Sustainable high-strength and dimensionally stable composites through in situ regulation and reconstitution of bamboo-derived lignin and hemicellulose contents

The development of modern construction and transportation industries demands increasingly high requirements for thin, lightweight, high-strength, and highly tough composite materials, such as metal carbides and concrete. Bamboo is a green, low-carbon, fast-growing, renewable, and biodegradable material with high strength and toughness. However, the density of its inner layer is low due to the functional gradient (the volume fraction of vascular bundles decreases from the outer layer to the inner layer), resulting in low performance, high compressibility, and significant amounts of bamboo waste. We utilized chemical and mechanical treatments of bamboo's low-density, low-strength inner layers to create lightweight, ultra-thin, high-strength, and high-toughness composites. The treatment included the partial removal of lignin and hemicellulose to alter the chemical components, followed by mechanical drying and hot pressing. The treated bamboo had 100.8 % higher tensile strength (150.35 MPa), 47.7 % higher flexural strength (97.67 MPa), and 132.0 % higher water resistance and was approximately 68.9 % thinner than the natural bamboo. The excellent physical and mechanical properties of the treated bamboo are attributed to the contraction of parenchyma cells during delignification, the interlocking due to the collapse of parenchyma cells during mechanical drying, and an increase in the density of hydrogen bonds between cellulose molecular chains during hot pressing. Our research provides a new strategy for obtaining sustainable, ultra-thin, lightweight, high-strength, and high-toughness composite materials from bamboo for construction and transportation applications.