http://www.straightdope.com/columns/read/106/what-makes-tape-stick-and-matches-light
A 1974 column, eh? Any more recent research on how adhesive tape really works?
I’m not a materials specialist myself, but I have talked to them with regards to tape and adhesives, especially in regards to shelf life, i.e. how long the tape can sit on the shelf and still be guaranteed to adhere when applied. I am informed that the adhesive is a chemical bonding process. If you apply the tape then the bonds form between the molecules of the tape and the material it is stuck to, but if left on the roll, over time the adhesive bonds to itself and becomes unsticky. Thus, you get an old roll of tape that can’t stick to anything.
Hm. THAT’S why old rolls of Scotch Tape won’t come unrolled. Thanks!
Wiki knows more than Cecil: http://en.wikipedia.org/wiki/Adhesives#Mechanisms_of_adhesion