Establishing CoaEx by extrusion and spinning of aligned polyelectrolyte fibers. Demonstration that, by using a combination of extrusion and spinning, aligned fibers can be produced from coacervate phases composed of oppositely charged polymers:
Schlenoff and coworkers introduced the concept of saloplastics, by extruding solid oppositely charged polyelectrolyte complexes using salt to plasticize the material. Perry and Schiffman showed in 2017 that fluid coacervates could be used for electrospinning and fibers were obtained consisting of oppositely charged polyelectrolytes. As stiffness and strength of a fiber can be greatly enhanced upon stretching of the polymeric chains, to establish CoaEx we go further: we spin and draw coacervates to produce aligned microfibers, due to reorganizing of electrostatic interactions, followed by dehydration. To obtain the fibers, we fed extruded material to the spinner and produced aligned and dehydrated fibers. As the viscoelasticity of coacervate-based materials is strongly dependent on salt concentration, spinning was optimized by adjusting the salt concentration.
Liquid, rubbery and rigid materials could be obtained from the same polyelectrolytes by just varying the amount of water and salt. Different oppositely charged polymer systems have been explored, e.g. the well-studied combinations poly(4-styrenesulfonic acid) (PSS)/poly(diallyldimethylammonium chloride) (PDADMAC) and keratin.
Post-processing was performed to improve mechanical stability, by means of rinsing to remove salts and by drawing. The mechanical properties were tested using dynamic mechanical analysis (DMA) and tensile testing. As the extent of hydration has a large influence on the mechanical properties, the extent of hydration in the different systems was measured using thermographimetric analysis (TGA) and related to the DMA data. In order to relate the morphology to the mechanical properties, the morphology of the materials was studied by scattering techniques (X-ray) and electron microscopy (scanning electron microscopy, SEM).
Since the tensile strength of a fiber is determined by intermolecular interactions, and electrostatic interactions can be very strong, this concept has resulted in strong high performance fibers using green processing.
