Just Like Chocolate
Recycling plastics for a greener future By: Molly Sun Every day, I cook up something new – fresh biscuits, fettuccine, and even soft-serve ice cream. But none of my creations are edible. The fluffy biscuits are buttery-yellow polyurethane foam, deceptively warm and soft. The fettuccine noodles are long, brittle strands of polyurethane film with a snap as satisfying as their alfredo-smothered twins. As a polymer chemist, I make and study polyurethane in all their weirdly delicious forms to figure out not how to eat them (to my regret on dinnerless late nights in the lab), but how to consume them as recyclable plastics. As they are, none of my plastic creations are recyclable either – a deep problem for a hungry world saturated with plastic waste. While consuming our leftovers presents an appetizing solution, the puzzle lies in how to make our used polyurethanes palatable again. Most plastics fall in a category called thermoplastics, meaning heat breaks down their molecular structure and makes them easy to reshape, like chocolate. For example, the polyethylene that makes up water bottles is a thermoplastic, so like chocolate, they are easy to melt down and mold into new shapes. The tiny molecular chains in thermoplastics are held together merely by weak electrostatic attractions, like strands of yarn bound to each other by a shock of winter static. However, most polyurethane has a particular chemical structure that prevents it from being remolded like thermoplastics. Its molecular strings are locked together by chains known as crosslinks, as if strands of soft, pliable yarn were linked by metal chain links. The presence of crosslinks dramatically changes the properties of […]
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