PVDF: a Fluoropolymer for Chemical Challenges

Electronically reprinted from August 2018

PVDF: A Fluoropolymer for Chemical Challenges

When it comes to selecting materials of construction, keep in mind the favorable properties of fluoropolymers for corrosive service

Averie Palovcak and Jason ince its commercialization in the Pomante, mid-1960s, polyvinylidene fluoride Arkema Inc. (PVDF) has been used across a Svariety of chemical process industries (CPI) sectors due to its versatility and IN BRIEF broad attributes. With flagship applications PVDF AND THE in architectural coatings and the CPI, the FLUOROPOLYMER FAMILY breadth of industries where PVDF is utilized today is expansive. PVDF components (Fig- COPOLYMERS CHANGE ures 1 and 2) are utilized and installed where FLEXURAL PROPERTIES engineers are looking to maximize longevity PVDF COMPONENTS and reliability of process parts in many CPI sectors, including semiconductor, pharma- FIGURE 1. A variety of fluoropolymer components are shown ceutical, food and beverage, petrochemi- here cal, wire and cable, and general chemicals. change the performance properties. Fluo- PVDF and the fluoropolymer family ropolymers are divided into two main cat- PVDF is a high-performance plastic that falls egories: perfluorinated and partially fluori- into the family of materials called fluoropoly- nated [1]. The partially fluorinated polymers mers. Known for robust chemical resistance, contain hydrogen or other elements, while fluoropolymers are often utilized in areas the perfluorinated (fully fluorinated) poly- where high-temperature corrosion barriers mers are derivatives or copolymers of the are crucial. In addition to being chemically tetrafluoroethylene (C2F4) monomer. Com- resistant and non-rusting, this family of poly- monly used commercial fluoropolymers mers is also considered to have high purity, include polytetrafluoroethylene (PTFE), non-stick surfaces, good flame and smoke perfluoroalkoxy polymer (PFA), fluorinated resistance, excellent weathering and ultra- ethylene propylene (FEP), polyvinylidene violet (UV) stability. fluoride (PVDF), ethylene tetrafluoroethyl- Fluoropolymers have carbon and fluorine ene (ETFE), and ethylene chlorotrifluoro- as the main components of their chemical ethylene (ECTFE). backbone. Small changes in percent fluo- PVDF is a partially fluorinated polymer rination or addition of other elements may consisting of repeated units of the vinylidene 400

350

300

C) 250 o

200

Temperature ( Temperature 150

100

0 PTFE PFA FEP ETFE ECTFE PVDF

Melting Degradation FIGURE 3. The processing temperature window for several fluoropolymers is shown here

temperature requirements must be the crystallinity of PVDF, resulting in taken into account when processing added ductility and increased elon- most fluoropolymers. gation [5]. Varying amounts of HFP FIGURE 2. These fluoropolymer tower packings are used in distillation columns Unlike its fluoropolymer counter- can be reacted with VF2 to yield parts, PVDF is the most benign to broad ranges of flexibility. Table 2 fluoride (VF2) monomer [(C2H2F2)]. process. PVDF has the widest gap gives an example of the range of Standard PVDF homopolymer is between its melt temperature and its flexural moduli of PVDF, both homo- 59.4% fluorinated and PVDF copo- degradation temperature, as shown polymer and copolymer, compared lymers (described in later sections) in Figure 3. In fact, PVDF does not to other fluoropolymers. can reach up to 65% fluorination. require special equipment and can Variations in material flexibility re- Generally, the higher the fluorine be processed on standard equip- sult in a wider range of components content, the higher the chemical ment used to process polyolefins, available in PVDF materials. While resistance, as the carbon-fluorine such as polyethylene (PE) and poly- PVDF homopolymer has a long leg- bond is one of the strongest known propylene (PP). acy of use in piping, valves, pumps in chemistry. PVDF homopolymers and other applications that require can tolerate chemistries from a pH Copolymers flexural properties high mechanical rigidity, the PVDF co- of less than 1 up to 12 and PVDF While PVDF is the strongest of the polymer range has a variety of melt- copolymers can extend that range fluoropolymers up to 140°C, PVDF processed components, such as wire from much less than 1 up to 13.5. copolymers can bring added de- and cable jacketing (Figure 4), tubing, While PTFE, with its high melting grees of flexibility. Copolymerization hoses and gaskets, to name a few. point of 325°C, is well known as a is a true chemical reaction. It does liner for high temperature applica- not involve additives or stabilizers PVDF components tions, PVDF homopolymer has a melt that can leach out over time. Some As previously described, the proper- point between 165 and 172°C and of most common comonomers are ties of PVDF make it useful across a maintains a Underwriters Laborato- hexafluoropropylene (HFP), tetra- variety of applications. The following ries (UL) relative thermal index (RTI) fluoroethylene (TFE), and chlorotri- are just a few highlighted components rating of 150°C [2]. Table 1 shows the fluoroethylene (CTFE). HFP is a fully heat deflection temperature of fluo- fluorinated monomer that disrupts ropolymers with PVDF holding mechanical integrity under pressure up to its usage certification temperature. Aside from PTFE, which is most often processed by sintering, most other commercial fluoropolymers are melt processable, and require high heat to process in a molten state [4]. Equipment used to make most fluoropolymer components must be therefore equipped to han- dle the associated thermal stresses. FIGURE 4. Wire and cable components are com- FIGURE 5. PVDF piping systems come in a various Special considerations related to monly made of fluoropolymers forms FIGURE 7. This flexible tubing is made from PVDF copolymers

