Extrusion of flexible microfiber suspensions*

The flow of fiber suspensions occurs in industrial processes such as paper making and filtration. Recently, flexible (high aspect ratio) polymeric microfiber suspensions have been demonstrated to form gel-like materials under shear stress or during extrusion. Using microscopic imaging, we systematically studied the extrusion process in three dimensions. We found that during extrusion and dependent of the extrusion flow rate the extrudate volume fraction varies relative to the initial suspension volume fraction. At a small flow rate, the channel is clogged and the extrudate is purely the solvent. At a higher flow rate, the microfibers are extruded but at a higher volume fraction than their pre-extrusion state. The extrudate volume fraction reaches a plateau when the pre-extrusion volume fraction exceeds a critical value. Using rheometric measurements, we observed that the critical volume fraction is related to the emergence of yield stress in the suspension. A model to rationalize the experimentally generated extrusion phase diagram will be presented.