Silk is a natural protein fiber of animal origin, composed mainly of the proteins fibroin and sericin. Silk fibers have significant historical value, therefore, knowledge of material’s condition and an understanding of degradation processes are crucial for their preservation. The degradation of silk is influenced by various factors, which cause irreversible changes in the structure of the material through hydrolysis and oxidation reactions. Various destructive and non-destructive analytical techniques are used for evaluation and characterization of silk.
In my master’s thesis the use of the spectroscopic techniques ATR-FTIR, which is already well established, and ER-FTIR, a non-contact technique that is still under development, was investigated for monitoring the condition and degradation of silk. The studied samples were exposed to different experimental conditions, such as impregnation with inorganic salts (weighting), treatment with buffers, and accelerated degradation (AD) at higher temperatures and different relative humidities. Using PCA, the relationships between spectral data and selected experimental parameters were analysed. The most pronounced grouping of samples was observed according to weighting, separation based on buffer treatment was also evident, while clear trends related to AD were not observed. For monitoring silk degradation, it is also important to evaluate changes in the secondary structure, which was performed by deconvolution of amide bands and quantitative determination of the content of individual secondary structures. In this case, limited repeatability was identified, particularly in the amide I and II regions, indicating the need for further development of method. The molecular weight of fibroin is an important indicator of the condition of silk, as it decreases with progressing degradation. Its determination is typically based on destructive techniques, such as viscometry, which are not suitable for the analysis of historical samples, as the samples should not be damaged. I aimed to develop a PLS model for predicting Mw based on spectroscopic data, with the goal of enabling non-destructive analysis. The results showed that this approach is promising, but limited by the size and representativeness of the calibration set.
The results of the study indicate that the combination of FTIR spectroscopy and chemometric methods has great potential for non-destructive monitoring of silk degradation. Future research could focus on expanding the sample set, as well as optimizing and improving the robustness of the methods.
|
