Answering Your UV Reflectivity Media Questions

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:

UV disinfection

What is the difference in exposure time for a virus vs a bacterium?

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  

Can I use lamps for both ozone and UVC?

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. 

How many UV disinfection cycles can microporous PTFE be subjected to?

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.

What is the efficacy of using UVC on a passenger train car (or any specific object)?

That will be completely up to the specific design of the equipment used for the disinfection process.

Most LEDs available have a dual crystal that uses UVC and UVA wavelengths.  Will this be less effective for disinfection?

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.

Any recommendations for a material for the rack that has minimal UVC absorption? 

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 the object you want to disinfect has a UV-resistant coating, can it benefit from a UVC disinfection? Or would the coating need to be removed?

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.   

UV energy

Would you say that energy concentration is uniform within a reactor? 

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.

Is UV-C reflection inside water also highly efficient?

Yes – Porex Virtek PTFE is a very efficient UVC reflector in the disinfection of water.

Will UVC go through 4mm glass or polycarbonate?

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.

With regards to UVC energy, is the 2-3% of lost reflectivity converted into heat or is it transmitted through the material? 

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).

If you have to ‘vent’ the energy from the disinfectant box, won’t the UVC light come out?

No – Not a significant amount.  If properly designed however, you can actually vent through the microporous Porex Virtek PTFE.

UV measurement

How do I purchase the dosimeters mentioned in the webinar, and are there special ones for different wavelengths?

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.

How do I calculate dosage per cm2

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. 

Do you use an integrating sphere to do your testing and make the 95% reflectivity claim? What is the sphere lined with? Are you measuring BRDF?

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).

Porex Virtek PTFE material

Is your material chemical resistant?  How do I clean it?

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.

What size(s) is the Porex Virtek PTFE material available in?

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.

How resistant is Porex Virtek PTFE to <200 nm UVC?

Porex Virtek PTFE is not recommended for wavelengths below 210 nm. 

How hydrophobic is microporous PTFE? Is it prone to biofilm formation?

Porex Virtek PTFE is extremely hydrophobic, and we do not expect any biofilm formation while exposed to UVC energy.

Does Porex Virtek PTFE transmit visible light?

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.

Do you have performance data on UV wavelengths below 220 nm?

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.

How does the thickness of Porex Virtek PTFE affect reflectivity?

Please reference the chart on the Porev Virtek PTFE Reflectivity section. Yes, thickness up to 1.2 mm will have some effect on reflectivity.

What’s the reflectivity degradation curve look like over time?

We are still doing some life testing, but we expect very little degradation over time in the 250-280 nm range.

What is the typical pore size or pore size distribution in Porex Virtek PTFE film?

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.

Porex Virtek PTFE usage

How will the Porex Virtek PTFE sheets be fixed on metal surfaces, and can this be done near/at melting point?

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.

How I can fix the Porex Virtek PTFE to the outside of a glass tube? 

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.

Is it possible to produce a part with a hole at the center and a specific thickness?

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.

What are the grades of Porex Virtek PTFE available?

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 

How do I select the right type of grade for my application?

A good deal of information is on the Reflectivity page, or you can contact us for more specific information.