Currently, the method of separating lignin generally have two: one is outside the plant component lignin dissolved removing lignin as an insoluble components are separated by filtration; the other is just the opposite, lignin as a soluble component, will Other components of plant cellulose is dissolved and then separated from the lignin. Separation of different extraction methods, the final lignin molecular weight and structure is not exactly the same, this will affect the performance of the lignin fibers and spinning after the final carbon fibers.

Originally extracted lignin is a wood piece with sulfite and sodium hydroxide were cooked at 130 ℃ ~ 140 ℃, decomposition. Wherein the cooking liquor lignin and sulfite lignin sulfonate effect dissolution, the lignin is acidified such that the lignin-containing precipitate by centrifugation and recovered by filtration, and dried to obtain a powder of lignin. At present, except in very few cases, basic non-recovery of lignin, cooking liquor melt spinning directly involved in lignin as a raw material fiber. However, the carbon fiber obtained in this way the final strength is not high, the reason is that the introduction of the lignin is extracted more sodium, calcium and inorganic impurities, after treatment and can not be removed, so that the carbon fiber structure defects.
In order to improve the final product – quality carbon fiber to reduce structural defects, in recent years developed a variety of lignin separation and extraction of new technology, which mainly include: high-pressure steam method (steam blasting method), organic solvent pulping, chemical modification France, the polymer blend method.

High pressure steam method (steam blasting method)

First person Jian Zhou vine replaced with high-pressure steam treatment of wood sulfite solvent, and then an alkali solution or an organic solvent extract lignin, and then under reduced pressure hydrocracking, and finally melt spinning in a nitrogen atmosphere, to thereby obtain lignin fiber (lignin-based carbon fiber precursor). As the raw yarn manufacturing process overcomes the disadvantages of introducing more impurities, so the final tensile strength of the carbon fiber increased from 1.25 kgf / mm2 up to 30 kgf / mm2 ~ 80kgf / mm2. On this basis, Sudo such as the use of steam explosion lignin prepared birch rule of law, and the use of hydrotreating melt modification of lignin can be used to obtain high-quality dope conventional melt spinning method.

The organic solvent pulping

Lignin extraction method currently used in more use of the inorganic base solution pulping, but also the use of an organic solvent pulping. The organic solvent is an organic solvent pulping acetic acid, phenol, methanol, ethanol, etc. for cooking, decomposition, the present study still in the laboratory stage. Uraki, who used acetic acid pulp, to obtain an organic solvent-dope. But in the spinning process, we found a relatively low overall mechanical properties of the spinning solution, which may be due to the dispersion and the pulping process lignin lignin portion of the hydroxyl groups are acetylated caused. Moreover, Kubo et also uses acetic acid as the solvent was softwood pulp lignin as a raw material, after removal of the polymer fraction and unstable substances, at a temperature of 350 ℃ ~ 370 ℃ direct spinning, spinning back without too raw silk Direct charring obtained pre-oxidation of carbon fibers. Although carbon fiber performance has declined, but still achieve the “general level” level, and the absence of pre-oxidation treatment reducing the production cost of carbon fiber.

Chemical modification method

Heat does not melt the lignin can become chemically modified lignin melt spinning, which is the most critical step of hydrogenation and heavy. Hydrogenation can eliminate the lignin present in the case of thermally labile functional group or bond, is converted into three-dimensional structure of the molecule can rotate; heaviness by vacuum heat treatment to remove low molecular weight substances can be volatile, so that the residual lignin molecular weight increase, increase spinnability.

In addition, phenol decomposition method is also one of chemically modified lignin. Ma Xiaojun, who found that, in liquefied timber system, the most likely lignin liquefaction, followed by hemicellulose, and cellulose, the most difficult is liquefied. And Sudo such as the use of phenol to lignin modification, then the same spinning, heat treatment and charring way to obtain carbon fibers. By hydrotreating carbon fiber compared it found that in quite other properties, the production of phenol from the original carbon fiber 15.7% ~ 17.4% increase to 43.7%, indicating that the method is superior to phenol-modified hydrotreating method.

How? It is not a deeper understanding of the lignin it? In addition to these, the existing science and technology is to be further contact with our daily life together, industrial paper waste water directly into rivers, not only cause instability in the food chain, for our lives but also has a very bad influence, and industry with black liquor is to be treated, turning waste into treasure, to ease the problem of river pollution now, which will help our lives.

Lignin as an industrial product, although we usually do not understand them, but in fact it is the existence of a wide range of our daily lives, the latter will lead everyone I look at their specific application, so that we really understand it , use it, and how? There arouse your curiosity it? Do you want to learn more about lignin knowledge it? You want to look at its specific applications? Look at China lignin trading network, Xiao Bian will take you to complete this paragraph adventure together, please look forward to it