Water Numbers of Nonionic Surfactants. I.

Discussions of Testing-Methods and Water Numbers of Sorbitan Fatty Acid Ester Derivatives

Abstract

Several discussions have been made about the titration methods of water numbers of non-ionic surfactants, reported by Greenwald et al. Author applied the methods to some sorbitan fatty acid esters and their polyoxyethylene derivatives.
Conditions of testing methods were defined as follow : 1) Mixed solvents of dioxane and benzene, containing 4 vol. % (DB-4) or 10 vol. % of benzen (DB-10) were most adequate. 2) In cases of sorbitan fatty acid derivatives, 1g of sample dissolved in 30cc of DB-4 was available. 3) Accuracy of weighing had to be kept within 1.0±0.02g. 4) Temperature of titrations at the end point was checked at 25.0°±0.3°C.
Water numbers of sorbitan fatty acid esters became lower in the following order; laurate>oleate>stearate, or mono->sesqui->tri-esters.
It was found that there were rectilinear relationships between water numbers of polyoxyethylene sorbitan fatty acid esters and amounts of added ethyleneoxides, and their slopes were affected by mol-ratio of fatty acids to sorbitol in the sorbitan fatty acid esters used as raw materials, reaction temperature of additional polymerization of ethyleneoxide, type and amount of metallic ions from catalysts.