Preparation of silica-silk fibroin-polyurethane composite films via a sol-gel route

A tetraethoxysilane (TEOS)-derived sol aged for 0 h-6 h at room temperature was mixed with a polyurethane (PU) matrix. A composite of silk fibroin (SF) powders and acrylamide (AAm) was dispersed in the sol-PU mixture and dried isothermally at temperatures between 25°C and 120°C to obtain composite films. Three competitive reactions take place, i.e., those between silica-silica, SF-PU and silica-organic phases, during formation of the composite films. These reactions determine the properties such as morphology and homogeneity of the composite films. IR absorption bands for amide groups (-CONH-), ν C double bond O (amide I, 1730 cm^-1) and δ N-H (amide II, 1530 cm^-1) become larger with decreasing aging time of TEOS-derived sol, or increasing drying temperature. DTA exothermic peak due to the thermal decomposition of SF-AAm composite, on the composite films prepared from the 0 h-aged sol or dried at more than 50°C, shifts toward higher temperature by 44 K or more than 63 K respectively, as compared to the SF-AAm composite. Shorter aging time of TEOS-derived sol and higher drying temperature increased the extent of dispersibility, among SF-AAm composite, PU and silica, to bring a composite film more homogeneous.