Supervisor: Prof. Colombini Perla, Prof. Frediani Pier
Title: Synthesis and Characterization of Polyesters for Applications in Restoration and Conservation of Cultural Heritage.
Abstract: Cultural Heritage, particularly stone monuments exposed to the outdoor environment, are subjected to deterioration by natural causes (light, water, wind, microorganism) and by anthropological ones (pollutants like carbon dioxide, sulphur and nitrogen oxides). Recently, the use of bio-renewable materials, like polyesters obtained from natural sources, is increasing responding to environmental issues. However, the application of polyesters in the conservation field is still restricted and its expansion is limited by the lack of suitable materials: our aim is to synthesize a new class of conservation materials made from bio-renewable feedstocks, possessing high protective capability and durability. Polylactic acid (PLA) is one of the most promising polymer in this class, due to its high mechanical strength and workability easiness and the fact that it can be mass-produced from agricultural byproducts. Lactide (lactic acid cyclic dimer) polymerization to PLA can be catalyzed by metal complexes in the presence of oxidryl and amine compounds as initiators. The product characteristics can be controlled through functionalization, either by employing a specific initiator or by using substituted lactides, containing the desired functional group. While with the former method the functionalization is restricted only to chain ends, the latter lead to a more profound modification of PLA structure as the functional group is distributed along the chain; the proprieties changes can be tuned by copolymerization of lactide with variable amount of functionalized monomer. Our initial interest is focused on the improvement of protection capabilities (with the introduction of UV-visible chromophores and hydrophobic groups), light and thermal stability (benzotriazole, HALS) and resistance to biodeterioration (quaternary ammonium compounds). The polymers will be characterized by means of several techniques (NMR, GPC, DSC, Py-GC/MS, IR, UV, Vis and fluorescence spectroscopies) and specific tests will be conducted to evaluate the performance in conservation (water absorption, color change, accelerated aging chamber).