Cellulose acetate was one of the first materials used for many of the things we use petroleum based plastics for now. Early Lego were cellulose acetate.

It's still used for lots of things.

Cellulose is a very useful chemical. It was generally replaced by petrochemical synthetic polymers for many of its original applications because the latter may be more stable at higher temperatures, under UV light, in contact with certain common chemicals (like water), etc. And most of the petro-plastics are cheaper to manufacture.

Cellulosic thermoplastics often appear in products where you don't want the plastic component to last forever, particularly textile fibers.

https://en.wikipedia.org/wiki/Cellulose_acetate

https://en.wikipedia.org/wiki/Cellulose_triacetate

https://en.wikipedia.org/wiki/Rayon

https://en.wikipedia.org/wiki/Cellophane

https://en.wikipedia.org/wiki/Lyocell

This 3D printing application seems similar to processes used to produce rayon and cellophane, but instead of producing the more universally useful fiber and sheet forms as a commodity, it forms an end-product directly and then stabilizes it chemically.

Both plastic and petroleum jelly are petroleum-based, but have drastically different properties.

The cellulose polymer acts as hard plastic.