The argument, which doesn't seem insane, is that this film is useful because it is particularly optically clear and strong, which are not properties I would have expected from cellulose. I agree 17 days is too short, but that seems like an interesting opportunity for future research. I would highlight that the number is 17 days when buried in wet soil, not sitting around on a shelf. Cardboard will break down when buried in wet soil, yet we use it extensively in packaging without issue.
> optically clear and strong, which are not properties I would have expected from cellulose
You never heard of Cellophane? https://en.wikipedia.org/wiki/Cellophane
Cellophane is still used to refer to LDPE grocery bags in former soviet immigrant diaspora
Yeah I know this usage from older people when I was a kid, they referred to any clear thin wrapping as cellophane where to me it was just plastic. My father told me that cigarette packs are kind-of environmentally friendly because they are made up of nothing but paper, tobacco obviously, cellulose acetate for the filters, and cellophane for the wrapper. Recently I got interested into whether they still use cellophane instead of plastic, so I did some * * * science * * * by dunking a wrapper in water (and yes, it did soak up some water) and burning some (it burns cleanly like paper with grey ashes, unlike plastic which stinks and leaves behind hard black tar). So apart from the printing colors, it looks bio-degradable, with the other reservation being that especially the filters will spend a really long time underground before becoming integrated.
Or movie / photographic film?
That's cellulose acetate, though (or, previously, nitrate.) Cellophane is just cellulose. It's like the difference between drinkable ethanol and ethyl-acetate nail polish remover, or between morphine and heroin. Clearly related but significantly different substances.
> which are not properties I would have expected from cellulose
You know why we've lost so much early cinema history to fire and moisture?
Because silent-film-era film is made of cellulose. It burns. Rapidly. Photography pioneers knew that. They used cellulose anyway because it's flexible and transparent. Right technological decision at the time.
We've known about cellulose properties for literally over a century. There's nothing new here.