Way back when I started this thread, I did some poking around on the internet. Apparently it's not the acidity of the zest, it's the 'essential oil' in the rind (which has a very fancy technical name). The oil works as a solvent on many petrochemicals, which includes some plastics and Styrofoam.
I also learned that, apparently, this oil is used to 'stress test' the resilliance of denture bonding materials.
I also learned that, apparently, this oil is used to 'stress test' the resilliance of denture bonding materials.