Formation of an Organic–Inorganic Hybrid Network Structure by In Situ Polymerization of Silicone to Protect Cultural Heritage Stonework

Yujia Memorial Archway in Jixian County, Hunan Province, can be considered a typical weathered stone artifact. Different ratios of 3-glycidyl ether propyl trimethoxy silane (GPTMS), 3-amino propyl triethoxy silane (ATS), and hydroxy silicone oil (PDMS-OH) were used to achieve in situ reinforcement of representative weathered stone samples, considering the permeability of the reinforcing material, its compressive strength, and weatherability. In a preliminary assessment, a reaction mechanism of interpenetrating hybrid organic–inorganic networks that can be bonded to the interface between the reinforcement material and the stone artifact is proposed. The amino group attacks the epoxy group by nucleophilic reaction to open the ring; a dehydration condensation occurs to form an epoxy organic network structure, while the silane hydrolyzes and condenses to form a Si-O-Si inorganic network structure. More importantly, the addition of PDMS-OH increases the flexibility and hydrophobicity of the material, further improving overall performance. A multiangle and multilevel comprehensive analysis of the composition, structure, hydrophobicity, macroscopic morphology, and microscopic morphology of the composites was carried out using Fourier transform infrared spectroscopy, Raman, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction, and other techniques. The restoration materials were applied to the weathered stone samples, and the restoration effect was evaluated for the permeability, compressive strength, water absorption, acid resistance, salt resistance, and freeze-thaw resistance of the strengthened samples. The results show that a GPTMS:ATS:PDMS-OH ratio of 14∶7∶9 is the best and can be applied to the in situ reinforcement of dolomite rocks.