Viton® Fluoropolymer

Coatings and sealants for varied industrial applications are made by dissolving compounds of low-viscosity FKM elastomers (e.g., Viton C-10, Viton A-35, Dyneon 2145) in methyl ethyl ketone, ethyl acetate, methyl isobutyl ketone, amyl acetate, or other related ketones [68], Such products have typical useful storage life of 7 days at 24°C (75°F) and cure within 2 weeks [80], This subject is covered in more detail in Modern Fluoropolymers (Scheirs, J Ed.), Chapter 23 (Ross, E. W. Jr. and Hoover, G. S.), John Wiley Sons, New York (1997). 

Fluoropolymer elastomers (or Viton, a registered trademark of the DuPont Performance Elastomer LLC) consist of hexafluoropropylene (HFP), vinylidene fluoride (VDF), and tetrafluoroethylene. The 3M Corporation uses the trade name Fluorel. The structures of each of these monomers are shown in Figure 8.14. The fluorine content of these terpolymers is typically around 70% for Viton. Four basic types of this material are shown in Table 8.8 however, Viton Extreme comprises more types. 

Hexafluoropropylene/vinylidene fluoride/ tetrafluoroethylene teipolymer, Viton A-100 Viton A-200 fluoroelastomer, tank coatings Hexafluoropropylene/vinylidene fluoride/ tetrafluoroethylene terpolymer fluoroelastomer, tank solution coatings Viton A-100 Viton A-200 fluoroelastomer, thin film Fluordatex 200 fluoropolymer modifier Dynasylan F 8815 fluoropolymer, coatings Dyneon THV 220A Teflon PTFE 30 Teflon TE-3667N... 

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. 

Base rubbers may be based on silicone, fluoropolymers, or hydrocarbons. Although silicone rubbers such as silicone S and G have been applied in stacks, it has become clear that they are not sufficiently stable [83-85]. Materials like ethylene-propylene-diene-monomer (EPDM), butyl rubber (IRR), or fluororubbers (FKM such as Viton )seem better suited. Further research is carried out to optimize properties like hardness, tensile strength, and stress relaxation. Also the morphology is being considered, with apparently a preference for profiled over flat gaskets. 

Other commercial fluoropolymers (all made by free-radical mechanisms) include polychlorotrifluoroethylene (Kel-F), which is similar to PTFE but which can be moulded at temperatures 300 °C. Polyvinylidene difluoride (PVDF) is a thermoplastic (T 160°C) and films of this material show piezoelectric behaviour. When copolymerized with hexafluropropene a very chemically resistant elastomer is obtained (Viton). Polyvinylfluoride (PVF) is another highly crystalline polymer (T 197°C) which is used for high-performance protective coatings. 

The addition of specific fluoropolymers to polyolefins allows for improved processability, including elimination of melt fracture (sharkskin), reduced die build-up, lowered processing viscosity, reduced die pressure and abihty to increase extrusion rates [278-282]. The fluoropolymers are generally added at levels of 100-1000 ppm. Vinylidene fluoride-hexafluoro-propylene fluorocarbon elastomers are often mentioned in the patent examples, such as the commercial systems carrying the tradename Viton duPont. 

Some fluoropolymers prepared by DT with iodo-compounds have already been commercialized such as Daiel, Viton, and Technoflon. Such fluoroelastomers may find applications in high technology such as in O-rings, gaskets, hoses, transportation, medical devices, and electronics. The control of the architecture and functionality of the polymer chains makes possible the preparation of peroxide curable fiuoroelastomer with improved properties as well as the development of advanced fluorinated thermoplastic elastomers. Another application of functional fluoropolymers prepared by DT with iodo-compounds is the preparation of membranes for fuel cells. 

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