Understanding the influence of mixing on a solvent‐free emulsification process for highly viscous polymers using a twin‐screw extruder

Abstract Twin‐screw extrusion with its capacity to handle high‐viscosity polymers can be used to create a continuous emulsification process without solvents but presently this approach is challenging to make stable due to the uncertain role of mixing. To address this challenge, the influence of mixing was studied by examining several process‐ and material‐related factors in this work. From the results, the kinetics of interfacial area growth between the polymer and water phases was described in terms of nucleation, propagation and termination stages, with the latter stage ideally corresponding to the dilution zone where phase inversion occurs. The nucleation stage was found to be strongly dependent on early water solubilization in the polymer, controlled by the acid number of the polyester, to determine the initial water fraction feasibly dispersed within this oil‐like phase prior to the dilution zone (referred to as the emulsion boundary). Propagation was influenced by surfactant concentration and strongly affected by residence time, with a longer dispersion zone or lower feed rate allowing for higher cumulative shear strain and a greater chance to completely emulsify the polymer. Ideally, these kinetic stages correspond with the physical zones of the machine else varying degree of emulsification are shown to result. Highlights Early water solublization in the polyester is dependent on the acid number Higher residence time impacted mixing more than shear rate Water fraction dispersible in the melt was strongly affected by mixing Emulsion boundary was adjustable by amount of mixing and surfactant