Inorganic Composition and Thermal Properties of Cocoon Fiber

Abstract

The changes of color, size and shape of Bombyx mori cocoon shells were observed from 25°C to 550°C. Only 1 % of the original cocoon shell weight remains as cocoon ash after treatment at 550°C. Theinorganic components were detected in the cocoon ashes such as calcium, potassium, sulfur, magnesium etc., using energy dispersion fluorescent X-ray spectrometer analysis system. The thermal properties of B. moricocoon shell subjected to heat-treatment were examined by thermogravimetry-differential thermal analysis-Fourier transform infrared absorption spectrometry (TG-DTA-FTIR) and scanning electron microscopy (SEM). Chemical changes started gradually at around 180°C, and a sharp decrease in weight was observedaround 280°C by TG curves. The IR bands appearing around 2380cm-1 (-OH stretching), 1760cm-1 (C=Ostretching), 1503cm-1 (N-H stretching), 1085cm-1 (C-N stretching) and 965cm-1 (-NH2 stretching) become stronger as an exothermic reaction around 280°C takes place. This is probably due to the cleavingof the main chain and the accompanying decomposition of the cocoon fibers. Similarly, a SEM micrographof raw silk fibers treated at 300°C shows a microtubule in the middle of the fibers of about 25μm diameter.This suggests that the thermal reactions starts in the middle of the fiber and forms a microtubule.