Skylark,
Unfortunately, by placing your notes in a book, you are exposing them to the acids present in the paper. It is really no different than using one of those unsuitable plastic holders.
In my experience, it would be wise to seek out some Mylar folders (as previously suggested by others in this thread). You should then keep the notes in a cool, dry place out of direct sunlight.
If you own some older notes which are hand-signed, the inks in those signatures may contain Iron or Copper that will corrode over time. This may result in what appear to be "burn" marks directly in the area of the signature. If you notice something like that, it is best to seek the advice of a professional conservator. (museums are a good place to ask around)
Hope this persuades you to take your notes out of your Encyclopedia Brittanica or favourite novels!
Cheers,
Dean.