Design Properties for Special Applications

Electrical Properties

The electrical properties of KYNAR PVDF grades 460 and 710-760 are shown in Table III. The combination of high dielectric strength and excellent mechanical properties over a broad temperature range is the reason that KYNAR resins are used for thin-wall primary insulation and as a jacket for industrial control wiring. Although its high dissipation factor limits the use of KYNAR resins at high frequencies, this property becomes an advantage in the fabrication of parts utilizing dielectric heating strengths.

Kynar electrical properties table.
III. Electrical properties for various grades of KYNAR Homopolymer resins at room temperature.

Dielectric Variations with Temperature and Time

Values reflect the method of sample preparation, which influences the characteristics of the polymer that dictate the electrical properties. Above 1 MHz, the dependence of these properties upon frequency, temperature, and nature of the sample is complex.

Optical Properties

KYNAR PVDF films up to 0.005 in (0.125 mm) thick are transparent to translucent. The transmission spectrum in Table IV shows how light transmission varies with thickness for KYNAR 460 resin. See Figure 5 for the infrared absorption spectrum.

Percentage transmission of extruded KYNAR PVDF film in the ultraviolet region as a function of thickness.
IV. Percentage transmission of extruded KYNAR PVDF film in the ultraviolet region (200-400 nm) as a function of thickness.

Infrared absorption spectrum of KYNAR PVDF film.
Figure 5. Infrared absorption spectrum of KYNAR PVDF film.

Stability to Effects of Weather and Ultraviolet Radiation

Table V shows that KYNAR PVDF Film maintains its mechanical properties throughout many years of outdoor exposure. Clear films, exposed to the sun at a 45° angle South, retain their tensile strengths over a 17-year period. During the first few months of exposure when normal crystallization takes place, the percent of elongation at break decreases to a level that remains essentially constant with time. In addition, the weathered films remain flexible and capable of being bent 180° without cracking.

Stress/strain properties of weathered Kynar film.
V. Stress/strain properties of 0.204 mm (0.008 in) weathered KYNAR PVDF film determined by ASTM method D882.

Outgassing Under High Vacuum

KYNAR homopolymer resins exhibit extremely low weight loss when exposed to high vacuum. At 100°C (212°F) and a pressure of 5x10 (to the power or 6) torr, the measured rate of weight loss is 13 x lO (to the power of 2) g/cm2.

Fungus Resistance

KYNAR resins will not support growth of fungi when tested as described in Method 508 of Military Standard 810B (June 15, 1967).

Solubility

KYNAR resins have limited solubility. Table VI lists active, intermediate, and latent solvents. Generally, KYNAR resins are not soluble in aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated solvents, alcohols, acids, halogens, and basic solutions.

Kynar Solvent properties.
VI. Kynar solvent properties.

Resistance to Nuclear Radiation

The resistance of KYNAR fluoropolymers to nuclear radiation is excellent. The original tensile strength of the resin is essentially unchanged after exposure to 1000 megarads (Mrads) of gamma radiation from a Cobalt-60 source at 50°C (122°F) and in high vacuum (10 to the power of 6 torr). The impact strength and elongation are slightly reduced due to cross-linking. This stability to effects of radiation, combined with chemical resistance, has resulted in the successful use of KYNAR PVDF components in plutonium reclamation plants. Tables VII and VIII show minimal changes in tensile properties of KYNAR homopolymer and KYNAR FLEX resins exposed to E-Beam radiation in doses up to 20 Mrads according to ASTM D882 testing.

Radiation Crosslinking

The different grades of KYNAR homopolymer resin are readily crosslinked and do not degrade when irradiated with moderate doses of high energy electron or gamma radiation. The efficiency of crosslinking is influenced by the grade, that is, molecular weight variations are important. Figure 6 shows the response of various grades to high energy electron beam irradiation in terms of the amount of polymer that becomes insoluble in dimethylacetamide (DMAC), an excellent solvent for non-crosslinked PVDF resins. Examples of KYNAR PVDF-fabricated products utilizing radiation technology are heat-shrinkable tubing and insulated wire capable of withstanding high temperatures.

KYNAR resistance to nuclear radiation.
Figure 6. Insoluble fraction of various grades of KYNAR Fluoropolymer and KYNAR FLEX Copolymer after electron beam irradiation.

KYNAR PVDF Tensile Modulus versus radiation dose exposure.
Radiation crosslinked K KYNAR PVDF Tensile Modulus versus radiation dose exposure (Kpsi).

KYNAR PVDF ultimate strength versus radiation dose exposure.
Radiation crosslinked KYNAR PVDF ultimate strength versus radiation dose exposure (psi).