"Polyethylene only rarely contains plasticizers, and it doesn't harden or crack unless continuously exposed to sunlight" I beg to differ, and I'm familiar with

"Polyethylene only rarely contains plasticizers, and it doesn't harden or crack unless continuously exposed to sunlight" I beg to differ, and I'm familiar with polyethylene (I spent too many years studying o-chem not to know something about it). I have hundreds of polyethylene storage containers ranging in size from 20 to 80 litres and their ages range from around 20 years old to new. They are stored in rooms with temperatures ranging from 15 to 25°C and an average RH of 55-65%. They are mostly stored in the dark (lights off) and they mostly contain old paper files although some contain books. For ages I couldn't figure out where the greasy, almost sticky film was coming from given the rooms are dry and the air is clean. (Mind you at first I didn't give it much thought.) After washing some to remove the film with just dishwashing liquid they were repacked and several years later the film was back and that's when the brittleness was noticed. Container lids were cracking on the bottom containers in stacks of only four to six high (max height 1.5m). Note, the washing had no noticeable effect, as containers of a similar vintage that were not washed were also brittle. When I checked I could easily crack the plastic of older containers with little bending. That wasn't possible with the newer units—they would deform out of shape but not crack—not without a lot of effort. That's a précis of a much longer story. Incidentally, there were several brands involved and all experienced similar problems with the greasy film. Note I'm not mixing products either, new units of brand A were compared with old brand A. I'd suggest my sample size is not insignificant, since the late 1990s I've had around a 1000 of these polyethylene containers and the evidence points to the fact that for this type of product polyethylene of that type is not fit for purpose. BTW, I ought to let you know I'm familiar with polyethylene from my work in RF engineering. And HDPE and that standard polyethylene does not behave that way. Moreover, some of the polyethylene I've used in recent years was manufactured in WWII and is still a viable insulator although (new old stock) coaxial cables with PE dialectic from that era are no longer as pliable as they once were (plastic jacket insulation taken into account).