A diverse family of resins features prominently across an equally diverse application spectrum

Fluoropolymers are a class of paraffinic polymers that have some or all of the hydrogen replaced by fluorine. These polymers exhibit exceptional chemical resistance and barrier properties, broad temperature resistance, good electrical properties, almost no moisture absorption, extremely low coefficients of friction, and resistance to weathering, among other attributes. These traits make them ideal materials for heat-resistant cabling, chemically resistant liners; gaskets; tubing; filters; valve, pump, and electrical components; coatings; and weather-resistant films, for example.

Various types of fluoropolymers are commercially available, including ethylene-tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) copolymer, perfluoroalkoxy (PFA) resin, polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene (ECTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride. Key global suppliers of these materials include Asahi Glass, Daikin Industries, DuPont, Dyneon, and Solvay Solexis. Fluoropolymers can be processed via extrusion, injection molding, compression molding, transfer molding, and blowmolding.

Construction profile rises

Due to the low surface tension of fluoropolymers, films processed from them (typically ETFE) are virtually self-cleaning, needing only rain to wash away accumulated dirt.

Films also exhibit very good tear and puncture strength and good hail resistance. Moreover, and importantly, they are rated flame retardant non-burning drip. These attributes make them suitable for use in various construction applications.

Usually extruded in thicknesses of 100-250 µm, the films can be readily conjoined by heat-sealing. They have been used a fair amount in roof structures for sports stadiums, swimming pools and botanical gardens, and extensively in greenhouses in Japan.

ETFE film will feature prominently at the 2006 World Cup soccer championships in Germany. Asahi Glass has supplied 150,000 sq2 of its Aflex film for the roof of the Allianz-Arena soccer stadium in Munich, where the opening match of the World Cup is to be held. The stadium is the world''s largest structure made of ETFE film. ETFE enabled a design where the side walls and roof are smooth and curved that also permeates ultraviolet light needed to grow the lawn on the pitch and enables light shows that use the side walls and roof as monitor screens.

IT support role

Fluoropolymers are also playing a key role in the IT revolution. Buildings in the United States that have cables that incorporate flammable insulating materials (such as polyethylene and PVC) in the plenums inside the ceilings, are required to route such cables through metal pipes in order to increase the flame resistance of the cables. If FEP is used as an insulating material, no metal pipes are required. Thus, FEP has come to be employed extensively as an insulating and jacketing material in limited combustible cables for LAN applications. FEP cables are now being used in more than 70% of high-rise building networks.

Reducing hydrocarbon emissions

In Japan, blow-by gas from diesel engines used to be released into the atmosphere, but to reduce hydrocarbon emissions, it must now be returned to the intake line. The turbo hose between the turbocharger and the intercooler is currently made from silicone rubber, but blow-by gas contains a small amount of engine oil mist and silicone rubber has poor resistance to oil. Therefore, engine manufacturers are looking to replace it with specialty fluoroelastomers such as TFE-propylene dipolymer and TFE-propylene-VdF terpolymer from Asahi Glass.

Fluoropolymers are also employed extensively in fuel cells, where they help form key components such as end plates and bipolar plates in fuel cell stacks, methanol and hydrogen tubing, manifolds, and valves and meters. Fluoropolymers also are employed as barrier resins in multilayer tubing for automotive fuel lines.

Performance advances

Suppliers are also making advances on the performance front. PTFE grade M-111 from Daikin, for example, features improved creep properties. Parts exhibit less deformation under load than conventional PTFE. It is a good choice for seals used under high temperatures and pressure. Another grade, M-112, offers fewer microvoids than conventional PTFE, plus good bend fatigue resistance. It is suited for dynamic applications such as bellows and diaphragms.

Asahi Glass, meanwhile, has developed a low-melting-point ETFE that retains the excellent heat resistance and other mechanical properties normally associated with EFTE. Melting point is 225°C, compared with 260°C for the company''s standard grade. Film with excellent transparency can be produced and processing can be performed over a wide temperature range.

Stephen Moore [email protected]