An Environment-Friendly Palm Fatty Acid-Based Polymeric Surfactants for Coating Applications: Physicochemical, Surface Tension and Low-Foaming Properties

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In this work, two environmental-friendly low-foaming surfactants, anionic oleic acid surfactant (AOAS), and non-ionic oleic acid surfactant (NOAS) were synthesized by copolymerization of palm fatty acids with fully bio-sourced and renewable starting materials using polyesterification method. The chemical structures of both surfactants were confirmed by nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) studies. Acid value determination showed that NOAS achieved a higher conversion rate of 97% than that of AOAS with only 78%. Differential scanning calorimetry (DSC) experiment demonstrated that both surfactants had low Tg, around − 94 °C to − 68 °C. Thermogravimetric analysis (TGA) exhibited polymer decomposition occurred above 150 °C. Gel permeation chromatography (GPC) measurement revealed that both surfactants were polydisperse, with NOAS had higher molecular weight than AOAS. Critical micelle concentration (CMC) of AOAS and NOAS were recorded as 0.0670 mM/L and 0.0999 mM/L respectively. The surface tensions of both AOAS and NOAS were 33.27 mN/m and 41.13 mN/m, respectively. The contact angle measurement indicated that NOAS had a better wettability than AOAS. Cloud point of NOAS surfactant was determined to be 89 °C. These surfactants had better solubility in a non-polar solvent like hexane compared to polar solvents like ethanol and water. The foaming test concluded that both surfactants presented low foaming behavior, with immediate foam height less than 1.5 mm. The physicochemical and surface tension properties confirmed the surface active properties of both AOAS and NOAS. The foaming test results recommended consideration of both AOAS and NOAS for low-foaming applications, particularly to reduce foam formation in coatings.