I'm pretty sure that happened a long time ago. But the latent value of the materials is hard to recover--you could recycle the paper, but that requires a lot of expensive equipment, and there are many accessible sources of pulp which are easier to collect. Such an endeavor would inevitably fail because it lacks the efficiencies of scale.

As an interesting aside, US pennies minted before 1982 contain $0.018 worth of copper. It's not nearly the problem that Zimbabwe has, because pennies makes up so little of the US currency in circulation. But one might think an enterprising entrepreneur could profit from this. But again the problem falls to inefficiencies of scale: you simply can't harvest and sort enough pennies quickly enough to make the effort worthwhile (machinery even exists for this purpose).

I remember someone observing that physical currency from 100 years ago was worth more than you'd've made by investing it in stocks, property, or any financial instrument you care to think of for those 100 years.

Maybe if you have a rare and beautifully printed treasury bond, it's worth more than the (now antique) cash it cost!

I bought a couple of the $100tn notes as a gift a few years ago. The frame I put them in cost more.

Curiously, the eBay price is higher now than it was then ($34 vs. $6.25). So they'll be back to being worth a trillion in about ... 185 million years at the current rate of increase.

That happened around 2009

http://www.theguardian.com/media/2009/jun/23/zimbabwean-cann...

That's already the case for the US penny.