Polymeric materials used for industrial design during XX century. Degradation study, structure/properties relations and conservations strategies

Polymeric materials have been extensively used in works of art and in design objects since last century. A large number of handmade and industrial objects, made of polymeric materials, represent today the development of 20th century society, and are conserved in museums and private collections. The polymeric material, if not suitably protected, may rapidly deteriorate: the knowledge about the stability and condition (state of conservation, restoration and treatment) of such objects is still limited and only few examples of protocols for the investigation and management of these items are available. In the work carried out during this thesis, the conservation issues of the Triennale Design Museum of Milano have been thoroughly investigated. A selection of very famous objects has been chosen for the scientific examination on the basis of the most urgent conservation needs. The items of the museum have been studied and compared to other items coming from a private collection. Starting from selected case-studies, three different polymeric materials have been analysed -poly(vinylacetate), ABS and cellulose acetate - with the aim of achieving enhanced competences in the field of polymer degradation in museum environment. The goal of this thesis is to define and test a micro- and non-invasive protocol for polymer characterization and degradation assessment: vibrational spectroscopic techniques have proved to be suitable for the analysis of micro-samples of few mg and combination with innovative imaging techniques (Fluorescence Multispectral imaging, Fluorescence Life Time Imaging) has been used extensively to assess the degradation of polymers under mild artificial and natural aging conditions. The degradation of PVAc in natural ageing condition proved to lead to the deacetilation of the polymer and to its localised deep oxidation. The degradation patterns under photo and thermal-oxidative aging have been studied since the initial degradation steps, revealing differences in the degradation behaviour: the phenomenon is mainly a temperature driven process, which leads to increasing unsaturation content. The presence of the plasticiser (DBP) enhances the deacetilation of the polymer and modifies the degradation patter of the polymer. Design objects made of ABS present diffuse phenomena of degradation of the rubber constituent and mechanical failure is a diffuse conservation problem. The assessment of the molecular modification have been implemented by the systematic analysis of specimens under mild and controlled aging treatment: ABS resin have been proved to be stable in thermal-oxidative conditions, while the photo-oxidative treatment leads to rapid degradation of the rubber phase, with formation of increasing content of oxidised groups. The analysis of cellulose acetate case-study revealed slight degradation phenomena affecting the internal side of the lamp. The analysis of the aged specimens revealed that cellulose acetate is stable under thermal-oxidative aging and only a partial degradation have been evidenced by spectroscopic data; on the other hand the photo-oxidative treatment leads to a greater modification of the polymer. The correlation between FTIR, NMR and fluorescence data permits the comprehension of the degradation phenomena of the studied polymers. Fluorescence multispectral imaging has proved to be a reliable method for the monitoring activity on site for polymeric works of art, granted that the degradation pathway of the polymeric material had been thoroughly elucidated.