Polyvinylidene fluoride (PVDF) is a white powder crystalline polymer with a crystallinity of about 68%, high mechanical properties, stronger than PTFE, excellent wear resistance, excellent compression resistance, and creep resistance. The PVDF film is flex resistant and its flexural life is as high as 75×103Â times.
The melting temperature of PVDF is 165 °C ~ 185 °C, the glass transition temperature is -35 °C, the long-term continuous use temperature range is -70 °C ~ 150 °C, and the initial thermal decomposition temperature is above 316 °C. Melting temperature is affected by polymerization temperature and molecular structure. Generally speaking, the lower the polymerization temperature, the higher the melting temperature; the more head-to-head or tail-to-tail structures in the connection structure, the lower the melting temperature.
PVDF has greater polarity, high dielectric constant, and large dielectric loss factor. Electrical properties are very sensitive to the effects of crystal structure and crystallinity. The volume resistivity is 2×104 Ω·cm, and the dielectric strength is also low. The water absorption is extremely low, so the electrical performance does not decrease significantly in high humidity and water-immersed environments.
PVDF is less resistant to chemicals than pTFE and pCTFE, and has good resistance to inorganic acids and bases, but poor resistance to organic acids and organic solvents. From room temperature to 10 °C, it can be dissolved or swelled by methyl sulfoxide, acetone, butanone, pentanone, cyclohexanone, acetic acid, methyl acetate, methyl acrylate, diethyl carbonate, dimethylformamide, hexamethylphosphoryltriamine, ethylene oxide, tetrahydrofuran, dioxane, etc.
The radiation resistance of PVDF is better than PTFE. After UV irradiation with wavelength 200~400 nm for one year, the mechanical properties were basically unchanged, but the mechanical properties were improved due to the cross-linking between PVDF molecules after irradiation with y-rays with a radiation dose below 10 Gy.
Since the difference between the melting temperature and decomposition temperature of PVDF is more than 130 °C, it has good hot workability. Usually the melt viscosity at 220 °C ~ 270 °C can meet the requirements of injection and extrusion molding. It can also be formed by molding, coating, and other methods. During processing, the screw and barrel should be made of special heat-resistant and corrosion-resistant alloy, and the molding mold should be made of chromium-plated hard steel or high-nickel stainless steel. Tape casting is mainly used to make thin films. Use dimethylacetamide to prepare a PVDF dispersion with a solid content of 20% or 45%, cast it on aluminum foil, heat-melt it at 204 °C ~ 316 °C, and quickly cool it with water to produce a strong and tough film. Films can also be prepared by spray molding.
PVDF is widely used to make piezoelectric and thermoelectric sensitive components with excellent performance, such as headset receivers and tweeters.
PVDF piezoelectric materials are used in ultrasonic detectors, auscultation sensors, blood pressure measurement sensors, and piezoelectric fuzes for military use. It can also be used for wire and cable coatings, wiring boards, heat shrink tubes, and printed circuit boards, etc. In the chemical industry, it is commonly used in pipeline anti-corrosion linings, sealing gaskets, corrosion-resistant gears, bearings and water-based coatings. In construction, PVDF can be used as a decorative and protective coating or film for indoor and outdoor buildings.
