This was an ornament I printed roughly 6 years ago. Being a Christmas ornament it spent most of those 6 years stored in my roof space.
Being in Australia this would have been subject to average temperatures of 30 to 35 degrees c but also peaks across summer approaching 70 degrees c. Also in high humidity.
The PLA crumbles into tiny pieces at the softest touch.
I thought it was interesting that PLA would start to break down in these conditions.
@cameron pla printers can leave undeveloped resin inside the print. Perhaps if there are voids or the like. These can slowly seep out, destroying the model.