Preparation, characterization and application of fluorinated acrylate copolymer emulsion for the conservation of stone building heritages in Putuo Zongcheng Temple, China

Abstract Recently, the stone building heritages in Putuo Zongcheng Temple are experiencing a certain degree of weathering damage, which mainly manifests in the blistering, fissuring, flaking and detachment of the carved balustrades of stone bridge, the footings of wall, the front paws and pedestals of stone lions. To prevent the deterioration of the stone building heritages, the fluorinated acrylate copolymer emulsion was successfully prepared with ethyl metrhacrylate, n-butyl acrylate and 2,2,3,4,4,4-hexafluorobutyl methacrylate as monomers. The structure and surface morphology characteristics of this copolymer were described the Fourier Transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM), respectively. The FTIR spectra confirms that the adopted monomers have been involved in during the copolymer polymerization process. The SEM images reveal that the surface of the prepared copolymer is obviously more dense, compact and smooth than the porous structure of stone building heritages. The ageing resistance of the copolymer was quantitatively studied by the ultraviolet aging test, the contact angle and imbibition spontaneous tests were adopted to estimate the wettability alteration of the copolymer emulsion for the stone samples. Results show that the mass loss rate of the prepared copolymer increases rapidly and then tends to be stable when irradiated by ultraviolet light. And the fluorinated copolymer with 16.65% HFMA content possesses the optimal ageing resistance and the superb hydrophobicity. The contact angles of the coated stone samples range from 91.90o to 119.80o, which are all larger than 18.80o-69.05o of the un-coated samples. Similarly, the spontaneous imbibition test also ensures that, both the maximum water absorption capacity and the imbibition equilibrium time of the samples treated by this copolymer emulsion are lesser. Considering the influence of water on rock weathering, the fluorinated copolymer emulsion coating is an potential method to avoid the degrading of stone building heritages, because it depresses the infiltration of water and then avoids or weakens the dissolution effect, salt crystallization, water absorption swelling and freeze-thaw weathering.