Fluoroelastomers based

Fluoroelastomer-based nanocomposites were prepared using various nanoclays and their different properties were studied [93-98]. 

Fluoroelastomers based on polyvinylidene fluoride (VDF) can be cross-linked by ionic mechanism. However, if the polymer has been prepared in the presence of a cure site monomer (CSM) it can be cross-linked (cured) by a free radical mechanism. 

Fluoroelastomers based on TFE and propylene (e.g., AFLAS) (see Section 5.1.1) swell to a high extent in aromatic hydrocarbons because of the relatively low fluorine content (54%). However, because of the absence of VDF in their structure, they exhibit a high resistance to highly polar solvents such as ketones, which swell greatly all fluoroelastomers containing VDF. In addition, elastomers based on copolymers... 

Hostalub . [Hoechst Celanese/Spec. Chem.] Fluoroelastomer-based processing aid for polyolefins. 

Chem. Desetip. One-component fluoroelastomer based on Viton Uses Sealant/caulk for industrial applies, such as Joint sealant for steel and concrete, door gasket adhesive on industrial ovens, adhesives for flue duct expansion Joints, acid-resist. Joint sealant for industrial flooring, hazardous abatement material, coatings for fuel inj. hoses in automobiles, coatings for equip, subject to corrosive liq., and adhesives for bonding rubber gaskets to metal... 

Bauerle, J., Paper 9, A New, Improved Processing Base-Resistant Fluoroelastomer Based on APA Technology, Viton TBR-S, ACS Rubber Div., October 2003. 

A comparison is made of standard kneading elements with tapered kneaders nsing results from several case studies. These case studies relate to the compounding of foamable, carbon black filled EPDM automotive weather stripping, an EPDM roofing compound and fluoroelastomer based compounds. 

Fluorocarbon elastomers also form the basis for a set of sealers. Hie monomers for these materials include hexafluor-opropylene, vinyUdene fluoride, and tetrafluoroethylene. The fluoroelastomer-based sealants were developed for the aerospace industry and have many of the same chemical resistance properties of PTFE but are also elastomeric in cbaracter. 

Soft reliners can weaken the strength of the heat-cured resin, because they reduce the thickness of the denture base and allow the diffusion of the monomer or solvent from the reliner into the base. Reflned dentures stain readily and are difficult to clean. A polyphosphazine fluoroelastomer has also been developed in an attempt to overcome the deficiencies of available liners (218). 

If the compound can be attacked by water, for example polyacrylate and fluoroelastomer elastomer based compounds, the preforms are air cooled. 

Based on the extensive work, Ghosh and De have concluded that fluoroelastomer and silicone mbber form technologically compatible blends of micro-heterogeneous stmcture with thermal stability between those for the blend components. The blend could be used as a replacement for fluorosilicone mbber. 

In fact, fluorinated polyphosphazenes are usually considered to be extremely stable towards chemical agents and aggressives due to the presence of C-F bonds in the side phosphorus substituents. PTFEP, for instance, appears to be completely insensitive to several, most common, solvents (aliphatic and aromatic hydrocarbons, alcohols and water), to acids (e.g. acetic acid), and to bases (e.g. pyridine and concentrated NaOH solutions), although some decomposition could be observed in triethylamine and in concentrated H2SO4 [41]. Phos-phazene fluoroelastomers, moreover, are known to be completely insoluble in aromatic solvents [533] and petroleum-resistant materials [502-506,552]. 

The first commercial fluoroelastomer, Kel-F, was developed by the M. W. Kellog Company in the early to mid-1950s and is a copolymer of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE). Another fluorocarbon elastomer, Viton A, is a copolymer of VDF and hexafluoropropylene (HFP) developed by du Pont was made available commercially in 1955. The products developed thereafter can be divided into two classes VDF-based fluoroelastomers and tetrafluoroethylene (TFE)-based fluoroelastomers (perfluoroelastomers).72 The current products are mostly based on copolymers of VDF and HFP, VDF and MVE, or terpolymers of VDF with HFP and TFE. In the combination of VDF and HFP, the proportion of HFP has to be 19 to 20 mol% or higher to obtain amorphous elastomeric product.73 The ratio of VDF/HFP/TFE has also to be within a certain region to yield elastomers as shown in a triangular diagram (Figure 2.2).74... 

Fluoroelastomers are for the most part based on the combination of vinylidene fluoride (VDF) with other monomers, which disrupt the high crystallinity typical for the PVDF homopolymer. The properties of the resulting elastomeric materials are determined by the short VDF sequences and low or negligible crystallinity. 

Copolymers of VDF and HFP, completely amorphous polymers, are obtained when the amount of HFP is higher than 19 to 20% on the molar base.6 The elastomeric region of terpolymers based on VDF/HFP/TFE is defined by the monomer ratios. Commercially, VDF-based fluorocarbon elastomers have been, and still are, the most successful among fluoroelastomers.7 The chemistry involved in the preparation of fluorocarbon elastomers is discussed in some detail in Chapter 2. 

Certain substrates (woven and nonwoven fabrics, foils, and films) are coated by dipping, spreading, or spraying with fluoroelastomers in liquid form. The older method using a solution of fluoroelastomers in volatile solvents (methyl ethyl ketone, toluene, etc.) is gradually being replaced by the use of water-based latexes (see Chapter 6). 

Coatings and sealants for varied industrial applications are made by dissolving compounds of low-viscosity FKM elastomers, such as VITON C-10, VITON A-35, or FLUOREL 2145, in methyl ethyl ketone, ethyl acetate, methyl isobutyl ketone, amyl acetate, or other related ketones.47 Such products have typical useful storage life of 7 days at 24°C (75°F) and cure within 2 weeks.58 The subject of coatings and sealants based on fluoroelastomers is covered in more detail in Modern Fluoropoly-mers (Scheirs, J., Ed.), Chapter 23 (Ross Jr., E. W. and Hoover, G. S.), John Wiley Sons, New York (1997). 

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