Ever wonder why old movies were dangerous? Not so much for the content of the storyline, but because they were made from a substance that was highly inflammable. Originally they were based on nitrocellulose - guncotton. Not exactly something you want to run through a hot projector with an arc lamp. But a much safer version of film would keep projectionists happy for many years: cellulose acetate.
And there's a lot more to this early naturally based plastic, from the original Lego bricks to gas mask eyepieces.