Polymer processing fluoropolymers

Table 8.47 shows the available options for the analysis of polymer processing aids, namely combustion and instrumental methods. The best method is dependent on PPA type, the level to be measured, and the available equipment (see also Section 8.2.1.2). Fluoropolymer processing aid concentrations can be determined by WDXRF configured to measure either fluorine or a tracer, and by EDXRF to analyse a tracer [29]. Calibration curves are required. At present, EDXRF or benchtop XRF units cannot directly measure fluorine. For resin or masterbatch producers who prefer to make on-line XRF measurements of processing aid concentrations (to letdown levels of 50-100 ppm), processing aids that contain a tracer (usually BaS04) are available. The analysis time is less than two minutes. 

The direct fluorination of inorganic,1,2 organometallic,3 5 and organic compounds,6-8 employing the LaMar9,10 and Exfluor-Lagow" methods, has impacted the synthesis of fluorinated compounds over the past 25 years. Among the most important applications of direct fluorination are the synthesis of fluoropolymers from hydrocarbon polymers and the conversion of the surface of the hydrocarbon polymers to fluoropolymer surfaces.12,13 The direct fluorination process is an excellent approach to the synthesis of fluoropolymers. 

Industrially, SCCO2 has been used extensively in polymer processing and synthesis. During the last 10 years, DuPont built a plant that can produce 1000 tonnes of Teflon and other fluoropolymers per year. The polymers produced in this plant are claimed to have superior performance and processing capabilities. Carbon dioxide is seen as the most viable industrial solvent for fluoropolymer synthesis, as hydrocarbon solvents can cause detrimental side... 

Polymers engineering polymers, elastomers, fluoropolymers, ethylene polymers, finishes, and performance films serving industries such as packaging, construction, chemical processing, electrical, paper, textiles, and automotive... 

All three commercial amorphous fluoropolymers. Teflon AF, Hyflon AD, and Cytop posses a unique set of properties. All dissolve in fluorinated solvents and thus may be spin coated to produce thin hlms and coatings. The polymers may also be extruded and molded using traditional polymer processing techniques. Note that the polymers are not soluble in hydrocarbon solvents or water and retain the chemical and thermal stability of perfluorinated polymers such as Teflon . These polymers have lower density than the well-known semicrystalline perfluorinated polymers such as pTFE that results in lower refractive index, lower thermal conductivity, higher gas permeability, and lower dielectric constant. The polymers are transparent and have excellent mechanical properties below their Tg due to their amorphous character. The presence of a heterocyclic ring in the polymer backbone of these materials is key... 

Of particular relevance to this chapter is the use of CO2 in polymer synthesis, in the manufacture of polymethylmethacrylate and polystyrene (Xerox) and for the production of fluoropolymers (DuPont). One of the main drivers for the latter was the phasing out of the chlorofluorocarbons (CFCs) used in the original process. The main advantage to this application is not necessarily the avoidance of the use of CFCs (although this is important), but the superior polymer processing properties made possible by the relative volatility of CO2 and its ease of removal. 

PVDFs cost, about the lowest of the melt-processible fluoropolymers, is an important advantage. Essentially all the common procedures available for thermoplastic polymers can be used with PVDF. Pennwalt Corp. is the leading producer and markets a full line of PVDF resins under the trade name of Kynar. 

The latest Viton FreeFlow additives are among those that have a reduced tendency to interact with other constituents of the formulation. Another new non-reactive fluoropolymer additive has been developed by Dyneon in association with 3M Canada to overcome similar problems, and has been found to perform well in LDPE and LLDPE film. The later versions of Dyneon polymer processing aids act as effective process aids in polyamides and PU, without the usual discoloration and processing problems. 

Dyneon acquired Solvay Fluoropolymers in 2001, including a PVDF manufacturing facility. In November 2004 it entered into an agreement with SpecialChem SA to moimt a web-based technical service facility for polymer process aids. The company employs more than 800 people worldwide. 

Several polymer processing aids (PPA) are available to eliminate or reduce melt fracture. An effective method to eliminate melt fracture in high molecular weight polyolefins is to add a small amount of fluoroelastomer [153], about 500 to 1000 ppm (parts per million). When a fluoroelastomer PPA is added to a polyolefin it usually takes a certain amount of time for a critical coating of fluoropolymer to form on the die. This conditioning time can vary from 5 minutes to more than 1 hour [154]. 

Electrospinning is a remarkably simple method for producing nanofibers of a wide range of polymers, including fluoropolymers [37]. In a typical electrospinning process, nanofibers are generated by the electrostatic force and sol-gel reaction. The nanofiber can be deposited on a substrate to form a nonwoven membrane. Electro-spun nonwoven membranes have several unique properties, such as adjustable pore... 

Fluoropolymers of the kind used as polymer processing additives (PPAs) are quite impervious to chemical attack and thermal degradation. They are of low surface energy, and are generally incompatible with other pol)nners. 

The brief description of the commercially important fluoropolymers indicates the techniques by which they can be fabricated. Generally, the processing method is dependent on the rheology of the fiuoropoly-mer in question. Table 3.6 summarizes the structure-rheology-fabrication technique characteristics of various copolymers. Melt viscosity values represent a wide range of shear rate for melt processible polymers in Table 3.6. Volume One focuses on fluoropolymers which are processed by non-melt methods.The present volume is devoted to the melt processible fluoropolymers. 

The present chapter covers information published by resin manufacturers about the commercially available grades of melt processible fluoropolymers. The first two polymers are perfiuorinated resins, followed by partially fluorinated polymers ethylene-tetrafiuoro-ethylene and ethylene chlorotrifiuoroethylene, andpoly-vinylidene fluoride and polyvinylfiuoride, and finally concluding with fluoroplastics polymerized in supercritical carbon dioxide. Commercially available resins have been classified by type, grade, and manufacturer. Properties of commercial grades have been presented in this chapter based on the literature published by the manufacturers. 

Multimodal fluoropolymers are superior in performance than unimodal fluoroplastics when used as polymer processing additive (6). 

M.P. Dillon, S.S. Woods, K.J. Fronek, C. Lavallee, S.E. Amos, K.D. Weilandt, H. Kaspar, B. Hirsch, K. Hintzer, and P.J. Scott, Polymer processing additive containing a multimodal fluoropolymer and melt processable thermoplastic polymer composition employing the same, US Patent 6 277 919, assigned to Dyneon LLC (Oakdale, MN), August 21,2001. 

Fluoropolymer polymer processing additives are required by pipe extmsion processes. They cause pressure reduction in extmder, decrease in torque and eneigy consumption, decrease in processing temperature, and increase of out-put. Pipes manufactured with processing additives have smooth wall finish (better esthetics and performance). 

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