Nonionic protective colloid

The protective colloid/wetting agent may be a single anionic agent Turkey Red Oil, for example, combines both functions but is prone to form a precipitate in hard water. Only anionic types are suitable, since nonionic and cationic types generally cause precipitation [31]. Most protective colloids are of the following types ... 

The stabilizing of aqueous latexes succeeded by using emulsifiers (anionic, nonionic) and/or their mixture, steric stabilizators (polyvinyl alcohol (PVOH), hydroxyethyl cellulose, polyethylene glycol, new protective colloids etc.), and polymerizable surfaces active agents, in general. Vinyl acetate (VAc) emulsion homopolymers and copolymers (latexes) are widely used as binders in water-based interior and exterior architectural paints, coatings, and adhesives, since they have higher mechanical and water resistance properties than the homopolymers of both monomers [2, 4, 7]. 

Then, with a moderate stirring speed, add 4.00 g of Cellosize hydroxy-ethyl cellulose WP-300 (a protective colloid), 2.00 g of Tergitol NP-40, 2.60 g of Tergitol NP-15 (two nonionic surfactants), 2.20 g of Alcolac Siponate DS-4 (an anionic surfactant), an 0.40 g of ammonium bicarbonate. 

Poly(vinyl acetate) emulsions can be made with a surfactant alone or with a protective colloid alone, but the usual practice is to use a combination of the two. Normally, up to 3 wt % stabilizers may be included in the recipe, but when water sensitivity or tack of the wet film is desired, as in some adhesives, more maybe included. The most commonly used surfactants are the anionic sulfates and sulfonates, but cationic emulsifiers and nonionics are also suitable. Indeed, some emulsion compounding formulas require the use of cationic or nonionic surfactants for stable formulations. The most commonly used protective colloids are poly (vinyl alcohol) and hydroxyethyl cellulose, but there are many others, natural and synthetic, which are usable if not preferable for a given application. 

Clearly, the smaller is the gold or rubin number, the more effective is the biopolymer at shielding the dispersion from coagulation by electrolytes. To describe this shielding phenomenon, Zsigmondy coined the term protective colloid ( Schutzkolloide ), which functions by protective action. From the results recorded in Table 2.1, it can be inferr that sodium casemate is considerably more effective in its protective action than is, say, dextrin or potato starch. Note that both of these latter polymers are nonionic in character. 

The emulsion polymerization of vinyl acetate may be unique among polymerization processes in that true latices have been formed with anionic surfactants, cationic surfactants, nonionic surfactants, or protective colloids, and with combinations of two or more such reagents, as well as without any added emulsifier. 

Nonionic surfactants such as polyoxyethylated fatty alcohols (such as Emul-phor ON-870 from GAP), alkyl phenyl polyethylene glycol ethers (such as the Tergitols from Union Carbide) and polyoxyethylated octylphenol may be used as protective colloids along with anionic surfactants or, in some cases, as emulsifiers in their own right. The block copolymers of polyoxyethylene and polyoxypropylene (Pluronics) solubilized vinyl acetate. Polymerization takes place at the interface of the surfactant-monomer droplet and the aqueous phase [151]. 

Cationic surfactants, in contrast to anionic surfactants, usually reduce both the number of particles involved in the polymerization and the rate of polymerization. The nature of the stabilizing emulsifier has a marked effect on the polymerization kinetics. For example, addition of a non-ionic stabilizer [e.g., poly(vinyl alcohol), a block copolymer of carbowax 6000 and vinyl acetate, or ethylene oxide-alkyl phenol condensates] to a seed polymer stabilized by an anionic surfactant decreased the rate of polymerization to 25% of the original rate. The effect was as if the nonionic stabilizer (or protective colloid) acted as a barrier around the seed particles to alter the over-all kinetics. It may be that the viscosity of the medium in the neighborhood of the nonionic surfactant coating of the polymer particle is sufficiently different from that of an anionic layer to interfere with the diffusion of monomer or free radicals. There may also be a change in the chain-transfer characteristics of the system [156]. 

Commercial PVA is available in a number grades which differ in molecular weight and degree of hydrolysis. The polymer finds a variety of uses. It functions as a nonionic surface active agent and is used in suspension polymerization as a protective colloid. It also serves as a binder and thickener and is widely used in adhesives, paper coatings, paper sizing, textile sizing, ceramics, and cosmetics. 

Auxiliaries. Dispersants ensure that the individual particles in the emulsion paint do not combine to form agglomerates. Protective colloids and emulsifiers are used during emulsion polymerization to ensure that small polymer spheres are formed in the aqueous phase but do not fuse together. They influence film formation of the emulsion paint and can cause foaming. Protective colloids include polyfvinyl alcohols) and cellulose ethers. Emulsifiers include anionic and nonionic surfactants. 

Uses SurfactanL thickener, stabilizer, film-former, suspending agent, protective colloid, coating agent in pharmaceuticals, tablet coatings, con-trolled-release prods., encapsulation, nonaerosol hairsprays tablet binder Prt rerties Off-wh. powd., tasteless 99% thru 20 mesh sol. in water (below 38 C) and many polar org. soivs. m.w. 80,000 vise. 300-600 cps (10% aq.) bulk dens. 0.5 g/ml soften, pt. 100-150 C pH 5.0-7.5 (2%) nonionic 5% max. moisture Klucel E Pharm [Hercules/Aqualonj... 

