The paper of mass-market paperbacks has a high acid content and over time the paper will crumble. Take a look at mmp from the 1950's if you don't believe this.

The paper of mass-market paperbacks has a high acid content and over time the paper will crumble. Take a look at mmp from the 1950's if you don't believe this. That is why librarians wash books, to get the acid out. Rag paper with no or little acid content will last 300, 400 years or more. Books from the incunabula, properly tended, have not crumbled into dust.