Nonionic surfactants ethoxylated sorbitan ester

A series of sorbitol-based nonionic surfactants are used ia foods as water-ia-oil emulsifiers and defoamers. They are produced by reaction of fatty acids with sorbitol. During reaction, cycHc dehydration as well as esterification (primary hydroxyl group) occurs so that the hydrophilic portion is not only sorbitol but also its mono- and dianhydride. The product known as sorbitan monostearate [1338-41 -6] for example, is a mixture of partial stearic and palmitic acid esters (sorbitan monopalmitate [26266-57-9]) of sorbitol, 1,5-anhydro-D-glucitol [154-58-8] 1,4-sorbitan [27299-12-3] and isosorbide [652-67-5]. Sorbitan esters, such as the foregoing and also sorbitan monolaurate [1338-39-2] and sorbitan monooleate [1338-43-8], can be further modified by reaction with ethylene oxide to produce ethoxylated sorbitan esters, also nonionic detergents FDA approved for food use. 

The most common nonionic surfactants are those based on ethylene oxide, referred to as ethoxylated surfactants. Several classes can be distinguished alcohol ethoxylates, alkyl phenol ethoxylates, fatty acid ethoxylates, sorbitan ester ethoxylates, fatty amine ethoxylates, and ethylene oxide-propylene oxide copolymers (sometimes referred to as polymer surfactants). Another important class of nonionics are the multihydroxy products such as glycol esters, glycerol (and polyglycerol) esters, glucosides (and polyglucosides), and sucrose esters. Amine oxides and sulfinyl surfactants represent nonionic with a small head group. 

Ionic detergents, such as cetyltrimethylammonium bromide or sodium dodecyl sulfate, give pore sizes between 2 and 4 nm, whereas nonionic surfactants such as the Pluronics and the Tween surfactant series (ethoxylated sorbitan esters) give materials with larger pores (around 10 nm) and thicker walls (Table 18.1). 

One area of rapidly expanding interest is the use of reverse micellar systems of sugar-based surfactants in the extraction of proteins and other sensitive materials. The use of hydrophilic, nonionic, sugar-based surfactants for membrane protein extraction is well known to be effective due to the mild, nondenaturing properties of these surfactants when compared with ionic surfactants or polyoxyethylene derivatives. For the same reasons, protein extraction into reverse micellar systems is now becoming a popular medium for such applications. Alkyl sorbitan esters and ethoxylated sorbitan esters, such as Tween 85 [107] and Span 60 [108], have been used successfully to form reverse micellar systems for protein extraction. Blends of Tween and Span have also been found to be effective for this purpose [109]. More recently, commercially available sucrose fatty acid esters have been shown to form biocompatible reverse micellar systems into which cytochrome c is effectively extracted [110]. 

Synonyms PEG 3000 soribtan monostearate POE (60) sorbitan monostearate Definition Ethoxylated sorbitan ester of stearic acid with an avg. of 60 moles EO Uses Surfactant in cosmetics in resinous and polymeric coatings in food pkg. Regulatory FDA21CFR 175.300 Canada DSL Manuf./Distrib. Somerset Cosmetic Co. Variati PEG 2000 sorbitan stearate. See PEG-40 sorbitan stearate PEG-16 sorbitan tallate Ionic Nature Nonionic Uses Surfactant PEG-20 sorbitan tallate Ionic Nature Nonionic... 

The commercial nonionic surfactants used in this study included two alcohol ethoxylates, Witconol SN120 (Witco Corp., New York NY) and Brij 35 (ICI, Wilmington, DE), and an ethoxylated sorbitan fatty acid ester, Tween 80 (ICI). Brij 35 was purchased from Sigma (St. Louis, MO), while SN120 and Tween 80 were provided by their respective manufacturers. All surfactants were used as received. 

Primarily for toxicity reasons, work has focused on the use of nonionic surfactants, particularly Tweens and Spans. Pouton (20) and Wakericy el al. (21) have screened a range of surfactants, finding that in general molecules with unsat-uraced acyl chains were most efficiem emulsifiers, particularly the oleates with an HLB value of approximately II. The authors also reported that the sorbitan esters and ethoxylated triglycerides such as Tagat TO were more efficient than the fatty acid ethoxylates, possibly due to the polydispersity of the latter. 

Ethoxylated alcohols Ethoxylated fatty acids Lauryl sulfates Mono and diglycerides Nonionic surfactants Phosphate esters Quaternary surfactants Sorbitan derivatives... 

For the above reasons, many personal care emulsions are formulated using nonionic surfactants of which the alcohol ethoxylates (the ICI Brij series), sorbitan esters (Spans), and their ethoxylates (Tween) are the most commonly used surfactants. These surfactants adsorb at the oil/water interface with the hydrophobic (alkyl) group pointing to (or dissolved in) the oil phase and the hydrophilic chain [mostly poly(ethylene) oxide (PEO)] remaining in the aqueous phase. These molecules produce a repulsive barrier as a result of the unfavorable mixing of the polar PEO chains (when these are in good solvent conditions) and the reduction in configurational entropy of the chains when these overlap. Such repulsion is usually referred to as steric stabilization (see below) (6). These nonionic surfactants, which are usually used in mixtures) have been successfully applied to prepare stable o/w and w/o emulsions. In addition, in some cases, they form liquid crystalline structures at the o/w interface and these prevent coalescence of the oil droplets (7). 

Formulation Surfactants are used for the formulation of many pharmaceutical formulations such as suspensions, emulsions, multiple emulsions, semisolid and gels for topical application. In all cases the surfactants must be approved by the Food and Drug Admins-tration (FDA) and this limits the choice in pharmaceutical applications. Several surfactant molecules have been approved by the FDA, both of the ionic and nonionic type. The latter are perhaps the most widely used molecules in pharmaceuticals, e.g., sorbitan esters (Spans) and their ethoxylated analogues (Tweens). Polymeric surfactants of the PEO-PPO-PEO block type or Poloxamers (ICl, U.K.) are also used in many formulations. Many pharmaceutical emulsions, e.g., lipid and anesthetic emulsions, are formulated using egg lecithin which has to be pure and free from any toxic impurities. 

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