Dispersion in water

Globular protein (Section 27 20) An approximately spheri cally shaped protein that forms a colloidal dispersion in water Most enzymes are globular proteins Glycogen (Section 25 15) A polysaccharide present in animals that IS denved from glucose Similar in structure to amy lopectin... 

Gum ghatti is the calcium and magnesium salt of a complex polysaccharide which contains L-arabinose, D-galactose, D-mannose, and D-xylose and D-glucuronic acid (48) and has a molecular weight of approximately 12,000. On dispersion in water, gum ghatti forms viscous solutions of viscosity intermediate between those of gum arabic and gum karaya. These dispersions have emulsification and adhesive properties equivalent to or superior to those described for gum arabic. 

Lysophosphohpids are soluble in water the others are dispersible in water. 

Commercial lecithin is insoluble but infinitely dispersible in water. Treatment with water dissolves small amounts of its decomposition products and adsorbed or coacervated substances, eg, carbohydrates and salts, especially in the presence of ethanol. However, a small percentage of water dissolves or disperses in melted lecithin to form an imbibition. Lecithin forms imbibitions or absorbates with other solvents, eg, alcohols, glycols, esters, ketones, ethers, solutions of almost any organic and inorganic substance, and acetone. It is remarkable that the classic precipitant for phosphoHpids, eg, acetone, dissolves in melted lecithin readily to form a thin, uniform imbibition. Imbibition often is used to bring a reactant in intimate contact with lecithin in the preparation of lecithin derivatives. 

Because of the zwitterion formation, mutual buffering action, and the presence of strongly acid components, soybean phosphoHpids have an overall pH of about 6.6 and react as slightly acidic in dispersions-in-water or in solutions-in-solvents. Further acidification brings soybean phosphoHpids to an overall isoelectric point of about pH 3.5. The alcohol-soluble fraction tends to favor oil-in-water emulsions and the alcohol-insoluble phosphoHpids tend to promote water-in-oil emulsions. 

Numerous recipes have been pubUshed which describe the preparation of methacrylate homopolymer and copolymer dispersions (65,66). A typical process for the preparation of a 50% methyl methacrylate, 49% butyl acrylate, and 1% methacrylic acid terpolymer as an approximately 45% dispersion in water begins with the preparation of the monomer emulsion charge. 

Almost all synthetic binders are prepared by an emulsion polymerization process and are suppHed as latexes which consist of 48—52 wt % polymer dispersed in water (101). The largest-volume binder is styrene—butadiene copolymer [9003-55-8] (SBR) latex. Most SBRlatexes are carboxylated, ie, they contain copolymerized acidic monomers. Other latex binders are based on poly(vinyl acetate) [9003-20-7] and on polymers of acrylate esters. Poly(vinyl alcohol) is a water-soluble, synthetic biader which is prepared by the hydrolysis of poly(viayl acetate) (see Latex technology Vinyl polymers). 

Starches, used first in the late 1930s for filtration control (71), are stiU in use in the 1990s. Com starch is most commonly used in the United States. Potato starch is also used in the United States but primarily in Europe and elsewhere. Both com and potato starches are pregelatinized before dispersion in water (72). The API specifications for drilling fluid starch are listed in Table 8 (73). 

Cold Applied Coatings/Adhesives. Cold appUed BUR appHcations do not require heating to fluidize the bitumen on the job. Simple appHcation and economical maintenance ate primary considerations. Bitumens are Hquefied by dissolving in a solvent (cutbacks) or dispersing in water... 

Typical commercial ethoxylated sorbitan fatty acid esters are yellow Hquids, except tristearates and the 4- and 5-mol ethylene oxide adducts which are light tan soHds. These adducts, as well as the 20-mol adducts of the triesters, are insoluble but dispersible in water. The monoester 20-mol adducts are water soluble. Ethoxylated sorbitan esters are widely used as emulsifiers, antistatic agents, softeners, fiber lubricants, and solubilizers. In combination with the unethoxylated sorbitan esters or with mono- or diglycetides, these are often used as co-emulsrfiers. The ethoxylated sorbitan esters are produced by beating sorbitan esters with ethylene oxide at 130—170°C in the presence of alkaline catalysts. 

Water-borne polyurethane coatings are formulated by incorporating ionic groups into the polymer backbone. These ionomers are dispersed in water through neutrali2ation. The experimental 1,12-dodecane diisocyanate (C12DI Du Pont) is especially well suited for the formation of water-borne polyurethanes because of its hydrophobicity (39). Cationomers are formed from IPDI, /V-methyIdiethan olamine, and poly(tetramethylene adipate diol)... 

