The Research On Property And Application Of Organic-Coatings For The Conservation Of Colored Cultural Heritage

There were a lot of reports on the stability of polymeric organic-coating materials. The changes of molecular structures, degradation depth, physical and chemical properties on the photo-degradation or thermal-degradation of these materials were detected by XRD, SEM and FTIR etc. Traditional requests for colored relic protection materials with a view to some basic requirements such as color, transparence and original state etc. However, there was little systemic, scientific and complete research on polymeric materials' photo-stability, especially researched for colored relic protection. Therefore, the ageing phenomenon happened, the surface of relics would yellow, dapple and shed off, the protective materials for colored relics were required with the excellent photo-stability.Eleven polymeric materials' degradation process and degradation mechanism were systematically studied by attenuated total reflection-Fourier transform infrared spectroscopy (FTIR- ATR). The results indicated that the changes of infrared spectra of these materials were different and the quantitative analysis results were not the same. Especially molecular structure changes for poly(vinyl-acetic acid) , MDI-polyurethane, polyurethanes and poly (acrylic acid) varnish were larger, while those of Primal AC33, B72, organic-silicon and UV326 modified B72 were smaller, which had the favorable ageing property.The color determinations for different pigments protected by these protective materials before and after ageing were investigated by a spectrophotometer, from which we can see that the changes for epoxy-resin and poly(vinyl-acetic acid) were larger than for other protective materials with the time of ageing. And what is more important for same protective material, different changes happened in different pigments. The changes of red lead and cinnabar were larger than those of other pigments. The reason was that different pigment absorbed different wavelength photons, which would complete the transition of the ground state to the excited state. Photo-irradiation changed the molecular structure and component of pigment, made the rupture of the chemical bond, and then lead the color change.Nowadays there is scarcely report on quantitative analysis adhesive strength of protective materials. We refitted a domestic instrument to the adhesive strength testing apparatus. The results indicated all materials after ageing enhanced the adhesive strength of pigments. For different protective materials, the degree of improvement was different. The adhesive strength of PrimalAC33, modified B72 and B72 was comparably better, followed the epoxy-resin, organic-silicon and poly(vinyl alcohol), the worst was that of poly(vinyl acetic acid), MDI-polyurethane, polyurethane and poly(acrylic acid) varnish. For different pigments, the adhesive strength in cinnabar and red lead were better than that in malachite and azurite, which related to the pigments' specialty, granularity, bonding force between pigment and protective materials, etc.B72 and B72 modified with UV326 were applied for protecting colored relics slice. Color determinations and adhesive strength were investigated by the spectrophotometer and the adhesive-strength testing apparatus, respectively. The results indicated that the color change of the modified B72 was less than that of B72, and the adhesive strength was higher in the modified B72, from which we could concluded that adding UV-absorber 326 to B72 reduced the ratio of the photo degradation and had the excellent resistance function to the photo irradiation.Thermal degradation experiment was adopted for effectively estimating the service life at room temperature of B72 and the modified B72. It could be estimated that the life length of B72 and the modified B72 were 10.65 years and 12.80 years respectively, which provided the scientific evidence for relic conservation.In conclusion, with the aim of determining the photo-oxidative stability of protective materials, the molecular structure changes, color determinations and adhesive strength were investigated, from which we picked out B72 and modified B72 with the excellent photo-oxidative stability into protecting the colored relics, the changes of color and adhesive strength were tested. From these experimental results, we concluded that adding UV-absorber 326 to B72 reduced the ratio of the photo-degradation. The UV-326 converted the ultraviolet into the harmless energy and had the excellent resistance function to the photo-irradiation. In all, the modified B72 was suitable to replace B72 and would be widely employed as the protective material in the relic conservation.