There are a few different kinds of pressed wood board. Egg tempera painters (many of whom do think about how archival their supports are, due to the medium itself having a proven archival track record) are commonly using untempered masonite, which is as indicated above, just pressed pulp without formaldehyde or oil type additives. There is a layer of Gesso between the board and the paint, but it is the good old fashioned hide glue kind. So.... pressed wood > glue/gelatin > image, sounds familiar!
Unfortunately, untempered masonite is hard to track down, as suppliers aren't always aware of their products contents. If I can track down a current brand name, I will update.