What is PVDF (Polyvinylidene Fluoride)?
PVDF or Polyvinylidene Fluoride is a semi-crystalline structured highly inert, tough, and stable thermoplastic fluoropolymer. It has a melting point of 175°C and service temperatures upto 150°C. It boasts overall great properties like fantastic chemical resistance, high crystallinity, and good thermal stability, to name a few.
Today it is sold under various brand names with added additives and melt flow rates to increase the processing capabilities and heighten properties for specific applications.
How is PVDF Made?
PVDF resin is produced by free-radical polymerization of 1,1-difluoroethylene (CH2=CF2). The polymerization occurs in the emulsion of the 10-150°C and 10-300 atm pressure. The obtained material is then processed into films, rods, tubes, and sheets.
The most common methods to produce PVDF polymer are – Chlorotrifluoroethylene (CTFE) or hexafluoropropene (HFP).
HFP made PVDF copolymer shows higher flexibility compared to PVDF homopolymer grades.
Comoolymes made by CTFE are even superior to polymers made by HFP. They are more flexible, have low shrinkage, and have a fantastic low-temperature performance range.
Furthermore, Polyvinylidene Fluoride is exposed to ionizing radiation using crosslinking, making various modifications to the thermal and mechanical properties possible. Additionally, different resins like acrylics and methacrylic and acrylic rubbers have partial compatibility with the polymer.
Properties of PVDF Material –
Let’s discuss the basic properties of PVDF polymer in detail:
Source: Royal Society of Chemistry
|Tensile Strength @23°C||50||
Mpa – ASTM – D638
W/m.k – ASTM C177
|Impact Strength||No Break||–|
|Melting Point||338-347||deg F|
|Dielectric Strength||20-25@ 1mm thick||
kV.mm – ASTM D149
|Elongation at Break @23°C||0.4||ASTM-D1894|
|Continues working temperature||150||°C|
|Coefficient of friction||0.4||ASTM-D1894|
|Limiting Oxygen Index||44||%|
1. Crystal Structure of PVDF:
As I mentioned earlier, it has a semi-crystalline polymer that is 50% amorphous. The structure is formed so that most of the VDF units are linked together from head-to-tail, and a very tiny number of units are linked head to head.
The fluoropolymer exists in four conformations – α, β, γ, and δ shape.
The C-F bonds are opposite to each other, and an alignment is created to obtain the highest dipole movement in the same direction. Taking about the β phase, it is the prudent phase to its piezoelectric characteristics of the resin.
The opposite direction of the dipole movement to crystallites results in zero net polarization.
PVDF has a good tensile modulus but fairs weak in the impact strength department. Rearrangements done using HFP and CTFE can help improve the flexibility and impact strength and decrease the tensile modulus.
PVDF is non-flammable and wouldn’t drip. It is self-extinguishing and has decent resistance to UV light.
The polymer has one of the highest heat deflection temperature under load(148°C @0.5Mpa) among commercial fluoropolymers and the lowest melting point(178°C).
Thanks to high crystallinity and high surface tension properties, PVDF polymers have meager imbuing values than other fluoroplastics. Same imbuing effects can be seen with gases and liquids as well. Having said that, the imbuing capability is completely dependent on the crystalline modification of parts.
4. Chemical Resistance:
All the fluoropolymers (including PVDF) contain varying chemical inoperativeness to a wide array of chemicals. The polymer is blended with organic solvents like animes and esters at high temperatures, making them capable enough to be applied as corrosion resistance glazing of chemical processing equipment.
PVDF partially exhibits excellent resistance to organic acids, aliphatic and aromatic hydrocarbons, and alcohols and halogenated solvents. However, it can also be readily attacked by strong bases and ketones.
5. Electrical Properties:
PVDF material possesses high dielectric strength and dissolution factor. However, it also suffers from poor electrical properties, which helps the polymer be easily utilized in films with piezoelectric behavior.
These films are extracted from B-phase conformation. Both the films’ surfaces will be glittered and put through high voltage, leaving them permanently polarized.
These films produce current when stretched or compressed at their melting point temperature.
Disadvantages of Polyvinylidene Fluoride –
We have gone through the sweeter part of the popular fluoropolymer, but let’s dive into a few limitations or drawbacks one might face using PVDF plastic or resin.
- Processing machinery need to be clean and tidy for optimum results
- Poor resistance to fuming acids
- High dissipation factor
- Decomposition by boron makes it difficult for the polymer to reinforce with glass fibers.
How to Process PVDF?
PVDF material is available in a wide variety of grades and forms like powders and pallets. It can be easily processed by traditional processing methods like Injection molding, extrusion, compression, and transfer molding.
Drying isn’t important but might be required in some operations.
The constant processing temperature – 190 to 280°C
Let’s see a comparison between injection molding and extrusion process attributes.
|Melt Temprature – 200°C to 270°C||
Attention must be given to removing dead spots, or it can lead to the creation of degradation.
|Advisable mold temprature is 50°C to 90°C||
Reemmded extrduion temprature – 230°C to 290°C
|PVDF’s higher melt viscosity becomes an important factor to keep the mold design accurate||
extrusion of PVDF doesn’t require additional aids, lubricants, and heat stabilizers
|Shrinkage – 3 to 4%||
Rececemneod L/D ration – 20
|Applications – Valves, filter plates, pipelines, coil bodies, fittings, etc.||
Applications – Pipes, tubes, heat shrinkable tubings, etc.
PVDF Applications –
- It has various electrical and electronics industry applications, ranging from wires and cables in aircraft, high-temperature wirings, home appliances, and industrial power control systems.
- Good corrosion properties by taking the help of some additives can improve its applicability to heavy industries like oil & gas, automotive, marine, and petrochemicals for gaskets, seals, linings, etc.
- It is lately utilized heavily in filtration equipment like housings, filters, membranes, etc.
- Polyvinylidene Fluoride is also used for making separators in lithium-ion batteries thanks to reliable thermal and chemical stability. These membranes are in demand as the market for electric mobility will see sizable growth in the future.
- Chemical processing equipment depends on PVDF resin to make flexible tubing and liners to be used in water systems, pipes of chemicals, automobile fuel lines, and storage.
- Piezoelectric films are very sensitive transducers. They are malleable, rigid, and lightweight; thus can be shaped into various geometries resulting in unique and innovative applications.
- It is also used for coating and layering applications on metals like aluminum and galvanized steel to improve their chemical resistance and weatherability.
The Future of PVDF –
PVDF Market, Volume(%), By Application, Global 2019
Source: Mordor Intelligence
According to a study conducted by MarketWatch, the global Polyvinylidene Fluoride was valued at USD 535.4 million in 2019 and is pegged to reach a value of USD 1567.5 million by the end of 2026, showing a CAGR of 16.4%, which is very impressive.
Sure the numbers have changed drastically because of the Covid-19 pandemic and saying anything about the short-term growth outlook for PVDF is very difficult. However, on the bright side, when writing this post, a vaccine has been created, people have started to come out and go to work, and the world is steadily opening up.
The Asia-pacific region is the largest producer of Polyvinylidene Fluoride( thanks to china) and will keep the leading position in the near future too (again, thanks to china :))
As the above chart shows, pipes & fittings, li-ion batteries, and semiconductor processing takes a major chunk of the market and is expected to grow even further in the future due to growth in the electronics and electrical mobility sectors.
Final Thoughts –
Thus, my thoughts were on PVDF plastic and resin. I believe it’s a very versatile and useful fluoropolymer. Kindly share your reviews in the comment box and let me know I have missed something.
Thank You very much:)