July 2, 2020
By: Gerry DiBattista, Vice President of Marketing – Porex Virtek PTFE
After one of our most popular webinars in The Science Inside series – How to Minimize UV Disinfection Efficiency Using Microporous PTFE recorded on June 3 and re-broadcast on June 30 in Asia Pacific – I decided to pull together the most frequently asked questions and share them more broadly. Over the past few months, I’ve enjoyed engaging with many people over social media, our website and our webinars to discuss how microporous PTFE can dramatically increase the performance of your UV disinfection chambers. I’ve grouped the questions we have received into some basic categories to make it easier to find your answers:
It really varies – your best current resource is this study: Fluence (UV Dose) Required to Achieve Incremental Log Inactivation of Bacteria, Protozoa, Viruses and Algae
Ozone that is generated comes from the secondary UVC peak of low-pressure mercury lamps (185 nm), however the amount of ozone produced by this wavelength is insufficient to disinfect compared to the primary UVC at 254 nm which is squarely in the germicidal zone. The ozone is considered more a pollution risk versus being helpful and can be minimized by using fused silica.
We have seen very little material degradation when exposed to high-energy UV between 220+ nm. We are performing some longevity testing but fully expect it to withstand several thousands of cycles.
That will be completely up to the specific design of the equipment used for the disinfection process.
UVA is ineffective in disinfection and any energy used in its generation will be mainly wasted. Porex Virtek PTFE is not affected by UVA light.
Here you would want to choose a material with decent reflection vs. absorption and something that will structurally function. A thin wire aluminum rack would likely be the preferred material vs any type steel or plastic which are highly absorptive.
If it is just the surface you are trying to disinfect, then the UV coating will not hurt this. If you are trying to disinfect the contents then the coating will need to be removed, and the jar will need to be made from a UVC transparent material. For example, TOPAS COC is UV transparent.
The only way to get uniform energy distribution is with a perfect sphere with 100% Lambertian distribution material (create an integrating sphere). Since the distribution follows the cosign rule, corners and other sharp edges can trap energy. Any rounding of corners and abrupt changes in geometry will improve results.
Yes – Porex Virtek PTFE is a very efficient UVC reflector in the disinfection of water.
Typically, UVC does not transmit through glass or polycarbonate and is mainly absorbed by the materials. Polycarbonate specifically will be damaged by almost all UV energy if not properly treated.
All materials will face some losses when energy strikes the surface and is redirected. In the case of Porex Virtek PTFE, of the total reflectivity stated, just under 2% is absorbed and the rest is transmitted (transmission is higher for thin materials).
No – Not a significant amount. If properly designed however, you can actually vent through the microporous Porex Virtek PTFE.
Dosimeters are tuned for specific wavelengths. The ones that are available today are tuned to respond to the standard low-pressure mercury UV lamps which emit at 254 nm. Although the current products will respond to wavelengths above and below this value, they will in general take longer to change color. You can find more info here.
The dosimeters are calibrated in mJ/cm2 – so all you need to do is look at the color change to get an approximate dosage. They come in 100 and 1000 mJ variations.
Yes – an integrating sphere is used to measure the reflectance. Integrating spheres are normally lined with a PTFE-containing liner due to its excellent reflectivity and very low energy absorption properties. Virtek is 100% PTFE and almost 100% Lambertian reflection (highly diffuse).
PTFE is extremely chemical resistant. In fact, it is one of the most chemical resistant materials available. We are still working on specific cleaning procedures depending on the application. You should avoid wet cleaning the PTFE surface too frequently (it is best to draw off any dust / dirt with a vacuum), but using mild soaps with a clean cloth followed by a wet wipe with another clean cloth should remove most contamination. You can also use cleaning alcohols followed by a dry wipe.
Currently, the master rolls are 330 mm (about 13”) wide, and the length will depend on the thickness of the material. The product can also be cut into sheets, die-cut into specific part geometries, or rolled into tube form.
Porex Virtek PTFE is not recommended for wavelengths below 210 nm.
Porex Virtek PTFE is extremely hydrophobic, and we do not expect any biofilm formation while exposed to UVC energy.
This will depend on the thickness of the material. PTFE is naturally very low energy absorbing between 200-2000 nm and almost all of the energy is either reflected or transmitted. At around 1.2 mm, the increase in reflectivity vs. transmission is nominal. However, in thicknesses below 1.2 mm, you will get some light transmission. Please refer to this reflectivity chart. The difference between the selected Porex Virtek PTFE material (e.g PMR05) and PMR20 will be transmitted energy.
Porex Virtek PTFE begins to absorb UV energy at between 200-210 nm. This absorbed energy will begin to break down the material, so we therefore do not recommend it being used below 210 nm.
Please reference the chart on the Porev Virtek PTFE Reflectivity section. Yes, thickness up to 1.2 mm will have some effect on reflectivity.
We are still doing some life testing, but we expect very little degradation over time in the 250-280 nm range.
Porex Virtek PTFE film comes in a variety of pore size/pore volume configurations. For the reflective media, typical pore volume runs between 30-40% and the pore sizes will vary from sub-micron to several microns in diameter.
The best way to adhere Porex Virtek PTFE to a surface is using a double-sided adhesive tape (like 3M 93020LE). Other methods such as gel adhesives or epoxies can also be used. Since Porex Virtek PTFE does not melt in the traditional sense, this method is not recommended.
Porex Virtek PTFE comes in a sheet format, so it can be cut to the proper width and length, and then wrapped around a glass time and the joint taped together.
We can do quite a bit with die cutting and a 3x3mm with a center hole is indeed possible. Please contact us for more information.
Porex Virtek PTFE is used in numerous markets and applications outside of high reflectivity. You can find these by typing “Virtek” into the search bar on this website. All of the high reflectivity materials can also be found on the Reflectivity page