Alkali-swellable latexes

HEUR/Hydrophobically Modified Alkali-Swellable Latex. 

Hydrophobically modified alkali-swellable latex thickeners (Chapter 25) can also be used as cothickeners for HEURs, and, like hydrophobically modified HEC, do not suppress the ICI viscosity of HEURs. Therefore, blend ratios of HEUR/hydrophobically modified alkali-swellable latex systems will have less HEUR thickener and be less expensive than HEUR/cellulosic systems. Some hydrophobically modified alkali-swellable latexes are even more cost-efficient than cellulosic thickeners, so a further savings may be realized. Another advantage to this approach is that the HEUR/hydrophobically modified alkali-swellable latex thickener systems are not biodegradable however. 

The reduction of scrub resistance is the main disadvantage of HEUR/ hydrophobically modified alkali-swellable latex thickener systems 18, 19). Hydrophobically modified alkali-swellable latex-thickened paints often show increased water and alkali sensitivity, reduced wet and dry adhesion, and lower scrub resistance than similar cellulosic-thickened paints. 

Two base paints should be blended, one with a high ICI viscosity and one with a low ICI viscosity, to obtain the desired ICI viscosity. During this process, the Stormer viscosity should remain constant. Typical thickener combinations used are HEUR/cellulosic, HEUR/hydrophobically modified HEC, and HEUR/hydrophobically modified alkali-swellable latex. 

Hydrophobically modified alkali-swellable latex thickener. 

Preparation and Characterization of Alkali-Swellable Carboxylated Latexes... 

The two associative thickeners examined in the remainder of this text whose synthesis has not been discussed are hydrophobe-modified alkali-swellable emulsions (HASE) discussed in Chapters 25, 27, and 28, and hydrophobe-modified (hydroxyethyl)cellulose (HMHEC, discussed in Chapters 17, 18, and 27). HASE thickeners, by far the lowest cost hydrophobe-modified thickeners produced, should have achieved the largest market share on the basis of cost of production, but this situation does not appear to be the case (discussed in Chapter 28) in large part because of the poor properties observed with the lowest cost latex, vinyl acetate, used to form the continuous film. The applied-film properties 46) of vinyl acetate can be substantially improved through the use of HEUR polymers. HMHEC, synthesized by a matured (30-year-old) commercial slurry process (47) has achieved commercial acceptance, in large part because of linear high shear rate viscosities achieved in blends with HEUR thickeners (Chapter 27). 

HASE (hydrophobically modified alkali-swellable emulsion, discussed in Chapters 25 and 28) and HEUR thickeners are readily displaced from acrylic latex surfaces (32) by sodium dodecyl sulfate (SDS). A surface-active cellulose ether was also reported (33) to desorb from monodispersed poly(styrene) latices with SDS addition. In these studies, the relative critical micelle concentrations of the anionic surfactant and thickener appear to be more important than buffering of surface charges. 

Uses Thickener for latex systems, textile coatings, adhesives Features High efficiency alkali swellable highest efficiency between pH 7-8 produces short and buttery rheology Properties Vise. 10 cps 30% NV by wt. 

The preparation of a synthetic latex is shown to be a very complex process that is affected by the monomers selected, surfactants, initiators and the polymerisation process. The semi-continuous process is the one most frequently used as it provides control of the polymerisation heat removal, as well as control of the composition of the copolymers comprising several types of monomer units. Some aspects of copolymerisation in emulsion and particle growth in the case of the semi-continuous process are discussed. The copolymers usually comprise 4 to 5 comonomers, some of them with functional groups. The functional groups serve as loci for crosslinking, improve colloid stability, increase polarity, improve adhesion and cause alkali-solubility and/or alkali swellability. High value polymer latices with special particle morphology, composition and other... 

Nishida, S., El-Aasser, M.S, Klein A, and Vanderhoff, J.W., Preparation and Characterization of Alkali-Swellable Caiv-boxylated Latexes in Emulsion Polymers and Emulsion Polymer ization, ed, Bassett, B.R., and Hamielec, A.E, ACS Symposium Series No. I65 ACS, Washington, I98I, pp.290-514... 

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