Friday, February 25, 2011

Highly Accelerated Aging

There's a report out (open access for all of 2011) about a new technique for rapidly accelerating the UV aging of coatings, in this particular study, exterior acrylic paints. Small pieces of paint (0.75 mm diameter) are exposed to UV light (Xe-Hg lamp) in a pyrolysis tube attached to a GCMS, allowing for analysis of the coating. One of the claimed results is quite amazing: that 10 hours of exposure to the Xe-Hg lamp is equal to 1000 hours exposure [*] to a metal halide lamp!

I have two issues with the report. 1) A natural exposure was never run, and 2) there was no discussion or even mention of what the exposed paint looked like!

Long-time readers of this blog will know that I am always leery of any claims of huge acceleration factors (huge being anything in double digits or more), so a 100x increase over an already accelerated exposure (the metal halide lamp irradiance between 300 and 400 nm was 75 mW/cm2 = 750 W/m2 which already 10x the normal exposure levels) is particularly challenging to swallow without further support - a control tested to actual outdoor exposure.

But how about including a snapshot or two of what the final exposed paint looked like? I'd love to know if what was left even looked like paint or was it more like the Flanders fields in 1918?Just one image of the final paint could be enough to justify the extreme exposures given to the samples and the corresponding claims. Until then, I remain a skeptic.

[*] The exposure time was broken into 8 hour cycles with 4 hours of irradiation followed by 4 hours of moisture condensation and no irradiation.


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