The effect of some foam boosters on the foamability and foam stability of anionic systems

The foaming properties of anionic surfactant solutions containing a nonionic surfactant, fatty acid N ‐methyl‐ethanolamide (NMEA), were investigated. Foamability, which is the foam‐generating power at the initial stage of foaming, was measured by a laboratory‐built foam‐testing apparatus, and also by the conventional Ross‐Miles test NMEA synergistically increased the foamability of anionic surfactant solutions, particularly when small amounts of NMEA were added. Shorter hydrocarbon chain lengths of NMEA, such as N ‐octanoyl‐ N ‐methylethanol (NMEA‐08) and N ‐decanoyl‐ N ‐methylethanol (NMEA‐10), showed better performance in the laboratory‐built foam tester. The results of the Ross‐Miles evaluation, however, were completely opposite. Compared with commercial nonionic boosters, such as fatty acid monoethanolamide, fatty acid diethanolamide, and lauramidopropyldimethylbetaine (LPB), NMEA was the most effective for increasing foamability of the solution at the initial stage. The most popular amphoteric foam booster, LPB, did not increase foamability but likely generated the initial foam volume on the Ross‐Miles test as a result of foam film stabilization. From these results, a foam‐boosting mechanism of NMEA different from that of LPB is suggested.