Structure and Miscibility of Tussah Silk Fibroin/Carboxymethyl Chitosan Blend Films

Tussah silk fibroin (TSF)/carboxymethyl chitosan (CMCS) blend films wereprepared by solution casting using water as a co-solvent. The conformationalchange of TSF and the miscibility of the two components in blend films wereinvestigated by using FTIR spectroscopy, X-ray diffraction, differential scanningcalorimetry and scanning electron microscopy. Blending with CMCS induces aconformational change in TSF from α-helix to β-sheet and the most completetransformation to β-sheet conformation occurs in blending with 5% CMCS. Amechanism is suggested for the conformational transition in which CMCS moleculesare used as the nuclei of TSF micelles and induce TSF molecules to self-assemble byforming intermolecular hydrogen bonds. When CMCS content exceeds 5% in the blendfilm, the content of β-sheet conformation is reduced. The blend film, with 15% CMCSand above, exhibits semi-miscible characteristics, because there is a possibility of atwo-phase structure formation in the blend film. However, the intermolecularinteractions between the two polymers occur in their amorphous regions as indicatedby FTIR analysis. The water solubility assays show that adding 3-7% CMCS results insignificant improvement in water resistance of the TSF films, especially in the blend filmwith 5% CMCS, which hardly dissolves in water. However, when CMCS contentexceeds 7% the water solubility of the blend films increases rapidly.