Synthesis, testing and application of moisture-curable polyurethane as a consolidant for fragile organic cultural objects

Abstract

To preserve fragile organic cultural objects in humid archaeological excavation sites, a moisture-curable polyurethane (MCPU) as a consolidant was synthesized and employed. Relevant instruments were utilized to test properties such as colour, transmittance, mechanical properties, hydrophobicity and ageing resistance. Furthermore, residues of Zhusi, a vessel made of plant fibres excavated in archaeological sites, were consolidated. The results illustrated that MCPU cured for 12 h formed transparent, colourless and flexible films. The transmittance of the cured films was over 80% in the wavelength range of 400–1100 nm. The tensile strength was 1.419 MPa, and the elongation rate was more than 1500%. The thermal ageing equation is lg τ = 5383.6639/T − 12.5728 (τ is the lifetime of the samples in hours and T is the thermodynamic temperature in K), meaning that at 15 °C, its lifetime is approximately 147 years. The Zhusi consolidation experiment showed that the mechanical properties were improved and deteriorated fibres were perfectly bonded, and the separated and broken fibres formed a complete structure without significant variation in appearance. Therefore, MCPU can be used as a consolidant for fragile organic cultural objects in very humid archaeological excavation sites. This work solves the problem of conservation of fragile organic objects in humid environments.