The Chemical Composition in the Raw Materials for Papermaking

The Chemical Composition in the Raw Materials for Papermaking

The main raw material for paper making is plant fiber. Besides the three kinds of major componentscellulose, hemicellulose, and lignin, there are also other auxiliary components contained in raw materials, such as resin, starch, pectin, and so on. The main chemical components of raw material for paper making include: First, cellulose In cotton, the content of cellulose accounts for more than 90%; wood and reed also contain 40% to 50% of cellulose. From the point of view of paper making, cellulose should be retained as much as possible in the pulping process, so as to increase the strength of paper. Second, hemicellulose In the plant fibers, hardwood and grass contain up to about 30% of hemicellulose; while coniferous wood contains only about 20%; and the content of hemicellulose in cotton is even less. In order to improve the strength of paper, it is also necessary to retain as much hemicellulose as possible in the pulping process. Third, lignin In coniferous wood, the content of lignin accounts for about 30%, while the grass generally contains about 20%; and cotton or flax do not contain lignin. The purpose of chemical pulping is to use chemicals to dissolve part of the bonding materials between the cells, making the fibers separate with each other and form into pulp. In addition to the three major components, raw materials also contain other components such as resin, starch, pectin, and so on. Generally speaking, these components only account for a small proportion in the raw materials, so they will not cause much difficulty in paper making process. However, if these components take up too much content, they should be removed by appropriate measures. First, resin and fat The content of resin and fat is very small in the raw materials, generally below 1%. But the content in pinus wood is much higher. Resin and fat have strong viscosity, which are easy to glue on the copper network and the pressure roller, causing difficulties in papermaking and reducing the quality of paper. Second, starch and pectin The content starch is very small in the raw materials. It is soluble in hot water, and has no impact on the pulping process and paper making. General materials do not contain much pectin, which is easy to be broken down and dissolved out by dilute alkali liquor. In plant, pectin exists in the form of pectin salts, so it is considered to be the source of ash in plant. Third, tannin and pigment The content of tannic acid and pigment is very small in the raw materials, so they are not be able to affect the process of paper making.

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