Extrusion characteristics of thermoplastic melts containing fluoropolymers

Abstract

This paper investigates the influence of fluoropolymers on the extrusion characteristics of three different thermoplastic melts. The presence of a small amount of fluoropolymer reduced the pressure drops, extrudate swell, and retarded the onset of surface defects in linear low density polyethylene (LLDPE), while little or no effect was found in polystyrene (PS) and polyamide 12 (PA 12). Among the fluoropolymers investigated in this study, vinylidene fluoride-hexafluoropropylene (VDF-HFP) copolymer was the most effective additive in reducing the pressure drop and extrudate distortion of LLDPE, polyvinylidene fluoride (FVDF) intermediate, and tetrafluoroethylene-hduoropropylene (TFE-HFP) copolymer exhibited the least effectiveness. Contact. angle measurements on the die surface indicated that all fluoropolymers preferentially deposit on the die surfaces during the extrusion of LLDPE and PS blends with small amounts of fluoropolymers.

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

“…Moreover, LLDPE is completely non-polar when the tested PPA has a low polar part of 1.0 mJ/m 2 . These values are in agreement with the literature: Lee and White [11] measured 23.8 mJ/m 2 at 200°C for polyethylene, and evaluated 14.2 mJ/m 2 at 200°C for copolymers of vinylidene fluoride and hexafluoropropylene. Besides, we note that the work of adhesion is quite high (40.2 mJ/m 2 ), which means that Wave numbers(cm -1 ) The FTIR spectrum of PPA indicated that the main phase was b-phase, which is relevant with a chemical synthesis in solution (Fig.…”

“…The main commercial fluoropolymer based PPAs are composed of copolymers of vinylidene fluoride and hexafluoropropylene, because of their efficiency in delaying the onset of sharkskin defects [11]. We used a such copolymer of vinylidene fluoride and hexafluoropropylene (KynarFlexÓ) provided by Arkema.…”

“…The surface energy of fluoropolymer is often noted as an important parameter for adhesion in PPA mechanism [7,11]. We decided to measure the surface energy of the different polymers with wetting equilibria and Young equation, and using the methods of equation of state and harmonic average [13,14].…”

“…Assuming a variation with temperature of dc/dT = À0.044 mJ/ m 2 /°C [11], it is possible to determine polymer surface energy at 200°C [12]. The spreading coefficient between the two materials is then defined as:…”

Basic Study of the Interaction of Thermoplastic Fluoropolymer Blends with Metal Surfaces During Extrusion.

“…1) More recently, it has been found that addition of small quantities of fluoroelastomers to polyethylene greatly reduces the pressure losses through dies during extrusion and improves extrudate quality. [2][3][4][5][6][7][8][9] It is our purpose in this paper to study the mechanisms of fluoropolymer depositions and the characteristics of die wall interaction in greater detail. We will look at the interactions of different polymers with fluoroelastomers.…”