High strength, superior fire retardancy, and dimensional stability of cellulosic hybrids

Abstract

Bamboo, a rapidly growing plant known for its remarkable strength-to-weight ratio and eco-friendly qualities, finds extensive applications in decorative construction materials and glue-laminated beams. However, the dimensional instability and flammability of natural bamboo limit its application range. In this study, a series of environmentally friendly methods are devised to produce functional bamboo hybrids possessing exceptional strength, excellent dimensional stability, and flame-retardant properties. These hybrids are created through bamboo delignification, in situ mineralization of CaCO₃, and hot pressing after impregnation with phenolic resin. The highly aligned and densified nanocellulose stacking between hydrogen bonds of the bamboo hybrids results in the high tensile (583.6 MPa) and flexural strength (374.8 MPa), as well as an excellent specific strength of 486.3 MPa (cm³ g)⁻¹. This value is significantly greater than those of other reported bamboo materials and most structural materials (e.g., steels and alloys). The favorable dimensional stability of the as-prepared bamboo hybrids is mainly associated with the impregnation of phenolic resin and mineralization of CaCO₃ with the improvement of hydrophobicity. Compared to natural bamboo, the total heat release and smoke production rate of the bamboo hybrid were reduced by 37.7% and 50.0% respectively. This study provides a green processing strategy to manipulate and functionalize the microstructure of bamboo into high strength, superior fire-retardancy, and dimensional stability in various applications, such as structural construction, aerospace, and automotive manufacturing.