CHEMICAL MODIFICATION OF SILK WITH AROMATIC ACID ANHYDRIDES

Bombyx mori silk fibers were chemically modified by acylation with aromatic acid anhydrides, such as phthalic and omicron-sulfobenzoic anhydrides. We examined the reactivity of these modifying agents toward silk fibers, the physical and thermal properties, and the dyeing behavior with acid and cationic dyes. The omicron-sulfobenzoic anhydride was more reactive toward silk fibroin than phthalic anhydride. The amount of both basic and acidic amino acid residues decreased after modification with aromatic acid anhydrides. The moisture regain of silk treated with phthalic anhydride remained almost unchanged, while that of the samples modified with omicron-sulfobenzoic anhydride increased linearly as the weight gain increased. Chemically modified silk fabrics showed improved crease recovery behavior, even though phthalic anhydride seemed more effective at comparatively low weight gain. The modification of silk with omicron-sulfobenzoic anhydride caused a drastic reduction of acid dye uptake and enhanced the affinity of silk for cationic dye. Silk fibers did not show any significant change in thermal behavior, regardless of the modification with omicron-sulfobenzoic anhydride. Silk fibers modified with phthalic anhydride showed on differential scanning calorimetry (DSC) curves a minor and broad endothermic peak at around 210-degrees-C, attributed probably to the breaking of the crosslinks formed between adjacent fibroin molecules.