ارزیابی تخریب چربی آزاد در چرم‌های تاریخی به ‌روش ATR-FTIR (نمونه‌موردی: مشک چرمی منسوب به دوره سلجوقی)

One of the main reasons for the historic leather samples becoming dry and brittle is the degradation of the excess residual fat in their structure; however, this subject has not been well-established so far. Therefore, in order to facilitate the grounds for an optimum conservation encounter, with the aim of understanding the harms imposed on the leather samples, characterizing the degradation process of the leather’s fat, as an important additive compound used in the leather making process, is significant and necessary. Thus, in this research, the excess residual fat in seven historic leather samples, belonging to a leather bag, discovered in Ghayen’s Ghal’e-Kuh historic site and attributed to the Seljuk period, was examined for the structural degradation assessment. For this reason, after having extracted the samples’ excess residual fat by dichloromethane solvent using the Soxhlet extraction apparatus, the structural assessment was done through the Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) technique. This method is useful for investigating the fat’s structural properties and their alterations, because it could demonstrate fat’s structural and molecular features based on the molecular vibrations of the structural bands. In addition, the mutton suet was simultaneously evaluated for its infrared spectrum so that it could be compared with the case study fat samples. According to the results, all samples were oxidized, and this degradation resulted in the fat’s structural alteration and production of the secondary compounds such as ketones, aldehydes, alcohols and carboxylic acids. Moreover, in addition to the oxidation, in some samples the nitration and sulfating of the fat were observed too. Accordingly, oxidation and degradation of the excess residual fat is characterized as the major factors of the severe dryness in the leather samples. More so, the fat oxidation products are also involved in the decay of the protein structures in the leather’s fat and subsequently extend its degradation.