Interesting perspective huanchin . What we hear in Europe is that bottle caps should stay ON, because then they can get recycled. It's worse if they get thrown (in the bin) separately, because then they are too small and will get sorted out during screening of contaminants. Of course, these practices look different everywhere, which underlines the need for a harmonised plastics system that works.
The key technical problem with a (PET) bottle is that the lid would be too brittle if made in the same material. That's why it's a different material (PP). Any smart ideas of how to keep the lid and bottle together anyway?
Interesting work! "Recycling is expensive and the cost is passed to the consumer as a “tipping fee”. A ton of recyclables costs $53 to dump at the landfill and nearly $200 if brought to the recycling center." --> it seems like a fee of roughly $0.20 kg for recycling. Considering that each packaging items weighs only a few grams (if plastic), would you think there are options to cover this in a sort of 'deposit fee' (which could almost go unnoticed)