Kynar Chemical Resistance and Purity Testing

Chemical Resistance of KYNAR Fluoropolymer

Many factors can affect the chemical resistance of materials. These include, but are not limited to, exposure time, concentration of chemical, extremes of temperature and pressure, frequency of temperature and pressure cycling or both, attrition due to abrasive particles, and the type of mechanical stress imposed. The fact that certain combinations of chemicals and mechanical load can induce stress cracking in many otherwise chemically resistant materials, both metallic and nonmetallic, is of particular significance. In general, the broader molecular weight distribution of KYNAR resins will result in greater resistance to stress cracking.

Such factors as permeability and adhesion affect the resistance of KYNAR PVDF coatings. Consequently, coatings may not exhibit exactly the same properties as melt-processed KYNAR resin. Maximum use temperature for dispersion-applied coatings should not exceed 100°C (212°F). However, assuming chemical resistance is still adequate, laminated systems can be used from 120° - 135°C (248° - 275°F).

Operating parameters are dependent upon the particular application of KYNAR resin and differ from those experienced in either laboratory testing or apparently similar field service. Because corrosive fluids or vapors are often mixtures of various individual chemicals, it is strongly recommended that trial installations be evaluated under actual service conditions.

For example, immersion testing of KYNAR resins in individual chemicals at a specific operating temperature, will not necessarily predict the performance of KYNAR PVDF-fabricated components when they are exposed to an exothermic reaction between the individual chemicals.

The chemical resistance of KYNAR fluoropolymer is indicated in the bull's-eye chart (See Figure 10). An alphabetic listing of chemicals with maximum usage temperature is available upon request from Elf Atochem's Technical Polymers Business Unit. In the chart, the behavior of KYNAR homopolymer resin at 93°C (200°F) in nine general chemical species is compared with that of other well known plastics. The rating system ranges from severe attack in the outer segment of the circle to inert in the bull's-eye.

Purity of KYNAR resins

Components formed from natural KYNAR resins and KYNAR FLEX resins do not produce particulate contaminants. Unpigmented KYNAR resins are 100% pure fluoropolymer and require no further additives in processing. KYNAR resins do not require stiffeners, stabilizers, or anti-oxidants, as do PVC, PE and PP. Nor do they call for the addition of external lubricants, such as calcium stearate, to the resin as a processing aid, as has been the case with some other PVDF resins.

Piping systems using natural KYNAR resins under dynamic flow conditions will not release particulates into the fluid stream. Table XII gives metallic ion extractible data generated from KYNAR FLEX pellets exposed to hot deionized water (DI) in a 24-hour static test.

Graphical representation of behavior of Kynar compared to other well known plastics.

Kynar DI Water Extraction Table.

Table XII : Method-ICP MASS Spectroscopy