Coagulation Strength of Some Adhesives for Conservation of Cultural Heritage

The coagulation strengths of some commercial alkoxy silanes for the conservation of stone cultural assets were compared using OH100, OM25 and OM50 (Wacker Chemie AG., Germany) and TOT (Tanaka Geological Corp., Japan). Compression tests of solidified model sand were conducted to measure the coagulation strength. The fracture forces for OM50 and OM25 were higher than those for OH100 and TOT, which indicate higher coagulation strength for OM50 and OM25. Thermogravimetric analysis revealed that all the alkoxy silanes examined were a mixture of monomeric alkoxy silane and its oligomer, where the order of oligomer content was OM50 > OM25 > OH100 > TOT. From ¹H pulse nuclear magnetic resonance analysis indicated that the order of molecular mobility in the solidified alkoxy silanes was TOT > OH100 > OM25 > OM50. The degree of crosslinking in the solidified alkoxy silane thus increased with the oligomer content. For this reason, the fracture force determined from compression tests, i.e., the coagulation strength, was higher for OM25 and OM50 than OH100 and TOT. The addition of a small amount of epoxy resin to OM50 was effective to increase the coagulation strength due to a lower crosslinking density caused by insufficient curing of the epoxy resin. The introduction of ductility to the adhesive layer was thus effective to develop strength.