is rendered water-dispersible by the grafting of the epoxy resins to acrylic polymer. 

Epoxy dispersions also can easily be blended with other waterborne polymers to make modified latex adhesives. The resulting hybrid adhesive produces performance properties and application characteristics that are superior to those of the originating latex system. 

Epoxy modified polymer latex systems offer improved handling performance and moisture and chemical strength advantages over unmodified formulations. The wide range of latex polymers and the range of waterborne epoxy dispersions offer the formulator a wide latitude in performance characteristics required by specific applications. 

The waterborne basecoat consists of a urethane or an acrylic dispersion with passivated aluminum for metallic glamour. The aluminum must be passivated to prevent reaction with water and the evolution of hydrogen gas. Passivating agents can include polymers, hexavalent chromium (now mandated for removal), or phosphate esters. The basecoat is pre-baked (with infrared or thermal ovens) to release the majority of the water prior to clear-coat application. 

Emulsions are dispersions of one fluid into another. Both oil-in-water and water-in-oil emulsions are encountered. Foams are similar to emulsions, but the dispersed phase is a gas. Emulsions are everywhere some examples of products that are based on emulsions are salad dressings, mayonnaise, egg yolk, milk, margarine, cream, ice cream, waterborne paints and bitumen. Emulsions are generally not stable, so they need to be stabilized against coalescence. One can use surfactants for that, or polymers, such as proteins and polysaccharides, or particles. 

The polymers used in waterborne coatings can be either soluble or dispersed in water (or a combination of water and a cosolvent). The problem of formulations containing soluble polymers is that the presence of polar/hydrophilic groups in the polymer makes the final films more sensitive to humidity. For this reason, a better solution is to formulate hydrophobic polymers that are stabilized in water by internal or external surfactants forming emulsions. Emulsified polymers have high molar masses but because they are dispersed in a particulate form, the viscosity of the media is not sensitive to their molar masses. Therefore, the physical properties are expected to be less dependent on the cure reactions. 

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