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«“√ “√ √“™∫— ≥±‘ µ¬ ∂“π Usa Sangwatanaroj, et al. 143 ªï ∑’Ë ÛÚ ©∫— ∫∑’Ë Ò ¡.§.-¡’ .§. Úıı Crystallinity (%) Degummed silk fibers C4 (hand) C4 (m/c) C6 (hand) C6 (m/c) C1 (hand) C1 (m/c) Chi (m/c) 100 80 60 40 20 0 Figure 4. Crystallinity of the degummed silks. [Cl for local Thai Silk; C4 for Chul 4; C6 for Chul 6; Chi for Chinese filaments; hand for hand reeling; m/c for machine reeling] Infrared Analysis All ATR IR spectra of the degummed silk filaments used in this study showed a similar spec- tral pattern. These spectra indi- cated that all the silk varieties had the same chemical structure with chemical groups assigned to various peaks as follows. Peak position at 3426-3413 cm -1 was assigned to be the N-H stretching, 2966-2920 cm -1 was the C-H stretching, 1646-1633 cm -1 was the C=O stretching and the N-H stretching (amide I), and 1517- 1509 cm -1 was the C=O stretching and the N-H stretching (amide II). This result indicated the existence of the amide group (NH-C=O) on polypeptide chains in silk fila- ments. Softening Point Silk does not melt when it is heated. In fact, it begins to yellow at around 100 º C, decomposes at 170 º C, and burns at 420 º C. In this study both the raw and degummed silk filaments were tested for their softening points and it was found that these raw filaments showed softening points ranging from 146 to 160 º Cwhile the degummed fila- ments showed slightly lower sof- tening points ranging from 145 to 155 º C because the silk sericin cov- ering the raw filaments surface can protect silk fibroin from heat. For the raw filaments, the re- sults showed that the local fila- ments reeled by machine rendered softening points in the range of 155-160 º C and that of the Chinese filament possessed a lower tem- perature at 149 º C due to the lower amount of sericin on the Chinese filament for heat protection (see the degumming loss section). On the other hand, the Chinese degummed filament showed its softening point (153 º C) in the same range of the local degummed filaments (151-155 º C). Silk fibroins of both the Chinese filament and the local filaments could have the same heat resistance. In terms of reeling techniques, the test results indicated that the local filaments reeled by hand had lower softening points (146- 153 º C for the raw filaments and 146-150 º C for the degummed filaments) than those reeled by machinery (155-160 º C for the raw