Rheology, microstructural characterization and physical stability of W/α-PINENE/W emulsions formulated with copolymers

Abstract

In this work the microstructure and the physical stability of emulsions containing α-pinene and gellan gum were studied as a function of Atlas™ G-5000/Atlox™ 4912 copolymer mass ratio, R, used as emulsifier. In order to reach this objective, electrolytic conductivity measurements, laser diffraction, confocal laser scanning microscopy (CLSM) and rheology were used. Electrolytic conductivity tests along with CLSM supported the formation of W/α-pinene/W multiple emulsions in all systems containing the most hydrophilic copolymer. Parameter R did not significantly influence either the mean diameters or the span when both copolymers were used. However the lack of Atlas G-5000, not only did it provoke an important increase of mean diameter of droplets, but it also caused the formation of a simple O/W emulsion instead of a multiple emulsion. All emulsions showed shear thinning flow behaviour. The mechanical spectra of multiple emulsions with R ≥ 2 were similar to each other and independent of aging time. A reduction of R led to a decrease in G′ and G″ values and aging time yielded increasing G′ values probably due to the occurrence of incipient creaming. Conversely, the emulsion without Atlas™ G-5000 showed a drop of viscoelastic moduli with aging time due to a coalescence process. These multiple emulsions may find applications in agrochemistry since some active ingredients may be encapsulated in the inner phase, enabling the delivery of hazardous ingredients in a safer way, along with the use of α-pinene which is an easily biodegradable green solvent.