FIGURE 6. Electrofusion is one joining method of dards [8]. Piping systems for waste PVDF systems drainage applications along with wire FIGURE 8. PVDF fittings are one example of and cables made with PVDF are injection-molded pieces where PVDF materials are specified to widely specified in the plenum areas bring long-lasting solutions. of buildings. Electrofusion is a spe- to bind the PVDF to another mate- Piping systems. PVDF piping sys- cialized pipe-joining technique for rial, such as polyurethane or poly- tems (Figure 5) have a UL RTI rating that industry, where built-in electric ethylene. With PVDF as the fluid of 150°C (302°F) and are available in heating elements are used to weld contact layer on the inside and an various forms: solid piping, lined metal the joint together, thereby minimizing engineering polymer material on the piping and fiberglass-reinforced dual human error in fabrication. outside, the cost of the multilayer laminate piping. Unlike metals, PVDF While PVDF piping systems are construction may be more econom- is non-rusting and lightweight, mak- used in areas where high mechani- ical for some applications. ing installation easier. cal rigidity is crucial, flexible tub- Injection molded components. PVDF piping systems can be ing options are also available that Piping systems and flexible tubing joined by various welding tech- take advantage of PVDF copolymer are usually created via profile extru- niques. Socket fusion is a recom- technology (Figure 7). With flexural sion but injection molding is another mended method in the CPI, as the moduli down to 10,000 psi, tubing method to create components in strong weld creates a lap joint that is important in applications like bev- specialized shapes and dimensions. can resist harsh chemistries, such erage and fuel lines that can be uti- From pumps, nozzles, and valves, as hydrochloric, sulfuric, and nitric lized in many market segments. The PVDF components can be mass in- acids. Butt fusion, one of the easiest beverage industry appreciates mini- jection molded (Figure 8). Recently, types of joining methods, is a choice mal cross-contamination of taste, PVDF components are being molded in areas where the chemistries are making PVDF tubing a long-lasting for conveyor belting for food-pro- more benign. Beadless and smooth choice. Several PVDF copolymers cessing facilities. inner bore systems leave no weld- are FDA compliant per Title 21 CFR Traditional materials used in plas- ing bump, which make them ideal 177.2600 and are listed to NSF 51 tic modular belting have faced scru- methods for the pharmaceutical for food contact. For fuel applica- tiny recently due to plastic bits con- and semiconductor industries. Both tions, the barrier properties of PVDF taminating food [9]. With PVDF, the of these industries need a smooth are used for low permeation of hy- higher mechanical and abrasion surface to minimize bacterial hang- drocarbons in flexible fuel pipes, resistance combined with outstand- ups and ensure the highest levels such as applications compliant with ing chemical resistance have proven of purity. Mechanically joined and UL 971 Nonmetallic Underground to be a longer-lasting solution. Both threaded systems are utilized for ap- Piping for Flammable Liquids. Fluid rigid and copolymer grades of PVDF plications where systems are taken handling systems with PVDF can apart to be cleaned. PVDF piping also be created in multilayer con- can withstand sterilization with satu- structions, where a tie layer is used rated steam at temperatures [6] up to 150°C depending on the joining method and design. Flexible tubing. Flame and smoke additives can be added to PVDF resins to meet the stringent standards of ASTM International E84 (UL723) 25/50 [7] and at least one formula- tion of PVDF holds a 0/5 ASTM E84 rating using no additives at all, and is compliant with U.S. Food and Drug Administration (FDA) and National FIGURE 9. Glass-reinforced PVDF resin can be FIGURE 10. PVDF rods can be machined into spe- Sanitation Foundation (NSF) stan- used for bolts cialized components TABLE 1. DEFLECTION TEMPERATURE OF FLUOROPOLYMERS* [3] TABLE 2. FLEXURAL PROPERTIES OF Material Melt point, °F