Polyvinylidene Fluoride (PVDF) is a semi-crystalline thermoplastic fluoropolymer produced by the polymerization of vinylidene difluoride. PVDF exhibits excellent resistance to corrosion, abrasion, and chemical attack along with inherent properties such as lightweight, weatherability and toughness. These qualities have enabled PVDF to find widespread usage in a variety of applications from coatings to advanced filtration membranes.
Physical and Chemical Properties
PVDF is a white resilient solid with a density of about 1.78 g/cm3. It displays outstanding chemical resistance towards corrosion from bases, acids and oxidizing agents. PVDF has excellent resistance to ultraviolet and weathering degradation as well. The polymer does not melt but softens gradually above 150°C and can be readily processed by methods like melt pressing or melt molding. PVDF has a monomer unit composed of one carbon and two fluorine atoms in a –CH2-CF2- repeating structure which gives rise to its strong CF bonds. This makes PVDF very stable chemically and thermally stable up to 130°C. The polar CF2 groups and non-polar CH2 groups in its backbone allow PVDF to be semi-crystalline in nature with a melting temperature range of 150-180°C depending on crystallinity.
Mechanical Properties
The semi-crystalline nature of Polyvinylidene Fluoride endows it with good mechanical properties in terms of strength and modulus. PVDF has a tensile strength in the range of 30-80 MPa and tensile modulus between 2.3-4.1 GPa. It exhibits excellent abrasion and impact resistance as well as flex endurance. Interestingly, the mechanical behavior of PVDF can be enhanced significantly through orientation processes like melt drawing and melt spinning. This helps achieve high strength PVDF fibers and films with tensile strength exceeding 500 MPa and modulus exceeding 10 GPa. The mechanical robustness of PVDF coupled with its outstanding chemical resistance make it suitable for applications requiring durable materials that can withstand corrosive environments.
Synthesis and Production
PVDF is commercially produced via free radical polymerization of vinylidene fluoride (VDF) monomer. The polymerization reaction requires an initiator like azobisisobutyronitrile (AIBN) to generate free radicals. The initiator decomposes at elevated temperatures to form reactive radicals that initiate the unsaturated VDF monomer. The vinylidene fluoride units then polymerize head-to-tail via the chain growth mechanism till termination occurs. Careful control over parameters like temperature, reaction time and solvent medium help regulate molecular weight and obtain high molecular weight PVDF resins. Commercially, PVDF is manufactured either as a suspension or emulsion polymerization process. Global PVDF production capacity stands at over 300 kilo tonnes annually with Arkema, Kureha and Solvay being some of the major producers.
Applications
The unique combination of properties exhibited by PVDF have enabled it to find relevance in a wide range of industrial applications. Some major application areas of PVDF include:
Coatings: PVDF forms durable weather and corrosion resistant coatings ideal for buildings, infrastructure, pipelines and electrical components. PVDF coatings offer over 25 years of protection.
Membranes: PVDF is used extensively for ultrafiltration, microfiltration and nanofiltration membranes used in water treatment, food & dairy processing due to its mechanical strength and chemical stability.
Wire and Cable: Insulation and jacketing materials for low and high voltage wire and cable benefitting from PVDF's ruggedness and dielectric performance.
Piping: Corrosion resistant pipes, valves and fittings for transport of harsh chemicals in industries like oil & gas, petrochemicals and semiconductor manufacturing.
Automotive: Seals, gaskets, diaphragms and hoses leveraging PVDF's heat and chemical resistance for applications in fluid transfer, pollution control devices like catalytic converters.
Battery Separators: Microporous PVDF battery separators used in lithium-ion batteries provide durability while maintaining high ionic conductivity.
PVDF has emerged as an engineering fluoropolymer of global significance owing to the unique balance of properties it offers. Advantages like high corrosion resistance, thermal stability, toughness and weatherability have made PVDF indispensable across industries as diverse as water treatment, construction, oil & gas, automotive, electronics and energy storage. Continuous innovation and expansion in application areas are further strengthening the commercial importance of PVDF. With its inherent qualities and growing end use, PVDF is poised for sustained growth in the coming decades.
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