The first problem is that there are thousands of different plastics, each with its own composition and characteristics. They all include different chemical additives and colorants that cannot be recycled together, making it impossible to sort the trillions of pieces of plastics into separate types for processing. For example, polyethylene terephthalate (PET#1) bottles cannot be recycled with PET#1 clamshells, which are a different PET#1 material, and green PET#1 bottles cannot be recycled with clear PET#1 bottles (which is why South Korea has outlawed colored PET#1 bottles.) High-density polyethylene (HDPE#2), polyvinyl chloride (PVC#3), low-density polyethylene (LDPE#4), polypropylene (PP#5), and polystyrene (PS#6) all must be separated for recycling.
Just one fast-food meal can involve many different types of single-use plastic, including PET#1, HDPE#2, LDPE#4, PP#5, and PS#6 cups, lids, clamshells, trays, bags, and cutlery, which cannot be recycled together. This is one of several reasons why plastic fast-food service items cannot be legitimately claimed as recyclable in the U.S.
Another problem is that the reprocessing of plastic waste—when possible at all—is wasteful. Plastic is flammable, and the risk of fires at plastic-recycling facilities affects neighboring communities—many of which are located in low-income communities or communities of color.