The topic came up this morning about what would be a good area to research for a Ph.D. nowadays. It was suggested biodegradable polymers, but I really dislike that area immensely. Biosourced polymers would be much better.
Biodegradable polymers have their uses, particularly within medical applications, but as a general commodity plastic, something to take on the Big 6, they will be inherently problematic. Inherently. As in you cannot avoid the problems. To most people, biodegradability is a way to address pollution problems, but biodegradability is not an effective solution because a polymer will never biodegrade the instant it is released into the environment. Look at paper, a readily biodegradable material, but even paper doesn't biodegrade instantly. Paper products are a very visible type of pollution. Do crews cleaning up along highways, in parks and other public places pick up paper or do they leave it because it will biodegrade? Of course they pick it up. When you see paper products spread across a field, are you happy and not concerned because there really isn't a waste problem since it will all biodegrade and take care of itself?
The minute any waste is released into the environment, it becomes pollution. Biodegradation is a long-term solution to immediate pollution, which means it isn't a solution at all. And while research on biodegradable polymers is not without merit, it is inherently limited in its potential to help civilization. No one has proposed or has even imagined creating a material that is smart enough to know when it should and shouldn't biodegrade, let alone one that would be able to biodegrade almost instantly once that decision is made. These are inherent limitations to biodegradability.
Biosourced polymers are quite different. Instead of being made from petroleum, they are made from bio-based feedstocks. For examples, Braskem has developed a process to make polyethylene from sugar cane. The sugar is fermented to yield ethanol, the ethanol is dehydrated to produce ethylene and then the ethylene is polymerized. You now have a bio-based polymer that is (nearly) identical to the petroleum-based polymer (the only difference being the presence of the C-14 isotope). And so the search is on for creating bio-based sources for the monomers currently used in making polymers. And the search is also on for identifying new, biosourced monomers that have been too difficult/expensive to produce from petroleum and that can be used to create novel polymers. Examples are various types of furans and isosorbide. Some of the resulting polymers could be biodegradable if you really are obsessed with that tact, but being biosourced does not mean that they are automatically biodegradable. (Bio-source polyethylene is just as non-biodegradable as petroleum-sourced polyethylene.)
Speaking strictly from a practical viewpoint, biodegradable polymers would not be my favorite subject to study in school because of the time-scale of the experiments. Once you have made your new polymer(s), testing for biodegradability takes weeks and months to perform. That's weeks and months before you get any feedback to let you know to stay-the-course or try something else. Industrial researchers can work with those time scales, but as a student? No way. Unless you want to take a decade to get that Ph.D.