THE CHANGE OF THERMAL CHARACTERISTICS OF TUSSAH SILK FIBROIN WITH DRAWING

Abstract

The α-β transition of Tussah silk fibroin drawn to the various ratios was studied mainly by means of differencial scanning calorimetry (DSC), thermomechanical anlaysis (TMA) and X-ray diffraction. The results are summarized as follows.(1) In the DSC curves of Tussah silk fibroin, immediately above an endothermic peak at 200°C, an exothermic peak occurs clearly at around 230°C for drawn specimen. From the results of X-ray diffraction patterns, this peak is attributed to the α-β transition. Moreover, Tussah silk fibroin film shows also the same behavior.(2) In the thermomechanical curves, Tussah silk fibroin shows very small shrinkage in a temperature range of 100 to 200°C, begins to elongate abruptly at this critical temperature (200°C) due to the unfolding of fibroin molecular chains. The elongation terminates in the vicinity of 230°C, and the length of fibroin increases abruptly when the temperature reaches 340 to 360°C. This elongation is supposed to be attributed to the conformational chang to the β-structure. At higher temperatures, the fibroin molecules again begin to shrink slowly owing to the entropy elasticity as they assume rubber-like structure in this temperature range.