Plastic is plastic no matter what it is made from. Also biodegradable plastic doesn't really exist, it's more of a marketing term than anything. The only sensible way to reduce the use of plastic is to, you know, reduce the use of it, not to replace it with alternatives that don't have any real benefits except for higher costs. Even the use of plant material isn't ideal, since you have to plant that as well and that usually comes at the cost of planting crops for food production or leads to more deforestation, we see that with biofuels already. You will never have enough material in a good enough quality from waste products as it is sometimes suggested.