First of all, biodegradable doesn't mean what you think it means. For example, PLA plastic is biodegradable - good luck trying to compost it at home.
Second, source material doesn't mean that the end result will be biodegradable as well. You will need to polymerise them and you'll end up with the same plastic and rubber as if you'd use oil. PLA is an example again! It's made from lactic acid, which you can and do eat. You can also eat pure PLA, but again - it's not compostable.