Use of Fluorocarbon Elastomers as Processing Additives for Polyolefins

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

“…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]. All these benefits were characterized in terms of fluoropolymer and polyolefin characteristics, extrusion throughput, presence or effects of other additives [6,7,12].…”

“…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].…”

Extrusion Defects and Flow Instabilities of Molten Polymers

“…Finally, concerning the material of the die, the same type of results as for the sharkskin defect is reported: the use of lowenergy surfaces (deoxidized brass, fluoropolymer additives) tends to reduce or even completely eliminate the oscillating defect (Lim, 1971;Rudin et al, 1990;Moynihan et al, 1990;Piau et al, 1995a;Wang and Drda, 1997b;Ghanta et al, 1999;Dao and Archer, 2002).…”

“…This was confirmed by Kalika and Denn (1987) and Ghanta et al (1999). Many authors have since shown that the use of fluorinated additives (Nam, 1987;De Smedt and Nam, 1987;Rudin et al, 1990, or low molecular weight materials (Sornberger et al, 1987), or walls of low surface energy (Moynihan et al, 1990;Piau et al, 1995a;Hatzikiriakos et al, 1995;Ghanta et al, 1999;Larrazabal and Hrymak, 2002) allow to completely suppress the defect. All these solutions induce macroscopic wall slip and we show in the next section how it can influence the sharkskin defect.…”

“…Moreover, it has been recently shown by Shaw (2007), who carefully studied 37 sets of data from 15 different laboratories, that the relationship between onset of sharkskin and kink was probably fortuitous. In addition, the idea of attributing the origin of the defect to a slip phenomenon has been totally contradicted by numerous studies that have shown, on the contrary, that the defect could be completely removed either by adding fluorinated polymers or low molecular weight additives (Nam, 1987;De Smedt and Nam, 1987;Sornberger et al, 1987;Rudin et al, 1990;Dubrocq-Baritaud, 2008), or by using walls with low surface energy (Moynihan et al, 1990;Piau et al, 1995b;Hatzikiriakos et al, 1995), two solutions that widely promote wall slip. Therefore, even though a weak slip may exist during the sharkskin defect, it can in no case be the cause of the problem.…”