The Waterborne Symposium 2025

Co-Authors:
Juliane P. Santos, Larissa C. C. de Almeida, Maira V. de Carvalho, Michael Praw

Abstract
"The emulsification of resins used in solvent-based coatings into water is a crucial strategy for developing environmentally friendlier water-based coatings. Among the various resins used in solvent-based coatings, alkyd resins stand out due to their partial renewability and extensive use in decorative and protective coatings. They offer excellent adhesion to a variety of substrates, high gloss, durability, and resistance to water, chemicals, heat, and solvents. However, due to environmental and GHS concerns, there is a trend towards emulsifying these polymers with emulsifiers to create stable oil-in-water emulsions for water-based formulations.

Long-in-oil alkyd resins with viscosities ranging from 5000 to 15000 cP at the emulsification temperature are typically emulsified using the phase inversion methodology with low shear mixing equipment. However, emulsifying higher viscosity resins, such as medium-in-oil alkyd resins, presents more challenges.

This work focuses on developing a special solvent and optimizing emulsifier compositions to reduce the viscosity of medium-in-oil alkyd resins, enabling their emulsification through phase inversion using low shear mixing equipment, and producing emulsions with particle size below 400 nm.

The prototype of an environmentally friendly solvent, designed for having Hansen Solubility Parameters (HSP) close to the ones of the alkyd resins, effectively decreases the viscosity of medium-in-oil alkyd resin at 80°C, the emulsification temperature, as confirmed by rheological measurements. A small amount (5 wt%) of this solvent reduced the viscosity by approximately 60%.

The emulsifier compositions include a special nonionic emulsifier designed for alkyd resin emulsification and a conventional anionic emulsifier. Interfacial tension evaluation between a model oil phase containing the emulsifier composition and water was used to select the most effective emulsifier compositions for reducing the interfacial tension, crucial for successful emulsification.

The study also explored the effects of two bases, sodium hydroxide and triethylamine, used for neutralizing the carboxylic groups of the resin, and the conventional anionic surfactant. The interfacial tension results indicated that compositions rich in the nonionic emulsifier could reduce the interfacial tension at 40°C from 18 mN/m to nearly 0 mN/m.

Based on the interfacial tension results, three compositions rich in the nonionic emulsifier were evaluated with each base. The alkyd emulsions neutralized with sodium hydroxide had a solid content of about 49 wt%, particle sizes ranging from 200 to 230 nm, and a zeta potential of around -40 mV. These emulsions, formulated with a drier recommended for water-based formulations, had a drying time close to 5 hours. The stable emulsions neutralized with triethylamine had a solid content of about 49 wt%, particle sizes ranging from 240 to 320 nm, a zeta potential of around -50 mV, and a drying time ranging between 3 to 4 hours.

The strategies developed in this work are also being applied to the emulsification of other resins, beyond alkyd resins. This includes important classes of resins such as epoxy resins. "