A comparison of melt fracture initiation conditions in capillaries and slits

Abstract An experimental study was carried out with the objective of comparing the critical conditions for the onset of gross extrudate distortion, usually called melt fracture, in capillaries and slits. Narrow and broad molecular weight distribution polystyrenes as well as low‐ and high‐density polyethylenes were used. The onset of melt fracture was observed to take place at higher shear stresses in slits than in capillaries. It is argued that the flow‐average value of the recoverable shear strain should be used as the criterion for the initiation of melt fracture.