สำนักราชบัณฑิตยสภา

The Journal of the Royal Institute of Thailand √–∫∫∑ÿ ππ‘ ¬¡¿“¬„µâ √–∫Õ∫ª√–™“∏‘ ª‰µ¬·∫∫‰∑¬ Properties of Industrial Thai Silks Reeled by Hand and by Machine Vol. 32 No. 1 Jan.-Mar. 2007 146 a larger denier of the local silk fila- ments reeled by machine when they were dyed at the same dye concentration. The internal prop- erties of silk such as birefringence, crystallinity, moisture content, etc. might not play significant roles in this case. The surface chemistry of the typical functional groups of silk fiber and the acidic dye can be a major attribute to the different color strength. The amount of all amino acid types, i.e., the non- polar amino acid, acid amino acid, basic amino acid and sulfur- complex amino acid, can interact with the acid dye via an acid-base interaction to give different color strength. We anticipate that a certain type of amino acid, for example glycine, in the sericin of the silk can be used a padding agent to enhance color reception and thus higher color strength. This research is now underway. In addition, the reeling method in relation to the denier could be another important contributor to color strength. According to the reeling methods, it was shown that machine reeled filaments had a slightly lower dye fixation (74 - 83%) than hand reeled filaments (78-85%). The machine reeled filaments had a lower denier than the hand reeled filaments (see the denier section) and thus it had a smaller surface area to accept dye and thus showed a lower dye fixa- tion measuring by the colorimetric method. Resistance to Acid, Alkali, and Bleaching Agent The raw and degummed silk filaments were tested for acid re- sistance by immersing in a solution of sulfuric acid in dyeing condition. After this acid exposure, a very low loss of the silk weight of 1-1.5% for the raw silk and 0.5-0.7% for the degummed silk was shown. This small weight loss could come from the loss of some water so- luble materials rather than from the loss from the sericin and silk fiber because sericin and fibroin proteins should have more resis- tance to acid than to alkali. The test results in this study indicated that all the silk varieties showed a high resistance to acid. There was an insignificant difference in the weight loss of the silk after the acid exposure between the silk reeled by hand and those reeled by machine, and between the Chinese silk and the local silk. Generally, silk fiber or fibroin can be damaged when exposed to alkali condition such as de- gumming due to their vulnerable peptide bonds to alkali. In this study, the raw and degummed filaments were exposed to sodium carbonate under a degumming condition and then were tested for weight loss. It was shown that the raw filaments lost 15.7-27% weight while the degummed fila- ments lost only 11-14.4% weight after an alkaline exposure. This weight loss came mainly from the loss of sericin, and partly from the loss of fiber and/or water so- luble substances. The Chinese raw silk lost the lowest weight of 15.7% while its degummed silk lost the greatest weight of 14.4% for this study, compared with the local raw silk of 23.1-27%, and the local degummed silk of only 11- 13.8%. Because among all the silk varieties, the Chinese raw silk con- tained the lowest content of sericin (see the degumming loss section) and thus it lost the lowest weight after the exposure. On the other hand, the silk fibroin of the degummed Chinese silk was dam- aged more by the alkaline solution than the silk fibroin of the degummed local silks. All the silk varieties in this study showed very low resistance to alkali. The silks reeled by hand and those reeled by machine showed an insignificant difference in the weight loss after the exposure. In other words, the silk reeling methods had no influ- ence on the silk resistance to alkali. In general, silk bleaching with an oxidizing agent of hydrogen peroxide is conducted at an alkali condition and silk can be damaged by these chemicals (hydrogen per- oxide and sodium carbonate). The oxidizing agent can oxidize the polypeptide chain in fibers, and degrade it as well as decrease the fiber strength. This leads to the loss of fiber but in a smaller degree when compared to the damage from the alkali degumming. In this study, it was shown that the raw filaments lost 7.4-9.8%weight and