Seica optical microscope.Picture 2. Silk samples closed in sealed vials after (left) and before (right) ageing.
The goal of the study of the silk degradation is to work out the optimal storage conditions including anoxia frames for the silk composed artifacts. The first approach to the problem is, however, optimizing the analytical methods to trace down silk changes imposed by the environment.
To study degradation processes small samples of the depicted above silks were aged in closed vessels (see picture 2) and in chambers at 150°C. The ageing conditions were chosen to observe maximum degradation effect but not exceeding the transition temperature for silk. The reactors were chosen to study the degradation phenomena with (closed vessels) and without (chamber) the influence of gaseous degradation products.
After having been removed from the reactors (past 1, 2, 4 or 7 days), samples were investigated by simple chemical and physical methods to obtain fast but rough evaluation of the degradation progress. These were colour change by VIS spectrometry, acidity by pH measurements (see picture 3) and tensile strength by mechanical properties measurements. All the indicators of degradation (delta E, tensile strength, pH) have shown significant changes upon ageing with the general tendency to deteriorate faster in the closed system than in the open one. In figure 1 the tendency of growth of delta E the parameter in the CIE Lab model with time of exposure to temperatures is clear as well as the fact that yellowing is stronger if sample was aged in closed system. The acidity of samples (see fig. 3.) also depends on the duration of being exposed to high temperature and the presence of the gaseous degradation products. The tensile strength experiments revealed that the strength of silk drops significantly with ageing time (see fig. 2.). Mechanical properties, although bearing high experimental error, seem to be most sensitive dependent on the conditions of aging. For example, the decrease of resistance to stress for a sample aged in the closed reactor for 1 day is comparable to the one aged in open reactor for 7 days.
To study degradation processes small samples of the depicted above silks were aged in closed vessels (see picture 2) and in chambers at 150°C. The ageing conditions were chosen to observe maximum degradation effect but not exceeding the transition temperature for silk. The reactors were chosen to study the degradation phenomena with (closed vessels) and without (chamber) the influence of gaseous degradation products.
After having been removed from the reactors (past 1, 2, 4 or 7 days), samples were investigated by simple chemical and physical methods to obtain fast but rough evaluation of the degradation progress. These were colour change by VIS spectrometry, acidity by pH measurements (see picture 3) and tensile strength by mechanical properties measurements. All the indicators of degradation (delta E, tensile strength, pH) have shown significant changes upon ageing with the general tendency to deteriorate faster in the closed system than in the open one. In figure 1 the tendency of growth of delta E the parameter in the CIE Lab model with time of exposure to temperatures is clear as well as the fact that yellowing is stronger if sample was aged in closed system. The acidity of samples (see fig. 3.) also depends on the duration of being exposed to high temperature and the presence of the gaseous degradation products. The tensile strength experiments revealed that the strength of silk drops significantly with ageing time (see fig. 2.). Mechanical properties, although bearing high experimental error, seem to be most sensitive dependent on the conditions of aging. For example, the decrease of resistance to stress for a sample aged in the closed reactor for 1 day is comparable to the one aged in open reactor for 7 days.
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