Hydrophobically modified water-soluble applications

Applications in which dynamic uniaxial elongational viscosities (DUEVs) have been important to the performance of water-borne formulations are discussed. The achievement of high viscosities at low shear rates with minimum mechanical degradation of the water-soluble polymer and with minimum viscoelastic effects in applications that involved converging flows are discussed. These two factors serve as driving forces for the acceptance of hydrophobically modified water-soluble polymers. Complexities arising from the combined contribution of shear and elongational deformations in applications and in their measurement are discussed in the final section. 

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. 

Associative ASTs. Nonionic and anionic associative thickeners are presently considered state of the art in many important industrial applications. The anionic associative thickeners are a subclass of hydrophobically modified, water-soluble polymers (HWSPs), and are predominantly represented by hydrophobically modified ASTs (HASEs and HASNEs), the chemical architectures of which were previously described. Because these polymers are very similar to conventional ASTs in molecular weight and carboxyl content, thickening is by a dual mechanism hydrodynamically (a function of molecular weight, anionic content, cross-link density, and other... 

There is a class of hydrophobically modified water-soluble polymers known as associative thickeners (AT polymers) that are used in cotmnercial applications for rheology control (11-22). AT polymers and their model polymers include copolymers of acrylamide or (meth)acrylic acid with associative comonomers containing an oligomeric ethylene oxide (EO) chain as a spacer between a polymerizable moiety and terminal hydrophobe (11-16,23), Associative comonomer units in such copolymers play a role as stickers in aqueous solutions. The content of associative comonomers in AT copolymers is usually veiy low (< 2 mol %) because AT polymers are... 

Wang TK, Iliopoulos I, Audebert R. Aqueous solution behavior of hydrophobically modified poly(acrylic acid). In Shalaby SW, McCormick C, Butler GB, eds. Water-Soluble Polymers Synthesis, Solution Properties, and Applications. ACS Symposium Series 467, 1991 218-231. 

Typical shell materials include gum acacia, maltodextrins, CDs, hydrophobically modified starch, and mixtures thereof. Other polysaccharides (alginate, carboxymethylcellulose, guar gum) and proteins (whey proteins, soy proteins, and sodium caseinate) may also be used nevertheless with lower application because of their low solubilities in water, although the addition of a small amount of these low solubility hydrocolloids has shown some beneficial effects on the stability of encapsulated ingredients (Gouin, 2004). 

---