Pressure oscillations and periodic extrudate distortions of long-chain branched polyolefins

Experimental Correlation between Mechanical Non‐Linearity in LAOS Flow and Capillary Flow Instabilities for Linear and Branched Commercial Polyethylenes

“…Large interest has been focused on the study of slip phenomena of polymer melts, mostly due to its relevance in industrial processes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] . This is particularly relevant, if one considers that the appearance of melt flow instabilities is a limitation for both maximum throughput and the type of material used in processes such as film and sheet extrusion.…”

Extrusion Defects and Flow Instabilities of Molten Polymers

“…Finally, the critical shear stress for the onset of instability is reported to increase as the molecular weight (Vlachopoulos and Lidorikis, 1971;Vlachopoulos and Alam, 1972;Vlachopoulos, 1974;Den Doelder et al, 2005) and the polydispersity (Baik and Tzoganakis, 1998) decrease. Kim and Dealy (2002b) found that the critical elongational stress is independent of molecular weight, but increases linearly with polydispersity index and level of long chain branching.…”

Flow instability for binary blends of linear polyethylene and long-chain branched polyethylene

“…Yamaguchi et al found that gross melt fracture of LDPE can be avoided by applying intense shear history, which weakens the relaxation mechanism associated with long-chain branches, by shear modification [51]. Doelder and Koopmans reported that the critical conditions for the appearance of gross melt fracture depend on molecular mass and branching [47]. Meller et al revealed that elongational stress decides the onset of gross melt fracture [38].…”

“…Since it is generally accepted that a high viscous polymer melt slips on the wall, the slippage can be the origin of surface instability [35,43,44]. Gross melt fracture is attributed to the flow instability at a die entrance, and associated with long time relaxation mechanism [38,[45][46][47][48][49][50][51]. Yamaguchi et al found that gross melt fracture of LDPE can be avoided by applying intense shear history, which weakens the relaxation mechanism associated with long-chain branches, by shear modification [51].…”