The addition of water to hydrophobic alkyd resin containing a hydrophilic nonionic surfactant (polyethoxylated-20-oleyl alcohol) was used to produce the emulsion morphology change from W/O to O/W in a small thermostated reactor (50 mL). The so-called catastrophic phase inversion of the water/alkyd resin system was detected by monitoring both, the viscosity by torque measurement and the electrical conductivity, until an equal weight fraction of water and resin is attained (fw = 0.5). The two methods provide similar values of the phase inversion point (PIP). Although the determination of the PIP exhibits a small inaccuracy, it is clear that different torque profiles and PIP are observed depending on the resin neutralization level, the surfactant concentration and the water addition rate. For the non-neutralized resin, both, PIP and emulsion drop size, decrease with surfactant concentration increase. The completely neutralized resin could be emulsified using a minimum of 2 wt% of surfactant in the final emulsion. In such a case the water fraction at which inversion occurs (fw,Inv = 0.36) is independent of the surfactant concentration and a small resin drop diameter (< 200 nm) can be obtained. A more precise study of the reached drop size of the emulsion versus resin neutralization (0, 25, 50, 75, 100 and 125%) indicates that a minimum diameter is obtained around 90-100% neutralization, with no effect of over-neutralization. For non-neutralized resin a maximum fw,Inv (0.25) can be obtained by reducing water addition rate allowing the production of 0.5 μm droplets in a longer process.
Available online 16 July 2017