Making Plastic from Milk?

I've just been searching the interweb and came across this hobby site. The article I had originally followed was for using pink and blue foam for terrain, but on the main site (http://www.stormthecastle.com/) this article and video caught eye - making plastic from milk. To be fair he uses vinegar as well. But that's it. Apparently the idea was from Leonardo Da Vinci.

In a hobby where resin and plaster are commonly used to create scenery how good (and cheap) would it be if we could use milk & vinegar instead? More investigations are needed...