Surface-active cellulosic polymer

Properties. Hydroxypropylcellulose [9004-64-2] (HPC) is a thermoplastic, nonionic cellulose ether that is soluble in water and in many organic solvents. HPC combines organic solvent solubiUty, thermoplasticity, and surface activity with the aqueous thickening and stabilising properties characteristic of other water-soluble ceUulosic polymers described herein. Like the methylceUuloses, HPC exhibits a low critical solution temperature in water. 

The classic studies of Saunders( 17) demonstrated that in the presence of excess surfactant methyl cellulose (MC) would desorb from monodispersed polystyrene latices. MC is one of the most surface active water-soluble polymers (W-SPs) and it will readily dominate the surface pressure 7T (7T = cre - cr t where cr is the surface tension of water and is the surface tension of the aqueous polymer solution) of the aqueous solution. For example, hydroxyethyl cellulose (HEC) lowers the surface tension of water much less than MC or HPMC, and when the combination of HEC and MC or HPMC in water is studied, there is no notable influence of HEC on the surface pressure (Figure 2). 

A new class of water soluble cellulosic polymers currently receiving attention Is characterized by structures with hydrophobic moieties. Such polymers exhibit definite surface activity at alr-llquld and liquid-liquid Interfaces. By virtue of their hydrophobic groups, they also exhibit Interesting association characteristics In solution. In this paper, results are presented on the solution and Interfaclal properties of a cationic cellulosic polymer with hydrophobic groups and Its Interactions with conventional surfactants are discussed. 

In many applications and formulations, WSPs with surface-active properties are desirable. These properties are imparted to a polymer by chemical modification of the hydrophilic WSP with appropriate hydrophobic substituents. Examples of commercially available surface-active WSPs based on cellulose include its methyl, hydroxypropyl, and methylhydroxypropyl derivatives. 

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. 

S. Alila, A.M. Ferraria, A.M. Botelho do Rego, and S. Boufi, "Controlled surface modification of cellulose fibers by amino derivatives using N,N -carbonyldiimidazole as activator", carbohydrate polymers, Vol. 77, issu 3, pp. 553-562, 2010. 

In the modification with water-soluble polymers such as cellulose derivatives and polyvinyl alcohol, small amounts of the polymers are added as powders or aqueous solutions to cement mortar and concrete during mixing. Such a modification mainly improves their workability because of the surface activity of the water-soluble polymers, and prevents the dryout phenomena (explained in Ch. 4, Sec. 3.1, Water Retention). The prevention of the dry-out is interpreted in terms of an increase in the viscosity of the water phase in the modified cement mortar and concrete and a sealing effect due to the formation of very thin and water-impervious film in them. In general, the water-soluble polymers hardly contribute to an improvement in the strength of the modified systems. 

Modification of cement mortar and concrete by small amounts of water-soluble polymers such as cellulose derivatives and polyvinyl alcohol is used popularly for improving workability. In this case, the water-soluble polymers are mixed with the mortar and concrete as powders or aqueous solutions, and act as plasticizers because of their surface activity. 

The cellulose types of chiral stationary phase currently available are coated on a wide pore silica support as opposed to being bonded to the silica surface. They take two basic forms, those derived from cellulose polymers and those derived from amylose polymers they are reported to have molecular weights of up to 40,000 Daltons. The basic difference between the two polymers is that the cellulose adopts a linear structure, whereas the amylose forms a helical structure. Both cellulose adn amylose unit contains 5 chiral centers. As a result the polymers contain a large number of chirally active sites and thus a relatively high probability of chird site interaction with the solute. The structure of the cellulose type of stationary takes the following form. 

Table 1.3 shows, for example, the surface tension of the solutions of some water-soluble polymers at 25°C (0.1% aqueous solutions of the polymers). Hydroxypropylcellulose (HPC) is a good example of a surface-active polymer. Water solutions greatly reduced surface and interfacial tensions. HPC functions as an assistant in both emulsifying and whipping. HPC combines organic solvent solubility, thermoplasticity and surface activity with the aqueous thickening and stabilizing properties of other water soluble cellulose pol miers. 

As flocculants for a wide range of substrates (such as cellulose fibres) and in water treatment. Reverse latexes are destabilised and reversed by adding excess water or possibly another surface active agent. Microlatexes prepared in microemulsion polymerisation are self-reversing and therefore do not require addition of another surfactant to favour this transformation. Furthermore, the corresponding polymers, confined within such small particles, with such low polydispersity, should exhibit better characteristics in this respect. 

This is the final category considered when the polymer is itself markedly surface active, the situation becomes very different in many cases the polymer alone will be able to sustain a foam generated from its aqueous solution. An example (61) of this is the hydro-phobically substituted cationic cellulose polymer Quatrisoft LM 200. Many other examples can be found in the literature, including proteins themselves and their derivatives. On addition of a surfactant, mixed adsorbed films will form and the film and foaming characteristics will depend very much on the specifics of the components themselves, the nature of their interaction, and their relative concentration. (See Fig. 11.)... 

Properties. Methylcellulose [9004-67-5] (MC) and its alkylene oxide derivatives hydroxypropylmethylcellulose [9004-65-3] (HPMC), hydroxyethylmethyl-cellulose [9032-42-2] (HEMC), and hydroxybutylmethylcellulose [9041-56-9] (HBMC) are nonionic, surface-active, water-soluble polymers. Each type of derivative is available in a range of methyl and hydroxyalkyl substitutions. The extent and imiformity of the methyl substitution and the specific type of hydroxyalkyl substituent affect the solubility, surface activity, thermal gelation, and other properties of the poljuners in solution. 

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