The plant-like impurities in the raw wool, such as grass seeds, wormwood, broken leaves, and hemp, are often entangled with wool. Although they are plucked, opened, and washed, they cannot be completely removed. The presence of these impurities not only brings many difficulties to the carding spinning, but also reduces the quality of the yarn, affects the appearance of the fabric, and is easy to cause dyeing, especially the dyeing of the dark color is more significant and must be removed by carbonization.

Charring is based on the different resistance of wool fibers and cellulosic materials to inorganic strong acids. Cellulose is treated with a strong inorganic acid at a certain temperature to cause hydrolysis to form a weakly hydrolyzed cellulose. It is then crushed and dusted to separate it from the wool.

As long as the process conditions are appropriate, the wool itself is not subject to significant damage.

The process conditions of carbonization should be strictly controlled, otherwise it will cause damage to wool fiber and cause rickets in the subsequent dyeing and finishing process. [If] in the drying and baking process, the temperature is too high or the time is too long, it will cause the hydrolysis of wool fibrin, the color becomes yellow, the strength drops, and at the same time, the dyeing ability of wool to acid dye is reduced, and Increased dyeing capacity for basic dyes, probably due to the formation of sulfamate: RNH2+H2SO4→NHSO3H+H2O

Washed hair, combed short hair and broken pieces can be carbonized by means of loose hair.

When the hair is carbonized, the dry wool can be immersed in room temperature water for 20 to 30 minutes to uniformly wet it. A small amount (such as 1.5~2%) can be added with a flattening plus O, a surfactant such as sodium alkyl sulfonate. To improve the wetting effect, and some to save the process of water immersion, dehydration, etc., the wetting agent is directly added to the acid without immersion treatment.

The concentration, temperature, time, and liquid rate of the acid solution during acid picking must be strictly controlled.

Some test data indicate that the concentration of sulfuric acid solution required for carbonization can be less than 45g/L. In actual production, it depends on the condition of wool containing plant impurities and the thickness of wool.

Next, three water washing tanks are generally used to neutralize the acid remaining on the wool fibers, and the charred plant matter is further washed away.

The acid on the wool fiber has two kinds of mechanical adhesion and chemical combination. The former can be washed off with water, and the latter must be neutralized with alkali.

Therefore, the first tank mostly uses water to remove the mechanically attached acid; the second tank adds soda ash to neutralize the chemically bound acid; the third tank is clean water, mainly to wash away the alkali remaining on the wool fiber after neutralization, in water washing And the process is shown in Table 2: