Bite and chew on a bit, but not shred or eat! When I first gave my then puppy a rinsed out plastic milk jug, she surgically removed the little plastic ring that remains on the jug when you first open the top! Lesson learned, from then on I removed that little piece before giving it to her! I also kept an eye on her and removed any that looked like they might be chewed on enough to be shedding pieces of plastic. The really great thing about using recyclables though is that (a) puppies seem to really like that plastic crinkle noise, and (b) we all have a renewable and free source of new toys for them >that's interesting you guys allowed your pups to bite and chew off plastic.
i actually did ONCE when my dog was little, gave him an empty arrowhead water bottle, after a while i noticed my dog had went ahead and opened the cap, so i immediately took that away, and later noticed him trying to chew off the head.
i thought i didn't want to risk having my dog cut up her lips and gums, let alone risk ingesting sharp plastic parts, so i never did.
for chewing, teetching, i froze about 10 wet towels and gave him that.
he would go through 1 wet towel PER 15 to 30 minutes, and later lose interest since they get warm again.