Grades fluorocarbons

Testing and Standards. Requirements for extmsion and mol ding grades are cited in ASTM specifications (79) and in Federal specification LP-389A of May 1964 (80). For fabricated shapes, FEP film and sheet are covered by Aeronautical Material Specifications (AMS) 3647 and LP-523 (81). Besides the specifications covered by the Fluorocarbons Division of the Society of the Plastics Industry, Inc. (82), other specifications are Hsted in Reference 83. 

Fig. 3. Heat and oil resistance of CSM compared to other elastomers by ASTM D2000. A—K iadicate grades of CSM. The other ASTM designations are as follows AM, acryhc elastomers CR, chloroprene mbber EPDM, ethylene—propjiene—diene mbber FKM, fluorocarbon elastomers FQ, fluorosiUcones ...

Compression Set Resistant. One property of fluorocarbon elastomers that makes them uniquely valuable to the sealing industry is their extreme resistance to compression set. Figure 4 plots compression set vs time for compounds prepared especially for compression set resistance (O-ring grades). 

Extruded Articles. In extmded article compounding, the most important parameters are scorch safety and flow characteristics (53). The bisphenol cure system again offers the best scorch resistance of the available fluorocarbon elastomer cure systems. Good flow characteristics can be achieved through proper selection of gum viscosities. Also, the addition of process aids to the formulation can enhance the flow characteristics. Typical formulations for extmsion grade fluorocarbon elastomers are given iu Table 7. 

Table 7. Fluorocarbon Elastomer Extrusion Grade Compound...

Extrusion. Extmsion techniques are used in the preparation of tubing, hose, O-ring cord, preforms and shaped gaskets. Typical extmsion conditions are 70 to 85°C for the barrel temperature and 95 to 110°C for the head temperature. The extmded forms are normally cured in a steam autoclave at 150 to 165°C. Some special grades of peroxide curable fluorocarbon elastomers can be hot air vulcanized. 

Certain grades and formulations of the fluorocarbon elastomers are qualified under the code of Eederal Regulations, 21, Eood and Dmgs, Part 177.2600 for use as mbber articles whose intended appHcations requite repeated or continuous contact with food. Elastomer suppHers will provide assistance in formulating for specified uses. 

For particularly difficult to adhere substrates such as metallized or fluorocarbon treated surfaces the same principles that are applied in freezer grade adhesives are used. For especially difficult situations, styrenic block copolymers are added to... 

Acrylic rubber Chlorinated polyethylene Chlorosulphonated polyethylene Ethylene-propylene copolymer Ethylene-propylene terpolymer Fluorocarbon rubbers (certain grades)... 

The first reactions of fluorinated olefins in C02 reported by DeSimone et al. involved the free-radical telomerization of 1,1 -difluoroethylene29 and tetrafluor-oethylene.30 This work demonstrated the feasibility of carrying out free-radical reactions of highly electrophilic species in solvents other than expensive fluorocarbons and environmentally detrimental chlorofluorocarbons. The work has since been more broadly applied to the synthesis of tetrafluoroethylene-based, nonaqueous grades of fluoropolymers,31,32 such as poly(tetrafluoroethylene-co-peduoropropylvinyl ether) (Scheme 2). These reactions were typically carried out at between 20 and 40% solids in C02 at initial pressures of between 100 and 150 bars, and 30-35°C (Table 10.1). 

Solid fluorocarbon elastomers are commercially available as pure gum polymers or precompounded grades usually with curing system included. Only a nucleophilic curing system is used in these compounds. Examples of commonly used curing systems are listed in Table 5.6.34... 

Fluorocarbons. There are eight types of common fluorocarbons. They differ primarily by the concentration and arrangement of fluorine atoms along their molecular chain. Chemical types, suppliers, and trade names are given in Table 16.10. Like other plastics, each type of fluorocarbon is available in several different grades. They differ principally in the way they are processed and formed, and their properties vary over the useful temperature range. 

