Gas entrainment in intermeshing co-rotating twin-screw extruders

The occurrence of gas entrainment into a polymeric phase in intermeshing co-rotating twin-screw extruders operated in starved conditions is investigated using an extruder with a transparent barrel. Three different aspects of entrainment are studied: the critical conditions above which it takes place; the phenomenology of gas entrapment; the quantity of entrained gas. The influence of the extruder operating conditions on these aspects is also addressed. The entrapment of gas into the processed liquid is found to be a common phenomenon in usual operating conditions. Gas entrainment takes place along the extruder starved regions, and therefore, the extension of such regions has been investigated both theoretically and experimentally.