Abstract
Our previous papers on this series described the manufacture of the compound filament which consists of cocoon fiber and synthetic one as core. The observation of the cross-section shows that the cocoon fibers are located around the core synthetic filament, being adhered by silk-gum or sericin.
The compound filament must be twisted to cover the weak adhesion of the cocoon and to avoid separation of silk filaments from the core filament during de-gumming.
The aspect of the compound filament resembles a multifilament yarn after twisting and degumming.
In this paper, effects of twisting and de-gumming of the compound filament on the geometrical structure and the cross-sectional shape of the yarn are studied. TETORON (PET filament) is used as the core filament. The results are as follows:
1) The core filament is reduced in length by twisting and de-gumming. When relatively large twist was given to the compound filament, most of the silk filaments are near the core in helical shape.
2) From the change of the length of the core filament, it is possible to know how many twists should previously be given to a compound filament to keep a good contact of the silk filaments to the core filament after de-gumming.
3) The cover-ratio is defined by the ratio of the total length of the parts covered by the silk filaments to the circumference of the core's cross-section. The equation of the cover-ratio is derived under the conditions that all silk filaments are located at the same distance from the center of the core filament and their directions from it are at random.
where Fc′: cover-ratio S: circumferece of the cross section of the core filament s: arc length that one silk filament covers the circumference n: number of the silk filaments
4) The values of cover-ratio measured are generally larger than those calculated from the above equation; especially when the compound filaments are twisted, the cover-ratio become larger, caused by the outer silk filaments thrusting themselves into the inner ones.
