RESUMO
Nonylphenol ethoxylates (NPEOn) exhibit outstanding application performances, especially in stabilizing silicone oil emulsions, but have been globally banned or use-restricted for serious ecological toxicity. A homologous series of nonionic surfactants, n-dodecylbenzyloxy ethoxylates (DBEOn), are molecularly designed and synthesized as alternatives to NPEOn, where the phenolic group of NPEOn was replaced by a benzyloxy group to counteract the harmful characteristics of NPEOn, while retaining the benefits. Based on computational studies, we propose a hypothesis that has a conjugation reduction effect (CRE) of DBEOn relative to NPEOn on the surfactant structure and properties that solves the biodegradation problem while maintaining the outstanding emulsifying capacity of NPEOn. A 7-day activated sludge assessment shows that DBEO8, a representative member of DBEOn, is almost 100% biodegradable and that the poor biodegradability of NPEOn may be improved by maintaining the vital benzene ring in DBEOn molecules, because the oxygen atom of the benzyloxy group is separated from the smaller conjugation system of DBEOn. Compared to NPEO10, DBEO8 has a similar cloud point but exhibits higher benzene solubilization and considerably higher emulsion stabilities for mineral oil, biomass oil, and especially silicone oil; this outcome is ascribed to a probable random coil configuration of PEO caused by the CRE of DBEOn. Therefore, molecular design produces DBEOn with both excellent biodegradability and outstanding application performances, especially in terms of excellent emulsion stabilities of various oils, as predicted by the CRE hypothesis, thereby serving as an effective alternative to NPEOn.
