This study investigates the degradation mechanism of silk fibroin through Fourier-transformed infrared spectroscopy (FTIR) analysis. The secondary structure of silk fibroin-based materials is monitored using FTIR, and various estimators are calculated to assess the impact of degradation conditions and aging time. The oxidation estimator shows consistent growth, indicating peptide bond oxidation from the early stages of artificial aging, regardless of the conditions. The environment influences the hydrolysis estimator, with water introduction leading to significant changes. The crystallinity estimator reflects the overall degradation level, affected by oxidation and hydrolysis. XRD and FTIR analysis of historical silk banners up to 500 years old demonstrate a decrease in crystallinity and an increase in hydrolysis and oxidation. The presence of water accelerates the oxidation process, while crystallinity changes are primarily driven by oxidation. Fibroin degradation affects both antiparallel and parallel regions, with water playing a crucial role in accelerating hydrolysis and causing structural shifts. This study enhances our understanding of silk fibroin degradation and provides valuable insights for preserving historical silk artifacts.

Understanding the structural degradation of silk fibroin is important for the diagnosis and conservation of historical textiles. In this study, X-ray diffraction (XRD) was used to compare model silk subjected to short-term in situ thermal treatment, long-term ex situ artificial ageing, and naturally aged historical silk samples dating from the 16th to the 19th centuries. Instead of relying on global crystallinity indices, a motif-resolved approach was applied based on characteristic diffraction markers.The analysis focused on Silk II reflections at 19.2°, 20.4°, 24.8°, and 30.5° 2θ, the amorphous halo centred at 22.6° 2θ, and an ageing-related short-range order (agSRO) signal in the 28.0–28.8° 2θ range. Across all ageing pathways, the most consistent structural change was the attenuation of the Silk II (020)/(210) reflections, indicating progressive loss of long-range inter-chain β-sheet order. More advanced degradation was associated with changes in the inter-sheet stacking motif at 24.8° 2θ, development of the agSRO signal near 28.6° 2θ, and increased contribution of the amorphous halo in historical samples.These results show that silk degradation is better understood as redistribution among specific structural motifs than as a simple decrease in crystallinity. By linking artificial ageing experiments with naturally aged historical objects, this study provides an XRD-based framework for comparing degradation pathways and supporting structurally informed diagnostics of heritage silk textiles.