Modification of alkylbetaine by incorporation of hydroxypropyl group: Preparation, surface activity, and biodegradability of N-alkoxy-hydroxypropyl-N, N-dimethyl-glycine betaine surfactants

Five novel zwitterionic surfactants with alkylbetaine structure incorporated by hydroxypropyl group have been prepared. The structure and composition of these compounds of high purity were identified by elemental analysis, IR, H-1 NMR, and C-13 NMR. Their isoelectric points have been determined by pH-titration method and lie in the range of 5.0-5.1. Surface tension experiment have demonstrated that these surfactants have higher surface activity than those without hydroxypropyl group. CMC, gamma(CMC), free energy of micellization and area per molecule in micelles of each surfactants have also been studied. Plot of log CMC vs. the length of alkyl chain gives a straight line. The addition of Na+ ions influences their CMCs slightly which is assignable to the inner salt-like structure of these molecules. All the surfactants prepared in this work have Krafft points below 0 degrees C, possess calcium stability >1800 and good Lime Soap Dispersing Property and foam property. Biodegradability of them has also been tested suggesting that they can be used without any environmental problems.