Strong/Stiff Exterior and Elastic Interior: An Effective Biomimetic Topological Structure for the Consolidation of Waterlogged Wooden Archaeological Relics during Dehydration

Waterlogged wooden archaeological relics are prone to lose their dimensional and mechanical stability during dehydration, thus developing a green/effective strategy for consolidating a waterlogged wood upon its drying has drawn tremendous attention. Inspired by the specific topological structure and superior mechanical properties of human bone, we reported an environmentally friendly biomimetic consolidation method for restoring the waterlogged wood in this work. Briefly, branched PEI (poly(ethylenimine)) molecules were first incorporated into the waterlogged wood matrix by submerging to formulate a spongy interior, mimicking the structure of cancellous bone; then, GA (glutaraldehyde) solution or BDDE (1,4-butanediol diglycidyl ether) solution was sprayed onto the surface of a PEI-treated sample to form a dense exterior, mimicking the structure of cortical bone. Through two systematic orthogonal experiments, we identified the feasibility of this strategy and screened out the optimum feeding composition of the three reagents (10 wt % PEI, 6 wt % GA, and 3 wt % BDDE). As to targeted samples (10 wt % PEI + 6 wt % GA and 10 wt % PEI + 3 wt % BDDE), their dimension shrinkage rates along the X-, Y-, and Z-axis were all below or close to 3%. To figure out whether the rationale behind this strategy fitted well with our theoretical assumption, we first investigated the composition and structure of the BDDE/PEI- and GA/PEI-treated waterlogged wood samples through scanning electron microscopy (SEM), Fourier transform infrared spectrum (FT-IR), thermogravimetric–differential thermal (TGA–DTA) coupling tests, etc. and proved their biomimetic structure. Next, we explained the consolidation mechanism of this method by analyzing the crystalline phase and mechanical properties of the BDDE/PEI- or GA/PEI-treated samples. We thought that PEI induced the noncovalent cross-linking and BDDE- or GA-induced covalent cross-linking-mediated ordered arrangement of cellulose along different planes at the edge and middle of the waterlogged wood, respectively, therefore constructing a strong/stiff exterior and an elastic interior. Because of this specific biomimetic structure, the BDDE/PEI- or GA/PEI-treated waterlogged wood demonstrated simultaneously high strength, stiffness, and mechanical buffer capability and therefore could resist shrinkage stress and maintain high dimensional stability upon drying.