Fluoroplastics

A number of thermoplastics produced in small quantities worldwide have already been described within the appropriate families of materials in earlier chapters, for example polyamides and polyimides. The present chapter accommodates the more important members of the thermoplastic groups not included in other sections. These include fluoroplastics, polysulphones and sulphide polymers. 

Note ETFE, copolymer of ethylene and tetrafluoroethylene MFA, copolymer of perfluoromethylvi-nylether and tetrafluorethylene PFA, copolymer of perfluoropropylvinylether and tetrafluoroethylene FEP, fluorinated ethylene-propylene copolymer PCTFE, poly(chlorotrifluoroethylene) PVDF, poly(vinylidene fluoride) VDF-HFP, copolymer of vinylidene fluoride and hexafluoropropylene. 

Source Scheirs, 1. in Modem Fluoropolymers (Scheirs, 1., Ed.), John Wiley Sons, New York, p. 2, 1997. (With permission). 

The exceptional chemical resistance, resistance to ultraviolet (UV) radiation, and thermal stability can be further explained by the fact that the C-F and C-C bonds in fluorocarbons are among the strongest known in organic compounds (Table 3.2) [4]. 

Fluorinated ethylene propylene (FEP), a copolymer of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP), is essentially PTFE with an occasional methyl side group attached. The methyl groups have effect as defects in crystallites and therefore reduce the melting point. These side groups also impede the slipping of the polymer chains past each other, thus reducing the cold flow. 

Epoxies and polyurethanes give good bond strengths with properly treated fluoroplastic surfaces.  

Since the 1960s, copolymerization techniques for FPs have produced different FPs with different degrees of ease of processing. In turn, performance trade-offs had to be made, but the significant properties were nevertheless retained, in differing degrees. 

2 —Mechanical Strength at Ambient Temp.— X O ECTFE Copolymer of ethylene and 

Standard injection and extrusion equipment is used with the lower-viscosity polymers fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene (ETFE), polyvinyli-denefluoride (PVDF), polyperfluoroalkoxyethylene (PFA), ethylene chlorotrifluoroethyl-ene (ECTFE), and others. This substitution, or copolymerization, where fluorine atoms have substitutes, results in property and processing changes. 

---

Manufacturers of PTFE include Daikin Kogyo (Polyflon), Du Pont (Teflon), Hoechst (Hostaflon), ICI (Fluon), Ausimont (Algoflon and Halon), and the CIS (Fluoroplast). India and The People s RepubHc of China also manufacture some PTFE products. 

Fluoroplastics. Conventional plasticizers are used as processing aids for duoroplastics up to a level of 25% plasticizer. However, certain grades of Kel-E (chlorotriduorethylene) contain up to 25 wt % plasticizer to improve elongation and increase softness the plasticizers used are usually low molecular weight oily chloroethylene polymers (5). 

Storage. Carbon steel and stainless steel should be used for all equipment in ethylene oxide service. Ethylene oxide attacks most organic materials (including plastics, coatings, and elastomers) however, certain fluoroplastics ate resistant and can be used in gaskets and O-rings. See Reference 9 for a hst of materials that are compatible with ethylene oxide. 

Copolymers of chlorotrifluoroethylene and ethylene were introduced by Allied Chemicals under the trade name Halar in the early 1970s. This is essentially a 1 1 alternating copolymer compounded with stabilising additives. The polymer has mechanical properties more like those of nylon than of typical fluoroplastic, with low creep and very good impact strength. Furthermore the polymers have very good chemical resistance and electrical insulation properties and are resistant to burning. They may be injection moulded or formed into fibres. 

In addition to the fluoroplastics and fluororubbers already described other fluoropolymers have been marketed. Polymers of hexafluoropropylene oxide are marketed by Du Pont (Krytox). These materials have a low molecular weight (2000-7000) and are either oils or greases. The oils are uses as lubricants, heat transfer fluids and non-flammable oils for diffusion pumps. The greases are also used as lubricants. They have good heat and oil resistance but it is said that explosions may result from contact with the surfaces aluminium or magnesium cuttings. 

The processing and applications of PTFE as descnbed in the first edition of this book are essentially unchanged All the fluoroplastics descnbed, with the exception of PTFE and PVF, can be processed by conventional thermoplastic techniques such as injection moldmg and extrusion [7, 30]... 

The construction materials for the plates include most corrosion-resistant metals, usually 304SS, 316SS, titanium, Incoloy 825 , Hastelloy , and others, plus nonmetallic fused graphite, and fluoroplastic Diabon F . Typical gaskets between the plates include nitrile rubber, butyl, and EPDM elastromers, Hypalon and Viton , based on the various manufacturers literature. 

MOST PLASTIC MATERIALS ACRYLICS ALKYDS FLUOROPLASTICS CELLULOSICS NO TRACK 78-420 70-360 80-310... 

Fluoroplastics 2.10-2.15 Yes Marginal Opaque 3000-5000 175 Ductile With care Flexible tubing... 

GRAPHITE. MOLYBOENUM OlSU LFIDE AND FLUOROPLASTIC FlLLEO COMPOUNOS... 

THERMOPLASTIC POLYESTER POLY IMIOES SOME POLYSTYRENES FLUOROPLASTIC COPOLYMERS SOME FLUOROPLASTICS UHMWPE... 

POLY IM IDES SILICONES FLUOROPLASTICS POLYAMIDE-IMIDE EPOXY POLYPHENYLENE SULFIDE 500-800 400-600 300-550 520-545 175-500 500... 

Fluoroplastic FPs have superior heat and chemical resistance, excellent electrical properties, but only moderate strength. Variations include PTFE, FEP, PFA, CTFE, ECTFE, ETFE, and PVDF. Used for bearings, valves, pumps handling concentrated corrosive chemicals, skillet linings, and as a film over textile webs for inflatables such as pneumatic sheds. Excellent human-tissue compatibility allows its use for medical implants. 

Feiring AE (1994) Fluoroplastics. In Organofluorine Chemistry Principles and Commercial Applications (Eds RE Banks, BE Smart, JC Tatlow), pp. 339-372. Plenum Press, London. 

Examples of external lubricants are metal soaps, paraffin waxes, silicones and fluoroplastics. 

Speciality thermoplastics polysulfone (PSU), PPS, fluoroplastics, PEEK, PEI, polyamide imide (PAI), liquid crystal polymers (LCP). 

Whitcon Fluoroplastic lubricants Whitford Chemical Corp. 

---