STRUCTURE AND DYEABILITY OF BOMBYX-MORI SILK FIBERS WITH DIFFERENT FILAMENT SIZES

This study deals with the analysis of structure, physical properties, and dyeing behavior of silk fibers with different filament sizes. Fine and coarse silk fibers were obtained from Akebono and Ariake cocoon v arieties, respectively. Both samples exhibited a fairly similar x-ray crystallinity, while the degree of molecular orientation increased wit h decreasing the fiber size. Tensile strength and energy of fine silk fibers were significantly higher, while elongation at break did not ch ange in relation to the fiber size. Fine silk fibers exhibited a sligh tly higher thermal stability, as shown by the upward shift of both the DSC decomposition temperature and the TMA final extension step at abo ve 300 degrees C. The TGA and DMA (E '') patterns remained unchanged r egardless of fiber size. The amino acid analysis confirmed the absence of any difference of chemical structure between fine and coarse silk fibers, the content of acidic, basic, and other characteristic amino a cid residues being exactly the same. Accordingly, both samples adsorbe d the same amount of hydrochloric acid. Exhaustion dyeing tests with v arious direct, acid, and reactive dyes showed the occurrence of apprec iable differences in the perceived color between fine and coarse silk fibers. The size of color difference was quantitatively evaluated by r eflectance measurements and discussed in relation to silk fiber morpho logy, structure, as well as dyeing conditions. The kinetics of diffusi on of two model dyes was not significantly affected by the different f iber size and structure. (C) 1996 John Wiley & Sons, Inc.