Grape Seed Proanthocyanidins: Novel Coloring, Flame-Retardant, and Antibacterial Agents for Silk

Grape skins and seeds rich in polyphenolic compounds are low-value byproducts from the wine-making. The valorization of such byproducts is of great significance. This work presented a novel application of grape seed proanthocyanidins (GSPs) in the dyeing and flame-retardant and antibacterial treatment of silk. The study on adsorption isotherms revealed that multiple interactions occurred between GSPs and silk, including electrovalent bonding, hydrogen bonding, and van der Waals forces. The color depth of silk mainly depended on temperature and GSP concentration. Dyed silk had acceptable color fastness to washing, rubbing, and perspiration. Postmordanting could improve light fastness. Changes in the tensile strength and flexural rigidity of dyed silk were in an acceptable range. A low concentration of GSPs imparted a durable antibacterial function to silk. The biggest highlight of this study was the improved flame retardancy of silk caused by GSP dyeing. GSPs increased the thermal stability and charring ability of silk at high temperatures, and their flame-retardant action worked in the solid phase. Mordanting had no substantial impact on the flame-retardant and antibacterial functions of dyed silk. The present research reveals that the valorization of GSPs for silk processing is feasible.