Adam Feinberg had no sooner made a bright yellow thin sheet of plastic than he had to shred it into little pieces. He chose an “I”-shaped mold for the logo of the University of Illinois at Urbana-Champaign where he is a chemis t. Then, he filled it with the plastic bits and stuck it in a hot oven.

“I opened up the mold and there was this beautiful yellow ‘I’,” he recalls. His new plastic passed the first test — it was moldable with heat like regular plastic. But there was another important step left in rethinking the world of durable plastics.

Dr. Feinberg placed the I under a white light, and five minutes later, only half of it remained. The other half had fallen on the ground. Pieced back together, the I had a hole in the middle and in its place was yellow goo.

The plastic did not simply melt. Its building blocks, the synthetic polymers within, had reverted to their molecular units. “It was a phenomenal feeling,” he said of the successful experiment.