| Abstract |
During the 1930’s, synthetic polymers were introduced to the conservation of cultural artifacts due to their high corrosion resistance and their optical properties which are comparable to those of traditional natural resins, since they are the first materials used as varnishes and protective coatings for the items that needed help. However, after prolonged application time, synthetic polymers undergo aging.
The aim of this research is to study and evaluate the leather and the functional life of the polymeric materials chosen to be used as a protective coating. This was achieved by examining their stability before and after the accelerated aging technique to compare how these two materials are affected by the passage of time. In this thesis, the challenge is to evaluate the aforementioned materials, the leather and the polymeric coatings used on them, comparing the changes they have undergone.
The polymeric materials selected for the study are Polystyrene (PS) and Poly (methyl methacrylate), PMMA] as a first approach. Accelerated aging applied to the polymers was accomplished by exposure to specific levels of temperature and humidity according to a protocol applied to the same origin samples in the field of cultural heritage.
An analytical methodology was set up to examine and study the physicochemical changes of leather samples with and without polymer coating using infrared spectroscopy (ATR, Attenuated Total Reflection) technique. Changes in the vitreous transition were investigated by DSC, Differential Scanning Calorimetry, in order to determine visual changes in the surface of the leather samples optical microscopy was utilized and the changes of color that the samples undergone during accelerated aging were identified by the colorimetry method. Finally, two complementary techniques have been added for better comparable results: the measurement of the contact angle defining the hydrophobicity imparted by the polymer coatings and the scanning electron microscopy (SEM) which showed us the surface morphology and the condition of the skin.
The results of the measurements provide important information on the material not only of our leather samples but also of the polymeric materials we used. It is possible to study their external morphology as well as to study the structure of their interior and to investigate them over time through simulation with artificial accelerated aging. The stability and resistance of a historical bookbinding leather to active substances can be assessed by using accelerating aging. With this methodology, modern leather samples, of the same tanning and processing, are subjected to special airtight stainless chambers and their behavior is studied in a practical laboratory period. Artificial aging aims to reproduce natural aging at a laboratory level and to draw useful conclusions about the stability and durability of historical and naturally aged leathers when exposed to similar conditions. Artificial aging is being implemented in recent years with an attempt to reproduce realistic environmental parameters that correspond to modern cities in the same proportions but at higher rates. Environmental parameters that are being studied in the case of leather and parchment are relative humidity, temperature, SO2 and NO2 pollutants and radiation. These parameters are adjusted according to the environment we want to simulate for our samples.
In particular, the methodology for testing and evaluating the conservation status of the polymers in parallel with that of the leather samples is as follows:
• Optical microscopy
• Water Capillary Absorption (Water Capillary Absorption)
• Portable Spectrophotometer (Colorimetry CIEL*a*b*)
• Attenuated Total Reflection (ATR, Infrared Spectroscopy)
• (TGA, Thermal Gravimetric Analysis)
• Contact angle measurement
• Scanning Electron Microscopy (SEM)
In order to better understand the structure of the work and the issues negotiated in it, its theoretical and experimental structure is briefly presented:
The first chapter, which is the theoretical part of the work, presents general information about leather, its chemical structure and its manufacturing technology, its deterioration and corrosion factors and finally the methods of preventive and invasive conservation. In the same chapter there is a parallel reference to the theoretical level in polymers, providing the reader with some basic knowledge for a better understanding of the subject, as well as for the damage they suffer and the factors that cause them.
The second chapter is devoted to the physicochemical methods of diagnosis and analysis used in the present thesis on leather and polymeric coatings, aiming at understanding their mode of operation and their instrumentation.
Finally, the third chapter consists of the experimental methodology of the study, the sample preparation methodology, the methods of analyzing the samples before and after the accelerated aging, the results and the conclusions of the research.
In each of the above chapters the bibliography is listed at the end of the chapter.
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