## 2 The Development of the Fluoropolymer Industry from 1930s \(\sim\) 1990s
### 1960s
The formability of PVF is very important for lamination applications. It is critical that the laminate can stand bending during the roll forming process. PVF laminated steel finds application in industrial plants, warehouses, highway sound barriers and parking garages and provides long lasting aesthetics. Currently, DuPont is still the main company for PVF production. With a recent expansion it plans to achieve $1 billion in sales by 2012. Compared to VF, vinylidene fluoride (VDF) has one more fluorine atom on the same carbon in its chemical structure. The free radical polymerization of VDF resulted in a partially fluorinated,  
Figure 4: The polymerization of VF. semi-crystalline polymer PVDF (polyvinylidenefluoride) (Figure 5), which was introduced by Pennsalt (now Arkema) with the tradename Kynar in 1961. PVDF is generally prepared by two kinds of polymerization methods, the suspension method and the emulsion method. Suspension polymerization produces PVDF with high head-to-tail structure in the polymer chains, which results in higher crystallinity, higher melting temperature, and better mechanical properties at elevated temperatures [17, 18]. PVDF is a polymer with several crystalline forms depending on the processing conditions. It has a melting temperature (\(\sim\)170 \({}^{\circ}\)C) significantly lower than that of the other fluoropolymers. The normal processing temperatures for PVDF are in the range 200-260 \({}^{\circ}\)C, and the continuous service temperature for PVDF is up to 150 \({}^{\circ}\)C. The crystallinity of PVDF increases significantly in the first week after processing and stabilizes after 4 weeks. This phenomenon increases crystallinity up to 65% and results in the intrinsic stress and the potential stress cracking. PVDF has very good chemical resistance to a wide range of chemicals, but it is not as good as that of other fluoropolymers. For example, PVDF can be swollen by polar solvents such as ethyl acetate and acetone. It shows medium flame resistance properties. PVDF also shares many of the characteristics of other fluoropolymers, such as thermal and oxidative stability, as well as outstanding weatherability. PVDF has substantially greater strength, wear resistance, and creep resistance than PTFE and FEP. PVDF undergoes cross-linking when exposed to ionizing radiation, which leads to a modification of its mechanical properties. PVDF has been used in the architectural coating industry, the wire and cable industry and the chemical industry for valves, pumps and bearings. Heat-shrinkable tubing made from PVDF is used in the electronics, aerospace, and aircraft industries. The alternative arrangement of fluorine and hydrogen atoms on the polymer main chain leads to an unusual polarity with a dramatic effect on dielectric properties. PVDF has a high dielectric constant (8 \(\sim\) 9) relative to the other fluoropolymers, and it also shows strong piezoelectricity. The promising developments include actuator materials, piezoelectric ceramics, piezoelectric composites and piezomicrosensors. The commercial PVDF products include Kynar from Arkema, Solef from Solvay, and Neoflon PVDF from Daikin. Solvay increased PVDF production capacity by 50% in 2011 to serve the strong growing demand. In the late 1960s, Nafion was discovered by [PERSON] of DuPont. Nafion is a fluoropolymer containing sulfonate groups onto a tetrafluoroethylene backbone (Figure 6) [19, 20, 21, 22, 23, 24, 25, 26, 27]. It is the first of a class of synthetic polymers with ionic properties which are called ionomers. Figure 5: The polymerization of VDF. Nafion is synthesized firstly by the copolymerization of TFE and a perfluoro(alkyl vinyl ether) with sulfonyl acid fluoride. The resulting polymer is extruded into films and treated with hot aqueous NaOH converting the sulfonyl fluoride groups (-SO\({}_{2}\)F) into sulfonate groups (-SO\({}_{3}\)Na). This form of Nafion, referred to as the neutral or salt form, is finally converted to the acid form containing the sulfonic acid (-SO\({}_{3}\)H) groups.