Problems Encountered In Acrylic Fiber Coloring

fibre

Speed is a measure of the relative rate of dyeing of polyacrylonitrile fibres.

In general, he depends on the physical structure of the fiber.

The speed and stability of acrylic fiber's coloring rate directly affect the dyeing effect of downstream processes, which is a vital parameter for the quality of acrylic fiber.

The factors affecting the coloring rate of acrylic polyacrylonitrile fibers are described below.

Acrylic fiber dyeing mechanism: polyacrylonitrile fiber macromolecule has acidity.

Cationic dyes can be regarded as an ion exchange process.

Ion exchange reaction between dye ion D+ and fiber FSO3H or FCOOH can be expressed as follows:

FSO3 - H++D+=FSO - D++ or FCOO - H++D+=FCOO - D++H+

In acrylic fiber, due to the existence of acidic groups and strong electric negativity of cyanide group, under the condition of dye bath, the surface of the fiber has negative charge, and has a high dynamic potential zeta potential. The value is about (44 ~ 58 mV).

The dyeing process is analyzed because the cationic dye and the acidic (cationic) group in the fiber are bonded by salt. The number of acidic groups in the fiber varies with the production process of the fiber.

The wet fastness of dyes that did not bind to acidic groups in fibers was poor.

Therefore, the saturation value of cationic dyes should not exceed the saturation value of ionic bond fibers.

1, the impact of polymerization production:

The fiber composed of 100% polyacrylonitrile has been first industrialized because of its excellent chemical and climate resistance.

But because of its dyeing difficulties, it is difficult to achieve commercial production.

The main reason is that the acrylonitrile has a fairly high two grade glass pition point (greater than 100 degrees Celsius).

Successful dyeing requires modification of polymers.

Acrylonitrile usually results in copolymerization with a monomer of 5% to 10% (mass fraction).

Some of these monomers contain sulfonic or hydroxyl groups, while others contain amine or quaternary amine groups.

This leads to a looser structure, which reduces the glass pition point to 85~95 C, which makes acrylic fibers have better dye permeability.

The introduction of cationic groups or anionic groups in fibers can make the yarn or fabric made of these two kinds of fibers obtain bright coloration.

The number of cationic groups or anionic groups is directly determined by the number of cationic groups or anionic groups in fiber, that is, the degree of fiber coloring, that is, the saturation of fiber dyeing.

For the understanding of fiber dyeing saturation, the greater the degree of fiber dyeing saturation, the faster the fiber dyeing rate will be under the same conditions.

Understanding the rate of fiber dyeing can be simulated by the number of theatre seats and the number of seats in the theatre, that is, the dye group. When the seated person is dyed, people will quickly find their seats when they enter the seats. But as the number of seats is increased, the seats will be less and less, and the chances of people finding seats will be slow. That is to say, the faster the seats do, the quicker the chance to find seats.

Increasing the Dyeing Group and modifying the ratio of polypropylene can change the fiber color rate.

But by changing the ratio of polymer to acrylonitrile, the structure of high polymer molecular weight has been changed in essence, and the style of fiber has been affected. Therefore, it is not enough to change the dyeing rate of polymer by modifying polymer.

2. Effect of spinning forming conditions on dyeing rate

1) effect of primary fibers

The surface of the liquid droplet first contacts with the coagulation bath and forms a thin layer quickly. The coagulant (water) in the coagulation bath is continuously diffused through the cortex to the inside of the fine flow, and the solvent (DMAC) in the fine stream is also diffused through the cortex to the coagulation bath. As the bidirectional diffusion continues, the cortex is thickened continuously. When the solvent concentration in the middle part of the fine stream falls below a certain critical concentration, the homogeneous solution of the homogeneous phase is separated, and the polymer is precipitated from the solution, forming the core layer of the primary fiber and forming a certain volume contraction - forming fiber.

