Chemical properties of FEP are similar to those of PTFE and PFA.
PFA Properties
PFA polymers are fully fluorinated and melt-processible. They have chemical resistance and thermal stability comparable to PTFE. Specific gravity of perfluoroalkoxy resins is in the range of 2.12e2.17. PFA has an upperm continuous use temperature of 260 C.
Crystallinity and specific gravity of PFA parts decrease when the cooling rate of the molten polymer is increased. The lowest crystallinity obtained by quenching molten PFA in ice was 48% (specific gravity 2.123).
Similar to PTFE, molecular weight of PFA cannot be measured by conventional techniques. An indirect factor called melt flow rate (MFR) also called melt flow index (MFI) is used which is the amount of polymer melt that would flow through a capillary rheometer at a given temperature under a defined load (usually in grams in 10 minutes). MFR is inversely proportional to viscosity; viscosity is directly proportional to molecular weight of the polymer.
PFA exhibits one first-order transition at 5 C in contrast to two temperatures for PTFE at 19 and 30 C. It has three second-order transitions at 100, 30 and 90 C.
PFA has excellent electrical properties such as high insulation resistance, low dielectric constant (2.1), and low dissipation factor. Dielectric constant and dissipation factor remain virtually unchanged in the range of 40 to 250 C and 102 Hz to 2.4 1010 Hz. Dielectric breakdown strength (short term) is 80 kV/mm for a 0.25-mm-thick film.
Chemical properties of PFA are similar to those of PTFE.PFA is attacked by radiation, and degradation in air begins at a somewhat higher dose than that of PTFE which starts to degrade at 0.02 Mrad.
FEP Properties
Fluorinated ethylene-propylene copolymers are fully fluorinated and melt-processible. They have excellent chemical resistance and thermal stability. Specific gravity of FEP resins is in the range of 2.13e2.15. FEP has an upper continuous use temperature of 200 C.
Similar to PTFE, molecular weight of FEP cannot be measured by conventional techniques. Like PFA, MFR is used to characterize molecular weight of FEP. MFR and the molecular weight are inversely related.
Molecular weight distribution is determined by measuring the dynamic module of the polymer melt using rheological analyses. Crystallinity of virgin (unmelted) FEP is 65e75%.
FEP exhibits a single first-order transition that is its melting point. Relaxation temperature of FEP increases with HFP content of the copolymer. FEP has a dielectric transition at 150 C which is unaffected by the monomer composition or crystallinity (specific gravity).
Chemical properties of FEP are similar to those of PTFE and PFA.
FEP is attacked by radiation, and its degradation in air begins at a dose of 0.2 Mrad (10 times higher than that of PTFE).
Post time: Mar-04-2018