Improving the Conservation Performance of Ivory Fossils by Constructing the QCB-n-HAP Composite System: A Case Study of Ivory Fossils in the Collection of the Songzi Museum

To mitigate cracking, pulverization, and surface spalling in ivory fossils caused by long-term burial and environmental erosion, we developed an organic–inorganic composite system based on quaternized carboxymethyl chitosan and nano-hydroxyapatite (QCB-n-HAP). Applied to degraded specimens from the Songzi Museum, this system significantly improved structural stability and long-term preservation. By systematically reviewing the technical limitations of existing conservation materials and accounting for the specific deterioration characteristics of the target fossils, we established a standardized restoration protocol following a “disease diagnosis–material matching–layered reinforcement–performance characterization” workflow. The QCB-n-HAP composite exhibits excellent interfacial compatibility with the organic components of ivory, enabling deep penetration and pore filling through synergistic hydrogen and covalent bonding. It overcomes the shortcomings of both conventional organic and inorganic materials, while offering favorable reversibility and durability. After treatment, the compressive strength of the fossil samples increased by 68%, crack bonding strength reached 1.2 MPa, and the mechanical property retention rate remained 92% after accelerated aging equivalent to five years of environmental exposure. The reinforcement layer could be completely removed without residue by mild treatment with dilute acetic acid for 30 min. This approach provides a novel technical strategy and theoretical reference for the conservation of Quaternary organic paleontological fossils.