Uses Binder, thickener, pigment/foam/filler stabilizer, dispersant, emulsifier, plasticizer, vise, control agent, sedimenting aid, and protective colloid in coatings, paints, resins, mining, batteries, insecticides, fungicides, herbicides, rubber, textiles, leather, ceramics, suspension polymerization, and pharmaceuticals Properties Gran. water-sol. nonionic 100% act. 

The organic melt is emulsified in water with the aid of a suitable nonionic agent and stabilized by a protective colloid, e.g. potato starch gelatinized with water. The system is crystallized by cooling, and the crystals are separated from the emulsion and washed with water. The operation may be repeated if required. A typical example is shown in Figure 8.57 where five or six emulsion-crystallization cycles yield an almost pure naphthalene at an overall yield of 70 per cent compared with a less pure product at a 2 per cent yield by seven conventional fractional crystallization steps. The high efficiency of the emulsion crystallization is apparently due to the fact that crystal agglomeration does... 

The stabilizing system significantly affects many colloidal and film properties of the VAc/BuA emulsion copol)nners. Berber and co-workers studied the semi-continuous emulsion copol)nnerization of this comonomer system in the presence of conventional nonionic emulsifiers and different protective colloids which were water-soluble pol3maer... 

Many surfactants of low molecular mass have been claimed as useful secondary stabilizers, but in practice few can be used without adverse side effects. One exception is the nonionic sorbitan monolaurate. Again, PVAs are much more widely used. However, this family is prepared by acid hydrolysis of low molecular mass polyCvinyl acetates) and has a random distribution of acetate groups (6). Initially, these materials, which are insoluble in water, were prepared as methanolic solutions (eg, Polivic S202) but more recently aqueous-based, low hydrolysis PVAs (eg, Alcotex A55 and Polivic S 404W), which are safer to handle and are environmentally more acceptable, have been developed and are now very widely used in the industry. Typical secondary protective colloids are listed in Table 3. 

Nonionic polymers, which can be used as stabilizers are, e.g., starches, polyvinyl alcohols, and polyacrylamides. Nonionic polymers work as protective colloids their mechanism of stabilization is Steric stabilization. Carboxy methyl cellulose bears a small anionic charge along the chain. However, it is often considered to act as a protective colloid. Actually, carboxy methyl cellulose can be considered to use both its protective colloid properties and its charge in stabilizing, thus acting as an electrosteric stabihzer. 

In addition to ionic surfactants, nonionic surfactant molecules can also adsorb onto the particle surfaces to impart satisfactory stabihty to colloidal dispersions [20, 21]. Some very old examples include India ink and carbon black particles dispersed in the continuous aqueous phase containing a natural gum. This kind of colloidal stabilization mechanism (termed steric stabilization) was first illustrated experimentally by M. Faraday [31, 32]. Some representative polymeric materials (protective colloids) that are effective in preparing steri-cally stabilized aqueous colloidal dispersions are summarized in Table 2.7 [21]. A portion of an effective protective colloid must be hydrophobic enough to show a strong tendency to adsorb onto the hydrophobic particle surface. Furthermore, the adsorbed macromolecules must form a relatively thick hydrophilic layer surrounding the particle, which serves as a steric barrier to prevent the colloidal particles from flocculation. 

Uses Dispersant, protective colloid for rewashing fast dyeings antiprecipitant for hardening agents and insol. cotton substances sequestrant for Ca and Mg ions Features Stable to alkalis, acids, reduction, and oxidation agents compat. with anionic and nonionic prods. precipitation may occur with cationic auxiliaries Properties Lt. straw liq. misc. with cold water sp.gr. 1.12 pH 7.5-8.5 (10%)... 

To obtain highly stable polymer dispersions, the particles are usually provided with ionic groups, for example by adsorption of anionic or cationic surfactants, or by incorporation of ionic groups into the polymer. Another, nonionic type of stabilization takes place via hydrophilic groups on the particle surface, for example by amino-or hydroxyl-containing monomers or protective colloids. Polymer dispersions used in industry usually are stabilized by both mechanisms (ionic and nonionic). The special nature of the particle surface, which differs from the particle interior, plays an important role in all applications. 

In addihon, there is a whole series of nonionic emulsifiers and protective colloids, which are frequently used in combination with ionic emulsifiers. Ethylene oxide-propylene oxide block copolymers, amphiphilic 2- and 3-block copolymers, polyvinyl alcohols, polyvinyl-pyrroHdone, aUcylpolyglycol ethers, etc. 

To this point, our discussion of the protective action of nonionic stabilizing molecules has been concerned exclusively with hydrosols. Realization that stabilization could similarly be imparted to colloidal particles in nonaqueous media was somewhat later in coming. This comment disregards, of course, the pragmatic technological application of the phenomenon in such products as paints, etc. 

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