PVDF (polyvinylidene fluoride), also known as PVDF2 and PVF2, is a member of the fluoropolymers family, a group of specialised, versatile polymeric materials with distinct properties resulting from a strong bond between their carbon atoms and fluorine atoms, as well as fluorine shielding of the carbon backbone. PVDF Material is a pyroelectric and piezoelectric speciality polymer that is used to make a variety of high-purity, high-strength, and high-chemical-resistance products for use in the electrical, electronic, biomedical, construction, fluid-systems, oil-and-gas, and food sectors.

What Do You Mean By PVDF?

PVDF is a thermoplastic semicrystalline polymer. Depending on the manner of production, the degree of crystallinity ranges from 35 to 70 per cent. It’s remarkable in that it has a unique combination of mechanical and electrical qualities (i.e., piezoelectricity), maintains high purity standards, and is resistant to a wide range of substances, including solvents, acids, and hydrocarbons.

PVDF falls in between polyethene (PE: (CH2=CH2)n and polytetrafluorethylene (PTFE: (CF2=CF2) in terms of chemical formula. It has the flexibility of PE and some of the stereochemical restrictions of PTFE due to its simple chemical structure. Depending on how the samples are prepared, the molecular and crystal structures of PVDF fluctuate.

PVDF Material has a unique crystalline polymorphism that is not present in any other synthetic polymer. PVDF comes in five different crystalline forms: alpha, beta, gamma, delta, and epsilon. The beta phase is the most prevalent, and it is joined by the alpha and gamma phases to form the major phases:

• The nonpolar alpha phase is formed during the melting process when the melt crystallises at any temperature.
• The beta phase is an orientated phase that occurs when a specimen is mechanically deformed below 70 °C via uniaxial or biaxial mechanical drawing. It is the most often used piezoelectric material.
• The gamma phase is a unique form that appears under certain conditions. Melt casting or solution casting can be used to produce it at temperatures close to the melting point of the alpha phase.

Properties of PVDF

Crystal Structure

It’s usually a semi-crystalline polymer with about 50% amorphous content. It has a fairly regular structure, with the majority of VDF units connected head-to-tail and relatively few monomer units joined head-to-head. This fluoroplastic is available in four different conformations and phases.

• The C–F bonds are polar, and the maximum dipole moment is generated by aligning all of the polymer’s dipoles in the same direction, which corresponds to the PVDF’s -phase. Due to the polymer’s piezoelectric properties, the -phase is the preferred phase.
• Crystallite dipole moments are orientated in opposite directions, giving in a net polarization of zero.

Physical Properties

Although it has one of the lowest melting points among commercial fluorothermoplastics, it has the highest heat deflection temperature under load. PVDF Material has a low penetration value compared to other fluoropolymers due to its strong crystallinity and surface tension. When it comes to gases and liquids, PVDF has poor permeability. The crystalline degree and the alteration of crystalline components, however, have an impact on PVDF permeability.

Mechanical Properties

PVDF has a similar tensile modulus to ETFE and ECTFE but a lower impact strength. The modulus is reduced when HFP or CTFE is added, but the elongation and impact strength is increased. PVDF is non-flammable and does not drop when exposed to flame. It is TL V0 compatible and self-extinguishing. The LOI stands at 44%. It also has a high UV light resistance.

Chemical Resistance

Chemical inertness differs between fluoropolymers like PTFE, FEP, PFA, and MFA and partially fluorinated polymers like CTFE (or PCTFE) and ECTFE. Fluoropolymers like PTFE, FEP, PFA, and MFA are chemically inert to a wider spectrum of chemicals than partially fluorinated polymers like CTFE (or PCTFE). PVDF Material may be dissolved in organic solvents like esters and amines at high temperatures, allowing it to be used as corrosion-resistant coatings on chemical process equipment and architectural panels. Mineral and organic acids, aliphatic and aromatic hydrocarbons, alcohols, and halogenated solvents are all resistant to PVDF parts.

Electrical and Piezoelectric Properties of PVDF

Piezoelectric and electrical PVDF’s properties Due to its high dielectric constant and dissipation factor, PVDF is largely employed in wire and cable isolation. However, due to their weak electrical characteristics, PVDF films with piezoelectric and pyroelectric activity can be made. Extruded films in B-phase conformation are used to make the films. The film is metallized on both sides and then exposed to a high voltage, leaving it permanently polarised. When stretched or compressed (piezoelectricity) or heated (pyroelectricity) to temperatures near the melting point, such films generate a voltage. Ferroelectricity can also be seen in polymer films.

What is PVDF Membrane?

PVDF is one of the most widely utilised membrane materials, and its exceptional features have attracted a lot of attention. PVDF is suited for use in biomedical membrane applications and wastewater treatment because of its thermal stability, chemical resilience, and processability to create membranes. PVDF Membrane is widely used in the treatment of wastewater. PVDF Material membranes are currently used in the following applications because of these characteristics:

• Pressure-driven wastewater and water treatment (e.g., microfiltration, ultrafiltration and membrane bioreactor)
• Membrane contactors are used in a variety of applications (e.g., membrane distillation, acid gas absorption and stripping, volatile organic compounds removal)

Because of its ease and ability to scale up manufacturing, phase inversion is now used to make the majority of commercial membranes. However, there are several disadvantages to PVDF membranes, such as wetting and fouling, which can be readily overcome by increasing surface roughness or increasing the membrane’s hydrophilic nature. Even with modification, it cannot be completely avoided. PVDF membranes, which have strong chemical and thermal stability, can be utilised as separators in lithium-ion batteries. The mechanical strength, pore size, and shutdown characteristics of these membranes are all excellent. Ion-exchange membranes are also made from these materials.

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