Rapid Processing of Whole Bamboo with Exposed, Aligned Nanofibrils toward a High-Performance Structural Material

Abstract

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.

Delignified Wood from Understanding the Hierarchically Aligned Cellulosic Structures to Creating Novel Functional Materials: A Review

“…It is common for DW-based materials to be described as an environmentally friendly alternative to conventional materials for certain products and devices. [164][165][166][167] This idea is based on the utilization of wood, which is undoubtedly environmentally friendly and sustainable. However, in the manufacturing of DW-based materials, the delignification process, utilization of various impregnating polymers, and manufacturing process of the final products (e.g., transparent wood) are not ecologically benign.…”

“…Furthermore, this work demonstrated the top‐down scalable method. The same research group reported [ 164 ] the fabrication of lightweight densified bamboo structural materials with an additional step of microwave treatment after delignification to drive water out of the delignified bamboo structure without altering the aligned nanocellulose's structural integrity. After hot densification, the modified bamboo reached a density of 1.0 g cm −1 with exceptionally high specific tensile strength of 560 MPa cm 3 g −1 .…”

Exploratory study into possible applications of Asian knotweed

“…In many Asian countries, natural bamboo is used to build houses, scaffolding and the like. Research by Chen et al (2020) shows that the mechanical properties of bamboo can be improved by pre-processing to increase its range of applications. The pre-processing consists of two stages -a shared delignification followed by microwave heating.…”

Investigation of the Release Mechanism and Mould Resistance of Citral-Loaded Bamboo Strips

“…Following the 'carbon neutral' goal of the Paris Agreement, the global market demand for low-carbon materials has been increasing [1,2]. As a natural low-carbon material, bamboo offers the advantages of sustainable logging and utilisation, high strength to weight ratio, high strength, and biodegradability [3][4][5]. It is not only commonly used in the construction, furniture, and interior decoration industries but also has significant application prospects in the aerospace domain [6][7][8][9].…”