Hydroxyethyl cellulose, hydrophobically modified

Dynamic Behavior of Hydrophobically Modified Hydroxyethyl Celluloses at Liquid/Air and Liquid/Liquid Interfaces... 

A new class of amphiphilic, surface-active graft copolymers, hydrophobically modified hydroxyethyl celluloses (HM-HEC s), are comprised of a cellulose backbone with short polyethylene oxide (PEO) and grafted alkyl side chains. They are excellent steric stabilizers of 0/W emulsions. 

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). 

Materials. Hydrophobically modified hydroxyethyl cellulose (HM-HEC) research samples were supplied by the Hercules Research Center. The compositions of the samples determined according to the preparation recipes, rather than by analysis, are summarized... 

Cationic/hydrophobe modified hydroxyethyl celluloses, (E) and (F), eliminate sperm penetration, even though they are not spermicidal. These DCEs physically impede sperm penetration, without affecting motility. 

THE SYNTHESIS OF HYDROPHOBE-MODIFIED HYDROXYETHYL CELLULOSE POLYMERS USING PHASE TRANSFER CATALYSIS... 

Nonionics (e.g., hydrophobically modified hydroxyethyl cellulose, HMHEC) Synthetic... 

The subject of surfactant-modified, water-soluble polymers, briefly discussed in Water-Soluble Polymers, is addressed in the last three sections (Chapters 16-28) of this book. These associative thickeners are covered in detail, ranging from the maleic acid copolymers of variable compositions introduced in various commercial markets in the early 1960s to the most recent entries (that is, in the open literature), hydrophobe-modified poly (acrylamide). Chapter 23 is complementary to the spectroscopic studies in Chapters 13-15 it explores new approaches to understanding associations in aqueous media. The three hydrophobe-modified polymers that have gained commercial acceptance in the 1980s, (hydroxyethyl)cellulose, eth-oxylate urethanes, and alkali-swellable emulsions, are discussed in detail. In particular, hydrophobe-modified (hydroxyethyl)cellulose, which is... 

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). 

Synthesis and Solution Properties of Hydrophobically Modified (Hydroxyethyl)cellulose... 

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. 

This chapter is concerned with just one of this class of thickeners, namely a hydrophobically modified (hydroxyethyl)cellulose (HMHEC), Hercules WSP D-47. Gelman and Barth (i) reported on the viscosity of such HMHECs. This sample contained up to four hexadecyl chains grafted to the cellulose backbone. The preparative route was that described by Landoll (2). The dilute solution properties were characterized by capillary viscom-etry, whereas the more concentrated solutions were characterized by continuous-shear viscometry, forced oscillation measurements, and shear-wave propagation. In addition, the adsorption onto polymer latex particles was investigated. 

Although in pxinciple associative thickenos could be prepared from any water-soluble polymer to which hydrophobic blocks can be attached, only three types are commercially available at present hydrophobe-modified polyfetl lene oxide), hydrophobe-modified alkali-soluble acrylic polymers, and hydrophobe-modified hydroxyethyl cellulose. However, the literature contains reports on other types, including hydrophobe-modified polyacrylamide [103], hydrophobe-modified hydroxypropyl guar [104], and a hydrophobe-modified cationic cellulose... 

ZH2 Zhao, G. and Chen, S.B., Clouding and phase behavior of nonionic surfactants in hydrophobically modified hydroxyethyl cellulose solutions, Langmuir, 22, 9129, 2006. 

The Synthesis of Hydrophobe-Modified Hydroxyethyl Cellulose Polymers Using Phase... 

Tanaka R, Meadows J, Williams PA, Phillips GO. Interaction of hydrophobically modified (hydroxyethyl) cellulose with various added surfactants. Macromolecules 1992 25 1304-1310. 

Hydrophobically modified polymer chains, referred to as associative thickeners, can produce gels at low concentrations, e.g. hydrophobically modified hydroxyethyl cellulose (Natrosol Plus, Hercules) or hydrophobically modified poly(ethylene oxide) (Rhom and Haas). 

Zhao G, Khin CC, Chen SB (2005) Nonionic surfactant and temperature effects on the viscosity of hydrophobically modified hydroxyethyl cellulose solutions. J Phys Chem B 109 14198-14204... 

The viscosity of a C-16 hydrophobically modified hydroxyethyl cellulose (CieHMHEC) is compared with an unmoved hydroxyethyl cellulose (HEQ in Fig. 29 [55]. The enhanced solution viscosity of the C-16 hydrophobically modified hydroxyethyl cellulose is the result of intermolecular associations via the hydrophobic groups. 

The hydrophobically modified hydroxyethyl cellulose is commercially available im-der the trade name Natrosol Plus firom Aqualon. The primary applications, sensitivity to electrolytes, and pH stability of this polymer is similar to HEC. A few examples of the use of associative thickeners in laundry prespotters and dentifrice formulations are Patent Applications WO 9531523 A1 [56] and JP 06166614 A2 [57] and JP 06100424 [58], respectively. 

Hydrophobically modified hydroxyethyl cellulose (HEC) has also been synthesized by post-polymerization reaction. HEC is reacted with low levels of certain reactive hydrophobes e.g. long chain alkyl epoxides, alkyl halides, acyl halides, isocyanates or anhydrides [1, 2, 25]. (Scheme 1.1 [3]). To handle the incompatibility of the hydrophobic reagent and hydrophilic polymer, the reaction is run in solution with a common solvent or in slurry ipedia. Slurry methods are preferred because of their lower reactor viscosities. A typical slurry process involves swelling HEC with isopropanol, adding NaOH in H2O, followed by addition of a long chain epoxide such as 1,2-epoxydecane, 1,2-epoxydodecane. 

We have successfully made networks of this type using hydrophobically modified hydroxyethyl cellulose (HMHEC), a nonionic cellulose ether, in two types of aqueous solvents, surfactant/water solutions and ethanol/water solutions. We have uncovered relationships between the solvent composition and the extent of cluster formation as well as the cluster composition. And we have fpund that we can indeed obtain higher loading of hydrophobic solutes than would be expected in equivalent volumes of water. 

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