Thickeners HASE hydrophobically modified alkali

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. 

Rheology results are shown in Figure 5 for combination of dispersants with a commercially available HASE (hydrophobically modified alkali swellable acrylic emulsion) thickener. 

Anionics (e.g., hydrophobically modified alkali-soluble emulsions, HASE) Inorganic thickeners... 

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). 

The AST process receiving the greatest industrial and academic attention by far has been that of emulsion polymerization, and because of the relative importance of the emulsion thickeners, these polymers will be the object of considerable discussion in this review. When conventional ASTs are specifically prepared by this process, alkali-swellable or alkali-soluble emulsions (ASE) are obtained. For conventional ASTs produced by processes other than emulsion polymerization (nonemulsion), the acronym ASNE has been adopted herein. The associative ASTs have analogous designations. HASE is the common acronym for hydrophobically modified, alkali-swellable or alkali-soluble emulsion, and HASNE is the adopted acronym for the associative nonemulsion thickeners. The family of AST polymers reflecting this classification scheme is shown in Figure 2. 

X HE RELATIVE COST OF MANUFACTURING hydrophobically modified, water-soluble polymers is the primary determinant in their market acceptance. The lowest-cost associative thickeners used in coating formulations are hydrophobically modified, alkali-swellable emulsions (HASE). The extensive history leading to the development of this technology is reviewed in the preceding chapter their utilization and limitations are discussed in Chapters 27 and 28. 

The rheological properties of hydrophobe-modified alkali-swellable emulsion (HASE) thickener solution are studied, with emphasis on surfactant and electrolyte (NaCl) effect. Similar studies in model HASE thickeners have been reported. Two commercial HASE thickeners (HASE-615 and HASE-935) are examined for comparison. In the absence of SDS, the NaCl addition changes solution viscosity depending on the relative concentration of the NaCl and thickener. The viscosities of HASE type thickeners are enhanced by an anionic surfactant, sodium dodecyl sulphate (SDS) and viscosity maxima are observed due to mixed micelle formation among thickener hydrophobes and surfactants. The addition of NaCl suppresses the viscosity of HASE-615/ SDS solutions, with HASE-935 at higher concentrations actually increasing in viscosity with NaCl addition. 2 refs. USA... 

There are three main classes of thickeners, which are commonly used CeUulosics (modified natural products, usually hydroxy-ethyl cellulose - HEC), HASE (hydrophobic-ally modified alkali-sweUable emulsions) and HEUR (hydrophobically modified ethylene oxide urethanes). 

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