Is that necessary for plastic? The name comes from the Greek for “to mould”. For me, anything that makes long chain mouldable polymers is a plastic. Milk makes Casein or Galalith plastic, PLA is commonly made of corn. There’s a ton of bamboo fabrics that are essentially nylon made from cellulose.

There’s a lot of sodium in most fizzy drinks, wonder if that rules them out for this. Or does it have to be sodium chloride specifically?