How are bio-based chemical fibers processed?
Traditional bio-based virgin fibers, that is, representatives of natural fibers are cotton fiber and mulberry silk. The history of producing cotton fiber and mulberry silk textiles in my country has lasted for thousands of years. "Lingluo satin" is used to describe the exquisiteness and high-end quality of silk fiber textiles. In ancient times, it was a symbol of power and wealth. The production of cotton fiber and mulberry silk mainly uses cotton and silk as raw materials, and is mainly prepared by a variety of physical means. In the early days of my country's liberation, hand-made "cotton bombing" was widely used among the people. It is a process of physically classifying cotton seeds and cotton fibers and further processing them into fiber products.
So, how are today's bio-based chemical fibers processed and prepared from biomass?
Processing of bio-based regenerated fibers
Taking regenerated cellulose fiber as an example, its processing can be roughly divided into two processes: cellulose raw material pretreatment and fiber forming:
Pretreatment of cellulose raw materials: Cellulose from raw materials cannot be used directly and needs to be purified before it can be used to prepare fibers. The purpose of purification is to remove lignin, hemicellulose and other substances from the raw materials, and then It is made into pulp (pulping process). Commonly used treatment methods include chemical treatment, most of which use acid-base hydrolysis. However, this treatment method is more harmful to the environment. A variety of new treatment methods have been gradually developed, such as biological treatment (using fungi and bacteria to remove Lignin, cutin and other substances), enzyme treatment, physical treatment (using mechanical force, high-energy radiation, microwave treatment), steam explosion, etc.
At first, the cellulose needed to make fiber mainly came from cotton and wood. However, due to the limitations of my country's cultivated land area and forestry resources, the source of raw materials began to shift to other renewable resources in my country, such as bamboo, hemp, banana, sugar cane, etc., especially It is some agricultural and sideline products, such as sugarcane bagasse, crop straw, coconut shell, etc. Using these agricultural and sideline products as raw materials for fiber can turn waste into treasure, reduce product costs, and provide broad possibilities for expanding production.
Fiber forming processing: After the fiber raw materials are pretreated, the next step is fiber forming processing. The spinning technology that has achieved industrialization is solution spinning, the most typical of which are the viscose method and the direct solvent method.
The viscose method is the most widely used cellulose fiber production method. The cellulose is first treated with a strong alkali to generate alkali cellulose, and then reacted with carbon disulfide to obtain sodium cellulose sulfonate, and then the derivative is dissolved in a strong alkali. Viscose (spinning solution), the spinning solution is pressed from the pores of the nozzle into a coagulation bath composed of sulfuric acid, sodium sulfate and a small amount of zinc sulfate to solidify and regenerate. After stretching and other processing, man-made fibers are obtained. The production process includes complex chemical reactions, long process flow, low production efficiency, and produces waste gases such as CS2 and H2S, wastewater containing acid, alkali, and Zn2+, and sludge containing CaO, Al2O3, MgO, Fe2O3, etc., consuming a large amount of water, Energy such as electricity and coal.
The direct solvent method is represented by the development of a new solvent system represented by N-methylmorpholine-N-oxide (NMMO). The NMMO production process is a process to produce cellulose fibers without chemical reaction. First, the pulp and NMMO containing crystal water are fully mixed and swollen, and then most of the crystal water is removed under reduced pressure and dissolved to form a stable, The transparent and viscous spinning solution is filtered, defoamed and then spun. It has the advantages of short process flow, low pollution, and good dissolution performance. The regenerated cellulose fiber produced by the NMMO method is called "Lyocell fiber" (lyocell), which is known as the green fiber of the 21st century.
