Influence of the nature of fluoropolymer processing aids on the elimination of sharkskin defect in LLDPE extrusion

Fluoropolymer-based processing aids (PPA) are commonly used to suppress sharkskin defects in polyolefin extrusion. PPA’s also lead to a decrease in die pressure and a slight increase in flow rate by coating die walls and inducing wall slip. The aim of this work is to investigate the influence of different types of PPAs on the physical parameters in the die at various scales. We used a modular slit die fed by an extruder to measure die pressure and velocity profiles by Laser Doppler Velocimetry (LDV), and to characterize die surface coating by Scanning Electronic Microscopy (SEM).