Lightweight
structural materials are critical in construction and
automobile applications. In past centuries, there has been great success
in developing strong structural materials, such as steels, concrete,
and petroleum-based composites, most of which, however, are either
too heavy, high cost, or nonrenewable. Biosourced composites are attractive
alternatives to conventional structural materials, especially when
high mechanical strength is presented. Here we demonstrate a strong,
lightweight bio-based structural material derived from bamboo via a two-step manufacturing process involving partial delignification
followed by microwave heating. Partial delignification is a critical
step prior to microwave heating as it makes the cell walls of bamboo
softer and exposes more cellulose nanofibrils, which enables superior
densification of the bamboo structure via heat-driven
shrinkage. Additionally, microwave heating, as a fast and uniform
heating method, can drive water out of the bamboo structure, yet without
destroying the material’s structural integrity, even after
undergoing a large volume reduction of 28.9%. The resulting microwave-heated
delignified bamboo structure demonstrates outstanding mechanical properties
with a nearly 2-times improved tensile strength, 3.2-times enhanced
toughness, and 2-times increased bending strength compared to natural
bamboo. Additionally, the specific tensile strength of the modified
bamboo structure reaches 560 MPa cm3 g–1, impressive given that its density is low (1.0 g cm–3), outperforming common structural materials, such as steels, metal
alloys, and petroleum-based composites. These excellent mechanical
properties combined with the resource abundance, renewable and sustainable
features of bamboo, as well as the rapid, scalable manufacturing process,
make this strong microwave-processed bamboo structure attractive for
lightweight, energy-efficient engineering applications.