To get bioplastic, you have to mix a biopolymer with a plasticizer and some additives. Biopolymer is responsible for the stability.
Plasticizer is for flexibility and the additives change the colors, for example. For a polymer you can use starch gelatin or agar. The most used plasticizer is glycerin. It interacts with the polymer and gives flexibility to the end product. Glycerin is used because it is very cheap and abundant. Heat all the ingredients slowly up so that they get liquid. Mix them up and let them dry for a few hours. Then you have got your own bioplastic. All in all you can say, bioplastic is manufactured out of natural materials. So if the product comes back into nature, it is ok because it is just a mixture out of natural materials. The good thing about such biodegradable plastic is that everybody can mix those ingredients at home. You can order them on the internet and use your stove to heat them up. At the end you can form the plastic in every form you want as long as it is liquid. For example, you can do cups for drinking or plates for food, some foil or other containers and boxes. The possibilities are endless. With food color you can paint the plastic as you wish. All in all this is a very good opportunity to produce useful plastic parts that you need and you cannot buy anywhere.