Synthetic fibers. Synthetic polyamide fiber

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Synthetic fibers began to be produced industrially in 1938. At the moment, there are already several dozen of them. All of them have in common that the starting material is low molecular weight compounds that are converted into polymers through chemical synthesis. By dissolving or melting the resulting polymers, a spinning or spinning solution is prepared. They are molded from mortar or melt and then finished.

Varieties

Depending on the features that characterize the structure of macromolecules, synthetic fibers are usually divided into heterochain and carbochain. The former include those obtained from polymers, in whose macromolecules, in addition to carbon, there are other elements - nitrogen, sulfur, oxygen, and others. These include polyester, polyurethane, polyamide andpolyurea. Carbon-chain synthetic fibers are characterized by the fact that their main chain is built of carbon atoms. This group includes polyvinyl chloride, polyacrylonitrile, polyolefin, polyvinyl alcohol and fluorine-containing.

The polymers that serve as the basis for obtaining heterochain fibers are obtained by polycondensation, and the product is molded from melts. Carbochains are obtained by chain polymerization, and the formation usually occurs from solutions, in rare cases from melts. You can consider one synthetic polyamide fiber, which is called siblon.

Create and use

Such a word as siblon turns out to be completely unfamiliar for many, but earlier on clothing labels one could see the abbreviation VVM, under which a high-modulus viscose fiber was hidden. Then it seemed to the manufacturers that such a name would look prettier than siblon, which could be associated with nylon and nylon. Synthetic fibers of this type are produced from a Christmas tree, no matter how fabulous it looks.

Features

Siblon appeared in the early 70s of the last century. It is an improved viscose. At the first stage, cellulose is obtained from wood, it is isolated in its pure form. Its largest amount is found in cotton - about 98%, but excellent threads are obtained from cotton fibers even without it. Therefore, for the production of cellulosewood is more often used, in particular coniferous, where it contains 40-50%, and the rest is unnecessary components. They must be disposed of during the production of synthetic fibers.

Creation process

Synthetic fibers are produced in stages. At the first stage, the cooking process is carried out, during which all excess substances are transferred from wood chips into the solution, and long polymer chains are broken down into separate fragments. Naturally, only hot water is not enough here, various reagents are added: natrons and others. Only pulping with the addition of sulphates produces pulp suitable for siblon production, as it contains fewer impurities.

When the pulp is already digested, it is sent for bleaching, drying and pressing, and then moved to where it is needed - this is the production of paper, cellophane, cardboard and fibers, that is, the main production. What happens to her next?

Post-processing

If you want to get synthetic and natural fibers, then you first need to prepare a spinning solution. Cellulose is a solid that is not easy to dissolve. Therefore, it is usually converted into a water-soluble dithiocarbonic acid ester. The process of transformation into this substance is quite lengthy. First, the cellulose is treated with hot alkali, followed by squeezing, and at the same time,unnecessary items. After squeezing, the mass is crushed, and then placed in special chambers, where pre-ripening begins - the cellulose molecules are almost halved due to oxidative degradation. Next, the alkali cellulose reacts with carbon disulfide, which makes it possible to obtain xanthate. This is an orange-colored dough-like mass, an ester of dithiocarbonic acid and the starting material. This solution was called "viscose" for its viscosity.

Followed by filtration to remove the last impurities. Dissolved air is released by "boiling" the ether in a vacuum. All these operations lead to the fact that xanthate becomes like young honey - yellow and viscous. At this point, the spinning solution is completely ready.

Getting fibers

The solution is pressed through the spinnerets. Artificial synthetic fibers are not just spun in the traditional way. This operation is difficult to compare with a simple textile, it would be more correct to say that it is a chemical process that allows millions of streams of liquid viscose to become solid fibers. On the territory of Russia, viscose and siblon are obtained from cellulose. The second type of fiber is one and a half times stronger than the first, is characterized by greater resistance to alkalis, fabrics made from it are hygroscopic, less shrinkage and wrinkling. And the differences in the production processes of viscose and siblon appear at the moment when the newly "born" synthetic fibers are in the precipitation bath after the spinnerets.

Chemistry to help

To obtain viscose, sulfuric acid is poured into the bath. It is designed to decompose the ether, resulting in pure cellulose fibers. If it is necessary to obtain a siblon, zinc sulfate is added to the bath, which partially prevents the hydrolysis of the ether, so the threads will contain residual xanthate. And what does it give? The fibers are then stretched and shaped. When there are xanthate residues in the polymer fibers, it turns out to stretch the polymer cellulose chains along the axis of the fiber, and not arrange them randomly, which is typical for ordinary viscose. After drawing, the bundle of fibers is cut into spatulas 2-10 millimeters long. After a few more procedures, the fibers are pressed into bales. A ton of wood is enough to produce 500 kilograms of pulp, from which 400 kilograms of siblon fiber will be produced. Pulp spinning takes about two days.

What's next for Siblon?

In the 1980s, these synthetic fibers were used as additions to cotton to make threads spun better and not break. Siblon was used to make substrates for artificial leather, and it was also used in the manufacture of asbestos products. At that time, technologists were not interested in creating something new, as much fiber as possible was required to implement the plan.

And in the West at that time, high-modulus viscose fibers were used to produce fabrics that were cheap and durable compared tocotton, but at the same time absorb moisture well and breathe. Now Russia does not have its own cotton regions, so great hopes are pinned on siblon. Only the demand for it is not very high yet, since almost no one buys fabrics and clothes of domestic production.

Polymer fibers

They are usually divided into natural, synthetic and artificial. Natural are those fibers, the formation of which is carried out in natural conditions. They are usually classified according to their origin, which determines their chemical composition, into animals and plants. The former consist of protein, namely carotene. It's silk and wool. The latter are made up of cellulose, lignin and hemicellulose.

Artificial synthetic fibers are obtained by chemical processing of polymers that exist in nature. These include acetate, viscose, alginate and protein fibers. The raw material for their production is sulfate or sulfite wood pulp. Man-made fibers are produced in the form of textile and cord threads, as well as in the form of staple fiber, which is processed together with other fibers in the production of various fabrics.

Synthetic polyamide fiber is obtained from artificially derived polymers. As a feedstock in this process, polymer fibers are used, formed from flexible macromolecules of a slightly branched or linear structure, which have a significant mass - more than 15,000 atomicunits of mass, as well as a very narrow molecular weight distribution. Depending on the type, synthetic fibers are able to have a high degree of strength, a significant value in relation to elongation, elasticity, resistance to multiple loads, low residual deformations and fast recovery after removal of the load. That is why, in addition to being used in textiles, they were used as reinforcing elements during the manufacture of composites, and all this made it possible to make the special properties of synthetic fibers.

Conclusion

In the past few years, one can observe a very steady increase in the number of advances in the development of new polymer fibers, in particular, para-aramid, polyethylene, heat-resistant, combined, core-shell structure, heterocyclic polymers, which include various particles, such as silver or other metals. Now nylon is no longer the height of engineering, as there are now a huge number of new fibers.