Removable/fluorescent adhesive made by melamine-formaldehyde cross-linked polyvinyl alcohol and its repair application in artifacts

Nowadays, most of adhesives used for artifacts are colorless and non-removable resins, which makes it difficult to detect repaired location and cause some damage to the artifacts. Herein, we devolved the removable and fluorescent adhesive with melamine-formaldehyde (MF) resin cross-linked polyvinyl alcohol (PVA). The polar sensitive fluorescent dye of 8-anilino-1-naphthalenesulfonic acid (ANS) was encapsulated in the branched MF pre-polymer, and the obtained ANS@MF was employed as cross-linker to prepare cross-linked PVA (ANS@MF-PVA) to yield a series of water-soluble fluorescent adhesives. The obtained ANS@MF-PVA adhesives are colorless and transparent and show strong blue-green fluorescence under UV excitation, enabling it easy to detect their precise location on artifacts. Compared with PVA adhesive, the fluorescent ANS@MF-PVA adhesives present a better thermal stability and enhanced mechanic performance. ANS@MF-PVA samples all show higher adhesive strength (298.25 N, 0.95 MPa to 466.63 N, 1.49 MPa) than pure PVA (201.25 N, 0.64 MPa), which is positively correlated with their MF content. The ANS@MF-PVA is applied to adhere the glass substrates, ceramics and pottery figurine, and demonstrated excellent fluorescence, easy removability, and high durability. We believe that the ANS@MF-PVA fluorescent adhesives will provide art conservators with a new tool to aid in the reconstruction or repair of artifacts.