Latexes stability

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

Salt effects in polyelectrolyte block copolymer micelles are particularly pronounced because the polyelectrolyte chains are closely assembled in the micellar shell [217]. The situation is quite reminiscent of tethered polymer brushes, to which polyelectrolyte block copolymer micelles have been compared, as summarized in the review of Forster [15]. The analogy to polyelectrolyte brushes was investigated by Guenoun in the study of the behavior of a free-standing film drawn from a PtBS-PSSNa-solution [218] and by Hari-haran et al., who studied the absorbed layer thickness of PtBS-PSSNa block copolymers onto latex particles [219,220]. When the salt concentration exceeded a certain limit, a weak decrease in the layer thickness with increasing salt concentration was observed. Similar results have been obtained by Tauer et al. on electrosterically stabilized latex particles [221]. 

Increase of ionic strength reduces the stability of electrostatically stabilized latex particles and causes them to coalesce at sufficiently high values. However the difference in the effects of potassium octadecanoate and sodium dodecyl benzene... 

Dissociation and Adsorption of Cations and Anions on Protein Stabilized Latexes... 

Dye intermediate, solvent extraction, refining petroleum, stabilizing latex, detergents, organic synthesis. 

In choosing an epoxy and polymeric latex, it is important that they have compatibility. Incompatibility usually occurs when the pH of the epoxy resin dispersion alters the pH of the latex into a range where the ionically stabilized latex is broken, causing agglomeration of the latex polymer. The pH of the epoxy resin s emulsion may need to be adjusted before blending with the polymeric latex. 

Since particle charge in these latexes is not pH dependent, the mechanism outlined above for the conventional electrocoating systems cannot apply. It was clear from the start that the difference in the behavior of sulfonium and quaternary ammonium stabilized latexes is related to the greater reactivity of the sulfonium ion. Though stable in dilute aqueous solutions, sulfonium ions might be expected to undergo rapid decomposition under the conditions obtained at the cathode surface while current is flowing. However, the specific reactions involved were not known. 

At low concentration it can be used in water repellent finishes without causing rewetting of the fabric after drying. SULFANOLE 634 can also be used to stabilize latex finishes and can be used in standard resin finishes. 

Grade Stabilized, latex, chlorine-containing elastomer, low molecular weight (liquid). 

Use Nondrying emulsifying agent solvent plasticizer in polishes in cosmetics in textile, paper, and leather processing low-temperature lubricant. Stabilizes latex paints against breakdown due to repeated freeze-thaws. 

Also, the solid particles may contain water-soluble substances, which undergo leaching and specific adsorption. Reference [1865] reports the IEP of phosphate-containing goethite. One sample studied in [32] contained sulfate and phosphate, and its IEP and PZC differed significantly. The silica studied in [2929] was prepared in the presence of a nonionic surfactant. No attempt was made to remove that surfactant from the final product. Phosphate-doped titania was studied in [2930] and polymer-stabilized latex was studied in [2931], A few results presented above have been cited by others as pristine PZCs/IEPs. 

The hairy particles stabilized by non-ionic emulsifier (electrosteric or steric stabilization) enhance the barrier for entering radicals and differ from the polymer particles stabilized by ionic emulsifier [35]. For example, the polymer lattices with the hairy interface have much smaller values of both the radical entry (p) and exit (kdes) rate coefficients as compared to the thin particle surface layer of the same size [128,129]. The decrease of p in the electrosterically stabilized lattices is ascribed to a hairy layer which reduces the diffusion of oligomeric radicals, so that these radicals may be terminated prior to actual entry. For the electrostatically stabilized lattices with the thin interfacial layer, exit of radicals occurs by the chain transfer reaction [35]. This chain transfer reaction results in a monomeric radical which then exits out of the particle by diffusing through the aqueous phase and this event is competing with the propagation reaction in the particle [130]. The decrease of kdes in the electrosterically stabilized latex... 

At the conclusion of polymerization, unreacted monomer is recovered by vacuum stripping, then is compressed, condensed, and purified for recycle in the process. A stabilizer, usually sodium carbonate, is then added to the latex at a level of about 0.4%, and the stabilized latex is spray dried. Alternatively some processes involve drum drying following by grinding. In these procedures that involve total drying of the latex, any catalyze residues, emulsifier, buffer, or other additives during the process end up with the product. Particles from emulsion processes are about 1 pm in diameter, about 1/100 of those encountered in suspension polymerization. 

Fig. 5.1. Plot of the turbidity of a polyfoxyethylene) stabilized latex as a function of temperature in 0-48 M MgS04 (after Napper, 1970a).

Fig. 5.3. (a) Plot of the turUdity as a fimctioii of wavelength for a polyfoxyethylene) stabilized latex (b) plot of the turbidity-wavelength exponent as a function of temperature for a poly(oxyethylene) stabilized latex in 0-39 M MgSO (after Dodd, 1980). 

Fig. 5.4. The temperature dependence of the Bingham yield value for a polyfoxyethylene) stabilized latex in 045 M K2SO4 (alter Hunter et al., 1975).

Fig. S.9. The dependence of the CFV and LCFT upon stabilizer surface coverage for poly(12-hydroxystearic acid) stabilized latex particles in n-heptane (after Napper, 1968b).

Fig. 6.1. The temperature dependence of the (+) CFP of a poIy(oxyethylene) stabilized latex in 0-39 M MgSOi- Also shown ( ) are the corresponding 0-pressures (after Evans el a ., 1975).

Fig. I3.I. The distance dependence of the steric interaction free energy for polystyrene stabilized latex particles in toluene 1, experimental results 2, theoretical mixing term 3, theoretical elastic term 4, total theoretical terms (after Doroszkowski and Lamboume, 1973).

Fig. 16.4. The reciprocal of the stability ratio of poly(oxyethylene) stabilized latex particles in the presence of free poly(oxyethylene) of different molecular weights curves 1,300000 2,10000 3, 4 000 4, 600 5, 200 (after Cowell et al., 1978).

Fig. 16.7. The three component diagram at 25 °C for poly(oxyethylene) stabilized latex particles (L) in aqueous (S) poly(oxyethylene) (P) solutions (a) stabilizer POE 750 with 10 000 free POE in water (b) same as (a) but in 0-065 M MgSO., same as (a) but with 1500 free POE (d) same as (a) but with 400 free POE. The numerals I and II denote dispersed particles only and dispersed particles plus floes respectively (after Cowell et al., 1978).

Generally, the mechanical and chemical stabilities of latexes are improved with an increase in the content of the surfactants selected as stabil izers, and the stabilized latexes can disperse effectively without coagulation in latex-modified mortar and concrete. On the other hand, an excess amount of surfactant may have an adverse effect on the strength of the latex-modified mortar and concrete because of the reduced latex film strength, the... 

The charge-stabilised latex had a ratio of 0.03 indicating essentially complete coagulation, whereas the methoxy PEG stabilized latex had a ratio of 0.60 indicating that a substantial proportion of the particles had remained in a colloidally stable form. 

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