Exploring the influence of wild silks composition on dyeing with turmeric and indigo: Spectroscopic insights

"Wild" silks, produced by various silkworm species, are often valued in textile production, but present greater challenges in dyeing compared to the "domestic" mulberry silk from Bombyx mori. This study investigates the reasons behind these challenges, focusing on key components such as fibroin, sericin proteins, and calcium oxalate crystals. The degumming process, which removes sericin, generally enhances dye penetration; however, its efficiency varies with the type of silk and its chemical composition. Using Fourier-transform infrared (FTIR), Raman spectroscopy, and UV-Visible spectroscopy, we characterized the composition of cocoon samples from 11 different silkworms, both with and without a preliminary degumming step, and assessed their dyeing behavior with turmeric and indigo dyes. FTIR provided insights into the molecular structure and physico-chemical interactions within the silk fibers, while UV-Visible spectroscopy quantified dye sorption. Our findings demonstrate that effective degumming is crucial for dye uptake, with greater degumming loss often leading to a higher and more homogenous dye sorption. In some cases, the degumming procedure did not completely remove sericin, the latter of which not only physically impedes dye penetration into the silk mass but also forms physicochemical interactions with the dye, influencing the overall sorption capacity. Additionally, the presence of calcium oxalate crystals - particularly in wild silks like Antheraea paphia - can further impede dye sorption. Corroborating images obtained using optical digital microscopy supported these findings.