It looks like wood, and it’s even made from wood. But what’s special about the so-called elastic wood made in Liangbing Hu’s lab at the University of Maryland, College Park, is that it can be squished—and it bounces—as if it were made of rubber. The recipe for elastic wood is fairly simple, but it’s harsh: Boil balsa wood in a solution of sodium hydroxide and sodium sulfite for several hours, freeze it for a couple of days, and then freeze-dry it for another day. The procedure breaks down the rigid structure of the wood by chemically chopping up the long molecular chains of lignin and hemicellulose inside the cell walls. This makes the cell walls thinner, and it also makes the cell walls release cellulose fibrils, which get tangled up and form a gel network inside the wood’s natural pores. The thinner cell walls make the wood squishy, and the water-filled gel gives the material the springiness that makes it flexible and bouncy, so bouncy that University of Maryland postdoc Chaoji Chen can bounce an elastic wood sphere like a Super Ball (below).
Credit: Liangbing Hu’s research group. Read the paper here (ACS Nano 2020 DOI: 10.1021/acsnano.0c04298).
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