The next three entries on this list are all biodegradable plastics called aliphatic polyesters. Overall, they aren't as versatile as aromatic polyesters such as polyethylene terephthalate (PET), which is commonly used to make water bottles. But since aromatic polyesters are completely resistant to microbial breakdown, a lot of time and effort is being pumped into finding viable alternatives in aliphatic polyesters.
Take polycaprolactone (PCL), a synthetic aliphatic polyester that isn't made from renewable resources but does completely degrade after six weeks of composting. It's easily processed but hasn't been used in significant quantities because of manufacturing costs. However, blending PCL with cornstarch reduces cost.
Biomedical devices and sutures are already made of the slow-degrading polymer, and tissue-engineering researchers dig it, too. It also has applications for food-contact products, such as trays.