Polyvinyl acetate particles

Latex Shelf Life. The shelf life of seed I was greater than 6 months, but none of the latexes produced in the tubular reactor had a shelf life of more than a week. Initially, a thin liquid layer formed at the top. After several weeks, a solid layer formed in the bottom of the container. Despite the high levels of emulsifier used, the large polyvinyl acetate particles separated quickly. No studies were made to increase the shelf life. 

There are four kinds of polymerization processes bulk, solution, emulsion, and suspension polymerization. As Table 4.7 shows [24], the heat of polymerization of vinyl acetate is high compared to other monomers hence, the control of temperature is difficult in bulk polymerization. In the case of emulsion and suspension polymerization, it is somewhat troublesome to separate dispersed polyvinyl acetate particles from the aqueous medium, and it is necessary to remove the emulsifier and stabilizer completely because these substances induce problems in the process of fiber-making. 

Like plasticizers, solvents cause the polyvinyl acetate particles to soften and swell, raising the viscosity of the emulsion (Fig. 17). Higher viscosity allows dilution of the adhesive with water, thus reducing the adhesive wet cost. Swelling and softening also destabilize the emulsion. This increases the setting speed and also allows the adhesive to coalesce into a film more rapidly and at a lower temperature than the neat emulsion. The improved coalescence results in greater water resistance for the film. 

Polyvinyl acetate (PVA), acrylic and other polymer dispersions have been widely used as anti-dust treatments for concrete floors for many years. In general, the polymer dispersions have been similar to those used in the manufacture of emulsion paints, and until recently have tended to be based on dispersions of relatively large polymer particles (particle size 0.15-0.25 x 10 m). Dispersions are now becoming available which offer superior performance as floor sealers. The chemical and water resistance of the various polymer dispersions which have been used in the past vary considerably from the PVA types, which are rapidly softened and eventually washed out by water, to acrylic and SBR types which exhibit excellent resistance to a wide range of chemicals. Water-based sealers are gaining wider acceptance because of... 

Organic solvents are most commonly used, and encapsulating polymers include ethylcellu-lose, NC, polvvinylidene chloride, polystyrene, polycarbonate, polymethylmethacrylate, polyvinyl acetate and others. Inter facial polymerization produces a polymer such as nylon at the interface between layered solns of two precursor materials such as (in the case of a nylon) a diamine and a diacid (Refs 3 11). If the particle or drop-... 

The determination of adsorption isotherms at liquid-solid interfaces involves a mass balance on the amount of polymer added to the dispersion, which requires the separation of the liquid phase from the particle phase. Centrifugation is often used for this separation, under the assumption that the adsorption-desorption equilibrium does not change during this process. Serum replacement (6) allows the separation of the liquid phase without assumptions as to the configuration of the adsorbed polymer molecules. This method has been used to determine the adsorption isotherms of anionic and nonionic emulsifiers on various types of latex particles (7,8). This paper describes the adsorption of fully and partially hydrolyzed PVA on different-size PS latex particles. PS latex was chosen over polyvinyl acetate (PVAc) latex because of its well-characterized surface PVAc latexes will be studied later. 

Latex. A milk-like fluid containing small particles of natural or synthetic rubber suspended in water. Synthetic latexes are made by carrying out a polymerization step in aqueous medium (an emulsion polymerization). Water-base paints are made from polyvinyl acetate latex created in this way. 

Polyvinyl acetate polymers synthesized by emulsion polymerization168, show strikingly different behavior188,189). Figure 41 shows Dz as a function of Mw. For the low molecular weights, D2 decreases as expected but from Mw = 14 106 onwards Dz remains constant. The measured samples were products obtained at different extents of monomer conversion. The soap surrounding the latex particles was removed and the samples were dissolved in methanol and measured. The behavior of Dz in this system is understood by recalling that... 

