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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 142 Chinese raw silk filament con- tained a highest moisture content of 10.2% while the local raw silk filaments contained a lower content of 7.4 -9.6%. The results from the degumming weight loss determination showed that the Chinese silk filament lost the least weight during degumming. In the other word, we could say that the Chinese raw silk filament con- tained the lowest amount of sericin, but it had the higher moisture con- tent than other raw silk filaments containing the higher sericin con- tent. This could mean that sericin content was not the only factor to influence the moisture absorption of the silk filament. Some other factors such as chain orientation, crystallinity and others could affect the moisture absorption as well. The effect of the reeling meth- ods on the silk filament’s moisture content studied was found that the two local degummed filaments had a similar moisture content for the hand reeled filaments and machine reeled filaments while the one local degummed filament showed a different result. In ad- dition, the local raw silk filament reeled by machine had a lower moisture content than that reeled by hand while the other two raw filaments showed the opposite result. From these outcomes, it was not possible to reach a defi- nite conclusion on how the reeling methods affected the moisture content of silk filaments because of the inconsistent test results from the non-uniformity of the natural fiber. Relative Density Silk density determination indicated that the raw silk filaments have a relative density in the range of 1.20-1.26 g/cm 3 and the relative density of the degummed silk fila- ments was 1.06-1.14 g/cm 3 . The degummed filaments showed a lower density than the raw filaments due to the loss of sericin upon degumming. Among all varieties, The Chinese silk fila- ment had the lowest density for both the raw silk filaments and the degummed filaments because the Chinese silk filament had a smaller size (denier), lower weight and lower sericin content than the local silk filaments. Again, it was not possible to find a relation- ship between the reeling method and silk density due to the same reason as mentioned previously. Birefringence The degummed silk filaments were tested for their birefringence in order to study the polymer chain orientation within the filaments. It was found that the local silk filaments reeled by machine had a similar birefringence (0.050-0.053) as that of the machine reeled Chinese silk filament (0.053). The polypeptide chains in these filaments could have a similar degree of orientation. Furthermore, the test results showed that the local filaments reeled by hand had a lower birefringence (0.041- 0.047) or a lower degree of poly- peptide chain orientation than those reeled by machine (0.050- 0.053). It is possible to say that the machine reeling process in- troduced a higher filament draw- ing speed and drawing ratio than the hand reeling process and thus it promoted better orientation of polypeptide chains in the machine reeled filaments. Crystallinity Generally, silk filament con- tains 65-70% crystallinity. In this study, the degummed silk filaments were determined for their crystal- linity using an X-ray analysis and results are shown in Figure 4. It was found that the local filaments reeled by hand contained 40-68% crystallinity while those reeled by machine contained higher crys- tallinity of 62-72%. It was also shown earlier that the hand reeled filaments had a lower birefringence than those of machine reeled fila- ments and thus showed the lower %crystallinity in there. Comparing the local filaments and the Chinese filament both reeled by machine, the test results showed that the local filaments had a higher % crystallinity (62-72%) than the Chinese filament (59%) while the similar birefringence in the range of 0.050-0.053 had been previou- sly reported. All the degummed filaments showed a similar pattern of X-ray diffractograms featuring a broad major peak located at 2 θ = 20.5 ˚ with various peak am- plitudes for each silk variety.