Can PVC/CPVC be an effective base material for a laser protective window or barrier?

We asked industry expert Robert Miniutti, and here’s what he had to say…

Let me start with an anecdote. Early in my career, I designed a welding protective sheet/window using cellulose acetate. It worked great for welding protection and can still be found in the market today. So, when I got my first request to make a laser protective window, cellulose acetate was my logical choice, right? Wrong. It turns out that when you hit a material derived from wood pulp mixed with flammable plasticizing materials with a direct laser beam, it bursts into flames. Lesson learned, and I moved on to cell cast acrylic which worked perfectly.

Fast forward to 2018 – As many can attest, I get a variety of questions about materials used in laser protection from distributors and end-users alike. These include questions about optical properties, physical properties, as well as environmental properties. Recently I started receiving numerous requests about PVC and its close cousin CPVC since the material has been suggested and sampled for use as a laser protective barrier with absorptive dyes.

In simple terms, what is PVC and CPVC?

PVC is a plastic material commonly used for drain pipes, electrical conduit, and similar applications. CPVC is more rigid chlorinated version and can be made in a somewhat transparent form or sheet.

So, in your opinion, can CPVC or PVC be an effective choice for a laser protective window?

Unfortunately, there are significant negative issues with PVC/CPVC that must be considered:

PVC and CPVC have significant health and environmental impacts. PVC and CPVC became very popular because they don’t burn easily, but instead merely smolder. This sounds like a great characteristic for laser protection, but it ignores dangerous dioxin vapors produced upon incineration. Regardless of industry spin, in a fire these dangerous gases are produced in your facility, car, train, plane or home. In the case of laser protection, virtually any laser exposure to a CPVC/PVC window will produce such fumes. Our tests show dioxin-laden fumes developing in under 10 seconds when exposed to a 40W light bulb, not to mention the ramifications of a direct laser exposure. There can be little dispute that end users of lasers in labs, hospital operating theatres, or laser marking and welding systems will likely be exposed to these fumes in any laser incident.
Disposal of a used window is problematic. Air burning incineration is completely out of the question which makes End-Of-Life (EOL) disposal challenging. Regulations in the EU make using PVC and CPVC nearly impossible, unless no other material is available. Polycarbonate, acrylic, and glass are all available and existing solutions for laser protection that can be readily disposed.
PVC and CPVC have a very low working temperature. If you run very hot water through a PVC pipe, it easily bends and deforms at about 165F. That’s not a good characteristic for maintaining dimensional stability, especially for large windows. Again, the current materials are all above this softening temperature.
PVC and CPVC suffers from haze, which exceeds optical standards requiring less than 2%. Up to 2% haze is typically considered acceptable for viewing windows, but haze higher than 3-5% is too high. “Peeking” is the leading cause of laser eye injury. The more difficult it is for a user to see though a window or lens, the more likely the user is to peek at the laser system, risking injury. This is why I strive to maximize visible light transmission, while also minimizing or eliminating haze in every acrylic window product produced.

Is this material really that bad to use?

Let me put it this way. As a result of the first two items above, prohibitions for the use of PVC are popping up regularly. In the transportation world (automotive, rail, and aerospace) as well medical fields (OEM and facilities including the operating theater), all have instituted prohibiting (or the goal of prohibiting) the use of PVC and CPVC. Bans in cities like New York, Boston, and Seattle are being implemented. In California, Proposition 65, which is now an enacted law, requires a “May Contain Carcinogens” warning label on any PVC or CPVC product sold. Failure to label carries a $1000/occurrence fine. Other U.S. States such as Vermont and Washington are following suit. On a national level, Sweden, Spain, and Germany have all set initiatives to ban PVC. On a corporate level, Apple, HP, Nokia, Samsung, Sony, Daimler Benz, Ford GM, Honda, Toyota, VW, Volvo, Wal-Mart, Microsoft, and Nike among many recognizable companies have banned and/or created phase out policies for PVC.

Overall, I just do not see any advantage to using a material like PVC or CPVC for a laser protective window designed to be hit by intense energy. I have included just a few links to help educate and find corroborating data.

PVC: A Truly Poison Plastic