The results showed that all batch polymerizations gave a two-peaked copolymer compositional distribution, a butyl acrylate-rich fraction, which varied according to the monomer ratio, and polyvinyl acetate. All starved semi-continuous polymerizations gave a single-peaked copolymer compositional distribution which corresponded to the monomer ratio. The latex particle sizes and type and concentration of surface groups were correlated with the conditions of polymerization. The stability of the latex to added electrolyte showed that particles were stabilized by both electrostatic and steric stabilization with the steric stabilization groups provided by surface hydrolysis of vinyl acetate units in the polymer chain. The extent of this surface hydrolysis was greater for the starved semi-continuous sample than for the batch sample. 

Recent investigations have shown that the behavior and interactions of surfactants in a polyvinyl acetate latex are quite different and complex compared to that in a polystyrene latex (1, 2). Surfactant adsorption at the fairly polar vinyl acetate latex surface is generally weak (3,4) and at times shows a complex adsorption isotherm (2). Earlier work (5,6) has also shown that anionic surfactants adsorb on polyvinyl acetate, then slowly penetrate into the particle leading to the formation of a poly-electroyte type solubilized polymer-surfactant complex. Such a solubilization process is generally accompanied by an increase in viscosity. The first objective of this work is to better under-stand the effects of type and structure of surfactants on the solubilization phenomena in vinyl acetate and vinyl acetate-butyl acrylate copolymer latexes. 

Figure 10. Density of different polymer latex particles as a function of centrifugation time (N = 40.000 min 1) (Y ) polyvinyl acetate (%) poly(vinylacetate-co-ethylene) (A) polystyrene (X) poly( butadiene-co-styrene) (O) poly butadiene)...

Figure 9 shows another example (39, 40). It is a polyvinyl acetate gel. The important fact with respect to polymeric supports is that the copolymers of the right-hand side of the maximum have the wrong structure. Microscopic investigations sometimes show particles shaped like a squeezed lemon in contact with a solvent they jump up to spherical particles. Thin sections sometimes show hollow... 

Chemical nature Non-ionic polyvinyl acetate emulsion Particle size 0.5 to 2 microns Appearance White, free flowing liquid... 

Polyvinyl acetate homopolymer emulsion. High molecular weight, large particle size resin. May be used with thermosetting resins, starches, softeners, nondurable water repellents and plasticizers. Base for adhesives. T(g) 28C. 

Emulsion—formation of small particles via micellar or homogenous nucleation Low dispersion viscosity compared to bulk high molecular weight good heat transfer Emulsifier impurity reactor wall fouling emulsifier impurity SBR, polyvinyl acetate, vinyl acrylics, etc. 

In the polymer industry, packing material, laminates including multilayer films, pellets or molded products can be analyzed by NIR. Even polymer latex particles with up to 99 % water content may be analyzed. NIR provides information about reaction mechanisms, polymerization, crystallinity, orientation, water content and hydrogen bonding, even during the process of polymer manufacture. For example the disappearance of the double bonds in polyethylene and polypropylene can be monitored. In the NIR spectrum C=C bonds lead to a combination band at about 4740 cm and a first overtone at about 6170 cm NIR spectroscopy is applied to characterize ester-, nitrile-, or amide-based acrylic and methacrylic polymers. Other examples are the identification of polyvinylchloride, polyvinyl alcohol and polyvinyl acetates or the analysis of polymerization in epoxy and phenolic resins. 

One method of providing a stable, pourable mixture of colloidal sihca-polyvinyl acetate with or without the carbonaceous material, e.g., pitch, is to make the liquid phase slightly thixotropic but not viscous. In other words, to make it so that it sets to a weak gel structure at once when undisturbed (to maintain all particles in uniform suspension) but when stirred, or even tilted to pour, the yield point is so weak as to permit ready transfer of the material and easy blending with the sand. 

Amorphous sUica-sodium sUicate-polyvinyl acetate of Si02/Na20 molar ratio 5 1 formed directly on the sand by addition of a uniform, stable mixture of aqueous silica sol of uniform particle diameter about 12 nm to the sand, mixing and then adding sodium silicate Si02/ Na20 molar ratio 3.25 1 and mixing for 2 min. 

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