The effect of die exit curvature, die surface roughness and a fluoropolymer additive on sharkskin extrusion instabilities in polyethylene processing

Molecular interpretation of the “stick–slip” defect of linear polymers

“…To determine the plateau modulus of HDPE, we used the coefficients of the relaxation time spectra derived from rheological characterizations of the literature. We found G 0 N = 649, 000 Pa at 190 • C with the data of Arda and Mackley [50] and G 0 N = 677, 000 Pa at 200 • C with those of Miller et al [51].…”

Multi-scale phenomena induced by fluoropolymer processing aids during the extrusion of linear-low density polyethylene

“…Another breakthrough is the reduction of die pressure [2,7] and extruder torque [8,9]. It was demonstrated that the die pressure decrease is actually caused by the change in wall flow conditions, without change in the intrinsic viscosity of the extruded polymer containing PPA [8,10]. Other interesting effects of fluoropolymers were reported, such as the reduction of extrudate swell or die build-up [5,7,9,11].…”

Fine lattice structures fabricated by extrusion freeforming: Process variables

“…Surface defects such as 'shark skin', 'dragon teeth' and 'strain rate chaotic deformation' can be found in thermoplastic and metal extrusion (Arda and Mackley, 2005;Kulikov and Hornung, 2001) but did not appear in filaments deposited by solvent-based extrusion freeforming, but wave distortion as shown in Fig. 9(a) could be generated.…”