Wool fabrics are favored by consumers because of their plump texture, smooth feel, good drape, noble and light comfortable wear. But how do these consumer-favored wool fabrics transpose to us after being sorted out by the dyeer? Let's talk about wool fabrics today.
Structure of wool
Wool is a slender, solid cylinder with a curled, rough surface, and consists of a layer of scales, cortex, and medulla. The finer the wool, the more scales, because the scale layer is stretched outward and protruding, increasing the friction between the fibers, resulting in mutual containment and felt shrinkage, and the hugging force under humid and hot conditions is strengthened. The cortical layer is composed of two parts, the positive cortical layer and the paracortical layer, which are the main components of wool and determine the physical, mechanical and chemical properties of wool fibers. The medullary layer is an opaque loose substance; the more medulla, the straighter and coarser the wool is, and the worse the quality.
Finishing process of wool fabrics
Because of the wide variety of wool fabrics, there are also certain differences in the finishing process, such as glossy fabrics may involve: raw blank repair → burned wool → washed→ boiled→ dyeing → absorbent → drying – the inspection → → brush bristles → shearing → to wet parking → steaming → voltage; and suede fabrics involve: preparing to → washing→ dehydration → shrinking→ washing→ dyeing → dehydration → drying → inspection → cooked → the brush → brush shear → steaming → steaming, so today to discuss the general finishing process purpose and principle.
01 Carbonization
Purpose: To remove plant impurities from wool. Principle: Using wool and cellulose impurities to resist acids differently, so as to remove impurities. The acid promotes the hydrolysis of cellulose impurities, making it brittle and removed by washing with rolling water; and the -NH2 on the wool adsorbs H+, which begins to absorb acid when pH = 5, and the pH = 1 reaches saturation, and there is no damage to the wool. If the acid absorption continues, the wool main chain is hydrolyzed, so the acid concentration and temperature need to be strictly controlled during the production process.
02 Wash it
Purpose: Purify and improve feel. Principle: Generally use surfactant to wash the billet, so as to remove impurities and improve the feel. The wool fabric is constantly moving and squeezing in the washing, and has a certain shrinkage effect. When the fabric is required to feel plump, the washing time can reach about 2 hours, and the general woolen fabric washing is 45 to 90 minutes. After washing, rinse with warm water of about 40 °C.
03 Boil it and steam it
Purpose: To make the fabric dimensionally stable, the tweed surface flat, the luster natural, the feel soft and elastic. Principle: Wool fiber in spinning, weaving, subject to uneven external forces, so that there is internal stress in the fabric, under humid and hot conditions, due to the internal stress relaxation, resulting in uneven contraction, in a longer period of humid heat treatment, re-establish a new crosslink in a new position, resulting in stereotyping effect.
04 Shrink it
Objective: Under certain temperature conditions, after wetting by the wetting agent, under the repeated action of mechanical external forces, the fibers bite and entangle with each other, so that the fabric shrinks, the thickness increases, and a layer of fluff is generated on the surface to cover up the texture of the process. Principle: The friction coefficient of the wool inverse scale (pointing to the tip of the hair) is larger than the friction coefficient of the movement along the scale (pointing to the hair root), which is called the directional friction effect. When the shrinkage agent is present, repeated and irregular external forces force the wool to move along the scale contraction, the wool roots bite each other, the fiber tip is in a free state to cover the surface of the fabric, because the arrangement of the fibers is more disordered, so the result of the movement tends to tighten.
05 Anti-felt shrinkage
Objective: To reduce the shrinkage of the wool fabric, so that the fabric can obtain dimensional stability and reduce the phenomenon of pilling. Principle: By reducing the directional friction effect, the inherent elasticity of wool is improved and wool is limited to move to each other. Wool-destroying flake layers and polymers are usually deposited on the surface of the fabric to prevent felt shrinkage.
Dyeing principle and process of wool fabrics
Dye classification
Wool fabric dyeing generally uses acid dyes and reactive dyes for wool
01
Acid dyes
Dyes containing water-soluble groups with low directness and the ability to dye proteins and polyamide fibers in acidic, weakly acidic or neutral dyes.
02
Active dyes for hair
Dye molecules have active groups, the active groups can produce chemical reactions with hydroxyl groups (-OH), amino groups (-NH2) on the fibers, etc., to form covalent bond binding, dye structure general formula: S-D-B-Re
Principle of dyeing
Dyeing protein fibers with acid dyes is based on the pore diffusion model;
【Channel diffusion model↑】
Strong acid bath, Langmuir type adsorption;
Weak acidic bath: pH<pI, Langmuir adsorption; pH>pI Fleindlisch type adsorption;
Neutral bath staining: pH = 6 ~ 7, Freiindlisch type adsorption. (pI: When the number of positive and negative ions on the fiber macromolecules is equal, the net charge of the fiber is zero, that is, it is electrically neutral and is in an isoelectric state, and the pH of the solution at this time is called the isoelectric point pI of the fiber).
Physical significance: Adsorption isotherm, you can infer the dyeing mechanism, control the dyeing process, slope change can judge the reasonable amount of dye range, improve dye utilization.
Dyeing process
Acid dye staining for weakly acidic bath staining
Dyeing Formula:
Dye: X%
Yuanming powder: 1-2g/L
Acetate 60% (pH= 4.5-5.5): 1-3%
Leveling agent: 0.5-1.5%
temperature
< 50 °C, unstained, scale layer; when > 60 °C, T↑, disulfide key is opened, and the rate of staining is increased. The temperature is controlled in the early stage to improve the uniformity of ↑ and the temperature is dyed at 95~100°C in the later stage, and the heat preservation is 30~60min.
Leveling agent
Neutral electrolytes Cl-, SO42-. Principle: competition dyeing, ion exchange with dye ions, so as to achieve the effect of leveling.
Source: Jiuli Textile Bleach expert Dr. Se Shang Fang Bu