Insight into the orientation behavior of thermal-aged and historic silk fabrics by polarized FTIR microspectroscopy

Abstract

Abstract Understanding the mechanism of silk degradation and evaluating the deterioration status is always a challenge, but fundamental for silk conservation and preservation. Polarized attenuated total reflection (Pol-ATR) Fourier-transform infrared (FTIR) microspectroscopy was employed to study the orientation behaviour of artificial-aged silk fibres in molecular level. Combined with wide angle X-ray diffraction (WAXD) study, the effect of crystal size and crystallinity on the orientation behavior of beta-sheets was investigated. It proved that the orientation structure of β-sheets fibrous was disrupted and greatly depend on the ageing degree. A comprehensive ageing mechanism of silk fibrous upon heat treatment was also proposed. In addition, the molecular order parameter of β-sheets crystallites (approximately at 1515 ± 3 cm−1) could be a degradation marker to reveal the orientation degree of β-sheets in silk fibrous. This hypothesis was also validated by examining the ageing of Chinese historic silk fragments unearthed from two archaeological sites. Component at 1616 ± 4 cm−1 would be potentially helpful to elucidate the molecular orientation for historic silk. Combined with thermal stability study, the ageing characteristics of two historic silk were compared. This research could provide with inspirations in obtaining a better understanding of silk degradation mechanism, evaluating the ageing status and providing with appropriate treatment for artificial aged and natural aged silk (historic silk).