You need to look into museum quality document preservation. There are companies that specialize in products for preserving documents. I have a bunch of catalogs from these types of companies because I have some rare books and rare records LPs I wanted to preserve. I visited a small museum in town and asked them and the led me in the right direction.
If you want to do it yourself, go to a comic book shop and get some acid-free ph absorbing backing board and some acid-free mylar comic book bags (but they're a bit small, you can cut them or they might have some bigger)