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Long-Term Protection Efficiency of Biodegradable Polymer Treatments on Limestone
(Izmir Institute of Technology, 2019) Kaplan, Zişan; Böke, Hasan; Sofuoğlu, Aysun; İpekoğlu, Başak
Synthetic polymers can be replaced by biodegradable ones as adhesive, water repellents and consolidants in stone conservation to preserve historic buildings from further deterioration. In this study, the long-term stabilities of two biodegradable polymers, polyhydroxybutyrate (PHB) and poly-l-lactide (PLA) and an acrylic polymer (Paraloid B72), which are commonly used in conservation works of artefacts, were evaluated on limestone through an UV lamp-weathering chamber. Chemical and morphological changes induced by accelerated weathering test were followed by Fourier Transform Infrared spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM) analysis. The protection efficiencies of the polymers were determined by following the changes in the color, capillary water absorption and static contact angle on the limestone surfaces in accordance with CEN standards developed by the European Committee of Standardization (CEN) for conservation of cultural property. PHB, PLA and Paraloid B72 coatings significantly increased hydrophobicity, decreased capillary water absorption and caused negligible change in the color of the limestone. All polymers showed chemical, physical and optical changes under accelerated weathering conditions. Paraloid B72 decomposed by the reduction of molecular weight, decomposition of ester group and formation of gamma lactones and hydro peroxides. PHB and PLA decomposed with formation of CO2 and hydro peroxide, hydrolysis of ester groups and reduction of the molecular weight. Chemical changes cause to etching, holes, voids, cracks and slight color differentiations on the coatings by chain scission, breaking of polymer bonds and formation of volatile gaseous products. Protection efficiencies of the PLA and PHB polymers almost same as that of the widely used acrylic polymer Paraloid B72. However, PLA and PHB seem to be promising polymers as protective agents due to their reversibility and biodegradability, low chromatic changes, good hydrophobic behavior and good stability to weathering in reducing the effects of outdoor exposure on limestone surfaces.
Conservation Approaches of Patina Formation on Marble and Travertine Surfaces in the Archaeological Sites
(Izmir Institute of Technology, 2017) Badur, Fulya; Böke, Hasan; Yalçın, Şerife Hanım
Patina, which is formed on the stone surfaces of historical buildings and monuments as a result of aging, is considered as a value of the building in the conservation of cultural heritage studies. It should be conserved on calcareous stone surfaces whether or not it represents protective characteristics, since it provides information about previous times. Within this respect, the determination of mineralogical composition, and microstructural and chemical characteristics of patina are critical for the conservation decisions. The aim of this study is to determine the characteristics of yellow patina formation on marble and yellow travertine surfaces to constitute a conservation approach in the archaeological sites. In this study, XRD, FT-IR, SEM-EDX, LIBS and TGA were used to determine the characteristics of yellow patina formation on marble and yellow travertine surfaces in Aizanoi, Aphrodisias, Sardes and Hierapolis. Analysis results indicated that yellow patina is mainly composed of calcium oxalate (whewellite or weddelite) minerals. CaO, MgO, Al2O3, SiO2, P2O5, K2O, SO3, FeO and Na2O were observed on the chemical analyses of the same samples. The results of LIBS and SEM-EDX showed that Ca increases, and other elements decrease from surface to the sound inner parts of the stone due to calcium oxalate and gypsum precipitation and clay deposition on the surfaces. The calcium oxalate patina forms a homogeneous film layer on calcite crystals. It is most likely formed by the reaction of calcite and oxalic acid produced by the biological formations on stone surfaces. It is colorless in original. The yellow color may be related with the FeO and clay deposition on the stone surfaces. The outcomes of the study proved the presence of a protective yellow patina formation on yellow travertine surfaces against the weathering effects of water which cannot be distinguished by naked eye. This patina presents same characteristics with the yellow patina on marble surfaces which should be conserved. The results of this study show that the determination of yellow patina is critical to keep irreversible cleaning interventions away from surfaces especially for the monuments that yellow travertine is used as building materials.

Phd Degree / Doktora

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