The PET, or poly(ethylene) terepthalate, is made by the estrification terepthalic acid ethylene gylcol. By soaking the PET in the NaOH solution with some heat, the PET is subjected to saponification (base hydrolysis of an ester) which breaks the PET down into the salt of the carboxylic acid (terepthalic acid) and the alcohol (ethylene glycol) that formed it.
Terepthalic acid is a colorless solid with very low solubility in water, so it makes sense that it would have settled out. Ethylene glycol is miscible in water, so it's in solution. Because of the hydrolysis the solution starts going bad from the moment you start using it. However, hardware store lye is cheap. And I suppose it cleans out your drain somewhat when you dump it.
I'm on the edge of my chemistry so if I have this all wrong, please jump in and correct me. Anyway, unfortunately I did not check the pH of the 1M NaOH solution before I started. So maybe it's the acid, or the ethylene glycol, or my solution is defective, not really sure.
At the moment, I am fooling with an alternative process that looks even more promising. Or it might be a bust!
More to come.