Hydrophobically modified rheological properties

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

Modification of poly(2-vinylpyridine) with a long-chain K-dodecyl bromide was the first published example of a polysoap in the literature [192]. (The term polysoap arises from the fact that the resulting modified polyelectrolyte displays similar properties to that of an ordinary soap [192,193].) Dependent on the aqueous solution conditions and the nature of the hydrophobe, modified polyelectrolytes can associate either intramolecularly or intermolecularly [194], and this has created interest from a technological perspective potential applications include use as associative thickeners and rheology modifiers [195]. 

During these developments, hydrophobically modified ethoxylated urethane (HE UR) thickeners were synthesized and patented (6, 7). Their application in coatings was discussed, but the emphasis was on improved barrier properties (8), not on rheological influences. The HEUR polymers of the... 

Hydrophobically modified water-soluble polymers (HMWSPs) exhibit enhanced solution viscosity and unique rheological properties. These properties can be explained in terms of intermolecular associations via hydrophobes. This chapter describes the synthesis and solution properties of HMWSPs, Particularly discussed are the solution properties of hydrophobically modified hydroxyethytjcellulose (HMHEC) in aqueous and surfactant systems, HMHECs interact with surfactants and thus modify solution viscosities. The structure and the concentration of the surfactant dictate the solution behavior of HMHEC. The unique solution properties of HMHEC can be exploited to meet industrial demands for specific formulations or applications. 

A few years ago, Landoll (2-4) reported that grafting a small amount of long-chain alkyl hydrophobes onto a nonionic water-soluble polymer leads to associative thickening behavior (i.e., enhanced viscosity, surface activity, and unusual rheological properties). This chapter deals with the general methods of preparation and solution properties of hydrophobically modified nonionic WSPs. Particularly described are the solution properties of hydrophobically modified (hydroxyethyl)cellulose (HMHEC) in aqueous and surfactant systems. 

Hydrophobically modified, ethoxylated urethanes (HEURs) are the thickeners of choice in exterior coatings and in corrosion-resistant, high-gloss industrial latex finishes. This chapter presents an overview of our research efforts and discusses approaches to the synthesis of HEUR polymers with different molecular architectures, geometrical influences on solution properties, and viable mechanisms by which this class of associative thickener effects desirable coatings rheology and applied film properties. 

Chem. Descrip. Hydrophobe modified ethoxylate Uses Rheology control agent, associative thickener for latex systems, high gloss and semi-gloss coatings, waterborne architectural and industrial paints, printing inks, suitable for acrylics, styrene-acrylics Properties Clear liq. dens. 8.75 Ib/gal vise. 1800 cps VOC 20% (EPA Method 24) 40% act., 40% water Use Level 1.0-3.0% on total wt. 

Middleton, J. C., D. F. Cummins and C. L. McCormick, Rheological Properties of Hydrophobically Modified Acrylamide-Based Polyelectrolytes, in Water-Soluble Polymers Synthesis, Solution Properties and Applications, Shalaby, S. W., McCormick, C. L., Butler, G. B., Eds., ACS Symposium Series No. 467, American Chemical Society, Washington, t)C, 1991, pp. 338-348. 

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... 

Water-borne paint. Mainly nonionic cellulose ethers are used as rheology modifiers for water-borne paint. The rheology control of the paint influences such properties as paint consistency, brush load, levelling, sagging and hiding power. Besides the thickening, the polymer takes an active part in the particle stabilization in the paint. This is by far the most important application for a hydrophobically modified cellulose derivative (HM-CD). 

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