The transition toward more sustainable coating technologies has accelerated in response to increasingly stringent VOC regulations and increased market demand for biobased materials. Within the resin design context, waterborne alkyds address sustainability through their high renewable content, derived directly from the oil modifiers, and the availability of low-VOC formulation strategies. Among these, external emulsification with surfactants is particularly versatile since it requires no chemical modification of the alkyd backbone and applies seamlessly across a wide range of alkyd architectures, from short-oil to very long-oil systems.

The most industrially applicable methodology for external emulsification is the catastrophic phase inversion (CPI), where water is gradually introduced into an alkyd–surfactant system under controlled shear, triggering a phase transition from water-in-oil (W/O) to oil-in-water (O/W). The success of CPI depends on a complex interplay of physical parameters (temperature, shear, water addition rate, vessel or agitator geometry) and chemical parameters (emulsifier ionic strength or hydrophilicity, alkyd polarity, neutralization parameters).

When these interdependent parameters are not selectively tailored to a given alkyd–emulsifier system, it often leads to emulsification failures, poor emulsion stability and inferior coating performance, thereby reinforcing the notion that external alkyd emulsification with surfactants is ineffective. To date, no study has systematically isolated the individual role of these variables or investigated their synergistic effects.

We evaluated a six-member Neptem™ emulsifier portfolio, comprising anionic and nonionic grades, fossil-derived and renewable-origin, across more than 30 industrial alkyds (short- to long-oil) to establish compatibility with varying alkyd structures. From that broad screening, seven medium-to-long-oil resins were selected to be presented herein for five focused studies: (1) the impact of mixing hydrodynamics, emulsification temperature and neutralization parameters on CPI performance; (2) benchmarking the biobased emulsifier, grade 21, against fossil-derived and benchmark alkyd surfactants at 6% and 8% loadings; (3) resin-specific emulsifier compatibility under constant CPI conditions; (4) impact of alkyd, emulsifier type or level and emulsification conditions on clear coat performance; (5) impact of emulsifier selection on paint performance.

Materials and Methods

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