In situ strategy to overcome the trade-off between deep penetration and high-density crosslinking in adhesives for painted architectural relics conservation

Abstract

Long-term conservation of fragile painted architectural relics demands adhesives that achieve both deep penetration and a high-density crosslinked network. Nevertheless, their simultaneous achievement presents a fundamental challenge. This inherent trade-off originates from the low solubility of highly crosslinked polymers, which impedes penetration and compromises consolidation efficacy. In this study, an efficient in situ crosslinking strategy is proposed to break this trade-off by employing a thiol-functionalized polyorganosiloxane precursor adhesive. This precursor achieves deep infiltration, followed by crosslinking via synergistic solvent-induced self-assembly and Fe³ ⁺ catalysis. Theoretical calculations corroborate that this synergy reduces the energy barrier for disulfide bond formation by 35.4%, enabling controlled in situ crosslinking without damaging painted architectural relics. Moreover, the adhesive demonstrates robust cohesive strength, enabling consolidated samples to maintain stability at 85% RH. These capabilities enable the adhesive to achieve not only stable consolidation but also effective restoration for fragile painted architecture. By modulating the crosslinking density within the flaking pigment layers, the adhesive reduces their elastic modulus by 99.8%, thereby plasticizing the brittle paint and facilitating successful reattachment. The restored regions retain structural integrity even after 1500 h of dry-wet cycling, demonstrating long-term durability. This in situ crosslinking strategy provides an avenue for integrated conservation of cultural heritage.