Mulberry silk is a continuous long fiber that is coagulated by secreting silk liquid when the cocoon is formed. Like wool, it is one of the earliest animal fibers used by humans. According to the different food of silkworm, it is divided into silkworm, tussah silkworm, cassava silkworm, camphor silkworm, willow silkworm and sky silkworm.

The silk sliver drawn from a single silkworm cocoon is called cocoon silk, which is made of two single fibers bonded and covered with sericin. The cocoon filaments of several cocoons are drawn out and wrapped by sericin. There are mulberry silk (also called raw silk) and tussah silk, which are collectively called silk. The silk from which the sericin is removed is called refined silk. Using them as raw materials, they can be processed into various types of fabrics using looms.

1. Shape size

Slender fiber

The variation range of cocoon silk length and diameter of mulberry and tussah silkworm (contains two silk fibroin fibers) is shown in the following table:

It can be seen from the table that although the amount of cocoon layer and cocoon type of tussah cocoons are larger than that of mulberry silkworm, because the diameter of cocoon silk is larger than that of mulberry silkworm, the length of cocoon silk is still shorter than that of mulberry silkworm. The diameter of the cocoon silk is mainly related to the size of the silkworm's spinning mouth and the draft ratio during spinning. Generally, the faster the speed, the thinner the cocoon silk.

2. Density

The density of sericin is greater than silk fibroin

The density of raw silk is 1.30~1.37g/cm3, and the density of cooked silk is 1.25~1.30g/cm3. The reason why the density of raw silk is greater than that of cooked silk is that the density of sericin is greater than silk fibroin. The density of sericin is closely related to its moisture absorption capacity. .

Among natural fibers, the density of mulberry silk is close to wool, and smaller than cotton and hemp fibers; compared with chemical fibers, its density is lower than polyester and viscose, but larger than nylon, acrylic, and polypropylene fibers.

3. Hygroscopicity

Silk has good moisture absorption

Under the standard conditions of a temperature of 20°C and a relative humidity of 65%, the moisture regain of mulberry silk is about 11%, and its moisture absorption is lower than that of natural fibers and higher than that of cotton fibers.

The good hygroscopicity of silk is because the protein molecular chain contains a large number of polar genes, such as -HN2, -COOH, -OH, etc. This is an important reason why silk products are comfortable to wear. Since the ratio of polar genes and non-polar genes in sericin is higher than silk fibroin, the hygroscopicity is higher than silk fibroin.

4. Strength and elongation

Raw silk has better strength and elongation

The strength and elongation of raw silk is good, the relative strength is 2.6~3.5cN/dtex, which is the best among textile fibers, and the elongation at break is about 20%. The strength and elongation of raw silk is not only related to its internal structure, but also related to processing conditions. For example, cocoon cooking, silk reeling tension, silk reeling speed, silk sheath length, etc. will affect the strength of raw silk. Due to the removal of the sericin in the cooked silk, the adhesion between the monofilaments is reduced, and the relative strength and elongation at break are reduced.

5. Color

White light yellow

The color of raw silk refers to the color and luster of raw silk. The color of silk varies with different raw cocoons, the most common of which are white and light yellow

The color of raw silk reflects its inherent quality to a large extent. For example, the white silk body of the general spring cocoon silk indicates that the silk body is soft, the surface is clean, the amount of glue is small, the strength and the abrasion resistance are poor; while the autumn cocoon silk The silk body is slightly yellow and has a soft luster, indicating that the amount of glue is large, and the strength and abrasion resistance are better. After being refined, raw silk has a unique luster of softness and elegance that other fibers cannot match.

6. cohesion

Cohesion is one of the important qualities of raw silk

Raw silk is made by reeling and combining several cocoons of cocoon silk. Due to the glue effect of sericin, the cocoon silk is not easy to disperse even after friction. This is the cohesive force of raw silk.

If the cohesive force of raw silk is not good, the thread will not stick firmly, have many cracks, have poor strength, and is not abrasion resistant. During the preparation and manufacturing process, it is easy to cut, float, hook and entangle. Therefore, cohesion is an important quality of raw silk. one. The cohesiveness of raw silk refers to the performance of this thread to resist friction without splitting. The sericin component is the main reason for the cohesion of raw silk.