Sustainable non-ionic surfactants from epoxidised linseed oil: synthesis, interfacial properties, foaming behaviour, and emulsification performance.

The development of sustainable surfactants from renewable resources is essential for reducing dependence on petroleum-derived chemicals. Herein, a series of bio-based non-ionic surfactants was synthesised from epoxidised linseed oil (ELO) through heterogeneous catalyst-assisted epoxide ring-opening with poly(ethylene glycol) (PEG) and monomethyl poly(ethylene glycol) (MePEG) of varying molecular weights. Five surfactants, designated ELO400, ELO400M, ELO750M, ELO1050 and ELO1500, were successfully prepared and characterised by FT-IR, NMR and size exclusion chromatography, confirming efficient PEG grafting onto the triglyceride backbone. The surfactants exhibited excellent interfacial activity, reducing the equilibrium surface tension of water to as low as 36.64 mN m-1 and displaying low critical micelle concentrations (CMC) of 0.96-1.15 g L-1. Dynamic surface tension measurements demonstrated efficient adsorption at the air-water interface, while Gibbs adsorption analysis indicated favourable molecular packing at the interface. Foam generation increased with PEG chain length, whereas shorter PEG chains produced more persistent foams. All surfactants formed stable emulsions in a demanding 50 : 50 toluene/water system, substantially exceeding the oil loading encountered in most industrial emulsification processes. Emulsion stability increased with PEG molecular weight, with ELO1500 maintaining a partially stable emulsion for more than 50 days. Cloud point increased systematically with ethylene oxide content and decreased slightly in the presence of inorganic salts in the order Na2SO4 > NaCl > NaNO2, consistent with Hofmeister effects. These findings demonstrate that PEG-functionalised epoxidised linseed oil is a versatile renewable platform for producing high-performance non-ionic surfactants with tunable interfacial properties for detergency, emulsification, coatings, personal care formulations and other sustainable industrial applications.