Improving the solid content of the raw material is also beneficial to improving spinning conditions and the properties of the structural synthetic fiber of the rigid fiber.

In other conditions, increasing the solid content in the spinning solution can increase the density of the primary fibers, reduce the number of holes in the fibers, increase the uniformity of the structure, increase the strength of the fibers, and decrease the dyeing rate.

Increasing the temperature of the bath, setting the bath temperature and increasing the volume of the coagulation bath can increase the speed of double diffusion and increase the forming condition of the fiber, which is the formation of the core structure. The shrinkage of the core and the core layer is inconsistent, resulting in uneven internal stress, resulting in cavity formation, loose structure, excessive fiber dyeing rate, resulting in dyeing and developing, and the dyeing rate increases. Otherwise, the fiber cavity decreases and the dyeing rate decreases.

2) washing and drafting changes the structure of fibers and changes the dyeing properties of fibers.

After leaving the coagulation bath area, the tow passes through the four cold roller into the four stage washing tank to remove the solvent.

There is a certain amount of solvent in the tow from the coagulation bath. If we do not remove this part of the solvent, there will be more adverse effects in the dyeing process, that is, uneven color. By increasing the temperature and flow rate of the washing water, the swelling of the fibers will accelerate, and the movement of DMAC molecules will accelerate. The DMAC will be diffused to the water. Meanwhile, it will be conducive to the diffusion of water into the tow, improve the efficiency of washing, achieve the washing effect and achieve the ideal dyeing effect.

Improvement through drafting

The degree of molecular orientation improves its physical and mechanical properties.

In the process of drafting, macromolecular or aggregated structural units are stretched and aligned along the fiber axis, accompanied by changes in phase states and other structural characteristics.

In drafting, the orientation of the macromolecules in the low order region of fibers is greatly increased along the axial direction of fibers, along with other structural changes such as density and crystallinity.

Due to the orientation of macromolecules in the fibers along the fiber axis, hydrogen bonds, dipole bonds and other intermolecular forces are formed and increased. The number of molecular chains that the fibers bear external tension increases, so that the breaking strength of fibers is significantly improved, the elongation decreases, the wear-resistance and the fatigue strength of various types of deformation are also improved significantly, and the dyeing rate of fibers is changed.

{page_break}

3. The influence of drying

Drying can make the fiber structure more compact and improve the physical and mechanical properties and dyeing speed of the fibers.

Supramolecular structure has been formed after washing and drafting, but there is a certain degree of internal stress and defects in the fiber aggregation state. Due to the uneven structure caused by the double diffusion motion, a large number of voids and cracks with different sizes are generated, which seriously affects the physical and mechanical properties and dyeing rate of the fibers.

The fibers are dried at suitable temperature, and the water gradually evaporates and moves out of the micropores, producing a negative pressure in the micropores, that is, capillary pressure.

At suitable temperature, the macromolecular chains move freely and cause thermal shrinkage, which makes the micropore radius shrink correspondingly. The distance between microfibrils is closer and closer, resulting in the sharp rise of intermolecular forces and finally the fusion of micropores.

By increasing or decreasing fiber pressure, fiber color can be reduced or increased.

4. Heat setting effect

Heat setting is to remove some unstable intermolecular forces caused by high tensile strength by exposing the fibers to a certain pressure. The reconstruction and strengthening become more stable intermolecular forces, so that most of the internal stress is eliminated, the structure is homogenized, the crystal area or quasicrystal region is strengthened, the order of the amorphous region is improved, and the setting pressure is increased, so that the fiber structure can be stretched, the fiber color rate is increased, and the rate of fiber color is reduced.

The above is the analysis of the factors affecting the dyeing rate of acrylic fiber. Combined with the production practice, we conclude that the stability of fiber dyeing rate is very important. Therefore, the most economical way to adjust fiber dyeing rate is to adjust the drying pressure of fibers, so as to ensure the stability of fiber dyeing rate and achieve double results.