Anisotropic Nature of Lightweight Wooden Metamaterials with Mechanical/Thermomechanical Multistability

Abstract

Nanoengineered wood provides a renewable structural material with 3D micro and nanoarchitectures, exhibiting many beneficial characteristics such as being lightweight in nature, mechanically strong, eco-friendly, thermally insulation, and low carbon footprint. Most nanocellulose aerogels lack sufficient mechanical strength, while nanowood involves a trade-off between mechanical strength and insulation performance. Here, a nanowood-derived product with mechanical/thermomechanical multistability called a wooden metamaterial, which is ultrastiff yet lightweight, is designed and synthesized. The self-healing behaviors of cellulose nanofibrils originally present in the cell walls and their combination with microscale mechanical constraints are utilized to form directional porous frameworks (porosity ≥98%) and encapsulated empty fiber lumen in predesigned macroscopic architectures. The wooden metamaterials are lightweight, showing ultrahigh specific strength (207.7 MPa cm3 g−1), and ultrahigh anisotropy with an approximate factor of 4. Wooden metamaterials have overcome the mechanical/thermomechanical deficiencies of existing building materials and advanced aerospace thermal insulators, and have great potential for revolutionizing architecture and manufacturing industries, particularly as a lightweight, eco-friendly, scalable, energy-efficient, and cost-effective.