Acetal translucent crystalline polymer is one of the stiffest TPs available. It provides excellent hardness and heat resistance, even in the presence of solvents and alkalies. Its low moisture sensitivity and good electrical properties permit direct competition with die-cast metal in a variety of applications. In addition, acetal has extremely high creep resistance and low permeability. Acetal is also available as a copolymer (Hoechst Celanese Corp. s Celcon) for improved processability. The homopolymer (DuPont s Delrin) has a very low coefficient of friction and its resistance to abrasion is second only to nylon 6/6. Acetals are frequently blended with fibers such as glass or fluorocarbon to enhance stiffness and friction properties. Acetal is not particularly weather-resistant, but grades are available with UV stabilizers for improved outdoor performance. Acetal, whether homopolymer or copolymer, is not used to any significant degree in forming structural foams. 

There are a number of grades of fluorocarbon rubber (copolymers, terpolymers and tetrapolymers) and they are mainly used in applications where the temperatures would degrade ethylene-propylene rubber products. They are able to withstand prolonged use at temperatures up to 200 °C. Typical conditions are high temperature (<150 °C) gaskets under flow or static conditions, in contact with aqueous or fatty foods (including oils). 

Figure 18.18 Map of dielectric properties of engineering plastics. Among engineering plastics, SPS (impact modified and GF-reinforced HB and IR grades) has very low dielectric dissipation factor and dielectric constant following those of fluorocarbon polymers. PSF, polysulfone PPE, poly(phenylene ether) PES, poly(ether sulfone) PAr, polyarylate...

Carbon dioxide is, by far, the most attractive SCF for many reasons It is inexpensive and abundant at high purity (food grade) worldwide and it is nonflammable, non-toxic, and environment friendly moreover, its critical temperature T = 31 °C) permits operations at near-ambient temperature which avoids product alteration and its critical pressure (= 74 bar) leads to acceptable operation pressure, generally between 100 and 350 bar. In fact, supercritical carbon dioxide behaves as a rather weak nonpolar solvent, but its solvent power and polarity can be significantly increased by adding a polar cosolvent that is chosen among alcohols, esters, and ketones. Ethanol is often preferred because it is not hazardous to the environment, not very toxic, and available pure at low cost. Hydro fluorocarbons (HFCs) are very costly and their specific properties rarely justify their use in the replacement of carbon dioxide. 

PVDE, Kynar and other related fluorocarbons HDPE, Petrothene LB 832 and other commercial grades LCP, Vectra A950... 

Recent experiments by the authors studied the water repellence of PET fabrics (technical fabrics), photochemically treated in the presence of, e.g., 1,5-hexadiene, 1,7-octadiene, diallylphthalate (DAP) and l//,l//,2//,2H-perfluorodecyl acrylate (PFDA). Exemplary experimental data are summarized in Fig. 13 showing drop penetration times in excess of 1 hour (measurements were stopped after this time) and DuPont grading of up to 8. The relevant values for the untreated fabrics were drop penetration time approx. 20 s and a DuPont grading 0. Based on the well-known effect of heat treatments on long-chain fluoro compounds (cf. Sections 4 and 5.1), the samples treated with PFDA were also characterized following a further heat treatment. As was found in the case of wet-chemical finishes and plasma-deposited fluorocarbon thin layers, the water repellence of the samples could be further enhanced by heat treatment in this case also. 

Melt-processable fluorocarbon parts have been snccessfnlly heat welded, and certain grades have been spin welded and hermetically sealed with indnction heating. However, becanse of the extremely high temperatures involved and the resnlting weak bonds, these processes are seldom used for structural applications. Flnorocarbon parts cannot be solvent welded becanse of their great resistance to all solvents. 

Because of the lower ductility of the fluorocarbon materials, snap-fit and press-fit joints are seldom used. Rivets or studs can be used in forming permanent mechanical joints. These can be provided with thermal techniques on the melt processable grades. Self-tapping screws and threaded inserts are used for many mechanical joining operations. In bolted connections some stress relaxation may occur the first day after installation. In such cases, mechanical fasteners should be tightened thereafter, stress relaxation is negligible. 

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