Def. temp. at 66 psi,°F At 264 psi,°F PLASTICS* PTFE 620 250 132 Material Flex modulus, psi PFA 590 164 118 PVDF homopolymer 740 300,000 FEP 554 158 124 ECTFE 240,000 ETFE 518 220 165 PVDF copolymer 2850 170,000 ECTFE 464 240 170 ETFE 170,000 PVDF 352 298 235 PVDF copolymer 3120 110,000 PVDF copolymer 2800 100,000 * ASTM D648 FEP 85,000 can be molded into a variety of parts. shapes make PVDF components PFA 85,000 Unmodified PVDF resins have a available to original equipment PTFE 72,000 shrink rate of about 2–3% depend- manufacturers (OEMs) that need PVDF copolymer 2750 60,000 ing on part geometry and thickness. the material properties of PVDF PVDF copolymer 2500 35,000 PVDF copolymer Ultraflex 10,000 Engineers must take these values without having to invest in injection into account when designing molds molding equipment. *ASTM D790 at 73°F for part production. PVDF sheets are commonly used Recently, innovations in modify- in the tank industry. Tanks can be References ing PVDF resins have produced fabricated using a variety of tech- 1. Ebnesajjad, Sina, “Applied Plastics Engineering Hand- products that have reduced shrink niques from solid PVDF, to linings book,” , Chapter 4, Introduction to Fluoropolymers, pp. 49–60. www.fluoroconsultants.com/sitebuildercon- values. By adding a carbon filler to on metal or fiberglass-reinforced tent/sitebuilderfiles/introductiontofluoropolymers.pdf. the PVDF resin, shrink rates similar tanks. Facilities that have corrod- 2. Sherman, L. M., “Glass Reinforcement Opens New Doors to polypropylene or polyethylene are ing or rusting metal tanks may find for PVDF Fluoropolymers,” Plastics Technology. August obtained. Thus, PVDF can be sub- PVDF sheet linings a viable solution 26, 2016, www.ptonline.com/articles/glass-reinforcement-opens- new-doors-for-pvdf-fluoropolymer. stituted into those molds with mini- to retrofit in the existing structure. n 3. Hanselka, R., Williams, R., Bukay, M., Materials of mal process adjustments. Addition- Edited by Gerald Ondrey Construction for Water Systems Part 1: Physical and ally, glass-reinforced PVDF resins Authors Chemical Properties of Plastics,. Ultrapure Water, July August 1987, pp. 46–50. (Figure 9) strengthen PVDF to yield Averie Palovcak is an applica- a flexural modulus (ASTM D790) tions engineer for the Technical 4. www.agcce.com/brochurespdfs/technical/pe-guide- Polymers Division of Arkema Inc. english.pdf. over 1 million psi, similar to that of (900 First Avenue, King of Prussia, 5. Dennis, G., Advanced Industry Applications for PVDF PEEK (polyether ether ketone) for a PA 19406; Phone: 610-205- Based Resins, The IAPD Magazine, April/May 2002, fraction of the cost. This glass-re- 7026: Email: averie.palovcak@ pp. 29–31. arkema.com). She graduated with inforced PVDF resin has a very low a B.S. and M.S. in biomedical en- 6. Gruen, H., Burkhart, M., O’Brien, G. Steam Sterilization gineering from Drexel University. of PVDF Piping Systems in PW and WFI for the Phar- shrink rate of less than 1%. maceutical and Biotechnology Applications, Ultrapure Stock shapes. Rods and sheets Water, October 2001. are produced with PVDF resins for Jason Pomante is the North Ameri- 7. Barbone, R., Morris, S., Seiler, D., Pipe Testing Methods making stock shapes (Figure 10). can market manager in the Techni- Put to the Test, Plumbing Systems & Design, Septem- cal Polymers Division of Arkema ber/October 2005. These components can be utilized (same address as above; Email: 8. Underwriters Laboratories, “Report on Molded Plastic by component fabricators to cre- [email protected]), and has worked for Arkema for over 15 Under the Classification Program,” Project Number ate specialized parts. Rods and years. He graduated from Lafayette 12CA32465, August 7, 2012. sheets can be cut, formed and ma- College in 2002 with a B.S.Ch.E., 9. Lyndell, C., “Koch Recalls Beef Contaminated with Plas- chined into components that have and holds an M.B.A. from Saint Jo- tic,. Food Engineering, April 13, 2018, www.fooden- seph’s University in 2010. gineeringmag.com/articles/97473-koch-recalls-beef- tight tolerances. Additionally, stock contaminated-with- plastic.

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