Recycling plastic is difficult because despite being labeled as PE, PET, PP, PS, ... most plastics [0] are customized by additives that change the material prop

Recycling plastic is difficult because despite being labeled as PE, PET, PP, PS, ... most plastics [0] are customized by additives that change the material properties (in the simplest case the color)[1]. Recently I saw an imprint on the tub of a washing machine that read "PP-K40". Searching for it revealed that this is polypropylene (not surprising) but 40% of the mass of the material is added calcium carbonate filler (very unexpected)! [0] https://en.wikipedia.org/wiki/Plastic#Common_plastics https://en.wikipedia.org/wiki/Plastic#Common_plastics [1] https://en.wikipedia.org/wiki/Plastic#Fillers https://en.wikipedia.org/wiki/Plastic#Fillers