I would contact University Archives -
https://www.universityproducts.com/
They have a deacidification spay which can be used on books, newspapers, etc. They can probably also answer your questions. Look at the bottom of their home page for links to customer service and how to videos.
I would suspect that you would spray this on the back. You could then encapsulate it in mylar.
https://www.universityproducts.com/b...ion-spray.html
Archivists and conservators use Bookkeeper Deacidification Spray on acidic books and documents. Neutralize acidic paper with Bookkeeper Deacidification spray. Magnesium Oxide is the neutralizing agent in Bookkeeper which permanently "fixes" in the cellulosic fibers and on the paper's surface. Bookkeeper uses only non-toxic and non-hazardous materials and dries odor-free on treated documents. Bookkeeper has been reformulated and is now safe for export.