Halloysite-based geopolymerization for the mineralization and stabilization of porous wood

Wood mineralization via geopolymerization presents a promising approach to enhance the stability, mechanical performance, and fire resistance of porous wooden substrates. In this study, archaeological wood samples were impregnated with halloysite nanotubes and subjected to alkaline treatment to promote the in situ formation of a geopolymeric aluminosilicate network. The effects of the treatment were evaluated through dimensional stability measurements, Dynamic Mechanical Analysis (DMA), Thermogravimetric Analysis (TGA), flame exposure tests, FTIR spectroscopy, pH monitoring, and colorimetric investigations. Geopolymer-treated wood exhibited superior dimensional stability and reduced compressibility compared to both untreated and halloysite-treated wooden samples. TGA and flame exposure tests evidenced enhancements of thermal stability and flame resistance. Interestingly, the geopolymer-treated woods formed a stable char avoiding complete volatilization during TGA experiments and flame resistance tests. FTIR analysis showed the loss of characteristic halloysite bands commonly used as indicators of its structural transformation during alkaline activation, alongside partial retention of native wood functional groups. Furthermore, the alkaline activation of halloysite provided a buffering effect during acidic aging, mitigating pH shifts and reducing color changes. Overall, halloysite impregnation combined with geopolymerization results in hybrid wood-inorganic materials that mimic natural mineralized woods, offering enhanced structural, thermal, and chemical resilience, and representing a versatile approach for the development of functional wood composites.