Polyvinylidene fluoride tensile strength

Polyvinylidene fluoride 100 5.5 6 N/A 0.12 Tensile strength, flexural modulus, HDT, Elongation at break, expensive. "D D ... 

Fluoropolymers have outstanding chemical resistance, low coefficient of friction, low dielectric constant, high purity, and broad use temperatures. Most of these properties are enhanced with an increase in the fluorine content of the polymers. For example, polytetrafluoroethylene, which contains four fluorine atoms per repeat unit, has superior properties compared to polyvinylidene fluoride, which has two fluorine atoms for each repeat unit. Generally, these plastics are mechanically weaker than engineering polymers. Their relatively low values of tensile strength, deformation under load or creep, and wear rate require the use of fillers and special design strategies. 

For example, two such polymers had melt viscosities of 11,000 poise (sheath) and 39,000 poise (core) at 260°C and 100 sec. Sheath and core were extruded, respectively, in a 25 mm diameter extruder at 265°C and 35 mm diameter extruder at 275°C. A 1.5 mm diameter concentric die allowed coating of the core with the lower viscosity polyvinylidene fluoride. The filament exited the die in a 250°C air atmosphere followed by cooling in a water bath at 30°C. The fiber next entered a hot oil bath at 165°C where it was stretched at a draw ratio of 5.4. It was subsequently stretched in a second hot oil bath at a draw ratio of 1.22 at 170°C. The last step consisted of relaxation by 5% in hot air at 80°C. A transparent lustrous fiber with a diameter of 128 pm was obtained in which the sheath comprised of 20% by volume. The filament had a birefringence of 0.0395, a tensile strength of 911 MPa, and a break elongation of 20%. Knot strength was 832 MPa and a break elongation of 15%. 

Increasing the crystalline melting point and mean crystal length in the molecular chain direction was found to substantially increase the tensile strength of the fiber. Polyvinylidene fluoride resin had to have... 

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