Fluoropolymers additives

Kharchenko S B, McGuiggan P M, Migler K B, Flow Induced Coating of Fluoropolymer Additives Development of Frustrated Total Internal Reflection Imaging, J. Rheol, 2003 in press. 

In blends, fluoropolymers are used in small quantities to enhance throughput, reduce the frictional properties, and increase the wear resistance. Blends comprising 0.3-50 wt% of a low molecular weight PTFE (T , < 350 °C) with engineering resin showed improved antifriction properties (Asai et al. 1991). LLDPE generally exhibits sharkskin melt fracture, but the use of fluoropolymer additives, such as the copolymer of vinyUdene fluoride and hexafluoropropylene, can help to eliminate the extrusion instability (Hatzikiriakos and Migler 2005). 

The latest Viton FreeFlow additives are among those that have a reduced tendency to interact with other constituents of the formulation. Another new non-reactive fluoropolymer additive has been developed by Dyneon in association with 3M Canada to overcome similar problems, and has been found to perform well in LDPE and LLDPE film. The later versions of Dyneon polymer processing aids act as effective process aids in polyamides and PU, without the usual discoloration and processing problems. 

The DuPont product is named Viton FreeFlow SC and RC and, unlike earlier types of fluoropolymer additives, they can be mixed into many pigmented masterbatches, with less interaction. The Dyneon grades are marketed as Dynamar PPA. The latest fluorocarbons comply with most world food contact legislation. 

Ebnesajjad, S. Morgan, R. A. Fluoropolymer Additives Plastics Design Library Elsevier Waltham, MA, 2012 p 152. 

Fluoropolymer additive was used in blown film made out of metallocene linear low density polyethylene. This additive improves processability and eliminates melt fracture. The fluoropolymer additive presence was associated with a substantial increase of dart impact strength (84%), and it had no effect on tear strength. Some slip agent of undisclosed composition was also used. With 3 wt% slip additive, the dart impact strength was reduced to the same level it had without fluoropolymer additive. The tear resistance was not affected by the addition of a slip agent. ... 

Figure 10.36. Apparent viscosity of HOPE vs. shear rate at two levels of fluoropolymer additive in ppm. [Data from Focquet, K., Addcon 95 Worldwide Additives Polymer Modifiers Conference, Book of Papers, Basel, April 5-6, 1995, paper 19,1-5.]...

Viscosity is a function of shear stress and seems independent of the amount of the fluoropolymer additive, but at the lower level of additive (400 ppm), extrudate shows melt fracture above a shear rate of 800 s. If more additive is added, material is processed successfully at 50% higher shear rate. This is obviously another element of cost and process design, because a higher shear rate also means higher production rate. 

Barrel, head, and gate pressures are frequently reduced by the presence of additives (see example in Figure 10.38). Reduced gate pressure and lower torque resulted from addition of fluoropolymer additive. Melt viscosity usually increases with the addition of inorganic antiblocking additives. When fluoropolymer additive was added, it reduced viscosity so that a combined action of the two reduced head pressure by about 20%. This reduction depends on the types of additives. The antiblocking additives which absorb a process additive will cause higher head pressure. ... 

Some of the discussed additives may affect electrical properties of the materials. There is not much information published on this subject. It is known from literature that fluoropolymer additives made a dramatic improvement in the processing rates of several polymers (ethylene oxide epichlorohydrin copolymer, silicone, polyacrylate, nitrile butadiene rubber, and ethylene propylene diene terpolymer) without affecting the dielectric constant and dissipation factors. It can be assumed that a similar effect can be obtained with some silicone additives, but in the remaining cases, these properties have to be analyzed if they are of importance. 

Ebnesajjad, Handbook of Adhesives and Surface Preparation ISBN 9781437744613 Ebnesajjad, Fluoropolymer Additives ISBN 9781437734614... 

It is noticeable that the above mechanism is based on studies of fatty acid amides while other slip agents are also used for various purposes related with reduction of coefficient of fnction. Fluoropolymer additives, for example, are used to improve film extmsion in which they act in a similar manner during process as amides act in the final film. Fluoropolymer additive is also not compatible with polymer matrix. During extrusion it migrates to the surface of metal and forms film which has pronounced effect on production parameters. It reduces melt fraction, viscosity, shear rate, and gate pressure. This makes production faster and eneigy use lower. Some of these additives are developed in such a manner that they migrate only in a molten state but are immobilized within material after material solidifies. This makes them essentially absent from the film surface which in some post process operation is an important requirement. ... 

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