Phase segregation lubricates paste extrusion

Extrusion is a critical process in the manufacturing of various organic materials, including animal feed, human food, pharmaceuticals, and biomass for bioenergy. During extrusion, a dense particle-fluid mixture, or paste, is pushed through a narrow channel under high pressure. Despite its widespread use, many questions remain about how particle-fluid interactions and frictional forces at the wall influence high-pressure paste flow, particularly whether laboratory-scale findings translate to more complex industrial settings. Here, we quantify for the first time how a micrometer thin fluid lubrication layer emerges from particle-fluid interactions during the extrusion of organic biomass, controlling friction at the paste-channel interface. This lubrication layer forms through a pressure-induced phase segregation process and is significantly thinner than the particle size, affecting their contact dynamics, making friction at the interface tunable. Our results reveal how the thickness of the lubrication layer is influenced by paste composition, enhancing our fundamental understanding of phase segregation during industrial extrusion processes and offering potential pathways for reducing energy consumption and product failure in the industrial material production.