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Besides plant fiber, different fillers need to be added according to different paper materials.
For example, copper-based antibacterial paper is made by compounding copper ions on the first monomer acrylonitrile of polyacrylonitrile (commonly known as acrylic fiber) to make a modified acrylic composite fiber, and then adding the modified acrylic fiber to plant fibers to match with various papers to make antibacterial paper.
Now the voice of environmental protection is growing. Paper mills have introduced different proportions of recycled paper, including 100% recycled paper and 50% recycled paper, which are suitable for different customers' needs. Recycled paper comes from waste paper and can be reused after disinfection, pulp crushing and other treatments. The purpose of pulp crushing system is to completely crush waste paper without damaging fibers and non-paper components.
Chemical composition of raw materials
Plant fiber mainly contains
1, cellulose
In cotton, the content of cellulose is above 90%; Wood, reeds and fillers also contain 40-50% cellulose. From the point of view of papermaking, cellulose should be kept as much as possible in the pulping process to improve the pulp yield and paper strength.
2. Hemicellulose
Among plant fiber raw materials, the hemicellulose content in hardwood and grass raw materials can be as high as about 30%; Generally, it only contains about 20% in cork; Even less in cotton. In order to improve the pulping yield and paper strength, some hemicellulose should be kept as much as possible during pulping.
3. Lignin
In cork, lignin content accounts for about 30%, while grass materials generally contain about 20%, and cotton and flax do not contain lignin. Chemical pulping is to dissolve some adhesion substances between cells with chemicals, so that fibers can be separated into pulp. The more lignin is contained in raw materials, the more difficult pulping is and the more chemicals are consumed.
Secondary components:
In addition to cellulose, hemicellulose and lignin, there are other components with less content, such as resin and ash. The content in common raw materials is not large, which will not cause too much difficulty in papermaking. But if the content is too much, we must take corresponding measures to get rid of some papers with special requirements.
1, resin, fat
Generally, the content of raw materials is less, all below 1%, but it is more in pine, which is sticky and easy to stick together. For example, it is difficult to make paper, and transparent resin spots are formed on paper, which reduces the quality of paper. They are easy to react with alkali to produce soap, but soluble in water, so pine trees with much resin are generally pulped with alkali to reduce the harm. Fat is generally harmless and can also be saponified and dissolved.
2. Starch and pectin
Starch is a storage substance in the cell cavity, with low content, easy to dissolve in hot water, and has no effect on pulping and papermaking. Generally, there is not much pectin in raw materials, which is easily decomposed and dissolved by dilute lye. It exists in the form of comb in plants and is considered as the source of ash in plants. The cell medium of bast fibers such as flax is mainly pectin, which can be degummed by boiling with a little alkali.
3. Tannin and pigment
Generally, the content of raw materials is small, harmless and easy to be drained by hot water. However, when the content is high, it should be extracted as early as possible, otherwise the pulp will become darker and not easy to bleach.
Step 4: Grey
Ash is an inorganic salt in plant fiber raw materials, mainly salts of potassium, sodium, calcium, magnesium, sulfur, phosphorus and silicon. The ash content of wood is between 0.2 ~ 1.0%, and the ash content of grass raw materials is slightly higher. General paper has no special requirements for the ash content in raw materials. However, when producing electrical insulating paper, ash must be removed to meet certain quality requirements. Grass raw materials, especially rice straw, have high ash content and high silica content, so it is difficult to recover alkali. Reducing or eliminating the interference of silicon in alkali recovery is an unsolved problem.
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