Do temperatures above 30C  degrade PET ropes? Shrink them?
Update
This may seem like an odd question, but there are lots of rope-washing guidelines that recommend temperatures below 30C for washing, along with air-drying at room temperature. Those precautions may make sense for dynamic ropes, whose nylon 6 yarns have been heat-treated beforehand to increase stretch, and may lose some of that stretch on re-heating. However, many static ropes are 100% polyester (PET).
Studies of PET yarns show no significant strength loss to 140C (Materials 2021, 14(7) p 1666; https://www.mdpi.com/1996-1944/14/7/1666).

Ropes may behave differently from single yarns, so I did a very quick test on 4 rope samples, two unheated, and two heated 48 min at "medium-high" (up to 72C) on my clothes dryer rack. The samples were pulled to breaking behind my Jeep, between two figure 8 knots. The rope (100% PET Edelrid 8mm kernmantle) was purchased from Hownot2.com. OF NOTE, the figure 8s were tied in the rope BEFORE being put in the dryer.

Here are the results. If anything, there may be a slight strength gain for the heated samples (but not statistically ignificant).  Remember, this applies to 100% PET ropes.


Some important updates: tests for 70C and 149C for 1 hour, knots tied AFTER heating and shrinkage. I carefully measured the ropes (~2m sections) before and after treatment, with a 2mm uncertainty. I first put my dryer on high for 60 minutes; to my surprise, the "High" setting actually yielded a slightly LOWER temperature than the medium high -- about 70C (measured by TC). Then I took two more samples and put them in the oven for 60 minutes, at about 149C.  After the heat treatments, I was very careful to dress the figure 8 knots all the same, and in the pull test behind my jeep, all sample had similar pull times before breaking. The results:



While whole ropes are not expected to reach 149C while  being cleaned, potions of the sheath can easily reach these temps during a long rappel, due to the accumulated heat in the rappel device, and the shrinkage actually takes place quickly.

Shrinking of PET ropes above the boiling point of water is well-documented. I took 6' of pure PET Maxim 8mm, carefully measured the length, and coiled it in the bottom of a 4 L cooking pot. I then poured 1.7L of boiling water (at 3000', 208F or 98C) on it.
I waited 30s, then pulled the rope out and found it had lost 1.7 (+/-) % of its length.