Mechanism of Fluoroelastomer Processing Aid in Extrusion of LLDPE**

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

“…The presence of fluoropolymer at the die/flow interface was early proved by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) [2,13]. More recently, Lavallée [14] has presented pictures of fluoropolymer deposits on gold and nickel surfaces.…”

“…For such applications, fluoropolymers are usually introduced at very low content, typically between 200 and 1500 ppm in weight. 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].…”

“…The first use of PPA was to eliminate sharkskin defect on linear polyethylene [2][3][4][5]. PPA also allow to increase extrusion throughput and to improve the optical properties of extruded films, such as haze and transparency, without mechanical deterioration [6].…”

Coating kinetics of fluoropolymer processing aids for sharkskin elimination: The role of droplet size

“…Rosembaum et al [24] have discussed the experimental observation that the time for complete coating of the surface of the die depends on shear rate, diameter and L/D of the die. The fluoropolymer coating has been observed to form streaks on the die wall in the direction of the flow [18,[25][26][27]. Recently, it was shown that the appearance of the streaks roughly coincides with slippage of the PE and elimination of sharkskin [18,25].…”

Influence of die surface on the efficiency of fluoropolymer processing aids during the extrusion of linear-low density polyethylene

“…Thanks to these new techniques and observations, it is now possible to get further information about the influence of process parameters in order to optimize PPA efficiency. Some studies have already looked at the influence of process parameters such as flow rate [9], or PPA parameters such as concentration [10] and particle size [6] on sharkskin defects.…”