Synthesis and Application of the Moisture-curable Polyurethane as a Consolidant for Cultural Objects
Supervisor:wang li qin
The environment of archaeological sites such as tombs and caves is usually very humid,and the relative humidity is generally above 90%.However,after a long period of burial,organic cultural objects are extremely fragile.When the fragile objects are touched,they will be broken,blown,and even cannot be extracted from the tombs.Therefore,rescuing these fragile organic cultural relics in the high-humidity environment of the archaeological sites is the primary task of cultural object preservation.These fragile cultural objects are usually transferred to the museum by means of reinforcement and re-extraction.There are many kinds of reinforcement materials,but the commonly used reinforcement materials are mainly used for normal atmospheric humidity.In high-humidity environments,these materials have a series of problems such as hard curing,no curing,whitening of cured materials or poor compatibility with organic cultural objects.Reinforcing the fragile organic cultural objects has become a bottleneck problem that restricts the preservation of archaeological sites.At the same time,with the rapid development of cultural heritage preservation in recent years,the urgency to strengthen and protect these fragile organic cultural objects is increasing.In order to solve the above problem of cultural object preservation,this paper has used the moisture-curable polyurethane(MCPU),which can cure with the moisture in the air,to strengthen the fragile cultural objects.The article designed,synthesized and characterized the MCPU reinforcement materials used in high-humidity environment,and improved aging resistance and mold resistance.On this basis,it was applied to the preservation of fragile cultural objects in lab and archaeological excavation sites,providing a new kind of materials for the preservation of fragile cultural objects.The main research contents include:(1)Synthesis and characterization of single component moisture-curable polyurethane(SCMCPU).The orthogonal test was designed to synthesize a SCMCPU prepolymer under the catalysis of dibutyltin dilaurate(DBTDL)using isophorone diisocyanate(IPDI)and polyethylene glycol 600(PEG600)as main reactants.The analyses of the morphology,structures,mechanical properties and aging resistance of the moisture-cured polyurethane prepolymer solution and cured film showed that the prepolymer solution in ethyl acetate was colorless,transparent,stable,and could be curable in a relative humidity from 30% to 100%.At the same time,the film has excellent mechanical properties,but it is easy to become yellow under ultraviolet light and heat aging conditions.(2)Synthesis and characterization of anti-aging moisture-curable polyurethane(AAMCPU).In order to improve the light and heat aging resistance of the moisture-curable polyurethane film,1 wt.% of bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate was added to the SCMCPU prepolymer system.The modification mechanism of HALS 770,the morphology,mechanical properties and aging resistance of the modified materials were discussed.The results showed that HALS 770 can be converted into renewable nitroxide radicals,capture the radicals produced during the aging process of MCPU and provide long-term stability.The isocyanate groups in the prepolymer reacted with HALS 770 to promote the curing of the MCPU prepolymer,which reduced the curing activation energy and shortened the curing time.The AAMCPU film is colorless and transparent,and the mechanical properties and water resistance have not changed significantly after modification.However,the addition of HALS 770 improves the light resistance and heat aging of the moisture-curable polyurethane film.(3)Synthesis and characterization of anti-mold moisture-curable polyurethane(AMMCPU).In order to improve the mold resistance of the MCPU film,the addition of 1.5 wt.% of Pimafucin to the AAMCPU prepolymer improved the mold resistance of the original material.The AAMCPU film is not easy to breed microorganisms,but the anti-mold effect on the reinforced cultural objects needs to be improved.The AMMCPU has excellent antimould effect,and the microbial reproduction was completely inhibited within 30 days after the addition of Pimafucin.The antimould effect is obvious.(4)Study on the preservation effects of cultural objects in high humidity environment.In order to explore the reinforcement process of MCPU and evaluate the reinforcement effect of the fragile excavated cultural objects at the archaeological site,the carbonized xuan paper samples,unearthed bamboo stalks,bone relics,and wooden artifacts were reinforced in a high-humidity environment using the MCPU.The reinforcement of the excavated lacquer ware was carried out at the archaeological excavation site.The results showed that even in a high-humidity environment(100% relative humidity),after the use of the MCPU to reinforce the fragile artifacts,the reinforcing agent could form a film on the surface of the cultural relics and fill the inside of the cultural relics,so that the reinforced cultural objects formed a whole,which increased the mechanical strength of the preserved objects and did not obscure the surface information of original objects.This paper firstly synthesized and characterized the MCPU for the reinforcement of fragile cultural objects that could be used in high-humidity environment,which achieved the effective extraction and protection of fragile cultural objects at the archaeological excavation site.The study solved the problem of the reinforcement of fragile cultural objects in high humidity environment,supplemented and enriched the cultural object protection material system and strengthened the scientific preservation of cultural objects.