PHYSICAL-PROPERTIES AND PHASE-SEPARATION STRUCTURE OF ANTHERAEA-PERNYI BOMBYX-MORI SILK FIBROIN BLEND FILMS

The physical structure and compatibility of solution-cast Antheraea pe rnyi/Bombyx mori silk fibroin blend films were studied by differential scanning calorimetery (DSC), thermomechanical (TMA) and thermogravime tric (TGA) analysis, dynamic viscoelastic measurement, infrared spectr oscopy, and x-ray diffractometry. The DSC curves of the blend films sh owed independent endotherms at 280 and 358-degrees-C, corresponding to the thermal decomposition of B. mori and A. pernyi silk fibroins with random coil conformation. The intensity was roughly proportionate to the amount of each component in the blend. The thermal behavior corres ponding to the conformational transitions induced by heating on A. per nyi and B. mori silk fibroins overlapped in the temperature range 190- 230-degrees-C. Thermal expansion and contraction properties, as well a s weight retention behavior of the blend films were intermediate betwe en the pure components, as shown by the TMA and TGA curves. The onset temperature of the storage modulus curve decreased markedly, approachi ng that of B. mori silk fibroin film when the amount of this component in the blend increased. The loss modulus curve of the blend films sho wed two peaks at ca. 190 and 210-degrees-C, the former corresponding t o B. mori, and the latter to A. pernyi silk fibroin. Infrared spectra of the blends exhibited absorption bands characteristic of the pure co mponents overlapping in the spectral region 2000-400 cm-1. The x-ray d iffraction peaks at 23 and 21.5-degrees, attributed to the crystalline spacings of A. pernyi and B. mori fibroins, respectively, overlapped in the diffraction curves of the blends, while the peak at 11.4-degree s, of A. pernyi, increased as the content of this fibroin in the blend increased. The degree of crystallinity, calculated from the x-ray dif fraction curves, diminished as the amount of B. mori silk fibroin decr eased. A low degree of compatibility exists between the two fibroins w hen they are cast from aqueous solution in the experimental conditions adopted in this work. (C) 1994 John Wiley & Sons, Inc.