CHEM 121 glossary
Biodegradable
Able to be broken down by living organisms (and water) into small, harmless molecules. Polymers with hydrolyzable backbone links, such as polyesters, can biodegrade; all-carbon backbones like those of PE and PP almost never do.
Example
PLA hydrolyzes back to lactic acid, but only quickly under the hot, moist conditions of an industrial composter; in a landfill or the ocean it lasts much longer.