“Water-shocked” wood becomes moldable

Prachi Patel: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics of sustainable materials, 3D bioprinting, autonomous materials, bioelectronics, perovskites, quantum materials, robotics, and synthetic biology. My name is Prachi Patel. Wood is a low-cost, sustainable material. For ages, humans have used its exceptional strength to make houses, ships, furniture, and sports equipment. Unlike metals and plastics, though, you can’t melt wood and form 3D shapes with it. Researchers at the University of Maryland have now found a way around that fundamental limitation of wood.

Liangbing Hu: For the first time we are able to shape the wood. You can mold the wood like you can mold plastic and metal. So you can create any kind of mold and you put wood in between, and you can create that kind of structures. In addition to properties, shape really matters.

Patel: Hu’s lab has been tinkering with wood for years. Wood is made of the fibrous materials cellulose and hemicellulose, and lignin, a polymer that glues those fibers together. Hu and his team start with hardwood species like bass, and use simple chemistry to remove the lignin. By removing some or all of the lignin, and then doing other processing, they’ve made wood white like Styrofoam, transparent like glass, and spongy like rubber. They have also compressed the material to make Super Wood that is stronger than steel. Now, they have made wood that is moldable.

Hu: In order to achieve this shape we’ve come up with a very unique process. First we remove some of the lignin inside the wood. And then we fully dry it.

Patel: As the wood dries, the cell walls contract. Wood also has hollow fibers and big open channels, called vessels, all of which close up as the material dries.

Hu: And then it’s very dry and very thirsty for water. And you put it in water and it sucks water very quickly. And this is the fun part. When you put the wood into water, the vessels will open up very quickly, but the fibers are small and they don’t have enough time to respond and by that time you’ve taken the wood out already. At that time you have this wood with partially open vessels, closely packed fibers, and allows you to have enough strength to bend.

Patel: The cells walls also expand rapidly and take on an accordion-like wrinkled structure. These wrinkles, and the space created by the partially open vessels allow the wood to be compressed and stretched. And the closely packed fibers give it enough strength to bend. The researchers could fold the wood, roll it up, and mold it into different shapes. The material did not break when folded and opened up over 100 times. The work could open up new uses of wood, Hu says.

Hu: For structural applications, there’s a range of applications. You can go from furniture to buildings to vehicles to even airplanes.

Patel: That is, to replace plastic and steel parts with sustainable, biodegradable wood.  This work was published in a recent issue of Science (doi: 10.1126/science.abg9556). My name is Prachi Patel from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Thank you for listening.