My following comment is not about clothes, but not long ago I washed some curtains that were hanging in a window for some fifteen years. The amount of lint that came out in the dryer was incredible. I'm talking inch-thick wad on the filter screen, growing another inch with continued drying, after being removed.
It was probably due to years of UV breakdown of the fibers from daylight.
The lint had a very homogeneous consistency: it was almost snow white with few inclusions deviating from that, almost resembling polyester pillow stuffing in some regards, except for having a different structure (much shorter fiber strands, probably).
It was probably due to years of UV breakdown of the fibers from daylight.