Stress distribution around capillary die exit: an interpretation of the onset of sharkskin defect

Effects of mineral fillers on polystyrene melt processing

“…The capillary flow of molten polymers has received much attention because at high flow rates the melt processing of the polymer are commonly accompanied by instabilities, which is called as sharkskin or melt fracture [6][7][8]. This is one of the problems in polymer processing that is not completely understood.…”

Stress relaxation characteristics and extrudate swell of the IUPAC-LDPE melt

“…Based on the sensitivity analysis of meshes in swelling simulation [17], a mesh of 360 elements with local refinements near the wall and the exit region is used to model the extrusion flowing. Venet and Vergnes [38] also adopted similar meshes to study the sharkskin defect of the swelling extrudate. Fig.…”

Relationships between molecular structure and sharkskin defect for linear polymers

“…According to the viscoelastic trumpet model, we can thus assume that the cracks propagate in the traction zone observed on the extrudate periphery at the die exit [11] and are controlled by the viscoelastic solid behaviour exhibited by the polymer when leaving the die. At the exit, the elastic energy stored during the flow along the capillary is released, leading to extrudate swelling.…”

“…In the literature on linear polyethylenes, the critical shear stress at the onset of sharkskin varies in the range of 0.1-0.2 MPa, depending on polymer and temperature [3,4,15,16,20]. Following the numerical simulations of Venet and Vergnes [11], the tensile stress at the die exit can be estimated to be around 45% higher than the wall shear stress. Accordingly, a critical stress of the order of 0.25 MPa is assumed.…”