Intensification of polyethylene extrusion devolatilization based on extensional flow field

Abstract The dispersion between the polyethylene melt and additives is poor when using the conventional threaded elements, which limits the improvement of devolatilization efficiency. Therefore, in this work, the screw elements were studied and modified to create an extensional flow field to further enhance the removal of 1‐octene from LLDPE. The results show that after modulating the extruder mixing section from a shear‐dominated flow field to an extensional‐dominated flow field, the polyethylene devolatilization efficiency is significantly improved, which can be attributed to the following two aspects: (1) The polyethylene molecular chains have a lower degree of cross‐linking and a higher degree of orientation after the introduction of the extensional flow field, which helps the diffusion of volatile small molecules in the polyethylene melt; (2) The extensional‐dominated flow field is more favorable to the dispersion and mixing of additives in the polyethylene melt than the shear‐dominated flow field, which can provide a larger gas–liquid mass transfer area to improve the devolatilization efficiency. Highlights The extensional flow field in a twin‐screw extruder is created. The devolatilization of 1‐octene from LLDPE is enhanced by an extensional flow field. The mechanism of enhanced devolatilization by extensional flow field is revealed.