The problem with PLA is the "glass" transition temperature of only 131F (~55C), and of course that it was engineered to biodegrade over time.
Here is a pretty interesting web article that I just found, which ironically discusses the pros and cons of using PLA in weather station components:
http://iepas.net/using-pla-for-long-term-outdoor-applications/
My personal experience with PLA is that it deforms (glass transition exceeded) in a closed car during the summer, which is why I would never use it in an outdoor structural application.....
Your experience may very well prove that PLA is not the best choice of material to be left in what is essentially a rolling, sealed oven, but it's meaningless in any other context.
Comparing what PLA does in an artificial enclosed environment, surrounded by glass, known for drastically increasing the ambient temperature, to what PLA will do when exposed to the natural , unadulterated elements of the real world is scientific folly.
"To biodegrade within 90 days, as described, the products have to reach 140 F for 10 consecutive days. This requires a special facility, which few consumers have access to. If your PLA products end up at the landfill, they will not degrade any faster than a petroleum-based product."
You can throw all the theory at me that you want, I'm a field research engineer with a Master's Degree, I study the environmental effects on electronics and enclosures for a living. I eat theory for breakfast - PLA is used everyday exposed to extremes of temperature at both ends of the spectrum, and works perfectly fine. It doesn't freeze and shatter in Alaska, and it doesn't turn into a puddle of goo in Arizona.
I print my PLA at 235°C nozzle temperature on a heated bed at 80°C, and my designs have NEVER failed due to exposure to he elements.
As a side note, PLA is considerably UV resistant.
If you have the time and desire to read an approximately 2,000 word document, I can prove to you why bringing up the "glass transition temperature" of PLA is meaningless in normal, everyday usage. It's a wonderful bit for discussion in the laboratory, but utterly meaningless in 99.9% of real world applications.
From the link that you posted - "Based upon some of the references I have mentioned, I do not think PLA would rapidly deteriorate as shown in a composting situation."
Again, from your link - "the rapid biodegradation often discussed requires a specific set of conditions, which are unlikely to naturally occur."
The paper's conclusion was NOT that PLA was a bad choice for their project, but rather that the author did not have the time to do the testing he would like to do, without delaying the forward progress of their project.
