Synergistic in-situ reinforcement of lignin and adhesive for high-performance aligned bamboo fibers composites

To replace plastics with bamboo, it is necessary to develop renewable, lightweight, high-strength, damping, and vibration-reducing bamboo structural materials that can be applied in buildings, transportation, and mechanical engineering applications. Here, a low-cost and high-efficiency top-down method was designed for processing natural bamboo into a lightweight and high-strength aligned bamboo fiber composite. This composite used oriented bamboo fibers that had their lignin and hemicellulose removed, which were used as continuous reinforcement materials, and phenolic resin was used as the adhesive, followed by hot pressing. A highly-interwoven structure was formed by the penetration of the adhesive and the combination of strong hydrogen bonds and chemical bonds formed during hot pressing. This resulted in the high performance of the composite, which exhibited a tensile strength of 421.5 MPa, a bending strength of 211.19 MPa, and an impact toughness of 26.7 J/cm2, which were respectively 2.50, 2.09, and 5.7 times higher than those of natural bamboo. Due to its low density (1.08 g/cm3) and specific tensile strength of 390 MPa g−1 cm3, it was superior to commonly used engineering structural materials such as aluminum alloy, steel, and titanium alloy. It also exhibited excellent damping and vibration reduction performance (with the first three damping ratios of 0.75 %, 0.68 %, and 1.75 %) and dimensional stability (with a 24-h water absorption thickness expansion rate of 7.75 %). Due to its excellent mechanical properties and dimensional stability under wet and hot conditions, this composite is expected to replace nonrenewable synthetic materials as a green and sustainable engineering structural material. It may find applications in drone wings, wind turbine blades, and automotive manufacturing.