There are several ways to make biodegradable plastic bags, but here is a general process that can be used:

Choose a biodegradable material: There are various types of biodegradable plastics available, including those made from corn starch, cellulose, and polylactic acid (PLA). Choose a material that is readily available and suitable for your needs.

Mix the biodegradable material with a plasticizer: A plasticizer is a substance that makes the plastic material more flexible and easier to shape. Add the plasticizer to the biodegradable material and mix thoroughly.

Heat the mixture: Heat the mixture to a temperature where it becomes a molten state. The temperature may vary depending on the type of biodegradable material you are using.

Form the plastic bag: Once the mixture has melted, it can be poured into a mold or extruded through a machine to create the shape of the plastic bag. The size and shape of the mold will depend on the desired size and shape of the plastic bag.

Cool and finish the plastic bag: Allow the plastic bag to cool and harden. Once it has hardened, it can be trimmed and finished as desired.

It's important to note that biodegradable plastics still have environmental impacts, and it's best to avoid single-use plastic bags altogether and use reusable alternatives.