Effect of Viscosity on Solvent-Free Extrusion Emulsification: Molecular Structure

A new continuous emulsification technique known as solvent-free extrusion emulsification (SFEE) was recently introduced to prepare submicron particles (100–500 nm) from high viscosity polymers (100–1000 Pa·s) with a twin screw extruder. The present study examined the influence of matrix viscosity on its dispersion mechanism using cross-linked polyester as a viscosity modifier. The investigation used an inline rheometer for transient and steady state viscosity measurements, and offline characterizations including Soxhlet extraction, colorimetric titration, and particle size analysis. Though it remained possible to produce particles close to their target size of 100–200 nm, particle size was notably increased by varying the matrix viscosity from 250 Pa·s for the neat polyester up to 630 Pa·s with the added modifier. The results point to thicker striated lamellae from less effective mixing prior to phase inversion when the matrix viscosity was increased without a corresponding increase in surface active species. The study was primarily focused on the dispersion zone revealing that a longer mixing zone for dispersing the water into the polyester was beneficial to forming smaller particles. A preliminary investigation on the downstream dilution zone was included, finding that a longer region produced smaller particles as well so long as the water temperature remained high.