1.1 Processing process of bio-based regenerated fibers
Taking regenerated cellulose fiber as an example, its processing process can be roughly divided into cellulose raw material pretreatment processing and fiber molding processing:
Cellulose raw material pretreatment processing:
Cellulose from the raw material can not be directly used, need to be purified to prepare fiber, purification of the purpose is to remove lignin, hemicellulose and other substances in the raw material, and then make it into pulp (pulping process). The commonly used treatment methods include chemical treatment, which is mostly treated by acid-base hydrolysis. However, this treatment method is harmful to the environment, and a variety of new treatment methods have been gradually developed. Such as biological treatment (using fungi and bacteria to remove lignin, keratin and other substances), enzyme treatment, physical treatment (using mechanical force, high-energy radiation, microwave treatment), steam blasting and so on.
Most starts to make fiber cellulose mainly comes from the need of cotton, wood, but of limited arable land and forest resources in China, the raw material source began to shift to other renewable resources in China, such as bamboo, hemp, banana, sugarcane, especially some agricultural and sideline products, such as bagasse, crop straw, coconut shell, etc., Using these agricultural and sideline products as raw materials for fiber can realize the conversion of waste into treasure, reduce product cost, and provide a broad possibility for expanding output.
Fiber forming processing:
After pretreatment of fiber raw materials, fiber molding is the next step. Solution spinning is the industrialized spinning technology, among which viscose method and direct solvent method are the most typical.
Viscose process is the most widely used methods of cellulose fiber production, fiber treated with alkali first generated alkali cellulose, reaction with carbon = _ sulfide to get cellulose sulfonate, then the derivatives dissolved in alkali viscose (dope), spinning solution from the shower nozzle pore medium voltage into by sulfuric acid, sodium sulfate and a small amount of zinc sulfate by coagulation, bath, regeneration, After stretching and other processing, artificial fibers are obtained. The production process contains complex chemical reactions, long process flow, low production efficiency, and the production of CS2, H2S and other waste gas, acid, alkali, Zn2+ wastewater, sludge containing CaO, Al2O3, MgO, Fe2Oz, etc., consumption of a large amount of water, electricity, coal and other energy.
The direct solvent method is represented by the development of new solvent systems represented by N-methylmorpholine n-oxide (NMMO). NMMO process is a process to produce cellulose fiber without chemical reaction. First, the pulp is fully mixed with NMMO containing crystal water, and then the bulk of crystal water is removed by decompression, dissolved, and a stable, transparent and viscous spinning stock is formed, which is filtered and defoamed before spinning. It has the advantages of short process flow, little pollution and good solubility. The regenerated cellulose fiber produced by the NMMO process is called Lyocell fiber, and it has been hailed as the green fiber of the 21st century.
It can be seen from the above content that solvent method can omit a series of chemical treatment processes, shorten the production process and reduce pollution. At present, researchers at home and abroad are working on the development of other solvent systems. Other solvents include ionic liquid and low temperature alkali/urea system, among which low temperature alkali/urea system is a cellulose dissolution system independently developed by China.
The research on the clean processing technology of cellulose fiber also includes the melt spinning method of cellulose ester, that is, the fiber raw materials are prepared by the derivatization of biomass raw materials, and then the melt spinning is carried out. However, due to the complex chemical structure of natural biomass raw materials, including multiple hydroxyl functional groups, it is easy to degrade at high temperature. Although its process has been reported, it has not yet become a commodity.
1.2 The processing process of bio-based synthetic fibers
The processing process of bio-based synthetic fibers is similar to that of traditional fibers such as polyester and polyamide, which are mainly prepared by melting polymerization and slicing, and then prepared by melting spinning. With the further development of the process, melt direct spinning process can also be developed.
Take polylactic acid as an example. The monomer of polylactic acid is lactic acid or lactide prepared by dimerization of lactic acid, which can be obtained by biological fermentation of corn, potato, beet and other crops as raw materials. The yield of these crops in China is very large, so the development potential of POLylactic acid fiber in China is very large. The production of polylactic acid (PLA) slice is usually a two-step process. First, lactic acid polycondensation is made into oligomer, and then lactide is made under the action of catalyst. Then, after distillation and purification in vacuum, catalytic ring-opening polycondensation is made into PLA. Further use of slicing, through melt spinning process, can be prepared a variety of specifications of POLylactic acid fiber for the downstream market applications. The processing process of bio-based synthetic fibers is similar to that of traditional fibers such as polyester and polyamide, which are sliced by polymerization and then prepared by melt spinning. With the further development of the process, melt direct spinning process can also be developed.
Take polylactic acid as an example. The monomer of polylactic acid is lactic acid, or lactide prepared by dimerization of lactic acid. Lactic acid can be obtained from corn, potato, beet and other crops by biological fermentation. The yield of these crops is very large in China, so PLA fiber has great development potential in China. The production of polylactic acid (PLA) slice is usually a two-step process. First, lactic acid polycondensation is made into oligomer, and then lactide is made under the action of catalyst. Then, after distillation and purification in vacuum, catalytic ring-opening polycondensation is made into PLA. Further use of slicing, through melt spinning process, can be prepared a variety of specifications of POLylactic acid fiber for the downstream market applications.
source: China Fibres Fashion
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