Methyl ester ethoxylates unsaturation, impact

Another feature that dilferentiates methyl ester ethoxylates from alcohol ethoxylates in unsaturatinon. Methyl esters, particularly those in the tallow range, are relatively highly unsaturated, generally more than 50%. Alcohols, in contrast, are typically fully saturated. The impact of unsaturation on performance can be significantly, and is addressed in the last section of this chapter. 

Variations in methyl ester purity or composition (unsaturation, carbon chain length distribution, etc.) do not appear to influence the ethoxylation reaction or overall ethoxylate quality. The purity of the methyl ester, however, does appear to impact color. A yellow-tinted methyl ester logically yields a yellow-tinted ethoxylate. 

The impact of unsaturation stems from the increase in rigidity caused by the presence of one or more double bonds to the alkyl chain. Although studies so far show that unsaturation has a relatively low impact on water solubility and viscosity, it has been reported to lower melting points by about 5-10°C [16]. Studies also show (Fig. 20) that unsaturation affects surface properties. Gibbs plots of 14.5-mole ethoxylates produced from hydrogenated and nonhydrogenated Cig is methyl ester show that unsaturation appears to increase surface tension below the CMC. This suggests that unsaturation reduces the hydrophobic character of the methyl ester chain. 

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