Plastics can be synthesized from most carbohydrate gases. You can make most carbohydrate gases from water & CO2 from the air. The problem is that it's very ene

Plastics can be synthesized from most carbohydrate gases. You can make most carbohydrate gases from water & CO2 from the air. The problem is that it's very energy-intensive, so the best way to create such plastics is by using excess renewable energy (e.g. peak solar) to create renewable carbohydrates. Currently, the tech has not been economically scaled yet, due to being new, and also not enough renewable capacity being available.