Silica-magnetite nanocomposite for hydrothermally softened bamboo: Catalytic lignin oxidation and multi-scale mechanical enhancement

The hydrothermal bending of bamboo, while enabling curved forms, induces problematic softening characterized by reduced stiffnes and increased creep, limiting structural applications. This study investigates a nanocomposite treatment where Moso bamboo is impregnated with amorphous silica and magnetite (Fe 3 O 4 ) nanoparticles, which catalyze lignin oxidation. A multi-scale analysis (DMA, nanoindentation, XPS, FTIR, XRD, three-point bending) compared untreated (B-0), hydrothermally treated (B–W), and treated (B-M) bamboo. The B-M composite achieved a macroscopic elastic modulus of 29,311 MPa—11% higher than B-0 and 26% higher than B–W—while providing a remarkable balance of high stiffness and reduced creep under the tested short-term conditions (20 min at 45 °C). Nanoindentation and XRD showed this enhancement is not due to higher cellulose crystallinity, but to two synergistic mechanisms: (i) mechanical reinforcement from silica infiltration into conductive tissues, and (ii) Fe 3 O 4 -catalyzed oxidation of lignin. XPS confirmed significant increases in carbonyl (+51%) and carboxyl (+40%) groups in B-M, strongly correlated with improved modulus (r = 0.98), toughness (r = 0.95), and flexural strength (140.5 MPa). Direct evidence of covalent Si– O –C bonding (Si 2p peak shift to 102.8 eV) confirmed chemical grafting. The treatment also provided hydrolytic stability: after re-immersion, B-M retained 73% of its stiffness advantage over B–W with 20% less creep. This approach effectively counteracts hydrothermal softening, offering, high-performance bamboo for structural applications.