Thanks for the write-up and opening the discussion. I agree that material degradation is something that should be thoroughly investigated. Caveat: I’m not a polymer engineer and have read/seen a few papers/talks on the topic, but I’m by no means deeply familiar with all the material types, etc.
Re. the Boeing study (working link, btw): The study used fairly low doses per disinfection cycle but simulated 25 years of service, totalling >108 J/cm² of far-UV exposure. Still just about a third of the bus study exposure, but already in the dose range where the bus study measured only marginal effects of additional far-UV on colour or mechanical properties.
Still, I don’t find myself overly worried (but again, not an expert and I also don’t have regulator-brain, so interpret this accordingly).
Far-UV doesn’t penetrate deeply and will likely not affect the mechanical properties of solid plastic objects. The bus study found effects in thin sheets of fibre-reinforced materials (in some directions), and I don’t doubt that, but in what situations is a 10% decrease in failure strength of thin polymer layers that relevant for consumers or regulators? I genuinely don’t know, and there might be specific circumstances in which parts must be replaced more frequently, or the plastic type needs to be switched, but I don’t think this will matter a lot in most settings. E.g., Boeing found “no adverse impact on the mechanical properties of thermoplastic and textile materials” in the airplane setting at the dose where the bus study already saw decreased tensile strength. I’m very interested in hearing counterexamples, though!
But ultimately, both Boeing and the bus study have only tested the materials present in those surroundings. Looking around in my office or the office of friends, I’m not sure how many of the materials overlap. There’s some testing behind closed doors from lamp manufacturers, but no public database of common materials and the impact of far-UV on them. We eventually want and need such a database to make the far-UV implementation as pain- and seamless as possible for building operators, etc., but I’m not sure how much the average office worker or regulator cares if the back cover of their monitors starts yellowing faster (like you said, open question: Market research opportunity!).
And in the beachhead markets for far-UV (long-term care homes, ICUs), the cost–benefit calculus is favouring far-UV so much that a premium for far-UV coatings will happily be paid if yellowing is even something they care about. And the plethora of single-use plastics are not affected.
Hi Sean,
Thanks for the write-up and opening the discussion. I agree that material degradation is something that should be thoroughly investigated. Caveat: I’m not a polymer engineer and have read/seen a few papers/talks on the topic, but I’m by no means deeply familiar with all the material types, etc.
Re. the Boeing study (working link, btw): The study used fairly low doses per disinfection cycle but simulated 25 years of service, totalling >108 J/cm² of far-UV exposure. Still just about a third of the bus study exposure, but already in the dose range where the bus study measured only marginal effects of additional far-UV on colour or mechanical properties.
Still, I don’t find myself overly worried (but again, not an expert and I also don’t have regulator-brain, so interpret this accordingly).
Far-UV doesn’t penetrate deeply and will likely not affect the mechanical properties of solid plastic objects. The bus study found effects in thin sheets of fibre-reinforced materials (in some directions), and I don’t doubt that, but in what situations is a 10% decrease in failure strength of thin polymer layers that relevant for consumers or regulators? I genuinely don’t know, and there might be specific circumstances in which parts must be replaced more frequently, or the plastic type needs to be switched, but I don’t think this will matter a lot in most settings. E.g., Boeing found “no adverse impact on the mechanical properties of thermoplastic and textile materials” in the airplane setting at the dose where the bus study already saw decreased tensile strength. I’m very interested in hearing counterexamples, though!
But ultimately, both Boeing and the bus study have only tested the materials present in those surroundings. Looking around in my office or the office of friends, I’m not sure how many of the materials overlap. There’s some testing behind closed doors from lamp manufacturers, but no public database of common materials and the impact of far-UV on them. We eventually want and need such a database to make the far-UV implementation as pain- and seamless as possible for building operators, etc., but I’m not sure how much the average office worker or regulator cares if the back cover of their monitors starts yellowing faster (like you said, open question: Market research opportunity!).
And in the beachhead markets for far-UV (long-term care homes, ICUs), the cost–benefit calculus is favouring far-UV so much that a premium for far-UV coatings will happily be paid if yellowing is even something they care about. And the plethora of single-use plastics are not affected.