Optimization of nonionic surfactants for hard-surface cleaning

The hard-surface cleaning performance of various nonionic homologs was evaluated as a function of carbon chain length, ethylene oxide (EO) content, blending and concentration. Results show carbon chain length to be very important to hard-surface cleaning. Performance significantly increases as carbon-chain length decreases, probably as a result of an increase in solvency properties as carbon chain length is decreased. EO content is also important, particularly if nonionics with longer carbon chain lengths are used. Surfactant concentration (dilution) has little effect on the optimum ethylene oxide content but significantly affects the optimum carbon chain length of the hydrophobe. With 5% homolog solutions, the optimally performing nonionic contains a C6 hydrophobe, but with 0.2% solutions, the optimal carbon chain length is shifted to the C8–C10 range. This is thought to result from a trade-off between the surfactant and solvent properties of the nonionic. Overall results show the optimal nonionic for hard-surface cleaning to consist of a blend of C6, C8 and C10 alcohols ethoxylated to a 50% EO level. Commonly used surfactant systems, e.g., alkylphenol ethoxylates and alkylphenol ethoxylate (APE)-butyl cellosolve (BC) blends, were also examined. Results show that alkylphenol ethoxylates give relatively poor performance compared with lower molecular weight linear nonionics because of the large size of their hydrophobe. Under concentrated use, a synergism does exist between APE and BC, but under dilute conditions, the addition of BC is ineffective. BC does not help the performance of low molecular weight nonionics. Surfactant-soil diffusion studies indicate that surfactant penetration of the soil may be the primary mechanism involved in the hard-surface cleaning of solid soils.