NONIONIC SURFACTANT POLARITY INDEX DETERMINATION BY INVERSE GAS-CHROMATOGRAPHY

Polyglycol nonionic surfactants are widely used in industrial and cons umer products. Two classes of these surfactants, made from selected co mbinations of 1,2-butylene oxide, propylene oxide and ethylene oxide, were compared to alcohol ethoxylate (AE) and nonyl phenol ethoxylate n onionic surfactants in this study. Polyglycol copolymers consisted of either a polypropylene glycol (PPG) or polybutylene glycol (PBG) centr al hydrophobe. Ethoxylation of the hydrophobes produced polyethylene g lycol hydrophilic blocks. Differences in hydrophobe polarity were dete rmined by inverse gas chromatography (IGC). IGC is a useful analytical method by which the physical and chemical characteristics of a materi al are studied. The stationary surfactant material under study was coa ted onto an inert support and used as the packing for the column. A pr obe mixture, containing simple organic molecules of varying polarity, was injected, and the retention characteristics were measured. The ret ention characteristics of the standard probe mixture were used to reve al relative polarity information about the stationary surfactant coati ngs. Polarities of the four hydrophobes were (in decreasing order): PP G, PBG, nonyl phenyl and fatty alkyl. Comparisons were then made betwe en the calculated hydrophile-lipophile balance values and polarity ind ices of the hydrophobes and their ethoxylates. The effects of hydroxyl groups on polarity were also studied and quantified.