Data di Pubblicazione:
2012
Citazione:
MICROORGANISMS VS. SYNTHETIC POLYMERS. ECOLOGY AND BIODEGRADATION / L. Giacomucci ; supervisor: F. Cappitelli ; coordinator: D. G. Daffonchio. Universita' degli Studi di Milano, 2012 Jan 26. 24. ciclo, Anno Accademico 2011. [10.13130/giacomucci-lucia_phd2012-01-26].
Abstract:
Despite synthetic polymers have been considered little or no deteriorable for many years, now we know they can undergo to chemical, physical and biological damage. Effects of biological degradation on polymers include masking of surface properties due to the presence of microorganisms inhabiting surfaces, embrittlement and loss of stability due to changes in chemical structure of polymers, presence of cracks and swellings due to penetration of microorganisms into the polymer matrix and changes in polymer colour due to excretion of microbial pigments. Microbial deterioration depends on the constitution and the properties of polymer materials as well as environmental conditions. Millions of tons of synthetic polymers used as adhesives, binders, coatings, inks, etc., are produced worldwide every year. In 1997 the worldwide paint and coatings industry represented a mature 50+ billion dollar market and synthetic polymers used in paint and coating industries account for approximately 45-55% of the worldwide decorative market. Deterioration of varnishes and binding media results in chemical changes that lead to an increase in the insolubility and polarity of the material, a reduction of the strength, and a change in colour, among others. As biodeterioration of synthetic polymers seriously compromises the adhesion and durability of the paint as well as its decorative/protective function, identification of the cause of synthetic polymer biodeterioration is of great importance.
Although biodeterioration of synthetic polymers in objects during their lifetime should be avoided to preserve the object function, synthetic polymer materials should be susceptible to degradation once they are disposed of and treated as waste. The major ingredients of paints are the pigment, a material which provides colour, and the binding medium, a film-forming material in which the pigment particles are dispersed and forms the matrix that hardens and binds the pigments on the painted surface. All the synthetic polymers used as paint and coatings binders are belonging to different chemical classes, the most important being acrylics, polyvinylacetate and nitrocellulose-alkyds. Microorganisms can assimilate and/or degrade these synthetic polymers because their chemical bonds are the same as those found in the natural polymeric matter, which is generally easily degraded. Bioremediation is widely used for the clean-up of environmental pollutants using microorganisms and could be successfully applied for the removal of synthetic polymers, including those present in paint and coating formulations.
The aims of this PhD project were to study both aspects of synthetic polymer biodegradation, in particular:
• Characterise the microbial community associated to biodeterioration of an acrylic polymer used as protective and consolidant, in order to identify microorganisms potentially active against synthetic polymers.
• Study bacterial degradation of nitrocellulose in order to develop a bioremediation process to remove nitrocellulose-based paints.
Chapter 3 reports a case-study about how a microbial community changes in the presence or in the absence of an acrylic polymer used as consolidants. Synthetic polymers have been widely applied as consolidants and protective in cultural heritage field for the treatment of objects and buildings to prevent further deterioration. The long-term efficiency of the consolidative/protective treatments was believed influenced mainly by chemical and physical agents (e.g. UV light and temperature) and therefore lots of synthetic polymers have been used in cultural heritage conservation without testing them against biological deterioration. As a result, treated objects are sometimes in worse conditions than untreated objects and, moreov
Tipologia IRIS:
Tesi di dottorato
Keywords:
artistic tiles ; cyanobacteria ; coloured alterations ; endolithic growth ; synthetic polymers deterioration ; nitrocellulose ; paint ; microbial degradation ; Desulfovibrio desulfuricans ; sulphate-reducing bacteria ; nitrite reductase ; dissimilatory nitrite reduction to ammonia
Elenco autori:
L. Giacomucci
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