A mass transfer model for a twin‐screw extruder

A mass transfer model was developed to represent the desorption of a volatile species from a molten polymer in an extruder consisting of co‐rotating twin screws in a figure‐eight bore. The melt undergoes a series of alternating exposure and mixing processes while being transported axially through the device. The model relates the ratio of entrance to exit concentrations of the volatile species to the dimensions of the screws, the rate of their rotation, the rate of polymer flow, and the diffusion coefficient of the volatile species in the polymer. Experimental data, obtained with a halocarbon‐polybutene system in a twin‐screw extruder, were compared with predictions of the model. For the observed performance, the model predicts a process screw length about 14 percent below the actual screw length in the experimental extruder.