Today’s the materials picture framers use are Acid-free and guaranteed to ward of the ill effects of acid damage for years. This was not the case in the past and is evidenced by the yellowing of old mounts and artworks on paper yellowing and becoming brittle and crumbly. They are the tell-tale signs of acid damage.
Not to say that your artwork will last hundreds of years. It is recommended that any valuable artwork be re-framed in new acid-free mount card every 5 to 10 years.
But that is for artworks in museums and not for you average artwork. Acid-free materials are meant to last up to 80 years.
Museum-grade mount card is made from 100% virgin cotton fibre and not wood. It is much more expensive but completely acid-free.