Polysorbate 20

Apr 1, 2011 | Contact Author | By: Mike Fevola, Johnson & Johnson
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Title: Polysorbate 20
Polysorbate 20x Emulsifierx Solubilizerx Sorbitolx
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Keywords: Polysorbate 20 | Emulsifier | Solubilizer | Sorbitol

Abstract: Polyoxyethylene (20) sorbitan monolaurate (INCI: Polysorbate 20), is a ubiquitous nonionic surfactant employed in the formulation of countless cosmetic and personal care products.

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M Fevola, Polysorbate 20, Cosm & Toil 126(4) 310 (2011)

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Polyoxyethylene (20) sorbitan monolaurate (INCI: Polysorbate 20), is a ubiquitous nonionic surfactant employed in the formulation of countless cosmetic and personal care products. The use of polysorbate 20 is reported in 85%, i.e. 68 of 80, of the product categories listed in the Personal Care Product Council’s On-Line INFOBASE, indicating its versatility and utility in a variety of goods.1–2 It can function as a solubilizer, emulsifier, stabilizer, dispersing agent or a wetting agent, among other functions. Beyond personal care, polysorbate 20 has similar functions in the formulation and processing of pharmaceuticals, food and beverage products, agricultural chemicals and household and industrial cleaning products.

 Polysorbate 20 is a complex mixture of laurate esters of sorbitol and sorbitol anhydrides (sorbitans), consisting predominantly of the monoester condensed with approximately 20 moles of ethylene oxide.1 The material generally conforms to the idealized structure shown in Figure 1—i.e., a four-arm, star-shaped oligomer of polyethylene glycol (PEG) grown from a sorbitan core with a laurate ester end-capping one of the PEG arms. This representative form of polysorbate 20 has an average molecular weight of 1,228 g/mol.

Chemistry and Manufacture

The key commodity feedstocks for polysorbate 20 are sorbitol, fatty acids with an average alkyl chain length of 12 carbon atoms, and ethylene oxide (EO).3–4 Sorbitol is a six-carbon sugar alcohol obtained from either the catalytic hydrogenation of glucose or the simultaneous hydrolysis and hydrogenation of starch, cotton cellulose or sucrose.5 The fatty acids consisting primarily of the C12 lauric acid are usually isolated by distillation of coconut or palm kernel fatty acids, which are obtained from saponification and hydrogenation of the respective oils. EO is a petrochemical intermediate produced by direct oxidation of ethylene gas using air or oxygen and a silver-based catalyst.

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Figure 1. Idealized chemical structure of polysorbate 20, where the average value of w + x + y + z = 20

Figure 1. Idealized chemical structure of polysorbate 20, where the average value of w + x + y + z = 20

The material generally conforms to the idealized structure shown in Figure 1—i.e., a four-arm, star-shaped oligomer of polyethylene glycol (PEG) grown from a sorbitan core with a laurate ester end-capping one of the PEG arms.

Figure 2. Two-step synthesis of polysorbate 20: a) simultaneous anhydrization of sorbitol and esterification with lauric acid to form sorbitan laurate, and b) base catalyzed ethoxylation to form polysorbate 20

Figure 2. Two-step synthesis of polysorbate 20: a) simultaneous anhydrization of sorbitol and esterification with lauric acid to form sorbitan laurate, and b) base catalyzed ethoxylation to form polysorbate 20

In practice, the latter route, shown in Figure 2, is employed commercially and depending on the exact process, may utilize either base catalysis as shown or a combination of acid and base catalysis.

Figure 3. Anhydridization of sorbitol to sorbitan and isosorbide

Figure 3. Anhydridization of sorbitol to sorbitan and isosorbide

Figure 3 depicts the four isomers of sorbitan that may form during the anhydrization of sorbitol— in this case, acid-catalyzed.

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