SOLVENT FREE EMULSIFICATION IN A TWIN-SCREW EXTRUDER

Abstract

<p>The production of latex in a solvent-free process within a twin screw extruder is of great industrial interest given the associated reduction in environmental impact when compared to conventional solvent-based emulsification techniques. The ability to produce latex continuously is also advantageous, compared to batch-wise solvent-based processes.</p> <p>The process of solvent-free emulsification in a twin screw extruder is studied. An inline fiber optic spectroscopic system was installed in the extruder to study the residence time distribution profile of resin through the emulsification process. A design of experiment study was performed analyzing the response of latex particle size from screw speed and feed rate factors. Finally, scanning electron microscopy was used to determine the morphology of the poorly- emulsified and pre-emulsified resin.</p> <p>Experimental results demonstrate that the residence time distribution of the polymer within the extruder is largely invariant of screw speed; the system also demonstrated a very low degree of axial mixing – which was not expected but can be attributed to high degree-of-fill within the screw. The results of the design of experiments study show that the final latex particle size is more influenced by the feed rate of the polymer than the screw speed of the extruder. These results were found to be consistent with the literature based on both batch- phase inversion emulsification as well as continuous polymer blending of immiscible phases. Finally, results from a study on morphology provided evidence of water domains within the pre-inverted polymer domains, analogous to a ‘water-in-oil-in water’ dispersion. Evidence of a bicontinuous network of polymer and water was also found to exist. The summation of these experimental results leads to the hypothesis that the solvent-free emulsification process is a phase inversion-type emulsification mechanism as opposed to a direct emulsification mechanism.</p>