Aluminized Cuben – Third Time is a Charm?
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We all owe a “thank you” to BPL DIY forum contributor Nathan Myerson. He is working on a project using the latest version of aluminized Cuben. He contacted me to offer a scrap, for “analysis and sharing of my test results with the community” based on a prior forum thread. See: Reflective Cuben Delaminating? – 6 month old news
The Brooks Range Rocket Tent material I tested on 4/8/11 was Cubic Tech CT2K.18/KM5 which I refer to as the “First Time Version”. The current scrap is labeled CT2K.18/KM7 which I refer to as the “Third Time Version”. The characteristics of KM6 remain a mystery, but I refer to it as the “Second Time Version”.
Picture of the “Third Time Version” scrap I used for testing:
“The Third Time Version” material characteristics that I measured are:
The “First Time Version” catastrophically delaminated during a Protocol B wet-flex aging test. Roger Caffin and I worked together on Protocol B testing procedures. In early 2011 he suggested that we use a Cubex wet-flex machine to achieve single cycle granularity and repeatability. This necessitated the purchase or construction of a fairly complex device which he volunteered to custom build. My concern, at the time, was that if a BPL forum member wanted to verify our Protocol B test results that he/she would have to first purchase or construct this specialized piece of test equipment. I lobbied for just using a standard washing machine and dryer to create wet-flex aging and he reluctantly agreed. After the publication of the Protocol B test results, I purchased a commercial Cubex machine and it is what I have since used for precise wet-flex aging.
I used a high quality fabric sample to correlate the crude Protocol B cycle with the fine granularity Cubex machine cycles.
The “First Time Version” aluminized Cuben delaminated between the first and second Protocol B aging procedure or at approximately 5,400 Cubex wet-flex cycles. After testing at fixed intervals up to 16,200 Cubex wet-flex cycles (3x the amount of wet-flexes needed to create a catastrophic failure in the “First Time Version") the “Third Time Version” maintained >3,515 mm H20 HH and had zero signs of delamination.
OK Now it Works – What is Different?
The "First Time Version" micrograph at 5mm field of view. Inside it looked like a Star War’s movie scene. There was no major aluminized surface voids, only micro-dot voids, and a large amount of celery-green color adhesive used. It looked really high tech but…
The "Third Time Version" micrograph at 5mm field of view. With all of the obvious fissures, I said to myself, “This material will never pass a large number of Cubex wet-flex cycles but, …
A much more detailed look at "The Third Version" shown at 600um field of view:
It is obvious from this micrograph that the aluminum coating was applied on only one layer of Mylar. One side is significantly shinier (lower emissivity) and that is the aluminized side.
@rememberthelorax
Colin,
That was a very well-reasoned question! The short answer is “I have not seen any emissivity specification for this product.” Now for the long answer (smile). For those not familiar with this topic, at minimum you need to understand that a material with an emissivity of 1.0 is a perfect radiator and 0.0 would radiate no heat.
As you stated, neither the generic Mylar base-layer “Space Blankets” nor the polyethylene base-layer “Heat Sheets” have any protective coating over their aluminum layer. The bad news is that this air exposed aluminum layer can quickly oxidize and/or rub off. The good news is that all other things equal, their “when new” emissivity should be lower. Theoretically, their average 1 micron thick aluminum coating should have an emissivity of .1 – .2 when manufactured and .2 – .4 after significant oxidation. In contrast, the Cuben material has Mylar on the outside. Mylar’s emissivity will vary with its thickness but, for a representative thickness of 10 microns it is ~.4.
Updated 8/20/14:
I built a new apparatus to test emissivity in the spectrum: LWIR 8-14um. It is based on the ASTM C1371 methodology; it uses a Fluke 62 Max+ and an Excel spreadsheet to compare/integrate a high emittance and low emittance reference sample to the test sample.
I only had the aged Cuben sample to retest. The original test showed the same value for both the new and aged Cuben. The corrected test values are as follows:
Above image is from a FLIR R&D manual,
@rememberthelorax
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