In the suspension polymerization of PVC, droplets of monomer 30—150 p.m in diameter are dispersed in water by agitation. A thin membrane is formed at the water—monomer interface by dispersants such as poly(vinyl alcohol) or methyl cellulose. This membrane, isolated by dissolving the PVC in tetrahydrofuran and measured at 0.01—0.02-p.m thick, has been found to be a graft copolymer of polyvinyl chloride and poly(vinyl alcohol) (4,5). Early in the polymerization, particles of PVC deposit onto the membrane from both the monomer and the water sides, forming a skin 0.5—5-p.m thick that can be observed on grains sectioned after polymerization (4,6). Primary particles, 1 p.m in diameter, deposit onto the membrane from the monomer side (Pig. 1), whereas water-phase polymer, 0.1 p.m in diameter, deposits onto the skin from the water side of the membrane (Pig. 2) (4). These domain-sized water-phase particles may be one source of the observed domain stmcture (7). 

Suspension Polymerization. Suspension polymerization is carried out in small droplets of monomer suspended in water. The monomer is first finely dispersed in water by vigorous agitation. Suspension stabiUzers act to minimize coalescence of droplets by forming a coating at the monomer—water interface. The hydrophobic—hydrophilic properties of the suspension stabiLizers ate key to resin properties and grain agglomeration (89). 

Carbonates. Basic zirconium carbonate [37356-18-6] is produced in a two-step process in which zirconium is precipitated as a basic sulfate from an oxychloride solution. The carbonate is formed by an exchange reaction between a water slurry of basic zirconium sulfate and sodium carbonate or ammonium carbonate at 80°C (203). The particulate product is easily filtered. Freshly precipitated zirconium hydroxide, dispersed in water under carbon dioxide in a pressure vessel at ca 200—300 kPa (2—3 atm), absorbs carbon dioxide to form the basic zirconium carbonate (204). Washed free of other anions, it can be dissolved in organic acids such as lactic, acetic, citric, oxaUc, and tartaric to form zirconium oxy salts of these acids. 

Effective antistatic agents must act at a relative humidity below 40%, preferably below 15%. The agent must form a film on various surfaces and be apphed from a solution or dispersion in water or other inexpensive solvents. The antistatic agent must not interfere with subsequent processing of the product, impair the hand, or affect color, odor, appearance, and performance properties of the substrate. It should be nontoxic and nonflammable. 

A specific polymorph may be absolutely essential for a crystalline product, for example, one polymorph may have a more desirable color or greater hardness or disperse in water more easily than another polymorph. Often, one polymorphic form is more stable than another (for example, at 80°C the orthorhombic I form of ammonium nitrate is more stable than the trigonal form) at conditions to which a product is exposed. An interesting approach to... 

Many proprietary carries are available as soHds (flakes or pellets) or in preemulsified form. These present some difficulties in the dyehouse. The former require dispersion in water through steam injection and addition to a preheated dyebath. The latter suffer from short storage life owing to separation of the emultion. Currently the industry prefers clear products easily emulsified by premixing with water at the time of use. 

Fig. 1. In an oH-in-water (o/w) emulsion (a), macroscopic oil droplets are dispersed in water. In a water-in-oH (w/o) emulsion (b), the situation is...

A waterborne system for container coatings was developed based on a graft copolymerization of an advanced epoxy resin and an acryHc (52). The acryhc-vinyl monomers are grafted onto preformed epoxy resins in the presence of a free-radical initiator grafting occurs mainly at the methylene group of the aHphatic backbone on the epoxy resin. The polymeric product is a mixture of methacrylic acid—styrene copolymer, soHd epoxy resin, and graft copolymer of the unsaturated monomers onto the epoxy resin backbone. It is dispersible in water upon neutralization with an amine before cure with an amino—formaldehyde resin. 

After hardening, UF-resins consist of insoluble, more or less three-dimensional networks and cannot be melted or thermoformed again. At their application stage, UF-resins are still soluble or dispersed in water or are spray dried powders, which in most cases are redissolved and redispersed in water for application. 

Suspension polymerization produces beads of plastic for styrene, methyl methacrviaie. viny l chloride, and vinyl acetate production. The monomer, in which the catalyst must be soluble, is maintained in droplet fonn suspended in water by agitation in the presence of a stabilizer such as gelatin each droplet of monomer undergoes bulk polymerization. In emulsion polymerization, ihe monomer is dispersed in water by means of a surfactant to form tiny particles held in suspension I micellcsK The monomer enters the hydrocarbon part of the micelles for polymerization by a... 

Globular protein (Section 27.20) An approximately spherically shaped protein that forms a colloidal dispersion in water. Most enzymes are globular proteins. 

---