system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can plastic “nurdles” be made into other plastic forms but formed plastic can no longer be as easily recycled?

To my knowledge, nurdles are the primary pellets that are used as the source to form all plastic pieces. If they get melted down and formed into other plastic parts, what changes that makes those formed parts so much more difficult to melt down into another form?
gpt
Once some types of plastic undergoes that melting process, it chemically changes and won't melt again, but burns instead. Try heating a plastic water bottle (don't).

You can re-melt other types of plastic, but with our current supply chain setup, it's cheaper to buy new pellets instead of collecting, transporting, cleaning, sorting, and recycling it. China used to buy a ton, but they've toned down recently.